ArticlePDF Available

Improved Vlasov Antenna with Curved Cuts and Optimized Reflector Position and Shape

Authors:

Abstract and Figures

This paper presents a Vlasov antenna with curved cut shape and improved reflector position and geometry suitable for high power microwave applications. The curved shape of the proposed cut totally eliminates the sharp edges and angles present in Vlasov antennas with step and bevel cuts. Furthermore, with the proposed reflector configuration, the wave is radiated in the direction of the axis of the waveguide. A Vlasov antenna, designed for operation at 3 GHz, is used to compare the three cut types. An additional comparison is conducted to validate the concept of the enhanced reflector position, using the bevel-cut antenna and the improved cut. The proposed antenna results in increased antenna gain and in good performance in terms of sidelobe level and half-power beamwidth, with maximum radiation directed toward the axis of the waveguide center.
This content is subject to copyright. Terms and conditions apply.
Research Article
Improved Vlasov Antenna with Curved Cuts and Optimized
Reflector Position and Shape
H. M. El Misilmani,1M. Al-Husseini,2and K. Y. Kabalan1
1ECE Department, American University of Beirut, P.O. Box 11-0236, Beirut 1107 2020, Lebanon
2Beirut Research and Innovation Center, Lebanese Center for Studies and Research, Beirut 2030 8303, Lebanon
Correspondence should be addressed to H. M. El Misilmani; hilal.elmisilmani@ieee.org
Received  October ; Accepted  January 
Academic Editor: Jun Hu
Copyright ©  H. M. El Misilmani et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
is paper presents a Vlasov antenna with curved cut shape and improved reector position and geometry suitable for high power
microwave applications. e curved shape of the proposed cut totally eliminates the sharp edges and angles present in Vlasov
antennas with step and bevel cuts. Furthermore, with the proposed reector conguration, the wave is radiated in the direction of
the axis of the waveguide. A Vlasov antenna, designed for operation at GHz, is used to compare the three cut types. An additional
comparison is conducted to validate the concept of the enhanced reector position, using the bevel-cut antenna and the improved
cut. e proposed antenna results in increased antenna gain and in good performance in terms of sidelobe level and half-power
beamwidth, with maximum radiation directed toward the axis of the waveguide center.
1. Introduction
High power microwave (HPM) sources, such as the back-
ward-wave oscillator (BWO), the gyrotron, and the vircator
(virtual cathode oscillator), generate power in cylindrically
symmetric transverse electric TE0𝑛 or transverse magnetic
TM0𝑛 modes. e sidelobe generation, gain reduction, and
inecient power loading on the antenna aperture make these
modes unsuitable for driving conventional antennas. is
gave the idea of using mode converters at the output of these
sources to convert these modes into a plane-parallel linearly
polarized beam.
AVlasovantenna[], which is one of the most known
mode converters used, is composed of a cylindrical waveg-
uide with a shaped end, which can directly radiate energy
from cylindrically symmetric modes in circular waveguides,
without the need for an additional mode converter. e two
well-known Vlasov antenna types come with a step cut and
with a beveled cut []. e rst type, a waveguide aperture
with a step cut, originally suggested by Vlasov, has sharp
edges and therefore may suer from electrical breakdown
when radiating HPM []. e beveled cut was suggested by
Wada and Nak aj i m a [ ] to avoid the sharp points of the
step cut, leading to a more suitable shape for usage in HPM
applications.
A comparison of the performance of bevel-cut and step-
cutVlasovantennasinHPMisconductedbyRuthetal.in
[], concluding that the bevel cut has better performance in
such applications. A series of Vlasov-type high power micro-
wave launchers have been investigated with several slant-cut
angles in []. Additional experimental results and theoretical
investigation of TE0𝑛 and TM0𝑛 mode Vlasov launchers
have been presented in [,]. Other studies focused on
increasing the gain of bevel-cut and step-cut Vlasov antennas.
Dahlstrom et al. added a reector to a bevel-cut Vlasov
antenna to increase its gain and better direct the main beam
[]. Fazaelifar and Fatorehchy proposed in []twomethods
for increasing the gain of a bevel-cut antenna, one using a
parabolic cylinder reector and the second using a horn.
Moreover, Zhang et al. studied the step cut in the presence of a
parabolic reector []. Other work discussed the use of dual-
reector in the presence of Vlasov antennas [,]. Improved
beam focusing of high powered microwaves radiating from a
Vlasov antenna has been also achieved by applying a are to
Hindawi Publishing Corporation
International Journal of Antennas and Propagation
Volume 2015, Article ID 193630, 12 pages
http://dx.doi.org/10.1155/2015/193630
International Journal of Antennas and Propagation
Y
X
Z
A
𝛼
(a) Bevel-cut design
Y
X
Z
A
B
(b) Step-cut design
F : Congurations and parameters of bevel- and step-cut Vlasov antennas.
thelauncheraperture[]. Moreover, Sealy et al. investigated
the use of corrugations with the are to enhance the pattern
performance []. Other studies used Vlasov antennas as a
component in several systems []. However, a Vlasov
antenna with either the bevel- or step-cut has its own
maximum radiation shied by some angle with respect to
the axis of the waveguide. e work by the authors in []
focused on optimizing the reector position to bring back the
maximum radiation along the axis of the waveguide antenna.
