In this study, a novel microstrip diplexer with four channels is designed by using codirectional split ring resonators (CDSRRs). Since CDSRRs provide dual resonance behavior, dual‐band bandpass filter with two poles at each passband can be created by coupling identical CDSRRs to input/output ports. Based on this approach, quad‐channel diplexer can be designed by coupling two more CDSRRs in different electrical length to another output. Both filters are fed by similar feeding lines. High isolation can be observed between the output ports by means of CDSRRs. The designed quad‐channel microstrip diplexer was also fabricated and tested for experimental verifications. The measured results are in a good agreement with the simulated results. Center frequencies of the channels were measured at 2.12, 2.45, 3.90, and 4.48 GHz with the minimum insertion losses of 2.27, 2.88, 2.00, and 2.71 dB, respectively. Isolation was observed as better than 44 dB from DC to 6 GHz.
In this paper, a novel dual wideband microstrip bandpass filter is proposed. The designed filter is constructed by two different stub loaded resonators located at the upper and bottom sides of the coupling line. The coupling transmission line is also connected to input and output (IO) ports. The upper resonator creates a wide passband, whereas the bottom resonator is used to create two transmission zeros in the passband. Thus, a wide passband can be divided into dual wide passbands. The bottom resonator is also utilized to improve the insertion and return losses in the passband. The designed filter is fabricated and tested in a very good agreement with the simulated results. The measured fractional bandwidths (FBWs) of the passbands are 44.6% and 24.2% at the center frequencies of 3.4 GHz and 5.51 GHz, respectively. The measured insertion losses in the passbands are 0.51 dB and 1.13 dB.
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