Broadband Microstrip-to-Coplanar Strip Double-Y Balun

A new version of the double-Y balun, transitioning from an unbalanced microstrip to a balanced coplanar strip (CPS) line, has been designed to feed a complementary spiral antenna with an input impedance of 100 Ω. Various versions of the double-Y balun have been investigated in previous literature for use with balanced mixers and pulsed antennas. Of the previous versions, the double-Y balun transitioning from a coplanar waveguide (CPW) to CPS was found to exhibit the widest bandwidth of operation while having little metal content (attractive for use in ground-penetrating radar applications). However, the double-Y balun transitioning from a CPW to CPS requires coplanar waveguide bridges at the junction; the inductive behavior of the bridges, in addition to CPW parasitic resonances, degrades the passband performance of the balun.