We demonstrate a novel and simple geometrical approach to cloaking a scatterer on a ground plane. We use an extremely thin dielectric metasurface to reshape the wavefronts distorted by a scatterer in order to mimic the reflection pattern of a flat ground plane. To achieve such carpet cloaking, the reflection angle has to be equal to the incident angle everywhere on the scatterer. We use a graded metasurface and calculate the required phase gradient to achieve cloaking. Our metasurface locally provides additional phase to the wavefronts to compensate for the phase difference amongst light paths induced by the geometrical distortion. We design our metasurface in the microwave range using highly sub-wavelength dielectric resonators. We verify our design by full-wave time-domain simulations using micro-structured resonators and show that results match theory very well. This approach can be applied to hide any scatterer under a metasurface of class C1 (first derivative continuous) on a ground plane not only in the microwave regime, but also at higher frequencies up to the visible.

A transparent dielectric resonator (DR) reflectarray that works in the C-band (6.5 GHz) is proposed in this paper. Here, the reflectarray element has a metallic stripof adjustable length placed underneathto act as a phase shifter. Floquet method isapplied for characterizing the reflection properties of the element anda 7×7 full-fledge reflectarray was constructed using glass and the low-cost FR4. By varying the length of the under-loading strip, it is found that the proposed DRA reflectarray element is able to provide a compensating phase of greater than 300˚. Measurements and simulations were conducted to analyze the reflection coefficient, antenna gain, and radiation patterns. The reflectarray has a maximum gain of 14.38 dBi in the broadside direction, and the 1-dB bandwidth of the DRA reflectarray is found to be around 8%. The use of DR has enabled antenna size miniaturization, and it can be useful for the design of small-size reflectarrays.

The one-step leapfrog hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method for lossy media is presented. By adopting the Crank-Nicolson and Peaceman-Rachford schemes, the derived method involves calculations of the lossy terms at two different time steps. Different from the original HIEFDTD method, the proposed method can also be considered as a second order perturbation of the conventional FDTD method. To verify the effectiveness of the proposed method, numerical experiments are performed by using different FDTD methods. It is shown that the proposed method can be more efficient than the conventional HIE-FDTD method with almost the same accuracy.

In this paper, we propose a planar metamaterial particle that consists of two bright elements imprinted on a dielectric substrate in the microwave region. The two bright elements are a circular ring resonator (CRR) and an asymmetric single-split rectangular resonator (ASRR). The structure exhibits a narrow transparency band in a wide absorption/reflection band through coupling between the two bright modes. We study the proposed structure through numerical simulation and experiment. We also test different orientations of the structure for possible application as an efficient frequency selective-band obscurant.

Two previously studied classes of electromagnetic media, labeled as those of Q media and P media, are decomposed according to the natural decomposition introduced by Hehl and Obukhov. Six special cases based on either non-existence or sole existence of the three Hehl-Obukhov components, are defined for both medium classes.

The main goal of the present paper is to analyze the structure of the near field radiated by scalar point sources. The motivations for this study are the strong connection with interaction problem and the need for some insights to be utilized in the later, much more involved study of the full-wave vectorial case. We first suggest that the radial direction is the most convenient at the current time for observing the structure of the near field and proceed to derive the radial Green's function of the problem in a simple analytical closed form. The obtained expressions are then studied and their physical features are illuminated, especially in connection with the engineering radiation problem. The overall understanding of the near field problem obtained here will help in guiding the devolvement for the more complicated sources sometimes encountered in applications and theory.

An off-grid direction-of-arrival (DOA) estimation method that utilizes a sparse array covariance matrix is proposed. In this method, the array covariance matrix is sparsely represented in the form of a vector and then modified to become an off-grid DOA estimation model according to the first-order Taylor series. By solving for the two sparse vectors in the resulting array covariance matrix, the off-grid DOA estimation can thus be achieved. We present an alternating iterative algorithm that exploits the alternating update of a convex optimization problem and a least-squares problem to solve for these two sparse vectors. Our method also extends the aperture. The effectiveness and efficiency of the proposed method are demonstrated in the simulation results.

Two finite-difference time-domain (FDTD) methods incorporated with memristor are presented. The update equations are derived based on Maxwell's equations, and the physical model is given by Hewlett-Packard (HP) lab. The first method is derived by calculating the memristance directly while the second method is derived by the relationship between electric charge and flux. Numerical results are given to discuss the accuracy, efficiency and stability of both proposed methods.

A wideband antenna with band notch function using electromagnetic bandgap (EBG) structure is proposed. The antenna is capable of reconfiguring up to three band notch operation. Three EBGs are aligned underneath the feed line of the wideband antenna. The transmission lines over EBGs unit cells perform as a band stop filter. A switch is placed on each of the EBG structure, which enables the reconfigurable band stop operation. The simulated and measured reflection coefficients, together with the radiation patterns, are shown to demonstrate the performance of the antenna.

