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Waveguides - Science topic

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I have designed two circular hollow waveguides in CST, one has a 1 mm radius and the other has 1.8 mm. i am plotting the phase constant (beta) vs frequency. I am confused about what this plot defines.
also, I get two different plots from the same design. 1 from the 2D results (s-parameters) and the other from the port information. (attached picture)
can anyone tell me whether these plots have the same meaning or relation? and what this plot defines. is it good or worse?
thanks
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Your top plot looks reasonable, but I would expect it to be in radians per metre. It looks like you have taken the phase change over a given length and divided by the length, but forgotten that the phase change can only get up to 2pi before it drops to zero again. The same applies to the second figure. You need to either use a very short length so that the total phase change never exceeds 2pi or unwind the phase by adding 2pi more at every step - some software packages have a function that does this.
The third figure looks like what I would expect for modes with different cutoff frequencies (wavelengths) in waveguide, where 1/(cutoff wavelength)^2+1/guide wavelength)^2 = 1/free space wavelength)^2. The vertical value is 2pi/(guide wavelength)
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How to assign waveguide port to an antenna which is bend in CST studio
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An sma or coaxial port is also a waveguide port, so won't solve it the problem. Adding a short length of line to the end, that has its end in the right plane and obeys all the rules, will work.
A discrete port will work. You just have to make sure the field and current patterns from the discrete port aren't too different to the proper mode, otherwise you get an inductive or capacitive mismatch between the port and the transmission line.
There are ways of avoiding the gap. For instance, make the metal thicker on one side so it overlaps the dielectric, then, after bending, insert the dielectric into the metal using the Boolean operation.
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I am trying to design a CPW-GCPW tapered transition. Can anyone recommend a book or a reference for these types of transition structures? (Like how to calculated the tapered length etc.)
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The catch for the design of such kind of structures is the right combination of protein and silicon computers; the silicon computer in genal will not tell you the shape you should use..but once you have a shape in mind you can nicely analyze it in great detail which is not to easy for the protein computer (your brain); there are many books which discuss tansitions of all kind..but the gernal rule it..avoid sharp steps and try to implement for or less smooth transients from one cross-section to another...use you intuition there...and then ask he silicon computer jow he likes this.
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As shown in the figure, I am using two coaxial cables for feeding, but the settings related to the waveguide port are always wrong. My purpose is to achieve dual polarization. How to set this feeding?Thanks.
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Malcolm White Combined with what you said and the help document, I changed the solver to frequency domain solver or time domain solver, which can be simulated normally, but an error will be reported when using the multilayer solver, it may be that the structure does not support this solver. Thank you for your help!
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Can anyone please tell how to design this structure(attached), for instance how to decide patch element size and size of via holes? what should be the gap between microstrip line and short element? what should be length and width of stripline etc..
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Smrity Dwivedi Thankyou, I have read all those papers but design dimensions is mentioned nowhere.
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I've included an example picture. Is this transition followed by Quarter Wave transfer rules? or, Can anyone assist me in properly identifying this transition section?
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You should know that this is not governed by quarter wave transition rules. A quarter wave transformer transforms between two different impedances not two impedances that are the same. The flare will introduce an effective lumped capacitance at the join and may be to compensate for other parasitic inductance or capacitance at the transition.
It probably isn't, but it may just be a badly designed transition. Not everything in published papers is good, especially if that wasn't the main point of the paper.
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"Solving adaptive frequency ..., process hf3d: Port 1 supports an additional mode that is part of degenerate group with mode 3. Randomly bad results can occur when not including all modes in a degenerate group".
It's a rectangular waveguide with "a = b", which has a square section, fed by wave port excitation. Commonly, the first two modes should be TE10 and TE01. However, the plot of E field excited by 1:1 is similar to TE11, when the wave port excitation is set with 2 modes. Besides, warning as mentioned is shown. When the wave port excitation is set with 3 modes, the first two modes' E field results are correct, but the warning is still existing. When the wave port excitation is set with 4 modes, warning disappears, but again, E field results are (maybe) wrong as mentioned. So I wonder why this happened, is there anything wrong with my simulation process or anything I missed. I'm new in this field, thank you for giving suggestion.
P.S. My goal is to show TE10 and TE01 individually in this square-section rectangular waveguide with no warning as mentioned, thank you.
Besides, it would be lovely if anyone can introduce what type(s) of mode(s) is/are excited in this case in reality, TE10 or TE01 individually? Or both at the same time? Or others?
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Unfortunately, strange things can happen for symmetric structures, many degenerate modes exist which don't always work well with HFSS.
I might suggest perturbing the dimensions of your waveguide slightly, such that -- for example -- a = b*1.001. This will break the degeneracy, but the solved modes should still be roughly what you would expect to exist.
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I can’t distinguish between TE and TM? I used the wave optics module, physics ( ewfd ) also physics (ewbe) then I used global evaluation then transmission but I can’t distinguish between TE transmission and TM transmission ???? so could you please help me to calculate the extinction ratio (ER) from the formula (1-a) and (1-b) attached in the file?
