Ultrawideband, high-gain, high-efficiency, circularly polarized Archimedean spiral antenna

Ultrawideband, high-gain, high-efficiency, circularly polarized Archimedean spiral antenna

Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7 Contents lists available at ScienceDirect International Journal of Electronics and Communications (AE...

2MB Sizes 0 Downloads 7 Views

Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

Contents lists available at ScienceDirect

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

Regular paper

Ultrawideband, high-gain, high-efficiency, circularly polarized Archimedean spiral antenna Huy Hung Tran, Tuan Tu Le ⇑ Division of Computational Physics, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City 70000, Viet Nam Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City 70000, Viet Nam

a r t i c l e

i n f o

Article history: Received 7 June 2019 Accepted 5 July 2019

Keywords: Spiral antenna Archimedean Circularly polarized UWB Unidirectional

a b s t r a c t This paper presents an ultrawideband (UWB) circularly polarized (CP) two-arm Archimedean spiral antenna with unidirectional radiation patterns. The antenna is directly fed by a 50-X coaxial cable and reflected by a circular cavity. The proposed design is able to exhibit high gain, high radiation efficiency as well as UWB CP operation by properly choosing the reflector’s dimensions and the spiral’s growth rate. This overcomes the critical drawback of the other reported UWB CP spiral antennas in literature, which always suffer from poor performance in the lower operating frequencies. The measured reflection coefficient and axial-ratio show a good performance over a frequency band 6–16 GHz. Furthermore, the values for gain and radiation efficiency of the proposed design are always better than 5.2 dBic and 85%, respectively. Ó 2019 Elsevier GmbH. All rights reserved.

1. Introduction Circularly polarized (CP) antennas with ultrawideband (UWB) characteristic have extensively been exploited in modern wireless communication. Various types of printed slot and monopole antenna have been proposed [1–6]. The most typical feature of these antennas is bi-directional beam since a ground plane reflector is not required. For applications, in which antennas are mounted on ground plane reflectors, antennas with unidirectional radiation characteristic are more preferred. At present, there are several approaches to design the unidirectional CP antennas with operating bandwidth (BW) of better than 85%, including array antennas [7–9], dual tapered slots [10]. However, these antennas required complicated feeding network and complicated structure due to the use of multiple layers is also another drawback of designs in [7–9]. To overcome these deficiencies, other approaches by using single-fed elliptical dipoles with cavity reflector [11] or single-fed bowtie dipoles with parasitic elements [12] have been proposed. Archimedean spiral antenna is also another solution to realize UWB performance with single feed [13]. In [14–17], the spiral antennas are designed with absorber or lumped resistors. In [18–20], a technique of using parasitic layers or hybrid reflector to enhance the performance of the Archimedean spiral antenna has been reported. In general, most of the spiral antennas (except ⇑ Corresponding author. E-mail address: [email protected] (T.T. Le). https://doi.org/10.1016/j.aeue.2019.07.006 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.

for [19]) suffer from poor performance with low gain and radiation efficiency in low frequency band. In this paper, a two-arm Archimedean spiral antenna with unidirectional CP beam for UWB applications is presented. In contrast to other reported designs in [14–17] which utilized absorber or resistor, the cavity reflector is adopted for high gain and high radiation efficiency. In terms of CP operation, we found that by properly choosing the spiral’s growth rate or the number of turns, UWB operation can be attained. This distinguishes the proposed design from the other reported spiral antennas and is the main contribution of our paper. In order to make the design procedure to be straightforward, the antenna is first designed in a freespace, and then over a planar reflector and cavity reflector to transform the bidirectional beam to unidirectional beam. 2. Design of the Archimedean spiral antenna in free-space Fig. 1 shows the top and cross-section views of the proposed spiral antenna in free-space. Unlike the conventional Archimedean spiral antenna, the two arms of the proposed design are etched on two different sides of a RO4003 substrate with a relative dielectric constant er = 3.38. The spiral’s arm is linearly proportional to the winding angle, u (rad), and the growth rate, a (mm/rad). Additionally, the winding angle u can be defined as a function of number of spiral’s turns (N), u = 2pN. In order to have good impedance matching, the spiral’s arms are respectively connected to the inner and outer conductors of a 50-X coaxial cable through a double-sided

