A low-profile high-gain filtering patch antenna with harmonic suppression

A compact high-gain filtering patch antenna with harmonic suppression characteristic is proposed. The antenna mainly contains a coupled transmission line and a central rectangular patch. The capacitive coupling between the coupled transmission line and the rectangular patch generates a radiating null at high frequencies. Then, acrossing the hybrid coupling principle, the structure of the microstrip-to-slotline transition builds two coupling paths, which generate a radiating null at low frequencies. In addition, two vertical slots are carved into the rectangular center patch to truncate the lateral current. That removes the higher order resonant modes and suppresses the parasitic passbands at high frequencies outside the passband. A fabricated 2 x 2 filtering antenna array is measured, showing a bandwidth up to 3.9% (8.68-9.03 GHz), a peak gain of 14.43 dBi, and two near-band radiation nulls located at 8 and 9.55 GHz, demonstrating good radiation performances and an isolation of 25 dB.