Sayan Chatterjee

This letter presents a non-linear phase modulated (NPM), dual beam, circularly polarized (CP) scalar impedance modulated (SIM) metasurface-based leaky-wave antenna (LWA) with butterfly-shaped beamforming, operates at fr = 15.5 GHz. A comprehensive NPM technique is analytically presented to obtain proposed metasurface based LWA. The proposed NPM function is numerically realized by its magnitude and phase response. Using NPM, a dual beam LP surface impedance (Zsurf) is analytically mapped into CP impedance with simulated and measured data validation of proposed dual beam, circularly polarized (CP) LWA. An overall dimension of 15λ ₀ ×7.5λ ₀ yields highly directive dual beam (i.e. {θ _n, ϕ _n } = {(-35°,0°), (32°,0°)}) with a maximum realized gain (gmax) of 21.52 dBic and half-power beamwidth (HPBW) of 4.2° each. A wideband axial ratio beamwidth (ARBW) of 1.8 GHz is obtained with an overall axial ratio (AR) of <1.2dB

The design of a fourth-order centrally corrugated double-folded hairpin line bandpass filter with a broad stopband and enhanced selectivity is demonstrated in this article. Initially, a double-folded hairpin-line bandpass filter (DFHLBF) is designed from a fourth-order conventional hairpin-line bandpass filter (CHLBF), which is centred at 2.5 GHz and has a fractional bandwidth of 3%. This results in a 68% size reduction. With this folding mechanism, the filter's skirt characteristic is only enhanced at the upper passband edge, resulting in an attenuation level of 40 dB at 2.65 GHz. The capacitive loading has then been incorporated by periodic rectangular corrugations that have disturbed the folded arms. Because of the high capacitive coupling between the folded arms, a symmetrical passband with an attenuation level better than 40 dB at both edges has been observed. Besides, a size reduction of 14% than that for the DFHLBF has been achieved. However, because of the imbalance of the modal phase velocities in the inhomogeneous microstrip filter construction, the stopband's attenuation level climbs to 8 dB. Rectangular meander spurlines have been added between the connected arms of the neighbouring centrally corrugated cells of the filters as a way to lower the attenuation levels of the harmonics. This creates a slow-wave effect between the odd- and even-modes of the propagating signals. This results in an overall size reduction of 81% over the standard hairpin-line filter and an enlarged stopband of up to 4.36f0 with a rejection level of 42 dB.

In this article, a novel method of fault detection in nonuniformly excited linear antenna array has been reported. This method uses an evolutionary algorithm-based technique to generate approximate radiation pattern in tune with reference faulty pattern for a nonuniformly excited linear antenna array. Based on the approximation, a binary sequence-based method of exact fault detection has been developed. In order to illustrate the effectiveness of the method, 12- and 20-element Dolph Tschebyscheff linear antenna array with amplitude fault has been considered. Superiority of the proposed method has been demonstrated through comparative study.

The article presents the design of a compact narrowband microstrip cross-coupled bandpass filter with improved selectivity and a wide stopband. The proposed fourth-order quasi-elliptic filter is designed at 2.5 GHz with a fractional bandwidth of 4% suitable for WLAN applications. At first, doubly-folded half-wavelength hairpin lines have been arranged symmetrically in a cross-coupled configuration combining the electric, magnetic, and mixed-coupling. Accordingly, a size reduction of 17% over the folded inline hairpin-line filter with the same specifications has been achieved. Moreover, the selectivity has been improved greatly by the introduction of two deep transmission zeros with an attenuation level of 48 dB at the edges of the passband. However, the presence of the spurious harmonics with an attenuation level of 10 dB limits the performance of the filter related to the stopband rejection. As a remedy, conventional and meander spurlines have been incorporated in each hybrid coupled section of adjacent cross-coupled cells for achieving the modal phase velocity compensation. Accordingly, an extended stopband with a rejection level of 38 dB up to $4f_{0}$ has been recorded by using a meander spurline and an overall size reduction of 33% has been achieved.

The present article exhibits the improvement in wide stopband harmonic suppression techniques of fourth-order compact hairpin-line Chebyshev type narrowband (4%) bandpass filter centered at 2.5 GHz by meander spur-line. Initially, the compactness of 42% over the conventional hairpin-line cell has been achieved by folding the open-end arms of the hairpin line to folded hairpin-line cell. Accordingly, the improvement of the skirt characteristics and the shifting of the harmonics to higher frequencies have been observed with the cost of harmonics attenuation levels' degradation. Subsequently, an improvement in the stopband rejection level of 40 dB up to 4f₀ has been achieved by incorporating meander spur-line to all the coupled edges of the adjacent folded cells of the compact filters along with compactness of 38%.