In this paper, a co-prime symmetric sparse cross array is employed to estimate two-dimensional (2-D) direction-of-arrival (DOA). Some special forth-order-cumulants (FOCs) of array received data are used to construct a high-order matrix that is equivalent to a cross-covariance matrix based on two uniform linear arrays. After some modifications, an existing 2-D DOA estimation algorithm becomes more effective, and it shows further improved performance when the co-prime symmetric cross array is utilized. Numerical simulations demonstrate the effectiveness of our methods.

The static circuit parameters extracted from the field results of non-uniform microstrip line provides an efficient way to predict dynamic effect of non-uniform structure. The predictable frequency range of the static circuit parameters on prediction of the transmission characteristics of step microstrip line is researched in this paper. The circuit parameters are extracted from the full wave results of step line, respectively, at three frequencies (9 GHz, 15 GHz and 20 GHz). On one hand, the time domain transmission characteristics of step line can be solved from the equivalent circuit constructed by these extracted circuit parameters. On the other hand, the frequency domain S-parameter can be derived by the static distributed characteristic impedance. By comparing these time and frequency domain results obtained from the static circuit parameters with those obtained directly from the full wave method, the available condition of the static circuit parameters of the step microstrip line can be analyzed. This comparison shows that the static circuit parameters can be used in frequency bands from DC up to 20 GHz. To verify the accuracy of the static parameters used to predict the transmission characteristics of step line, the measured S₁₁ is also given for comparison with static circuit parameters measurements.

Based on a space folding transformation, we propose a new way to hide an object in full space,namely, to cover-up the scattering of the hidden object with the scattering of a background object so that only the scattering of the background object can be detected by an outside observer and the hidden object disappears electromagnetically (a very weak ``ghost image'' or perturbation may appear inside the strong background object image in an experiment). The present method is essentially different from previous methods of cloaking an object. This work furthers efforts to achieve invisibility and conceal an object in a real environment in full space.

Microwave tomography (MWT) and a radar-based region estimation technique are combined to create a novel algorithm for biomedical imaging with a focus on breast cancer detection and monitoring. The region estimation approach is used to generate a patient-specific spatial map of the breast anatomy that includes skin, adipose and fibroglandular regions, as well as their average dielectric properties. This map is incorporated as a numerical inhomogeneous background into an MWT algorithm based on the finite element contrast source inversion (FEM-CSI) method. The combined approach reconstructs finer structural details of the breast and better estimates the dielectric properties than either technique used separately. Numerical results obtained with the novel combined algorithmic approach, based on synthetically generated breast phantoms, show significant improvement in image quality.

A novel multiband, dual-polarization, beam-switched dual-antenna design, covering some LTE and WLAN bands, has been proposed for indoor base stations. The proposed design consists mainly of dual modified monopole antennas. The horizontal antenna consists of four printed monopole elements, and the control circuit using p-i-n diodes has been implemented for feeding to each monopole element. The vertical monopole antenna beam patterns are controlled by reconfigurable frequency selective reflectors (RFSR) technique. The p-i-n diodes have been utilized for switching mechanism to feed the four RFSR. The measured and simulated results indicate that the antenna system possesses multiband and dual polarization. It has been observed from the simulated and measured reflection coefficients |S₁₁| that the presented dual antenna system supports both LTE (1.7-2.1 GHz) and WLAN (2.5 GHz and 5.8 GHz) band frequencies. Moreover, the radiation characteristics show dual-polarization behaviors of the presented antenna system and beam switching states suitable for small cell indoor-base stations.

A new dual-polarized antenna loading frequency-selective surface (FSS) is proposed for 5G wireless local networks (WLANs) application. The antenna consists of two orthogonal bow-tie dipoles and a ground plane. A new wideband FSS is designed comprising ring-slot connecting rectangular slots. The reflection coefficient of wideband FSS is less than 0.9 from 4-6.5 GHz. The phase of reflection coefficient is -163°at 5.5 GHz. The novel cell analyzed by the equivalent circuit is given and simulated. The wideband FSS is employed as a superstrate layer for bandwidth enhancement and radiation gain improvement of the antenna. After loading wideband FSS, the measured bandwidth is 5.3-6.3 GHz (17.2%) with S₁₁ and S₂₂ both less than -10 dB, which cover various 5G WLAN bandwidths. The gain of the antenna is 12.1 dBi at 5.5 GHz. The bandwidth of antenna with FSS increases 40%, and gain improves 5.6 dBi. The simulated and measured results agree well.

A compact printed dual-band antenna for WiMAX/WLAN applications is proposed in this paper. The dual-band monopole antenna consists of a triangular patch and two folding arms shorted to the ground plane. The proposed antenna features a low profile and compact dimension. To avoid via process in the fabrication, the triangular patch. The two folding arms are separately constructed on the two sides of a FR4 substrate. By employing this structure, five different resonances can be yielded. The triangular patch provides two resonant modes (4.62 GHz and 7.05 GHz), two folding arms produces three resonances at 2.43 GHz, 3.43 GHz, and 6.59 GHz. A prototype of the dual-band antenna is experimentally fabricated and tested. The measured results shows good impedance bandwidth and radiation pattern.