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to know the difference between different polarizations
read from the following book:
Introduction to Optics 3rd Edition
by Frank L. Pedrotti (Author), Leno S. Pedrotti (Author), Leno M. Pedrotti (Author)
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Hello everybody i want to excite double ridge waveguide using coax connector in hfss but i am not able to do it. I excited the single ridge waveguide but i didn't face this problem in single ridge waveguide. I am attaching my hfss file if anybody can help me i would be very thankful
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Hello,
Few papers are attached for your help.
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Hello good time
What metals can be used in the design of high frequency devices such as Coaxial transmission lines , waveguides, coaxial to waveguide adapters? (Diamagnetic, paramagnetic or ferromagnetic)
For example, can I use tungsten rod , which has a magnetic permeability coefficient of 1, to build a coaxial transmission line? (What is the appropriate magnetic permeability number for the metal used to have low insertion loss(S21)?)
Thank You
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Hello to all
Two questions
1. Does the use of metals with high magnetic permeability, such as iron alloy in the waveguide, cause insertion losses?
2- What about chrome or copper plating?
If you know the article in this field, please introduce it. Thank you
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Please find the attached files.
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I was trying to simulate the Directional Coupler example in Comsol and I started to have some questions. One of my questions is: Why he uses two input ports using the same boundaries and two not excited ports using others same boundaries? Other question: Can I use Beam Envelope with couplers with more than 2 waveguides? Would I have to use more ports in this case?
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I don't know
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I am trying to simulate LNOI waveguide ( lithium niobate waveguide on SiO2). During simulation I found that as I increase the core size (0.5um to 0.9um), Neff increases. In commercial available LNOI, LN thickness vary from 500nm to 900nm. Now anyone would choose core size 0.9um because its giving higher Neff, then what is the point of having LNOIs with LN thickness vary from 500nm to 900nm?
  • Doubts regarding Mode: How do I find TE mode(for which I want to design waveguide)?Is it mode 2 in simulation, with TE polarization fraction 99?
  • Regarding Boundary condition: In attached screenshot I have chosen metal boundary. Should I choose PML instead? If simulation time is not of concern. Because both boundary conditions are giving me different results, metal boundary shows more number of modes supported compared to PML one.
An screenshot of simulation(capture) is attached for reference.
  • I did one more simulation with core size 0.8um with PML BC (earlier it was at 0.9um with metal BC) to avoid other modes. In screenshot capture2 you can see there are two TE modes(both are fundamental- with gaussian profile), how is that possible!?
Thanks for reading. Please share your thoughts.
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Thank you so much Amirhassan Shams-Ansari for answers.
I am encountering few more issues:
  • When I change the span of simulation, number of modes appearing in Mode list of Eigen solver analysis window change. Not only that but the polarization fraction of mode 1 also changes! My only guess was probably modes' order changes when I vary anything (span or core size). So how to track fundamental TE mode when I do the sweeping?
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I am researching on SIW fed DRA antennas
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Hello,
Few files are attached for help.
Thanks,
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Dear Sir,
We are using HFSS Simulator and trying to plot radiation pattern for two case, of a slot cut on waveguide wall as fallowed
Case one:
A slot cut on broad wall of waveguide located quarter wave away from shorting placed at one end of waveguide.
Case two:
A slot cut on narrow wall of waveguide located quarter wave away from shorting placed at one end of waveguide.
The waveguide length is taken typically 200mm.
Global coordinate is laying at the center of the waveguide.
After executing the model and displaying the 3D radiation pattern, displayed pattern is centered at the present coordinate system ie at the center of the waveguide. But we want it should be at center of the slot which is cut on the broader wall of the waveguide and located at around 12 mm away from the shorted port of the wave guide. Can you please tell us how to relocate or plot the radiation pattern cantered at the slot of given waveguide structure.
One way to do this is to rebuild the entire model with respect to coordinate centered at the slot of the waveguide structure. But this will be a very Involved and time taking work, to model and always may not be possible. Thus we are looking some other approach. Please tell us how to proceed.
any ones early reply/suggestion in this regard will be highly appreciated.
Thank you
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Dear Shrivastav a.k. Sir,
Please use the following steps:
1. Create an offset coordinate system with origin as your slot center
2. now create a infinite sphere with required theta/phi range and use this coordinates system in setup.
3. Plot radiation pattern by using this infinite sphere..
Pics are attached for your ref.
Regards
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I am trying to design a PIN Diode switch for a WR90 Rectangular waveguide ( X - Band) using HFSS software. I have learnt from some discussion that PIN Diode can be modelled using sheets and boundaries but how exactly that model i can use inside a waveguide as a switch? what are the parameters or extra devices i need to add? I couldn't find any open publications on PIN Diode switch in x-band rectangular waveguide Can someone recommend me some books or publications or blogs for better understanding of PIN Diode simulation in HFSS inside a waveguide.
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Hello,
Few papers are attached for your help.
Thanks,
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Hello all! I'm trying to recreate 2d map of modes for waveguide in Matlab. So I have waveguide, then border, then air. I calculate eigen vectors and values for air and structure, calculate reflective and transmission indices. And then add exponents and create map. But I don't get picture like in the article. So you can compare my picture and the one I need to get. I don't have any circular waves in the air and oscillations in structure are much smaller. How can I solve this two issues? Thank you in advance.
