An SIW-Based Wideband Endfire Filtering Magneto-Electric Dipole Antenna for Millimeter-Wave Applications

A wideband endfire substrate-integrated waveguide (SIW) magneto-electric (ME) dipole antenna with a filtering function is investigated for millimeter-wave (mm-wave) applications. The antenna mainly consists of an open-ended SIW that works as a magnetic dipole, two pairs of electric dipoles, and two reflecting walls. Fed by a coaxial probe, the equivalent magnetic dipole and the electric dipoles can be excited simultaneously to provide a wide impedance passband; moreover, a radiation null can be naturally generated by the probe-fed SIW at the upper band edge, and the filtering effect is realized in the upper stopband. In order to suppress the lower-band radiation, a complementary split-ring resonator (CSRR) is further etched around the feed probe. Consequently, a wideband endfire ME-dipole antenna with a quasi-elliptical bandpass filtering response is obtained. For validation, a prototype is fabricated and measured, and it shows a -10-dB impedance bandwidth of 46.3%, an in-band peak gain of 6 dBi, and a good out-of-band suppression level of about 25 dB; furthermore, due to the reflecting walls, the average front-to-back ratio (FTBR) can reach as high as 18 dB.