4458 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO.

9, SEPTEMBER 2018

Design of a 360° Scanning Circularly

Symmetric Polygon Lens
Tuan Minh Nguyen , Toan K. Vo Dai , Student Member, IEEE, and Ozlem Kilic, Senior Member, IEEE

Abstract— This paper presents a 360° scanning circular

microwave lens based on the Bootlace lens design concepts.
However, instead of allocating the beam ports and receiving ports
on two opposite sides of the lens, the polygon lens alternates the
beam and receiving ports in an interleaving order on all sides and
allows the use of circular symmetry to cover 360° scanning. In this
paper, a new analytical approach is proposed which minimizes the
phase errors for the “perfect” focal points of the lens to design
the polygon lens. In order to evaluate the proposed method,
an octagonal lens was designed and fabricated. Each facet of the
lens feeds a four-element rectangular patch array. The results
show a full 360° coverage in the band of interest. Comparisons
between measurements and simulations show a good agreement.
Index Terms— 360° scanning, analog beamforming, Bootlace
lens, microwave lens, Rotman lens.

I. I NTRODUCTION

O VER the last few decades, electronically scanning anten-

nas have witnessed increased demand in applications
ranging from radar [1], imaging [2], [3], analog and digital
Fig. 1. Rotman lens design geometry and parameters.

in (1)–(3), the receiving contour Pi (x, y) and the delay line

hybrid beamformer [4], and radar system for automotive appli- lengths Wi are determined. This strategy implies that there are
cations [5], etc. Among the beamformer technologies, Rotman always three perfect focal beam ports and any nonfocal beam
lens is a broadband, true-time delay analog beamforming ports residing in between may generate some phase error
network that feeds a linear array with an appropriate phase √ √ √ √
taper to electronically scan the beam [6]. The Rotman lens F1 (x, y)Pi (x, y) εr +Wi εe + Di sin 1 = f 1 εr +W0 εe
design was based on the generalized design equations for (1)
arbitrary lens shapes, i.e., the Bootlace lens, proposed earlier √ √ √ √
F0 (x, y)Pi (x, y) εr +Wi εe = f 0 εr +W0 εe
by Gent [7]. Fig. 1 shows the concept for a printed Rotman
lens for a three-input four-output system. Each input port (2)
√ √ √ √
corresponds to a different beam position by generating the F2 (x, y)Pi (x, y) εr +Wi εe − Di sin 2 = f 1 εr +W0 εe .
proper phase taper across the array ports. Since its invention, (3)
much effort was made to optimize the Rotman lens design
formulations based on optical phase tracing methods [8]–[17]. A drawback of any Bootlace lens in general is its limited
Rotman lens design concepts have also been applied to imple- scanning range due to the geometric configuration of the
ment waveguide lenses [18], substrate-integrated waveguide beam ports and the inherent scan constraints of linear arrays.
lenses [19], and microstrip lenses [20], [21] for millimeter- An existing solution, which imposes a symmetry condition to
wave applications [22], [23]. create a circularly symmetric lens, was proposed in [24]. This
The conventional Rotman lens starts with three perfect idea is promising since the basic properties of the Bootlace
focal beam port centers (F1 (x, y), F0 (x, y), and F2 (x, y)), as lens can be preserved while achieving a full 360° coverage.
depicted in Fig. 1, on the arc of a circular beam contour, and by Other techniques to obtain the coverage of 360° angular
simultaneously solving the three-phase equations, as described range in azimuth have been implemented before. For instance,
in [25], a 24-beam slot array antenna fed by a Butler matrix
Manuscript received September 25, 2017; revised May 2, 2018; accepted is fabricated based on a substrate-integrated waveguide, and
May 21, 2018. Date of publication June 8, 2018; date of current version the structure consists of six four-beam single layers. In addi-
August 31, 2018. (Corresponding author: Tuan Minh Nguyen.)
The authors are with the Department of Electrical Engineering and Com- tion, Fonseca [26] design a closed cylindrical beamforming
puter Science, The Catholic University of America, Washington, DC 20064 network based on a specific arrangement of alternating power
USA (e-mail: 11nguyen@cua.edu; 30vodai@cua.edu; kilic@cua.edu). combiners and power dividers to feed a circular array. In [27],
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org. a homogeneous ellipsoidal lens was designed to feed a planar
Digital Object Identifier 10.1109/TAP.2018.2845441 circular tapered slot antenna array.
0018-926X © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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NGUYEN et al.: DESIGN OF A 360ł SCANNING CIRCULARLY SYMMETRIC POLYGON LENS 4459