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

y

9

0

w

l2

|S11| AR

ro

l1

ws Transition

Rs

-10

6

-20

3

AR (dB)

x

|S11| (dB)

z

-30 2

(a)

6

14

18

Gain (dBi)

y

Fig. 1. (a) Top-view and (b) cross-section view of the spiral antenna. The optimized dimensions: Rs = 24 mm, w = 1.4 mm, ro = 2.5 mm, ws = 1.8 mm, l1 = 3.9 mm, l2 = 2.2 mm, number of turns N = 1.5, growth rate a = 2.28 mm/rad.

strip line transition, which has been thoroughly investigated in [21]. Fig. 2 shows the simulated performances of the spiral antenna in free-space. It can be seen that the antenna has good 3-dB AR BW in the frequency range from 3 to 18 GHz. Meanwhile, good impedance matching BW of |S11|  –10 dB over extremely wide frequency range is also obtained. Within this band, the antenna radiates bidirectional radiation patterns with gain varying from 2.0 to 6.6 dBic and radiation efficiency of greater than 92%. 3. Design of the Archimedean spiral antenna over planar reflector The bidirectional beam from the spiral antenna is transformed into the unidirectional beam by using a reflector. Fig. 3 shows the geometrical configuration of the spiral antenna over a circular planar reflector. In this design, the coaxial line goes through the reflector and connects to the radiator. The dimensions of the radiating element are fixed at optimal values as in the caption of Fig. 1. Since the usable BW of the proposed spiral antenna in freespace is from 5.0 to 18.4 GHz, the distance between the radiator and the reflector, Hc, is theoretically chosen as a quarterwavelength at 5.0 GHz. This is due to the fact that the performance at lower frequency range is more sensitive to the variation of Hc. Fig. 4 shows the antenna characteristics for different values of Hc. With Hc = 15 mm, the antenna has the lowest operating frequency at 5.0 GHz. However, the broadside gain suffers from a significant degradation at around 9.0 GHz because the antenna height Hc corresponds to the half-wavelength at this frequency. By gradually decreasing Hc, the depression in the gain curve tends to shift to higher band. At the same time, the lowest operating frequency occurs at higher frequency. It is noted that as Hc decreasing, the reflected electromagnetic waves from the reflector cause significant effect on the antenna input impedance. Smaller Hc results in more variation in the reflection coefficient at low frequencies

0

1.0

9

z

(b)

22

Frequency (GHz) (a)

Hs

x

10

Gain Efficiency

6

0.6

3

0

0.8

2

6

10

14

18

Efficiency

2

0.4 22

Frequency (GHz) (b) Fig. 2. Simulated (a) |S11|, AR, and (b) gain, radiation efficiency of the spiral antenna in free-space.

z x

y Rre

Hc

Fig. 3. Cross-section view of the spiral antenna over planar reflector. The optimized dimensions: Hc = 8 mm, Rre = 35 mm.

[13]. In this paper, the optimized value of Hc is 8 mm and the antenna is capable of generating good performance over wide range of frequencies from 6 to 16 GHz. Across this band, the broadside gain varies from 4.6 to 9.6 dBic. Next, another key parameter, which is critical to determine the operating BW of the antenna over planar reflector, is the number of spiral’s growth rate, a. Its effects on the antenna characteristics are investigated and the simulated results are shown in Fig. 5. In this study, the growth rate (a) and the number of turns (N) are adjusted so that the overall size of the spiral antenna Rs is constant. As observed in Fig. 5, the AR is significantly affected by N and a, especially in high frequency region. This is due to the fact that the operation characteristics of spiral antenna strongly depend on how tight wrapping of the spiral’s arms is [22,23]. The tighter wrapping causes increased coupling between the spiral arms in active region and the AR is therefore improved. In our case, the tighter wrapping

3

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

0

9

Axial ratio (dB)

|S11| (dB)

-10

-20

Hc = 4 mm Hc = 8 mm Hc = 12 mm Hc = 15 mm

-30

-40

4

8

12

16

Hc = 4 mm Hc = 8 mm Hc = 12 mm Hc = 15 mm 6

3

0

20

4

8

12

Frequency (GHz)

16

20

Frequency (GHz)

(a)

(b)

Broadside gain (dBi)

15 Hc = 4 mm Hc = 8 mm Hc = 12 mm Hc = 15 mm

10

5

0

4

8

12

16

20

Frequency (GHz)

(c) Fig. 4. Simulated (a) |S11|, (b) AR, and (c) broadside gain of the spiral antenna over planar reflector for different values of Hc.

