Highly selective phase shifter using stub-loaded coupled-line resonators

In this letter, a novel phase shifter with high selectivity is proposed and developed. It is divided into the main line together with the reference line. Firstly, the main line is a bandpass filter implemented by using the new coupled feed lines loading stub-loaded coupled-line resonators. Varying the coupling coefficient and the electrical length of the loaded branch can reasonably allocate the passband and transmission zeros/poles. Then, the reference line is a uniform microstrip line with an electrical length related to the phase shift degrees. Compared with conventional phase shifters, this phase shifter has the advantages of good frequency selectivity, as well as easy adjustment of the phase shift value. Finally, the phase shifter of 45 degrees similar to 180 degrees are designed, simulated, and the value of 180 degrees is fabricated and measured. The simulations are in good agreement with the actual measurements.