Synthetic aperture interferometric radiometer (SAIR) requires lots of antennas, receivers, and correlators to accurately reconstruct the brightness temperature (BT) distribution of the scene. Aiming to reduce the complexity of the hardware requirements in SAIR system while maintaining the image quality, a new optimal sparse reconstruction method is developed in this paper. Different from the existing imaging methods, the proposed method constructs the optimal receiving array with a few elements by evaluating the mutual coherence and the array factor of the sensing matrix in SAIR system, so as to achieve high-quality reconstruction of the BT image. Numerical simulations and experiments demonstrate that the proposed method can reconstruct the BT image by solely using a few receivers with higher image fidelity than the competing methods.

A W-band dual-circular-polarization (dual-CP) monopulse Cassegrain antenna for polarization detection of radar target is presented in this letter. The proposed antenna consists of a main reflector, a sub reflector, a dual-CP feed source based on the septum polarizer, and a comparator. Two orthogonal circular-polarized signals [left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP)] electromagnetic wave can be transmitted and received simultaneously by this antenna. The principle of the antenna is introduced and analyzed, and then a prototype of the antenna is simulated, fabricated, and measured. Measured results are in good agreement with the simulated ones. At 94 GHz, the gains of the LHCP and the RHCP sum beam (SUM beam) are 38.6 dBi and 38.8 dBi counting the insertion loss of the comparator, which indicates that the radiation efficiency is better than 44.2%. The 3-dB beamwidth is about 1.5° with a sidelobe level (SLL) of -16.6 dB, and the axial ratio is lower than 1.43. A null depth of -26 dB for the difference beam (DIFF beam) is observed, and the gain ratio between the LHCP monopulse beams is 5.9 dB. Measured results demonstrate that the proposed antenna is very applicable in the polarization detection of radar target at W-band.

A sensor to accurately predict chemical concentrations has been proposed in this research work. Inspired by Metamaterials, the sensor is composed of Complementary Split-Ring Resonators (CSRRs) and utilizes the Machine Learning technique to accurately predict the concentrations. The sensor is designed to maximize the interaction of the Material Under Test (MUT) with the sensitive regions of the CSRRs. The usage of costly and complex fluidic channels and sample containers is avoided by using filter paper for the liquid MUT placement in between the resonators. The proposed sensor is small (2.3 cm × 2.3 cm), simple, employs a low-cost fabrication technique and offers an alternate sensing mechanism that requires a minimal amount of the MUT. The multiple resonances exhibited by the proposed sensor add to the reliability and accuracy of the sensor.

In this paper, a high front-to-back ratio (FTBR), broad bandwidth planar printing structure, and electromagnetic dipole complementary antenna that generates end-fire radiation pattern is investigated. The antenna consists of a segmented loop, planar electric dipole, and microstrip coupling feed structure, which are printed on the top and bottom surfaces of a dielectric substrate. The segmented loop is equivalent to a magnetic dipole. A high front-to-back ratio is achieved by combining the electric dipole and equivalent magnetic dipole with the same radiation intensity and antiphase. The proposed antenna is fabricated and measured. The measured results show that the proposed antenna achieves an impedance bandwidth of 48.05% (1.66 GHz-2.71 GHz). The largest gain can get to 3.89 dBi, and the maximum front-to-back ratio is 25.4 dB in the frequency band. The measured results are well consistent with simulated ones.

Many static and rotating electric energy converters make use of inductive coils as filters, reactive loads or exciters, where a sudden variation of the magnetizing current can produce severe overvoltage with potential subsequent insulation damage. In some applications the overvoltage is the result of a superposition of travelling voltage waves in a supplying line. Traditional tools for studying such phenomena are based on ordinary differential equations that can heavily handle variable parameters, especially if they change according to the rapidity of the observed overvoltage. In this paper the transient voltage distribution in the excitation winding of a salient pole synchronous generator is simulated by solving the problem entirely in the frequency domain, i.e., without any use of the traditional ordinary differential equations solvers. Thismakesit possible to tune the parameters of a simplified electric model to the frequency response of the studied winding. It is shown that for highly inductive windings a single transmission line model with frequency dependent parameters can reproduce voltage transients very accurately, in a broad interval of frequency, relevant for power electronics and electromagnetic compatibility applications. Furthermore, the paper presents the experimental setup which has been needed for generating the fast varying voltage edges.