By using some special passive structures and correction of boundary conditions, a novel method to improve the electromagnetic (EM) simulation accuracy is proposed. With this method, the substrate parameters, such as thickness, loss, dielectric constant, loss tangent, sheet resistance, square capacitance and conductivity of the metal, can be described more accurately, and a lot of high frequency effects caused by skin effects, parasitic effects, coupling between micro-strip lines and fluctuation from the sheet resistance, etc. can also be simulated more precisely. Then an accurately scalable small-signal model for millimeter-wave HEMTs is proposed and presented. Combined with distributed modeling, pulsed IV and S parameter measurements, this model can be made scalable freely. The measurements agree with simulated results very well, which also proves that this method applied to the scalable small-signal models has a good consistency and accuracy.

This paper describes the concept and the development of key components of a novel multiple-beam antenna for satellite applications. The antenna is designed to be used in a transparent high-rate data relay system that links several low earth orbit (LEO) satellites to a single ground station via a satellite positioned on a geostationary orbit (GEO). The proposed antenna is based on the concept of an array-fed reflector. The antenna can track LEO satellites by switching between different subarrays of a bigger multifeed array using a reconfigurable switch matrix based on radio frequency micro-electro-mechanical system (RF MEMS) switches. The radiation characteristic of the antenna is further improved by combining digital beamforming with beam switching. In order to validate the proposed antenna concept and to show its suitability for space applications a demonstrator has been built. Measurements of the antenna's key components and of the demonstration system are given.

This paper presents the simulation and fabrication of a new power divider/combiner based on a new waveguide H-plane folded magic-T structure. Measurements of the fabricated magic-T confirm the accuracy of the optimization algorithms existing in the CST software (Genetic algorithm, Particle Swarm Optimization algorithm PSO, etc.). The magic-T structure exhibits moderate bandwidth response in the frequency range of 8-10 GHz. Also, it shows that the return loss is better than -15 dB, the insertion loss about -3.4 dB, and the isolation between the two output ports better than -25 dB in the frequency range of 8.4-10 GHz, with good transmission phase characteristics. Based on this magic-T structure, a 1:4 power divider/combiner is simulated and tested. The measured results show that the insertion loss is about -6.5±0.25 dB, the return loss less than -15 dB, the isolation among the output ports less than -25 dB, the combining efficiency about 89%, and the transmission phase differences are about ±2° in the frequency range of 8-10 GHz.

The 2 × 2 multiple-input-multiple-output (MIMO) capacities of three types of colocated dual-polarized loop (DPL) antennas with different current distributions and isolations are investigated in the free space (FS) channel, the corridor with perfect electric conductor walls (PEC corridor) and the corridor with concrete walls (CON corridor), separately. Capacity results show strong dependences on both the structure and the position of the DPL antenna, in addition to the propagation conditions. For all the three propagation scenarios, the largest capacity can be reached is in the PEC corridor, employing the DPL antenna with a uniform current distribution and a high isolation. Specifically, for a 20 dB signal-to-noise ratio (SNR), the maximum dual-polarized MIMO capacity is 13.1 bps/Hz, which is 1.97 time of that obtained by the one-polarized loop. It is also noted that, the rich-multipath environment can increase the robustness of the DPL MIMO system and the difference of the MIMO capacity obtained by different antenna structures will get smaller with respect to that in the FS channel.

In this letter, a new image fusion methodology for integration of SAR and optical images using combined dictionary is proposed. The approach taken is based on sparse and redundant representations by employing a combined dictionary consisting of wavelets, shearlets and discrete cosine transform (DCT). Wavelets and shearlets provide pointlike and curvelike structures for the optical image, and DCT are taken as obtaining the best performance on SAR image. The experimental results demonstrate feasibility and effectiveness of the method.

A novel wideband balun filter based on a symmetric four-port balanced circuit is proposed in this paper. A pair of open coupled lines is used to realize DC suppression and in-band balance improvement for the balun bandpass filter. The bandwidth can be easily adjusted by changing the characteristic impedance of transmission lines in the balanced circuit. For the proposed balun bandpass filter, excellent in-band balance performance (amplitude and phase imbalance are less than 0.25 dB and 1.3˚ respectively) over the passband are achieved. A wideband balun bandpass filter prototype with center frequency 3.75 GHz and 3-dB bandwidth 33.8% is designed and fabricated. Good agreement can be observed between the measured results and theoretical expectations.

