The paper presents a dual‐wideband bandpass filter using multilayer broadside‐coupled microstrip‐coplanar waveguide (CPW) structure. The half‐wavelength stepped‐impedance resonators at the top and bottom layers are broadside coupled in the vertical direction through a CPW‐multimode resonator (CPW‐MMR) at the mid layer, which forms a mixed MMR. The ultra‐wideband obtained from tight coupling is split into two passbands by introducing extra transmission zeros, good impedance matching is achieved by adopting open‐ended microstrip stubs on the input and output microstrip feed lines, and the dual‐wideband characteristic is realized. The proposed filter is small in size, and its operation bands and the bandwidth of the stopband are adjustable. Both experiments and computer simulations were conducted, and the measured results are in good agreement with the simulation results.
In this paper, a broadband transition structure from microstrip line to slotline with band-notched characteristic is proposed. To match the 50 Ω microstrip line, 4 Chebyshev impedance transformations are used in the transition structure, and its bandwidth is widened. There is a fan-shaped radial line at the microstrip terminal. A U-shaped slot is etched on the microstrip line with stepped impedance matching to achieve band-notch characteristic. By changing the length of the slot, the band notch is realized at different frequencies. Simulation and optimization of the transition structure are made by using the high frequency simulation software HFSS to achieve the band-notch function at 3.37-3.84 GHz and 10.67-11.14 GHz. In the rest of the band, return loss S 11 is less than −15 dB, and voltage standing wave ratio (VSWR) is less than 1.5.
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