Gain-enhanced SIW cavity-backed slot antenna by using TE410 mode resonance

Accepted Manuscript Regular paper Gain-Enhanced SIW Cavity-Backed Slot Antenna by Using TE410 Mode Resonance Ziqiang Xu, Jiahao Liu, Si Huang, Yuanxun Li PII: DOI: Reference:

S1434-8411(18)30735-0 https://doi.org/10.1016/j.aeue.2018.10.039 AEUE 52566

To appear in:

International Journal of Electronics and Communications

Received Date: Revised Date: Accepted Date:

26 March 2018 20 October 2018 31 October 2018

Please cite this article as: Z. Xu, J. Liu, S. Huang, Y. Li, Gain-Enhanced SIW Cavity-Backed Slot Antenna by Using TE410 Mode Resonance, International Journal of Electronics and Communications (2018), doi: https://doi.org/ 10.1016/j.aeue.2018.10.039

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Gain-Enhanced SIW Cavity-Backed Slot Antenna by Using TE410 Mode Resonance Ziqiang Xu 1*, Jiahao Liu1, Si Huang2, Yuanxun Li1 1

School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu, China. (* [email protected]) 2 Department of Electrical Engineering, University of Arkansas, Fayetteville, USA. Abstract: A gain-enhanced low profile substrate integrated waveguide (SIW) cavity-backed slot antenna is presented in this paper. By etching three parallel transverse slots on the center and both edges of the rectangular SIW cavity as the radiating elements, higher resonance mode of TE410 can be excited to achieve gain enhancement. Radiating mechanism and parameter effects of the three radiating slots have been investigated. Using the proposed multi-slot structures, an antenna is designed, fabricated and characterized, respectively. The fabricated antenna demonstrated a gain of 9.2 dBi, a front-to-back ratio of 17 dB, and a maximum cross-polarized radiation level of -19.7 dB at 10 GHz. Furthermore, the proposed antenna constructed using a single-layer printed circuit board (PCB) yields a better radiation performance and configuration advantage over that of the conventional planar antenna by taking advantage of the TE 410 cavity resonance. Keywords: SIW; higher resonance mode; multi-slot structures; cavity-backed antenna; gain enhancement. 1. Introduction The rapid development of wireless communication systems desires antennas with good radiation and configuration performance including low profile, low cost, light weight, easy fabrication and integration with planar circuits [1-4]. Cavity-backed antennas have been investigated for their high radiation performance in radar systems, while microstrip slot antennas have been extensively studied for their excellent configuration characteristics. Due to conductor losses and bidirectional radiation, radiation efficiency and forward gain of microstrip slot antennas are low. In order to address these drawbacks, a metallic reflector or cavity-backed of one quarter wavelength of the slot is employed. For a cavity-backed slot antenna presented in [5, 6], conventional short-ended metallic waveguide with depth of a quarter of wavelength serves as the backed cavity. However, these antennas are bulky, heavy, and expensive to fabricate, making them not suitable for some applications in satellite, aircraft, and high density microwave communication systems [7]. In order to eliminate the above mentioned drawbacks, substrate integrated waveguide (SIW) technology has been applied to cavity-backed slot antennas [8-10]. The SIW structures, which are synthesized in a planar dielectric substrate with arrays of metallic via holes using standard printed circuit board (PCB) or low-temperature co-fired ceramic (LTCC) process, provide a low-profile, low-cost, and low-weight advantage while still maintain their high performance [11-16]. A series of planar cavitybacked antennas based on SIW technology have been proposed [17-21]. In [17], a planar cavity-backed slot antenna based on SIW technology was first reported to generate radiation when TE 210 mode resonance

1

is excited in SIW cavity, with an average gain of 5.3 dBi within bandwidth. Moreover, by using hybrid resonance mode of TE110 and TE120 resonance in the SIW cavity, a cavity-backed slot antenna has been proposed in [18], and its fractional bandwidth is enhanced to 6.3 % with its gain slightly improved to 6 dBi. For gain improvement and size reduction, a SIW cavity-backed meandered slot antenna with lateral slots as inductive loads has been investigated in [19], in which radiation is generated by TE 120 mode resonance in the SIW cavity with a 6.1 dBi gain at 5 GHz. Furthermore, many gain enhancement methods have been taken into antenna designs. In [20], by etching two parallel slots at cavity edges as radiating elements to excite TE120 resonance only, the antenna gain has been improved to about 7.1 dBi. Additionally, a 2×2 array proposed in [21], which consists of four SIW cavity backed-slot antennas with a gain of 6.4dBi for each element, achieves a high overall gain of 12.1dBi. Although the cavity-backed slot antennas presented in [17-21] exhibit the desired features of low profile and gain improvement, they still have comparatively low-mode excitation, namely TE110 or TE120 resonances, in the SIW cavity. In this paper, a gain enhanced low profile SIW cavity-backed slot antenna is presented. Its gain improvement is achieved by etching three parallel transverse slots on the center and both edges to excite higher mode resonance of TE410 in the rectangular SIW cavity. By taking advantage of the TE410 cavity resonance, the proposed antenna not only obtains improved gain compared to those of the conventional SIW cavity-backed slot antennas using lower modes resonance, but also yields good radiation performance and configuration advantage of the planar antenna.

