In this paper, a wideband circularly polarized corrugated G-shaped grounded ring slot antenna is presented. The proposed antenna structure is excited using a coplanar waveguide-fed monopole antenna, which is placed inside a corrugated G-shaped grounded ring. Due to the asymmetry in the ground plane, two orthogonal modes, having equal magnitude and out of phase by 90° are excited, resulting in circular polarization (CP). The generation of the CP in the proposed antenna structure is explained using thin dipole current element approximation. A prototype of the proposed antenna is fabricated and tested. The measured results exhibit a 3 dB axial ratio bandwidth of 37.6% (2.22–3.25 GHz), and reflection coefficient bandwidth (|S11| ≤ −10 dB) of 47.91% (2.13–3.47 GHz). Additionally, the design guidelines are also presented for G-shaped grounded ring slot antennas.

This paper presents the design and analysis of a miniaturized, coplanar waveguide-fed ultra-wideband monopole on-chip antenna with band-notch characteristics. By incorporating a “U”-shaped slot in the feedline, a band-notch is realized in the frequency range of 7.9–8.4 GHz to avoid interference from the X-band uplink satellite communication system. The proposed antenna achieved good voltage standing wave ratio (VSWR) characteristics with VSWR value <2 for the frequency range of 2.5–20.1 GHz excluding the band-notched frequencies. The fractional bandwidth and bandwidth ratio are obtained as 156% and 8.04:1, respectively. Dominant factors that affect the center frequency and bandwidth of the notched band are thoroughly investigated. This paper addresses both frequency as well as time domain behavior of the proposed structure. Standard 675 µm thick, high resistive silicon substrate (ρ≥8 kΩ-cm, εr = 11.8, and tan δ = 0.01) is used to design the proposed compact antenna structure with a layout area of 8.5 × 11.5 mm2. Fabrication process steps along with simulated and measured data are presented here. A close analogy between simulated and measured data is observed.

An inscribed hexagonal fractal slotted patch antenna with some additional geometry and slots is proposed for the optimization in this paper. This research work is concerned with the optimization of this slotted fractal antenna with the help of the curve-fitting method in conjunction with the modified version of Lightning Attachment Procedure Optimization (MLAPO) technique. The data required for the curve-fitting technique and for the optimization technique have been obtained by varying some of the parameters of the proposed antenna. Different equations are developed to know the relations between these parameters of the proposed antenna. The MLAPO technique is applied thereafter to calculate the different optimized geometrical parameters to optimize the bandwidth for the proposed antenna. The optimized geometrical parameters are verified with the help of a parametric variation to justify the reliable optimization. The bandwidth obtained by the MLAPO technique has been found to be better than that obtained by PSO and normal LAPO algorithm. The prototype of the optimized antenna is fabricated and the experimental results are found to be compatible with the results obtained by simulation. The proposed optimized antenna may be utilized in various applications in C and X bands.

A multi-input multi-output (MIMO) antenna is designed and discussed for multi-band applications. The constituent antennas are composed of four L-shaped elements and a ground plane. When placed beside each other to form a MIMO antenna, a T-bar shaped parasitic structure is also embedded between the antennas on the backside of the substrate to increase the inter-element isolation. The triple-band performance of the antenna is observed at 2.15–2.73 GHz, 3.1–3.9 GHz, and 5.04–6 GHz. The isolation level of more than 20 is seen over the operating frequency range. The fabricated prototype of the MIMO antenna size is very compact (20 × 40 mm), printed on the FR4 substrate. Based on simulation and experimental results, the proposed design is useful for WiMAX and WLAN applications.

This paper proposes the novel application of three meta-heuristic optimization algorithms namely crow search algorithm, moth flame optimization, and symbiotic organism search algorithm for the synthesis of uniformly excited multiple concentric ring array antennas. The objective of this work is to minimize the sidelobe level (SLL) and maximize the peak directivity simultaneously. Three different cases are demonstrated separately with various constraints such as optimal inter-element spacing and/or optimal ring radii. Comparative study of the algorithms using common parameters such as SLL, directivity, first null beam width, best cost, and run time has been reported. Investigation results prove the superiority of case 3 over other cases in terms of directivity and SLL. This work demonstrates the potential of these algorithms.

