In this article, a novel dual-band differential bandpass filter using (SIRs) is designed. To demonstrate the design ideas, the differential and common mode equivalent half circuits are built and studied. Two resistors are connected between the two ends of the SIRs to consume the power in common mode. A capacitor is connected between the Ground and Center of the SIR to adjust the spurious frequencies, also strength the coupling of the two SIRs. The theoretical analysis shows the second band can be obtained by the proper impedance ratios of the resonances and the capacitor connected to the resonator. Two through ground vias (TGVs) connecting the top and bottom sides of the SIR filter, are used to realize the common mode rejection. To investigate the proposed filter in detail, a set of design equations are derived based on the circuit theory and transmission line theory. A phototype dual-band differential filter operating at 1.5 and 2.75 GHz has been realized to validate the proposed concept and theory. V C 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:468-473, 2015.

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In the 5G communication utilizing millimeter-wave (mmWave) band, multilayer configuration is popular for mmWave antenna with module-level integration and high-density design. However, multilayer construction adds several substrate layers and metallic ground layers to RF signal paths, which induces extra capacitances and inductances to the original antenna, thereby deteriorating impedance matching, and distorting radiation patterns. In this paper, we investigate the influence of multilayer structure on antenna performances, and apply substrate integrated coaxial line (SICL) design to eliminate these interferences from multilayer configuration. Equivalent circuit model of the multilayer configuration with SICL is presented and verified by simulations. A mmWave antenna unit and the 1 Â 4 array in multilayer configuration with SICL design are measured. Experiments show that SICL design enables impedance matching and radiation patterns to be maintained without distortions when applying multiple layers to the mmWave antenna, validating this method. It can be applied to 5G mmWave antennas that desire multilayer construction.

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