a b Fig. 1. Geometry and E-field distribution of the proposed SIW cavity backed slot antenna. a Geometry b E-field distribution

2

2. Antenna Configuration and Radiating Mechanism The configuration of the proposed cavity-backed slot antenna is shown in Fig. 1. The proposed antenna is constructed on a single layer PCB with its rectangular SIW cavity realized by a metallized through via-hole array. To mimic the conventional metallic cavity, the conditions of Dv/Pv≥0.5 and Dv/λo≤0.1 must be satisfied by the SIW cavity to achieve a negligible attenuation constant and leakage from the spacing between adjacent via holes, where λo stands for free space wavelength. Three parallel transverse radiating slots are etched at the center and both edges of the SIW cavity on its ground plane, while parasitic radiation generated by the 50 Ω grounded co-planar waveguide (GCPW) can be effectively isolated. For measurement convenience, a section of 50 Ω microstrip line is added at the end of the GCPW, forming a feeding network to stimulate the SIW cavity. The proposed antenna is simulated using a finite element method. Electric field diagram of the proposed antenna at 10GHz is shown in Fig. 2. The radiation is generated by TE410 mode resonance in the SIW cavity. This is very different from that of conventional cavity-backed antenna in which the backedcavity behaves as closely spaced reflectors. Radiating mechanism of the proposed antenna is shown in Fig. 2. When the SIW cavity is in TE410 mode resonance, dominant electric fields at two sides of the middle slot are in opposite phase. While for the edge-side slots, cavity-side electric fields have periodical phase offset against that of wall-side. Consequently, electric displacement vectors across the slots are in the same phase, thus energy can radiate into space by slots with enhanced gain. Due to the low profile configuration, the proposed antenna has an inherent drawback of narrow band with a fractional bandwidth about 1.7%, but it presents good isolation performance from 5GHz to 15GHz. To broaden its bandwidth, increase in substrate thickness [17], hybrid mode resonance [18], and widening of the slots [22] can be employed.

S=E×H ●

●

× ●

●

×

● ● ●

× ●

●

E

×

H

● ×

× ×

● ●

● ●

× ×

●

×

●

●

●

● ●

×

×

×

×

×

×

● ●

●

×

● ×

×

●

● ●

● ×

●

● ●

●

Fig. 2. Radiating mechanism of the proposed antenna.

3

15.5 Lceff=31.0 mm Lceff=31.5 mm Lceff=32.0 mm Lceff=32.5 mm Lceff=33.0 mm

Frequency (GHz)

15.0 14.5 14.0 13.5 13.0 12

14

16

18 20 Wceff (mm)

22

24

Fig. 3. Effects of length and width of SIW cavity on TE410 mode resonant frequency.

3. Parameters Analysis Effects of length and width of SIW cavity on TE 410 mode resonant frequency are shown in Fig. 3. As can be seen, the resonant frequency of the SIW cavity is affected by cavity’s length and width simultaneously, which can be estimated by subsequent equations (1)-(2) [23]. To achieve demanded frequency responses during design process of the proposed SIW antenna, cavity configuration including feeding probes ought to be controlled and tuned together. f 410 

Lceff

1 2 r  reff

 4   Lceff

2

  1      Wceff

2

 1 r  ,  reff  2 

Dv2 Dv2 Dv2 Dv2  Lc  1.08  0.1 , Wceff  Wc  1.08  0.1 Pv Lc Pv Wc

(1)

(2)

Effects of length and width of SIW cavity on central radiation frequency generated by TE 410 mode resonance are shown in Fig. 4, in which Ls=11.5mm. As shown, the plots in Fig. 4 are similar to those in Fig. 3, except their frequencies are slightly different caused by differences in Ls.

