When a narrow straight slot is etched obliquely in the upper metallic strip of a microstrip line, a bandstop response can be observed from the terminations of the microstrip line. The whole circuit behaves as a single-stage bandstop filter, of which the center operation frequency and the fractional bandwidth can be adjusted by changing the length and the inclined angle of the slot, almost independently. Parametric studies are made to demonstrate the filtering performance, via numerical simulations. An LC equivalent circuit model is given to explain the bandstop behavior, shows its potential use in high order filter design. Samples are designed, fabricated and measured for verification, the experiment results show that the filters have good bandstop performance. It can be used as an alternative or complementary candidate for the traditional spur-line bandstop filter.
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