Monopulse Multiband Offset-Parabolic Reflector Antenna And It’s Feed

In the field of radar application,array and reflector antenna are two main kinds of antennas. Array antennas especially the phased array antennas are wildly used for its highly directive patterns and the electronic scanning capability, however it is hard to design and it costs a lot to achieve these goals. Reflector antennas can also achieve highly directive patterns and high gains. What’s more, the reflector antenna is often easier and more economic to design compared with the array antenna. For example, it’s very perfect for the long-range radar. As is known to all, aperture blockage is the problem often confront when designing the prime focus antenna, while offset reflector antenna has lower aperture blockage. The offset reflector antenna designed here is cut from a rotating parabolic antenna. The antenna in this article is used for receiving signals and finding the direction of the target. The operating frequency band of the reflector antenna is 1~12GHz. For its wide bandwidth, four sets of feed are designed. They work in the frequency range of 1~2GHz, 2~4GHz, 4~8GHz and 8~12GHz separately. As more than one set of feeds exist,determining the position of every set of feeds is important. The main contents of this article are as follows:Firstly,determining the focal length-to-diameter ratio of the parent paraboloid, the aperture size and offset distance of the offset paraboloid. In addition, try to compute the far radiation field of the reflector antenna with the surface current method. As is shown at the end of the article the second radiation patterns computed by MATLAB have good agreement with the results simulated by the HFSS software.Secondly, the design of feeds. Once the size of the reflector is determined, the properties of the reflector antenna totally depends on feeds. The antenna chosen for feed here is the double ridged horn. Various methods are used to improve the impendence matching properties of the feeding point. As a result, the VSWR of all the feeds are all below 2, the feed of the X band and the S band are all below 1.8.At last, studying the effect on the second far radiation field of moving the feed off axis laterally. In amplitude-comprised direction-finding system, two identical antennas are normally symmetrically placed in either side of the reflector. As is mentioned before, there are more than one set of antennas exist, so feeds are placed asymmetrically in order to solve the problem that the cross beams overlap too much when one pair of feeds are placed symmetrically. The goal is achieved successfully.