Bandwidth and Gain Enhancement of a Single-Layer Filtering Patch Antenna Using Reshaped TM₁₂ Mode

A single-layer filtering microstrip patch antenna with gain enhancement in the boresight direction is proposed. The antenna mainly consists of an outer ring patch and an inner rectangular patch with six shorting vias. Operating at the higher order TM 12 mode, the rectangular ring patch is used for the first time to simultaneously provide an enhanced gain in the passband and a radiation null at the lower band edge. On the other hand, the rectangular patch placed inside the ring patch introduces another radiation null at the upper band edge due to the embedded structure (topology). In addition, the fundamental TM 10 mode of the rectangular patch is excited, desirably increasing the bandwidth of the passband. Consequently, both good radiation and filtering performance is achieved, without using any filtering circuits. For demonstration, an antenna prototype is designed, fabricated, and measured, which operates at the 5.2 GHz WiFi band and suppresses the interference of 5.9 GHz Internet of Vehicles band. The prototype features an impedance bandwidth of 6.9%, a peak gain of 9.0 dBi, and an out-of-band radiation suppression level of over 16 dB.