In this paper, a reduced-size dielectric resonator antenna with switchable diversity patterns is proposed. Ring- and linear-shaped slots are etched in the ground plane of the antenna so as to generate two modes $TE_{\delta 11}^x$ and $TE_{\delta 12}^x$ at a center frequency of 19 GHz. Moreover, two groups of PIN diodes are integrated into these slots to short one group of slots, and let the other group generates the required mode. Thus, the antenna is able to generate two switchable patterns with an envelope correlation coefficient of 0.4. Furthermore, the antenna size is reduced to half of its original size by placing a copper sheet over certain plane of the antenna structure. The antenna achieves wide bandwidths of 17.6–20.9 GHz (17.1$\percnt $) and 18.3–21.6 GHz (13.8$\percnt $) in cases of exciting $TE_{\delta 11}^x$ and $TE_{\delta 12}^x$ modes, respectively. The antenna also attainsa high gain of 7.1 and 3.2 dB at the center frequency.

In this paper, an algorithm for extracting and localizing a radar pulse in a noisy environment is described. The algorithm combines two powerful tools: wavelet denoising and the short-time Fourier transform (STFT) analysis with statistical-based threshold. We aim to detect radar pulses transmitted by any radar in blind mode regardless of the intra-pulse modulation and parametric features. The use of the proposed technique makes the detection and localization of radar pulses possible under very low signal-to-noise ratio conditions (−18 dB), which leads to a reduction of the required signal power or alternatively extends the detection range of radar systems. Radar classes pattern-based analysis is used in blind mode to decrease the probability of false alarm.

The temperature dependence of the dielectric parameters of tissues and tissue-mimicking phantoms is very important for non-invasive temperature measurement in medical applications using microwaves. We performed measurements of this dependence in the temperature range of 25–50°C using distilled water as a reference liquid commonly used in dielectric property studies. The results were compared with the literature model in the frequency range of 150–3000 MHz. Using this method, the temperature dependence of dielectric parameters of a new muscle tissue-mimicking phantom based on agar, polyethylene powder, and polysaccharide material TX-151 was measured in the temperature range of 25–50°C. The temperature dependence of the dielectric properties of this new muscle phantom was fitted to that of the two-pole Cole–Cole model and the deviation of the results between measured and modeled data was quantified.

This paper presents the filter design in the student design competition of EuMW 2019. This contest motivates students for the design and implementation of a dual-band bandpass filter able to get outstanding performance, where different implementation technologies, such as microstrip, coplanar, multilayer microstrip, substrate integrated waveguide, and some others can be effectively employed. Filters are evaluated by considering a figure of merit (FoM) defined by the insertion loss level, selectivity, spurious-free response, and size. To this end, three viable dual-band bandpass filters with different feeding technologies, resonators, and design topologies are investigated for the optimal FoM.

In this paper, the design and analysis of a complementary Sierpinski Knopp fractal antenna are presented. It is realized by applying the Sierpinski Knopp space-filling curve on the basic square monopole antenna. The performance metrics of the antenna such as S11 (reflection coefficient), voltage standing wave ratio, radiation pattern, gain and current distribution at resonant frequencies are analyzed by using ANSYS Electronic Desktop software package. FR4 dielectric material is used as a substrate in which the radiating element of an antenna is printed. Vector network analyzer and anechoic chamber are used for measuring the fabricated antenna in order to validate the simulated data. The proposed antenna resonates at three frequencies that are 2.08, 4.93, and 6.46 GHz with a reflection coefficient of −20.5, −23.1, and −24.3 dB, respectively. The suggested antenna covers the frequency bands for mobile satellite service, Public Protection and Disaster Relief communication devoted to the emergency management system and INSAT C band applications.

In this paper, a novel alternating direction method of multiplier (ADMM) is proposed to solve the inverse scattering problems. The proposed method is suitable for a wide range of applications with electromagnetic detection. In order to solve the internal ill-posed problem of the integral equation and make the reconstructed images more closer to the ground truth, first, the augmented Lagrangian method is introduced to transform the complex constrained optimization problem into the extremum problem of unconstrained cost function. Therefore, two artificial regularization factors of the cost function are optimized. Then, this proposed method decomposes the unconstrained global problem in the inversion process into three linear sub-problem forms of contrast source function, contrast function, and dual variables. And the form of the updated algebra for each sub-problem is not complicated. By cross-iterating and updating contrast source function, contrast function, and dual variables, the global minimization of the cost function can be accurately found. Finally, the proposed method is compared with the existing well-known iterative method for solving the inverse scattering problem. Both the numerical and experimental tests verify the validity and accuracy of the proposed ADMM.