Frequency (GHz)

11.0 Lceff=32.5 mm Lceff=33.0 mm Lceff=33.5 mm Lceff=34.0 mm Lceff=34.5 mm

10.5

10.0

9.5 12

14

16

18

20

22

24

Wceff (mm)

Fig. 4. Effects of length and width of SIW cavity on radiation frequency generated by TE410 mode resonance with Ls=11.5mm.

4

Ls=10.0 mm Ls=10.5 mm Ls=11.0 mm Ls=11.5 mm Ls=12.0 mm Ls=12.5 mm Ls=13.0 mm

Frequency (GHz)

11.5

11.0

10.5

10.0

9.5 12

14

16

18 20 Wceff (mm)

22

24

Fig. 5. Radiation frequency generated by TE410 mode resonance with Lc=33.6 mm.

Wceff = 17.0 mm

Ls = 11.0 mm

Wceff = 18.0 mm

Ls = 11.5 mm

Wceff = 19.0 mm

Ls = 12.0 mm

a Fig. 6. E-field distribution and surface currents of TE410 mode resonance. a E-field distribution while Ls=11.5mm. b Surface currents while Wceff=18.0mm

b

Effects of length of slot on central radiation frequency generated by TE 410 mode resonance are shown in Fig. 5, in which Lc=33.6mm. It is known that slot length Ls has notable effects on operating frequency for the slot antenna. Comparing to Lceff or Wceff of the cavity size, slot length Ls primarily determines central radiation frequency of the proposed antenna. As shown in Fig. 6(a), electric field in SIW cavity widens as Wceff is elongating. Meanwhile, equivalent length of slot elongates as well as the length of displacement currents crossed slot. All these contribute to lower central radiation frequencies. These explain well the phenomenon that cavity size, namely Lceff or Wceff, has influence on the central radiation frequency. Moreover, when slot length and electric field that mainly determined by cavity size matches each other, the distance of the displacement currents crossed slot is roughly equal to the slot length Ls. Under these circumstances, the slot antenna achieves good impedance matching and surface currents Js flow through slot edges dominantly, which are shown in Fig. 6(b). When Wceff is unchanged, as surface currents

5

shown in the figure, distance that displacement currents crossed slot elongates along with slot length extending, which lead to a lower central radiation frequency. From Fig. 5 to Fig. 6, we can infer that cavity size, Lceff or Wceff, plays a dominant role in deciding the central radiation frequency when Ls is slightly less than Wceff, which is shown in the left side of Fig. 6. On the contrary, Ls contributes to regular adjusting central radiation frequency when Ls is less than Wceff to a certain extent, which is illustrated in right side of Fig. 6. Ls can be determined by: Ls 

co 2 f o r  reff

,  reff 

(5)

-10

Magnitude (dB)

Magnitude (dB)

-10

1  r 2

-20

-30

-20

-30

Lcpw2=1.7 mm Lcpw2=1.8 mm Lcpw2=1.9 mm

Lcpw1=25.8 mm Lcpw1=25.9 mm Lcpw1=26.0 mm

-40 9.95

10.00 10.05 Frequency (GHz)

-40 9.95

10.10

10.00 10.05 Frequency (GHz)

a

b -10

-20

-40 9.95

Wms=1.3 mm Wms=1.4 mm Wms=1.5 mm

10.00 10.05 Frequency (GHz)

10.10

Magnitude (dB)

Magnitude (dB)

-10

-30

10.10

-20

Ggcpw=0.6 mm Ggcpw=0.7 mm Ggcpw=0.8 mm

-30

-40 9.95

10.00

10.05

10.10

Frequecny (GHz)

c d Fig. 7. Effects of parameters of grounded coplanar waveguide on S11 of the proposed antenna. a. Lcpw1; b. Lcpw2 c. Wms; d. Ggcpw

Lcpw1 plays an important role in stimulating TE410 mode resonance in the SIW cavity, whereas it has little impact on S11 parameter shown in Fig. 7(a). However, as shown in Fig. 7(b), operation frequency can be tuned by Lcpw2 to a certain extent when Lcpw1 is a constant by impedance matching. In any case, Wms is the most direct way to regulate impedance matching within antenna elements, which has a

6

significant effect on the S11 parameter as shown in Fig. 7(c). GCPW as well as three slots, not only operate as exciting port, but also serve as perturbations in exciting high mode resonance of TE 410 and suppressing disturbed mode resonance. GCPW crossed two slots adjusts TE410 mode resonance in SIW cavity which is dominantly stimulated by Lcpw1 and Lcpw2. Effects of Ggcpw on S11 of the proposed antenna is shown in Fig. 7(d), in which their different magnitudes as well as central radiation frequency shift are caused by mismatch of impedance. 0

Simulated Measured

9.6

-10

-20

9.2

Gain (dBi)

Magnitude (dB)

9.4

9.0 -30

8.8 -40 9.90

9.95

10.00

10.05

10.10

Frequency (GHz)

Fig. 8. Photograph of the proposed SIW antenna. (Left: top view, Right: bottom view)

Fig. 9. Simulated and measured S11 and gain at boresight direction of the proposed antenna.

