Metasurface: Changing polarization from linear to circular for airborne antenna

Metasurface: Changing polarization from linear to circular for airborne antenna

Int. J. Electron. Commun. (AEÜ) 116 (2020) 153086 Contents lists available at ScienceDirect International Journal of Electronics and Communications ...

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Int. J. Electron. Commun. (AEÜ) 116 (2020) 153086

Contents lists available at ScienceDirect

International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue

Regular paper

Metasurface: Changing polarization from linear to circular for airborne antenna Zixiang Lin a,b, Ruipeng Liu b, Xia Wang b, Hongxing Zheng a,b,⇑, Mengjun Wang a,b, Erping Li a,c a

Sate Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin, China School of Electronics and Information Engineering, Hebei University of Technology, Tianjin, China c Zhejiang University-UIUC Institute, Zhejiang University, Hangzhou, China b

a r t i c l e

i n f o

Article history: Received 17 June 2019 Accepted 17 January 2020

Keywords: Dual circular polarization Metasurface Ultra-wideband Airborne antenna

a b s t r a c t To implement the circular polarization antenna on the airborne electronic platform, a new technique of polarization change is investigated in this paper. A metasurface structure consisting of a 5  5 array has been designed. Each unit of the metasurface structure is a stack circular ring, and two orthogonal dipoles in a ring can convert the linear polarization wave into circular one. An ultra-wideband (UWB) antenna is designed combining with the metasurface structure. To filter some interference signals from special frequency bands such as WLAN and WiMAX, dual notched-bands have been designed on the UWB antenna. Therefore, dual circular polarization radiation character at two bands of 4 GHz–7.9 GHz and 8.1 GHz 12.4 GHz is achieved. The antenna with metasurface is operated at 2.6 GHz–13.6 GHz excepting for two notched-bands of 3.15 GHz–4.3 GHz and 5.5 GHz–5.75 GHz. Fabricated sample has been verified by experiment, and the results indicate that the design is available. Ó 2020 Elsevier GmbH. All rights reserved.

1. Introduction Nowadays, for the airborne electronic system, anti-interference ability and wider frequency band are very required. The antenna is an important device for transmitting and receiving wireless signal, and plays an irreplaceable role in the airborne communication system. In order to obtain the good performance of airborne communication system, on the one hand, the polarization of antenna is controlled. Because multiple polarizations of antenna will improve the channel capacity [1,2], and circular polarization wave has obvious advantages in anti-interference [3,4]. The communication quality will be improved if signal is transmitted by circular polarization wave [5,6]. Simultaneously, circular polarization wave can be received by any linear polarization antenna. Linear polarization wave can also be received by any circular polarization antenna [7]. This feature reduces the difficulty of deployment during antenna installation. Hence, the dual circular polarizations antenna is much more required. On the other hand, the operating bandwidth of antenna is an important affecting factor on performance of airborne communication system. The channel capacity is proportional to operating

⇑ Corresponding author at: School of Electronics and Information Engineering, Hebei University of Technology, Tianjin 300401, China. E-mail address: [email protected] (H. Zheng). https://doi.org/10.1016/j.aeue.2020.153086 1434-8411/Ó 2020 Elsevier GmbH. All rights reserved.

bandwidth of antenna by Shannon’s theorem, so the ultrawideband (UWB) antenna is a good choice for airborne communication system. In ultra-wideband application, the parallel-plate etched slot antenna of high efficiency possesses great advantages. In [8] and [9], some good performances of post wall-based parallel-plate slot antenna have been contained. Moreover, monopole ultra-wideband patch antennas are commonly applied in ultra-wideband communi- cation system because they are cheap and low loss [10,11]. Though, the ultra-wideband property is implemented by the above two types antenna, dual circular polarization can’t be implemented at the same time. Most UWB antennas radiate linear polarization wave [12–14]. But the linear polarization wave is easily affected by multipath interference, rain, snow, and fog in propagation process. The circular polarization character is difficult to implement from ultrawideband antenna. In general, the circular polarization is achieved by two orthogonal linear polarization waves or 90° phase different feed [15,16]. As a result, many researchers dedicate to research of circular polarization antenna. A dual circular polarization antenna with ring slot has been designed for K-band downlink and uplink, by applying sequential rotation technique [17]. A dual circular polarization antenna has been designed to operate on Beidou navigation satellite system (1.59 GHz–1.63 GHz and 2.39 GHz–2.57 GHz), whose circular polarization is implemented through applying method that invert-L and perturbation are

