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Based on the aforementioned parameter values, the 10 x 10 TCA shown in Fig. 6 was modeled using commercial CAE simulation software. Figures 7(a) and (b) depict the VSWR and gain of the TCA with and without the RFSS. As can be seen, the impedance bandwidth with the RFSS can achieve a bandwidth of 12.8:1 (1.5 to 19.2 GHz), while without the RFSS, the performance is sectioned into two bandwidths. Figure 7(b) shows that the gain decreases drastically at 10.7 GHz without the RFSS, corresponding to the short-circuited frequency point, while a wide bandwidth is maintained with the RFSS. Without the RFSS, the gain of the antenna array is reduced by 0.5 to 2.8 dB.

UWB Arrays Employ TCAs, Fig. 6

UWB Arrays Employ TCAs, Fig. 7

Figures 8 and 9 show the normalized E- and H-plane radiation patterns at 1.5, 10.7, and 19.2 GHz. In the mainlobe direction, the pattern exhibits a null at 10.7 GHz without the RFSS. With the RFSS, the null is suppressed, indicating the suppression of ground-plane shorting. Figures 10(a) and (b) show the TCA VSWR and gain with scan angle. The impedance bandwidth is 1.5 to 19.2 GHz for a scan angle of 0 deg. As the scan angle increase, the VSWR also increases and the impedance bandwidth decreases. The TCA can be used to realize an impedance bandwidth of 8.9:1 within a ±30-deg. scan angle.         

UWB Arrays Employ TCAs, Fig. 8

UWB Arrays Employ TCAs, Fig. 9

UWB Arrays Employ TCAs, Fig. 10

The copolarized and cross-polarization patterns with scan angles of 0, ±10, ±20, and ±30 deg. at 10.7 and 19.2 GHz indicate stable performance at those frequencies (Figs. 11 and 12). It is reasonable to conclude that the radiation of TCA with RFSS is stable over whole bandwidth within the ±30 deg. scan angle, the sidelobe level is below -10 dB, and the cross-polarization level is below -40 dB.

UWB Arrays Employ TCAs, Fig. 11

UWB Arrays Employ TCAs, Fig. 12

Because of the metal ground planes in many antenna arrays, a TCA can be short circuited at a particular frequency, limiting its impedance bandwidth. To solve this problem, a TCA was designed with an RFSS. Using a TCA with a tightly coupled bowtie antenna as its radiation element, the impedance bandwidth was greatly improved by inserting an RFSS between the array and ground plane, which suppressed ground-plane reflections and avoided the short-circuited frequency.

Simulated results show that the impedance bandwidth of the TCA with RFSS was 12.8:1 (1.5 to 19.2 GHz), while without the RFSS, the impedance bandwidth was split into two bands. In these bands, the scan impedance bandwidth was 8.9:1 (1.8 ~ 16 GHz) with a scan angle of ±30 deg. The sidelobe levels were below -10 dB, the cross-polarized levels were below -40 dB, and the gain of antenna array was reduced by 0.5 to 2.8 dB without the RFSS. The TCA with the RFSS offers broad bandwidth, low profile, and easily conformal installation, and is well suited for UWB phased-array antenna systems.

Zhihui Hu, Engineer

Yonghua Jiang, Professor

Xiang Ling, Engineer

Naval Aeronautical and Astronautical University, Yantai, People’s Republic of China.

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