Table 1 Geometrical parameters of the proposed SIW cavity backed slot antenna (Unit: mm) Lc

33.6

Ls

11.5

Dv

1.0

Wc

19.6

Ws

0.5

Pv

1.5

Hc

0.762

Os

2.8

Ov

1.2

Lms

4.5

Wms

1.4

Gcpw

0.7

Lcpw1

27.55

Lcpw2

1.8

4. Fabrication and measurement The proposed antenna has been fabricated on Rogers Duroid 5880 substrate with a relative permittivity of 2.2, a loss tangent of 0.001 and a thickness of 0.762mm as shown in Fig. 8 with its detailed dimensions listed in Table 1. Simulated and measured results of S11 and gain at boresight direction of the proposed SIW cavity-backed slot antenna are shown in Fig. 9. It can be seen that the measured results are in good agreement with the simulated results within operation bandwidth. Its measured bandwidth of

7

170MHz is higher than the predicted bandwidth of 140MHz. This discrepancy is attributed to some errors such as roughness of metal surface, fabrication tolerance and SMA transistion loss, which lead to degradation of quality value and broaden bandwidth. Measured results in Fig. 9 shows that the proposed antenna has a high gain which is more than 9dBi within impedance bandwidth, which is only slightly smaller compared to the simulated value. Furthermore, the simulated radiation and total antenna efficiency are plotted in Fig. 10, which are greater than 90 and 80% in the working bandwidth, respectively. 100

Efficiency (%)

80

60 Simulated total efficiency Simulated radiation efficiency

40

20 9.7

9.8

9.9

10.0

10.1

10.2

10.3

Frequency (GHz)

Fig. 10. Simulated radiation and total efficiency of the proposed SIW antenna.

0

0 330

330

30

300

-20

60

60

-40

270

90

Gain (dB)

Gain (dB)

300

-20

-40

270

90

-40

-40

-20

30

0

0

240

120

Co-E Co-H Cross-E Cross-H

0 210

-20

240

0 150

180

a Fig. 11. Radiation pattern of the proposed antenna. a Simulation b Measurement

120

Co-E Co-H Cross-E Cross-H

210

150 180

b

Measurement of radiation pattern was carried out in a microwave anechoic chamber without a large metal plate as the ground plane. Simulated and measured radiation patterns are plotted in Figs. 11(a) and (b) which show the measured pattern agrees well with the simulated pattern, except for some

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deteriorations in the back lobe and cross polarization components. The degeneration is caused by the test fixture including SMA connectors and the manufacturing tolerance of PCB process, such as conductor and dielectric loss, and wrinkles of conductor surface and edge, etc. The far-field co-polarized and crosspolarized radiation patterns of the proposed SIW cavity-backed slot antenna have been measured at 10GHz in E-plane and H-plane. The measured radiation patterns are shown in Fig. 10(b) which shows that the measured half power beamwidths (HPBWs) in the E- and H planes are about 100° and 75°, respectively. It can be observed that the three parallel radiating slots generate a narrower E-plane copolarized radiation pattern. In the E-plane, the measured cross polarized levels (CPLs) within HPBWs are less than -31dB and the measured front-to-back ratio (FTBR) is -17.0dB. In the H-plane, the measured CPLs within HPBWs are less than -19.7dB and the measured FTBR is -17.3dB. The performance comparison between the proposed work and some previously reported SIW based antennas is summarized in Table 2. As can been seen, the proposed antenna exhibits the feature of gain improvement while the overall performance is comparable. Table 2 Performance comparison between the proposed work and some previously reported work.

Properties

Center freq. (GHz)

-10dB, BW (%)

Peak gain (dBi)

Ref. [17]

10

1.7

5.5

Ref. [18]

10

6.3

6.0

Ref. [19]

5.2

1.34

6.1

Ref. [20]

10

1.5

7

This work

10

1.7

9.2

5. Conclusion A gain enhanced SIW cavity-backed slot antenna is presented in this paper. Gain enhancement is achieved by exciting higher mode resonance of TE 410 in the rectangular SIW cavity formed by three parallel transverse slots etched at the center and both edges of the rectangular SIW cavity. Radiating mechanism and parameter effect of the proposed antenna have been studied and analyzed. The fabricated antenna achieved a gain of 9.2 dBi, a front-to-back ratio of 17dB and a maximum cross polarized radiation level of -19.7dB at 10GHz. The proposed antenna constructed on a single layer PCB, still retains good radiation performance of conventional cavity-backed antenna and configuration advantages of conventional planar antenna.

