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.

A smart antenna synthesis approach is described as automatically choosing the optimum antenna type and providing the best geometric characteristics under the demands of antenna performance. Different antenna performance characteristics are examined, and using decision tree classifier, the optimal antenna is suggested using an intelligent antenna selection model. Finally, the geometric characteristics of the antenna are given before the fuzzy inference system is developed by merging five primary learners to fully exploit the benefits of each type of learner. Rectangular patch antenna, pyramidal horn antenna, and helical antenna are the three types of antennas that are classified by a decision tree classifier, and the optimal antenna size parameters are determined using a fuzzy inference method. The performance of decision tree classifier measured using accuracy and FIS is measured using Mean Square Error (MSE) and MAPE. The system demonstrates excellent capability in parameter prediction with antenna categorization with a MAPE of less than 5.8% and accuracy over 99%achieved in our proposed method. The recommended methodology might be widely applied in actual smart antenna design.

We propose a miniaturized triple band printed monopole antenna for 5G, WLAN, WiMAX and X-band applications. Slots are etched in a printed rectangular monopole to design the antenna. A slot etched in a rectangular monopole increases the capacitance and therefore, decreases the resonant frequency or miniaturizes the antenna. Slots in a rectangular monopole antenna also create different current path lengths which resonates at different frequencies. Three slots are etched, and parameters are optimized to achieve triple bands to operate over 5G (3.3 to 3.6 GHz), WiMAX (3.4 to 3.6 GHz), WLAN (5.725-5.875 GHz), WLAN 5.9 GHz band (5.850-5.925 GHz) and X-band (7.3-7.9). The lower 45 MHz (5.850-5.925 GHz), and upper 30 MHz (5.895-5.925 GHz) of WLAN band also find applications for automobile safety in Cellular Vehicle-to-Everything (C-V2X) technology. The radiation patterns are nearly omnidirectional. The antenna is fabricated on a 0.154λ₀×0.143λ₀ board area, where λ₀ is the free-space wavelength at 3.3 GHz. The measured results are in close agreement with the simulation ones.

This article presents a coplanar waveguide (CPW)-fed super wideband (SWB) elliptical slot monopole (ESM) antenna for wireless applications. The SWB impedance bandwidth (IBW) is achieved by symmetrical excitation of defective ground plane with a dodecagon-shaped annular ring (DSAR) radiator. The dimension of a prototype proposed antenna is 0.239λ_l × 0.253λ_l × 0.004λ_l mm³ (λ_l corresponding to the wavelength for the lowest operational frequency). A high bandwidth ratio of approximately 16.34:1 is produced by the combined radiation, with observed -10 dB IBW from 1.613 to 26.357 GHz (176.93%). Despite the cross-polarization levels being significantly suppressed in the H-plane, the basic concepts of an SWB antenna design have been successfully presented. Additionally, compared to other antennas mentioned in the literature, the proposed ESM antenna has a wider IBW. Successful fabrication, implementation, and comparison of the prototype with the experimental results are presented in this article.

Due to the restriction of the low-resolution systems and the interference of background clutter and environmental noise in the exploration process, the traditional classification and recognition algorithms of conventional radar for aircraft targets have low accuracy and poor feature stability. To solve the above problems, this paper proposes to apply high-order cumulant spectrum and deep convolutional neural network (CNN) to feature the extraction and classification of aircraft target radar echoes. Firstly, analyze the high-order statistical characteristics of aircraft echoes, calculate their bispectra, and then enhance the generated bispectrum dataset. Finally, use the augmented dataset to train and test the deep CNN, and obtain the final classification and recognition results. Experimental results show that the proposed method can accurately classify and identify multiple aircraft targets in the dataset, indicating that the bispectral features can better reflect the target characteristics, and the classification method combined with the deep learning model has good classification and identification performance and noise robustness.

