Differential RF Phase Shifter With Harmonic Suppression

For the first time, a differential phase shifter with harmonic suppression is proposed. Not only does the proposed structure provide a constant differential phase shift over a wide bandwidth, but it also has good harmonic rejection. Compared to the existing coupled-line phase shifters, the proposed stub-loaded transmission line configurations show good performance, with simplicity in both design and fabrication. Design formulas for the structure are derived using an analytical technique. Optimal design parameters for typical differential phase shifts which are independent of substrate used and operating frequency are provided to allow for a quick design procedure. To illustrate the principles, a broadband 45 ° phase shifter with harmonic suppression is designed, fabricated, and measured. It achieved excellent performance with small insertion loss, small phase deviation within the desired bandwidth, and good out-of-band rejection.