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It looks like you have PEC boundary conditions at the top and bottom of the picture. That would turn the right hand side of the picture into a wide waveguide with a mixture of modes in it, which is what it looks like. You should have open or infinite or absorbing boundaries top and bottom, like it seems you have on the right hand side.
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I have designed one patch later I used transform option and rotated it to 45 degrees for 8 element circular array.
But it throws an error saying "Waveguide ports must be aligned with Cartesian coordinate planes for the transient solver."
I think when I rotate it to 45 degrees obviously then cartesian coordinate what I want is tilted. Then how should I design circular array.
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A curved bend with the inside radius more than 3 times the track width should be fine.
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When implementing RF circuits in rectangular waveguide, we use stubs/screws/iris to realise capacitance, inductance. What what are the dimension we should choose for particular Capacitance and inductance values?
From a research paper i came to know that the ratio of the post diameter to the wide side of waveguide should be less than 0.25 (diameter of post/a < 0.25), But how to determine exact dimension for respective capacitance and inductance values.
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you will probably find the answer here
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I need to input multiple input through waveguide designed in comsol. I can design a single input of wavelength. How can I input a multiplexed input?
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If you are doing a frequency sweep, you will be looking at one frequency at a time. So either you use superposition, or you do a transient analysis.
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Which one is more effective when we use Mach–Zehnder interferometer as a modulator-
1) overlap the two arms in the end of the source.
2) split them as we do in the Y-branch waveguide.
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What do you mean by overlap in MZI?
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I am using MCK swissto12 characterisation kit and after performing calibration with VNA, but when it comes to connect MCK with the waveguide, it appears that results are flawed as S21 does not change either by connecting MCK together (as thru) as even by giving any gap? Any views.
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What frequency band is your kit, and what frequencies are you measuring over?
Have you put the waveguide adaptors on the right way round - it looks as if they can be fitted 90 deg rotated in which case no power can get through the join.
In the "how it works" video on the https://mck.swissto12.ch/ page it looks to me as if the first adaptor has been fitted the wrong way round - that is what marketing people do when they don't get supervised properly! You will also notice that the waveguide opening at one end is 90 deg rotated from the one at the other - that is why the connector is on the wrong way. I expect that would stop it from working too! (unless the object you put in the middle rotates the polarization 90 deg) Also the connectors have left hand threads - maybe they do?
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Hi, I am new to this and trying to design a waveguide at 850 nm. So I simulated the structure in Lumerical for different core sizes. These three graphs(attached) are the results I got for mode 1( which I think is a fundamental mode). How do I conclude the result, should I choose the core size for which TE fraction is 1? How TE/TM ratio and other parameters will affect the optimization process? Also I'd like to know how optimization process will differ for single mode.
Thanks for reading. I really appreciate any suggestion.
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There is not always a straightforward answer and the decisions you want to take depends on various constraints (Is it purely theoretical or do you plan something experimental as well; Thickness avaiable in the Fab you intend to use; Quality of materials; material losses; safety margins, etc. etc.).
For practical issues of simulation (in particular in lumerical) and decision making, I can highly recommend the book by Chrostowski and Hochberg (silicon photonics design: from devices to systems); No matter if you work with silicon photonics or any other material, the decision making and design principles are the same.
If you intend a real experiment, it is very common that you actually fabricate not just one waveguide, but actually fabricate a whole series of thicknesses or width (or whatever paramterers you have freedom of choice) to get a real feel for "the right" waveguide for your application. Usually simulation is one thing, but in reality sometimes the waveguide, which is according to the simulation the "best", in reality sometimes isn't.
Regards,
Michael
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Hello everyone,
I am trying to obtain dispersion of a finger shaped resonator in Mode Solver. But the dispersion of the bend waveguide calculate it as a ring/circle resonator. Is there any way to obtain the dispersion of different shaped resonators in Lumerical? Thanks.
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Hello,
Few papers are attached for your help.
Thanks,
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Effective index of a waveguide (in Photonics) is a ratio (a number) and has no units. Why is it written as [a.u] in some scientific papers?
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You don't need any units for the effective index in my opinion.
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I made evaporated Cr/Au patterns through lift-off process on silica on Si.
Then, I sputtered Cr on the wafer and pattered the Cr layer for SiO2 dry etch mask formation.
Cr/Au was for heater on silica waveguide, and etched trench was for thermal isolation between waveguides.
After SiO2 etch process, Cr etchant did not remove completely the Cr hard mask on Au layer.
On the other hand, Cr on SiO2 was removed without problem.
The residual Cr was confirmed by measuring the surface profile, showing ~100nm thickness.
Has anyone experienced something similar?
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Hi, there are two types of chromium etchant, what you observe happens quite frequently using the mixture of perchloric acid and ceric ammonium nitrate on heterostructures which have undergone certain processes. Instead the Cr etchant based on sodium hydroxide and potassium permanganate does not have such issues. You can find different commercial solutions CR etch 100, 200, 210... tailored for different material selectivity but i do not expect particular problems for gold.
