ABSTRACT In this paper, a compact wideband circularly polarised (CP) nonuniform metasurface (MTS) antenna loaded with parasitic elements is proposed. Characteristic mode analysis (CMA) is employed to analyse the proposed MTS antenna. The nonuniform MTS radiator is formed by elliptical‐shaped patches etched with circular slots of different diameters and fed by a Y‐shaped microstrip line through an L‐shaped coupling slot. Furthermore, four parasitic patches are placed along the edge of the MTS to enhance the impedance bandwidth (IBW) and axial ratio bandwidth (ARBW). The measured IBW and 3‐dB ARBW are 50.7% (4.37–7.34 GHz) and 35.3% (4.55–6.5 GHz), respectively. A maximum gain of 7.1 dBic is achieved at 5.3 GHz. The novelty of this study lies in the utilisation of nonuniform elliptical‐shaped MTS elements combined with parasitic patches, which effectively enhances the CP bandwidth.
ABSTRACT This paper presents the design, modelling, and experimental validation of a broadband 1‐bit reconfigurable transmitarray (RTA) for transmissive beamforming at 11.7 GHz. A receive–transmit (Rx–Tx) unit cell is developed by introducing interdigital structures on both the receive and transmit layers, providing capacitive loading and additional high‐frequency current paths without requiring an air gap. The proposed unit cell achieves a 3‐dB transmission‐loss bandwidth of 23.1% from 10.48 to 13.18 GHz, with a transmission loss of 1.6 dB and a 1‐bit phase difference within 180° ± 20° at 11.7 GHz. To connect the unit‐cell scattering response with array‐level performance, an end‐to‐end link gain model incorporating frequency‐dependent EM‐acquired complex radar cross section (CRCS) patterns is proposed. The model evaluates both the RTA antenna radiation gain and the RTA scattering characteristics, including its RCS and equivalent relay‐gain interpretation. A 32 × 32 RTA prototype with a 32.5 × 32.5 cm 2 aperture is fabricated and measured. The measured results demonstrate beam scanning from 120° to 240°, a boresight gain of 20.7 dBi, a maximum scanning loss of 3.5 dB and a 3‐dB gain bandwidth of 19.7%. The proposed model effectively predicts the main‐beam direction, gain trend and gain‐frequency response.
ABSTRACT Four new fractal frequency selective surfaces (FSS) wideband discriminators for instantaneous frequency measurement (IFM) systems based on the balanced Gray‐code are presented in this paper. The use of a balanced binary code in the design of the discriminators enables the implementation of a 4‐bit IFM system using only dual‐band discriminators, operating in the 1.2–5.6 GHz range. The FSS patterns are based on recursive Sierpinski space‐filling geometries, which allow a significant reduction in the size of the discriminators while enabling dual‐polarisation operation. The numerical analysis is compared with the experimental data with good agreement, demonstrating the feasibility of compact low‐frequency FSS‐based IFM.
ABSTRACT In this paper, a low‐cost, flexible, ultrathin absorber comprising a simple square patch‐shaped frequency selective surface (FSS) is proposed for wearable applications. The FSS‐based absorbing structure contains a periodic graphite patch pattern placed on a thin paper substrate and backed with a copper foil‐based ground plane. The dimension and periodicity of the unit cell are 0.31 and 0.36, respectively, whereas the thickness of the absorber is approximately , where is the wavelength of free space at 10 GHz. The characteristics of the FSS absorber are optimised in terms of unit‐cell periodicity and dielectric substrate height using a full‐wave high‐frequency structure simulator (HFSS) software. The effects of the parameters are also examined using an equivalent circuit approach. The proposed absorber shows insensitivity towards the angle of incidence and the angle of polarisation. Finally, a prototype model is fabricated, measured and validated with simulation results. Good agreement is observed between the simulated and experimental models. The proposed absorber finds application in the fields of wearable electronics, medical applications and automotive applications for the effective mitigation of the EMI.
ABSTRACT A broadband reflective Linear‐To‐Circular Polarization (LTCP) converter is proposed in this work. Such a mechanically simple structure converts a linearly polarised incident plane wave into a circularly polarised reflected one with a minimum loss. In its design, an anisotropic metallic grating printed on the interior side of an inhomogeneous superstrate is utilised. Each re‐radiating element of this array is composed of a double concentric ring in which the inner ring is attached to two arc lines. The inhomogeneous superstrate, formed by a low‐cost FR4 dielectric slab with periodically drilled air holes to reduce structure loss, is mounted above a copper plane with an optimised spacing to minimise reflective wave loss. The dimensions of its unit cell are 10.6 × 10.6 × 1.8 mm 3 (0.25 λ × 0.25 λ × 0.043 λ ), where λ represents the free‐space wavelength of the lowest frequency in the operating bandwidth. To validate the numerical results, the designed structure with 12 × 7 cells is fabricated and tested. Measurements demonstrate the Axial Ratio (AR) < 3 dB, indicating near‐ideal circular polarization and the Polarization Conversion Rate (PCR) approaches unity within 7.2∼12.6 GHz. Such a structure can be used in various applications, such as weather monitoring multi‐beam/beam scanning antennas, wireless/radar tracking and navigation systems.
