Compact Isolation-Enhanced Dual-Band ±45° Polarization Beam-Scanning Millimeter-Wave Antennas With Dual-Band Bandstop Structures

A compact dual-band ±45° polarization beam-scanning antenna with enhanced isolation has been designed for millimeter-wave (mm-wave) communications. Compared to the conventional planar bandstop structure, the proposed simple 3-D bandstop structure offers greater design freedom in achieving dual-band bandstop characteristics. On the one hand, a 3-D bandstop structure is placed under each antenna element to improve the element port isolation by more than 20 dB in the low- and high-frequency bands. On the other hand, a different 3-D bandstop structure is inserted between the two elements in the center of the array. Both improve the isolation of all ports of the array by more than 15 dB in both passbands. The introduction of them does not take up any additional space, thus maintaining the compact size of the array and having little effect on its performance. For both orthogonal polarizations, the −10-dB return loss bandwidth of the array covers 23.9–29.3 GHz and 36.4–43.5 GHz, with a maximum scanning angle up to ±66° and ±33° in the low- and high-frequency bands, respectively. This proposed array covers dual band, offers wide beam-scanning performance, and supports dual-polarization, making it suitable for applications in 5G mm-wave mobile terminals with limited space.