In this paper, we rst design a bevel-cut Vlasov antenna
operating at  GHz with the aim of obtaining maximum
gain. Next, a step-cut version is designed to have radiation
in the same direction as the bevel-cut counterpart, and a
comparison of the performance of both is conducted. Later, a
newcutshape,bettersuitablefortheuseofVlasovantennas
in HPM applications, is presented and its advantages are
reported. Furthermore, the optimized reector position for
Vlasov antennas is presented, which will help, with the proper
rotation angle, to orient the generated waves along the +
direction, which is the axis of the waveguide in our case.
In addition, with our proposed conguration, the reector
is directly attached to the waveguide structure, decreasing
the size of the usual Vlasov antennas with reectors, and
eliminating the need of extra components to hold the waveg-
uide and reector together. e proposed reector is applied
to bevel-cut and step-cut Vlasov antennas and then further
enhanced with curved edges to be applied to the curved cut
to evaluate its performance.
2. Vlasov Antennas
Both step- and bevel-cut Vlasov antennas are the result of
shaping the end part of a circular waveguide. For operation
at  GHz, the used circular waveguide has a radius of  mm
and a length of  mm.
2.1. Vlasov with Bevel Cut. AVlasovantennawithabeveled
cut is shown in Figure (a).ecutangleis the single
parameter available for optimization, and it has the main
eect on the gain and radiation patterns of the antenna. e
angle that maximizes the gain of the antenna is given by []
=sin−1 0𝑛
(2),()
where 0𝑛 is the th root of the equation 0(0𝑛)=0,is the
wavelength, is the inner radius of the waveguide, and 0is
the Bessel function of the rst kind and zeroth order.
For the TM01 circular waveguide designed for  GHz, =
4.5cm and =10cm. Also, 01 =2.405,sothebevelcutwill
be calculated as follows:
=sin−1 (2.405×10)
(2×4.5)= 58.32.()
e highest gain according to the equation is obtained at
acutangleof58.32. is result has been veried by simula-
tions using ANSYS HFSS. For this angle, the resulting peak
gainis.dB.egainpatterns,computedinCSTMWS
for both =0
and =90
planes, are shown in Figure .
Maximum radiation is obtained in the =32
and =90
direction.
2.2. Vlasov with Step Cut. AVlasovantennawithabeveled
cut is shown in Figure (b). e step cut is determined by the
two parameters, and ,asindicated.evalueofis xed
at . mm, which is the same value obtained with the bevel
cut aer nding the angle . For comparison purposes, the
step-cutVlasovisdesignedsothatithasthesamedirection
of maximum radiation obtained with the beveled cut. For
this purpose, via CST simulations, is found to be  mm.
Itwasnoticedthat,asthevalueofdecreases, the angle of
maximum radiation increases. e gain patterns of the step-
cut Vlasov antenna, in the =0
and =90
planes, are
shown in Figures (a) and (b), respectively. As is the design
aim, the main lobe peaks at =32.
ComparingthetwoVlasovantennatypes,itisveried
that the step cut gives better performance in terms of max-
imum gain and half-power beamwidth (HPBW). However,
the beveled cut results in lower sidelobes, and this comes in
addition to its suitability for HPM applications.
3. Improved Cut
e conventional Vlasov antennas may suer from electric
breakdownwhentheyradiateatHPM.Althoughthebeveled
cut was introduced to avoid the sharp edges present in the
step cut, it results in a decreased gain and an increased HPBW
of the antenna. A new cut shape, introduced by the authors in
[], is shown in Figure .isshape,totallybasedoncurves,
International Journal of Antennas and Propagation
−25
0
30
30
60 60
9090
12
120
120
150
150
180
−6.5
(a) 𝜙=0
plane
0
30
30
60 60
90
90
6.5 12
120
120
150
150
180
−25
(b) 𝜙=90
plane
F : Gain patterns of bevel-cut design (using CST).
0
30
30
60 60
90
90
12
120
120
150
150
180
−25 −6.5
(a) 𝜙=0
plane
0
30
30
60 60
90
90
12
120
120
150
150
180
−25 −6.5
(b) 𝜙=90
plane
F : Gain patterns of step-cut design (using CST).
(a) D view
R1
R2
R3
Y
L
X
Z
(b) Parametrized dimensions
F:Vlasovantennawithproposedcut.
goes ahead of the beveled cut in removing the sharp edges
and corners and is a result better suitable for applications
involving HPM.
In this design, we have the exibility to optimize several
parameters to reach the desired gain, HPBW, and direction of
maximum radiation. ese are the radius of Curve  (), the
radius of Curve  (), the radius of Curve  (), and the
separation between Curves  and , noted by on Figure .
To compare it with the step- and bevel-cut versions,
a Vlasov antenna based on the same waveguide and on
theproposedcutisdesignedsothatithasthemaximum
radiation in the same =32
and =90
direction. Tabl e 
lists the obtained parameters of the new design. e resulting
patterns are shown in Figure .
e gain patterns resulting from the step, the beveled,
and the proposed Vlasov cuts are compared in Figure .e
International Journal of Antennas and Propagation
0
3030
60 60
90
12
120
120
150
150
180
−25 −6.5
90
(a) 𝜙=0
plane
0
30
30
60 60
90
90
12
120
120
150150
180
−25 −6.5
(b) 𝜙=90
plane
F : Gain patterns of the proposed Vlasov antenna (using CST).
0
5
10
0 50 100 150
Absolute gain (dB)
Step cut
Bevel cut
New cut
𝜃(deg)
−150
−5
−10
−15
−20
−25
−100 −50
(a) 𝜙=0
plane
Step cut
Bevel cut
New cut
0
5
10
Absolute gain (dB)
−5
−10
−15
−20
−25
0 50 100 150
𝜃(deg)
−150 −100 −50
(b) 𝜙=90
plane
F : Comparison of the gain patterns of the step, the beveled, and the proposed Vlasov cuts.