Axial ratio (dB)

9

N = 1.0, α = 3.42 N = 1.5, α = 2.28 N = 2.0, α = 1.71 N = 2.5, α = 1.37

6

3

0

4

8

12

16

20

Frequency (GHz)

(a)

(b)

Broadside gain (dBi)

12 N = 1.0, α = 3.42 N = 1.5, α = 2.28 N = 2.0, α = 1.71 N = 2.5, α = 1.37

8

4

0

4

8

12

16

20

Frequency (GHz)

(c) Fig. 5. Simulated (a) |S11|, (b) AR, and (c) broadside gain of the spiral antenna over planar reflector for different values of spiral’s growth rate (a) and turns (N).

4

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

12 GHz

8 GHz

Physical size of the radiating source

(a) 8 GHz

12 GHz

(b) Fig. 6. The simulated E-field distributions of the antenna for the case (a) N = 1, a = 2.28 and (b) N = 2.5, a = 1.37.

Rt z x

Hc

Rb y

Fig. 7. Cross-section view of the spiral antenna over cavity reflector. The optimized dimensions: Hc = 8 mm, Rb = 32 mm, Rt = 42 mm.

can be achieved by decreasing a and increasing N. For instances, with N = 2.5 and a = 1.37 mm/rad, the strongest coupling is achieved and this makes the performance at low frequency band becomes better. However, as the frequencies increases, the quality of the CP radiation starts to deteriorate. This can be attributed to the effects of the center transition, which is used for impedance matching aspect. In terms of gain, the gain values are quite stable in the frequency range below 11 GHz. Out of this band, the varia-

12 28 mm 32 mm 36 mm 40 mm

Broadside gain (dBi)

Broadside gain (dBi)

12

8

4

0

4

8

12

16

20

34 mm 38 mm 42 mm 48 mm 8

4

0

4

8

12

Frequency (GHz)

Frequency (GHz)

(a)

(b)

16

Fig. 8. Simulated broadside gain of the spiral antenna with different values of cavity’s dimensions (a) Rb, (b) Rt.

20

5

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

tion is more significant. This phenomenon can be explained by observing the simulated E-field distributions for the case (N = 1, a = 2.28) and (N = 2.5, a = 1.37) as shown in Fig. 6. In fact, the antenna gain is defined by [24]:

Ae  4p

The proposed Archimedean spiral antenna has been fabricated and measurement has also been implemented to prove the concept. Fig. 10 shows the simulated and measured |S11| and AR of

ð1Þ

k2

0 where Ae is the effective radiating area and k is the wave-length. As observed, at 8 GHz, the Ae for both cases is quite similar. It is consistent with the results in Fig. 5(c), in which the gain values for both cases are just slightly different. At 12 GHz, the difference is more significant, which results in more different between the gain values at this frequency. Based on the parametric studies, it has been found that with N = 1.5 and a = 2.28 mm/rad, the antenna achieves the best performance in terms of |S11|, AR as well as broadside gain.

9

|S11| (Mea.) |S11| (Sim.) AR (Mea.) AR (Sim.)

-10

|S11| (dB)

6 -20 3

Axial ratio (dB)



