Broadband, high gain 2 x 2 subarray and 2 x 8 cavity-backed antenna arrays for 5G mmWave applications

In this study, linearly polarized 2 x 2 subarray and 2 x 8 element cavity-backed antennas are proposed for 5G millimeter-wave (mmWave) applications. Initially, the 2 x 2 subarray is designed, manufactured, and tested. According to the measured results, the 2 x 2 subarray has a wide fractional bandwidth (FBW) of 24.7% (|S-11| < -10 dB, 22.3-28.6 GHz) which covers the main spectrum allocations for the 5G cellular network. A broadband 1 x 4 corporate feed network is designed, which is challenging and crucial, to form 2 x 8 antenna array. The experimental results show that the final 2 x 8 antenna array has a wide FBW of 23% (|S-11| < -10 dB, 22.3-28 GHz), with a boresight gain of 20.5 dBi. Throughout the operating band, a stable gain of 19.5 +/- 1 dBi is achieved. The 2 x 8 antenna array has good and stable radiation characteristics; SLLs are less than -13 dB and XPol is better than -20 dB for both E- and H-planes across the entire operating frequency. Stubs are added between adjacent subarrays in the E-plane to suppress mutual coupling and to improve gain of 2 x 8 antenna, which results in broadband impedance characteristics. The size of the 2 x 8 antenna array is 6.3 lambda(omicron) x 8.1 lambda(omicron) x 1.3 lambda(omicron), where lambda(omicron) is the free space wavelength at 25 GHz. These results show that the proposed antenna has potential for 5G millimeter-wave applications requiring broadband and high gain.