Compact Millimeter-Wave 3D Printing Balun-Fed Filtering Antenna with Flexible Responses Based on Half-Mode Groove Gap Waveguide

A design method of millimeter-wave (mm-wave) 3D printing balun-fed filtering antenna with flexible working responses based on half-mode groove gap waveguide (HM-GGW) is proposed in this communication. Initially, a fourth-order wideband filtering balun is developed using two HM-GGW resonators with mode TM₀₁₁, mode TM₂₁₀, and two resonant irises (RIs). Owing to the odd symmetry of the electric-field of the half-TM₂₁₀-mode, the required 180° phase reversal is attained at the output ports of the balun. Besides, based on the change of the topology, the coupling coefficients can be adjusted by changing the parameters of the cavities and the irises, resulting in that the wideband filtering balun is converted into a dual-band filtering balun. Then, owing to the connection of the open-ended waveguides, the filtering antennas are realized. For verification, wideband and dual-band filtering antennas working in the Ka band were made using 3D printing technology. As expected, the final wideband filtering antenna achieves a broad impedance bandwidth (IBW) of 11.5 %, and exhibited a peak gain of 9.7 dBi. While the dual-band one achieves -10-dB IBWs of 1.7 % and 2.5 %, and exhibited a peak gain of 8.2/8.7 dBi. Both of the filtering antennas achieve three adjustable radiation nulls, having satisfactory filtering performance.