Coupled-Ladder Reflectionless Filters

This presentation will describe the circuit manipulations required to convert a well-known Cauer, or ladder topology filter prototype, to a coupled-ladder reflectionless filter prototype, without compromising the optimal transmission response and achieving theoretically perfect impedance match at both ports and at all frequencies. This relatively recent solution to a circuit design problem dating back almost 100 years (referred to then as constant-resistance networks) has sparked a resurgence in interest in absorptive filtering techniques. Practical implementations of coupled-ladder reflectionless filters ranging from discrete lumped-elements to monolithic microwave integrated circuits (MMICs) have produced low-pass, high-pass, and band-pass filters operating from the HF to mm-wave bands, and recognition of their advantages has led to increasing adoption as the preferred solution in a number of real-world applications.