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I want complete information about calibration methods of Network Analyzer. I want step-by-step calibration steps.
Is it better to measure waveguide components SOLT or TRL ??
What is the difference between SOLT and TRL?
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From Few Discussion i got to know about PIN Diode Equivalent RLC circuit. Then in hfss created 2 cylinder blocks both in contact to each other, then for one cylinder i gave inductance and for other i gave resistance and capacitance for Diode off condition. Similarly for DIode ON condition, for one cylinder i gave inductance and for other resistance. But it is not working as expected. Please need some help to design it.
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Dear Raj:
You can benefit from this valuable Courses about your topic:
"Ansys Learning Fourm HFSS"
In it you will find the answer to all your questions at:
Please go through "Cosimulation Using Ansys HFSS” course to learn about how to do cosimulation using Ansys HFSS and Circuit from below link:
You can design the PIN diode equivalent circuit in the Circuit and connect it to the HFSS design to see the performance.
I hope it will be helpful..
Best wishes...
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In case of W-band (70GHz to 110GHz) microstrip to waveguide trasition how to define fractional bandwidth if fc is 92.5GHz and BW is 5.32GHz?
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Hi,
Here is the definition of fractional bandwidth:
In your case, the FBW = 5.32/92.5
Kindest Regards
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What are the points that we need to consider in selecting the width of the waveguide in designing a ring resonator. Also, how to select the gap spacing between the ring resonator and the bus waveguides?
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Does the waveguide height matters in terms of TE and TM polarizing modes?
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Hello friends ,,
I measure a waveguide path with a network analyzer (a path containing several waveguides that are connected in different dimensions). whose S21 is -2.5 dB, which should be less than -1.2 dB . And the S11 value is equal to -20 dB.
Question 1 :
Is it true that the insertion loss (S21) of a waveguide depend on two factors?
1- Return loss
2- Parameters such as wave leakage, waveguide material, etc.
Question 2 :
According to the relations below :
0.1 dB Reverse Power or (S21) = VSWR 1.3 =Return Loss : -17dB .
Is it possible to conclude that since the amount of return loss is good (RL=-20dB), then the value of -2.5 dB (S21) is due to wave leakage?
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Dear Vahid,
In that case I would check for wave leakage, material losses and calibration.
Cheers
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Hello .
I want to design and build a waveguide load in X Band.
1- How to design that the VSWR is maximum 1.1? (What should I use inside the waveguide, what material? With what dimensions?)
2-How to test it with Network Analyzer after making it?
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Buy a sheet of microwave absorber, cut a long triangle with a sharp point and glue it to one large wall of the waveguide with the point pointing towards where the power comes from, or glue two to both large walls. The longer the triangle and the sharper the point the better the match, generally. You can do it with stepped absorbers, or a pyramidal absorber too. It is hard to design to a vswr of 1.1 unless you design a stepped absorber and are very sure of its complex dielectric and magnetic constants, but making a taper longer will usually improve the vswr. The sharpness of the point is important. If it needs to cope with high power the sharpness of the point can be a problem because it may melt if the absorber has high absorption.
You could glue it to the side walls but it may need to be longer, depending whether the loss is magnetic or resistive.
You can also use a vane of nichrome on kapton film between slits on the centre-lines of the wide faces of the waveguide. If you do this you can adjust the way it tapers in while looking at the S11. https://www.dupont.com/products/kapton-rs.html might also be suitable.
You can test it on a Vector Network Analyser (VNA) with a good coax to waveguide adaptor. 1.1 vswr is about -26 dB so if you want to be reasonably accurate the adaptor needs to have S11 less than -40, unless you can calibrate on the waveguide side, using waveguide open short and load, for instance.
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Why in Lumerical software when simulating a graphene plasmonic waveguide, the transmission amplitude is greater than 1 when the imaginary part of the surface conductivity is negative?
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I think you didn't enough time to get the convergence.
Graphene waveguides have some dissipation, so the transmission amplitude would be less than 1.
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Hello dear engineers.
I designed a coaxial adapter for X-band waveguides. Now I want help to test and tune with the network analyzer device. How should I test it? If you know a reference, please help Thanks
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Impedance of normal size waveguide is 300 ohms or more and varies with frequency. There are standard equations. See https://www.microwaves101.com/encyclopedias/waveguide-wave-impedance, but it is more complicated than this, so look at more references. There is (at least) one definition of impedance that depends on the height to width ratio, and one that doesn't. Even your smallest height waveguide will be more than 50 ohms. I don't think you will find a 50 ohm waveguide load. Your transition should look like 50 ohms from the coax end and like whatever impedance the waveguide is from the other end. If it has no or very small (-20dB?) reflection seen from the coax end, and small losses (it probably will have) then it will have a low reflection from the waveguide end too. Lossless components without ferrites in have th same match (S11=S22 S21=S12) from both directions.
answer to 3
If you put a horn with a gradual taper (and no step) on the end of the waveguide it will be a good load - it will radiate with low reflection. Also if you put a piece of absorber with a good point and a long taper in the guide, it will be a good load, if the taper is long enough. You can't get a good load by putting a different size waveguide on, there will be a reflection from the step in nearly every case. Reflection = bad load
I don't understand question 1
2 yes - with no step in the waveguide, or a taper between the two sizes, several wavelengths long.
