Millimeter-Wave Compact Wideband High-Gain 8 × 8 CP Filtenna Array With Densified 16-Way SIW Feeding Network

This paper presents a millimeter-wave compact wideband high-gain 8 × 8 circularly polarized (CP) filtenna array with densified 16-way substrate integrated waveguide (SIW) feeding network. First, a parallel-series 2 × 2 CP patch subarray without power distribution network is designed by exciting four TE^S₂₁₀ and two quasi-TE^R₂₁₀ modes, simultaneously, in a single SIW cavity. By properly setting perturbed via-slot groups, hexagonal radiating apertures, and square patches etched with a 45°-inclined center slot, three axial ratio (AR) minima are created to realize wide AR bandwidth. Additional bandpass filtering response can also be observed, which helps to realize high-selectivity CP filtenna array design. The densified 16-way feeding network mainly consists of four sequentially rotated SIW 4-way power dividers, and two filtering SIW TE₁₀-to-TE₂₀ mode 2-way power dividers. The former is constructed based on the anti-phase field distribution of TE₂₀ SIW mode, and the latter features additional filtering response and simple structure. An 8 × 8 CP filtenna array centered at 28 GHz was fabricated and tested. The measured results show a -10-dB impedance bandwidth of 14.4%, a 3 dB AR bandwidth of 15.3%, a peak gain up to 23.9 dBic, and high out-of-band rejection levels better than 39 dB.