A Compact Microstrip Antenna With Extended Half-Power Beamwidth and Harmonic Suppression

A half-power beamwidth (HPBW) extended patch antenna with harmonic suppression is proposed in this article. The antenna consists of one driven patch and two parasitic patches. The parasitic patches are placed parallel to the two adjacent edges of a driven patch. By introducing four sets of shorting pins near the outer edges of the patches, surface currents on the patches flow through the pins to the edges of the ground plane periodically, making those edges radiate as electrical dipole elements. Huygens'-like radiation with extended HPBW and low back-lobe level is formed by the interaction of dipole and patch-like radiation sources. On the other hand, the resonance at the second harmonic frequency is suppressed, and resonances at higher order modes are shifted away from the third harmonic frequency because of the joint effect of introducing shorting pins and coupling between patches. The mechanism of the antenna is analyzed. A verifying prototype is implemented. In the measurement, the antenna operates at 5.23 GHz. HPBWs of 135°/132° are found, while front-to-back ratios of 13.5/13.3 dB are achieved in the XoZ/YoZ-plane. Resonances at the second and third harmonic frequencies are successfully suppressed.