This work introduces a novel compact 4-element MIMO antenna in the form of a q for use in the X-band. The proposed antenna has a footprint of 25 × 25 mm² and can be easily produced using a FR-4 epoxy substrate. The antenna consists of a 50-ohm microstrip line connected to ground and four q-shaped radiators. The antenna's impedance matching characteristics were analysed by performing a parametric study on its several parameters. The antenna has excellent impedance matching capabilities and operates between 7.2 GHz and 12.6 GHz. By utilising the connected ground technique and placing radiating elements in an orthogonal orientation, we can achieve isolation of greater than 15 dB. The measured and simulated results demonstrate the antenna's high peak gain of > 4 dBi and high radiation efficiency of > 90%, as well as its good impedance bandwidth (S₁₁ ≤ 10 dB) and isolation (S₂₁/S₃₁/S₄₁ of ≥ 15 dB). The presented antenna is a good option for X-band applications because its envelope correlation coefficient (ECC) is less than 0.00001, total active reflection coefficient (TARC) less than -10 dB, channel capacity loss (CCL) less than 0.03 bits/sec/Hz, and mean effective gain (MEG) less than -3 dB.

To utilise maximum amount of available optical energy it is necessary to design a solar cell with minimum reflectance from its surface. Broadband anti-reflection coatings are essential elements for improving the photo current generation of photovoltaic modules. The vast majority of antireflection coatings are required for matching an optical element into air. In this work, we choose the substrate of the structure that has an index sufficiently higher than the available thin film materials to enable the design of high performance antireflection coatings. This high index substrate is silicon (Si) of refractive index 3.54 at design wavelength 500 nm. Quarter wavelength optical thicknesses (QWOTs) of films of various dielectrics are coated with refractive indices calculated by ``Root-Principle''. The reflection spectra of visible radiation in normal and oblique incidence with antireflection coatings up to six layers will be analysed to achieve nearly zero reflectance.

We propose an original and detailed investigation of a moving dielectric half-space with oblique plane wave incidence, by using the Finite Difference Time Domain (FDTD) method. In our FDTD program, movements are implemented by changing positions of the interfaces at different time instants, through the classical FDTD time loop. With this ``brute-force'' approach, time is implicitly absolute, and Voigt-Lorentz transformations are not implemented. This technique is suitable for non-relativistic electromagnetic problems with moving bodies, thus for most encountered electromagnetic problems. We analyze the transmitted and reflected waves, for different speeds, different refractive indices, and different incidence angles. Based on the obtained results, we derive several analytical formulas for the reflection coefficients, transmission coefficients, Doppler frequency shifts, and angles of transmission and reflection. These formulas are validated by full-wave electromagnetic simulations and are in agreement with the literature. The electric field distribution obtained at time instants is also studied.

A multi-band microstrip patch antenna consisting of an elliptical shape patch with four triangular-shaped arms mounted on a Rogers AD255C substrate with coaxial feed technique to cover 1720 MHz for 2G, 2120 MHz for 3G, 2372 MHz for 4G, and 3536 MHz for Sub-6 GHz 5G wireless communication applications is proposed in this paper. The antenna is designed by exciting a dominant & its orthogonal as well as higher order TM^z_mn0 modes based on cavity model-circular patch theory and then reshaped to an elliptical shape to get the resonance at desired bands. A Characteristics Mode Analysis (CMA) is used for computing electromagnetic resonance frequencies in conducting bodies. A radiating characteristic of the proposed antenna structure is analyzed and verified using CMA technique for target applications frequencies. The CMA demonstrates that the proposed antenna resonates at 1728 MHz, 2127 MHz, 2358 MHz, and 3436 MHz, making them suitable for use as multi-band antenna for 2G, 3G, 4G, and Sub-6 GHz 5G applications respectively after proper feeding. A simulated bandwidth at -10 dB return loss is 23 MHz (1707-1730 MHz) for 2G, 34  MHz (2104-2138 MHz) for 3G, 18 MHz (2364-2382  MHz) for 4G, and 67 MHz (3499-3566  MHz) for Sub-6 GHz 5G applications. The simulated peak gains are 6.29 dBi, 7.08 dBi, 4.51 dBi & 6.18 dBi which are validated by measured results at the respective resonant frequencies. An overall dimension of the proposed antenna is 100×100×3.175 mm³. The proposed antenna was simulated by CST Studio Suite 2020. Measurement was done for the fabricated antenna which shows good agreement with simulated ones. The proposed multi-band antenna with low complexity & easy design offers a quasi-omnidirectional radiation pattern and performance improvement.