Synthesis and design of suspended substrate stripline filters for digital microwave power amplifiers

In this paper, a synthesis method for suspended substrate stripline filters for digital microwave power amplifier applications is presented. The synthesis method combines a lumped element and full-wave mixed approach in a very efficient way. In order to achieve high amplifier efficiency the filter must exhibit a high input impedance in the stopband. This has been implemented for the first time by using a capacitively end coupled filter combined with stepped impedance resonators. A third order filter was designed. Simulations show that the final stage drain efficiency of the power amplifier and suppression of out-of-band frequency components can be significantly improved when the new structure is used.