5. Measurement results

-30 4. Design of the Archimedean spiral antenna over cavity reflector

-40 It has been illustrated in Section 3 that the unidirectional spiral antenna is able to produce UWB operation in terms of reflection coefficient and AR. Besides, the antenna also obtained a good broadside gain of better than 6 dBi for the frequency range below 11 GHz, but this value is significantly decreased in higher band. To solve this problem, the cavity reflector is utilized to improve the broadside gain in the higher band [25,26]. The geometry of the spiral antenna over cavity reflector and its optimized dimensions are illustrated in Fig. 7. In this design, all the dimensions of the spiral and the distance from the spiral to the reflector (Hc) are fixed at optimal values as presented in the captions of Figs. 1 and 3. Here, only the parameters related to the cavity (Rb, Rt) are adjusted to optimize the antenna’s gain. For illustration, Fig. 8 shows the gain characteristic with different values of Rb and Rt. As observed, tuning Rb or Rt has significant impact on the gain values, particularly in upper band. The reason is that using cavity reflector can better collimate energy in the forward direction by restricting both the back and side radiations. Changing the cavity’s shape leads to different back and side radiations and consequently, the energy in the forward direction can be adjusted. Finally, Fig. 9 shows the performance comparison of the spiral antenna over planar and cavity reflectors. It observes a small difference of the AR and |S11| BWs between these cases. However, the broadside gain is significantly affected and the maximum enhancement is from around 5 to 8 dBic around 14 GHz.

|S11| (dB)

6 -20 3 -30

-40

4

8

12

16

20

0

16

20

0

1.0

12

8 0.6

0

0.4

Gain (Mea.) Gain (Sim.) Efficiency (Mea.) Efficiency (Sim.)

4

4

8

0.2

12 Frequency (GHz)

Radiation efficiency

Broadside gain (dBi)

0.8

0.0 20

16

Fig. 11. Simulated and measured broadside gain and radiation efficiency of the spiral antenna over cavity reflector.

12

Broadside gain (dBi)

-10

12

Fig. 10. Simulated and measured |S11| and AR of the spiral antenna over cavity reflector.

Axial ratio (dB)

|S11| (Planar Ref.) |S11| (Cavity Ref.) AR (Planar Ref.) AR (Cavity Ref.)

8

Frequency (GHz)

9

0

4

8

4 Planar reflector Cavity reflector 0

4

8

12

Frequency (GHz)

Frequency (GHz)

(a)

(b)

16

Fig. 9. Simulated (a) |S11|, AR, and (b) broadside gain of the spiral antenna over planar reflector and cavity reflector.

20

6

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7

and the radiation efficiency of better than 85% are also achieved within the usable BW. Fig. 12 shows the antenna’s measured radiation patterns at different frequencies of 8, 11, and 14 GHz along with the simulated results. The patterns including both the right-

the proposed design. It observes a well matched between simulation and measurement, and the fabricated antenna has usable BW of 90.9%, starting from 6 to16 GHz. In addition, as presented in Fig. 11, the gain at broadside direction from 5.2 to 9.3 dBic

(dBic)

0

12

330

RHCP (mea.) RHCP (sim.) LHCP (mea.) LHCP (sim.)

0 330

30

30

0 60

300

-12

60

300

-24 -36

90

270

90

270

-24 -12

120

240

120

240

0 150

210

12

150

210

x-z plane

y-z plane

(a) (dBic)

0

12

330

RHCP (mea.) RHCP (sim.) LHCP (mea.) LHCP (sim.)

0 330

30

30

0 60

300

-12

60

300

-24 -36

90

270

90

270

-24 -12

120

240

120

240

0 150

210

12

150

210

x-z plane

y-z plane

(b) (dBic)

0

12

330

RHCP (mea.) RHCP (sim.) LHCP (mea.) LHCP (sim.)

0 330

30

30

0 -12

60

300

60

300

-24 -36

90

270

90

270

-24 -12

120

240

120

240

0 12

150

210

150

210

x-z plane

y-z plane

(c) Fig. 12. Simulated and measured radiation patterns of the spiral antenna over cavity reflector at (a) 8 GHz, (b) 11 GHz, and (c) 14 GHz.

H.H. Tran, T.T. Le / Int. J. Electron. Commun. (AEÜ) 109 (2019) 1–7 Table 1 Performance comparison among UWB CP Archimedean spiral antenna. Ref.

Overall size (km)

Operating BW (%)

Gain (dBic)

Efficiency (%)

[14] [15] [16] [17] [18] [19] [20] Prop.

