Compact, broadband, transformer-based hybrid quadrature coupler

Abstract

A compact, broadband, transformer-based quadrature hybrid coupler (QHC) (34) offers improved gain and phase imbalance across a broadband frequency range compared to conventional QHCs (30). The QHC (34) comprises a combination of a conventional transformer-based QHC (30) and a bridged constant-resistance T-shaped full-step delay element (32). The QHC (34) functions as a 90° phase-shift divider and combiner. Applications of the QHC (34) include balanced amplifiers and load-modulated balanced amplifiers (LMBAs). The constant-resistance network provides a discrete equivalent of a dispersion-free broadband transmission line, increasing the bandwidth of the QHC (34). It introduces constant phase delay for all frequencies.However, beyond a mere combination of these two circuits, the innovative QHC(34) merges several of the passive elements (inductors / transformers) to reduce the number of components, and some capacitors are conveniently placed in the center of the transformer, resulting in a compact, broadband QHC(34). Publication Figure: 8.