A High-Power Non-Isolating RF Power Combining Network based on Transmission Lines

a Industrial radio-frequency (RF) power applications often require a high-performance power combiner network to efficiently merge power from multiple power amplifiers (PAs) and deliver it to the load, at a single operating frequency or within a narrow frequency band. Key requirements for such a combiner include small size, high efficiency, and minimal reactive loading effects due to parasitics. While power combiners based on coupled transmission lines offer advantages in terms of size and efficiency, the existing literature primarily focuses on achieving broad frequency response rather than efficiency optimization. This paper addresses this gap by exploring the design of narrow-band RF combiners using transmission-line conductors. We present a lumped-element circuit model tailored for this application, and further propose a tuning technique that minimizes reactive loading and impedance distortion while maintaining high efficiency within the desired frequency range. A 1 kW combiner network operating at 13.56 MHz is prototyped, and a custom test procedure is developed for power loss and impedance distortion measurements. The model and tuning technique are validated through small-signal measurements and high power tests, with results showing improved impedance distortion (improving VSWR from 1.19:1 to 1.03:1 with 50 Ω load) and high combiner efficiency (>99.3%, or <0.031 dB insertion loss) at full rated power.