We study the rectangular tips of the dipole photoconductive antenna, which has been widely used for terahertz radiation and detection, with different blend radii effect on the emission performance of terahertz (THz) radiation. For the amplitude of THz radiation pulse is proportional to the local electric field in the gap, the increased maximum bias electric field by blending tips is able to achieve higher THz radiation power. Both considering the influence to the maximum bias electric field and the emission efficiency, the blend radius of the rectangular tips is suggest to be larger than 5 μm and the radiation power is largely enhanced. Comparing to the previous work, our method has better THz radiation performance.

Unlike some traditional polynomial phase signal (PPS) parameter estimation methods restricted to monocomponent case, this paper focuses on the parameter estimation of multicomponent PPSs mixed in a single channel, which is more sophisticated and always involves the cross-term issue. In this investigation, based on the model of multicomponent PPSs in additional white Gaussian noise, we partition the maximum likelihood estimation into two consecutive steps. The first one involving estimation of polynomial coefficients is intensively studied using importance sampling, while the second one involving the estimation of amplitude and initial phase is trivial. Numerical experiments show satisfactory estimation performance even if the parameters are closely spaced.

DeDesign procedure for a modified Composite Right/Left Handed (CRLH) unit cell is represented. The ferroelectric interdigital capacitor (IDC) is used as a tuned capacitor, and spiral inductor is utilized to implement inductors. A modified CRLH unit cell is attained by moving the shunt inductor of conventional unit cell to both ends with doubled values. In this manner, only one bias network would be required for each unit cell. The parameters of the designed unit cell are obtained so that the Bloch impedance to be equal to 50Ω and the Bloch propagation constant to have one zero at the operational frequency. The operational frequency is chosen equal to 11.45 GHz, which is in the Ku-band and in middle of the up-link satellite communications. To design the modified unit cell, initially, the unit cell without a shunt capacitor is constructed. This would result in Π-model structure for which the element dimensions are varied to reach the desired values. Next, the shunt capacitor is added to the model and its length is varied until the balanced condition is achieved.

In this paper, transmission properties of stacked split ring resonators metasurfaces in free space and under normal incidence are investigated experimentally and numerically. Emphasis is put on studying the interaction between adjacent SRRs metasurfaces. The thorough analysis of the electromagnetic fields shows that both magnetic and electric coupling can occur between adjacents metasurfaces for vertical and horizontal polarization. In addition, we found that all propagating bands within our spectral window (up to 20 GHz) support right-handed behaviour. Both simulation and experiment results in the microwave regime are in good agreement.

Antenna array beamformers suffer from performance deterioration in the presence of mutual coupling (MC) between array sensors. In this paper, we present a theoretical analysis in terms of the output signal-to-interference-plus-noise ratio (SINR) for the performance of antenna array beamformers under MC effects. Based on the model of a distortion matrix to encapsulate the MC effects, a closed-form expression for the SINR is derived that is shown to accurately predict the SINR obtained in simulations. This theoretical formula is valid for any distortion matrix estimated from collected measurement data. The SINR formulas provide insights into the influence of the MC effects on the performances of the linearly constrained minimum variance (LCMV) beamformer and the eigenspace-based (ESB) beamformer. It is shown that the ESB beamformer outperforms the LCMV beamformer under MC effects. Moreover, we derive the formulas for computing the eigenvalues of signal correlation matrix under MC effects. Simulation results are presented for confirming the validity of the theoretical results.

In this paper, a novel design of dual-band microstrip antenna with complementary split ring resonators (CSRRs) is presented. A simple and successful dual-band antenna can be realized by etching three CSRRs in the ground plane of a conventional patch antenna. The proposed antenna shows good performances at both resonant frequencies. The CSRRs embedded in the ground plane make a major contribution to the first operating band, but has minor effect on the second operating band. It is beneficial for designing a dual-band antenna as well as a miniaturized antenna flexibly. The simulation results are analyzed and compared with measured results in a good agreement.

The microwave backscattering of the sea surface is investigated with the wedge-shaped breaking waves for the super events at low grazing angles (LGA). According to the relationship between the wave breaking and the whitecap, the finite three-dimensional wedges are utilized to approximately model the breaking waves, of which the spatial distribution is simulated with whitecap coverage. The phase-modified two-scale method (TSM) and method of equivalent currents (MEC) are used to calculate the surface and volume scattering of sea surface and breaking waves respectively. The sea spikes in LGA are observed by this model, and the strong directionality is caused by the breakers. Considering the Bragg phase velocity, orbital motion of facets and wind drift, the Doppler spectrum is simulated with the time series of sea clutter. Included the breaking waves, the scattering model indicates that the enhanced non-Bragg scattering leads to the extended Doppler spectrum width. The numerical results agree with the measured data well at LGA. Compared with the statistical models, the complex physical mechanism of the sea scattering is explicitly described in this paper.

