Compact and broadband directional coupler for high power applications

Abstract

A compact, flat coupling, and broadband directional coupler are presented for high-power applications in the frequency band of 100 ∼ 1000 MHz. The coupler is mainly composed of two compact semi-flexible coaxial cables with the length of the λ 0/4 (λ 0 is the free-space wavelength at the frequency of 850 MHz), four chip ceramic capacitors, and two air wound inductors that can tune the coupling coefficient. The phase inverter of the coupler is well designed and experimentally validated. The directional coupler exhibits high performance in the whole operation frequency band with low insertion loss (less than 0.3 dB), high directivity (more than 18 dB), and high power (up to 300 W). The amplitude imbalance of the coupling coefficient is less than 0.3 dB. The measured results exhibit good consistency with the theoretical analysis. And the proposed design method can be readily extended to other low-cost, high-power, and broadband directional couplers.