Antennas - Science topic

Y Hatziiouannou uses an approximate formula for the 'local' grazing angle of a scattered wave propagating along varying surface in Eq. B.10 in , Appendix B, in

and we applied this further in subsequent work. I'm not sure if this is what you need although it's certainly related and I hope it's helpful.

Hello Vikash, If you are looking for this to work as an antenna then it should exhibit some gain in some direction (for an array you can point in the specific direction). Now,

From your return loss response (we typically look at 10 dB impedance bandwidth as acceptable) it look like it works with 200 -300 MHz of bandwidth. You have to ask yourself as Nitin pointed out , if this was your target. The gain also seems very low as Nitin and Malcolm pointed out.

Typically what I would do is the following:

1) Define your target for bandwidth, Gain and polarization and beam direction

2) Use design equations to make the array

3) Next first look at bandwidth of the antenna if it meets the requirements

4) Plot a 3D plot of the Gain to look at shape in general at desired center frequency

5) If that looks OK, go ahead and plot radiation pattern in the plane which containing beam direction by specifying theta and phi to select plane

6) Finally look at antenna radiation efficiency and input impedance (in case you want to connect with any driving circuit)

Thanks

Dear Vincent,

The drive test is one of the powerful methods to monitor the received signal quality in diverse paths in the area to be covered by the base stations. Such tests can be obtained from the mobile operators. The measured received signal strength together with the base satiation operating conditions can be used to assess the channel communication channels and develop real channel models. The ITU publish practical channel models for different wireless communication technologies.

I think in order to access data on the communication channel from the mobile operators you can ask them directly.

Best wishes

In principle, you could get an indefinite rectenna array over the walls of the building. But it won't be very practical since the ambient RF power density is low. The recycled energy would a limited amount of "expensive" energy compare with the large scale and "cheap" solar energy. It is more realistic to coat the building with low cost and thin film solar panels. Regards

For measurements, you will need to be able to rotate the antenna. The receiving antenna is positioned exactly opposite i.e. parallel plane to the transmitting antenna, separated as far as possible. An appropriate measuring device is connected to the receiving antenna - an oscilloscope or a spectrum analyzer - connect a signal generator to the transmitting antenna and transmit a steady signal - typically a continuous wave - and take measurements at the receiving end...turn the transmitting antenna in steps of 5 degrees, and depending on the antenna being tested, you can measure right up to 180 degrees in each direction - clockwise and anti clockwise...or even a full circle; then plot it in MS Excel for the radiation pattern. (input the far-field range numbers into an excel format and generate 2D polar plots of those numbers. I have not used it, but I believe that feature is already built into MS Excel; it's called the Chart Wizard. You probably want the 'Radar' plot. Copy and paste the numbers into Excel, and if you don't have a complete 360-degree data set, then select the data and run the Chart Wizard.)

Here are some other useful links:

You may also like to try this software: Polar plot

gain of antenna should look like band pass filter.

It depends on the use and application scenarios actually. E.g., if it is targeted for UE design, many things have to be taken into account, not only technically but also commercially. If you take a look at this article, Cellular User Equipment: From Theory to Practical Hardware Design, u will notice some challenges for 5G UE. On the other hand, some famous corporates, according to their published information, are also in favor of sub-array-like ideas for both basestation and user equipment. http://www.telecomtv.com/articles/5g/qualcomm-unveils-5g-nr-mmwave-test-device-and-collaborates-with-nokia-on-testing-15936/

You should get the results at frequency at which you have designed your structure rather than what you have mentioned in HFSS. I guess you know your design frequency, try to optimize the dimensions of your structure so that you get results on that only. Generally you will not get the results using the exact dimensions you would have calculated in theory, since there are lots of assumption and approximations. Theoretical values will give you a starting point, in simulations the software performs closed loop calculations which yields better results than theoretical ones (not drastically different though), so try to change the dimensions, usually you should use a little smaller dimensions than obtained in theory. I hope that answers your query.