This work presents new method, retrieved results and validation for complex and frequency dependent permittivity and permeability parameter extraction of two composite, homogeneous and isotropic magnetically loaded microwave absorbers. Permittivities and permeabilities are extracted from free space transmission measurements for frequencies from 22 up to 140 GHz. For validation of the results reflection measurements (samples with and without metal backing) are performed and are compared with simulations that use extracted models. The proposed new method solves some shortcomings of the popular methods: extracts both permittivity and permeability only from transmission parameter measurements, gives good results even with noisy data, does not need initial guesses of unknown model parameters.

This study presents a design of a compact stub-type bandpass filter with capacitively loaded stubs and a fold-back structure. This paper employed the fabrication process of low-temperature co-fired ceramic (LTCC) for filter realization of a multi-layer structure. The proposed filter structure required adding end capacitors to stubs to extend their electrical length, while achieving a length reduction of 30%. This study provided design curves to determine the dimensions of the end capacitor for reaching maximum electrical length extension. In addition, a fold-back configuration was applied to halve the filter size. An experimental filter operating at 5.8 GHz was fabricated and measured to validate the design concept, achieving a highly compact size of 14.3×8.2×0.76 mm³.

In this paper, several configurations of a rotary magnetic refrigerator are proposed and investigated using three dimensional finite element method simulations. Their electromagnetic performance is analyzed considering the magnetic flux density, the forces and the torque. The rotor is a single permanent magnet while the stator is made of four refrigerant beds and a magnetic yoke. Multipole stators or rotors with 4, 6 and 8 refrigerant beds have been tested. The beds can be fitted or set at the inner surface of the yoke. The yoke can have smooth or salient poles. To minimize the magnetic torque, an original structure is proposed and tested. It is composed of two half-systems assembled with a 45^o angle shift between rotors or stators. Because of the large amount of data, a suitable procedure to achieve an effective comparison between all configurations is established.

An analytical solution for the scattering of an electromagnetic plane wave from a perfect electromagnetic conducting (PEMC) circular cylinder coated with chiral material is derived. The PEMC cylinder as well as coating layer is of infinite length (2-D problem). Parallel polarization of the plane wave is considered for the analysis. The response of the chiral coated geometry has been observed for DPS-chiral, DNG-chiral and chiral-nihility coating layers. Also the behavior of the monostatic echo width for DPS-chiral and DNG-chiral layers has been studied against the admittance parameter. Results of bistatic echo width for the PEMC, PEC and PMC core have been presented. Under special conditions our results are in a very good agreement with the published literature.

In this paper, several simple antenna designs based on the use of an active dipole placed above a ground plane with an array of parasitic dipoles are presented. The parasitic dipoles are used to modify the pattern of the active dipole yielding a pencil beam of moderate gain. The use of one active element provides a very simple feeding network that reduces the complexity of the antenna. The proposed technique optimizes the geometry and configuration of both active and parasitic elements. It is shown that the performance of the designed antennas is considerably better than that of a similar antenna without parasitic elements.

This paper formulates a simple vector integral expression for electromagnetic waves received after scattering from a surface. The derived expression is an alternative to the Stratton-Chu equation frequently used for polarimetric surface scattering. It is intended for use in polarimetric Global Navigation Satellite System (GNSS) ocean remote sensing, or any type of polarimetric remote sensing from surfaces, when the surface roughness pattern is known from simulation or data. This paper is intended to present a complete accounting of the steps leading to the simpler vector integral expression. It therefore starts with the scalar case, using Maxwell's equations and Green's theorem. It principally treats the case of a transmitter within the integration volume, but discusses how the formalism changes if the transmitter is outside of the integration volume, as with plane waves. It then shows how the scalar expression can be extended to a vector expression for the component of the electric field in an arbitrary receive-polarization direction due to scattering from a rough surface of an incident wave with an arbitrary transmit polarization. It uses the Kirchhoff, or tangent-plane, approximation in which each facet on the ocean is considered to specularly reflect the incoming signal. The derived vector expression is very similar to that for a scalar wave, but it includes all vector properties of the scattering. Equivalence is demonstrated between the Stratton-Chu equation and the derived, simpler expression, which is operationally easier to code than the Stratton-Chu equation in many modeling applications.

