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High‐performance, wideband three‐stage power splitters based on substrate integrated waveguide (SIW) are presented. Broadband‐tapered microstrip transitions are used for feeding the SIW structures, which provide 7.5 GHz bandwidth from 21.5 to 29 GHz with return loss below −20 dB. In addition, various T junctions are tuned, not only to provide broadband performance up to mm‐wave frequencies but also offer low‐phase and amplitude imbalance when cascaded in multistage 1 × 8 splitters. 1 × 4 and 1 × 2‐T junctions are adjusted through parametric analysis to provide wide bandwidth of 3.5 GHz at 24.5 GHz and −15 dB reflection coefficient. The optimal microstrip transitions and T junctions are used to design a broadband, eight‐way power splitter with 15 dB return loss from 23.0 to 26.4 GHz and phase and amplitude imbalance of ±2.5° and ±0.8° dB, respectively. Furthermore, optimum positions of all inductive posts in terms of guided wavelength are also provided for assisting the direct design of mm‐wave, high‐performance power splitters.

A compact antipodal log periodic slot‐loaded circular Vivaldi antenna with dimension (L × W) 45 × 60mm is presented. Structural modification to the conventional antipodal Vivaldi antenna results in miniaturization, improved impedance and pattern bandwidth performance. Proposed designs are prototyped and measured to validate wide‐impedance bandwidths from 5 to 40 GHz. These are compared to measurements on similarly fabricated traditional antipodal and circular Vivaldi antennas which shows a bandwidth only up to 26 GHz. In addition, the measured antenna gain and radiation efficiency of the log periodic slot‐loaded circular Vivaldi antenna are also found higher than the conventional designs. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:159–163, 2017