In this paper a CPW-fed annular slot antenna is miniaturized with enhanced impedance bandwidth using a reactive impedance surface (RIS) substrate. Such meta-surface (RIS) is realized by patterning 3×3 array of circular elements over an inexpensive FR-4 substrate which is backed by a circular metallic plane. Due to the compensation of electric and magnetic energy stored by antenna and RIS substrate respectively, the antenna resonance frequency is shifted by 53.6% compared with a simple slot antenna. By the inclusion of such reactive surface, input impedance of the antenna is reduced, and a remarkable improvement in impedance bandwidth from 11.66% to 64.26% is also noticed. Therefore, both miniaturization and bandwidth enhancement are achieved simultaneously with the present loading technique. The directivity of the RIS loaded antenna is increased further by loading a concentric metallic ring over the RIS loaded structure at a height above the RIS plane. The Ring & RIS loaded structure is fabricated for measurement purpose. A good agreement is obtained between the simulated and measured results for both RIS loaded and Ring & RIS loaded configurations. The ring loading over the RIS antenna provides improvement in directivity about 5 dB. The peak gain and bandwidth are measured as -1.03 dBi and 58.62%, respectively.

A triple-band planar electromagnetic band-gap (EBG) structure used for gain enhancement and wideband radar cross section reduction (RCSR) of antenna is presented in this paper. Three band-gaps of an EBG structure are realized by introducing two pla-nar spiral inductances on a planar EBG structure. An equivalent model of EBG is given to further understand the formation of three band-gaps. The proposed EBG is placed around antenna units and arrays to calculate the affection of the RCS and the gain. Due to the band-gaps of the EBG structure, RCS of antennas is reduced, and the gain of antennas is enhanced. Results show that the RCS is reduced as much as 20 dB from 9 GHz to 21 GHz, and both of bandwidth and gain of antennas can be slightly enhanced. Two antenna units operating at 8.6 GHz are fabricated and measured to verify the correctness of simulation. Measured and simulated results are in good agreement.

A compact circularly polarized antenna using a wide L-shaped slot and a microstrip feedline is proposed. The measured results demonstrate that the antenna has an axial ratio (AR) < 3 dB bandwidth ranging from 5-8.5 GHz and an S₁₁ < -10 dB bandwidth ranging from 4-8.6 GHz. The antenna is very simple, composed of an L-slot and a microstrip feedline placed beneath and to the edge of the L-slot. The size of the antenna is 20 x 20 mm² which is attractive for compact wireless devices that operate in C-band. The antenna has very low cost and does not require: a large size, truncated corners, reflecting surfaces, complex feeding structure, and via connections, which increase fabrication cost and design complexity.

In this paper, a novel wideband quasi-Yagi antenna is proposed and investigated for multiple-input multiple-output (MIMO)/diversity antennas applications. An aperture-coupled balun is adopted with a curved Yagi radiator for the antenna to realize wideband property. The proposed quasi-Yagi antenna has high radiation efficiency and stable end-fire radiation patterns, operating in a wide bandwidth from 7 to 13.8 GHz. Then a pattern diversity antenna is developed using two elements, which are overlapped partly and placed in opposite orientations. The measured 10-dB bandwidth of the MIMO antenna is from 6.3 to 13.6 GHz. Meanwhile, isolation between the two ports is better than -26 dB. The radiation patterns and envelope correlation coefficients are also presented. The proposed pattern diversity antenna is validated to perform stable behaviours over a wide bandwidth, and it will find applications in wireless communications and radars systems.

Matrix method for phased array calibration is an excitation reconstruction method by solving the linear equations based on the linear relationship between the measured near-field data and element excitations. In this paper, we propose a modified matrix method, in which the phased array model is simplified, to measure the element excitations of planar phased array. Our method reduces measurement time greatly at the cost of introducing some calibration errors. The introduced calibration errors can be minimized with the array excitation strategy proposed in this paper. Experimental results validate the effectiveness of our methods in calibrating planar phased arrays.

A very compact ultra-wideband (UWB) multiple-input-multiple-output (MIMO) ground linearly tapered slot Antenna (LTSA) is presented in this paper. On a cost-effective FR4 substrate, it consists of a ground plane and two microstrip feedlines. Its overall dimension is only 22×26 mm². To miniaturize the dimension of the antenna, two linearly tapered slots on the ground plane act as the main radiator. Then it does not need extra large radiation patch. In particular, a simple embedded three-level stepped slot on the central ground, brings high isolation in the whole UWB band. In addition, two rectangular slots cut in the feedlines widen the impedance bandwidth. Simulated and measured results verify S₁₁<-10 dB and S₁₂<-18 dB at 3.1 GHz-12 GHz and good diversity performance. Therefore, the proposed MIMO antenna has potential for portable devices applications.