The next generation 4T4R Multiple Input Multiple Output (MIMO) antenna solution is gradually accepted by operators in many countries as a mainstream expansion to long term evolution (LTE) networks. Using limited spectrum and high capacity, operators have successfully adopted multi-sector 4T4R MIMO deployment and achieved a 70% increase in capacity without increasing spectrum, thus paving way for state of art next generation wireless networking environment requiring antennae that are robust, small size, lighter, preferably with circular polarization. MIMO antennae provide optimality by arresting multipath fade effect and ensuring data link that is reliable. MIMO realizes efficiency in mobility with increase in capacity of links and several sub-bandwidths using polarization diversity providing better cybersecurity. This work therefore is an investigation on a small size 4T4R MIMO antenna for the use in a sub-6 GHz new radio (NR) band in a fading environment with good inter element as well as radiation isolation compared with earlier research. A rectangular patch with loaded slots is designed to obtain small size. Stubs and parasitic elements are introduced between the elements for better mutual coupling performance. Performance of the antenna is stable, with the test results agreeing. The parametrics follow the coefficient of transmission isolation technique to obtain an optimal envelope correlation coefficient.

An efficient biochemical sensor for the detection of cholesterol concentration using 1-dimensional photonic crystal (1D-PhC) based cavity structure has been proposed in this paper. The structure comprises a 1-dimensional alternating dielectric photonic crystal designed as (A/B)²/D_d/(A/B)² for measuring cholesterol concentration in blood, where `A' and `B' represent high and low refractive index materials, respectively. A cavity containing the cholesterol is inserted in the middle of the structure to assess its concentration. The transfer matrix method is used to analyze the reflection characteristics of the proposed multilayer structure. Sensitivity is analyzed by taking the difference in shifted resonant wavelength by infiltrating varying cholesterol concentrations ranging from 200 to 300 mg/dl. After rigorous optimization, it has been observed that the maximum sensitivity of 2.9 nm/(mg/dl) or 325 nm/RIU can be achieved.

We propose a transmission metasurface (TMS) with ultra-high polarization conversion properties and carrying orbital angular momentum (OAM) vortex waves based on Ku-band's unique periodic unit cell structure in Ku-band. The TMS periodic unit cell structure consists of four cascaded metal layers with parallel-stripe double-arrow and three dielectric layers. We theoretically explain the ultra-high polarization conversion properties of the periodic unit cell by introducing the Jones matrix. Meanwhile, the transmission loss of the periodic unit cell is less than 2.92 dB, and a phase shift of 2π is obtained in 17-19 GHz. We design OAM modes of ±1, ±2, and ±3 for 2π full-phase controlled TMSs by combining the multilayer cascade structure with the Pancharatnam-Berry (P-B) phase principle. The processed TMS produced a vortex wave with an OAM mode of +2 and achieved a polarization conversion rate (PCR) of 83.3% under left-hand circular polarization (LHCP) to right-hand circular polarization (RHCP) in agreement with the simulated and measured data. The results show that vortex waves also have the advantages of high efficiency, broadband, and high mode purity. The generated vortex waves are available for fast beam alignment, which is significant for unmanned aerial vehicles (UAVs) and satellite communications in the Ku band.