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inserted in radiation patch [18]. A circular annular ring patch antenna with circular polarization is designed in [19] whose operating band is 1.92 GHz–2.025 GHz. Although circular polarization antennas has been achieved by using the methods above, the antenna is still limited in a narrow operating bandwidth. If the existed antenna is transformed to circular polarization, antenna structure must be improved furtherly. Recent years, with the development of microwave techniques, metasurface, an artificial electromagnetic material, is considered to convert the linear polarization incident waves into circular polarization reflected waves [20–22], and it can improve the performance of antenna in terms of axial ratio bandwidth and axial ratio bandwidth [23]. Simultaneously, the structure of the metasurface consisting of 4  4 rectangle loops is designed with a diagonal microstrip [24]. After that, a 3  3 rectangle with slots metasurface structure is also designed [25]. Nevertheless, both techniques can convert the linear polarization wave into circular polarization wave, the above circular polarization conversion is single one. This must be improved in order to meet dual circular polarization requirement. In this approach, a circular polarization technique has been developed. Use of metasurface structure, a 5  5 array is designed to implement the conversion of circular polarization from learner linear one. The element of metasurface is wheel-shaped with two orthogonal dipoles and four quarter circular rings. The dual notched-bands UWB is combined with metasurface. Then, dual circular polarizations are implemented at dual wide-bands. Fabricated sample has been verified the design. The rest parts of this paper are organized as follows. By using the high frequency simulation software (HFSS), a wheel-shaped reflective unit and 5  5 metasurface structure is designed in Section 2. The 5  5 metasurface structure is verified by a dual notched-bands ultra-wideband antenna in Section 3, which can convert linear polarization incident waves into left-hand and right-hand circular polarization waves. Then fabricated samples of designed above have been tested, and experiment results are discussed in Section 4. Finally, conclusions on this approach are given at last Section. 2. Metasurface design 2.1. Element of metasurface As an element of the metasurface, two orthogonal dipoles are composed of four branches, as shown in Fig. 1(a). ! It will reflect electromagnetic waves E m when the incident ! ! ! electromagnetic wave E u arrives. The E u and E m are expressed as

! ! E u ¼ r Eu ejkz

ð1Þ

r

When incident wave arrives metasurface, the angle between ! vector direction of incident wave E u and x-axis is a certain angle a, as shown in Fig. 1(a). Then phase difference w = bx - by is achieved. The bx and by are phases that x-axis and y-axis compo! nent of reflective wave E m , respectively. Therefore, the incident ! ! wave E u and reflected wave E m can be also expressed as

  ! ! ! E u ¼ x cosa þ y sina Eu ejkz

ð3Þ

  ! ! ! E m ¼ x ejbx cosa þ y ejðbx wÞ sina Em ejkz

ð4Þ

The (4) will be transformed if the a and w is 45° and ± 90°, respectively, we have

! Em ¼

pffiffiffi 2 jbx ! ! x  j y Em ejkz e 2

ð5Þ

So, the left-hand and right-hand circular polarizations reflected wave is achieved when incident wave arrives metasurface. We proposed circular polarization reflect element is wheel shape, as shown in Fig. 1(b). In the middle of a reflect element, the four branches are equivalent to two orthogonal dipoles above. And, the four arc-shaped rings possess reclamation function for a and W, so that the circular polarization reflect wave is achieved. The detail dimensions of a circular polarization element are shown in Table 1. The reflection coefficients |S11| and transmission coefficients | S21| of a reflected element is observed, as shown in Fig. 2. It can be seen that the reflection coefficient is greater than 10 dB when the incident wave impinges of the element, and transmission coefficients are less than 80 dB. That is, most of incident wave is reflected to free space. 2.2. Metasurface structure In airborne electronic system, the space of antenna is limited, so the proposed metasurface structure is a compact array of 5  5, which consists of elements above, as shown in Fig. 3. Distance between each element is 1 mm. The substrate is polytetrafluoroethylene (PEFE) board which dimension size D1  D2  H1 = 57  57  1.524 mm3 (H1 is the thickness of the substrate). It is applied to changing the polarization of the airborne antenna. The reflection coefficients S11 and transmission coefficients |S21| of metasurface is also observed, as shown in Fig. 4. It can be seen that the reflection coefficient is greater than 10 dB when the incident wave impinges of the element, and transmission coefficients are less than 20 dB. Therefore, most of incident wave is also reflected to free space.

