An On‐Board Ultra‐Small Wide‐Beam Circularly Polarized Microstrip Antenna

This paper presents the design of an ultra‐compact circularly polarized (CP) satellite antenna integrated with gradient shorting strips. By etching gradient rectangular slots on the diagonal and opposite sides of a square radiating patch, and arranging gradient shorting strips around these slots, the antenna achieves an 84.8% size reduction compared to a traditional half‐wavelength air microstrip antenna, with minimized electrical dimensions of 0.195 λ ₀ × 0.195 λ ₀ × 0.027 λ ₀. Notably, the gradient shorting strips act as parasitic elements to effectively broaden the antenna beam. Measurement results show a 4 dB gain improvement at ±70° elevation angles relative to the conventional air microstrip antenna. The antenna exhibits a port return loss (RL) better than −10 dB over a 27.8% bandwidth (340–450 MHz) and maintains an axial ratio (AR) < 3 dB across a 25.3% bandwidth (345–445 MHz). At the center frequency (400 MHz), the main radiation gain is ~6.0 dB with a −3 dB gain bandwidth of ~4.6%.