This paper underscores the paramount significance of through-wall communications by providing a comprehensive exploration of pivotal aspects like wall characterization, relevant technologies, versatile applications, and future prospects. Through-wall communication has the potential of being adopted in diverse fields, from indoor wireless communications, ground penetrating radar, through-wall radar imaging, to even power transmission. To augment the efficiency and reliability of signal detection, a whole variety of tools, such as antenna elements, frequency-selective structures, metasurfaces, and lenses, are exploited. By surveying the landscape of relevant technologies and applications in the existing literature, this paper serves as a beacon for researchers and engineers alike. Furthermore, it extends an invitation for pioneering exploration in this field, advocating the examination of tunable and adaptive systems, as well as the untapped potential of 3D printing in reshaping the future of through-wall communications.

In this paper, a very efficient procedure for designing waveguide combline bandpass filters with an advanced electrical response is presented. The proposed technique is based on a segmentation strategy, which reduces the number of variables to be optimized by dividing the design process into simpler stages. The electrical response of an appropriate equivalent circuit model of the waveguide structure considered in each stage is used to generate the target curve needed in the optimization process. Moreover, the well-known Aggressive Space Mapping technique has been also implemented to improve the computational efficiency of the whole method. In order to validate the proposed design procedure, two high-order combline bandpass filters, with symmetric and asymmetric electrical responses including transmission zeros, have been successfully designed and simulated with full-wave analysis tools. Furthermore, as an experimental validation, a prototype of the symmetric filter has been manufactured, showing a good agreement between simulated and experimental data.

In this paper, a method to reduce mutual coupling between an E-plane and H-plane coupled microstrip patch antenna is presented. Two dual differentially fed square patches are designed in a 1 × 2 antenna array configuration. To minimize mutual coupling and its effects, coupled split-ring resonators (SRRs) are designed, characterized and positioned between the patches. Circular SRRs are designed and coupled to produce a band-stop response to suppress surface waves propagating within the dielectric substrate while enhancing isolation. Mutual coupling interactions and the suppression mechanism are discussed in relation to the patches and SRRs. The patch radiators are dual differentially fed to achieve polarization diversity. E- and H-planes decoupling is achieved between the two patches throughout their bandwidth while maintaining good antenna performance. A prototype of the antenna array and the SRR is fabricated and measured to validate the decoupling approach. With a separation distance of 0.49$\lambda$ between the patches, the measured S-parameters show an impedance bandwidth of |S11|≤−10 dB, covering 9.27–9.46 GHz, and −38 dB and −35 dB mutual coupling for E- and H-planes, respectively, are observed throughout the antenna operating bandwidth.

This paper presents a new probe feed, high gain and compact Substrate Integrated Waveguide (SIW) H-plane horn antenna, in which both TE ₁₀ and TE ₃₀ modes of the structure are simultaneously excited leading to a uniform field distribution along radiating aperture. Also, to reduce Side Lobe Level (SLL) of the antenna and to enhance gain, a dielectric slab and a row of patches are placed at the front of the aperture. The proposed SIW horn antenna is numerically investigated using High Frequency Structure Simulator (HFSS) software. The simulation results of the proposed antenna including reflection coefficient, radiation patterns and antenna gain are reported. Results illustrate that the new structure provides gain of 9.5 dBi at the center frequency of 20 GHz, which is nearly 3 dB higher than that of the conventional SIW H-plane horn antenna.