T : Parameters of the proposed Vlasov antenna.
Parameter Value (mm)
Waveguide radius 
Waveguide length 
1 .
2 .
3 

obtained peak gain values are given in Table .BothCSTand
HFSS reveal that the proposed Vlasov antenna has a higher
peak gain, which overcomes the decreased gain issue that the
bevel cut has.
e compared HPBW and sidelobe level ratio (SLR)
results, computed in CST, are listed in Tab l e  . In addition
to totally eliminating the sharp edges and corners that limit
theperformanceoftheantennaathighpowersandproviding
higher peak gains, the results have shown that the proposed
cut gives a smaller HPBW and a better SLR in the =90
plane, a better SLR compared to the step cut in the =0
plane, and a slightly narrower beam in the =0
plane
when compared to the bevel cut. ese observations are also
veried using HFSS simulations.
e reection coecient plots, for the three cut types, are
given in Figure .Asshown,thethreeantennasoperateatand
around  GHz with very low  values.
4. Vlasov with Reflector
Vlasov antennas radiate waves with maximum radiation
obtained in a shied direction. is was proven through
our simulations in Section , for which the three designed
International Journal of Antennas and Propagation
T : Compared peak gain, HPBW, and sidelobe level ratio (SLR).
Antenna Gain (dB) HPBWSLR (dB)
CST HFSS =0plane =90plane =0plane =90plane
Bevel cut . . . . . .
Step cut . .  . . .
Curved cut . .   . .
2.4 2.6 2.8 3 3.2 3.4 3.6
Reection coecient (dB)
Frequency (GHz)
Step cut
Bevel cut
Proposed cut
−15
−10
−20
−25
−35
−30
−40
(a) 𝑆 using CST
2.4 2.6 2.8 3 3.2 3.4 3.6
Frequency (GHz)
Step cut
Bevel cut
Proposed cut
Reection coecient (dB)
−15
−10
−20
−25
−35
−30
−40
(b) 𝑆 using HFSS
F : Comparison of the reection coecient, using both CST and HFSS.
antennas radiate in the shied directions corresponding to
=
𝑚=28
and =90
, computed using HFSS. However,
it is preferred to have the maximum radiation of the antenna
directed in a well-known and easy-to-locate direction. is
refers to the axis of the waveguide in our case. In addition,
the HPBW in =0
plane is large for the three radiated
antennas, and it is hard to highly increase the gain of these
antennas. In order to achieve rotation of the maximum point
of radiation of any of the Vlasov antennas and the curved-
cut shape antenna and decrease the HPBW in =0
plane, an optimized reector is proposed in the following
work.ereectorhastheshapeofahalf-hollowcylinder.
A conventional reector is used with the step- and bevel-
cut antennas designed, whereas for the optimized curved-
cut shape proposed in Section  an optimized reector
having also curved edges instead of the sharp corners of the
conventional reector is proposed. In both cases, the two
reectors have several parameters that aect the radiation:
the starting point of the reector, the radius of the reector,
the length of the reector, and the angle of rotation of the
reector with respect to the waveguide axis. All these param-
eters have been optimized to obtain the desired radiation
patterns.
300 mm
200 mm
R = 60 mm
58.32
17.5
148.5 mm
D = 90mm
X
Y
Z
F : Bevel-cut Vlasov antenna with reector.
4.1. Bevel-Cut Vlasov Antenna with Reector
4.1.1. Design and Simulations. Using the bevel-cut antenna
design in Section ., the maximum radiation is obtained in
the shied direction corresponding to =
𝑚=28
and
=90
, computed using HFSS. A conventional reector
having the shape of a half-hollow cylinder is then attached to
the bevel-cut Vlasov antenna as shown in Figure . e added
reectorhastheoptimizedvaluesofmmforthecylinder
International Journal of Antennas and Propagation
Reection coecient (dB)
With reector
Without reector
2.4 2.6 2.8 3 3.2 3.4 3.6
Frequency (GHz)
−55
−50
−45
−40
−35
−30
−25
−20
−15
F : Reection coecient computed using HFSS, with no-
reector case shown in red (dashed), and with reector in blue.
radius and a length of  mm. Upon rotating the reector
by a specic angle, it is seen that as the angle increases the
shi angle approaches origin. e initial bevel-cut Vlasov
antenna gives a maximum computed gain of .dB, with the
maximum radiation along the =28and =90direction.
e optimized reector angle for perfect direction along the
+axis is seen at angle of 17.5. For thisangle, the maximum
radiation is back along the axis of the waveguide; that is,
=0and =90.ebevel-cutantennaoperatesatGHz
as shown in the reection coecient plot (11)inFigure .
Ithasagainof.dBandareducedHPBW,asindicatedin
Figures (a) and (b). It is shown that, for the case with the
reector, the maximum radiation is redirected along the axis
of the waveguide.
4.1.2. Verication of the Results Using CST. e same design
simulated in Section . using HFSS has been also tested using
CST. e gain patterns in the two cases (without and with
reector) are shown in Figure . As can be seen, the max-
imum gain of the antenna is redirected along the axis of the
waveguide. e D gain patterns comparing the two cases are
shown in Figure . Furthermore, the peak gain has increased
from . to  dB, and the HPBW has decreased in the plane
of interest, that is, =0plane, from 58.4to 41.7.
