Novel stacked‐defected ground structures for ultra‐wideband low loss balun designs

A novel stacked‐defected ground structure (SDGS) for ultra‐wideband and low‐loss balun design was developed. The balun implements an inductive compensation method on a multilayer liquid crystal polymer (LCP) substrate to control phase and amplitude imbalances. Based on a 15‐dB input return loss and 0.5 dB insertion loss criterions, the balun has a measured bandwidth from 70 MHz to more than 2.1 GHz, a measured amplitude and phase imbalances are less than 0.5 dB and 5°, respectively. With a compact size of 36 mm × 51 mm × 0.23 mm, the 0.5 dB loss‐balun achieves both the largest bandwidth ratio (30:1 ratio) and the most improved imbalances reported to date on a printed circuit board.