Fig. 3. Pair of symmetric opposite sectors in the circular lens.

in detail in Fig. 3, there are M beam ports (Fi , i = 1,

2, . . . , M) as well as M receiving ports (P j , j = 1, 2, . . . , M),
represented by the circles and the squares, respectively. The
line I0 connects the centers of the opposing circular arcs,
Fig. 2. Circular lens concept. and “O” denotes the center of the circle. Each beam port
position on the circle is identified by angle θi measured from
In this paper, we propose a generalized analytical approach the center of the opposing circular arc with respect to line I0 in
to design a circularly symmetric polygon lens to cover the full a counterclockwise fashion, facing the beam ports. Similarly,
azimuth scan range, i.e., 360°. While an asymmetric solution each receiving port is identified by angle ϕ j . The angles
can also be obtained by our proposed approach, circular (in degrees) are computed using (4) and (5), where θ is defined
symmetry allows us to design just a single pair of mutually as the maximum subtended angle between two extreme ports
facing facets to achieve a partial scan, and then duplicate to of a circular arc, and depends on the total number of facets
complete the 360° scan range. An octagonal lens is designed assumed in the design (6)
and fabricated to validate the proposed concept. Measurements
θ
are provided that support the simulation results. θi = ± × 2i (4)
4(2M − 1)
II. C IRCULARLY S YMMETRIC P OLYGON L ENS C ONCEPT θ
ϕj = ± × (2 j − 1) (5)
4(2M − 1)
The circularly symmetric polygon lens is a microwave lens
that can feed an even number of phased arrays around its 3600
θ= . (6)
facets, and therefore can scan 360°. The concept is shown NP
in Fig. 2 for a polygon with N p = 2N facets with prime Once θi and ϕ j are computed for a given M and N p , the next
syntax indicating the symmetric counterpart of a particular step is to calculate the actual port positions based on the value
facet. Hence, each sector (1 . . . N) associates with a symmetric of the radius R of the circle where all beam ports and receiving
opposite sector (1 . . . N  ), which results in the requirement of ports reside. The port coordinates are determined using the
a polygon with an even number of facets. Each facet supports geometric relations in the following equations:
both beam ports and receiving ports.
As can be observed in Fig. 2, the beam and receiving ports x i|2 j + yi|2 j = R 2 (7)
are distributed along each circular arc, or inner contour, with yi = x i × tan θi (8)
radius R in an interleaving fashion. The linear array elements, y j = x j × tan ϕ j . (9)
which are connected to the receiving ports, reside on the
facets of N p dimensional polygon that encompasses the circle. The remaining unknowns in the design are the delay line
Similar to the Bootlace lens design, delay lines T j connect lengths T j . After solving for all of the phase center coordinates
the receiving ports to the linear array elements. Because the and the delay lines, the symmetric opposite sectors can be
beam ports interleave with the receiving ports, the number of realized. By rotating the opposite sectors by θ each time for
beam and receiving ports need to be equal for a uniform scan. N − 1 times, we can complete the design of the circular
As a result, there is one shared beam between a particular lens.
facet and its neighbor, e.g., facet Q and facet N in Fig. 2. Based on the desired gain, beamwidth, and the number of
This shared beam port also guarantees that the outer beam of scan steps, the performance of the lens can be optimized by
facet Q would not overlap with that of the adjacent facet to varying the total number of facets N p and the radius of the
maintain a uniform scan. circular contour. We discuss in detail the algorithm reported
Due to the inherent symmetry, only two symmetric opposite earlier in the literature for a 360° scanning lens as well as our
sectors (e.g., Q and Q  ) are used to derive the design formula- proposed algorithm to formulate general design equations for
tions, since the results will be valid for all sectors. As depicted the polygon lens in Section III.