4.2. Step-Cut Vlasov Antenna
4.2.1. Design and Simulations. Again, using the step-cut
antenna design in Section .,themaximumradiationis
obtained in the shied direction corresponding to =
𝑚=
28and =90
, computed using HFSS. e same reector
used in Section . is then attached to the step-cut antenna
as shown in Figure .Here,is the distance between the
waveguide port and the start of the reector. e gain patterns
of the designed step-cut antenna are shown in Figure .By
inspecting Figure (b), the concept of rotating the reector
is validated and maximum radiation is obtained back along
the waveguide axis for a rotation angle of 17.5similar to
the one used for the bevel-cut case. e design has been
also simulated using CST showing the same results with
an increment in gain from . dB to .dB with a large
decrement in HPBW in the plane of interest (=0
)from
55to 41with negligible changes in the =90plane.
5. Improved Curved Cut with Optimized
Reflector Position
Aer modifying the cut of the Vlasov antenna in order to
optimize its performance as described in Section ,inthis
section the optimized reector proposed in Section  will be
used to validate the concept of rotating the reector in order
to radiate the wave generated along the +direction on the
novel cut shape. However, in order to also avoid having sharp
corners in the reector, an optimized one is proposed here
to be attached to the curved-cut shape antenna. Figure 
shows the proposed combined antenna joining the curved-
cut antenna and the curved-edges reector with its optimized
parameters. e parameters of the curved-cut antenna are
thesameasthoseusedinthepreviousdesigninSection 
and are listed in Ta b l e  . In order to get the optimized values
of the reector radius and length indicated, the following
parametric study has been done.
5.1. Parametric Study
5.1.1. Radius Study. In order to choose the appropriate value
of the reector radius, the radius has been varied from  mm
to  mm. e realized gain value at each value of radius
is shown in Figure (a), and the gain pattern in the plane
of interest (=90
) at each radius value is also shown in
Figure (b).
Inspecting Figure (a), it is seen that the realized gain in
the plane of interest (=90
) increases as the radius of the
reector increases, till reaching a maximum value at a radius
of  mm. However, inspecting the gain pattern in the =
90plane in Figure (b),itisseenthatatthisradiustheSLL
and HPBW are higher than those with the second maximum
value of gain at a radius of mm. Hence a radius of  mm
is suggested to be the optimized value taking into account the
value of gain, SLL and HPBW.
5.1.2. Length Study. In order to choose the appropriate value
of the reector length, the radius has been varied from
 mm to  mm. e realized gain value at each value of
length is shown in Figure (a), and the gain pattern in the
plane of interest (=90) at each length value is also shown
in Figure (b).
Inspecting Figure (a), it is seen that the realized gain in
the plane of interest (=90
) increases as the length of the
reector increases, till reaching an approximate maximum
value at a length of  mm, aer which the value of gain
might increase but in very small steps compared to the
increase in the length. In addition, inspecting the gain pattern
in the =90
plane in Figure (b),itisseenthatatthis
chosen value of length the SLL and HPBW are better than
International Journal of Antennas and Propagation
−30
−60
−90
−120
−150
−180
−1.00
−9.00
−17.00
0
30
7.00
60
90
120
150
(a) Red in the plane formed by the 𝑋-axis and the point
of maximum radiation (𝜃=𝜃
𝑚,𝜙=90
), blue in 𝜙=0
plane
−30
−60
−90
−120
−150
−180
−1.00
−9.00
−17.00
0
30
7.00
60
90
120
150
(b) 𝜙=90
Plane
F : Simulated gain patterns computed using HFSS, with initial bevel-cut results shown in red (dashed) and proposed design results
in blue.
−25
0
30
30
60 60
90 90
13
120
120
150150
180
−6
(a) 𝜃=𝜃
𝑚,𝜙=90
plane
−25
0
3030
60 60
90 90
13
120
120
150
150
180
−6
(b) 𝜙=90
plane
−25
0
30
30
60 60
90 90
13
120
120
150
150
180
−6
(c) 𝜙=0
plane
−25
0
3030
60 60
90 90
13
120
120
150
150
180
−6
(d) 𝜙=90
plane
F : Bevel-cut simulated gain patterns using CST: (a) and (b) without adding the reector and (c) and (d) aer adding the reector.
International Journal of Antennas and Propagation
(a) Without reector (b) With reector
F : Bevel-cut D gain patterns using CST: (a) without reector and (b) with reector.
300 mm
200 mm
R = 60 mm
17.5
D = 90mm
X
Y
Z
L = 130 mm
B = 35 mm
A = 148.5 mm
F : Step-cut Vlasov antenna with a reector.
those with the higher values. Hence a length of  mm is
suggested to be the optimized value taking into account the
value of gain, SLL, HPBW, and antenna structure size.
5.2. Simulations and Results. Taking into account the opti-
mized values of the reector parameters, the proposed com-
bined antenna suitable for high power microwave applica-
tions has been simulated using CST with the radiation pattern
results shown in Figure .
e maximum radiation of the curved-cut antenna with-
out using the reector was shied in the direction corre-
sponding to =
𝑚=28
and =90
,asdepictedin
Section .InspectingFigure , the concept of rotating the
reectorisvalidatedandtheradiationin=90plane is now
directed towards the +plane,ascanbeseeninFigure (b).
In addition, the proposed combined antenna also increases
the gain of the antenna from . dB to . dB and decreases
its HPBW in the =0
plane from 58to 41,withminor
changes in the =90
plane. e same result has been also
achieved using HFSS with an increment in gain from . dB
to . dB as shown in Figure .
