In this paper, a compact circularly polarized antenna based on a resonant quadrifilar spiral structure for the application of UHF RFID handheld reader is proposed and demonstrated experimentally. To reduce antenna size and improve impedance matching, the original resonant arms are revised by bending inverted-F structures and printing them on dielectric substrate, and the four arms are fed by a four-way phase shift network. Such an antenna indicates stable circular polarization performance and wide beam-width. The gain bandwidth (>2 dBi) can cover the frequency band from 902 MHz to 928 MHz, which is suitable for most of the popular UHF RFID system in the world. Moreover, the 1×4 array and 2×2 array based on previously demonstrated antenna unit are numerically investigated. The array performances, including the gain, beam scanning and low side-lobe are discussed.

A modified Koch fractal shape is used to decrease the dimensions of an antenna and resonates at more than one band for agricultural application. A new feeding technique of aperture coupled method called a non-uniform annular Photonic Band Gap is applied in order to integrate the designed antenna to the active elements. Subsequently, a transmission line transformer is designed using Genetic algorithm to achieve a perfect matching between the active element (amplifier) and the load (antenna). The proposed antenna is designed and fabricated. The results show that the proposed antenna has a high gain of 20.5 dB, 21 dB, and 22 dB at 0.915 GHz, 1.8 GHz and 2.45 GHz respectively with a compact size and low cost. The results predict its prospect as a promising alternative to the conventional one, which is compatibly applicable to agriculture applications especially when multiband function is required.

Based on the theory of Babinet's principle, a type of dual-polarized antenna working in C band with complementary structures is designed. The structures comprise a wire loop antenna and a slot loop antenna, which is complemented and fed by a coaxial line. A ground is placed to improve the front-to-back ratio of the antenna. The performance of the antenna is studied numerically and experimentally. A prototype antenna was built, stable and symmetric radiation patterns are obtained within the frequency of 4.9 GHz~5.1 GHz, and the port isolation is less than -24dB. The measured results coincide with the simulated ones. This explains the feasibility of the proposed dual-polarized antenna.

An electromagnetic interference (EMI) shielding material based on the composite of BaFe₁₂O₁₉, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) was proposed. The constituents of the composite were brought together through mechanical mixing and the in-situ polymerization of aniline on the BaFe₁₂O₁₉ and MWCNT surfaces. A series of composite with different MWCNT wt% loadings (0, 5, 10, 15, 20 and 25wt%) was prepared, and its effect on the EMI shielding performance was investigated. X-ray diffraction analysis was performed on all synthesized composites to confirm the phase formations. FESEM micrographs reveal the PANI particle formation on both BaFe₁₂O₁₉ and MWCNT surfaces. Electromagnetic measurements were done by using a rectangular waveguide connected to a network analyser to obtain the permeability, μ_r, permittivity, ε_r, and shielding effectiveness (SEA and SER). The increase in the MWCNT loading results in the enhancement of the composite's shielding performance to a certain limit. Optimum EMI shielding performance are shown by sample PBM4 (20wt% MWCNT) with SER and SEA values of 5.14 dB at 8.2 GHz and 36.41 dB at 12.4 GHz, respectively. influence of different MWCNT loadings (0, 5, 10, 15, 20 and 25wt%) on the EMI shielding performance of a composite consisting of BaFe₁₂O₁₉, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) were investigated.

A novel 1.8 GHz compact microstrip low-pass filter (LPF) based on quasi-yagi defected ground structure (DGS) and compensated capacitors is proposed in this paper. The filter has a very sharp cut-off frequency response with low insertion loss and achieves a wide reject band with overall 20 dB attenuation from 2.8 GHz up to 10 GHz. The equivalent circuit model of Yagi-DGS-unit is derived using AWR software, and the circuit parameters are extracted by using a simple circuit analysis method. The advantage of this structure is that the reject band can be controlled by tuning the dimension of Yagi-arms at higher frequency rang. The proposed 1.8 low-pass filter is designed using microwave office electromagnetic software and fabricated on the RO4003 ceramic structure with dielectric constant of 3.38. The compact filter occupies an area of (0.45λ_g × 0.35λ_g) with λ_g = 44 mm. A comparison between simulation and measurement results confirms the validity of the LPF configuration and design procedure. In order to improve the compactness of the proposed LPF, a new multi-layer method has been employed. Finally, a new minimized LPF-topology 50% more compact than the conventional is realized.

This paper proposes a compact Radial Line Slot Array (RLSA) antenna for 5.8 GHz Wi-Fi devices, which meets market needs. Various small RLSA antenna models with radius of 140 mm, were designed using extreme beamsquint technique. The models then were simulated to result in a best model. A prototype of the best model was then fabricated and measured to verify the simulation. The measured parameters are: a gain of 18 dBi, bandwidth of 1 GHz, beamwidth of 20˚, and mainlobe to sidelobe ratio of 15 dB, which meet antenna specifications for market needs. The prototype was tested as an antenna for a Wireless Fidelity (Wi-Fi) device in order to show its performance. The test showed that the prototype worked properly. Lastly, we compared the size of the prototype with the average size of various antennas available in markets. We found that the prototype had the advantage of small size and flat, with similar performance.

