A Compact Wideband Microstrip Filter Using Folded Multiple-Mode Resonator

A compact wideband microstrip filter using a folded multiple-mode resonator is proposed. The filter contains only one resonator, which operates as not only a resonant element but also an open stub. The filter simultaneously realizes a broad passband, a compact size, and two transmission zeros at both the lower and upper stopbands. The transmission zero mechanism is investigated in detail through the simple transmission line equation. A lucid equivalent circuit is given both for analysis and initial design of the proposed filter. The fabricated filter shows the merits which are listed as follows: compact size and sharp skirts.