3.1. UWB antenna with two band notches

R2

N2

N1

x (a)

ð2Þ

3. Design of uwb antenna with dual circular polarization

R1 G1

y

! ! E m ¼ r Em ejbr ejkz

(b)

Fig. 1. (a) is two orthogonal dipoles forming an element of the metasurface to reflect electromagnetic waves, (b) is wheel shaped metasurface element for forming circular polarization.

To stop WLAN and WiMAX bands in the UWB communication system of airborne electronic devices, a compact dual notched bands UWB antenna is designed, as shown in Fig. 5. From a classical rectangular patch antenna, three corners of the patch have been cut off to enhance the bandwidth. Its dimension size is details listed in Table 2, where the radiation patch is obtained by simulating study. The operating bandwidth is stable when the rectangular radiation patch is cut off four/three orthogonal triangles. However, to adjust the input impedance convenience, the radiation patch is cut off three orthogonal triangles; and one of them is remained, formed irregular patch. Then two C-shaped slots are etched on

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Z. Lin et al. / Int. J. Electron. Commun. (AEÜ) 116 (2020) 153086 Table 1 Dimensions size of an element (unit: mm). Dimensions

R1

R2

N1

N2

G1

Size

5

3.5

2.5

1

1

W

0 -80

W2

-6 |S 11| -8

-140

|S 21| -160

-10

2

4

6

8

10

12

14

Lf

W1 Wf1

L

W4

W3

Wf

L5

-120

|S21| (dB)

-4

G

L6

|S11|(dB)

-100

L4 L3

L1

-2

W

(a)

(b)

Fig. 5. Geometry of dual notched-bands UWB antenna: (a) top view, (b) bottom view.

Frequency (GHz) Fig. 2. |S11| is the reflection coefficient of an element when incident wave arriving at the element surface. |S21| is the transmission coefficient of an element when incident wave arriving at the element port.

D1

After, the simulated S11 is obtained, as shown in Fig. 6. We observe the pass band of S11 less than 10 dB at 2.8 GHz–13.8 GHz excepting for dual notched-bands of 3.15 GHz–3.95 GHz and 5.5 GHz–5.75 GHz. Latter is WLAN and WiMAX bands. In boresight direction, the gain is also simulated use of the same dual notched-bands UWB antenna model, as shown in Fig. 7. The maximum gain is 8 dBi, and the gain at low frequencies is significantly higher than the one at high frequencies.

D2

3.2. Completion of dual circular polarizations

Fig. 3. Metasurface geometry is consisted of 5  5 wheel-shaped array on the PEFE board with H1 thickness.

0

0 -20

-5

-60

-10

|S11| |S21|

-15

2

4

6 8 10 Frequency (GHz)

12

|S21|(dB)

|S11|(dB)

-40

-80 -100 -120 14

Fig. 4. |S11| is reflection coefficient of metasurface when incident wave arriving at the metasurface. |S21| is transmission coefficient of metasurface when incident wave arriving at the metasurface.

the patch, formed dual notched-bands. The substrate is also PEFE board with 31  22  1.524 mm3 in size, and the relative permittivity is er = 3.5.

