Open-Boundary Quad-Ridged Horn Antenna Loaded with Absorbing Materials

This paper proposes an open-boundary quad-ridged horn (OQRH) antenna loaded with absorbing materials. The inner ridge profile features a smooth transition from an exponential curve to an arc to optimize impedance matching. By loading absorbing materials on the outer edges of the ridges, the diffracted fields can be effectively suppressed, the performance of the main-lobe radiation pattern of the OQRH can be improved, the cracking of the radiation pattern can be effectively avoided, and the phase center can be stabilized. After optimization, within a ±30° conical angle, the fluctuation of the phase center is kept within ±0.08λ in the 0.3-0.8 GHz frequency band. The antenna exhibits symmetric radiation characteristics, with a half-power beamwidth (HPBW) exceeding 60°. The gain is stable, ranging from 4.5 dBi to 6.5 dBi, and the cross-polarization level is below -30 dB.