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The binary particle swarm optimisation (BPSO) in conjunction with the time‐domain discrete Green's function (DGF) method is proposed for designing of printed ultra wideband (UWB) antennas. In the DGF method, on one hand, a three‐dimensional problem is reduced to a two‐dimensional one, and on the other hand, the broadband frequency characteristics of the antenna are achieved with a single simulation run. Furthermore, the spatial discrete representation of the current on the antenna, in the DGF method, facilitates implementation of its combination with the BPSO algorithm. Two different UWB antennas are designed using the proposed approach. First, an antenna is designed to minimise voltage standing wave ratio (VSWR). The experimental result shows that the antenna has a VSWR about <1.5 over the UWB range. Second, an antenna is designed to have not only low VSWR, but also stable radiation pattern over the UWB range. The experimental results show a good impedance matching and stable omnidirectional pattern over the UWB range.

In this article, a new wideband diplexer for microwave frequencies is proposed. This diplexer is designed based on the combination of spoof surface plasmon polariton structures with substrate integrated waveguide (SIW) structures. In the proposed diplexer, bandpass filters were designed within a frequency range of 6–9.2 GHz (bandwidth of 40%) and 11.7–16.2 Hz (bandwidth of 29%) by creating rectangular grooves on the top and bottom of the metallic layers of the SIW. These grooves generate surface plasmon waves in the SIW structure that limit the dispersion curve to an asymptotic frequency and cause a high cut‐off frequency. The low cut‐off frequency of the filters is determined by the SIW dimensions. Moreover, the two filters were fed using a microstrip T‐junction with stepped impedance transformation. By optimizing the feed lines, the electromagnetic waves in each working band are directed to the filter of that band, and finally, the filters create a proper attenuation outside the band. A sample of the diplexer is fabricated and tested to verify the design. The simulation results are in good agreement with the experimental results. This diplexer can be a good candidate in microwave frequencies for telecommunication systems.