This article proposes a design of miniaturized high selectivity band‐pass filter by using a dual‐mode patch resonator with two pairs of uniform slots set in the four corners. The effect of the pairs of the slots on the resonant modes of the square patch resonator is investigated first. For filter design, the slots set in the four corners of the patch resonator are provided as the perturbation elements to tune the resonant modes and thus form the filter response. The pairs of the slots reduce the fundamental resonant frequency and thus miniaturize the filter size. The designed filter is simulated and measured at 1.95 GHz for the fifth generation applications with narrow bandwidth. High band selectivity is obtained due to the creation of transmission zeros near the passband edges. The filter performances are measured by network analyzer and the results are discussed.

In this paper, we develop a bandpass filter using a stub-loaded stepped impedance resonator (SLSIR) and calculate the even and odd resonant modes of this type of resonator using the input impedance/admittance analysis. In this study, two impedance ratios and two length ratios are operated as the design parameters for controlling the resonant modes of the SLSIR. Several resonant mode variation curves operating three resonant modes with different impedance ratios and two length ratios are developed. By tuning the desired impedance ratios and length ratios of the SLSIRs, compact ultra-wideband (UWB) bandpass filters (BPFs) can be achieved. Two examples of the UWB BPFs are designed in this study. The first example is UWB filter with a wide stopband and the second one is dual UWB BPF, namely, with UWB performance and a notch band. The first filter is designed for a UWB response from 3.1 to 5.26 GHz having a stopband from 5.3 to 11 GHz, with an attenuation level better than 18 dB. The second filter example is a dual UWB BPF with the frequency range from 3.1 to 5 GHz and 6 to 10.1 GHz using two sets of the proposed SLSIR. The measured results have insertion loss of less than 1 dB, and return loss greater than 10 dB. Furthermore, the coupling structures and open stub of the SLSIR also provide several transmission zeros at the skirt of the passbands for improving the passband selectivity.