Abstract: In ordinary quad-ridged flared horn (QRFH) feed, the illuminating efficiency will drop sharply as the operating frequency increases, which leads to a limited operation bandwidth. A dielectrical loading technology is proposed to solve this problem in this paper. The investigations show that the dielectric rod at the center of the QRFH could stabilize the phase center and widen the beam width, and thus expand the radiation bandwidth of the QRFH feed from 5:1 to 10:1. Simulated results show that the reflection coefficient is lower than -10 dB. When the feed is used to illuminate a 10 m diameter reflector (f / d = 0. 36), the aperture efficiency is higher than 50% across the whole bandwidth.