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4460 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 9, SEPTEMBER 2018

III. D ETAILS OF THE C IRCULAR L ENS D ESIGN

A. Currently Reported Circular Lens Solution
A solution for a circular lens has been reported in the liter-
ature earlier by assigning a predetermined radius value [28].
The approach involves the use of an optimization algorithm
to form a set of delay lines that generate the least average
phase error from all beam ports to all receiving ports. The
objective function to minimize the average phase error ϕ is
calculated as in (10), in which D j is the array element position
corresponding to the receiving port P j , and i corresponds to
the scan angle of beam port Fi , which is determined by the
number of facets of the polygon. The optimization is applied
after all variables except the delay line lengths are known.
Hence, the optimization algorithm is simple to implement, and
is able to find the best solution for a particular radius R, which Fig. 4. Different array sizes for a given gain drop level to determine the
is chosen by the user input parameters for the circular lens.

360   √
M M
√
ϕ = | εr Fi P j − εeff T j − D j sin i |. (10)
M 2
i=1 j =1
G AF (Mmin ) = G min − G el . Now, in order for the circular
lens to scan contiguously while maintaining the minimum gain
However, for an optimal solution, the phase error should be requirement, we need to satisfy the condition in (13) which
a function of all design parameters, including the radius of the states that the total beamwidth covered by the linear array at
circle R and transmission line lengths T j . The solution offered each facet (i.e., M × BW) must be at least 360°/N p degrees,
in [28] assumes an a priori knowledge or a good guess for and the value of N P is chosen such that it is the smallest even
this value. A change in the radius leads to a change in all port integer. We note that our convention for all gain values are
positions Fi and P j . As a result, the optimization algorithm in dBi in the calculations as follows:
which assumes one of the design parameters as known cannot
offer a general solution that our method inherently provides. M × BW°(G min , M) × N P > 360°. (13)
Any assumption of a priori knowledge likely needs some
iterative guesses for a successful result, while we solve for At this stage, we want to use (13) to determine the array
all unknowns simultaneously at the first attempt. dimension, the polygon shape, and the number of scan steps.
Fig. 4 shows the beamwidth and the reduction in gain from
the peak value for different array sizes ranging from M = 3
B. Proposed Circular Lens Solution
to M = 10. We observe in Fig. 4 that for a given array size M
Based on the previous discussion on the optimization and the minimum required gain G min , the beamwidth can be
approach, we are interested in an analytical solution, which computed, and finally the polygon shape N p is determined
accounts for a set of input parameters. A designer usually from (13). Hence, all the possible polygon shapes N p are
wants to have an antenna system that can scan in the full known from the designer input parameters including the min-
azimuth domain with a minimum gain G min requirement imum gain to scan, the antenna fed by the circular lens, and
everywhere in the scan region. Assuming a linear phased array the size of the linear array.
with half wavelength spacing, the gain can be calculated as We now consider a particular case and assume that the
G arr (M, θ ) = G el (θ ) + G AF (M, θ ). (11) antenna designer would like to have a system that can cover
the entire azimuth plane with a minimum gain of 10 dBi;
In (11), G arr (M, θ ) is the total gain in dBi of the linear i.e., G arr ≥ (G min = 10 dBi). In our analysis, we also
phased array which is a function of the array size and the assume using a patch antenna with a peak gain G el = 6.8 dBi
observed far-field angle θ , G el (θ ) is the gain pattern in dBi for the elements of the arrays. Equation (11) suggests that
from a single element, and G AF (M, θ ) is the array factor G AF ≥ 3.2 dBi, and the minimum number of array ele-
in dBi of that array. For simplicity, we neglect mutual coupling ments is determined as M ≥ 3 from (12), as observed in
effects between the antenna elements, so the gain of the array the peak gain values for G AF (M) in Fig. 4. The smallest
can be computed using the following equation [29]: array can be used that needs to have three elements since
2 × AF(θ )2 G AF (3) = 4.7.
G AF (M, θ ) =  π . (12) Now, to illustrate how (13) can be applied to solve for the
0 AF(θ )2 sin θ dθ polygon shape, we compute the product in (13) for M ≥ 3
In the rest of this paper, the peak values of the gain elements. The orange line in Fig. 5 shows this product,
functions will be denoted by dropping the angular dependence; while the solid blue line is the corresponding beamwidth
i.e., G el will refer to the peak gain for G el (θ ). in degrees for different arrays of patch antenna. As the
Once G min and G el are given, the minimum number of array size increases, the product becomes larger; hence,
linear array elements Mmin is determined using (12), where the value of N p gets smaller. As a result, possible polygon

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NGUYEN et al.: DESIGN OF A 360ł SCANNING CIRCULARLY SYMMETRIC POLYGON LENS 4461

Fig. 6. Phase tracing for three focal beam ports.