In this work linear random arrays are studied. It is shown that random symmetric linear arrays can be more easily characterised (with respect to the asymmetric ones) in terms of the first and second order statistics of the array factor magnitude. In particular, the non-stationarity of the array factor can be taken into account while studying the array response. Accordingly, this leads to more accurate predictions as far as the side-lobe level is concerned.

Effective electromagnetic parameters (EEPs) of periodic structures fabricated mainly by carbonyl iron powders are calculated in this paper. A method of inverting the scattering parameters obtained from simulation software was used. The effect of the absorbent volume ratio and the cycle length on EEPs was studied and analyzed. The correlation of the shapes with EEPs was also researched. The empirical formulas were proposed to calculate EEPs, in which the interaction between two adjacent cells was considered. By using this method, any material could be designed as a periodic structure with controlled EEPs, and the values of EEPs were located between the electromagnetic parameter (EP) of air and that of the original material by a specific rule. The EEPs can be used to design new absorbers as the fundamental data of electromagnetic property of some fresh materials.

The concept of virtual experiments is based on the idea of solving the inverse scattering problem by processing a suitable recombination of the available data, instead of those arising from the measurements. By properly designing such experiments (and without additional measurements), it is possible to enforce some peculiar field's or contrast source's properties, which can be helpful to perform the inversion in a more simple and reliable way. In this paper, we show that the factorization method can be used as a tool to design the virtual experiments. In doing so, we also provide, for the first time, an insight into its physical meaning. As an example, we exploit the virtual experiments designed via FM as the backbone of a linearized inversion approach for quantitative imaging of non-weak targets.

The paper introduces a new method for eliminating multiple-time-around detections in coherent pulsed radar systems with single constant pulse repetition frequency. The method includes the phase modulation of transmit pulses and corresponding phase demodulation at reception, which is matched to signals from the unambiguous range interval, and subsequent coherent integration followed by successive CFAR processing in range and Doppler domains. The performance of the proposed method is studied by means of statistical simulations. It is shown that the elimination performance can be essentially improved by optimizing the transmit phase modulation code. The optimization problem is formulated in terms of least-square fitting the power spectra of multiple-time-around target signals to a uniform power spectrum. Several optimum biphase codes are designed and used in the performance analysis. The analysis shows that the method can provide very high probability of elimination without noticeable degradation in the detection performance for targets from the unambiguous range interval.

This study is focused on how to obtain the effective or equivalent properties of inhomogeneous materials, which, contrary to the usual metamaterials, are assumed to possess only a sandwichlike form of heterogeneity. More specifically, the aim is to see how the method of inversion, and associated type and amount of data, condition the outcome of the inversion, notably as concerns the possibility or not of exotic features such as simultaneous negative permittivity and permeability in certain frequency intervals. Two inversion schemes are considered and compared: the Nicolson-Ross-Weir (NRW) scheme and an optimization scheme. The adopted form of the optimization scheme provides only numerical retrievals, but it applies to any number of far-field data couples, which fact makes it a useful tool for determining whether the retrieved properties of an inhomogeneous material really are independent of the angle of incidence as is required for effective properties. It is shown, via the optimization scheme, that the apparently infinite number of solutions predicted by the NRW scheme is reduced to a single solution-closest to the predictions of a mixture model-when the constraint of independence with respect to angle of incidence is invoked. Moreover, this solution exhibits none of the exotic features of the properties of the usual metamaterials except temporal dispersion and loss even when the component materials of the inhomogeneous layer are neither dispersive nor lossy.

Brain stroke incidences have arisen at an alarming rate over the past few decades. These strokes are not only life threatening, but also bring with them a very poor prognosis. There is a need to investigate the onset of stroke symptoms in a matter of few hours by the doctor. To address this, Electromagnetic Impedance Tomography (EMIT) employing microwave imaging technique is an emerging, cost-effective and portable brain stroke diagnostic modality. It has the potential for rapid stroke detection, classification and continuous brain monitoring. EMIT can supplement current brain imaging and diagnostic tools (CT, MRI or PET) due to its safe, non-ionizing and non-invasive features. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. In this paper, a comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented. The head model also incorporates the heterogenic and frequency-dispersive behavior of brain tissues for the simulation setup. To study the interaction between microwave signals and the multilayer structure of head, a forward model has been formulated and evaluated using Finite Element Method (FEM). Specific Absorption Rate (SAR) analysis is also performed to comply with safety limits of the transmitted signals for minimum ionizing effects to brain tissues, while ensuring maximum signal penetration into the head.

As important fundamental equipment, high voltage switchgears are widely used in electric power systems and directly relative to the power reliability and quality. Partial discharge (PD) online monitoring is one of the most effective methods used for insulation testing and diagnosis in high voltage switchgears and power systems. This paper proposes a unique ultra-wide-band (UWB) antenna with high performance for PD ultra-high-frequency (UHF) detection in high voltage switchgears. Actual PD experiments were carried out, and the designed antenna was used for PD measurements. The measured results demonstrate that the proposed antenna has wide work frequency band, good omnidirectional radiation patterns and appreciable gain, which indicate that the proposed antenna is suitable for UHF online monitoring of PDs in high voltage switchgears.

