Array antennas synthesis is one of the most important problems in the optimization of antenna and electromagnetics. In this paper, a recently developed metaheuristic algorithm, known as the Gravitational Search Algorithm (GSA), is employed for the pattern synthesis of linear and non-uniform planar antenna arrays with desired pattern nulls in the interfering directions and minimum side lobe level (SLL) by position-only optimization. Like other nature-inspired algorithms, GSA is also a population-based method and uses a population of solutions to proceed to a global solution. The results of GSA are validated by comparing them with the results obtained using particle swarm optimization (PSO) and some other algorithms reported in literature for linear and planar array. The side-lobe level and null depth obtained from gravitational search algorithm for planar array are improved up to -30 dB and -200 dB, respectively. The results reveal the superior performance of GSA to the other techniques for the design of linear and planar antenna arrays.

A broadband rectangular waveguide calorimeter for power sensor calibration in the millimeter-wave region is presented in this study. The calorimeter has a dual-load structure, an operational frequency range of 26.5 GHz to 40 GHz, and high substitution efficiency and sensitivity. Its effective efficiency uncertainty is 0.74%~1.1%.

In this paper a symmetrically structured meander line antenna placed around a T-shaped junction with truncated ground planes is proposed for on-body applications. The designed antenna has a percentage bandwidth of 69.04% covering the GSM 1800 band internationally accepted industrial scientific and medical (ISM) 2.4-2.5 GHz band, 4G LTE band 7 (2.5-2.69 GHz). The antenna is compact in nature with a size of 30×40×1.6 mm³. SAR reduction is achieved without the attachment of any auxiliary unit. It is found that the application of designed truncated ground planes around positions of high electric field (E-field) region is an effective solution in reducing Specific Absorption Rate (SAR) significantly through field cancellation technique. In addition maximum temperature elevation due to electromagnetic wave absorption has also been computed. The antenna is simulated over a homogenous human dry skin model as well as head model. The proposed design is fabricated and measured, and it is found to be compatible for real world applications while considering its miniaturization, radiation patterns and SAR limitations.

Finite Difference Time Domain (FDTD) method is widely used in the simulation of various kinds of antennas. In this paper, research on the numerical simulation of the fragment-type antenna by using FDTD is conducted. The fragment-type antenna structures with different cell sizes and different overlapping sizes are simulated and measured. The validity of the numerical simulation of the fragment-type antenna by using FDTD is verified through the comparison between the simulated and measured return losses. In addition, its efficiency in terms of computation time shows great potential in engineering applications, especially when the design matrix is large enough.

In this paper, an antenna with reconfigurable radiation pattern in H-plane at 2.45 GHz for high power applications is presented. It is based on a 3-slot array in E-plane covered partially with two mobile metallic flaps in order to reduce their length, and in consequence, they ensure the mechanical reconfiguration pattern in H-plane. The power distribution of the array is ensured with a power splitter in E-plane, and the uniform and in phase field distribution on the slots is ensured with a sectorial horn placed before the splitter. To reduce cost and weight, the power splitter is realized with metalized wood.

In hyperthermia treatment planning (HTP) the goal is to find the amplitudes and phases of antennas in the applicator to efficiently heat the tumor. To do this prior information regarding tumor characteristics such as the size, position and geometry, in addition to an exact model of the hyperthermia applicator is needed. Based on this information, the optimal frequency of operation can be determined. In this paper the optimum frequency for hyperthermia treatment based on the tumor and applicator characteristics, using time reversal as the focusing technique, is studied. As prior information, we consider tumor size and position, the number of the antennas in the applicator and the frequency characteristics. The obtained optimal frequency range is found using hyperthermia quality indicator values calculated from simulations. We also determine the optimum position of the virtual source in the initial step of the time reversal method to increase the quality of the treatment.

This paper presents a C-band wide stopband bandpass filter (BPF) using quarter mode substrate integrated waveguide (QMSIW) cavities. The BPF is simply constructed by combining S-shaped slot and L-shaped slot loaded quarter-mode substrate integrated waveguide. A special negative coupling scheme with symmetrical S-shaped slots on the top and bottom metal planes connected by metallic vias is developed. The proposed structure provides more design flexibility in arranging the pitch of vias owing to the extended slot length. The filter has fractional bandwidth of 25% at center frequency of 5.5 GHz with return loss better than 24 dB and insertion loss less than 1.1 dB. Moreover, its first spurious response occurs at 22.5 GHz (about four times the central frequency), exhibiting an extremely wide stopband performance. An experimental SIW filter was fabricated, and good agreement was achieved between the simulated and measured results.