A compact dual-band frequency reconfigurable microstrip-line fed open-end omnidirectional slot antenna is proposed in this paper suited for cognitive radio front end system. The antenna is capable of frequency switching at different frequency bands by changing the resonance length using two PIN diodes. The resonance frequency is tuned by a single varactor diode, placed at a certain location along the slot. The proposed antenna has a wide tuning range in the dual bands: 1.57 to 3.1 GHz and 3.8 to 5 GHz. The designed antenna has compact size of 40×40 mm². An approximate transmission line model of the proposed antenna is derived to calculate the proper positioning of the diodes, and the design has been verified through numerical simulations and measured results.

This paper presents the analytical design formulas for the bandpass filters which are built on the asymmetrically coupled-line conductor-backed coplanar transmission lines (CBCTLs) in multilayer configuration. The full-wave simulation is employed to characterize the far-field patterns of space-wave and surface-wave radiations as well as the frequency-dependent conductor, dielectric, and radiation losses. Good agreement among the results of full-wave simulation, transmission-line model, and measurement justifies the design procedure and validates the analytical design formulas. By properly placing the dielectric materials in multilayer configuration, a bandpass filter for minimizing the radiated power loss and improving the stopband characteristic can be achieved.

In some satellite navigation receiver systems, there is not enough space to settle several antennas for multi-port multi-band application generally. A triple-deck circularly polarized antenna with three ports for receiving and sending satellites signal is studied in this paper. The design idea in this paper is to place several single-feed microstrip antennas layer by layer for saving space. All patch antennas are probe-fed, and the probe connected to the upper patch goes through the clear hole in lower substrates. The structure of the multi-band antenna is investigated thoroughly. How to tune this kind of antenna is a big problem in application, and one special parameter is given to adjust the performance of the antenna. The designed triple-deck antenna works at the bands of GPS, BDS and 1.66 GHz independently. The formal two bands are RHCP, and the third band is LHCP, so it can receive and send signals at the same time. Both simulated and measured results show that all three working bands can cover the system use differently. Axial ratio less than 3 dB at center frequency is obtained, and absolute gain at center frequency is more than 4 dBic. The advantages of this antenna are compact in size for multi-port multi-band use and easy fabrication.

In this paper, a design of a dual-band series-fed dipole pair (SDP) antenna using proximity-coupled strip and split-ring resonator (SRR) directors is presented. Two different types of directors are placed close to the top element of the SDP antenna. First, a thick strip director is used to enhance the bandwidth and gain characteristics of the SDP antenna. Next, a pair of SRR directors is appended to both sides of the strip director to create a new resonance for dual-band operation. The performance of three different SDP antenna structures (with a strip director, with a pair of SRRs, and with both directors) are compared with the conventional SDP antenna without directors. When the strip and SRR directors are used together, the mutual coupling might affect the impedance matching of the original frequency band of the SDP antenna, and the distance between the two directors is an importance parameter to decide the performance of the antenna. The effects of the distance between the strip and the SRR directors on the input voltage standing wave ratio (VSWR) and realized gain characteristics are studied. A prototype of the proposed dual-band SDP antenna operating in the global positioning system L1 (1.563-1.587 GHz) and 1.7-2.8 GHz bands is designed and fabricated on an FR4 substrate. The experiment results show that the antenna has dual-band characteristics in the 1.56-1.63 GHz and 1.68-2.87 GHz frequency bands for a VSWR < 2. Measured gain is 5.9-7.5 dBi in the former frequency band, whereas it ranges from 6.2 dBi to 7.3 dBi in the latter.

Two compact differential bandpass filters (BPFs) based on coupled-line resonators and loaded capacitors are proposed in this work. By properly designing the coupled resonator and the loaded capacitance of original filter model, differential-mode (DM) passband responses and common-mode (CM) rejection can be obtained .For validation, two differential BPFs named Filter I and Filter II are discussed and experimentally characterized. One more DM transmission zero generated by out-of-phase cross-coupling is employed to control the DM bandwidth and sharpen the selectivity in Filter I while lumped capacitors are loaded in Filter II to replace capacitive coupled resonators for miniaturized size. Both filters are centered at 4.5 GHz with about 9% DM fractional bandwidth (FBW), less than 1.5 dB insertion loss, more than 15 dB return loss, and wideband CM suppression with more than 18 dB rejection. Furthermore, the size of Filter II is substantially smaller than Filter I and previously reported differential BPFs.

The number of composite insulators used in power transmission lines increases year by year. To detect and assess the aging status accurately concerns the security and stability of the power system. In order to achieve nondestructive testing of the sheds of composite insulators, a unilateral mini Nuclear Magnetic Resonance (NMR) sensor is proposed in this paper. The design of the magnet body and the optimization of the RF coil are presented. The Carr-Purcell-Meiboom-Gill (CPMG) sequence was employed to record the 1H relaxation curves of the sheds of three composite insulators from 110 kv lines with different service years. The curves were fitted to both single exponential function and inverse Laplace transformation functions. The results demonstrate that an increase of service year of the insulator results in a decrease of the effective transverse relaxation time (T_2eff). It is indicated that the sensor has a potential to assess the aging status of the composite insulators.