Dear Praveen,

Several properties of the materials influence the behavior of the antenna. For instance, the bandwidth and the efficiency of UWB antenna are mainly determined by the permittivity and the thickness of the substrate. The use of textiles in wearable antennas requires the characterization of their properties. Specific electrical conductive textiles are available on the market. If an ordinary textile fabrics used as substrates little information can be found on the electromagnetic properties of regular textiles. Therefore your research should mainly focused on the analysis of the dielectric properties of normal fabrics. In general, textiles present a very low dielectric constant that reduces the surface wave losses and increases the impedance bandwidth of the antenna. However, textile materials are constantly exchanging water molecules with the surroundings, which affects their electromagnetic properties. In addition, textile fabrics are porous, anisotropic and compressible materials whose thickness and density might change with low pressures. Therefore it is important to know how these characteristics influence the behavior of the antenna in order to minimize unwanted effects. This was my experience so far, I wish you all the best.

Gain and frequency are not used to calculate the amount of power radiated. 4 dBW is 2.5 Watts. 100 mW lost in resistance, leaves 2.4 W radiated. This assumes none of the 2.5 W was lost in dielectric or magnetic materials, or reflected back to the load.

The slot size determines the coupling so a minor change in its size would result in non optimum excitation due to impedance mismatch. Impedance mismatch means that there there has been a phase shift in impedance from its zero value at resonance. From the equation Frequency x Time = Phase, frequency is expected to change as phase changes.

1. First calculate the diameters of inner and outer conductors of coaxial cable so that its impedance would be 50 ohms taking into consideration the dielectric material in between.

2. Draw first the outer cylinder with its surface as outer conductor and its fill as your dielectric where you have to choose its material from library

3. subtract the diameter of inner conductor from the outer one.

4. draw another cylinder with same dimensions and orientation as the subtracted cylinder to replace it but this time it will be totally conductor

5. choose an excitation port as a circle the same size as the outer cylinder and place it on one cross sectional side of the cylinder

6. on the other side connect two conductor wires; first wire connecting inner cylinder to radiating patch of the antenna; the second wire will connect the outer surface with ground of antenna.

I think it would be easier if you do it on CST

Would be happy to get feedback from you

Good Luck!

If this may help please find attached my paper for SIW horn mm-wave antenna fabricated and measured using PCB. You will find comparison with a much more advanced technology, namely Low temperate Co-fired Ceramic, LTCC. I think the major differences are:

1. PCB is much cheaper and Easier to fabricate

2. LTCC is much more accurate in dimensions of fabrication unlike PCB, where the latter causes deterioration of electrical performance especially at higher frequencies

3. Dielectric loss for LTCC is relatively low at higher frequencies

4. LTCC multi layer structure integrates both passive and active elements e.g. System On Chip

5. Possibility of Mass production

6. Although LTCC may have a high dielectric constant which decreases efficiency, this can be compensated by incorporating a cavity in its multilayer structure

7. Last please take a look on how the mm-wave antenna using PCB in the paper was measured for S11. The idea of mounting a rectangular waveguide on the antenna for measurement was interesting which took place in Germany.

Good Luck!

Thanks Marcelo for the reply but my supervisor just told me today that to keep it as it is in this stage,later we'll also feed other dipoles..

Thank you Mansour sir for your reply.

This is a very general question. As it is mentioned before, there are various kinds of antennas: dipoles, patches, horns, spirals, log-periodic, dielectric resonators, reflectarrays, ... Some of them are not resonant. Moreover, even for resonant antennas within the same class there is a variety of conditions. For example, resonant frequencies of thin and fat dipoles of the same length are different. And if you make a monopole (half of the dipole mounted on a ground plane) to be a monocone, it becomes wideband. There is no a single formula.

Dear Sir,

Thank you for accepting my answer and following back, i am preferring lower frequency is suitable for designing. But keep in mind when your designing at lower frequency the dimension of antenna size will larger than higher frequency.

Use a linearly polarized antenna and rotate it while keeping it in the same position pointing at the antenna under test. The square root of the variation in received power is the axial ratio.

Try to reduce the permittivity of dielectric material.. do try and error see what happen

Dear Mohammed, Progress In Electromagnetics Research (PIER) Letters publishes peer-reviewed It is an open access, on-line journal in 2008, and freely accessible to all readers via the Internet. it takes two weeks to give you the editor opinion.

All the best.