In this paper, a novel design of open slot antenna for bandwidth enhancement is proposed and investigated. The bandwidth enhancement of the proposed antenna is achieved by simply attaching a rectangular stub to the circular radiating patch. Experimental results indicate that the bandwidth of the antenna can achieve an operating bandwidth of about 139% over a wideband frequency range from 2.57 to 14.23 GHz. This antenna has a small size of dimensions 20×35 mm² and is suitable for wideband applications in various wireless communication systems.

An improved CPW-fed configurations with dual-mode double-square-ring resonators (DMDSRR) for tri-band application is proposed in this paper. The resonant frequency equations related to DMDSRR geometry are introduced for simply designing tri-band bandpass filter (BPF). Resonant frequencies and transmission zeroes can be controlled by tuning the perimeter ratio of the square rings. To obtain lower insertion loss, higher out-of-band rejection level and wider bandwidth of tri-band, the improved coplanar waveguide (CPW) fed and the step impedance resonator (SIR) and meander line dual-mode perturbations are designed. The effective design procedure is provided. The proposed filter is successfully simulated and measured. It can be applied to WLAN (2.45, 5.20 and 5.80 GHz) and WiMAX (3.50 GHz) systems.

Nyquist folding receiver (NYFR) is a new kind of interception architecture, which can simultaneously intercept wideband signals in multi-Nyquist zones with one or two analog-to-digital converters (ADCs). A parameter estimation algorithm of the linear frequency modulated (LFM) signal intercepted by an improved NYFR is presented. Firstly, the NYFR is improved by introducing a synchronous mechanism, and we denote this structure as a synchronous NYFR (SNYFR). Secondly, taking LFM as an example, the input and output noise distributions of an SNYFR are discussed. Then, a fast parameter estimation algorithm is derived from the frequency spectrum of the output signal, and an advice for the design of local oscillator signal is given. Simulations show that the parameter estimation accuracy is close to the maximum likelihood when the signal to noise ratio (SNR) is above -3 dB.

In this paper, a high-efficiency wireless energy transmission via magnetic resonance is experimentally implemented in a resonator with the various sizes of transmitting and receiving coils and the receiving coil having two shapes of rectangular and circular types. The transmission efficiency is analyzed by varying the transmission distance. The resonance between the transmitting and receiving coils is achieved with lumped capacitors terminating the coils. The transmission efficiency of the resonator consisting of a circular transmitting coil with a diameter of 60 cm and rectangular receiving coil with a one side length of 10 cm is about 80% at the transmission distance of 20 cm. The transmission efficiencies of the wireless energy transmission resonator consisting of a receiving coil with the size of iPhone4 are about 75% and 40% at the transmission distances of 20 cm and 50 cm.

Circular synthetic aperture radar (CSAR) is different from other usual SAR modes, e.g., Stripmap SAR or Spotlight SAR, which takes a circular path rather than a straight path. It can provide not only two-dimensional (2-D) high resolution images but also three-dimensional (3-D) information about the target. In this paper, 2-D CSAR imaging containing 3-D information about the target is discussed. Considering the limited bandwidth of radar system and the limited angular persistence of the reflector's scattering characteristic in a real scene, we combine the data extrapolation technique based on the autoregressive (AR) model with the non-coherent combination of the sub-aperture images based on the approximate Generalized Likelihood Ratio Test (GLRT) technique to get a 2-D CSAR image with resolution improved and with aspect-dependent reflectivity characteristics kept. The GTRI T-72 tank dataset is processed to test the algorithm.

The potential field generated by two charged cylindrical perfect electrical conductors sandwiching a dielectric plane of finite thickness, and the influence of the dielectric plane on the field, is analysed. In particular, the field profile is examined when the cylinders are (i) rotating at some constant angular velocities, and (ii) surrounded, respectively, by uniform dielectric tubes of finite thickness.

Systems that employ stimulating and implantable monitoring devices utilize inductive links, such as external and implanted coils. The calculation of the mutual inductance and the magnetic force between these coils is important for optimizing power transfer. This paper deals with an efficient and new approach for determining the mutual inductance and the magnetic force between two coaxial coils in air. The setup is comprised of a thick circular coil of the rectangular cross section and a thin wall solenoid. We use an integro-differential approach to calculate these electrical parameters. The mutual inductance and the magnetic force are obtained using the complete elliptic integrals of the first and second kind, Heuman's Lambda function and one term that has to be solved numerically. All possible regular and singular cases were solved. The results of the presented work have been verified with the filament method and previously published data. The advantage of these proposed formulas for mutual inductance or for the magnetic force is that they give the solution in the analytical and the semi-analytical form either for regular cases or singular cases. It is not case with already known methods in which it is necessary to take particular care of these cases of consideration.