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This paper presents the design of 2.5D frequency selective surface (FSS) for X and Ku band applications. Proposed FSS's unit cell is constructed with two independent slitted rings on both side of the FR4 substrate and is connected with metallic vias. The FSS offers a wide stop band performance from 6.26 to 18 GHz, with a fractional bandwidth of 96.7% measured at S21 < −10 dB and has a low insertion loss (IL) of 0.018 dB. The footprint of the FSS is only about 0.11λL ${\lambda }_{L}$ with the shielding effectiveness of 83.365 dB, and the transverse electric and transverse magnetic mode performances are stable up to 70 degrees. Prototype FSS is fabricated and measured for its performance validation. The performance validation is carried out using applied wave research and the equivalent circuit model tools. [ABSTRACT FROM AUTHOR]

This paper presents the design and prototype development of a compact frequency‐selective surface (FSS) for shielding WLAN signals. The FSS unit‐cell geometry is evolved by modifying the arms of the conventional crossed dipole element. The footprint of the unit cell is only 6 mm × 6 mm × 1.6 mm. The proposed FSS offers stop band characteristics at 5 GHz for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the FSS offers angular stability up to 60°. A prototype of the proposed FSS is fabricated and measured to validate its simulations. Measured bandwidth of the stop band is 410 MHz, referenced at −20 dB for both TE and TM modes. Equivalent circuit model of the FSS is derived and the results are compared with the simulations. [ABSTRACT FROM AUTHOR]

This paper presents the design of multiband frequency reconfigurable patch antenna with switchable radiation pattern and polarization states. The antenna design is based on a circular patch radiator with a pair of metallic strips placed on diametrically opposite sides of it. Circular polarization (CP) from the antenna is excited by etching a pair of slots with a coaxial feed. When the diodes are OFF, the antenna resonates at 4.2, 6.6 GHz, (C band) and 8.07 GHz (X band) and the main beam is located at 0⁰ with CP at X band. The resonance at 4.2 and 8.5 GHz are observed when one of the diode is ON. The main beam at X band is being shifted from −30⁰ to 0⁰ and +30⁰ in the elevation plane during the change in operating modes. Peak gain of the antenna is 6 dBi in all the operating modes. [ABSTRACT FROM AUTHOR]

Summary: This paper proposed the design of a broadband linear‐to‐circular reflecting polarizer for X‐band applications. The polarizer is designed with three‐arm dipole‐shaped unit cells with a full ground plane to get wideband performance. The incident linear polarized wave is converted to a right‐handed circularly polarized wave upon reflection from the polarizer. The footprint of the unit cell is 9 × 9 mm, which is printed on a FR‐4 substrate. Fabricated prototype is measured for its performances like polarization conversion ratio (PCR), fractional bandwidth, and aperture efficiency. The PCR is about 97%, and the fractional bandwidth is 64% with the aperture efficiency of more than 80%. Polarizer performance is analyzed in transverse electric and transverse magnetic modes, and they are stable up to 40° of various incident angles. The polarizer exhibits the 3‐dB axial ratio bandwidth from 8 to 12 GHz, which is suitable for satellite applications. [ABSTRACT FROM AUTHOR]

The coronavirus disease 2019 has severely affected the financially constrained small and medium enterprises (SMEs). In response, various countries employed several policies to support SMEs. Using rich firm‐level data from 34 countries, we study the impact of the pandemic‐led crisis on cash‐strapped SMEs and the role of governments in offsetting losses. Our results suggest that (i) government support programmes target mostly financially constrained firms; (ii) firms adjustments to the pandemic are associated with the likelihood of government support; (iii) financially constrained firms are more likely to lay off workers; and (iv) financially constrained firms layoff more male employees than female employees. [ABSTRACT FROM AUTHOR]

In this study, a passive Vivaldi antenna design is proposed for radar cross section (RCS) reduction using object shaping method. The implementation of annular slot along with exponential curves in the radiator reduced the scattering along the surface of the radiator. This contributes reduction in structural mode RCS throughout the operational bandwidth without affecting the impedance performance of the antenna. Monostatic RCS of the antenna is discussed for two incident angles. A minimum RCS reduction of 13 dB is achieved when the incident angle is Θ = 60° and a maximum of 19 dB reduction is achieved at Θ = 75°. The proposed antenna offers symmetric radiation pattern in both azimuth and elevation planes and also maintains co-polarisation to cross-polarisation ratio of 19 dB throughout the X-band (8-12 GHz). Prototype antenna is fabricated and tested to validate the simulated results. [ABSTRACT FROM AUTHOR]

In this study, a modified antipodal Vivaldi antenna (AVA) with low cross-polarisation is proposed for ultrawideband communications. The bandwidth offered by conventional single petal AVA is enhanced by adding another petal. This dual petal antenna occupies a small volume of 60 × 60 × 0.8 mm3 and provides operating bandwidth from 2.4 GHz to frequencies >14 GHz. The proposed antenna configuration provides low cross-polarisation level which is <-15 dB over the entire operational band. The designed antenna offers realised gain >5 dB and an average group delay variation of 0.5 ns. The prototype antenna is fabricated and tested to validate the simulation results. [ABSTRACT FROM AUTHOR]