Design of Compact Microstrip Sept-Band Bandpass Filter With Flexible Passband Allocation

A compact sept-band bandpass filter (BPF) with flexible passband allocation has been presented. By introducing the multiple coupling paths, all passbands can be fully controlled and designed independently. The first and last resonators are used to not only create one of the passbands but also serve as the input and output coupling structure for the other passbands. Thus, more operating bands can be obtained without increasing extra circuit area. The special arrangement of resonators could help to reduce the filter size and create more operating bands. For demonstration, a two-pole sept-band BPF centering at 1.05, 1.3, 1.5, 1.8, 2.05, 2.35, and 2.85 GHz has been designed and fabricated with microstrip technology. The sept-band BPF has an extremely small size of 0.14 λ
_g
by 0.19 λ
_g
. Moreover, good agreement is achieved between simulation and measurement.