You should take a look at the CTIA Test Plan for Wireless Device Over-the-Air Performance, https://ctia.org/docs/default-source/certification/ctia-test-plan-for-wireless-device-over-the-air-performance-ver-3-7-1.pdf. There you'll find the radiated performance criteria being applied to GPS receivers in all wireless devices. You'll note that they're concentrating on the total isotropic sensitivity (full integral of the receive sensitivity (EIS) pattern) and subsets of that for the upper hemisphere where the satellites will be located. Note however that this if or a complete device and thus marries the performance of the antenna, receiver, and any platform interference from CPU and display components as well as other radios into one single performance metric.

If you're asking about antenna performance solely, then in addition to the pattern related factors (e.g. how uniform of a signal do you receive from the upper hemisphere) you also need to consider antenna efficiency (internal losses, VSWR/mismatch) as that will tell you how much of the energy impacting the antenna reaches the receiver.

To find out how big to make the port all you have to do is to pick the stripline metal then go to Macros, from here you select solver then port then discrete port. Fill in all parameters if they are not already filled in then Click calculate. You get the multiplying factor. This helps you work out the size of your port. Go back to your simulation clear the microstrip metal. Contruct the 4 points of your port with the data you have. Click waveguide under simulation. You will have a discrete waveguide port.

Interesting...

Dear Sandip,

First of all you have to use the ISM band which is distributed on a number of subbands. Please for the details of these subbands please see the attached link:https://www.ofcom.org.uk/__data/assets/pdf_file/0022/103297/fat-ism-frequencies.pdf

According to your requirement of minimum attenuation of the environment, you have to use as small frequency as possible,

According to your second requirement of compact antenna you have to use as high frequency as possible because the size of the antenna is in the order of half wavelength. The subband must be wide enough to satisfy the wide band communication required for video transmission.

So, accordingly i would propose you to use the UHF range around the 430 MHz.

You can find a very powerful one chip configurable wireless transceivers form many semicondcutor companies like TEXAS instrument and ST micrelectronics and other famous companies.

These are some guide lines that may help you to realize your wireless link.

Best wishes

Dear Adama,

You have to firstly calculate the free space wave length lambda0,

Lambda0= c/f, with c the speed of light in free space= 3x10^10 cm/sec,

with f= 2.45 Ghz, then lambd0= 3x10^10/2,5 x10^9= 12 cm,

so the given dimensions in units of wavelength are to divide the lengths in centimeters by the wavelength lambda0,

60/120, 60/120, 1,6/120 = 0.5 lambda0, 0.5 lambda0.,0.013 lambda0,

If the material has a dielectric constant epsolon r, then the lambdamedium= lambd0/ sqroot of epsilonr,

So the the above numbers will be multiplied by the aqroot of epsilonr to be, 0.5 epsilon r lambdam, 0.5 eosilonr lambdam.,0.013 epsilonr lambdam

Best wishes

The 2dBi figure is the maximum under ideal conditions. You need to reduce this gain because of antenna pattern considerations, absorption into the body and polarisation mismatch to give the required signal level margin. Under the circumstances 0dBi seems very optimistic to me. I would be inclined to play safe and go for -10dBi!

If you are using CST

I have attached photo to follow steps also and explanation too

only four step to follow

1. select the solver first ( if time domain)

2. then go to simulation setting

3.select the source type as a selection in simulation setting

4. then select excitation list and there you can change amplitude and phase of signal also

Thank you very much dear Pranita Hetwade

I think Shrivaj is correct. With er of 4.4 and loss tangent of 0.02 there should be losses of about 1 dB per (free space) wavelength in your substrate. This may give a false impression of a good match at 40 GHz where the wavelength is 7.5 mm.

Dear laxmikant

For a dual feed antenna, you can easily maintain the phase as required. For example, If you want to design circularly polarized antenna, 90 degree phase can be easily maintained through orthogonal feeds. You can refer the link given below for dual feed having dual polarization characteristics.

The antenna can be fed easily in orthogonal position and probably having simple structure.

For a single feed antenna, it is difficult to maintain the phase as required. For example, for circularly polarized antenna, it is difficult to maintain 90 degree phase. For multiple polarization using a single feed, you can refer the link given below:

For dual polarization, the various techniques such as multiple feed, crossed feed etc. available in the literature.

You can refer the paper entitled "A Multimode Wideband +-45 degree Dual-Polarized antenna with embedded loops" doi: 10.1109/LAWP.2016.2594240 for dual slant linear polarisation.

Hope you find your answer after go through these papers.