To implement dual circular polarizations, the designed dual notched bands UWB antenna is placed on the metasurface with an air gap G2 = 4.5 mm, which is distance between antenna and metasurface. The top view of antenna with metasurface is shown in Fig. 8. Here, the M1 = 19 mm, a distance from the left side of the antenna to left side of the metasurface. The M2 = 16.75 mm, the distance from the top side of antenna to the same side of metasurface. Reflection coefficient, S11 has been simulated, as shown in Fig. 9, and is expressed by the S11-UWM in the figure. The performance of antenna is improved with metasurface. The operating bandwidth is slightly moved to 2.6 GHz–13.6 GHz. The notched band of WiMAX is slightly winded for 3.15 GHz–4.3 GHz. And, the S11 of 9.1 GHz10 GHz is a few increased because the quarter impedance matcher is deteriorated. However, the result is acceptable. As comparison, the S11 of designed antenna without metasurface is depicted in the same figure as shown the curve of S11-UWB. Obviously, the metasurface can help us to improve the bandwidth property of notched-bands UWB antenna. In boresight direction, the axial ratio of dual notched-bands UWB antenna with metasurface is simulated, result as shown in Fig. 10 where expressed by AR-UWM. As comparison, the axial ratio of designed antenna without metasurface is depicted in the same figure and express for AR-UWB. We can observe that axial ratio is sharply declined to less than 3 dB at dual bands of 4 GHz–7.9 GHz and 8.1 GHz–12.4 GHz. Then the circular polarization is implemented at operating band above. By the way, the notched bands of 4 GHz–4.3 GHz and 5.5 GHz– 5.75 GHz are deducted. The axial ratio does not appear characteristic of the circular polarization in this band. From Fig. 10, the circular polarization bandwidth occupies 79.1% for entire operating band (excepting for dual notchedbands).

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Table 2 Dimensions of antenna (unit: mm). Dimension

L

W

Lf

L1

L2

L3

L4

L5

Size

31

22

11

20

6.5

5

5

9.5

Dimension

Wf

L6

Lf1

Wf1

W1

W2

W3

W4

Size

3.6

4.5

7.5

0.4

7

8.5

16.5

3

0

0

-20 |S11|(dB)

|S11| (dB)

-10

-20

-40

-30

UWB UWM -40

2

4

6 8 10 Frequency (GHz)

12

14

Fig. 6. Simulated reflection coefficient of the UWB antenna with dual notchedbands.

-60

2

4

6 8 10 Frequency(GHz)

12

14

Fig. 9. Reflection coefficient of dual notched-bands UWB antenna with/without metasurface (UWM/UWB).

10

5

15 Axial Ratio (dB)

Gain (dBi)

20

0

-5

2

4

6 8 10 Frequency (GHz)

12

14

10 UWM UWB

5

0

2

4

6 8 10 Frequency (GHz)

12

14

Fig. 7. Simulated gain of the UWB antenna with dual notched-bands. Fig. 10. Simulated axial ratio of dual notched-bands UWB antenna with/without metasurface (UWM/UWB) at 2 GHz–14 GHz.

M2

M1

Fig. 8. Geometry of ultra-wideband antenna with metasurface for circular polarization.

Then, the surface current distribution, which is an element of metasurface, is observed, as shown in Fig. 11. From the figure, it can be seen that current distribution on a circular ring is clockwise, Fig. 11(a) and (b), and counterclockwise, Fig. 11(c) and (d), when the fed phase of ultra-wideband antenna is 0°, 90°, and 180°, 270°, respectively. And the angle a is rotated to 45°, and ± 90°

phase different w is achieved, by four arc-shaped rings. So, the left-hand and right-hand circular polarizations are implemented. In the boresight direction, the gain of dual notched-bands ultrawideband antenna with metasurface is also observed by simulation. The result is indicated in Fig. 12. It can be seen that the gain of antenna with metasurface is reduced by comparing Fig. 12 with Fig. 7. The reason is analyzed. An air gap exists between antenna and metasurface, so that most of the electromagnetic energy is radiated from air gap. So the gain of antenna with metasurface is reduced in direction of boresight. The Radiation patterns of the designed antenna with metasurface are also simulated. The results are depicted in Fig. 13. Both E-plane and H-plane radiation patterns are shown in the same figure in each point. It can be seen from the figure that the radiation directionality is gradually deteriorated from the low-frequency to high-frequency because cross- polarized components are increased with frequency. When the UWB antenna is placed on metasurface, notched band is slightly affected. But the antenna can be still utilized in considerable frequency bands. The two bands of dual-circular polarization wave are reflected by metasurface so that the UWB antenna can effectively reduce interference of multipath, fog, rain, and snow, etc.

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The mag(Ex) is approximately equal to mag(Ey). From Fig. 14 and Fig. 15, both phase difference w and amplitude of electric field component mag(Ex), mag(Ey) indicates our designed assemble antenna with excellent characteristic of dual circular polarization. These results have been validated by experiment which will be discussed next.

