Self-Packaged Wideband Filtering Baluns Based on Suspended Coplanar Waveguide-Microstrip Hybrid

In this article, wideband filtering baluns based on self-packaged suspended coplanar waveguide-microstrip (SCPW-MS) hybrid technique have been proposed. First, a new wideband filtering balun with high selectivity and low loss is presented, and the broadband performance is achieved by the double-sided structure of coplanar waveguide (CPW)-microstrip hybrid with three-line coupling. The circuit is modeled, analyzed, and implemented by multilayer PCB technique, and the design has been demonstrated by experimental results with a fractional bandwidth (FBW) of 42%, a magnitude imbalance of no more than 0.67 dB, a phase imbalance of no more than 3.9°, and an insertion loss of about 0.47 dB. Then, a wideband filtering balun by using balanced network and dual-layer multiresonator-coupled topology is also developed, which has a measured FBW of 50.4%, an insertion loss of 0.68 dB, an in-band amplitude imbalance of no more than 0.46 dB, and an in-band phase imbalance of no more than 3.2°. The measurements of the new designs agree with predictions. An isolation improvement design is also presented. The advantages of self-packaging, reduced electromagnetic wave leakage, and improved design flexibility as well as wideband which are due to the SCPW-MS dual-layer hybrid routing have been demonstrated.