1-6 GHz 35W Balanced GaN-HEMT Power Amplifier with Innovative Quadrature Couplers
Abstract — This paper presents a 1 – 6 GHz, 35 W high efficiency GaN-HEMT balanced power amplifier utilizing an innovative topology ultra-wideband 3-dB quadrature couplers. Load-pull analyses through simulations as well as simple-model output matching design are applied to driver and output stages design. New topology of small-size quadrature thin-film 3-dB couplers are realized to form the balanced configuration. The amplifier delivers 45.5 – 46.5 dBm continuous wave output power with an average power-added efficiency (PAE) of 24 – 35% across the 1 – 6 GHz band. The amplifier has a flat linear gain (61 ± 1.5 dB), very good input and output matching (VSWR lower than 1.5) and need a single +27 V supply with a 4.5 – 6.5 A current at maximum output power.
Keywords — ultra-wideband, GaN-HEMT, balanced amplifier, quadrature coupler.
INTRODUCTION. Development of telecommunication networks supporting various data transmission ranges and standards instigate developers to search and find engineering solutions for construction of efficient transistor power amplifiers overlapping the maximum possible continuous frequency band. Broadening of the frequency band complicates matching 50- Ohm transistors significantly. In order to achieve the required parameters in a broad frequency band, developers use various well-known  amplifier circuit design methods, such as reactive matching (RM), reactive lossy matching (LM), negative feedback (FB), and travelling-wave amplifier (TWA). The RM and LM circuits allow to realize the high input power and PAE of an amplifier, but at the same time it is often too hard to ensure good input and (or) output matching. The FB and TWA circuits, vice versa, provide an optimized match but limit the maximum attainable power-added efficiency of an amplifier.