In passive radar systems, target echoes are submerged in the sidelobes of the static clutter, which includes multiple reflection echoes from the objects located in the operating environment of the considered system. This undesired part of the collected signals degrades the detector performances. Consequently, the reduction of the static clutter contribution is essential to ensuring an efficient operation of passive radars. In the literature, many algorithms and methods have been proposed for clutter suppression, where a good quality of the received signals is required to ensure an efficient clutter suppression. These methods require a considerable amount of data to operate which increases the complexity and the calculation load of the algorithms. In this paper, an important contribution is brought by simultaneously improving the signals quality and reducing the calculation load in the static clutter suppression process. Since the static clutter can be considered as time-invariant, the proposed approach exploits the specific architecture of the DVB-T signals to provide a noise reduction in the receiving channels by averaging the received signals after being split into symbols. Three different methods are proposed to examine the efficiency of the proposed approach. The performances of the proposed approach are validated through a set of simulations and verified using real data.

The aim of the next-generation 5G wireless network is to provide high data rates, low latency, increased network capacity and improved quality of surface (QoS) for wireless communication and internet of things (IoT). The millimetric wave communication is a promising technique with the capability of providing multi-gigabit transmission rate, network flexibility and cost-effectiveness for 5G backhauling. Smart antennas are a critical requirement for the success of millimetric wave communication system, and these antennas have the capability to form a high gain beam in desired direction and a null towards interfering signal. Directional beam-forming mitigates the high path loss associated with millimetric communication & improve signal to interference noise ratio. This article presents comparative analysis, effectiveness, and current limitations of various beam steering techniques for 5G networks based on some figures of merit with the aim of highlighting areas of improvements for each beam steering technique.

In this paper, the development and design of angle independent Metamaterial Microwave Absorbers (MMAs) are presented. The unit cell consists of four trapezoids that are linked by consolidated resistors with the coextensive squares. The absorber is built on a dielectric substrate (FR4) with a thickness of 0.256 mm (λ/144) and a dielectric constant of 4.3. The wideband absorption is acquired in the range of 2.21 to 6.61 GHz with a wide band of 4.40 GHz with absorptivity above 90%. In the area of interest, a flat band is obtained, and to examine the current distribution and electric field in the respective region two peaks are considered at a frequency of 2.49 and 5.68 GHz, with maximum absorptivity of 92.50% and 92.14% respectively. The presented absorber is examined under different angles for phi and theta variation. From the phi variation, it is observed that for all the angles absorptivity does not vary which confirms that the absorber acts as an angle independent. The fabricated sheet consists of an array of a unit cell, which is examined inside an anechoic chamber with the help of two horn antennas and VNA. The tested and simulated results are compared, and it was observed that they are in close agreement. At last, the presented and already reported MMAs are compared, and it is observed that the presented one operates for the low frequency with higher bandwidth. The presented absorber can be practically used for defense applications for Radar Cross Sections (RCS) reduction.

This paper presents the design of a frequency reconfigurable monopole microstrip patch antenna for wireless communication applications. The proposed antenna functions in one single-band mode and one dual-band mode, depending on the diode switching configuration. When the diode is in the OFF state, the proposed antenna operates at single band 5.8 GHz (WLAN), and in the ON state, the antenna operates at dual bands 1.8 GHz (GPS/RADAR) and 5.2 GHz (WLAN). To enhance the gain of the proposed reconfigurable antenna, a multilayer frequency selective surface (FSS) reflector is presented. A significant enhancement in gain has been achieved in a low-profile design. The average peak gain of the antenna has been increased from 4 dBi to 6 dBi as a consequence of the use of the FSS reflector. The simulation of the proposed design is carried out using CST (Computer Simulation Technology) based on the FIT (Finite Integration Technique) numerical method. To validate the simulated results, a prototype of the antenna was fabricated and measured using PIN diodes. The simulated and measured results of the proposed antenna exhibit a reasonable agreement.