Fig. 5. Beamwidth at 10 dBi and the corresponding product in (13) for
different array sizes.
since it is one parameter of the inputs. After that, in the
initialization step, the angles and the exact coordinates of
TABLE I
all ports can be computed, and therefore the problem now
P ROPOSED A NALYTICAL S OLUTION C OMPARISON
is to optimize the delay lines for the best phase error solution.
On the other hand, with our approach, instead of assigning the
circle radius R, we try to solve for R using the phase equations
from the three focal ports, as inspired from the conventional
Rotman lens design (1)–(3). Fig. 6 shows the rays to be traced
from the three focal beam ports (F1 , F2 , and F3 ) to the first
receiving port. The corresponding phase equations are shown
in (14)–(16), which was known as Gent’s optical path length
equations [7].
Using the fact that the length of an arbitrary chord inside
the circle can be expressed in terms of R, θ , and ϕ, (14)–(16)
can be written as in (17)–(19), as well as in matrix form (20).
Since this matrix is an overdetermined system, the radius R
and the delay line T1 can be approximated using the method
of ordinary least squares, as in (21). The remaining delay line
lengths are computed using the rest of phase equations from
all beam ports (22). Hence, the proposed analytical method is
able to solve for the optimal circular lens geometry with the
least phase error
√ √
εr F1 P1 + εeff T1 + D1 sin 1
√ √
= εr F1 O + εeff T0 (14)
√ √
εr F2 P1 + εeff T1
√ √
= εr F2 O + εeff T0 (15)
√ √
εr F3 P1 + εeff T1 − D1 sin 3
√ √
= εr F3 O + εeff T0 (16)
√ √
2R εr [cos (θ1 + ϕ1 ) − cos (ϕ1 )] + εeff T1
shapes are determined. For instance, we observe that for = D1 sin 1 (17)
M = 4, we achieve about 60° scan range for one facet of √ √
the lens, ideally. As a result, we need a polygon of eight 2R εr [cos (ϕ1 ) − 1] + εeff T1
facets. =0 (18)
After the set of input parameters are determined, the ana- √ √
2R εr [cos (θ3 − ϕ1 ) − cos (ϕ1 )] + εeff T1
lytical solution of the lens is carried out, as summarized
in Table I, which also includes a comparison with the existing = −D1 sin 1 (19)
optimization method. As can be observed from Table I, in the [ A][x] = [b] (20)
optimization approach described above, the designer needs to −1
have experience in deciding the circular contour radius value [x] = ([ A]T [ A]) [ A]T [b] (21)

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4462 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 9, SEPTEMBER 2018

TABLE II
P OSSIBLE C IRCULAR L ENS S OLUTIONS

Fig. 7. Prototype of octagon microstrip lens.

smallest total area. In terms of the switch matrix complexity,

the octagon offers a better solution while maintaining a similar
surface area to that of dodecagon.
where
⎡ √ √ ⎤ The “best” circular lens among these solutions depends on
2 εr [cos(θ
√ 1 + ϕ1 ) − cos(ϕ1 )] √εeff the priorities for the system design. First of all, the dimen-
[ A] = ⎣ √ 2 εr [cos(ϕ1 ) − 1] √εeff
⎦ sion of a solution can be evaluated in terms of the radius.
2 εr [cos(θ3 − ϕ1 ) − cos(ϕ1 )] εeff Looking into (17)–(19), it can be concluded that the radius is

