A compact decoupling structure, implemented by the postwall slotline (PWS) based stepped impedance resonator (SIR), is proposed for enhancing the isolation between patch antennas. A pair of SIRs are placed between microstrip antennas to cut off the coupling path, which enhances the decoupling performance greatly at resonance frequency. Meanwhile, designed with a combination of conventional slot line (CSL) and the PWS, the decoupling structure has a compact profile and thus is suitable for miniaturized element space. A two-element patch array is designed and fabricated to verify the decoupling effectiveness of the proposed structure, by providing simulated and measured results. Realized gain of the antenna with proposed structure is about 5.4 dBi. High isolation of 30.4 dB at 5.7 GHz is achieved and the edge-to-edge distance is 0.059 ${{\lambda}_{0}}$ with the decoupling structure. Moreover, with the decrease of element distance, isolation improvement will be significantly enhanced. The compact size and isolation performance show the potential of the structure to be applied in antennas arrays including multi-input-multi-output (MIMO) systems and adaptive arrays.

A horizontal azimuth pattern-reconfigurable antenna with configurable parasitic element arrays for WLAN applications is proposed in this paper. It consists of a control board, a central series-fed omnidirectional microstrip array, four configurable parasitic elements, a bottom conducting plate, and a top supporting plate. The omnidirectional microstrip array is adopted as an exciter, around which the four same parasitic element arrays are arranged at four corners. The p-i-n diodes as switches are placed between the parasitic element arrays and the conducting plate to control the fifteen radiation patterns of the proposed antenna. The parasitic element arrays are configured as reflectors or directors by switching the p-i-n diodes on or off. The bandwidth achieved ranges from 5.00 GHz to 5.27 GHz. A gain of 8.52 dBi is obtained when the antenna reaches the maximum gain in the H-plane at 5.2 GHz. Good agreements between the simulated and measured results were observed. The proposed parasitic structure which has the same structure with the driven element can enhance the horizontal azimuth gain of the antenna. Only 4 p-i-n diodes are used to produce up to 15 useful beam configurations with a gain range of 4.56-8.52 dBi at the horizontal azimuth.

In this letter, a postwall-slotline stepped impedance resonator (PWS-SIR) is proposed and applied to a bandpass filter (BPF) with a wide stopband. The proposed PWS-SIR-BPF comprises three U-shaped PWS-SIRs and two microstrip-slot feeding transitions. A PWS has a much lower impendence which a conventional slotline (CSL) cannot reach, so a much smaller impendence ratio of the PWS-SIR can be achieved. Consequently, a wider stopband simultaneously can be realized for the proposed filter. The designed PWS-SIR-BPF, as well as a CSL-BPF, have been fabricated, measured, and compared to verify the features of the PWS-SIR. The measured results are consistent with the simulation ones. The PWS-SIR is 7.3 mm (0.22λ₀) long, 67% of 11.1 mm (0.34λ₀) of the CSL resonator. The first spurious resonance frequency of the PWS-SIR-BPF is extended from 9.8 GHz (2f₀) to 23 GHz (4.7f₀).