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A compact single M-shaped probe fed circularly polarised filtenna (filtering antenna) without extra filtering circuit is presented in this study, in which three pair slots with different lengths are etched on its parasitic patch to produce radiation nulls at both band edges of its operating band. Furthermore, a single M-shaped probe feeding structure is used to improve the selectivity, especially for the lower band edge. By merging the filtering circuit into a radiating element, a good selectivity in the gain response can be realised without influencing the operation band aperture efficiency. A sample is fabricated and results show that the proposed filtenna has an operating bandwidth of 13% (| S 11

A multi-layer interleaved folded half-mode substrate integrated waveguide (HMSIW) dual-band filter is proposed. The TE 101 and TE 102 mode of the HMSIW resonators form dual-band response by vertical coupling, and the bandwidth of the two passbands can be independently designed by adjusting the coupling apertures. Moreover, three transmission zeros (TZs) are obtained to improve out-of-band rejection, and the TZs can be flexibly designed below or above the passband. By vertically superimposing the HMSIW cavity, the HMSIW filter can be extended to multi-pole dual-band filters. A dual-band filter with centre frequency of 3.05 and 4.7 GHz was fabricated and measured to verify the proposed method. The simulated and measured results are in good agreement.

Miniaturised band-absorptive frequency selective rasorbers (FSRs) with wide absorption bands for single-polarised and dual-polarised applications are proposed here. These FSRs are both constructed by a lossy layer and a lossless layer, in which I-type metal strips are utilised to reduce the size of the unit cell of the FSRs. The equivalent circuit models (ECM) of the FSRs are presented and analysed. A prototype of the dual-polarised band-absorptive FSR is fabricated, assembled, and tested. The measured results show that a wide absorption band (| S 21 |≤–10 dB and | S 11 |≤–10 dB) from 3.93 GHz to 8.07 GHz with a bandwidth of 69%, and a low-pass band (| S 21 |≥–1 dB) with frequency lower than 880 MHz has been achieved for the dual-polarised band-absorptive FSR.

This study develops a differential-fed filtering patch antenna, which features superior frequency selectivity, compact size, low cross-polarisation, and symmetrical radiation patterns. The proposed antenna consists of a rectangular patch on the top layer, which is differentially fed by a balun bandpass filter on the bottom layer. A pair of rectangular coupling slots were etched on the middle layer for energy coupling. The patch antenna performs not only as the radiator but also as the last resonator of the whole filter circuit for compactness. A prototype of the proposed filtering antenna operating at 2.45 GHz was fabricated and tested. The measured in-band peak gain is 5.9 dBi with steep roll-off at band edges, and the out-of-band gain is less than - 25 dBi. Moreover, symmetrical radiation patterns and low cross-polarisation levels of - 22 dB are also realised for the proposed filtering antenna.

Frequency-selective surfaces (FSSs) with two sharp sidebands have been investigated, which are constructed by cascading and shunting two substrate integrated waveguide cavities (SIWCs) of different sizes with periodic slots at top and bottom metal surfaces. The lower and upper sharp sidebands are induced by two transmission nulls that are generated by coupling between the slot aperture resonance and the resonances in the two cavities. Samples of the shunted SIWC-FSS with different size cavities were fabricated. Measured results are in good agreement with the predicted ones and its performance, such as high selectivity and passband bandwidth, is stable at oblique incidence.

This paper proposes a dualband frequency-selective surface (FSS) based on substrate-integrated waveguide (SIW) technology. This novel dualband FSS is constructed using double square loop slots (DSLSs) and an SIW cavity. Its frequency performance is investigated by numerical simulation using the finite difference frequency domain (FDFD) method. Another dualband FSS, constructed using convoluted double square loop slots (CDSLSs) and an SIW cavity is also investigated in order to get close passband spacing. Simulation results show that these dualband FSSs have the advantages of higher selectivity and passband insensitivity to the incident angles and polarisations, compared with conventional multiband FSSs. Experiments are carried out to verify the simulated results, and the measured results show a promising performance of the proposed FSS.