Wideband radar cross-section (RCS) reduction of a microstrip patch array antenna is proposed and investigated. The design is based on replacing the solid metal ground of the antenna with a frequency selective surface (FSS) consisted of miniaturised hexagonal loop elements. The stop band of the FSS is coincident with the antenna working frequency band which is from 3.3 to 3.4 GHz. The FSS acts as the ground plane in the stop band and is transparent to the incident waves in the other frequencies. Therefore, preserving the antenna propagation characteristics, wideband RCS reduction is achieved from 4 to 16.5 GHz for vertical and horizontal polarisations. It is shown that using this FSS has a negligible effect on the impedance bandwidth, pattern and gain of the antenna. Also, there is a good agreement between the simulation and measurement results.

This paper presents a novel inhomogeneous hemispherical dielectric lens. The proposed lens is designed based on the ray inserting method (RIM). Applying this approach, a uniform distribution of the rays' end points over the lens plane aperture is achieved while lens matching to the environment refractive index is perfectly fulfilled. We can change the antenna features such as sidelobe level and gain by controlling the end point of each ray propagated through the hemispherical lens. The refractive index of the designed hemispherical inhomogeneous lens is derived and it is validated using COMSOL Multiphysics. The proposed lens is realized using material drilling and multilayer techniques. Analysis of the realized lens is performed using CST-Microwave Studio. The structure has been fabricated. The results of a simulation and experiment indicate good performances of realized planar lens in a wide frequency bandwidth. Comparing with other hemispherical lenses like classical half Maxwell fish-eye, the improvements in the gain, sidelobe levels, and input matching are achieved by using the RIM.

Abstract-We analyze both theoretically and experimentally subwavelength focusing by using a planar hyperbolic metamaterial (HM) at microwave frequencies. The proposed HM consists of microstrip transmission lines (TLs) loaded by lumped components and exhibits a very flat wave vector iso-frequency dispersion diagram over a wide frequency range, and thus able to transport spectral component with large wavenumbers. This flatness is here exploited to provide subwavelength focusing with a full width half maximum (3-dB power width) of about and at 0.5 and 1 GHz, respectively, where is the guided wavelength in the TL microtrip grid. Numerical simulation results are in good agreement with measurement ones. Moreover, we also investigate the capability of the proposed HM to resolve sources with subwavelength distance of about and at 0.5 and 1 GHz, respectively.Index Terms-Hyperbolic metamaterials (HMs), subwavelength focusing, subwavelength resolution, transmission lines (TLs).

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Here, a new strategy of ultra‐broadband monostatic and bistatic radar cross‐section reduction (RCSR) was theoretically investigated. A circular configuration of perforated dielectrics, as the coating layer, was designed to have full control on the bistatic RCS signatures of flat metallic objects. Using the proposed phase cancellation method, a customised level of bistatic RCSR (BRR) as well as operating frequency bandwidth were interpretively achieved. The presented study offered a robust and straightforward RCSR technique which does not rely on conventional blind optimisations. The coating layer was capable of reducing the monostatic and BRR of >10 dB in a broad frequency range from 8.3 to 23.1 GHz (BW = 94%). The results were significantly improved compared to those of preceding researches. Besides, unlike the preceding researches, the performance of the designed coating layer was analytically justified under TE and TM polarisations of oblique incidences. A good agreement was observed between numerical simulations and theoretical predictions, confirming the polarisation‐independent feature of the designed stealth coating layer for incident angles up to 60∘. These superior performances and the flexibility of design guarantee the applicability of the proposed RCSR approach for various stealth applications.