R proportional to the array size. So, a lens with a smaller array
[x] = is a better solution in terms of overall dimensions, as can be
T1
⎡ ⎤ observed from the radius values in Table II. The next criterion
D1 sin 1
[b] = ⎣ 0 ⎦ is the switch matrix complexity. In this aspect, the octagon
−D1 sin 1 circular lens is slightly more desirable since it only requires a
√ √ switch with 32 ports while the dodecagon requires 36 ports.
εr Fi P j + εeff T j + D j sin i As a result, with our analytical approach, we are able to
√ √
= εr Fi O + εeff T0 (22) discern between these possibilities to choose the most suitable
solution, accounting for the designer priorities for achievable
where
gain, overall dimensions, and design complexity.
i = 1 . . .M
j = 2 . . .M V. E XPERIMENTAL VALIDATION
Based on the discussion above, an octagon lens was selected
for fabrication and measurement. We used Roger duroid 5870
IV. T RADEOFF A NALYSIS with εr = 2.33 and d = 0.79 mm, as shown in Fig. 7.
With the proposed analytical approach, the designer is able The numbering convention in Fig. 7 is such that the beam
to choose the best option among possible solutions. In this ports on one facet are assigned odd numbers, whereas the
paper, we assume that the optimal solution is evaluated in corresponding receiving ports are marked with even numbers.
terms of overall physical dimensions and the switch matrix So, there are four beam ports and four receiving ports in each
complexity. We will use the same example in Section III-B; facet, which implies that there are a total of 32 beam ports
i.e., the circular lens scans in the azimuth plane with a corresponding to the total of eight arrays with four elements.
minimum gain of 10 dBi, using a patch antenna with a peak It is noted that a gradual taper for the horns is necessary and
gain of 6.8 dBi. We choose a center frequency of 12 GHz. With the width of each microstrip horn should be around λ/2 for
the beamwidth analysis and the condition in (13), all possible an optimal radiation to the parallel region. The designer can
polygons (i.e., N p values) for different array sizes up to vary the number of ports, or the polygon shape, or add some
12 elements are determined. As a result, there are four dummy ports at the outer ports and terminate them to satisfy
possible solutions, which correspond to the dodecagon, octa- this criterion. The parameters of the octagon lens are provided
gon, hexagon, and square polygons, as depicted in Table II. in Table III.
As N p increases, the number of facets increase, which To validate the overall performance of the octagon lens
typically results in smaller array sizes for the same total which would include multiple reflections and coupling in
number of beams. For instance, the square polygon, while the lens cavity, which were not taken into consideration in
intuitive to design, has the largest area, and requires 10 beam the simple design equations, we investigate and compare the
ports and receiving ports on each facet. On the other hand, results between the simulated model and a fabricated proto-
the dodecagon lens has the fewest number of ports and the type. The octagon lens was simulated using the commercial

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NGUYEN et al.: DESIGN OF A 360ł SCANNING CIRCULARLY SYMMETRIC POLYGON LENS 4463

TABLE III
FABRICATED O CTAGON L ENS PARAMETERS

Fig. 8. Phase difference between measurement and simulation.

Fig. 9. Amplitude level between measurement and simulation from (a) beam
software FEKO. The S-parameter simulation results, therefore, port 1 and (b) beam port 3.
can be obtained by solving the entire lens using the full-
wave method, which takes into account the coupling effects
among all ports. Similar to [28], the phase response from all
beam ports in one facet is measured and compared with the
simulated model. Fig. 8 shows the phase comparison between
measured and simulated values across the four output ports for
each input port at a center frequency of 12 GHz. We observe
a good agreement with a maximum phase deviation of 13°.
The received amplitude levels of input ports 1 and 3 at a
center frequency of 12 GHz are shown in Fig. 9(a) and (b),
respectively. In order to compare the amplitude response
accurately, the external loss from the measurement process
has been compensated. The received amplitude level shows a
good agreement with a maximum mismatch of 2 dB. We note
that during the S-parameter measurements, all ports other than
the two ports under test were terminated with 50 loads. Fig. 10. (a) Single patch dimension. (b) Linear patch array of four elements.
To investigate the effect of the errors in amplitude and
phase values, we fed the measured S-parameter data to a limited by the antenna element. Fig. 11 shows the measured
patch array in FEKO, to simulate the radiation pattern. The return loss of all four receiving ports in the band of interest
patch element was designed at a center frequency of 12 GHz from 10 to 14 GHz. The lens ports yield a good return loss
with an input impedance of 50 using an inset feed. of more than 15 dB from 10 to 13 GHz, thus providing a
Fig. 10(a) shows the design details of the single patch while broadband performance. Hence, the bandwidth of the overall
Fig. 10(b) demonstrates the fabricated patch array support- system is determined by the bandwidth of the array elements
ing one of the facets of the octagon lens, with a 1 by 4 that the lens feeds.
switch matrix. The microstrip Rotman lens itself is inher- The patch array is used to radiate the received fields at the
ently broadband, but the overall bandwidth of the system is output ports of each facet, whereas the beam ports steer the

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4464 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 9, SEPTEMBER 2018

Fig. 11. Return loss of the receiving ports from 10 to 14 GHz.

