Analysis and Design of a 3 dB Tunable Lumped-Element Directional Coupler

An analysis of a 3 dB lumped-element directional coupler(LEDC)based on arbitrary terminal impedance is described numerically.To solve the conflicted requirement for broad bandwidth and small size in LEDC,a new structure of coupler is introduced,which can significantly improve bandwidth and whose size is only 3 cm×4 cm on the conditions of the frequency domain of 410 MHz to 490 MHz.The measure results are in good agreement with simulations despite the unexpected resistor loss.