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Minimized reflectionless bandpass filter with four notches and low insertion loss

ABSTRACT A size-minimized low-insertion-loss reflectionless bandpass filter with four notches is presented in this paper. The insertion loss of two quasi-elliptic-type filters is studied and optimized by a new approach based on cascade resonators branches. Parameters extraction procedure for the desired position of notches is illustrated. The inband performance, bandwidth and notch width are studied. This novel approach brings lower insertion loss. It can be extended to reflectionless bandpass filters with arbitrary number of notches. The size of filter is also minimized. This filter is designed, simulated, fabricated and measured. It is centered at 3.481 GHz with a 3-dB bandwidth of 276 MHz. The minimum measured in-band insertion loss, including the loss of SMA interface, is 1.239 dB. Four notches are located at 2.827, 3.238, 3.825 and 4.306 GHz, respectively. S11 of this filter is less than −10 dB during 2–5 GHz.