Modified Inverted Microstrip Integrated Filter

The novel modified inverted microstrip integrated lowpass-bandpass circuit is developed, fabricated, and experimentally verified. The most of the communication applications prefer to use a lowpass filter prior to a bandpass filter with input and output ports on the same side of the board. The narrow frequency within the C band having a center frequency of 4.7 GHz is passed with a lowpass cut-off frequency of 2.14 GHz. A highly suppressed lowpass stopband of 20 dB up to 13.6 GHz is achieved using an inverted microstrip model with a high Q factor. The bandpass frequency band ranges from 4.6 GHz to 4.9 GHz at the stopband of the lowpass filter and fractional bandwidth of 6.3% is obtained with 27.2 dB passband return loss. The ultra-compact model with a normalized circuit size of 0.0142 λ
g
²
is accomplished.