Research Of Waveguide Duplexer

The satellite communication systems have been widely used due to the rapid development of the technology, and more demands are required, such as multiple-band, multiple-polarized and broaden band. By using the reflector antenna systems, the satellite communication can realize the goal that one antenna working in multiple frequency bands simultaneously. The duplexer placed in the front of the feed plays an important role. It can not only achieve the frequency divided, polarization changed and polarization divided of the signal, but also have a direct effect on the radiation performance of the feed system. The overall structure of the diplexer consists of the following three parts: the ortho-mode transducer, the band pass filter and the circular polarizer. their detailed introduction and research have been proposed in this paper, the specific research results are as follows:1.The main function of the ortho-mode transducer(OMT) is separating the polarization signals. By replacing septum in traditional OMT with post, the OMT can avoid the disadvantage that the septum is easily distorted in the actual processing. Based on the theory-the multiple resonance can broaden the operating bandwidth, through the coupling slot a shorted piston is added to achieve the wide band. In the rectangular waveguide, another post is added near the shorted piston to compensate the impedance mismatch caused by the resonant window. For the matching design of emission band, it mainly uses the three order Chebyshev ladder converter.2. In the coupled port of OMT, a band pass filter is loaded. It can achieve high isolation by preventing the signal transfer between transmitting and receiving bands. Due to the advantages, such as good matching performance and simple processing, the inductance diaphragm filter has been favored by researchers. However, because of the produced spurious pass-band, this filter cannot achieve the suppression of emission band signal. To obtain good performance of the band suppression results, we combine the ridge theory to design the filter. The existence of ridge waveguide makes the 10 TE mode’s cutoff wavelength become longer, and the higher harmonics appear in the farther frequency. The simulation results show that, compared with the inductance diaphragm filter, the band rejection performance of the single ridge waveguide band pass filter has been greatly improved, and the size is reduced, realizing the miniaturization design.3.The circular polarizer refers to a device that can converse the linearly polarized signal to circular polarized. Bases on the rectangular waveguide, a circular polarizer is designed in this paper. The main parameters are the length of square waveguide, the number of iris diaphragm and the distribution forms. Considering the compact design, the structure of the band pass filter is made. Finally, the overall structure of the duplexer is proposed.