This paper presents the design and analysis of a rectangular slot antenna for producing a directional radiation pattern over a wide bandwidth of 6–9 GHz. A basic wideband slot antenna is designed for the desired frequency band by microstrip offset feed technique. This antenna is then loaded with a superstrate and a reflector, both made of conducting sheets. Analogous to a three-element Yagi antenna, the superstrate enhances the boresight gain, while the reflector improves the front-to-back ratio (FBR) of the basic slot antenna. The antenna is optimized for superior wideband performance with boresight gain ≥5 dBi, peak cross-pol level ≤−10 dB and FBR ≥10 dB, over the −10 dB impedance band of 6–9 GHz, which in this paper is termed as the radiation bandwidth. Prototype measurement demonstrates a radiation bandwidth of 6.05–8.22 GHz (or 30.41%), which is in decent agreement with the simulation.

A flexible broadband antenna with high radiation efficiency for the Internet of Things (IoT) applications is presented. The design is based on a U-shaped and a triangular-shaped radiator with two tuning stubs. A 50 Ω coplanar waveguide (CPW) transmission line is employed to feed the antenna. The proposed antenna is fabricated on a flexible substrate from a composite synthesized by mixing natural rubber with SiO2 as a filler. The radiating elements, along with the CPW, are built using a highly conductive woven fabric. Results show that the antenna has a simulated and measured impedance bandwidth of 0.856–2.513 GHz and covers the most commonly used wireless communication standards and technologies for IoT applications. The radiation efficiency of the antenna reaches over 75% throughout the operating frequency band with satisfactory radiation patterns and gain. The flexible antenna was also tested under bending conditions. The presented results demonstrate that bending has a minor effect on the antenna performance within the target frequency range. The measured results show a good agreement with simulations.

The microwave waveguide and resonator methods are compared as applied to the experimental determination of the dielectric properties of high loss liquids. A differential microwave waveguide cavity for measuring high loss liquids complex permittivity in a small volume has been designed and studied. This cavity consists of two circular waveguide cells with central rods made of quartz and surrounded by high loss liquid tested. The cells have different lengths to eliminate complex propagation coefficient measurement errors due to the diffraction effect on the ends of the layered waveguide cells. We have measured the wave amplitude and phase coefficients for the waveguide cavity to estimate physical properties of a high loss liquid under test. The resonant frequencies and the Q-factor of a semi-disk dielectric resonator with high loss liquid filling a capillary have been measured. We have selected water-ethanol solutions as a high loss liquid under test for both techniques. We have determined the measurement sensitivity for these two techniques. The measuring results are discussed. Both the waveguide and resonator methods provide comparable sensitivity and can be successfully used for the complex permittivity characterization of high loss liquids in small volumes.

Microwave imaging is an efficient technique that can be used for the early detection of breast cancer. Therefore the current research article presents the microwave imaging of two spherical tumors (radius 4 and 5 mm) in the breast phantom by using the monostatic radar-based technique. This is carried out by using an ultra-wideband (4.9–10.9 GHz), three-layered stacked aperture coupled microstrip antenna (SACMPA) with a defected ground structure to scan the breast phantom and make near field S parameter measurements from a breast phantom. The S parameter data from different locations and at different time intervals are noted and then used in a beam-forming algorithm; Delay and Sum to process it and form a 2D image of the tumor location in the breast phantom using MATLAB.

The proposed SACMPA is a three-layered structure with overall dimensions of 37 × 43 × 4.85 mm3 that shows an impedance bandwidth of 6 GHz (4.9–10.9 GHz) and a simulated peak gain of 6.32 dB at a frequency of 9.1 GHz. The validation of S parameters and gain results are done using a Vector Network Analyzer (VNA) and an anechoic chamber. The experimental validation of the proposed microwave imaging procedure is done by allowing the SACMPA to radiate parallel to the breast phantom made from polythene (skin), petroleum jelly (fat), and wheat flour (with water as tumor) and record the S parameters on the VNA. The proposed microwave method is safe for human exposure as the antenna also shows simulated specific absorption rates of 0.271 and 1.115 W/Kg (on the breast phantom) at frequencies of 5.7 and 6.5 GHz, respectively (for 1 g of body tissue).