In this work, we show that it is possible to produce a planar electromagnetic jet using a flat structure consisting of elementary cells based on lumped elements and fed with a source line. A combination of elementary cells may represent a gradient index, locating the electromagnetic energy in a small area, consisting of a few cells and having a size of about 0.75λ. The theoretical framework of the study is based on the Wave Concept Iterative Process method (WCIP) formulated in both spectral and spatial domains. An analogy with an optical model based on optical paths equality enables predicting the location of formation of this spot. The use of such a system can provide solutions for the development of new kinds of applications such as engraving sub-wavelength, data storage, improved scalpel optics for ultra-precise laser surgery, and detection of cancer.

This paper presents a novel effective calibration technique applicable to phased array radars. The real embedded patterns of the array elements are measured independently in operating mode, taking antenna coupling and other parasitic effects into account. The proposed calibration technique requires minimal modification of the radar hardware. A set of angular-dependent error coefficients, which are compensated during the calibration process, are extracted for one received pulse for one/each angular direction of interest. The performance and effectiveness of the hereproposed calibration technique are assessed by means of modeling and experimental verification.

An approach of miniaturizing planar Yagi array using metamaterial is presented in this paper. In this methodology, metamaterial structures are incorporated in the antenna in place of directors. An investigation in reflection and radiation characteristics of the antennas is done, and the findings are presented. The metamaterial loaded antenna shows improved directivity and efficiency of 16.3% and 2.95% with respect to the microstrip Yagi antenna while achieving a noticeable size miniaturization of 33.3%. Also, a better matching, compared to Yagi antenna, is observed in this proposed design. The fabrication and measurement of ones.

This paper presents a method of designing a bandpass filter using hybrid polynomials. Two different approaches are discussed in this paper. The first method uses class hybridization of a lowpass Chebyshev and highpass maximally flat to achieve the hybrid filtering function (HFF). The second method employs both Chebyshev polynomials of the first and second kinds to form a modified Chebyshev polynomial. Both methods achieve a narrowband dual-band lowpass prototype (DBLPP) without much deviation from classical methods of synthesis. The designs can be adapted into a modified interdigital prototype which will be shown in this paper. The results and measurements reflect a good adherence to the theoretical calculations.

In this paper, novel compact low-pass filters using Hi-Lo technique and meander method are proposed. Series of the proposed filters are designed by adding modifications along the microstrip line (meander inductor) and by using U-form topology. The size of the proposed filter can be reduced by 15% compaired to the conventional filter while maintaining the optimal low-pass features. The compact meander LPF consists of two thin microstrip lines, which are connected with 50Ω microstrip feed lines and a microstrip patch placed in the middle of the structure. The thin lines and the microstrip patch correspond to inductance and capacitance, respectively. The proposed meander Hi-Lo topology has been mounted on an RO4003 substrate with a relative dielectric constant ε_r = 3.38, thickness h = 0.813 mm and loss tangent 0.0027. The compact L-band low-pass structure has a size of (0.263λ_g×0.175λ_g) where λ_g = 57 mm is the wavelength at the cutoff frequency 2.85 GHz. In addition to a good compactness, the structure exhibits a simple design, very low insertion loss in the passband (L-band) of less than 0.3 dB, and it achieves a wide rejection bandwidth with a 20 dB attenuation from 5.3 to 6.3 GHz. The excellent LPF characteristics are verified through simulations and measurements where a good consistency can be observed. Such compact filter structures are expected to be used in various microwave system applications.

A compact dual-polarization, ultra-wideband quad-ridged horn antenna has been proposed for breast imaging. CST Microwave Studio Simulation has been used to design the horn antenna. The antenna size was reduced, and impedance matching was achieved by a modest change in the dielectric constant of the matching liquid and by the introduction of four semi-elliptical structure at the flared ridges. To test the polarization isolation, many field probes were distributed at different positions in front of the antenna. The probes have been set to measure both vertical and horizontal electric field components at each location. Results show that adding elliptical parts can provide impedance matching over the whole frequency band of the antenna. Measurements show high isolation between the transmitted vertical and horizontal electric fields. Almost 40 dB polarization isolation exists at boresight of the antenna over the entire frequency band. This characteristic is central to polarimetric radar work. Effective gain and ports isolation were obtained.

In this study, a trapezoidal-rule integrator and inverting a differentiator are employed to form the transfer function of an approaching integrator in the Z domain. The integrator was implemented to verify the feasibility of the technique, and the integrator exhibited an operating frequency of 1.45 to 6 GHz. Adding microwave integrators to a receiver's radio frequency (RF) circuits in a communication link improves the signal-to-noise ratio (SNR). As a result, an experimental environment was constructed in a wireless local area network (WLAN) band (2400 to 2483.5 MHz). In addition, the RF transmitter emitted the main signal at 2.45 GHz, which included the high-frequency interfering signals at 3.5, 4.5, and 5.5 GHz. The integrators and low-pass filters were implemented to perform signal analysis of the RF signals. To compare the interference suppression of the integrators with the interference suppression of the original and low-pass filters, the receiving power of the main signal and the interfering signals from the different frequencies in the end of the receiver were analyzed. The experimental results indicated that inserting integrators into RF circuits improved the SNR of the communication link by up to 10 dB.

