A novel compact diplexer based on folding microstrip lines

In this paper, we proposed a compact diplexer based on folding microstrip lines. The folding microstrip lines have the characteristics of inductance and capacitance. They have filter function and compact size. The proposed diplexer employs filters with folding microstrip lines for band selection and separation. A prototype diplexer is designed at 900MHz and 1800MHz, which is proposed for GSM/DCS dual band cellular system applications. The measured insertion losses are better than 2dB for the two channels with better 30dB isolation. The diplexer collectively has the advantages of low insertion loss, high isolation, compact size and easy fabrication. The design methodology, simulated and experimental results are discussed throughout the paper.