1.44  1.44  0.07 1.60  1.60  0.07 0.21  0.21  0.09 0.24  0.24  0.13 0.13  0.13  0.04 1.47  1.47  0.29 N/A 1.68  1.68  0.16

100.0 107.7 94.7 100 166.2 60.8 163.7 90.9

4.5–9.0 4.5–9.0 5.0 to 3.1 6.0 to 7.5 0.2–6.2 6.0–9.5 10 to 10 5.2–9.6

40–97 45–97 N/A 6–82 22–78 N/A N/A 85–94

km: free-space wavelength at the lowest operating frequency.

hand CP (RHCP) and left-hand CP (LHCP) are plotted in two different planes (x-z and y-z planes). The results indicate that the antenna exhibits good unidirectional radiation patterns. Across the operating BW, the front-to-back ratio is always better than 16 dB and the polarization isolation at broadside direction is higher than 12 dB. Additionally, the antenna’s half-power beamwidth (HPBW) gradually decreases from lower to higher operating frequency. The reason is that the HPBW of an antenna is inversely proportion to the operating frequency [27]. This is a drawback of the spiral antenna in comparison with other CP antennas with wide HPBW such as quadrifilar helix [28–31], metasurface [32], patch [33], dipole [34], and so on. Finally, comparisons between the reported UWB CP spiral antennas and this work are summarized and given in Table 1. As observed, the proposed antenna has the best gain and efficiency over the operating BW. The designs in [14–18,20] have larger operating BW than that of the proposed structure, but they suffer from low radiation efficiency and/or low gain in the low frequencies. In [19], although high gain radiation can be achieved, its essential disadvantages are higher profile and smaller operating BW in comparison with our design. 6. Conclusion This paper demonstrated a unidirectional CP Archimedean spiral antenna with UWB operation. The antenna is simply fed by a 50-X coaxial cable and reflected by a circular cavity. By properly choosing the number of spiral’s turns or growth rate and the dimensions of the cavity reflector, the antenna can realize UWB operation with high gain and high radiation efficiency. The measured operating BW is from 6 to 16 GHz and within this band, the broadside gain and radiation efficiency is always greater than 5.2 dBic and 85%, respectively. Declaration of Competing Interest The authors declared that there is no conflict of interest. References [1] Saini RK, Dwari S. A broadband dual circularly polarized square slot antenna. IEEE Trans Antennas Propag. 2016;64(1):290–4. [2] Wang L, Fang W, En Y, Huang Y, Shao W, Yao B. A new broadband circularly polarized square-slot antenna with low axial ratios. Int J RF Microw Comput Aided Eng 2018:e21502. [3] Tang H, Wang K, Wu R, Yu C, Zhang J, Wang X. A novel broadband circularly polarized monopole antenna based on C-shaped radiator. IEEE Antennas Wireless Propag Lett 2017;16:964–7. [4] Li Z, Zhu X, Yin C. CPW-fed ultra-wideband slot antenna with broadband dual circular polarization. Int J Electron Commun 2019;98:191–8. [5] Chaudhary P, Kumar A. Compact ultra-wideband circularly polarized CPW-fed monopole antenna. Int J Electron Commun 2019;107:137–45.