Fig. 13. Circulators connected at the receiving ports to reduce the spillover
effect.

As in any Bootlace lens design, there are inefficiencies due

to the presence of inactive ports, such as the dummy ports on
the sidewalls of Rotman lens. The circular lens design pro-
posed in this paper as well as in [28] has similar inefficiencies
due to the inactive beam ports residing between the array ports
on the receiving facet. The efficiency of each beam port in our
design is the ratio of the total power received by the receiving
ports in the opposite facet to the total radiated power by the
beam port. Due to symmetry, the efficiency should be the
same for all facets. In addition, we expect that the efficiency
of all beam ports within a facet is fairly uniform based on our
Fig. 12. Simulated radiation pattern of the circular lens based on its measured S-parameter measurements, shown in Fig. 9. We observe a
output signal. (a) From one facet. (b) From all facets. fairly uniform efficiency of 60% across all beam ports.

radiated beam. The radiation pattern of one pair of sectors VI. C ONCLUSION
at 12 GHz is shown in Fig. 12(a), while the full coverage In this paper, we propose a novel design of a 360° scanning
of the octagonal lens generated by all eight sectors is shown polygon lens. The design formulation involves simultaneously
in Fig. 12(b). The peak gain achieved is 11 dBi with the solving three optical phase equations, using the Bootlace lens
corresponding beamwidth of 15° so that at least 10 dBi gain is model, for three focal beam ports residing on a circular
achieved as the lens transitions from one beam to the next. The inner contour. The advantages of this analytical design are
scanning range of one facet would not cover 45° or ±22.5° the simplicity and the generalization when compared with
as can be observed in Fig. 12(a) because the beam that earlier proposed designs. As an example, an octagon lens
scans to the maximum range, i.e., −22.5°, is generated by was fabricated for experimental validation of our design. The
the shared beam port to avoid overlapping. It is important to comparison between measurements and simulations shows
note that our full-wave simulation for the radiation pattern good agreement over the band of interest.
obtained in Fig. 12 incorporates all coupling effects between
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[12] A. F. Peterson and E. O. Rausch, “Scattering matrix integral equation
analysis for the design of a waveguide Rotman lens,” IEEE Trans.
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[13] L. Schulwitz and A. Mortazawi, “A new low loss Rotman lens design
using a graded dielectric substrate,” IEEE Trans. Microw. Theory Techn., Toan K. Vo Dai (S’15) received the B.Sc. degree in
vol. 56, no. 12, pp. 2734–2741, Dec. 2008. electrical engineering from The Catholic University
[14] J. Dong and A. I. Zaghloul, “Hybrid ray tracing method for microwave of America (CUA), Washington, DC, USA, in 2015,
lens simulation,” IEEE Trans. Antennas Propag., vol. 59, no. 10, where he is currently pursuing the Ph.D. degree
pp. 3786–3796, Oct. 2011. with the Department of Electrical Engineering and
[15] M. Rajabalian and B. Zakeri, “Optimisation and implementation for a Computer Science.
non-focal Rotman lens design,” IET Microw. Antennas Propag., vol. 9, He is currently a Graduate Research Assis-
no. 9, pp. 982–987, Jun. 2015. tant with the Department of Electrical Engineer-
[16] N. J. G. Fonseca, “A focal curve design method for Rotman lenses with ing and Computer Science, CUA. His current
wider angular scanning range,” IEEE Antennas Wireless Propag. Lett., research interests include the bioinspired opti-
vol. 16, pp. 54–57, Apr. 2016. mization method, antenna design, and satellite
[17] C. M. Rappaport and A. I. Zaghloul, “Optimized three-dimensional communications systems.
lenses for wide-angle scanning,” IEEE Trans. Antennas Propag., vol. 33,
no. 11, pp. 1227–1236, Nov. 1985.
[18] K. Tekkouk, M. Ettorre, L. Le Coq, and R. Sauleau, “Multibeam SIW
