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In this letter, an improved broadband transition between microstrip and empty substrate integrated waveguide (ESIW) is proposed. The transition structure consists of a gradient microstrip line, a taper extended into ESIW, and ESIW section. Compared with the previous studies, the gradient microstrip line is introduced to expand the operating bandwidth and get a better performance, especially for the thinner dielectric substrate. The simulated and measured results have a good agreement. A back‐to‐back transition is designed, manufactured, and tested. For a single transition, the return loss and insertion loss are better than 13.5 and 0.75 dB from 6.6 to 16.45 GHz (85.5%), respectively. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2227–2231, 2016

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A novel miniaturised dual-band bandpass filter (BPF) based on defected split-ring resonators (SRRs) and irregular stepped-impedance resonators (SIRs) is proposed. By applying defected SRRs embedded with eight combinations of three whole or broken grooves, which are formerly used for divination, the passband of 2.35-2.52 GHz with wideband harmonic suppression is achieved for WLAN applications. To create one more passband of 5.09-5.3 GHz, the irregular SIRs are etched inside the defected SRRs. Finally, such a prototype is designed and fabricated with the dimension of only 20 × 20 mm 2 (0.27λ g × 0.27λ g). The measured results of this dual-band BPF agree well with the simulations verifying the proposed idea.