The proposed bandstop filter (BSF) consists of a dual mode E-shaped resonator and a microstrip feeding line. By adjusting the resonator's central strip, the first two resonant frequencies could be moved together to build the stopband. The gap between the resonator and the feeding line is used as the coupling structure. Two arms of the resonator are bent to realize the balanced coupling, thus two refection zeroes could be observed beside the stopband after adjusting the arms' bend rate carefully. Filter samples are designed, fabricated and measured. As a result, a rejection level of-16.7 dB is achieved at the central frequency 6.01 GHz whereas two reflection zeros (<-45.0dB) at 5.64 GHz and 6.24 GHz could be observed as predicted. The measured reflection is below-30.0dB in its passband.
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