4. Experimental results discussion

(a)

(b)

(c)

(d)

Fig. 11. Surface current distribution of an element at 6.1 GHz when the feeding phase is (a) 0°, (b) 90°, (c) 180°, and (d) 270°. (a) and (b) appear on clockwise distribution, (c) and (d) on counterclockwise distribution.

10

Gain (dBc)

0

-10

-20

-30

2

4

6

8

10

12

14

Frequency (GHz)

Fig. 12. Simulated gain of the dual notched-bands UWB antenna with metasurface.

3.3. Verification of dual circular polarizations For verifying the dual circular polarization, the phase difference

w of electronic filed component is observed in boresight direction when feeding phase is 90° and 270°. The result is shown in Fig. 14. It can be seen that w of 4 GHz–7.9 GHz and 8.1 GHz–12.4 GHz is about 90° and 270° (equivalent to 90°). And then amplitude of electronic filed component mag(Ex) and mag(Ey) are also observed, as shown in Fig. 15.

-10

120

E-plane H-plane

60

150

60

120

E-plane H-plane 30

0

330

180

0

300

210

330 240

300

270

270

(a)

(b)

E-plane H-plane

60 30

-20

180

0

-30

-30

210

-10

150

-20

-30

240

-10

150

30 -20

180

90

90

90 120

The dual notched-bands UWB antenna, metasurface and both mounted together have been fabricated. Photographs are shown in Figs. 16–18. The air gap between antenna and metasurface is replaced by a Teflon foam board, the er = 1.003 for the Teflon foam. The reflection coefficients of dual notched-bands UWB antenna and it with metasurface are measured by PNA-X Network Analyzer N5244A in our laboratory. Results are depicted in Fig. 19 where expressed by E-UWB and E-UWM. As comparison, the simulated results are illustrated in the same figures as shown the curve, SUWB and S-UWM. Both experimental and simulation results are in agreement very well. However, we must note from figure that the notched bands are shifted because of the sample production errors and interference of experimental environment. The S11 at 7.5 GHz–9. 5 GHz band is affected by metasurface seriously. Because a quarter wavelength impedance matcher is inserted between radiation patch of ultra-wideband antenna and feed microstrip of ultrawideband antenna to implement impedance match at 7.5 GHz– 9 GHz, the much reflection and transmission of incident wave inside impedance matcher is affected by reflection wave of metasurface, and the production errors etc exacerbate abovementioned affection. Then the gain of dual notched-bands ultra- wideband antenna and it with metasurface are also measured by using Obit 6. The experimental results are indicated in Fig. 20 where also expressed by E-UWB and E-UWM, respectively. The simulated results are depicted in the same figures for comparison where the curves are expressed S-UWB and S-UWM. From Fig. 20, we can observe that experimental results are in agree with simulate results. However, the minor fluctuations appeal on gain curves because of production errors and measurement errors Radiation patterns are also obtained by using Obit 6 in our laboratory, at the frequency of 3.1 GHz, 6.1 GHz, and 11 GHz. Results are plotted in Fig. 21, and are expressed E-plane-E and H-plane-E, respectively. As comparison, the simulated results are depicted in the same figures as shown the curve, E-plane-S and H-plane-S. From figure, the experiment results are in agree with simulation very well at what we care the frequencies in both E- and H- planes. It is illustrated that our design is available.

210

330 240

300 270

(c)

Fig. 13. Simulated radiation pattern of dual notched-bands UWB antenna with metasurface at (a) 3.1 GHz, (b) 6.1 GHz, and (c) 11 GHz.

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Phase diffrence (°)

100

0

90°-FP 270°-FP

-100

-200

-300 4

6

8

10

12

14

Frequency (GHz) Fig. 14. Phase difference of electric filed x- and y- components, when the fed phase (FP) is 90° and 270°, at 2 GHz–14 GHz.

Fig. 18. Photograph of dual notched-bands UWB antenna together with metasurface, (a) top view and (b) side view.

