technology is to solve the limitation of the band of the data transmission.one effective solution is introducing the dual-circularly polarized antenna[2].

The essential purpose of the reflectors is to transform the medium gain radiated by the feeders to a high gain with pencil beams to improve the resolution. Consequently, the dual-circular polarized reflector antennas are more promising in the satellite radars.

In this paper, we present an X-band dual circularly polarized offset reflector antenna with a more compact structure. The offset reflector antenna consists of a single metallic reflector and a circularly polarized horn feed. The design of the horn feed is a key factor which can influence the performance of the reflector antennas. And the design is based on the septum polarizer[3]-[7] that can achieve the dual-circularly polarization.

2 Geometry description and Design

2.1 Feeder Design

Feeders of the reflector antenna are essential components. The commonly type of the feeder is the horn antenna. We here present a novel circularly polarized horn feed with the septum polarizer for its smaller size and excellent dual circularly polarization performance. The main feature of the septum polarizer is can achieve the right-handed or left-handed circularly polarization waves by two ports respectively. As shown in Figure 1, the schematic drawings of the horn feed with the septum polarizer are provided. The critical specifications for the septum polarizer is to obtain simultaneously, a quadrature phase shift between the two orthogonal signal components, excessively low insertion loss

as well as a good return loss and isolation at the input ports.

Figure1. The schematic drawing of the horn feed

2.2 Reflector design

In the circularly polarized single offset reflector antenna [8]-[9], Figure 3 shows that an offset parabolic reflector is used. The focus of the reflector is located at the phase center