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The dimensions of the ports of the coaxial to waveguide adapters in the X-band that I designed are as follows: 5.08 * 22.86 And 2.8 * 22.86 Now my questions are:
1- Do I just have to measure the adapters with a 50 ohm waveguide load a quarter of the wavelength?
2. For each of the adapters, should the size of the waveguide load port be the same as the adapter port?
3- Reference for designing 50 ohm waveguide load, please introduce because waveguide loads available in the market with dimensions of 11.16 * 22.86 are standard and are larger than my adapter ports.
Thank you dear friends and engineers
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Where could I find some numerical results of the P(beta) (power vs effective index) characteristic related to a single layer nonlinear optical waveguide with lambda=0.515 microns, df=1micron, nc=1.55, nf=1.57 and ns=1.55 with nonlinear (Kerr) cladding coefficient n2c=1e-9 or other ? I simply need numerical data for comparison with my method.
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Hello
by using COMSOL Software Programm
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I have tried with tetrahedral meshing , check feeding with discrete port instead of waveguide port. Also tried port with global coordinates instead of local coordinates, but failed to run simulation.
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A discrete port should work - on a coax feed then a break in the centre conductor right by the feed might be a good place. You need to make sure the impedance is right.
If it is a coax feed than you can easily have a short coaxial cable from the waveguide port to the feed point. This is a transmission line. A coaxial port is a waveguide port in CST. You can remove the phase due to the line length later in post processing by moving the reference plane.
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I am fabricating a optical micro ring resonator where the width of the main waveguide and ring wave guide is 1 um. I am wondering what should be (optimum) height of the waveguides so that it supports a single mode with maximum confinement.
Thanks.
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Substrate is SiO2/Si. no there is no separating layer.
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Can any body tell me the procedure of making hardware of any microstrip line to rectangular waveguide transitions or suggest me the name of person who can make this hardware. its very urgent...
thanks...
+917983388622
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maybe we can discuss this privately :my e-mail
in any case there are several standard methods of doing this..(like Malcolm indicated already) and it all depends on your particular parameters
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I designed a Quarter wave transformer for a circular waveguide. I need to find the phase-shifted by the wave for a particular dimension in the waveguide. How to do it in CST MWS.
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The angle will always be in the range 0 to 360 degrees, or -180 to 180 degrees, so you need to use some way of making sure the length doesn't have extra wavelengths (n*360 degrees extra) in it. One way is to start at a low frequency where it is certain to be less than a wavelength, and observe how the phase increases with frequency.
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Dear All,
I want to simulate an ITO based plasmonic modulator. In the reference paper, Si waveguide is ground (V=0V) but I don’t know how do it in optical simulation region like Lumerical Mode Solution. I locate an ITO thin layer on the Si waveguide and apply zero voltage to ITO layer by Drude model script. But my simulation results are wrong. I attached paper at the following. Thanks.
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The most straight forward way to do this is by using Lumerical's Charge Simulator along with mode simulator or FDTD as suggested by Lalit Singh. Voltage can be applied in Charge Solver by using its boundary conditions. You can define a metals touching Si and ITO and then give one electrode 0V while a constant or a set of voltage can be applied to the other electrodes.
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My system is like few obstacles are placed inside a parallel plate waveguide. An acoustic wave with certain frequency will be generated from one end of the waveguide and will be observed from the other side. I have to find transmission vs frequency and reflection vs frequency graph by building the model in comsol. Any kind of help would be appreciated.
Thanks in advance!
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Thank you Tanwin for your response. I figured it out long time ago. Actually I was working in acoustic domain in COMSOL.
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I'm working on 1.55um waveguides with one or two bilayer or trilayer graphene layer. I have a MATLAB code that calculate refractive index of graphene and I use that calculated refractive index to calculate waveguide different modes neff(effective mode index). My problem is that my calculated indexes and absorptions are not similar to a source that I'm using specially in trilayer graphene waveguides. Is there special way to simulate graphene in COMSOL and how I should simulate bi & trilayer graphene in COMSOL?
I attached one of my simulated file corresponding to fig5.19b in the source
my source: Finite Element Characterisation of Graphene-Silicon Hybrid Waveguides by S.N.Mathivanan University of London
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Dear Matin,
sorry to see that your very interesting technical question has not yet received any expert answers. As a synthetic inorganic chemist I'm unfortunately not an expert in this field enough to give you a qualified explanation. Perhaps the following potentially useful article might help you in your analysis:
Gate-controlled topological conducting channels in bilayer graphene
This paper has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file.
In my experience it often pays off to directly search the "Publications" section of RG to find and access helpful literature.
Good luck with your work and best wishes!
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I have a planar SSPP TL or Waveguide in xy plane, which guides waves in y direction. The wave-guide ports are in xz plane (see attached file), I want to use Eigenvalue analysis which needs non-open boundary conditions. I want to know the way that I should define background and boundary condition for SSPP TL.
