A design method of matching circuits for a compact diplexer using SAW filters

Recently, multiband wireless communication systems are widely used worldwide. The diplexers which can separate two frequency bands are very important circuits for these systems. In this paper, we describe a design method of matching circuits which are comprised of four lumped elements for a compact diplexer. It is suitable for the diplexers which are fabricated on a printed circuit board (PCB). The designed diplexer can consist of chip capacitors, chip inductors and SAW filters on the PCB. A prototype diplexer for W-CDMA Band V Rx and GPS is fabricated using this method. Insertion losses are less than 2.2 dB and isolation is higher than 48 dB. It also achieves a compact size (8 × 8 mm).