A Broadband Millimeter-Wave Filtering Antenna with Multiple Nulls and Flat Gain Based on ISGW

This paper designs a filtering antenna with four radiation nulls, utilizing an integrated substrate gap waveguide (ISGW) for feeding. The main body of the filtering antenna is composed of three rectangular patches. These multiple patches not only extend the bandwidth of the antenna but also generate a radiation null at high frequencies based on the cross-coupling theory. To enhance the stopband suppression at low frequencies, a innovative defected ground structure is employed, creating a radiation null at the low-frequency. Additionally, to further improve the antenna’s roll-off rate, two pairs of rectangular slots are etched on the patches, generating two radiation nulls at low and high frequencies, respectively. The use of the ISGW waveguide suppresses spurious components, ensuring that only quasi-TEM mode can propagate within the antenna’s operating range and improving the front-to-back ratio. Simulation results demonstrate that the proposed filtering antenna achieves a 14.6% impedance bandwidth from 24.1 GHz to 27.9 GHz, with smooth gain across the passband and an average realized gain of 7.6 dBi. The proposed antenna generates four radiation nulls at 22.7 GHz, 23 GHz, 28.1 GHz, and 29.6 GHz.