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Mahdi Siasifar In most simulators, there shouldn't be any ports in an eigenmode simulation, only periodic boundary conditions. There are many helpful documents online for performing these analyses in various software, see for example here: http://www.emtalk.com/tut_2.htm
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Hi researchers, I have a double ridged horn antenna design and trying to improve S11. I'm trying to get the area in the black circle below -10dB as you can see on the S11 graph. I'm using CST2017 so, I tried to change a lot of parameters such as waveguide sizes, horn aperture sizes, flare angle, aperture length, distance between two ridge, thickness of ridge , etc. Normally increasing antenna sizes work but I dont want my antenna get bigger than it already is. Is there another way to do this. I'm open to any suggestion or article.
Thanks in advance...
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You can lower the cutoff of double ridge waveguide by reducing the gap between the ridges and making the ridges wider, and also making the guide higher as well as wider. You may be able to make it higher even if you don't want to make it wider. If your feed is from coax (or microstrip, or slotline) to double ridge waveguide then lowering the cutoff of the double ridge guide should work. You need to get the transition right from coax, or anything else, to double ridge.
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I need some guidance regarding the undesired resonances in a waveguide cavity with respect to the position the stubs. I have attached figures to give a background of the problem.
In fig. 1, two stubs were introduced (to create transmission zeros) in the waveguide cavity at the junction near port 1. Two transmission zeros at frequencies equal to 10 GHz and 13.5 GHz were generated with the help of stubs but at the same time two undesired resonances were also generated as shown in the attached results.
In fig. 2, we have changed the position of the stubs. The stubs were introduced in the waveguide cavity at the junction near to port 2. Two transmission zeros were created at the same frequencies but with no undesired resonances.
I want to know the reason why we have undesired resonances in the first case while we don’t have any undesired resonances in the second case. Many thanks.
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Good question and I agree with Dr. Jamil & Dr. Smrity.
Good luck
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Hi Everyone,
I want to know is there any way to do nonlinear simulation in lumerical interconnect except using the thermal nonlinear waveguide? I designed a waveguide and import the properties from FDE to interconnect. Now I want to see some nonlinear aspect of it by setting up a high power loopback system. Will it be possible to see any phase changes in the loopback in Lumerical interconnect?
Thanks.
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Hello,
hope this paper help you:
Silicon photonic waveguides & nonlinear optical effects
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Dear All,
I have 2 full 2port s-parameters in 30mm waveguide section.
1. 30mm with air
2. 25mm with air and 5mm with material
And I want to extract the s-parameter of 5mm material from the above data.
I think that "de-embedding S-parameter" is solution.
But I don't know how to solve it.
Please give me a hint or calculate the solution.
Thank you very much!
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Maybe you could try first to do a de embedding exercise on a coax structure (in a way like VNA calibration with open short load standards and then go to the waveguide method. One "catch" in particular with the waveguide method are evanescent field from higher order modes in particular for your type of structure (5 mm material near the port)
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Spin-wave can be excited by microstrip line, coplanar waveguide, microwave cavity, spin-torque nano-oscillators, etc. Among all these, which method is the most efficient to excite spin-wave?
Regards.
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Thanks for your comment. I have excited MSSW in ferrite film via a microstrip line, i.e., using electrical transmission spin-wave microscopy. However, the weak spin-wave transmission signal is getting masked by the electromagnetic transmission between two microstrip antennas. So, I want to understand which micro-wave method will be best for exciting magnetostatic spin-wave.
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Many Thanks!!
Please tell me a little bit about the coplanar waveguide and its working formula.
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Dear Prof Smrity,
These papers are excellent, informative work and good references.
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What would be a good way of measuring the return loss of fabrics in the microwave frequencies? I see papers published where they put the fabric between two waveguides (not clear if it is inside the waveguide or just sandwiched between the two waveguides. Any suggestion? Can one just use the N1501A Dielectric Probe Kit since the dielectric constant of the fabrics are low to begin with? Thank you for any suggestion.
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of course the comment by Malcom is correct in principle; but still if you can put your fabric between two waveguide flanges (i do not refer to the N1501A kit specifically) can be a good starting point when you measure both in reflection and also in transmission; just doing this in the frequency domain at a single frequency may be prone to errors thus using the time domain transform can give additional cross- check possibilities. It also depends on the ballpark of losses of your fabric(perhaps you have in mind to test fabrics with woven in metallic wires (for EM shielding).then the waveguide flange method is not bad to start with. And for real low loss "foils" or layers you can apply the waveguide resonator method.
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Which MTM would be best for the gain enhancement of Slotted waveguide Antenna? I know we need negative refractive index MTM but which shape or type i.e. single layer double layer would be the best?
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Dear Muhammad Umer Shahzad
It depends on the frequency range. In the literature same authors suggest two layers of MTM to increase the gain of a UWB antenna; one layer for lower frequencies and the second one for higher frequencies. Others considered one layer to increase the gain over a wide bandwidth as in the reference below. You need to compare the performance of MTM structures using floquet ports over the frequency of interest. I suggest the following youtube video as well which can help you to simulate your MTM structure:
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I have tried to etch AlGaAs waveguides using a gas mixture of BCl3/Ar/N2 with gas flow rates of 20/5/3 sccm. The coil power is 750 W and the platen power is 100 W. The chamber pressure is 4 mTorr. I use a PECVD SiN hardmask. What could be causing the porous sidewall? I have attached two SEMs showing the highly porous waveguides.
