Compact transversal signal-interaction wideband bandpass filter with multiple transmission zeros and wide stopband

In this paper, a compact wideband bandpass filter with multiple transmission zeros and a wide upper stopband is proposed based on the transversal signal-interaction concept. The filter has two transmission paths for signals to travel from the input port to the output port. The wideband bandpass filter is designed with a center frequency of 4.29 GHz (f0) and a 3-dB fractional bandwidth of 71.3 %. Six transmission zeros from 0 GHz to 4.2 f0 can be achieved due to the superposition of signals of the two transmission paths and the virtual short effect of open stub. The designed and fabricated wideband bandpass filter is of minimum insertion loss of 0.3 dB, group delay in the passband below 1.1 ns, and upper-sideband rejection up to 18 GHz (4.2 f0). Additionally, the proposed filter possesses compact size, and the overall circuit only occupies 0.23 lambda g x 0.15 lambda g (lambda g is the guide wave length of 50 Ohm microstrip line at 4.29 GHz). Measurement and simulation results are in good agreement.