−30
−60
−90
−120
−150
−180
−1.00
−9.00
−17.00
0
30
7.00
60
90
120
150
(a) Red in 𝜃=𝜃
𝑚,𝜙=90
plane, blue in 𝜙=0
plane
−1.00
−9.00
−17.00
7.00
−30
−60
−90
−120
−150
−180
0
30
60
90
120
150
(b) 𝜙=90
plane
F : Step-cut simulated gain patterns, with initial step-cut
results shown in red (dashed) and proposed design results in blue.
International Journal of Antennas and Propagation
D = 90mm
X
Y
200 mm
R = 60 mm
Z
300 mm
L=148.5 mm
Rc=15.85 mm
Rc=15.85 mm
17.5
F : Enhanced Vlasov cut with a rotated optimized reector
with curved edges.
T : Comparison of the radiation characteristics of the three
designed antennas, with and without having the enhanced suitable
reector computed using CST.
Antenna Reector HPBW
Gain (dB)
=0plane =
𝑚plane
Bevel cut Without . . .
With . . 
Step cut Without  . .
With   .
Curved cut Without   .
With .  .
Combining all the simulations of the three designed
antennas, with and without having the enhanced suitable
reector, Tabl e  compares the radiation characteristics of the
various cases studied. As listed, in addition to bringing back
the maximum radiation along the axis of the waveguide, the
proposedcombinedantennaalsoincreasesthegainofthe
antenna and decreases its HPBW.
Observations. Several simulations have been done to study
the eect of each parameter of the Vlasov antenna with
curved-cut and improved reector position and shape on the
radiation performance. e following observations have been
inspected.
(i) As the starting point of the reector goes backward to
the start of the Vlasov antenna, the gain decreases and
the HPBW highly increases. is change also aects
the point of maximum radiation which will be rotated
by a certain degree from the axis of the waveguide.
(ii) As the rotation angle of the reector increases, the
gain slowly increases with minor variations in HPBW.
However, this change also aects the point of max-
imum radiation which will be rotated by a certain
degree from the axis of the waveguide.
(iii) As the radius of the reector decreases, the gain slowly
decreases and the HPBW increases.
10.8
11
11.2
11.4
11.6
11.8
12
12.2
40 45 50 55 60 65 70
Gain (dB)
Reector radius (mm)
Gain
(a)
−25
5
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
30
3.5
60
90
120
150
180
210
240
270
300
330
−15.5 −6 13
Ref Radius =40
Ref Radius =45
Ref Radius =50
Ref Radius =55
Ref Radius =60
Ref Radius =65
Ref Radius =70
0
(b)
F : Simulatedgain patterns computed using CST: (a) realized
gain values and (b) D gain patterns.
Hence, care should be taken in choosing the optimized values
for each of these parameters in order to attain the desired
performance.
One example on the use of such optimizations is to
extend the reector length to  mm, decrease the angle of
rotation to 15, and increase the starting point of the reector
(noted by ) to  mm. Applying these changes, the gain will
increase to . dB and the HPBW in the =90plane will
decrease to 37,withtheHPBWinthe=0
kept constant
at 41.1.
6. Conclusion
e Vlasov antenna, originally designed with a step cut made
to one end of a circular waveguide, has been improved by
 International Journal of Antennas and Propagation
11.4
11.5
11.6
11.7
11.8
11.9
12
150 160 170 180 190 200 210 220
Gain (dB)
Reflector length (mm)
Gain
(a)
Ref Length = 180
Ref Length = 190
Ref Length = 200
Ref Length = 210
Ref Length = 220
0
30
60
90
120
150
180
210
240
270
300
330
13
−25 3.5−15.5 −6
(b)
F : Simulated gain patterns computed using CST: (a) realized gain values, (b) D gain patterns.
−25
0
30
30
60 60
90 90
13
120
120
150
150
180
−6
(a) 𝜙=0
plane
−6−25
0
30
30
60 60
90 90
13
120
120
150
150
180
(b) 𝜙=90
plane
F : Gain patterns of the proposed curved-cut antenna with the optimized reector position and shape, computed using CST.
−30
−60
−90
−120
−150
−180
−1.00
−9.00
−17.00
0
30
7.00
60
90
120
150
F : Gain patterns of the proposed curved-cut antenna with the optimized reector position and shape, computed using HFSS: red
(dashed) in =0plane and blue in =90plane.
International Journal of Antennas and Propagation 
Nakajima who implemented it using a beveled cut. e latter
cut gets rid of the sharp corners present in the former one,
which makes the antenna supportive of higher microwave
powers, but this comes at the cost of reduced antenna
gain and broader beam widths. In addition, the maximum
radiation of these two antennas is shied by some angle in
the =90plane, assuming the antenna is directed along the
+axis.Inthispaper,animprovedshapewithcurvedcuts
for high power microwaves applications has been suggested,
leading to higher gain, decreased HPBW, and decreased
sidelobes levels. Furthermore, two optimized reectors, one
with enhanced position and the second with additional shape
enhancement having curved edges, are proposed, with the
ability to radiate the maximum radiation back to the +
axis and further decrease the HPBW. is concept has been
validated using the bevel- and step-cut Vlasov antenna, and
with the new curved cut proposed in this paper.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
Acknowledgments
is work is partially supported by an Associated Research
Unit (ARU) Fund from the Lebanese National Council for
Scientic Research and by the Electromagnetics and Radio
Frequency Research Group (EMRF) Fund at the American
University of Beirut.
References
[] S. N. Vlasov and I. M. Orlova, “Quasioptical transformer which
transforms the waves in a waveguide having a circular cross
section into a highly directional wave beam,Radiophysics and
Quantum Electronics,vol.,no.,pp.,.