This paper presents a new design of a compact microstrip ultra-wideband (UWB) single notch-band bandpass filter (BPF) along with its equivalent circuit model. The basic structure of the proposed filter consists of dual symmetrical multiple-mode resonator (MMR), four stub-loaded stepped impedance resonators (SLSIRs), two defected ground structure (DGS) units and a coupled folded arm resonator (CFAR) with feeding line. The presented filter is tested using R&S® ZNB20 vector network analyzer (VNA) to validate the simulated results. A good agreement between the measured and simulated (EM and circuit model) results is achieved.

The concentration induced permittivity change involves a dispersion which occurs at the resonant frequency, and is often not predictable by simulation using the traditional Cole-Cole model. To overcome this problem, a new Lorentz's model is proposed as a substitute for the Cole-Cole model. Under this new model, the glucose concentration is expected to be measured at the contact interface in the form of a resonant frequency shift. With the help of the model, a contact-based meander-line antenna sensor (CMS) is realized with a high ``sensitivity of 1.3158 dB/(mmol/L) in terms of d |S<sub>11</sub>|/dC, or of 17~18 MHz/(mmol/L) in terms of'' dω/dC. The model has been experimentally validated with in-vitro measurements and for proof-of-concept with in-vivo clinical investigations in the microwave frequency. Consistent with the predictions of model, a linear ``correlation is observed not only between the resonant frequency shift and the glucose concentration, but also between the S-parameters magnitude and glucose'' concentration.

In this paper, a microstrip millimeter-wave (MMW) array antenna with a Defected Ground Structure (DGS) has been presented for the applications of fifth generation (5G) wireless networks. This novel antenna, which has small dimensions with higher gain, can be used for licensed 5G applications in many countries, like the United States of America, Canada, Australia, Japan, India, and China. It also covers a band that is planned for licensed use in some countries, like Colombia and Mexico. The proposed model has a single element design, and for gain and efficiency enhancement, a two-element array has been designed. Both single and two element models resonate at a frequency of 39.96 GHz. Using a commercial electromagnetic simulator (CST-Studio), the model was designed and optimized with the goal of achieving a return loss rate of less than -10 dB. The proposed antenna is built on a compact Rogers substrate (RT-5880) with dimensions of 6 mm x 6 mm for the substrate of the single element and 9 mm x 13 mm for the two-element array. The substrate has a thickness of 0.508 mm, a dielectric constant ε_r of 2.2, and a loss tangent tanδ value of 0.0009. This suggested design is small, low profile, and simple to guarantee the dependability, mobility, and high efficiency needed to be used with a variety of 5G wireless applications. The high gain of 11.6 dBi for the two-element array model of the proposed antenna is one of its distinctive features. The suggested single element model has an impedance bandwidth of 2.3 GHz, and 2.1 for the two-element array model, satisfying efficiency of approximately 73.5% for the single element and 85% for the two-element array model, respectively. The proposed structure, compared to other designs found in the literature, has smaller size while maintaining other parameter values of comparable orders.

In the paper, a compact single-fed wide-beamwidth circularly polarized (CP) antenna is proposed. The main radiator of the antenna is a bent dielectric resonator (DR), which is conformal to a rectangle substrate with the same curvature and is excited through a crossed-two-ring slotted ground fed by a T-shaped feeding line. By bending the DR to different curvatures, the half-power bandwidth (HPBW) of the dielectric resonator antenna (DRA) can be adjusted. Besides, to improve the 3-dB axial ratio (AR) beamwidth, as well as further enhance the HPBW, a copper reflector is inserted below the DRA. A prototype operating in BeiDou Navigation Satellite System (BDS) B1 band (1.561 GHz) was designed, and measurement was done to verify the simulations. Measurement results show that from 1.55 GHz to 1.58 GHz, the return loss is more than 10 dB and the AR is less than 3 dB. At 1.561 GHz, the measured 3-dB AR beamwidths are 165° and 210° at xoz and yoz planes, respectively, while the HPBWs are 143° and 154° at the two planes.