Dear Vikas

The substrate height is mentioned in the respective material data sheet provided by the manufacture. Generally, the variants of the material Rogers substrate height is 5 mil, 10 mil, 20, mil, 31 mil, 62 mil available as per data sheet. The rogers RT-duroid 5870/5880 substrate material data sheet is enclosed for your reference. Similarly, you can find the height of other material data sheet.

Hope you find the answer.

From layout click on momentum ---> component-->create update. Now go to library and select this component and place it in schematic.

If you don't want to measure the result which is the best solution then there are many commercialy available modelling packages using FDTD, FE, TLM and boundary element algorithms. All will give you answers. Beware, these are sophisticated tools and you really have to know what you are doing when using them. In particular, the way in which you describe the antenna feedpoint is critical for the S11. Never accept a modelled answer at face value. You must always test your model by varying its parameters and looking for convergence. Also, remember that a model is a model and not reality.

If the frequency of the interfering sources is different from the frequency of the strong signal you can detect the weak signals by means of filters.

An other solution you can acquire the signal and correlate it with every source in this way if the sources are not correlated then you can separate them by this method. You can also make Fourier transform of the detected signal and distinguish the signals by their frequencies. The last method is similar to the filter method.

Best wishes

Please check this article:

If you make your antenna small it will be inefficient. This is a fundamental law of physics. You may be able to use an inefficient antenna. If an antenna is smaller than about 1/3 wavelength across, the best efficiency you can get is proportional to the volume of the sphere you can fit it in (including its image in the ground plane) divided by the volume of a sphere one sixth of a wavelength radius.

The inefficiency happens because, for the small antenna to radiate much, it needs the integral of current times length to be high enough. For small sizes this usually requires high currents, which have high conductor losses. They also have high stored energy, which usually also means high losses in a resonant circuit. High stored energy also usually means very narrow bandwidth, which can mean problems getting the tolerances good enough, or having low transmission speed, although the losses linked with the inefficiency broaden the bandwidth.

Read Wheeler, about small antennas, or The Small Antenna Handbook, Hansen and Collin.

Fractal antennas don't get round the difficulties I have described, and are often not the best kind of antennas.

For example: If you want a 100 MHz antenna 5 cm long (rather than 1.5 m) then it may be a bit less than 1% efficient, so you may need 20 W or more to get 100 mW from it, even if it is designed well.

Long wave (1500 m wavelength) receive antennas in radios are usually very small compared to a wavelength, and they are very inefficient, but that doesn't matter because the noise signal in the atmosphere at that frequency is massive, and so unless the signal they want is bigger than that noise - so VERY big - they can't use it anyway, and an inefficient antenna is fine. If you are transmitting, antenna efficiency is much more important, which is why long wave transmitters are usually hundreds of feet tall or long - but wasting 10 or 20 w in your case is insignificant compared to wasting 100 MW or more in their case!

Dear Cheah,

Yes you can implement a preselector filter at the antenna side. However the RF filters design is critical especially at 5 GHz. In the design you have to choose passive components with a self resonance frequency below your design specifications. It is not simple to find inductors with an high L values with a self resonace frequency greater than 5 GHz. You can see the coilcraft inductors. In my opinion at 5 GHz you can design filters using microstrip circuit as for example coupled lines or interdigital lines.

Regards

Thank you for the responses. I'm looking for commercial antennas that are suitable for LHCP GPS signals.

So far I have a lead with antcom antennas but any other suggestions are welcome.

I've plotted data (gain and rE_total both) of an antenna (equilateral TDRA). I think your simulation is correct. Getting +35dB for rE_total is possible but we are interested in gain, not e_total. Therefore, observe gain, not rE_total.... Plot gain_total or (gain_theta and gain_phi)... You will get actual results... Don't worry, your data is correct, I hope. But, use small step size and double check convergence.

Please use use small step size in freq sweep. Your data related to S11 shows that the step size is large. Do not use that. Always try to use smallest step size to get accurate results. Please give at least double convergence in simulation.