The influence of seaming stitches on the shielding effectiveness (SE) of electromagnetic shielding (EMS) fabric is huge, but there is not an ideal computation model for the SE of the EMS fabric with the seaming stitch at present. This paper proposes a computation model of the SE based on the equivalent seaming gap. Firstly, a structure model of the equivalent seaming gap is constructed according to the equivalent dielectric principle. The computation method of the structural size of the equivalent seaming gap model is determined by the parameters of the stitch length, number of the stitch type, needle number, and sewing thread. A computation model of the SE based on the equivalent seaming gap structure is built according to the EMS theory. The method of the correction coefficient of the model determination is given. Finally, the samples with seaming stitches are made to test the SE using the waveguide method. The computation results with the proposed model are compared with the experimental ones. The results show that the proposed model can well calculate the SE of the EMS fabric with the seaming stitch. The study in this paper can provide a foundation for further study of the influence of seaming stitches on the SE of the EMS fabric and possesses reference significance for the design, production, evaluation and related theoretical research of the EMS clothing.

We propose an approach to characterize the AC underwater radiation produced by a ship over a shallow water medium using dipole sources distributed over an interior surface to the ship. The proposed approach relies in the accurate and efficient representation of dipole sources over the shallow water medium that characterize the behavior of the electric or magnetic field. The approach is reduced to the solution of the resultant matrix system from the dipole representation. These systems are ill-posed, i.e., if the matrix systems are not solved by special regularization methods, the resultant solution will amplify the measurement noise. The regularization method applied is the least squares QR iterations combined with a new stopping rule that uses a numerical estimate of the measurement noise. Numerically generated data is used to study the validity of the different dipole representations. Finally we validate our methodology using magnetic measurements that result from degaussing coils of a mid-size vessel.

In this paper, an L-band wideband quad-ridged waveguide orthomode transducer (OMT) for the Five hundred meter Aperture Spherical radio Telescope (FAST) is presented with a simple design principle. By designing two critical parts of the OMT separately and introducing matching rings into two orthogonal probes, an improved wideband performance has been realized successfully. The OMT is designed to operate across the 0.95 GHz-1.9 GHz band, and the simulation shows a return loss better than -20 dB for both polarizations, cross-polarized isolation levels over 45 dB and insertion loss lower than 0.15 dB over the entire bandwidth. The measured results are in good agreement with the simulations.

A wideband orthogonally polarized resonant cavity antenna (RCA) with double-layer Jerusalem Cross type partially reflective surface (PRS) as superstrate is presented in this paper. The PRS is analyzed using equivalent circuit modelling and full wave simulations. Two-port dual-polarized aperture coupled microstrip patch has been used as primary feed antenna. Measured results show that the antenna structure exhibits 10 dB return loss bandwidth of 14.7% at 10 GHz (9.4-10.9 GHz), and the isolation between the feeding ports is better than 18 dB over the bandwidth. The cross-polarization levels in both E and H planes are better than 15 dB. The peak directivity of the antenna is 13 dBi in the entire band. The antenna is suitable for marine and weather Radar applications.

An asymmetric stepped-impedance ring resonator (ASIRR) is proposed for the design of a triple-bandpass filter. This resonator is applied to creat the former two passbands by utilizing a stepped-impedance circular ring and the third passband by introducing two asymmetric coupling structures. It is found that the S-parameter performance can be improved by adding a pair of shorted and open stubs, the second passband and the stopbands on both sides of the third passband can be tuned by adjusting the length of open stubs. A prototype filter operating at 1.04, 3.52 and 5.57 GHz is designed, fabricated, and measured with the corresponding fractional bandwidths of 23.1%, 7.4%, and 4.1%. Good agreements between the simulated and measured results are achieved for the ASIRR filter. Also, four transmission zeros are generated.

Magnetic induction tomography has been under consideration for imaging electrical conductivity distributions within the human body. Multi-coil systems are most commonly employed for this task, requiring a numerical solution of Maxwell's equations at each position of the coil array. An alternative uses a single coil placed near the conductive target while measuring coil self-impedance changes (``coil loss'') at a number of unique locations. Recently, a closed-form solution of Maxwell's equations, in the form of a 3D convolution integral, was found for a single coil consisting of concentric circular loops that relates impedance change to an arbitrary conductivity. Its development required spatially uniform permittivity and permeability, yet showed quantitative agreement with experiment. Here, we provide a much more critical test of the convolution integral in experiments that allow large permittivity changes over coil dimensions. Loss is measured while the coil is placed at known positions relative to plastic columns of variable diameter which are filled with salt solutions of varying conductivity. In all cases, coil loss varies linearly with conductivity and with zero intercept. Quantitative agreement is observed only when column diameter is greater than or equal to coil diameter. Because of linearity, the convolution integral is useful for image reconstruction, though contrast could be either reduced or enhanced in those circumstances when relative permittivity change exceeds ~70.