High-Frequency Balun With Compact Size and Low Loss on Self-Packaged Air-Filled Suspended Line

In this article, a kind of miniaturized broadband balun is proposed and designed with high operating frequency and low insertion loss based on the low-cost self-packaged air-filled suspended line and its specialized extended filter theory. The filter theory is extended as follows. First, through making clear the out-of-phase outputs, impedance property of half-wavelength resonator, and miniaturized resonator topology, the three-port balun circuit could be synthesized with exact element values, according to the required in-band ripple and bandwidth. Second, the quantitative design of quasi-lumped component based on self-packaged air-filled suspended line is executed to obtain low-loss balun at high frequency within the compact size. Third, taking full advantage of features of circuit topology and physical structure, the direct feeding method and the strong coupling strength provided by these double-layer quasi-lumped components guarantee a wide operating band. For validation, one fourth-order balun operating at 10 GHz and one sixth-order balun operating at 6 GHz are fabricated and measured. The good performance validates the proposed design approach and low-loss compact self-packaged structure.