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6. Acknowledgments This work was supported by the National Natural Science Foundation of China (61301052), the Sichuan Science and Technology Program (2017GZ0020, 2018GZ0010), and Chengdu Electric Vehicle Industry Cluster Collaborative Innovation Project (2017-XT00-00002-GX). 7. References [1] Wu K, Cheng Y J, Djerafi T, et al. Substrate-integrated millimeter-wave and terahertz antenna technology. Proc IEEE, 2012; 100(7): 2219-2232. [2] Xu Z, Zhou Q, Ban Y, Ang S. Hepta-band coupled-fed loop antenna for LTE/WWAN unbroken metal-rimmed smartphone applications. IEEE Antennas Wireless Propag Lett 2018; 17(2): 311-314. [3] Li Y S, Mittra R. A three-dimensional circularly polarized antenna with a low profile and a wide 3-dB beamwidth. J Electrom Waves Appl 2016; 30(1):89-97. [4] Li MY, Xu ZQ, Ban YL, et al. Eight-port dual-polarized MIMO antenna for 5G smartphone applications. IET Microw Antennas Propag 2017; 11(12): 1810-1816. [5] Nakano H, Iwatsuki M, Sakurai M, et al. A cavity-backed rectangular aperture antenna with application to a tilted fan beam array antenna. IEEE Trans Antennas Propag 2003; 51(4): 712-718. [6] Hong W, Behdad N, Sarabandi K. Size reduction of cavity-backed slot antennas. IEEE Trans Antennas Propag 2006; 54(5):1461-1466. [7] Kumar A, Raghavan S. Broadband SIW cavity-backed triangular-ring-slotted antenna for Ku-band applications. AEU-Int J Electron Commun 2018; 87: 60-64. [8] Bozzi M, Georgiadis A, Wu K. Review of substrate-integrated waveguide circuits and antennas. IET Microw Antennas Propag 2011; 5(8):909-920. [9] Mukherjee S, Biswas A, Srivastava K V. Broadband substrate integrated waveguide cavity-backed bow-tie slot antenna. IEEE Antennas Wireless Propag Lett 2014; 13(6):1152-1155. [10] Moscato S, Moro R, Pasian M, Bozzi M, Perregrini L. Innovative manufacturing approach for paper-based substrate integrated waveguide components and antennas. IET Microw Antennas Propag 2016, 10(3):256-263. [11] Massoni E, Silvestri L, Alaimo G, Marconi S, Bozzi M, Perregrini L, Auricchio F. 3-D printed substrate integrated slab waveguide for single-mode bandwidth enhancement. IEEE Microw Wireless Comp Lett 2017; 27: 536-538. [12] Xu J, Chen ZN, Qing X, et al. 140-GHz TE20-mode dielectric-loaded SIW slot antenna array in LTCC. IEEE Trans Antennas Propag 2013; 61(4):1784-1793. [13] Li R, Tang X, Xiao F. Design of substrate integrated waveguide transversal filter with high selectivity. IEEE Microw Wireless Comp Lett 2010; 20(6): 328-330. [14] Hu J, Hao ZC, Hong W. Design of a wideband quad-polarization reconfigurable patch antenna array using a stacked structure. IEEE Trans Antennas Propag 2017; 65(6):3014-3023. [15] Tan L, Xu Z Q, Chen Z, et al. A multilayer t-septum substrate integrated waveguide filter. Electromagnetics 2017; 37(4): 203-211. [16] Kang H, Park SO. Mushroom meta-material based substrate integrated waveguide cavity backed slot antenna with broadband and reduced back radiation. IET Microw Antennas Propag 2016; 10(14):1598-1603. [17] Luo G Q, Hu Z F, Dong L X, et al. Planar slot antenna backed by substrate integrated waveguide cavity. IEEE Antennas Wireless Propag Lett 2008; 7:236-239. [18] Luo G Q, Hu Z F, Li W J, et al. Bandwidth-enhanced low-profile cavity-backed slot antenna by using hybrid SIW cavity modes. IEEE Trans Antennas Propag 2012; 60(4):1698-1704.

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