Meanwhile, the sidewall quality is slightly better when the N2 gas flow is 2 sccm. That is contrary to what the literature suggests, where nitrogen is supposed to assist in the passivation of the waveguide during etching.
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Hello Bo Xue Tan
I wonder if the effect depends on the Al/Gas ratio?
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Surface plasmon resonance (SPR) slides contain a glass slide with 50nm thick gold coating on top of it. Instead of using the Kretschmann setup with a bulky prism and having to worry about alignment, why do we not use the SPR slides as a waveguide and just shine led at the edge of the slide and have a spectrometer at the other end? Then you place some solution on the gold film and there should be a change in the spectrum. Ensuring everything is covered up so there is not ambient light, what are some issues with this idea or considerations?
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Hello All,
Can we generate supercontinuum in photonic crystal waveguides? What are the pre-requisites to start with? And is there any software that will be helpful for simulation?
Thanks in advance
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Yes! Photonic crystals are actually good candidates for supercontinuum generation. There are two factors to achieve a wide spectrum exploiting self-phase modulation, field confinement, and material nonlinearity. Photonic crystals are very good at achieving very good field confinement , resulting in large effective nonlinearity coefficients. For short waveguides (1 mm-1 cm) dispersion is not important, the only remaining factor is the material from which the photonic crystal is made, through its nonlinear refractive index
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Is they is any technique to reduce the HPBW of H-Plane of Slotted waveguide Array Antenna except increasing the number of slots and subarray technique?
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If you change the slot shape - perhaps to an H, it may narrow the element pattern by making the field along the radiating part more even, but if the array has more than 2 or 3 elements this will not narrow the H-plane pattern. The width of the beam is determined almost completely by the width of the array.
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do i have to calculate the K-factor?, because when I change the size of my port, I get different but wrong results, I have to calculate the capacitance from my S11(I have two interdigital capacitors in parallel),I used multipins the waveguide properties
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You must increase the port size until the impedance is stable, and you must include more modes in the calculation, this is done in the port settings.
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Do you know any wet etching techniques and/or etching solutions (acids) other than the one proposed that might work ? feel free to suggest. The waveguide being used is a deep-etched InP(3.36)-Q(3.19) waveguide.
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Hi Isis.
Try using HBr mix. It is a very strong acid and we have used it for InP etching successfully.
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I'm curious about this paper's subsequent investigation, it provide a effective way by employing centered vias instead of iris-type vias to improve the SIW crossover's isolation, but there's no explanation about why it can improve the isolation.
References:
Salem Hesari, S., Bornemann, J.: ‘Substrate integrated waveguide crossover
formed by orthogonal TE102 resonators’. Proc. 47th European Microwave
Conf., Nuremberg, Germany, October 2017, pp. 1–4
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I guess, the question was why are there posts in the center and not irises at walls. Probably, for rejecting lowest eigenmodes. Why is there an additional post beyond that split, I am not sure.
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Using COMSOL I am trying to find out modal overlap between TE00 and TE20 mode, only in the core area of a ridge geometry. It will be helpful if someone can provide me any hint to solve it out...  
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Sorry for the late answer. In case it is still useful, you can divide the computation of both modes on two different studies. Then you will have two different datasets. After that you can use the Join dataset operator two join these two datasets and a Surface Integration over the the Derived Results. Just ask in case if you need more help. Good luck.
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Currently I need to generate secondary electron yield properties for Which I need Particle vs Time in CST PIC solver.
For hexahedral meshing, Eigen solver is used. A fixed frequency with 4 modes using JDM is implemented. Do I need a waveguide port with zero reflection or fields generated without wave port are acceptable? I have used periodic boundaries, but some referenced papers also suggest phase shifts in order to obtain travelling wave.
Further more, The PIC solver hampers ram (98%) when simulated with imported E and H-fields. Is only E-field enough. Various megawatt powers are applied through PIC waveguide excitation list.
Need help in these ambiguities to save simulation time and generate good SEY and PvsT.
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Fields with no ports are acceptable unless you are interested in transient effects. For traveling wave periodic structures are needed, otherwise you need to create a correct superposition of the solutions with E- and H- walls in the resonant mockup with a correct number of cells. This can be a source of errors - periodic walls are much simpler.
Are you simulating multipactor discharge? Then H-fields are important too. You can consider TRACK solver, however.
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Hi every body,
I want to design a ring coupled to a bus waveguide and obtain critical coupling.
I am doing simulation in 2D, so I use effective index method to replace the 3D structure by 2D one. The waveguides are of silicon with the width of 500 nm and the height of 220 nm, the radius of the ring is 10 um. And the fundamental TE mode is used. In fact, I got the transmission spectrum and I see the dips, but they are very shallow and it seems that I could not reach the critical coupling yet ( in order of 10^-5 dB!). I changed the gap between the ring and the bus repeatedly, although the spectrum changed, but still the dips were really shallow! Could you please guide me to solve this problem?