This paper presents a novel design method to the absorber screen based on the receiving antenna technique. When the electromagnetic waves is incident upon the surface of absorbing structure, part of the electromagnetic energy transforms into current absorbed at the port, and the remaining energy is reflected. The former mechanism is similar to the receiving antenna. Hence, a dual-polarized magneto-electric dipole antenna is selected and optimized to obtain a broadband absorber screen unit after comparing the similarities between the antenna and absorber. The measurement results show that the finite 6×6 array absorber has a 73% bandwidth for 10 dB RCS reduction, while its thickness of substrate is below 1/9 wavelength of the center frequency in free space. The novel absorber screen can also be used in dual polarization because of its symmetrical property. The simulation and measurement are performed at the normal incidence in this paper.

A low-profile antenna is proposed in this letter for realizing dual polarizations with omnidirectional radiation patterns. Vertical polarization is obtained by a modified annular ring slot antenna, and horizontal polarization is obtained by a modified printed arc dipole array. By combining the ground plane of the ring slot antenna and the dipole array on the same layer, the profile of the antenna is reduced to minimum extent. The proposed prototype has a low profile of 0.024λ0 (λ0 is the free-space wavelength at 2.4 GHz). To verify the design, the proposed antenna is fabricated and measured. Measured reflection coefficients, isolation, and radiation patterns results agree well with the simulated data. The common band of vertical and horizontal polarizations makes the proposed antenna satisfy the WLAN diversity systems with omnidirectional characteristic.

In this paper, a novel multiband wearable fractal antenna which suitable for GPS, WiMax and WiFi (Bluetooth) applications is presented. This antenna is designed to operate at four resonance frequencies are 1.57, 2.7, 3.4 and 5.3 GHz. The proposed wearable antenna may be attached to human body, so the specific absorption ratio (SAR) must be calculated. Therefore, another design to reduce SAR value with a spiral metamaterial meandered in the ground plane is introduced. In addition, a wearable fractal antenna system integrated on a life jacket is also presented.

New phasing element for a wideband microstrip reflectarray is presented. It is formed by a phase-delay line attached to a circular ring loaded with a circular disc microstrip. The structure is enclosed by a circular ring element with a pair of gaps. It is shown that the new phasing element offers a wider bandwidth with an increased phasing range that is useful in reflectarrays phase compensation procedure. Full wave EM simulations is carried out. The results of the simulations show the possible wideband operation of the designed reflectarray. Good agreement exists between simulation results and measurements by waveguide simulator method. The mutual coupling effect for a realistic reflectarray configuration with non-identical cells is accounted for by using the perturbation technique.

For the difficulty of calculating and measuring coupling electromagnetic quantity of complex multi-cavities, a microwave chaotic double cavity model is designed, and a new method is put forward to analyze the coupling effect of the double cavities. The new method combines Random Coupling Model (RCM) and network cascade theory and can successfully predict the Probability Density Function (PDF) of the induced voltage at target point of the double cavity compared with other methods. Experiment is added to verify the effectiveness of the new method in this paper. In addition, the new method provides a new approach to analyze and predict the coupling electromagnetic quantity of the complex double cavities in practical engineering.

Multilayered dielectric rods are widely used, and the analysis of their electromagnetic scattering properties is very important in practical design. Based on our former work on the single layer dielectric rod forest, the equivalent microwave network method (EMN) is applied to analyse the concentric and eccentric multilayered dielectric rods in this article. The key step is to obtain the reflection matrix of the multilayered dielectric. Based on the EMN method, the electromagnetic scattering properties of a novel electromagnetic band gap (EBG) structure are calculated. The EBG structure is formed by periodically embedding multilayered dielectric rods into the original dielectric between power/ground planes. The accuracy and efficiency of the EMN method are verified by comparing with the simulation results by the FIT simulator CST. In addition, the EMN method takes about 1 minute to obtain the results, while the simulator takes nearly 20 hours with the same computer.

In multi-circular synthetic aperture radar (MCSAR) mode, resolution and sidelobes are two important parameters to consider when representing imaging quality, as in other SAR imaging modes. In this paper, three-dimensional (3-D) resolution and cone-shaped sidelobes of MCSAR are analyzed for a point target in the scene center under the Nyquist sampling criterion. The results of the analysis show that resolution can be improved, and cone-shaped sidelobes can be suppressed by increasing the system bandwidth and the length of synthetic aperture in the elevation direction. But this will make the system of acquiring data more difficult. It turns out that some digital signal processing techniques can enhance 3-D imaging quality of MCSAR. In this paper, a simple method based on spectrum extrapolation and interferometric phase masking is proposed to improve 3-D resolution and suppress cone-shaped sidelobes of MCSAR. Experimental results regarding a tank model in a microwave anechoic chamber demonstrate that this method is effective.

