Single-layer symmetrical full-port quasi-absorptive filtering phase shifter

In this article, a single-layer symmetrical full-port quasi-absorptive filtering phase shifter is presented. The proposed phase shifter is composed of a main quasi-absorptive filtering branch, a reference quasi-absorptive filtering branch, and two delay lines. The proposed phase shifter achieves both phase controlling function and quasi-absorptive filtering function for the first time. Each quasi-absorptive filtering branch can realize the quasi-absorptive filtering function. Meanwhile, the constant phase shift can be obtained by combining the two quasi-absorptive filtering branches and the two delay lines. The design formulas can be derived from the even- and odd-mode network analysis, and then two quasi-absorptive filtering phase shifters can be devised easily and quickly. For verification, a 90° quasi-absorptive filtering phase shifter, which is critical for circularly polarized antenna systems, is simulated, manufactured, and measured.