Higher-Order Filtering Attenuator Design Considerations for Filter Shape Optimization

Filtering attenuators (filtenuators) combine the frequency selectivity of filters with the controlled loss of an attenuator in a single component. Often, the filtenuator is made of three resonators or less to minimize the complexity of the design and the resistive π-network distribution is straightforward. However, the resistive network distribution is less clear for high-order filtenuator designs. This paper presents an alternative method of loading a filtenuator that has more than three resonators and is compared to the traditional π-network method of loading a resonating circuit. A detailed analysis of the resistive network distribution is conducted to optimize the filter shape using a fifth-order Chebyshev bandpass filter topology. A 900 MHz fifth-order filtenuator with 6.5 dB of passband loss is designed using the optimized distribution method, and the measured results are compared to simulation.