A Study on 8-Pole Waveguide Filters with Triple-Passbands

Abstract

This paper presents a study on two 8-pole waveguide filters with triple passbands for Ka band satellite applications. The performances of the triple-passband filter designed newly to improve the electrical performances was compared with those of the former filter. The transfer function and coupling matrix of the filters are obtained from the transmission and reflection zeros optimized to the optimum electrical performances. Dual-mode circular waveguide cavities were adopted for realization of two triple-passband filters. Very good agreement between the measured and simulated results of them was obtained. The new design result has better performance than the former one in return loss (over 18dB) and insertion loss (under 0.9dB) in each band. The new design has been successfully demonstrated and should be useful in recent complex communications systems. This paper presents an 8-pole triple-passband waveguide filter with high electrical performances for Ka band satellite applications. The characteristic function of the proposed filter is composed of four transmission zeros and eight reflection zeros due to 8-pole in-line dual-mode configuration. The transmission zeros and the reflection zeros of the triple passbands filter are appropriately placed to enhance the performance of insertion loss. In this paper, two, four, and two reflection zeros are assigned to the first passband, the second passband and the last passband, respectively. To confirm the enhancement of electrical performance, the filter proposed in this paper is realized and compared with the triple-passband filter described in Ref. 4. Very good agreement between measured and simulated response is shown. It is also shown that the proposed filter has better performance than the former filter in return loss and insertion loss. II. Design An 8-pole filter with in-line dual-mode configuration as shown in Fig.1 can have eight reflection zeros and four transmission zeros. A filter with triple passbands in a single structure can be realized by properly adjusting the positions of the reflection zeros and the transmission zeros. Therefore, the positions of the transmission zeros and reflection zeros should be carefully optimized for better filter performances. In this paper, we decided to place two transmission zeros in the stopband to get better isolation characteristics between two adjacent passbands. Each passband is designed to have at least two reflection zeros. There can be two kinds of filters that satisfy above conditions and have triple passbands with 8-pole in-line structure, according to the number of reflection zeros in each passband. One has three, two, and three reflection zeros in the first, second, and last passband, respectively. The other has two, four, and two reflection zeros in the