[] S. N. Vlasov and I. M. Orlova, “Quasioptical transformer which
transforms the waves in a waveguide having a circular cross sec-
tion into a highly directional wave beam,Radiophysics Quan-
tum Electronics,vol.,no.,pp.,.
[] S. N. Vlasov, L. I. Zagryadskaya, and M. I. Petelin, “Trans-
formation of a whispering gallery mode, propagating in a cir-
cular waveguide, into a beam of waves,Radio Engineering and
Electronic Physics, vol. , no. , pp. –, .
[] G.S.LingandC.W.Yuan,“DesignofaVlasovantennawith
reector,International Journal of Electronics,vol.,no.,pp.
–, .
[] H. Zhou and X. Yang , “Design of novel VLASOV-type antennas
for high power microwaves (HPM),” in Proceedings of the IEEE
34th International Conference on Plasma Science (ICOPS ’07),p.
, Albuquerque, NM, USA, June .
[] O. Wada and M. Nakajima, in Proceedings of the EC6 Joint
Workshop on ECE and ECRH, Oxford, UK, September .
[] B. G. Ruth, R. K. Dahlstrom, C. D. Schlesiger, and L. F. Libelo,
“Design and low-power testing of a microwave Vlasov mode
converter,” in Proceedings of the IEEE MTT-S International
Microwave Symposium Digest,vol.,pp.,June.
[] C.Vollaire,L.Nicolas,K.A.Connor,S.J.Salon,B.G.Ruth,
and L. F. Libelo, “Microwave radiation from slant cut cylindrical
antennas—modeling an experiment,IEEE Transactions on
Magnetics,vol.,no.,pp.,.
[] P. J. Sealy and R. J. Vernon, “Low-power investigation of TEn
and TMn mode Vlasov launchers (Gyrotron applications),” in
Proceedings of the Antennas and Propagation Society Interna-
tional Symposium,vol.,pp.,.
[] P. J. Sealy and R. J. Vernon, “Equivalence-principle model for
radiation from TE0𝑛 and TM0𝑛 mode step-cut and slant-cut
Vlasov feeds,” in Antennas and Propagation Society International
Symposium,vol.,pp.,London,Canada,.
[] R. K. Dahlstrom, L. J. Hadwin, B. G. Ruth, and L. F. Libelo,
“Reector design for an X-band Vlasov antenna,” in Proceedings
of the Antennas and Propagation Symposium Digest,vol.,pp.
–, May .
[] M. Fazaelifar and M. R. Fatorehchy, “Design, fabrication and
test of parabolic cylinder reector and horn for increasing the
gain of vlasov antenna,Progress In Electromagnetics Research
Letters, vol. , pp. –, .
[]X.Zhang,Q.Wang,Y.Cheng,andS.Wen,“Designofa
G Hz Vlasov (antenna) mode converter,” in Proceedings of
the International Workshop on Microwave and Millimeter Wave
Circuits and System Technology (MMWCST ’12), pp. –,
Apri l .
[] J. A. Lorbeck and R. J. Vernon, “Singly curved dual-reector
synthesis technique applied to a quasi-optical antenna for a gy-
rotron with a whispering-gallery mode output,IEEE Transac-
tions on Antennas and Propagation,vol.,no.,pp.,
.
[] B. Wang, C.-H. Du, P.-K. Liu, Z.-H. Geng, and S.-X. Xu, “P-
: study of a Vlasov mode converter for GHz whispering
gallery mode gyrotron,” in Proceedings of the IEEE International
Vacuum Electronics Conference (IVEC ’10), pp. –, IEEE,
Monterey, Calif, USA, May .
[]J.Braunstein,K.Connor,S.Salon,L.Libelo,andC.D.
Schlesiger, “Analysis of ared end for Vlasov-type antenna:
comparison of D nite element analysis with experiment,
IEEE Transactions on Magnetics,vol.,no.,pp.,
.
[] P. J. Sea ly, R. J. Vernon, and J. A. Lorbeck, “Vlasov feeds
with corrugated ares for pattern enhancement,” in Proceedings
of the IEEE Antennas and Propagation Society International
Symposium, vol. , pp. –, June .
[] A. D. R. Phelps, P. R. Winning, and S. N. Spark, “Broadband
quasi-optical mode converters for high power microwaves,
in IEE Colloquium on Antenna and Propagation Problems of
Ultrawideband Radar,pp.,London,UK,.
[]T.A.Spencer,C.E.Davis,K.J.Hendricks,R.M.Gilgen-
bach, and M. J. Arman, “Long-pulse Hyrotron-backward-wave
oscillator experiments,” in Proceedings of the IEEE International
Conference on Plasma Science,.
[] B. Wang, C.-H. Du, P.-K. Liu, Z.-H. Geng, and S.-X. Xu, “P–:
study of a Vlasov mode converter for GHz whispering gallery
mode gyrotron,” in Proceedings of the IEEE International Vac-
uum Electronics Conference (IVEC ’10), pp. –, Monterey,
Calif, USA, May .
[] H. M. El Misilmani, M. Al-Husseini, K. Y. Kabalan, and A. El-
Hajj, “Optimized reector position for vlasov antennas,” in Pro-
ceedings of the Progress in Electromagnetics Research Symposium
(PIERS ’13), pp. –, Stockholm, Sweden, August .
 International Journal of Antennas and Propagation
[] H. M. El Misilmani, M. Al-Husseini, K. Y. Kabalan, and A.
