In future 6G millimeter-wave/sub-THz vehicle-to-everything communication systems, vehicles are expected to be equipped with massive antenna arrays to compensate for the severe path loss. However, vehicle-to-vehicle (V2V) direct links are prone to blockage by surrounding vehicles. Emerging metasurface technologies enable the control of the electromagnetic wave reflection towards the desired direction to boost communication performance. Reconfigurable intelligent surfaces (RIS), and the pre-configured counterpart intelligent reflecting surfaces (IRS), are promising low-cost relaying systems for 6G. This paper proposes the usage of conformal metasurfaces (C-RIS or C-IRS) deployed on vehicles’ body to mitigate the blockage impact by creating artificial reflections, compensating for the non-flat shape of the vehicle’s body with proper phase patterns. We analytically derive the phase pattern for a cylindrical C-RIS/C-IRS, accounting for the shape of the car body, which generalizes the conventional planar ones. We propose a novel design for optimally pre-configured C-IRS proving its benefits in a V2V highway scenario. The traffic simulation results show a reduction of blockage probability by 20% for C-IRS and 70% for C-RIS as a benchmark, as well as a remarkable improvement in average signal-to-noise ratio by 10-20 dB for C-IRS and 30-40 dB for C-RIS.

In this article, we introduce a synthesis-based design approach for waveguide filters, including singlets. As is known, a singlet block comprises one resonator coupled to source and load plus an additional coupling between source and load. In this way, a pole-zero pair is produced, thus allowing the introduction of a transmission zero in the frequency response. Structure making that uses cascaded singlets (especially implemented in waveguide technology) has been successfully used to realize compact and quasi-in-line pseudoelliptic filters. The design of this configuration suffers, however, from a severe drawback; while an isolated singlet can be exactly synthesized, when these blocks are put in cascade, nonresonating nodes (NRNs) are required to allow the cascade connection. Consequently, the resulting topology includes both cross couplings and NRNs, for which no exact synthesis solution is till now available (all the design solutions proposed in the literature are based on optimization). The new design procedure here proposed overcomes this drawback, allowing the synthesis of the equivalent circuit of the cascaded-singlet topology. Once this circuit is obtained, the dimensioning of the singlets can be carried out by exploiting a full-wave simulator according to the procedure described in the article. The proposed design approach allows a very accurate initial dimensioning of the filter, which represents an excellent starting point for final adjustments/optimizations. A detailed design example is presented in the article showing how to practically implement the novel procedure. This new approach is also experimentally validated by a waveguide filter prototype, previously designed by optimization and fabricated. It is shown how this filter can be redesigned with the novel procedure, obtaining very similar physical dimensions in a noticeably shorter time.

A general design procedure for inline waveguide filters with frequency-variant couplings (FVCs) is presented. The goal of the design is the introduction of transmission zeros (TZs) in the filter response. The filter design starts with the synthesis of a low-pass prototype with FVC, adopting a method that recently appeared in the literature. The low-pass prototype is then denormalized to obtain an equivalent circuit of the filter suitable for waveguide implementation. The last step of the design consists of the dimensioning of the physical structure of the filter, including the frequency-dependent couplings, by exploiting the equivalence with the synthesized equivalent circuit. The design procedure can be applied independently on the specific structure implementing the FVCs. In the case of narrowband filters, the resulting structure may not require any further refinements by means of numerical optimization based on full-wave modeling. A design example illustrates the details of the procedure implementation. The validation of the procedure is presented through the design and fabrication of a substrate integrated waveguide (SIW) filter with two coincident TZs.