Compact notch filter design using stepped impedance resonators for sharp roll-off and large wideband rejection

This article presents the design of a compact notch filter with a sharp roll-off and high rejection over a wideband. The filter comprises stepped impedance resonators that are interconnected to each other at strategic points on the resonator for optimal 3 dB roll-off and high rejection over a wide stop-band. The fabricated third-order filter exhibits a steep 3 dB roll-off and rejection exceeding 50 dB over the frequency range 2.70–6.19 GHz

Dual-Band RFID Tag Antenna Based on the Hilbert-Curve Fractal for HF and UHF Applications

A novel single-radiator card-type tag is proposed which is constructed using a series Hilbert-curve loop and matched stub for high frequency (HF)/ultra high frequency (UHF) dual-band radio frequency identification (RFID) positioning applications. This is achieved by merging the series Hilbert-curve for implementing the HF coil antenna, and square loop structure for implementing the UHF antenna to form a single RFID tag radiator. The RFID tag has directivity of 1.75 dBi at 25 MHz, 2.65 dBi at 785 MHz, 2.82 MHz at 835 MHz and 2.75 dBi at 925 MHz. The tag exhibits circular polarisation with -3 dB axial-ratio bandwidth of 14, 480, 605 and 455 MHz at 25, 785, 835 and 925 MHz, respectively. The radiation characteristics of the RFID tag is quasi-omnidirectional in its two orthogonal planes. Impedance matching circuits for the HF/UHF dual-band RFID tag are designed for optimal power transfer with the microchip. The resulting dual-band tag is highly compact in size and possesses good overall performance which makes it suitable for diverse applications

Compact Quad-Band Bandpass Filter Based on Stub-Loaded Resonators

This paper presents a planar quad-band bandpass filter with high out-of-band rejection. The filter is based on intercoupled stub-loaded resonators, where pairs of resonators are electromagnetically coupled to each other and the feedlines. This results in excitation of passbands, where the first and the third passbands are generated by /4 resonators. The second and the fourth passbands are excited by /2 resonators. The proposed technique provides sufficient degree of freedom to control the center frequency and bandwidth of the four passbands. In addition, the five transmission zeros created around the passbands results in a quad-band filter with high selectivity, sharp 3 dB cut-off frequency, high isolation, and low passband insertion-loss. The proposed technique was verified practically. Design methodology and experimental results of the prototype filter are provided

Wideband Planar Array Antenna Based on SCRLH-TL for Airborne Synthetic Aperture Radar Application

This paper presents empirical results of a novel planar microstrip array antenna based on a simplified composite right/left-handed transmission-line (SCRLH-TL) for application in circularly polarized synthetic aperture radar (CP-SAR) systems operated in UHF, L, S and C-Bands. The array antenna consists of 6×6 matrix of spiral shaped radiating elements that are excited through proximity-coupled, single feed-line. Pattern synthesis technique is used to determine the excitation coefficients (amplitude and phase) to apply to the individual array elements to achieve the required pattern shape. The array antenna has dimensions of 111.5×96.06 mm2. The measured impedance bandwidth of the antenna is 3.85 GHz for S11 < -10 dB from 300 MHz to 4.15 GHz, corresponding to a fractional bandwidth of 173%. Maximum gain and radiation efficiency measured are 4.8 dBi and 79.5%, respectively, at 2.40 GHz. The antenna has a 3-dB axial-ratio bandwidth of 3.94 GHz from 144 MHz to 4.66 GHz. The antenna’s beamwidth in azimuth and elevation planes vary between 60° and 120° across its operational frequency range from 300 MHz to 4.15 GHz. The antenna design fulfills the challenging electrical and physical specifications required for CP-SAR employed onboard unmanned aerial vehicle (UAV)

A Compact UWB-BPF based on Microstrip-to-CPW transition with multiple Transmission zeros

Proposed in this manuscript is a miniaturized Ultra-Wideband (UWB) bandpass filter (BPF) based on broadside coupled technology wherein microstrip and coplanar waveguide (CPW) are present on either side of the substrate. The ground plane of the proposed BPF contains a short-circuited multiple mode resonator (MMR) based CPW which is electromagnetically coupled through the dielectric to two open circuited microstrip lines on the top. The MMR is initially designed to allocate its first three resonant modes quasi-equally within the specified UWB spectrum. Later, the back-to-back arrangement of microstrip lines is optimized to generate a tightly coupled broadband response. This configuration generates an UWB response possessing insertion loss <0.26 dB in simulation, two transmission zeros at the lower and upper passband edges that improve selectivity and a wide stopband with appreciable attenuation. The predicted theory is validated by testing the simulation result against the measured data of the fabricated prototype. The prototype measures only 14.6×9.2 mm2