El-Hajj, “Improved Vlasov antenna with curved cuts for high
power microwaves,” in Proceedings of the 11th International
Conference on High Performance Computing and Simulation
(HPCS ’13), pp. –, July .
... The antenna is made of a cut at the end of the open-ended waveguide, diagonally. In the Vlassov antenna, its main-lobe derivate from the bore-sight about 30°, which makes the antenna unusable in some applications [6][7][8][9]. To shoot at a target point, the first thing that comes to mind is to derivate the antenna or the entire system, including the power supply, the pulse shaping system, the electromagnetic diode, and the antenna; but this is impossible in many cases. ...
... In (8), to minimise the length of the antenna, n = 1. So from (7) and (8), we have L1 = 95.28 mm. ...
Article
Full-text available
In this study, a design, simulation, fabrication, and measurement of the TEM‐TE11 mode converter antenna (MCA) like a pelican beak are investigated. The working frequency of the pelican beak‐shaped MCA (PBMCA) is the frequency in the range of 3.9–4.6 GHz (700 MHz bandwidth). Due to increasing the antenna cross‐section, the probability of the electrical breakdown dramatically reduces. Electrical breakdown may occur at very high power outputs of the electromagnetic sources. The power‐handling capacity of the PBMCA is 829 MW, at the centre frequency. The antenna is simulated and measured at three frequencies. The simulation results are a good agreement with the measurement results.
... The optimization of radiation capture is also critical for future applications in dielectric-based, high-power THz sources [4]. A Vlasovstyle antenna is a commonly used mode converter that is composed of a cylindrical waveguide with a shaped end [5]. The sidelobe generation, gain reduction, and inefficient power loading in Vlasov antennas make these modes unsuitable for driving conventional antennas. ...
... Table 2 shows radiation plots for the different frequencies, giving an easy reference of the angles and gain. The specific angle cut for the dielectric structure aids in the control of the diverging THz beam and ultimately directs the radiation forward [5]. The produced THz radiation is useful to probe the electromagnetic fields during the dielectric wakefield acceleration (DWA) interaction because the electric fields that actually are the wakefield leak out the end of the tube as THz radiation. ...
Conference Paper
Full-text available
Wakefields generated from dielectric structures driven by relativistic beams have demonstrated utility for high-gradient acceleration, phase space manipulation, and generation of THz radiation. The produced THz radiation is also useful to probe the electromagnetic fields during the dielectric wake-field acceleration (DWA) interaction. However, effective diagnostics requires effectively out-coupling of the radiation into free space for transport to appropriate interferometry diagnostics. We conducted simulations using CST Studio for a 10 GeV electron beam with FACET-II parameters in a slab-symmetric dielectric waveguide with the goal of optimizing the collected radiation signal. We studied various termination geometries including unperturbed, top-bottom offset, metallic horn antenna, and Vlasov-style antenna. Simulations indicate that the Vlasov-style antenna geometry, defined by an angled termination of bare material, is optimal. Detailed parametric studies were conducted on a variety of dielectric materials including quartz, diamond, and silicon. The coherent Cherenkov radiation (CCR) for the various cases was also computed as a function of beam ellipticity, for both symmetric and asymmetric drive beams.
... Therefore, one should try to have the output electric field of an electromagnetic diode in this mode. A Vlasov mode converter antenna can convert a TM 01 mode to TE 11 mode using a diagonal cut-off or step in a circular waveguide [13][14][15][16]. The major problem of the structure is the deviation of about 30 • from the bore-sight, which makes it unsuitable in many applications. ...
Article
Full-text available
A design and simulation of the mode converter antenna (MCA) with right‐hand circular polarization, at 10 GHz frequency, is presented. The circularly polarized mode converter antenna (CPMCA) consists of two inner conductors and a body. The TEM mode is converted into a circular polarization TE11 mode, using the inner conductors connecting the coaxial waveguide in two vertical and horizontal directions. The sidelobe level is less than −15 dB at the working frequency. The S11 and axial ratios of the CPMCA are about −16.5 and 0.15 dB, respectively. Also, the axial ratio is in the acceptable range.
... 참고문헌의 안테나들은 HPM 소스를 활용하며 특히, 특 정한 모드의 입력을 받아야 한다. 원형도파관에서 구형도 파관 [1] , 원형도파관에서 곡선으로 잘려진 블라소프 안테 나 [2] , TEM 모드를 입력으로 받아야 하는 고출력 나선 배 열 슬럿 안테나 [3]~ [9] . 등이 있다. ...
... Denisov [3] proposed a weakly elliptic profile for the waveguide section to convert TE0n modes into waves close to a Gaussian distribution, which is potentially helpful for a focused radiation, but the method was not beneficial on the system integration due to the changed cross section and increased length of the waveguide. A metallic photonic-band-gap (PBG) structure [4] and a curved cut shape [5] were suggested, respectively, to improve Vlasov launchers, but fabrications of these structures would be issues if the frequency goes higher, so these methods are less suitable for millimeter waves. ...
Article
In this paper, an antenna with 8 GHz (7–15 GHz) bandwidth is designed, simulated, fabricated, and measured. Commonly, for the effective use of electromagnetic sources, mode converters are used to transform donut-shaped patterns to directive patterns. This paper introduces a novel antenna called the pattern director antenna (PDA) that solves most problems associated with the azimuthally symmetric output modes of high-power microwave sources. The PDA accepts directly (without the need for mode conversion) an azimuthally symmetric generated mode of an electromagnetic source and converts it to radiate a directive pattern. For the proof of concept and validation of the design by simulations, the 3D printing technology [using polylactic acid (PLA)] is used to fabricate the PDA and measure its radiation patterns and return loss. The selected material is cheap and also environmentally friendly. The antenna was coated with aluminum to become a conductor. The gain is from 16.8 to 21.8 dB in the frequency range. The S 11 , main lobe deviation (MLD), and sidelobe level (SLL) are less than −15 dB, 2°, and −7 dB, in all frequency range, respectively. The simulation results are in good agreement with the measurement.