A new compact interdigital capacitor loaded open slot antenna and its lumped model are presented in this letter. Equivalent model analysis shows that the introduction of the interdigital structure increases the capacitive element of the slot and thus reduces the operating frequency of the slot antenna. And the antenna operating frequency as well as its size can be easily reduced by simply increasing the capacitance of the interdigital capacitor and the characteristic impedance of the slot. Experimental results of the exemplary antenna agree well with those of the full-wave simulation, proving that the proposed open slot antenna structure is viable in antenna design.

Two numerical methods are proposed to solve the electric impedance tomography (EIT) problem in a domain with arbitrary boundary shape. The rst is the new fast Fourier transform subspace-based optimization method (NFFT-SOM). Instead of implementing optimization within the subspace spanned by smaller singular vectors in subspace-based optimization method (SOM), a space spanned by complete Fourier bases is used in the proposed NFFT-SOM. We discuss the advantages and disadvantages of the proposed method through numerical simulations and comparisons with traditional SOM. The second is the low frequency subspace optimized method (LF-SOM), in which we replace the deterministic current and noise subspace in SOM with low frequency current and space spanned by discrete Fourier bases, respectively. We give a detailed analysis of strengths and weaknesses of LF-SOM through comparisons with mentioned SOM and NFFT-SOM in solving EIT problem in a domain with arbitrary boundary shape.

In this paper, a novel quasi-periodic structure for rectangular waveguide technology is proposed. The constituent unit cells of the structure feature a resonant behavior, providing high attenuation levels in the stopband with a compact (small period) size. By applying a smooth taper-like variation to the height of the periodic structure, very good matching is achieved in the passband while the bandwidth of the stopband is strongly increased. Moreover, by smoothly tapering the width of the structure, a band-pass frequency behavior is obtained. In order to demonstrate the capabilities of the novel quasi-periodic structure proposed, a band-pass structure with good matching, wide rejected band, and high-power handling capability has been designed, fabricated, and measured obtaining very good results.

In this study, a Six-port Reflectometer (SPR) with dielectric probe sensor is used to predict relative dielectric, ε_rof normal and tumorous breast tissue in frequency range from 2.34\,GHz to 3.0 GHz. Other than that, a superstrate with an exterior copper layer is overlaid on the surface of a primitive Five-port Ring Circuit (FPRC), which is also a denominated, enhanced superstrate FPRC. It is the main component of the SPR and is presented in this paper as well. The enhanced superstrate FPRC is capable of improving its operating bandwidth by 26{\%} and shifting the operating centre frequency to a lower value without increasing circuit physical size. The detailed design and characteristics of the FPRC are described here. In addition, the enhanced superstrate FPRC is integrated into the SPR for one-port reflection coefficient measurement. The measurement using the SPR is benchmarked with Agilent's E5071C Vector Network Analyzer (VNA) for one-port reflection coefficient. Maximum absolute mean error of the linear magnitude and phase measurements are recorded to be 0.03 and 5.50°, respectively. In addition, maximum absolute error of the predicted dielectric and loss factor are 1.77 and 0.61, respectively.

A clubs-shaped wideband antenna with reconfigurable radiation pattern is proposed. This antenna is composed of two tapered slots of mirror symmetry, embedded with two PIN diodes and fed by a 50 Ω coplanar waveguide (CPW). By controlling states of PIN diodes, two tapered slots can be shut down or opened. Consequently, the proposed antenna works in three radiation modes: one monopole pattern with a simulation frequency band (3.93-5.55 GHz) and two end-fire patterns with an identical band (3.29-6.13 GHz). The antenna is fabricated and tested. Measured results show good agreement with the simulation, which denotes that it is suitable for wideband wireless communication systems.

Low-Loss resonators with high Q factor have special importance in modern microwave telecommunications systems. In this paper, a modern dual-band CSRR with high Q factor is first examined using SIW technology on a surface waveguide. It should be noted that the proposed structure paves suitable way for emitting and propagating wave in two passing bands (approx. 4.7 and 5.3 GHz) below cutoff frequency waveguide. High Q factor and its high small sized percentage is the salient specification of this structure as compared to other similar planar resonators proposed in various references. At the end of this paper, three applications of this resonator are studied in designing a small multi-band filter with high Q factor, a small multi band diplexer with low passage bandwidth and a planar oscillator with low-phase noise. According to the scientific literature, the proposed oscillator was found to enjoy the best performance at low phase noise for planar microwave oscillators.

A new technique for mutual coupling reduction, based on the application of electric resonator, is presented in this paper. In this method, first a custom-designed unitcell is presented that provides a proper S₁₂ response for the mutual coupling reduction, and then, this unitcell is used in a two-element array of wideband dipoles. According to the results, this unitcell provides a maximum reduction of 15 dB in the frequency response of the antenna array while does not have a considerable effect on the reflection coefficient and radiation pattern of the antenna. To verify the results, the antenna is fabricated and measured, and there is a very good agreement between the simulation and measurement.