Direct Synthesis Technique for Dual-Passband Filters: Superposition Approach

In this brief, a technique is proposed for the synthesis of dual-passband filters. Different from conventional techniques based on low-pass prototype, the technique in this brief can directly synthesize filters in bandpass form. Each passband of the filters can be accurately and separately designed, and then, their characteristic functions are superposed to obtain the final characteristic function for the dual-passband filters to be synthesized. Network matrix derived from this technique is physically meaningful, while coupling matrices derived by conventional techniques can be considered as its low-pass approximation. The proposed technique is simple and fast.