I think you will find the answer here:

For more information, see these books:

J.R. James, P.S Hall, "Handbook of Microstrip Antennas" (Peter Peregrinus,1989)

G. Kumar, K.P. Ray "Broadband Microstrip Antennas" (Artech House,2003)

Usually antenna will not burn you SDR front-end. If the antenna is not 50 ohm, then the efficiency of the system will be reduced. The receiving of the weaker signals will be more challenging. Furthermore, if you know the direction of arrival of the signal (For example, line of sight communication) then the highly directive antenna would be mostly useful. If you communicating in the high mulitipath channel (Non line of sight case) you would prefer to use omnidirectional antenna.

Dear Hans Van Leunen,

Thanks for sharing your article. Do you know the orbital angular momentum in reference of optics. That is variation in phase of optical wave front. Same concept is also true for EM radiation through antenna. OAM occur due to orbital motion of electron and spin angular momentum occur due to spin of electron along its own axis.

In optics its very easy to demonstrate the OAM as compare to radiation through antenna.

Higher frequency (~THz) electromagnetic wave, similar to a moving photon (rest mass ~0).

MASER may be the suitable example.

Hello,

Gain > 4 dB could be obtained for different number of loads and this is shown clearly in the following document (e.g. after 500 MHz in Figure 2.13):

From what I understand, there are a lot of choices in UHF antenna design. They all have their own advantages and disadvantages. But I would like to suggest for you to develop your own novel design of antenna based on your requirement. However, there are several critical criteria that should be taken into account. You might want to look for them in J. Li, T. Jiang, C. Wang, and C. Cheng, “Optimization of UHF Hilbert Antenna for Partial Discharge Detection of Transformers,” IEEE Trans. Antennas Propag., vol. 60, no. 5, pp. 2536–2540, 2012.

I don't have the code for it, but you can refer to Eq. 1.33 and 1.36 on the book "Wideband Beamforming - Concepts and Techniques"

( ).

I highly recommend this book if you are starting on the field of Wideband BF.

If permittivity (er) is increases (1) lamda_g will be decreased, hence resonant frequency will reduce (2) maximum amount of E-fields will be confined in the dielectric media. Hence, less radiation, Hence, gain will reduce. (3) Amount of Electric stored energy will increased. hence, Q will increase (4) as Q is increasing, BW will decrease (5) lamda_g will be decreased, hence compact antenna can be designed (6) More no of bands will be accommodated. hence, multiband antenna is possible

You can find the microstrip antenna concepts in a survey paper " Design and performance issues of Microstrip antennas".......

Hello,

For coming and cross polarization, phi 90 has to be taken, it gives both polarization. First check excitation angle and then make it as references. Horizontal angle will be 0 degree from plane of excitation and vertical will be 90 degree from the reference. - 45 degree can be neglected.

Thanks

Dear Mothana,

Adding to the above colleagues, it seems that you speak about a single user MIMO system for space multiplexing. If this is the case then you can calculate the maximum channel capacity C bits per second of a specific user.

C= min( Nt, Nr) Wch log2 (1 + S/ min( Nt, Nr) (I+N)),

where the Bandwidth Wch is that of the single user, Nt is the number of transmit antennas, I interference power, N is the noise power and S is the total signal power radiated from all antennas and reached to the receiver antennas.

In case of a Nt=Nr=Na the above relation can be reduced to the expression:

C= Na Wch log2(1+ S/( Na (I+N)),

Best wishes

Thanks Pranita. I have gone through the video. Can you suggest me any material/ Book on equivalent circuits of an antenna and mathematical analysis.

It looks helpful as all fundamentals are covered. Thank you Mr. Hafiz Saad Khaliq.

I have extracted RNA from whole bees including their heads with good success. I would only lose maybe one or two samples per 24, but then would just try taking these through Qiagen plant mini kit protocol again and it would work on these samples, suggesting that it was probably an issue with my technique or having too much RNA that would clog the filter. I used beta mercaptoethanol for the RNA extraction followed with a Qiagen plant mini kit. The key I found was not to use the g column filter in the kit because sometimes these would get clogged and no RNA yield would result. I used a DNAase treatment on the column which has to be used anyway because the g-column doesn't work well enough to remove all of the genomic DNA. Using a DNAse treatment on the column works much better than treating the extracted RNA later with DNAse. My RNA yield did not correlate necessarily with the pigment of the solution. I was able to get at least 50 ng/ul of RNA extracted for all samples needed for my qPCR gene expression study. From my experience using phenol chloroform DNA extraction or other RNA extraction methods there are always a few samples that do not yield much DNA/RNA for whatever reason. Therefore, I think this method works just as well as others when bee heads with compound eyes are included. Attached you will find the study where I used the methods above.