7

[6] Li J, Shi J, Li L, Khan TA, Chen J, Li Y, et al. Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio. IEEE Access 2018;6:64063–70. [7] Chung KL. High-performance circularly polarized antenna array using metamaterial-line based feed network. IEEE Trans Antennas Propag 2013;61 (12):6233–7. [8] Liu Q, Chen ZN, Liu Y, Li C. Compact ultrawideband circularly polarized weakly coupled patch array antenna. IEEE Trans Antennas Propag 2017;65 (4):2129–34. [9] Lee WS, Oh KS, Yu JW. A wideband planar monopole antenna array with circular polarized and band-notched characteristics. Prog Electromagn Res 2012;128:381–98. [10] Chang YL, Jiao YC, Lin C, Zhang L, Chen TG. A wideband circularly polarized cross-shaped linearly tapered slot antenna. Microwave Opt Technol Lett 2018;60(10):2406–11. [11] Zhang L, Gao S, Luo W, Young PR, Li Q, Gen YL, et al. Single-feed ultrawideband circularly polarized antenna with enhanced front-to-back ratio. IEEE Trans Antennas Propag 2016;64(1):355–60. [12] Feng G, Chen L, Wang X, Xue X, Shi X. Broadband circularly polarized crossed bowtie dipole antenna loaded with parasitic elements. IEEE Antennas Wireless Propag Lett 2018;7(1):114–7. [13] Kaiser JA. The Archimedean two-wire spiral antenna. IRE Trans Antennas Propag 1960;8(3):312–23. [14] Nakano H, Sasaki S, Oyanagi H, Yamauchi J. Cavity-backed Archimedean spiral antenna with strip absorber. IET Microw Antennas Propag 2008;7(2):725–30. [15] Nakano H, Satake R, Yamauchi J. Extremely low-profile, single-arm, wideband spiral antenna radiating a circularly polarized wave. IEEE Trans Antennas Propag 2010;58(5):1511–20. [16] Shih TY, Behdad N. A compact, broadband spiral antenna with unidirectional circularly polarized radiation patterns. IEEE Trans Antennas Propag 2015;63 (6):2776–81. [17] Zhong YW, Yang GM, Mo JY, Zheng LR. Compact circularly polarized Archimedean spiral antenna for ultrawideband communication applications. IEEE Antennas Wireless Propag Lett 2017;16:129–32. [18] Udaiyakumar R, Maheswar R, Janani T, Vigneshram R, Amiri JS, Yupapin P. Performance enhancement of shorted polygonal Archimedean spiral antenna using hybrid reflector. Int J Electron Commun 2019;107:1–8. [19] Liu X, Geng J, Liang X, Jin R, Zhang C, Wang K. An improvement to directional equiangular spiral antenna with wide CP band, high gain and low profile. Prog Electromagn Res C 2014;48:53–60. [20] Liu C, Lu Y, Du C, Cui J, Shen X. The broadband spiral antenna design based on hybrid backed-cavity. IEEE Trans Antennas Propag 2010;58(6):1876–82. [21] Tran HH, Nguyen-Trong N. Simple design of broadband circularly polarized two-arm Archimedean spiral antenna. Int J RF Microw Comput Aided Eng 2019:e21813. [22] Bawer J, Wolfe JJ. The spiral antenna. 1958 IRE International Convention. Record. 1960;8:84–95. [23] Elmansouri MA, Filipovic DS. Low-dispersion spiral antennas. IEEE Trans Antennas Propag 2012;60(12):5522–30. [24] [accessed June 29, 2019]. [25] Tran HH, Nguyen-Trong N, Le TT, Abbosh AM, Park HC. Low-profile wideband high-gain reconfigurable antenna with quad-polarization diversity. IEEE Trans Antennas Propag 2018;66(7):3741–6. [26] Ta SX, Choo H, Park I, Ziolkowski RW. Multi-band, wide-beam, circularly polarized, crossed, asymmetrically barbed dipole antennas for GPS applications. IEEE Trans Antennas Propag 2013;61(11):5771–5. [27] [accessed June 29, 2019]. [28] Bai X, Yang D, Tang J, Geng J, Jin R, Liang X. A novel dual-band circularlypolarized wide-beam quadrifilar helix antenna. In: Proceedings of the 2012 IEEE international symposium on antennas and propagation. [29] Son WI, Tae HS, Yu JW. Compact square quadrifilar helix antenna for SDARS application in portable terminals. Electron Lett 2011;47(4):232–3. [30] Li Y, Mittra R. A three-dimensional circularly polarized antenna with a low profile and a wide 3-dB beamwidth. J Electromagn Waves Appl 2016;30 (1):89–97. [31] Tranquilla JM, Best SR. A study of the quadrifilar helix antenna for global positioning system (GPS) applications. IEEE Trans Antennas Propag 1990;38 (10):1545–50. [32] Liu S, Yang D, Pan J. A low profile circularly polarized metasurface antenna with wide axial-ratio beamwidth. IEEE Antennas Wireless Propag Lett 2019;18 (7):1438–42. [33] Chen X, Yang L, Zhao JY, Fu G. High-efficiency compact circularly polarized microstrip antenna with wide beamwidth for airborn communication. IEEE Antennas Wireless Propag Lett 2016;15:1518–21. [34] Zheng DZ, Luo Y, Chu QX. Cavity-backed self-phased circularly polarized multidipole antenna with wide axial-ratio beamwidth. IEEE Antennas Wireless Propag Lett 2017;16:1998–2001.