This paper presents the design, fabrication, and measurement of triple band metamaterial absorber at 8 GHz, 10 GHz and 12 GHz which are in the X-band frequency range. The unit cell of the metamaterial consists of three concentric copper rings at different radii, printed on 0.8 mm thick FR4 substrate in order to obtain triple resonant frequencies. The highly symmetrical ring structure in nature makes this absorber insensitive to any polarization state of incident electromagnetic (EM) waves for normal incident waves. The proposed structure is capable to operate at wide variations angle of incident wave. The simulated result shows that the triple-band metamaterial absorber achieves high absorbance for normal incident electromagnetic waves of 97.33%, 91.84% and 90.08% at 8 GHz, 10 GHz and 12 GHz respectively, when subjected to normal incident electromagnetic. With metamaterial absorber maintaining 50% of absorbance value, the corresponding full width half maximum (FWHM) are 5.61%, 2.90% and 2.33%. The operating angles in which the metamaterial structure can maintain 50% absorbance at TE mode and TM mode are 670 and 640 respectively. The experimental result verifies that the absorber is well performed at three different resonant frequencies with absorbance greater than 80%.

A pattern synthesis approach based on a modified alternating projection method in an affine coordinate system is proposed in this paper. The approach is suitable for large planar arrays with periodic parallelogram element layout. According to the affine transformation theory, the radiation pattern of the array with a periodic parallelogram element layout could be written down immediately from that of a conventional one with rectangle cells when a pattern invariant group is defined. Just as known, the conventional alternating projection method is sensitive to the starting point and easy to fall into local optimum; in this paper we introduce a modified alternating projection method with a variable projection operator. To verify the rationality of the proposed method, several examples have been performed on our personal computer. Results show that the method could quickly synthesize the array patterns to the required with high accuracy. In addition, if the array has a triangle or parallelogram element layout, the required antennas to fill up the aperture is reduced when compared with the conventional one with antennas arranged along a rectangle grid. In our examples, the maximum reduction is about 18.09%, which is quite beneficial to reduce the weight and cost of the array.

One of the most important aspects for body centric communication is the development of the textile antenna for on-body communication. Antennas for on-body environment usually suffer performance degradation caused by the human body. Apart from that, textile antenna gets easily bent, flexed, wrinkled or wet. This paper presents an investigation on three different designs and types of planar antennas, which are single band textile dipole antenna, fractal Koch multiband dipole antenna and monopole ultra wide band antennas. The performance of the antennas has been evaluated in terms of bending, wetness condition and on-body simulation. The results show that the bending effect is not critical in free space for the planar antennas, but the performance is notably degraded under wet condition while the antenna reflection coefficient is shifted when placed on the human body.

A coupled-line circuit structure is proposed in this paper to design a modified Schiffman phase shifter with short reference line. Based on the traditional transmission line theory and ABCD parameters, closed-form mathematical equations for electrical and scattering parameters are obtained. Obviously, this proposed coupled-line phase shifter has several advantages such as arbitrary phase difference, easy implementation, and analytical design method. Finally, two examples of microstrip coupled-line phase shifter, which have fractional bandwidth over 45%, are fabricated and measured. Good agreements between the simulated and measured results verify our design.

A compact ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna with a small size of 22×36 mm² is proposed for portable devices. The MIMO antenna consists of two symmetric slot antenna elements with back-to-back separation of 7 mm. Adjusting the open-ended stepped radiator and position of the microstrip line can realize UWB impedance matching. In order to achieve wideband and high isolation, a cross-shaped decoupling slot and connecting metal line are etched on the ground plane. The cross-shaped slot between the antenna elements is used to decrease the mutual coupling caused by near-field at middle and high bands. The connecting line can be interpreted as a neutralized line, which produces an additional current path for the coupling ground currents. Measured S-parameters show that the isolation is better than -16 dB across the UWB of 3.1-10.6 GHz. The radiation pattern, gain, and envelope correlation coefficient are also measured. The proposed antenna with a simple structure and compact size achieves good impedance matching and excellent port isolation simultaneously, and is a good candidate for UWB MIMO systems.

A miniaturized annular ring slot antenna is presented. The antenna consists of an annular ring slot structure and a novel folded matching structure. The annular ring slot structure is printed on a substrate and shorted concentrically with a set of conductive vias. The additional matching structure is a ring cavity attached to the back of the annular ring slot structure. Firstly, the diameter of the proposed antenna is reduced by using the folded matching structure comparing with traditional annular ring slot antennas. Secondly, the impedance matching of the proposed antenna is achieved by optimizing the size of the matching structure. A prototype of the proposed antenna with a height of 3.048 mm (0.03λ) and a radius of 47.2 mm (0.4λ) is designed, fabricated and measured. The antenna resonates at 2.67 GHz and has a monopole-like radiation pattern, which shows that the antenna is suitable for the applications of taking off, landing, and long distance communications for a small or mini UAV.

In this paper, a cross-slot-coupled dual-band circularly polarized (CP) hybrid dielectric resonator antenna (DRA) is presented. The design concept is based on using a cross-slot as both a feeding structure of the DRA and an effective radiator. Full wave simulation is used to verify the proposed design concept in this paper. A prototype antenna is designed, fabricated, and measured. Good agreement is obtained between the simulated and measured results.