Compact diplexer based on double-sided parallel-strip line

A novel compact diplexer based on a double-sided parallel-strip line with an inserted conductor plane is proposed. The novelty of the proposed structure is to utilise the isolation feature of the inserted conductor plane to provide two separated transmission paths for the RF signals. Based on this new technique, no extra combination circuits with impedance transformers at the input port are required, which greatly simplifies design procedures and reduces circuit size. A demonstration diplexer was designed and fabricated, and simulated and measured results with good agreement are presented.