A novel dual-polarized band-absorptive frequency selective rasorber (FSR) is proposed in this paper. The FSR is constructed by twolayer cascaded printed circuit boards, in which meander-line square loops with and without lumped resistors loaded on the top and bottom surfaces of the two substrates. Its operating principle is analyzed and an accurate equivalent circuit model is presented. A prototype has been fabricated, assembled and measured. The measured absorption band is from 4.8GHz to 6.81GHz (34.6%), with a thickness of λa/8 at 4.8GHz. Moreover, it is almost transparent to electromagnetic waves below 1.54 GHz. The measurement results achieve a good agreement with the simulated results, which verifies the effectiveness of the design.

In this letter, a compact bandpass filtering power divider with tunable bandwidth based on spoof surface plasmon polaritons (SSPPs) and substrate integrated waveguide (SIW) is proposed. The hybrid-SIW-SSPP structure shows good potential to expand the scope of bandwidth control of the device. The bandwidth can be designed in a wide range by simply optimizing its dimensions or loading interdigital structures (ISs). Defected ground structure (DGS) is also introduced on the bottom layer to further improve the out-of-band suppression. And good isolation can be obtained via additional resistors welded across the SSPP slot. A prototype loaded with dumbbell-shape DGS and two resistors is fabricated with an overall size of 45 mm $\times18$ mm $\times0.5$ mm. Both $S_{21}$ and $S_{31}$ are around −3.8 dB within the whole $X$ -band. The simulated and measured results agree with each other well.

A planar dual-band shared-aperture array antenna for the ${K}$ -/ Ka -band low Earth orbit (LEO) satellite communication is presented in this article. Substrate integrated coaxial line (SICL)-fed bow-tie transverse slots and substrate integrated waveguide (SIW)-fed slot pairs are employed to provide ${K}$ -band horizontal polarization and Ka -band vertical polarization, respectively. The ${K}$ -band and Ka -band radiating elements share a common metallic-via-array, which can effectively improve the port-to-port isolation. Furthermore, the port-to-port isolations in both bands can be also improved by introducing the high-pass characteristic of SIW and out-of-phase cancellation between two current paths. For the sake of achieving low-profile height and compact size, the ${K}$ -band feeding network is subtly buried between Ka -band shielding cavities. As a proof-of-concept example, a shared-aperture dual-polarized array antenna operating at ${K}$ -/ Ka -band is designed and fabricated for verification by using a multilayer printed circuit board (PCB) technology. The measured results show a good concordance with the simulated one, indicating that the proposed antenna has the advantages of wideband, high isolations, low profile, and easy planar integration, which can be adopted for the millimeter-wave (mm-Wave) LEO satellite communication system.

In this paper, the integration design of a millimeter-wave filtering patch antenna array fed by a substrate integrated waveguide (SIW) four-way anti-phase filtering power divider is proposed. The multilayer four-way anti-phase filtering power divider handily implemented using the intrinsic field distribution of TE ₂₀ -mode in SIW is proposed for miniaturization. The signal of the lower substrate integrated waveguide cavity (SIWC) bandpass filter is directly coupled to the upper TE ₂₀ -mode SIW through a coupling slot. The intrinsic field distribution of TE ₂₀ -mode SIW is used to generate anti-phase signals. This filtering power divider can be utilized as the feeding structure of a millimeter-wave filtering antenna array. To verify the design concept, a 28-GHz SIW-fed $1\times 4$ filtering patch antenna array with three-layer substrates is designed and fabricated. The measured results show a fractional bandwidth of 5.03% ranging from 27.15 to 28.55 GHz, a peak gain of 11.1 dBi, cross-polarization levels lower than −20 dB, symmetric radiation patterns in both $E$ -plane and $H$ -plane, and high selectivity.

This letter presents a novel class of compact dual-mode bandpass filters based on half-mode substrate-integrated waveguide (HMSIW) cavities. By using both TE ₁₀₂ and TE ₃₀₁ modes of the HMSIW rectangular cavity as resonant modes and TE ₁₀₁ mode as nonresonating mode, a novel HMSIW doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located at one side or both sides of the passband. Therefore, flexible responses can be obtained. A two-pole HMSIW filter with asymmetric response and a four-pole HMSIW filter with quasi-elliptic response have been designed, fabricated, and measured, to demonstrate and verify the proposed structure. Compared with substrate-integrated waveguide (SIW) counterparts, the dual-mode HMSIW filters have the advantage of smaller size.

A three-dimensional (3-D) structure is proposed in this article for ultra-wideband absorber design. The ultra-wideband absorber is implemented by properly combining two subabsorbers. The first subabsorber operates in its fundamental mode (f₀) and the third-order mode (3f₀). Its lossy layer is designed with an infinite impedance at the second-order mode frequency (2f₀). The second subabsorber is designed to operate in its fundamental mode frequency, which is corresponding to 2f₀ of the first subabsorber. A double-sided parallel-strip line (DSPSL) is employed to produce the required infinite impedance of the first absorber. A simple equivalent circuit model of the DSPSL is established to explain the operating principle. A conventional parallel LC circuit is also provided for comparison to show the advantages of the DSPSL. Single-polarized and dual-polarized ultra-wideband absorbers are designed by combining these two subabsorbers, and their simulated fractional bandwidths (FBWs) of 151.6% and 150.9% are achieved, respectively. A prototype of the dual-polarized ultra-wideband absorber is fabricated and measured to validate the design concept. Its measured absorption band from 1.50 to 12.31 GHz with an FBW of 156.6% is in a good agreement with the simulated one. The proposed absorber features a wide absorption band and few lumped elements, which makes it more useful in practical applications.