Planar rat-race couplers and Wilkinson power dividers for quad-band applications using extended Pi-shaped impedance transformers

This paper presents a novel design for planar quad-band rat-race couplers (RRCs) and Wilkinson power dividers (WPDs). To achieve quad-band operation, a quad-band impedance transformer circuit is proposed in the form of an extended Pi-shaped structure. For demonstration purposes, prototypes of an RRC operating at 0.8/1.6/2.484/3.284 GHz and a WPD operating at 0.7/1.21/1.792/2.303 GHz were designed, fabricated, and measured. Good agreement between simulations and measurements was achieved. The measured results indicate that the RRC exhibits an insertion loss of less than 1.48 dB, isolation better than 23 dB, and input return loss exceeding 19.87 dB at four operating frequencies. Meanwhile, the quad-band WPD achieves an insertion loss of less than 0.69 dB and isolation better than 21.25 dB.