Zhongxiang Shen

A Thin and Broadband Absorber Using Double-Square Loops

This letter presents a design of thin and broadband absorbers using a two-dimensional (2-D) periodic array of double-square loops printed on a dielectric substrate. Lumped resistors are inserted into the four sides of the loops to absorb the incident electromagnetic wave. Simulated and measured results for the radar cross-section (RCS) of a finite 2-D array of double-square loops are in good agreement and both show that the novel absorber can reduce a conducting plates RCS greatly over a wide frequency range.

Electromagnetic Scattering by a Conducting Cylinder Coated with Metamaterials

The electromagnetic scattering from a conducting cylinder coated with metamaterials, which have both negative permittivity and permeability, is derived rigorously by using the classic separation of variables technique. It is found that a conducting cylinder coated with metamaterials has anomalous scattering cross section compared to that coated with conventional dielectric materials. Numerical results are presented and discussed for the scattering cross section of a conducting cylinder coated with metamaterials.

A Novel Band-Reject Frequency Selective Surface With Pseudo-Elliptic Response

A novel frequency selective surface (FSS) exhibiting pseudo-elliptic band-reject response is presented. The proposed FSS consists of a two-dimensional periodic array of microstrip lines. For an incident wave of linear polarization perpendicular to the printed lines, virtual magnetic walls are formed between the microstrip lines. Since a microstrip line shielded with magnetic side walls supports two quasi-TEM modes, the two-dimensional array effectively forms a dual-mode resonator. The elliptic response is thus realized by coupling the incident wave to both modes of the resonator. A wideband pseudo-elliptic response is achieved by including higher-order modes of the array. To analyze this FSS, we treat it as a cascaded junction of air-to-microstrip line discontinuities, and investigate the problem using the full-wave mode-matching method. We provide useful design guidelines for both narrow-band and wide-band FSSs, while explaining the effect of various geometrical parameters on the performance of this FSS. Narrow-band and wideband FSS prototypes are fabricated and measured results validate our design concept. This new class of FSS is easy-to-assemble, exhibits a superior performance, and is thus potentially useful for many practical applications.

Backscattering Cross Section of Ultrawideband Antennas

Backscattering of ultrawideband (UWB) antennas is theoretically and experimentally studied in this letter. The finite-difference time-domain (FDTD) method using Berengers perfectly matched layer absorbing boundary condition (PML-ABC) is employed for simulation and the measurement is carried out in indoor environment. Monostatic radar cross section (RCS) of square-slot antenna and printed circular-disc monopole antenna (PCDMA) terminated with three different kinds of loads are numerically calculated and experimentally verified. They are in good agreement in the frequency range from 3 to 11 GHz. Afterwards, scattering characteristics of the structural and antenna modes of two kinds of UWB antenna structures are extensively characterized in both the frequency domain and time domain

On the Design of Single-Layer Circuit Analog Absorber Using Double-Square-Loop Array

A detailed study of a single-layer circuit analog absorber using double-square-loop array reveals that three resonances can be obtained within its operating frequency band. An equivalent circuit model is proposed to explain how these three resonances can be produced and its absorption bandwidth can be widened. Simple guidelines for the design of this double-square-loop absorber are then formulated. It is shown through measurements that the fractional bandwidth of 126.8% is realized for at least 10 dB reflectivity reduction under the normal incidence. Furthermore, the total thickness of the proposed design is only 0.088λL at the lowest operating frequency. A good agreement between simulated and measured results demonstrates the validity of our design.

An inverted microstrip-fed cavity-backed slot antenna for circular polarization

This letter presents a compact circularly polarized cavity-backed four-slot antenna using an inverted configuration. The four-element slot antenna is fed by a microstrip network on the topside of the substrate, while a metallic cavity of rectangular shape is placed in the slot side of the substrate. The measured 10-dB return loss and 3-dB axial ratio bandwidths at the center frequency 6 GHz are 26.6% and 15%, respectively. The measured antenna gain for right-hand circular polarization (RHCP) is 8.7 dBi at 6.0 GHz.

Inverted microstrip-fed cavity-backed slot antennas

This article presents a study of microstrip-fed cavity-backed slot (CBS) antennas using a new inverted configuration. The inverted structure places the metallic cavity in the slot side of the substrate, which renders a number of advantages. Two inverted microstrip-fed cavity-backed antennas, including single CBS antenna and an eight-element CBS array, are simulated, fabricated, and tested. Measured data verify the assertion that the inverted configuration is a better arrangement for designing microstrip-fed CBS antennas and arrays.

Hybrid PO-MoM analysis of large axi-symmetric radomes

Over the last three decades, intensive work has been done to develop techniques aimed at accurate and efficient analysis of antenna radome systems. Some applications involve radar operating in the millimeter wave range and for those cases the radome size can be on the order of one hundred wavelengths or so in length. For practical simulations of such large radomes, a hybrid physical optics-method of moments (PO-MoM) technique is presented for accurate and efficient analysis of electrically large radomes. The procedure combines the method of moments (MoM) for modeling the tip region of the dielectric radome and ray optics in conjunction with physical optics (PO) for treating the flatter smooth section of the radome. Calculated far-field patterns using the new technique agree well with measured data for a reflector antenna radiating in the presence of a large radome. The computational time for simulating the performance of a 46/spl lambda/ reflector in the presence of an 88/spl lambda/ long radome was a mere 4 h on a 233 MHz PC.

A new dual-polarized broadband horn antenna

This letter describes a new design of dual-polarized broadband horn antennas. The bandwidth of the designed horn antenna is from 2 to 26.5 GHz. A novel coaxial line to quadruple-ridged waveguide transition is introduced to improve the return loss performance of the horn antenna. Measured results for VSWR, isolation, gain, and radiation pattern of the designed horn antenna are presented.

A hybrid FD-MoM technique for predicting shielding effectiveness of metallic enclosures with apertures

In this paper, a hybrid technique combining the finite-difference (FD) method and the method of moments (MoM) in the frequency domain is proposed to predict the shielding effectiveness of rectangular conducting enclosures with apertures under external illumination. The interior and exterior regions of the enclosure are analyzed separately by employing the field equivalence principle. Internal electromagnetic fields are discretized using the (FD) method, while external fields are formulated by the MoM. Enforcement of continuity of the tangential magnetic field over the aperture surface gives the desired equation to solve for electromagnetic fields everywhere. Numerical results for the shielding effectiveness of a rectangular cavity with apertures calculated by the new hybrid technique are presented and validated by comparing with experimental data.