Circular polarisation can be achieved using one of the following ways:

1. Feed with 90 deg. phase shift, like hybrid coupler

2. Transmission line feed, power divider and keeping one of the line wavelength/4 ahead or behind.

Also, using various design patterns like:

1. A Cross-Slot of Unequal Arm length

2. Y-Shaped Slot of Unequal Arm Length

3. Designs with Slits

4. Designs with Spur Lines

5. Designs with Truncated Corners

6. Designs with Peripheral Cuts

7. Designs with a Tuning Stub

For more details you can refer "Compact and broadband Microstrip Antennas" by Kin-Lu Wong

This demonstration given in the video is very useful. See the video: https://youtu.be/kws5Bwatvl4

Is necessary know more about the antenna (wavelength, dielectric constant, tangent loss, etc). But in normal common situations waveport should work. Good luck

Can you get your magnetic probe to work at plasma cut-off frequencies corresponding to densities you wish to measure? Your magnetic probe probably has no directionality at GHz frequencies, so you may not have great localisation of the measurement, although a reflection and range may give you some information.

The circuit parameter model can be obtained if you know the target model and simulated or experimented diode performances (both DC and AC). You may need software such as ADS (previously EEsof) which has optimizing engine to do.

Positioning based on RSS mainly makes sense in line-of-sight propagation, where the distance to the user (i.e., the user position) determines the RSS and the multiple antennas can be used for angle-of-arrival estimation. This is a typical setup for array signal processing.

In non-line-of-sight scenarios, where Rayleigh fading is a useful model, positioning based on RSS will be very difficult, I believe, since the position and the RSS are only vaguely correlated due to the scattering. However, fingerprinting based methods can potentially be used.

This file is an example to answer your question.

Because I don't know the detail of your project,so I've

just provide an general case of antenna design to answer your question.

One can improve gain by using defected ground surface (DGS), using electronic band gap structure (EBG) or using antenna array.Its all depend upon your application requirement and your interest in implementation.

If you are looking for an antenna for LTE Advanced, then the operating frequency ranges are probably the most important, followed by the number of antennas.

1. No. of Antennas (I believe it is 8*8 or 8*4). But why?

The number of antennas helps to increase the capacity. The more antennas, the faster you can transmit/receive (as each antenna can send its own bitstream) and/or the more users you can serve. The actual number of antennas is determined by the limitations of the equipment (how many RF ports/channels the specific equipment can support). The latest base stations (BS) can have large (e.g. 8*8) MIMO arrays. The user equipment (UE) terminals are limited in size (to fit in the palm of a hand) and so cannot fit so many antennas.

2. Radiation Pattern?

3. Beamwidth?

4. Gain?

These are all related. The gain tells how well antenna focuses the electromagnetic radiation and thus how far it can send the signals. The gain is directly linked to the beamwidth. The narrower the beamwidth, the higher the gain. You can see a compromise here - it is possible to either send signal far (but in one direction) or cover a large area around the BS.

The radiation pattern describes the shape of the gain versus angle. Most antennas for BS are designed to radiate within a given sector (e.g. 120 degrees wide).

Well.. I must add that the No of antennas adds a multiplier effect here. Subject to applying appropriate signal processing techniques, one can consider that effective gain due to N antennas can be made to be N times higher than the gain due to a single antenna. Thus, a BS can choose to use many antennas to reach a far away user or to send intensive data stream to a nearby user or it can use each individual antenna to connect to a different group of users etc. The more antennas one has, the more flexibility one can afford, in addition to just capacity.

5. Specific Absorption Rate?

The SAR is mainly relevant to the UE antennas (as the SAR should be limited, to avoid directing too much energy into person's head or arm). The SAR is usually regulated by local regulators (spectrum or health ones).

6. Bandwidth (20 MHz*5 = 100 MHz channels through carrier aggregation).

The aggregation feature refers to aggregating the channels within the same frequency band (e.g. 2100MHz) or can be used to aggregate channels over different frequency bands (e.g. 1800MHz and 2100MHz).

7. Efficiency?

The efficiency for BS antennas is usually high (90% and up) whilst the efficiency for UE antennas is more difficult to make high.

