A low–loss 6–pole canonical dual–mode filter for the output multiplexer of broadcasting satellite transponders in the 12–GHz band

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Abstract
This paper describes the development of a filter for the channel multiplexer in the 12‐GHz band broadcasting satellite transponder with a high transmitting power (above 200 W). The filter for high‐power multiplexer must have a very low loss, to maintain the satellite transmitting power and to secure thermal stability. It was found that the use of a 6‐pole elliptic filter is better than that of a 4‐pole elliptic filter from the viewpoint of the insertion loss and the heat dissipation. The 6‐pole canonical filter is designed using TE113 dual‐mode. In the thermal design, super‐invar with small thermal expansion coefficient is used for the cylindrical waveguides of the filter, and copper with high thermal conductivity is used for the iris plate. Improving the heat dissipation and suppressing the temperature‐rise, the deterioration of the filter characteristics caused by the temperature variation is prevented. The experimental filter realized the insertion loss of less than 0.3 dB, the loss variation of 0.1 dBp‐p and group‐delay variation of 5 nsp‐p within the channel. No significant deterioration of the filter performance was observed through the thermal test of 0°C to 90°C and the high‐power test of 200 W. As a result, it was demonstrated that the proposed filter has better electrical and thermal performance than the previous 4‐pole elliptic filter, being suited as the filter for the multiplexers in high‐power broadcasting satellite transponders.

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