In this letter, a novel ultra-wideband (UWB) bandpass filter (BPF) configuration with a quad-mode resonator (QMR) structure is proposed, which hasa highly selective and compact performance. The QMR is composed of a funnel-shaped resonator loaded in the middle and a low-impedance folded microstrip line. Initially, the resonant frequencies are uniformly distributed in the UWB passband by varying the length of QMR physical stubs, and later the three-line parallel coupled lines are employed to enhance coupling to obtain a flat passband. The feedlines are then loaded with a pair of λ/2 stepped impedance radial stubs (SIRSs) to provide excellent band-stop characteristics. Finally, a filter prototype is created, and its performance is evaluated using the generated data. The proposed UWB filter has sharp roll-off ratio of 99 and 63 dB/GHz, respectively, at the lower and upper edges of the passband.

A wide-band dual-circularly polarized transceiver antenna with high port isolation is proposed in this paper. The antenna element uses M-shaped and U-shaped microstrip lines to excite the quasi-cross-shaped aperture to achieve wide-band and lower cross-polarization level. Dual-circular polarization is accomplished via the sequential rotation technique. To obtain high port isolation of the antenna, phase cancellation technique and decoupling structure are utilized. The measurements show that the impedance bandwidth with reflection coefficient less than -10 dB is larger than 34.5% (4.6-6.5 GHz) for left-hand circular polarization (LHCP) port and 29.8% (4.86-6.5 GHz) for right-hand circular polarization (RHCP) port, while the 3 dB axial ratio bandwidth for LHCP and RHCP is greater than 29.1% (4.8-6.4 GHz) and 32.7% (4.7-6.5 GHz), respectively. The port isolation of the antenna is higher than 30 dB in 4.5-6.5 GHz band. The peak gain is about 12 dBic.

A super wideband coplanar waveguide-fed antenna is proposed for Microwave Imaging (MI) applications. The antenna comprising a slotted patch and a defected ground structure (DGS) loaded with a stub has been prototyped on a 1.6 mm thick glass-reinforced FR4 material with an εr of 4.4. The antenna has a size of 0.12λ₀×0.12λ₀ at the lowest operating frequency of 1.21 GHz. The slotted patch coupled well with the stub-loaded DGS in the ground plane and led the proposed antenna to obtain a range of operational bandwidth from 1.21 GHz to 24.66 GHz. Initially, with a rectangular patch, a super wideband antenna with five notch bands is achieved. To eliminate four notch bands and realize the super wideband two rectangular slots are etched in the patch. The last notch band is eliminated by loading the ground with a stub. To make the proposed antenna a compact space-saving one, the patch is fitted in a hexagonal slot etched in the ground. The experimental result reveals a super wideband performance of 181% (1.21 GHz-24.66 GHz) with a consistent radiation pattern and peak gain of 9.4 dB in a compact area of 30 mm².

When a planar microstrip patch antenna is conformed to any non-planar surface (e.g., aircraft, missiles etc.), the curvature of the host surface affects its design parameters, which in turn affects its radiation performance. Therefore, achieving a target radiation performance with a planar antenna on a non planar host surface is always a big challenge for an antenna designer. To address this issue, a report on an electromagnetic simulation-based method to optimize a planar-shaped microstrip antenna array conformed to a cylindrical surface is presented here. HFSS was used to investigate the role of different design parameters of the antenna array in the planar and cylindrical planes (for different radius of curvature). Finally, using these simulation observations, the dimensions of the planar antenna conformed to a cylindrical surface (with a radius of curvature of 110 mm) were optimized to achieve a target output performance (in terms of gain, return loss, and VSWR) while retaining its radiation pattern geometry as well as polarization characteristics. A planar 2×2 circularly polarized antenna array with a conical beam pattern from the published literature was used to carry out the current work. After rigorous optimization, return loss < -19 dB, VSWR of 1.807, and as much as 8.135 dBi gain at 2.45 GHz have been achieved. This report should be a useful guide for mounting any planar antenna array on a non-planar host surface. And it will also be helpful to design conformal microstrip antennas for different practical applications.