8. Polarization?

Usually vertical polarization.

I do not know if something like this

or

may assist.

In simple terms, an antenna is a transducer intended to transfer the electromagnetic energy between air and cable. The antenna you have selected is not meant to be mounted to a metallic antenna (as per the specifications you referred to). Placing it close to metal may lead to 2 consequences:

a) nearby metal "loads" your antenna, which changes the antenna’s input impedance and so the antenna becomes poorly matched and cannot transfer the electromagnetic energy between the air and cable properly. Most of the energy just gets reflected back.

b) the metal behind the antenna also affects the radiation pattern. An antenna radiates part of the energy directly into the air and part of the energy towards the metal. The metal reflects this energy and sends it back to the air. However, if the antenna is closer than 1/4 wavelength to the container, the copy of the signal reflected by the metal starts to cancel out the direct signal due to destructive interference. As a result, whatever manages to overcome the impedance matching problem (a) and gets radiated out of the antenna, is effectively being cancelled by a copy of itself reflected from the metal.

To make matters worse, both effects affect all bands of interest, and in a different manner.

A) A proper solution to address both parts of the problem is to find or design an antenna intended to be able operate when mounted on metal surface. This should really be fairly easy your bands of interest are around 1 GHz and above, so many designs will be compact and efficient.

A usual complication is to get all bands working. Assuming you need large quantify of inexpensive antennas, people like http://poynting.tech/ can do the design, if you cannot find a supplier.

B) If, for some reason, you have to use your specific already procured antenna PC104.07.0165C from Taoglas, you can try to improve the impedance matching and reduce or eliminate the radiation cancellation effects by playing with the distance between the antenna and the metal. You would be looking for at least 1/4 of the wavelength of interest.

Clarification: The “free space wavelength” is calculated as 3e8/frequency(Hz) for free space (air). If you will use some plastic (i.e. dielectric material) between the antenna and metal (which is perhaps a more practical approach for mechanical considerations), then you will need to compensate for the fact that plastics are thicker than air and so the formula will be (3e8/sqrt(eps_r))/frequency(Hz), where eps_r is the dielectric constant/permittivity of the plastic (usually between 2 and 8). You can look up some details at

http://maxwells-equations.com/materials/permittivity.php

and

permittivity values at for example

or

NB! This approach (B) will not give the same optimum impedance match as for the free space (you will still loose some dB), but will offer much better energy transfer as compared to not using the approach (B). Please however note that placing the antenna near metal (within around 1/8 to 1/4 of the wavelength of the metal will result in a stronger radiation perpendicular to the metal and very weak radiation in the plane of the metal.

I hope this helps. Good luck!

There's also another way to approach this problem, in addition to Dr Zekry's approach, and that is to find the maximum bit/sec capacity theoretically possible. Without assuming any particular modulation scheme, but instead by using the desired signal to noise ratio as a constraint. The general idea is this. For a given RF channel bandwidth, and a specification of the minimum possible signal to noise ratio I can expect, what is the maximum theoretical bit rate?

Shannon's equation is used. But note that Shannon's equation applies to using a single antenna at the transmitter and receiver. If you allow for multiple antennas in the transmitter and multiple antenna in the receiver, in that one RF channel, and you have multiple de-correlated propagation paths, you can do better. For instance, in a 2X2 antenna example, with ideal decorrelation of the signal paths, you can double the channel capacity without requiring a higher SNR.

Anyway, back to basics. Here is Shannon's equation:

Capacity (b/s) = Channel Bandwidth (Hz) * logbase2(1 + S/N)

Note that S/N is the power ratio of signal and noise, expressed as a ratio and not in dB!

So for example, with a bandwidth of 20 MHz (single LTE channel) and a marginal SNR let's say 8 dB (small antenna at the mobile device), the maximum possible capacity comes out 57.4 Mb/s.

You will get better if you assume that higher SNR is okay. Same 20 MHz channel, allow 15 dB of marginal SNR, and now you get 100.6 Mb/s capacity.

You can see in the equation that doubling the RF channel bandwidth, keeping the rest the same, and you double the capacity.

So this approach allows you to get an answer that is the theoretical best, without taking modulation or FEC schemes into accoount.To be realistic, though, you should probably degrade the SNR by at least 3 dB, to get results that can be achieved in the real word. So, instead of 8 dB SNR, you might actually assume you have 5 dB of SNR. This sort of thing.