slotted waveguide antenna system fed by a compact dual-layer Rotman
lens,” IEEE Trans. Antennas Propag., vol. 64, no. 2, pp. 504–514,
Feb. 2016.
[19] Y. J. Cheng et al., “Substrate integrated waveguide (SIW) Rotman lens
and its Ka-band multibeam array antenna applications,” IEEE Trans. Ozlem Kilic (SM’90) received the D.Sc. and M.S.
Antennas Propag., vol. 56, no. 8, pp. 2504–2513, Aug. 2008. degrees in electrical engineering with a focus on
[20] O. Kilic and S. Weiss, “Rotman lens designs for military applications,” electrophysics from The George Washington Uni-
Radio Sci. Bull., no. 333, pp. 10–24, Jun. 2010. versity, Washington, DC, USA, in 1991 and 1996,
[21] T. K. Vo Dai, T. Nguyen, and O. Kilic, “A non-focal Rotman lens design respectively, and the B.S. degree in electrical and
to support cylindrically conformal array antenna,” ACES Express J., electronics engineering from Boğaziçi University,
vol. 1, no. 7, pp. 205–208, Jul. 2016. Istanbul, Turkey, in 1989.
[22] N. Jastram and D. S. Filipovic, “Design of a wideband millimeter wave She was an Electronics Engineer with the U.S.
micromachined Rotman lens,” IEEE Trans. Antennas Propag., vol. 63, Army Research Laboratory, Adelphi, MD, USA,
no. 6, pp. 2790–2796, Jun. 2015. where she managed small business innovative
[23] T. Nguyen, T. K. Vo Dai, and O. Kilic, “Rotman lens-fed aper- research programs for the development of hybrid
ture coupled array antenna at millimeter wave,” in Proc. IEEE Int. numerical electromagnetic tools to analyze and design electrically large
Symp. Antennas Propag. (APSURSI), Fajardo, PR, USA, Jun./Jul. 2016, structures, such as the Rotman lens. She was a Senior Member of the Technical
pp. 63–64. Staff and a Program Manager with COMSAT Laboratories, Clarksburg, MD,
[24] A. I. Zaghloul and J. Dong, “A concept for a lens configuration for 360° USA, with a specialization in satellite communications, link modeling and
scanning,” IEEE Antennas Wireless Propag. Lett., vol. 8, pp. 985–988, analysis, and phased arrays and reflector antennas for satellite communications
Aug. 2009. system, for five years. In 2005, she joined The Catholic University of
[25] P. Chen et al., “A multibeam antenna based on substrate integrated America (CUA), where she is currently the Associate Dean of engineering
waveguide technology for MIMO wireless communications,” IEEE and a Professor with the Department of Electrical Engineering and Computer
Trans. Antennas Propag., vol. 57, no. 6, pp. 1813–1821, Jun. 2009. Science. Her current research interests include antennas, wave propagation,
[26] N. J. G. Fonseca, “Design and implementation of a closed cylindrical satellite communications, numerical electromagnetics, and microwave remote
BFN-fed circular array antenna for multiple-beam coverage in azimuth,” sensing.
IEEE Trans. Antennas Propag., vol. 60, no. 2, pp. 863–869, Feb. 2012. Prof. Kilic has been serving leadership and editorial positions in a number
[27] J. Zhang, W. Wu, and D.-G. Fang, “360° scanning multi-beam antenna of organizations such as the IEEE AP-S, USNC URSI, and ACES and has
based on homogeneous ellipsoidal lens fed by circular array,” Electron. wide range of experience in education, membership development, technical
Lett., vol. 47, no. 5, pp. 298–300, Mar. 2011. committees, government/industry interface, and program management. She is
[28] J. Dong, “Microwave lens designs: Optimization, fast simulation also serving as the Director of the Engineering Center for Care of Earth,
algorithms, and 360-degree scanning techniques,” Ph.D. dissertation, CUA, based on her past experience in applying microwave remote sensing
Dept. Elect. Eng., VirginiaTech, Falls Church, VA, USA, 2009. technology to monitoring of the vegetation and forest coverage on earth, and
[29] C. A. Balanis, “Arrays: Linear, planar, and circular,” in Antenna Theory, her personal interest in the well-being of earth as human population and needs
3rd ed. Hoboken, NJ, USA: Wiley, 2005, ch. 6, sec. 10, pp. 349–362. increase.

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