Low-pass filter design applying short-parallel coupled lines associated with open stubs

This paper proposed a novel low-pass filter design which applies short-parallel-coupled lines with open stubs. Transmission zeros created in the stopband, induced by the parallel open stubs, makes a sharp frequency response above cutoff frequency and results in a wide rejection bandwidth. The circuit analysis of the short-parallel coupled line is performed by the pi-type equivalent circuit. One 5-th order and one 7-th order Chebyshev low-pass filters both with cutoff frequency 2.45GHz and 0.01dB ripple were demonstrated to verify this design method. The measured and simulated results are in good agreement within the frequency of interest.