Thanks Puran for showing the way :P

You can reach any number of bit/s/Hz per user. It all depends on the simulation parameters that you select. In practice, if you use 64-QAM with 5/6 code rate, then the you achieve 6*5/6=5 bit/s/Hz. This is the maximum spectral efficiency in some version of LTE. With that I want to say that any number between 0 and 5 bit/s/Hz are reasonable numbers in practice, it just depends on how good your channel is.

If you want to plot a CDF curve, then you need to obtain many independent random realizations of the thing that you are interested in. Then you can put these numbers in a vector and use cdfplot in Matlab to plot them.

You are going to have to be more specific about the reflections. Balanis says a lot about reflections. What two kinds do you mean and on which page(s)?

Hello,

Magnetron antenna is used for excitation at a particular frequency, as its dominant mode is TM01 mode because of slow wave structure, so your waveguide should also be designed for particular mode otherwise final structure is complex one. First, which type of magnetron you are going to use, cavity or linear, that should be first decided. As an excitation source, you can use a loop wire antenna like helical TWT antenna. Decide position of source from the waveguide and design magnetron as an loop antenna in CST or any other software.

Thanks,

Firstly, You need to define and set the parameters of the antenna of your geometry such as the frequency,mode,E-field and so on before any computation is done. Thereafter, you can run it and the far-field antenna parameters will be calculated and will be made available in the 2-D/3-D results, and depicted in the main window when a plot is selected. Additionally,I will urge you to go through the demo that comes with the CST software .It will assist you greatly in this regard.

Hope it helps.

Best regards,

L

ya . definitely

Dear Sir

I meet the same error with you. Have you found the solution?

I found a chapter " Characterisation and Channel Modelling for Satellite Communication Systems " which mention about the use of hypergeometric function.

Regards

In the VHF range (free space wavelength roughly one meter) this is certainly possible..the only question is the bandwith. A resonant antenna can be highly effective but is not very broadband (like may of the "hidden"antennas in cell phones these days). Maybe there are certain requirements on the directional patten and polaristion in addition to the bandwidth. Would you need both TX and RX in the same place? I sometimes hear from my students that an antenna has to be lamda/4 or lamda/2 depending how its made.And then I ask them :Do you have am AM radio in the 1 Mhz band.(1 Mhz =300 meter free space wavelength)...what its max linear dimension..does it work?

In simple words: electrically small antennae (there are many books on this) can alway work and they work very well if resonant but there are certain rules to respect.

This is because the wave on the guiding structure has to match the phase of the radiated wave (the humps and dips of the sine wave have to match). A fast wave has a wavelength longer than a wave in free space, so there is an angle for the wave in free space at which the phase of the guided wave is the same as the phase of the radiated wave. For example, if the guided wave has infinite wavelength then this is a match for a wave radiated at 90 degrees (normal to the surface). For shorter guided wavelengths the wave goes off further from normal, until when the guided wavelength is the same as the free space wavelength the radiated wave is parallel to the guided wave. For shorter wavelengths than this (slow waves) there is no direction where the phases match, and radiation can happen when there are discontinuities, such as slots or probes, perhaps every 2 wavelengths, so that the phase at those discontinuities can again match the phase of the radiated wave, ignoring the changes inbetween.

Please refer http://library.iugaza.edu.ps/thesis/111659.pdf

Your Question is related with convergence (or 'correctness') of the solution, which in HFSS for Driven simulations is evaluated on the basis of the scattering parameters observed at each port.

HFSS uses adaptive meshing, which is to say that it sets up an initial mesh, solves the fields, and then re-meshes based on where the fields have a high concentration and/or gradient. Each re-meshing step is called an "adaptive pass". Importantly, at each step, the scattering parameters are evaluated at each port, and compared to the previous step. The difference between the two is called "delta S".

So, in order to make sure a simulation is correct, HFSS does adaptive passes until the delta S falls below a set threshold. HFSS also gives you a large degree of control over this process: you can set delta S to be whatever you want, and you can also tell it to do a maximum number of passes, such that the simulation will stop whether or not the scattering parameters have converged.

Hope this helps!

Dear Mr. Muhammad Usama,