Article
This paper investigates the design, simulation, fabrication, and measurement of a compact mode converter antenna (MCA). The smile-like MCA (SMCA), at 12 GHz frequency, is designed. Due to the increase of the antenna cross-section, the probability of the electrical breakdown is dramatically reduced. Electrical breakdown may occur at very high-power outputs of the electromagnetic sources. The power capacity level of the SMCA is 648 MW. Also, the length of the antenna is 0.47λ. Simulation results indicate 99% mode conversion efficiencies. The return loss is −22 dB, the gain is more than 19 dB, and the sidelobe level is less than −37 dB. Also, the bandwidth is 200 MHz, for both E and H planes. The maximum main lobe deviation from the bore-sight is less than 0.2°. The simulation results are in good agreement with the measurement results.
Article
This paper investigates the design, simulation, fabrication, and measurement of a compact mode converter antenna (MCA). The smile-like MCA (SMCA), at 12 GHz frequency, is designed. Due to the increase in the antenna cross-section, the probability of the electrical breakdown is dramatically reduced. Electrical breakdown may occur at very high power outputs of the electromagnetic sources. The power capacity level of the SMCA is 648 MW. Also, the length of the antenna is 0.47 λ. Simulation results indicate 99% mode conversion efficiencies. The return loss is −22 dB, the gain is more than 19 dB, and the sidelobe level is less than −37 dB. Also, the bandwidth is 200 MHz, for both E and H planes. The maximum main lobe deviation from the bore-sight is less than 0.2°. The simulation results are in good agreement with the measurement results.
Conference Paper
Full-text available
This paper presents an improved Vlasov antenna with a novel cut shape suitable for high power microwave applications. The curved shape of the proposed cut totally eliminates the sharp edges and angles present in Vlasov antennas with Step and Bevel cuts. A Vlasov antenna, designed for operation at 3 GHz, is used to compare the three cut types. In addition to being better suitable for high power microwave applications, the proposed cut results in increased antenna gain and in good performance in terms of sidelobe level and half-power beamwidth.
Conference Paper
Full-text available
This paper presents a Vlasov antenna with optimized reflector position and angle suitable for high power microwave applications. With the proposed configuration, the reflector is directly attached to the waveguide, which is an advantage and makes it simpler to radiate in the direction of the axis of the waveguide. Bevel-cut and Step-cut Vlasov antennas, designed for operation at 3 GHz, are used to validate the effect of the reflector. In addition to proper radiation of the direction of maximum radiation, the optimized reflector results in increased antenna gain and reduced half-power beamwidth.
Conference Paper
Preliminary results of experimental and theoretical investigation of TE/sub 0n/ and TM/sub 0n/ mode Vlasov launchers that might be used with some gyrotrons are discussed. Experimental radiation patterns taken directly from the half-cylinder baffle and also from the parabolic-cylinder reflector that it feeds are presented. Variations of the half-cylinder baffle and orientation position of the parabolic reflector are considered.
Conference Paper
A circular waveguide with a shaped open end forms the launcher component of a Vlasov mode converter. The authors compare the gain patterns obtained for an open end with a step cut with that for one with a beveled cut. The determination of the gain pattern is the first step in the design of a high-power mode converter intended for X-band (8 to 12 GHz). It is concluded that the optimum waveguide for use in a Vlasov mode converter for high-power microwaves remains the 30 degrees bevel cut. The step-cut waveguide has a slightly inferior gain pattern, and, moreover, the sharp corners on the waveguide edge could cause breakdown problems for high-power applications.
Conference Paper
An equivalence-principle-based model for predicting the radiation from TE/sub 0n/ and TM/sub 0n/ mode step-cut and slant-cut Vlasov feeds is discussed. Theoretical far-field and numerical near-field radiation patterns are compared to measured results. Experimental investigations of currents are reported, and simulation of perturbed waveguide currents is explored.
Article
Abstract—This paper proposes two methods for increasing the Gain of Vlasov Antenna.The first method, using a Parabolic Cylinder Reflector, results in a 7 dB increase in the Gain.The second method, constructing a Horn on the aperture, increases the Gain by about 5 dB. The results were checked using a prototype antenna and there was a close agreement.
Article
A Vlasov antenna (mode converter) for a center frequency of 220 GHz, which includes a Vlasov-type step-cut launcher and a parabolic reflector, is proposed in this paper. It converts the TE03 mode in circular waveguide to a highly Gaussian-like beam at the output window. Optimization is carried out and good results have been achieved with the VSWR 1.2 at 190–250GHz and the conversion efficiency greater than 80%. Simulation results showed that the radiation gain of the Gaussian-like beam is 31.8dB.
Article
A Vlasov mode converter for a 94 GHz whispering gallery mode gyrotron, consisting of a Vlasov-type helically-cut launcher and two curved-mirror reflectors, is proposed in this paper. Applying the geometric optics theory and the vector diffraction theory, a numerical simulation code of the quasi-optical converter system is programmed. Simulation results indicate that the TE12,2 whispering gallery mode inside the 94 GHz gyrotron is converted into a highly Gaussian-like beam at the output window.