0 -10

Ex Ey

2

|S11|(dB)

mag(Ex) (mV), mag(Ey) (mV)

3

1

0

-20 S-UWB E-UWB S-UWM E-UWM

-30 -40 4

6

8

Frequency

10 (GHz)

12

14

Fig. 15. Amplitude of electric field x- and y- components at 2 GHz–14 GHz, in boresight direction.

2

4

6

8

10

12

14

Frequency (GHz) Fig. 19. Simulated (S-UWB) and experimental (E-UWB) reflection coefficient of dual notched-bands ultra-wideband antenna without and with metasurface.

10

Gain (dBi)

0 S-UWB E-UWB S-UWM E-UWM

-10

-20

Fig. 16. Photograph of dual notched-bands UWB antenna fed by microstrip, (a) top view and (b) bottom view.

-30

2

4

6 8 10 Frequency (GHz)

12

14

Fig. 20. Simulated (S-UWB) and experimental (E-UWB) gain of dual notched-bands ultra-wideband antenna with and without metasurface.

5. Conclusion

Fig. 17. Photograph of metasurface composed by 5  5 wheel shaped orthogonal dipoles array, other side of it is metal film.

A good property metasurface for converting the linear polarization to dual circular polarizations has been designed. Its performance has been verified by experiment. A dual notched-bands UWB antenna together with the metasurface are implemented, which is with dual circular polarizations at 4 GHz–7.9 GHz and 8.1 GHz–12.4 GHz. It can occupy the 79.1% of entire operating bandwidth. Practically, the perfor- mance of antenna operating at 9.1 GHz–10.6 GHz is a bit not good because the quarter impedance matcher is affected by the metasurface. These problems will be studied in future work.

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Z. Lin et al. / Int. J. Electron. Commun. (AEÜ) 116 (2020) 153086 E-plane-E H-plane-E E-plane-S H-plane-S

90 120

-10

60

150

30

60 30

0

330 300

60 30

-20

180

0

180

0 -30

210

330 240

-10

150

-30

210

E-plane-E H-plane-E E-plane-S H-plane-S

90 120

-20

-30

240

-10

150

-20 180

E-plane-E H-plane-E E-plane-S H-plane-S

90 120

300

210

330 240

300

270

270

270

(a)

(b)

(c)

Fig. 21. Experimental radiation pattern of dual notched-bands UWB antenna with metasurface at (a) 3.1 GHz, (b) 6.1 GHz, and (c) 11 GHz, simulation results are also depicted in.

Funding information National Natural Science Foundation of China, Grant Number: 61671200; Key Project of Hebei Province Natural Science Foundation, Grant Number: F2017202283; Hebei Province Graduate Student Innovation Fund Project Grant Number: CXZZSS2018013. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.aeue.2020.153086. References [1] Kim D, Zhang M, Hirokawa J, Ando M. Design and fabrication of a dualpolarization waveguide slot array antenna with high isolation and high antenna efficiency for the 60 GHz band. IEEE Trans Antennas Propag 2014;62 (6):3019–27. [2] Zhou SG, Huang GL, Chio TH, Yang JJ, Wei G. Design of a wideband dualpolarization full-corporate waveguide feed antenna array. IEEE Trans Antennas Propag 2015;63(11):4775–82. [3] Chen P, Hong W, Kuai Z, Xu J. A substrate integrated waveguide circular polarized slot radiator and its linear array. IEEE Antenna Wirel Propag Lett 2009;8:120–3. [4] Hao ZC, Liu X, Huo X, Fan K. Planar high-gain circularly polarized element antenna for array applications. IEEE Trans Antennas Propag 2015;63 (5):1937–48. [5] Zheng S, Gao S, Yin Y, et al. A broadband dual circularly polarized conical fourarm sinuous antenna. IEEE Trans Antennas Propag 2017;66(1):71–80. [6] Le TT, Tran HH, Park HC. Simple-structured broadband dual-slot circularly polarized antenna. IEEE Antenna Wirel Propag Lett 2018;17(3):476–9. [7] Wu J, Li M, Behdad N. A wideband unidirectional circularly polarized antenna for full-duplex applications. IEEE Trans Antennas Propag 2018;66(3):1559–63. [8] Hirokawa J, Ando M. Sidelobe suppression in 76-GHz post-wall waveguide-fed parallel-plate slot arrays. IEEE Trans Antennas Propag 2000;48(11):1727–32.

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