I have some more questions:
1- When we say the critical coupling means equivalence of internal loss with coupling loss, and it causes a case where we have destructive interference in the bus, and so no power at output, what really happens?
2- For an ideal case, where α=1 (it means that internal loss of ring is zero), and so for getting critical coupling t=α=1 and κ=0, how the critical coupling happens? It seems there is no coupling to the ring because of zero coupling coefficient.
Thanks in advance,
Zeinab
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Hi , I am doing a hexagonal ring resonator structure b/w 2 waveguides using photonic crystal. What is the formula that can be used to get the design parameters of a ring resonator? Design parameters in the sense ., Radius and thickness of the diaphragm, lattice constant, radius of hole, radius of hexagonal ring & gap b/w ring and waveguide.
Thanks and Regards in advance
Yashaswini
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Hello
Why using a radius with 5 μm in the waveguide at photonic integrated circuits while a radius with 7 μm has minimum loss?
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Dear Fatimah,
As colleagues wrote above there are several possible reasons for that ( if you asked about a cross-section of a waveguide) such as:
1) Amount of modes (normally it should be single-mode to avoid beats between modes and optical losses for high order modes due to scattering on walls what is explained lower factor of mode confinement ),
2) Propagated polarizations (it depends on requirements for PIC as well as technology peculiarities),
3) Dispersion engineering (that is the crucial thing for success if there are tasks in microcombs in optical resonators),
4) Stresses in waveguide films that appear during sputtering/oxidation/deposition.
If you wrote about bending radius then the answers of Malcolm White and Mursal Ayub Hamdani described it.
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Can anyone help me for band structure calculation of 2D photonic crystal waveguide in Rsoft software?
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can any one tell me how to add new rod with with new radius in BandSolve
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To Generate particle vs time results for a particular period of time (e.g. 20ns), the waveguide is assigned Furman secondary properties in material settings.
The model is imported form CST MWS to CST PIC and its EM fields are also imported as ASCII.
Among the parameters of setup and analysis, how to particularly set input power (in MW) so that viable results are generated.
For example, I need to generate particle vs time for 1.5MW, 2.5MW, and 3.5MW. how to set them prior simulation.
Also SEY remains the same post simulation. In some papers it is noted that some data points are exported and SEY results are then generated in Excel. Is there a direct way to generate SEY in CST post processing?
kind regards.
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You can use Field scaling either in Field Import or PIC solver setup windows. If you have the fields from MWS, you can check what power level P0 corresponds to these field strengths. The scaling factor in OPIC would be k=sqrt(P/P0). Alternatively, you define field excitations in PIC solver via a port and define the signal power level in PIC solver setup.
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Periodic boundaries conditions in HFSS. Master/slave vs. PEC/PMC
Hi, Does anyone know the difference between different periodic boundary conditions in HFSS. What is the difference between linked boundary conditions (Master/Slave) and PEC/PMC boundary conditions(waveguide simulator).
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Magnetic-field on the slave boundary is forced to match the magnitude and direction (or the negative of the direction) of the magnetic-field on the master boundary.
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Hi, whenever i use circular array i get this error "Waveguide ports must be aligned with Cartesian coordinate planes for the transient solver"
Does anyone use circular array with waveguide ports? Any recomendation would be so helpful.
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As a proposal you can use regular polygons instead of a circle. Then you can use rectangular waveguides.
Best wishes
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I am now working on the coupling between vertical-cavity surface-emission laser(VCSEL) and waveguide. However, the window design for laser emission is larger than the waist of Gaussian beam emitted from VCSEL.
Does the light come from the center of emission window of the VCSEL or, practically, there is a chance that the light center will deviate from the center of the window? Usually how far it will deviate from the center of the window? (what is tolerance)
Do you have any references for that?
I appreciate your suggestion about this problem!
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Do you know that the output from your VCSEL has a mode profile which is Gaussian?
VCSELs typically support multiple transverse modes, and the intensity profile can vary strongly between different samples of the same device, and may also depend on the drive current.
You may find the section on polarisation mode partitioning of interest if your waveguide is sensitive to polarisation orientation.
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Hello everyone,
I am trying to simulate waveguide structures in COMSOL in the wave optics, frequency domain ,mode analysis. I try to simulate structures such as: berried waveguide, diffused waveguide, ridge waveguide and i get weird results- unconfined modes (see images attached).
i was told that maybe the equation of the refractive index profile is not implemented-but i cant find this equation and where it is defined. does anybody know where i can find this equation or having any other solution for my problem?
thanks
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Hello, are you sure that with your parameters (wavelength, refractive index and waveguide geometry) your mode should be confined? Maybe in this case your structure does not physically support the mode and your result is correct.
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Which waveguide i have to choose?
How to excite TM 11 mode in RECTANGULAR waveguide by side insertion
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TM11 is not the dominant mode.
Which mode do you want to excite? Are you certain it is TM11?
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  • I am characterizing simple cotton textile by using the waveguide method and extracting permittivity from S parameters through Nicolson-Ross-Weir Method. At some frequencies, I am getting peaks on the negative axis side as well. What could be the possible reason of those negative values?
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That is believable