A compact, single-layered substrate integrated waveguide (SIW) filtenna with parasitic patch is synthesized and designed. A half-mode substrate-integrated rectangular cavity (HMSIRC) is adopted as the first stage resonator to reduce the circuit size. A parasitic patch functioning as the last stage resonator as well as the radiator is arranged closely to the HMSIRC so as to enhance the operational bandwidth and facilitate the filtering performance. Two broadside radiation nulls are realized at both the upper and lower band-edges to sharpen the band-edge roll-off rate: One is generated by the interaction between the HMSIRC and the parasitic patch, and the other is introduced by placing two pairs of shorting posts under the parasitic patch. The standard filter synthesis technology is utilized to guide the filtenna design. The optimized prototype was fabricated and measured. The measured results, in good agreement with simulated values, indicated the proposed filtenna provides a 5.1% fractional bandwidth, a maximum realized gain of 6.3 dBi, and a flat passband gain response along with excellent out-of-band selectivity, even with ultra-low profile 0.015λ0 and small volume 0.005λ03.

In this letter, a compact, low-profile, bandwidth enhanced, dual-cavity substrate integrated waveguide (SIW) filtenna is demonstrated. Two SIW cavities are stacked vertically on top of each other. A complementary split ring resonator (CSRR) slot is etched in the top surface of the uppermost cavity, causing the top surface to act as a patch antenna. The operational impedance bandwidth is significantly enhanced by merging the three resonances that arise from this configuration. One is introduced by the patch and the other two are inherently generated by the two cavities. A metallized coupling post is introduced from the ground plane through both cavities to the upper surface to excite the fundamental resonant mode of the patch, as well as to electromagnetically couple the two cavities. The optimized filtenna was fabricated by standard printed circuit board (PCB) technology and tested. It has a low profile 0.03λ0 and compact size 0.62 λ0 ×0.62 λ0 at its center frequency, f0 = 2.95 GHz. The measured results agree well with their simulated values. They demonstrate a 6.3% fractional bandwidth, a maximum realized gain of 6.73 dBi, a flat gain profile within its passband, and excellent out-of-band selectivity.

Scalar holographic surfaces (HSs) with a unique polarization-insensitive property are presented. The proposed HSs are constructed by sinusoidally modulated loop-wire unit cells, which can support both TE mode and TM mode propagation with the same phase velocity. The modulation principle in terms of refractive index is presented, which is convenient for HS designs concerning both TE and TM modes. A scalar polarization-sensitive HS using square patches exhibits a mismatch in the E- and H-plane beamwidths due to the sin (φ) circumferential illumination of the x-directed dipole, resulting in a low aperture efficiency. Two novel scalar HS designs using loop-wire configuration in square lattice and hexagonal lattice are proposed which exhibit the polarization-insensitive property with nearly circularly symmetric E- and H-plane beamwidths when illuminated by an x-directed dipole. Both simulations and measurements are carried out in this paper, which agree well with each other.

In this communication, a compact vertically-integrated full-duplex filtenna is developed by using common feeding and radiating substrate integrated waveguide (SIW) cavities. A rectangular dual-mode SIW cavity, operating at its two orthogonal TE120 and TE210 modes, is first employed as the common feeding cavity to realize two passbands. And then, a common radiating square slot-loaded SIW cavity is vertically integrated with the common feeding cavity so as to enhance the operational bandwidth and improve the frequency selectivity for both two passbands. Two metallic posts are utilized to achieve the desired coupling strength between the feeding and radiating cavities for the two passbands, respectively. By properly arranging the locations of two input ports and coupling regions, high isolation between the two input ports is realized. The detailed design process based on the coupling matrix is presented. To verify the proposed concept, a prototype is fabricated and measured. The measurement results agree well with the simulated values, showing the maximum broadside realized gains of 4.36 dBi and 4.83 dBi, and the impedance bandwidths of 3.2% (4.03–4.16 GHz) and 3.9% (4.81–5 GHz) for the lower and upper passbands, respectively. The proposed antenna also exhibits good performance in terms of port isolation, flat in-band gain response, and out-of-band frequency selectivity.

A new design method to significantly expand the axial ratio (AR) bandwidth of a single-fed, low-profile circularly polarized (CP) antenna without relying on any complex feed network or occupying a large transverse dimension is presented. First, four small patches arranged in chessboard pattern are utilized as the main radiator, and meanwhile, a cross slot with unequal slot lengths is adopted to excite triple sequentially orthogonal modes, aiming to attain two CP modes (AR ₁ and AR ₂ ). Second, in order to further considerably enhance the AR bandwidth and concurrently reduce the overall size, the feeding cross-slot resonance is favorably excited and effectively coupled by the chessboard patches to produce a new slotline-based CP mode (AR ₃ ) located before AR ₁ . Finally, an I-shaped top-loaded monopole fence, as a new degree of design freedom, is employed to collaboratively regulate these multiple resonances to form a wide AR bandwidth covering AR ₁ , AR ₂ , and AR ₃ . Results show that, on the premise of keeping the inherent compact-size and low-profile advantages of microstrip antenna, the 3 dB AR bandwidth is remarkably enhanced up to 30.1% by the combination of the three CP modes. Based on the design method, a wideband polarization-reconfigurable antenna with switchable linear polarization (LP), left-handed circular polarization (LHCP), and right-handed circular polarization (RHCP) states is further designed and experimentally validated. The measured results demonstrate that, with quite compact transverse size ( $0.16\lambda _{0}^{2}$ ) and low profile ( $0.04\lambda _{0}$ ), a wide overlapped bandwidth (27.6%) of the polarization-reconfigurable antenna is successfully accomplished.

This work presents a compact, low-profile, wideband, polarization-reconfigurable antenna with right-handed circular polarization (RHCP), left-handed circular polarization (LHCP) and linear polarization (LP) diversity. The antenna consisting of quadruple identical gap-coupled square patches, possesses dual wideband degenerate modes, which could be properly allocated by controlling ON/OFF states of four PIN diodes integrated in an overlying specially-engineered driven element to dynamically produce RHCP, LHCP and LP radiations. Owing to the collaboration between the gap-coupled patches and such a reconfigurable driven element, the proposed design could operate in a wide overlapped bandwidth of 7.1% in the three dynamical states while keeping a compact size of 0.56λ0×0.56λ0 and a low profile of 0.037λ0. Benefiting from the advantages of low profile, compact size, and wideband operation in three polarization-reconfigurable states, the proposed antenna is quite suitable for space-limited, wideband, intelligent and anti-interference wireless systems.