This paper discusses methods for expanding fields radiated by arbitrary sourcesenclosed by a certain minimum sphere in termsof Complex Source Point (CSP) beams. Two different approaches are reviewed; the first one is based on a spectral radiation integral, where the Fourier-spectrum is obtained by far field matching. The second approach consists of two steps: first, the equivalence principle is applied to a sphere enclosing the real sources, and a continuous equivalent electric current distribution is obtained in terms of spherical waves; then, the continuous current is extended to complex space and its SW components are properly filtered and sampled to generate the discrete set of CSPs. In both cases, the final resultis a compact finite series representation with a number of terms that matches the degrees of freedom of arbitrary radiated fields;it is particularly efficient when the fields are highly directional and the observation domain is limited to a given angular sector. The fact that the CSPs rigorously respect Maxwell's equations ensures the validity of the expansion from near to far zone and allows one to incorporate the CSP representation in a generalized admittance matrix formalism for the analysis of complex problems.

A new theory on designing electromagnetic/optical devices has been proposed, namely, a surface transformation (ST). Compared with Transformation Optics (TO), we do not need to consider any mathematics on how to make a coordinate transformation, and what we need to do is simple to design the shapes of the input and the output surfaces of the device with pre-designed functions. Unlike the devices designed by TO which are often inhomogeneous anisotropic media, all the devices designed by ST only need one homogeneous anisotropic medium (referred as the optic-null medium) to realize. Our method will lead a new way to device design without considering any coordinate transformations.

This paper presents the improved isolation property of the signals among transmitter and receiver antennas. The separation wall is laid at the center of the antennas to improve the isolation level between them. The introduced separation wall has serrated edges mounted on three sides i.e., top, left and right sides. These mounted serrated edges are implemented to reduce the diffraction which may occur due to the linear edge of the wall. The Fresnel diffraction problem has been solved using analytical method in order to get the optimized structure of the serration. The Fresnel diffraction patterns due to the different sizes of the serration are obtained, and their relative powers are compared to each other. The implemented antenna system with the serration wall is composed of corrugated feed horn, orthogonal mode transducer, and offset dual-reflector parabolic antennas. The effect of serration is well demonstrated by the measurement of isolation level of the antenna system. The measured results show that the serrated edges enhanced the isolation property among transmitter and receiver antennas.

A novel dumb-bell-shaped defected ground structure (DB-DGS) with embedded capacitor is presented in this paper. Compared with conventional DB-DB-DGS structure, the proposed DB-DGS exhibits many attractive characteristics including double resonance, high Q value and compact size. The equivalent lumped circuit model for the novel DGS is developed, and its parameters are extracted. Based on this new DB-DGS, a low-pass filter (LPF) using the novel DB-DGS has been constructed, which provides a more steep rejection property, a wider stopband and compact size. The proposed structure is experimentally verified through the demonstration of a low-pass filter design.

Here we present the design of a low loss top metal silicon (Si) hybrid dielectric-loaded plasmonic waveguide (TM-SiHDLW) and a compact, high performance optical resonator by numerical simulation based on finite element method. The waveguide adopted a thick (200 nm) top metal stripe structure to yield optimal performance due to reduced Ohmic loss in conductor around the stripe edge/corner. Moreover, a relatively thick (150 nm) dielectric spacer between the Si ridge and the metal stripe was employed to achieve both long propagation length and good field confinement. The effect of a thin (10 nm) silicon nitride (SiNx) layer covering the waveguide which was added for minimizing uncertainties on optical properties of SiHDLW resulting from high density of dangling bonds on Si surface was also investigated. Simulation results show that there is no significant degradation on the performance of the TM-SiHDLW. For the proposed plasmonic waveguide, a propagation length of 0.35 mm and a mode area around 0.029 μm² were demonstrated. The TM-SiHDLW waveguide was then used as the basis for anoptical resonator, which was designed to operate at the fundamental TE₀₁₁ mode for yielding high quality factor at a relatively small footprint size. A metal enclosure was also adopted to reduce the radiation loss, and a high quality factor of ~1900 was obtained, more than double the results in other disk or ring resonators of comparable size. Compared to the resonatorsbased on a rounded top metal Si hybrid dielectric-loaded plasmonic waveguide (RTM-SiHDLW) which has a much longer propagation length than the TM-SiHDLW, as reported in our previous work, the performance is essentially the same. This is simply because, for the resonators, the radiation loss is the dominate loss mechanism and the dissipation in the waveguide structure itself, thus, contribute little to the final quality factor of the plasmonic resonators.