Bandwidth extension of planar antennas using embedded slits for reliable multiband RF communications

In this paper a technique is described to extend the impedance bandwidth of patch antennas without compromising their size. This is accomplished by embedding capacitive slits in the rectangular patch with a truncated ground-plane, and exciting the antenna through a meandered strip-line feed. The proposed antenna was fabricated on standard FR-4 substrate with permittivity of 4.6, thickness of 0.8 mm and loss-tangent of 0.001. The performance of the prototype antenna was verified through measurements. Characteristics of the antenna include an impedance bandwidth of 5.25 GHz (800 MHz–6.05 GHz) for VSWR<2 corresponding to a fractional bandwidth of 153.28%, peak gain of 5.35 dBi, radiation efficiency of 84.12% at 4.45 GHz, and low cross-polarization. These attributes make the antenna applicable for stable and reliable multiband applications in the UHF, L, S and major part of C-bands. The antenna offers advantages of low cost, low profile, ease of manufacturing, durability and conformability

Compact and broadband 4×4 SIW Butler matrix with phase and magnitude error reduction

A novel two-layer 4 4 Butler matrix by feeding substrate integrated waveguide is designed and realized. The proposed Butler matrix has broadband operation frequency range of over 8.5 to 10.6 GHz with excellent phase and amplitude performance. The proposed design in this letter prevents the loss of amplitude and phase shifts in Butler matrix and decreases amplitude imbalance to less than 0.6 dB. This is achieved by reducing the size of Butler matrix and avoiding the use of a line length which causes a phase shift

A Novel Monofilar-Archimedean Metamaterial Inspired Leaky-Wave Antenna for Scanning Application for Passive Radar Systems

A novel backfire-to-endfire leaky-wave antenna is presented with ability to scan from -25ο to +45ο. The antenna is based on metamaterial transmission-lines (MTM-TLs) and is implemented using Monofilar Archimedean spiral and rectangular slots, spiral inductors and metallic via-holes. The slots act as series left-handed capacitances, and the spirals with via-holes provide the shunt left-handed inductances to realize the metamaterial antenna. A prototype antenna was fabricated prototype on FR4 dielectric substrate, which has an electrical size of 0.0302λo×0.0357λo×0.0008λo, where λo is free space wavelength at 165 MHz. Measured bandwidth of the antenna is 710 MHz (165-875 MHz) corresponding to a fractional bandwidth of 136.5%. The main advantage of the antenna is its ability to scan over a wide angle from -25 degrees to +45 degrees with acceptable gain and radiation efficiency of 1.2 dBi and 50.1%, respectively, measured at 400 MHz. The wide scanning attributes of the antenna make it suitable for passive radar applications to scan across the VHF-UHF bands for FM-Radio, television, mobile phones and GPS applications

A technique to suppress mutual coupling in densely packed antenna arrays using metamaterial supersubstrate

A simple and practical technique for reducing the mutual coupling between neighbouring antennas is presented for application in densely packed antenna arrays. This is achieved by locating between the radiation elements a smaller patch with metamaterial decoupling structure (MTM-DS). In this case the radiating elements are circular patches and the MTM-DS is constructed from a hexagonal slit resonator. The consequence of implementing the MTM-DS patch is significant reduction in mutual coupling between adjacent radiating patches by 60%, improvement in impedance match by 200% and substantial increase in the antenna’s fractional bandwidth by 369%. Since the ground plane is unaltered the front-to-back ratio is unaffected too. The proposed technique is easily realizable and can be used effectively in beam scanning applications

Multi-Way and Poly-Phase Wideband Differential Phase Shifter Based on Metamaterial Technology

This paper presents multi-way and poly-phase differential phase shifter (DPS) based on metamaterial technology to realize delay lines of equal length. The proposed phase shifter provides the required phase shift relative to the reference line over a wide bandwidth. Several DPS phase shifter designs were fabricated and tested to verify their performance. Measured results show that the proposed phase shifter has phase deviation of less than ±4° and return-loss better than 10-dB with an insertion-loss of less than 1 dB across 2.2 to 4.4 GHz