Electromagnetic behaviour of chemical vapor deposition (CVD) graphene at low frequencies is still a mystery. No conclusion is made from the experimental point of views. Here, we systematically investigate the electromagnetic response of graphene at microwave frequencies, which are from direct current (DC) to 40 GHz. Both a coplanar transmission line embedded with different-sized graphene akes of 48 × 48 and 48 × 240 um² and a microwave termination based on the graphene sheet of 6 × 6 mm² are manufactured through the chemical vapor deposition (CVD) and standard microfabrication procedures. We conclude that graphene behaves as a frequency-independent surface resistance at the microwave frequencies, which is consistent with the theoretical model by rigorously solving the Maxwell's equations with the Kubo formula. The work offers a simple, accurate, and conclusive electromagnetic analysis to graphene and thus is of great help to design graphene incorporated microwave components and devices.

A compact wideband quarter mode substrate integrated waveguide (QMSIW) band-pass filter with wide stopband performance is presented in this paper. Compared with conventional SIW cavity, the QMSIW cavity occupies only one fourth of the size. A meandered H-shaped slot is etched on the cavity to change the current direction for size reduction. In order to prove the validity, a compact fourth-order band-pass filter with wide stopband is fabricated on a single-layer Rogers RT/Duroid 5880 substrate. The measured in-band insertion loss is only 1.02 dB including the loss caused by two connectors, and the stopband attenuation in the frequency band from 4.02 GHz to 12.63 GHz is better than 25 dB. The whole size of the filter is only 20.6×26.8×0.254 mm³.

This paper deals with a technique for classifying jet aircrafts from JEM (Jet Engine Modulation) signal. A novel method to recognize an engine model by analyzing JEM spectrum using frequency mask is proposed. The frequency mask extracts and analyses the spectral component at the frequencies that are predicted from the blade number of a jet engine and the estimated spool rate. The proposed method does not need a complicated logical algorithm for finding the chopping frequency or the pre-simulated engine spectra used in previous methods. In addition, we suggest a method to precisely estimate the spool rate in the spectrum domain of JEM signal, which plays an important role in generating the frequency mask. The classification experiments using the JEM signals measured from two fabricated engine models verify that the proposed algorithm has good performance in the recognition of jet aircrafts.

The rectangular wave beams-based geometrical optics (GO) and physical optics (PO) hybrid method is applied to the radar cross section (RCS) simulation of complex target. In the implementation process, the incident wave beam is divided into plenty of regular rectangular wave beams. The RCS of target is subsequently harvested from the sum of the contributions from rectangular wave beams. And Open Graphics Library (OpenGL) is used to accelerate ray tracing for the GO/PO method. Here, each pixel corresponds to a rectangular wave beam, which improves the defect that the pixel number should be larger than the patch number on the model and the efficiency in the general OpenGL based GO/PO method. In addition, the patch size in the presented method can be arbitrary as long as the model is described accurately with these patches. The simulation results prove this point and show that the proposed rectangular wave beam-based GO/PO method is feasible and can keep a high calculation accuracy and efficiency with a low pixel number.

Synthetic aperture radar (SAR) raw signal simulation is profoundly useful for validating SAR system design parameters, testing the effectiveness of different processing algorithms, studying the effects of motion errors, etc. Simulating signal data in frequency domain is more efficient than in time domain. However, the former is difficult account for the effects of both sensor trajectory deviations and antenna pointing error for the stripmap SAR mode. In this paper, we attempt to extend the possibility of extending the Fourier domain approach to account for trajectory deviations as well as antenna beam pointing errors, which is more concerned for airborne SAR systems. After demonstrating a full two-dimensional Fourier domain simulation, an efficient simulation approach is proposed under certain reasonable assumptions. The proposed approach has higher computational efficiency than simulation in time-domain and also allows for imaging an extended scene. The validity of the proposed approaches is analyzed and discussed. Finally, numerical examples are presented to verify the effectiveness and efficiency of the approach.

An improved range-Doppler algorithm (RDA) is proposed to reconstruct images from synthetic aperture radar (SAR) data received at high squint angles. At a higher squint angle, a larger synthetic aperture is required to receive sufficient amount of data for image reconstruction, and the range migration also becomes more serious, which demands more computational load and larger memory size. The proposed method can generate better SAR images with less computational load and memory than the conventional RDA, which is verified by simulations.

A novel selectable multiband isolation of Double Pole Double Throw (DPDT) switch with switchable transmission line stub resonators has been proposed for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands. In this paper, two DPDT switch designs are proposed; the first design is a fixed DPDT switch, and the second is a selectable DPDT switch. The second design allows selecting only one band and unselecting the other or selecting both of them. However, the first design does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at center frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between allpass and bandstop responses using discrete PIN diodes. The key advantage of the proposed DPDT with switchable transmission line stub resonators is a multiband high isolation with minimum number of PIN diodes. Therefore, the simulated and measured results showed less than 3 dB of insertion loss, greater than 10 dB of return loss and higher than 30 dB of multiband isolation in 2.3 and 3.5 GHz bands.