Boyu Zheng

Effect of a finite ground plane on microstrip-fed cavity-backed slot antennas

This paper examines the effect of a finite ground plane on microstrip-fed cavity-backed slot antennas. The uniform geometrical theory of diffraction is employed for calculating the diffracted fields from the edges of a slot antennas finite ground plane. Measured and simulated results are presented to illustrate the edge effect of a finite ground plane on a slot antennas return loss and radiation pattern. It is demonstrated that the finite ground plane has a small effect on a slot antennas radiation performance, which suggests that slot antennas are a superior candidate for mobile terminals compared to microstrip patch antennas.

On the design of wide-band and thin absorbers using the multiple resonances concept

This paper describes how one can design a wide-band and thin absorber using the multiple resonances concept. Employing a simplified and yet intuitive equivalent circuit model, we can demonstrate that a thin absorber with a wide bandwidth can be designed by introducing multiple resonant circuits in the substrate backed by a planar conductor whose radar cross-ection (RCS) is to be reduced. A few design examples, including double square-loop printed on a substrate, circuit analog (CA) absorber using multiple resistor-loaded dipoles, and shunt-series connection of transmission line structures are presented to demonstrate the wide-band performance of a thin absorber utilizing a structure with multiple resonances. Both simulated and measured results are provided and compared.

Analysis of Dielectric-Loaded Waveguide Slot Antennas by the Hybrid Mode-Matching/Moment Method

This paper presents a hybrid technique combining the mode-matching method and moment method to analyze various slots cut in the wall of a rectangular waveguide partially filled with a dielectric slab. The waveguide slot structure is decomposed into two parts: a dielectric-loaded waveguide T-junction and an open-ended waveguide radiating into half space. The T-junction is analyzed by the mode-matching method, while the open-ended waveguide is characterized by the moment method with the modal functions in the slot being the full domain basis functions. A new approach for computing multidimensional integrals is proposed in the formulation of the open-ended waveguide, which greatly reduces the computation effort. The T-junction and the open-ended waveguide are then cascaded to obtain the final scattering parameters of the slot structure. Numerical results for different slots on a dielectric-loaded rectangular waveguide calculated by the hybrid method are presented and validated by comparing with measured and simulated data by Ansofts HFSS. Good agreement is observed for all the cases considered. Parametrical studies are also conducted to examine the effect of the dielectric slabs thickness and relative permittivity on slot antennas impedance/admittance.

Effect of a finite ground plane on circularly polarized microstrip antennas

In this paper, the geometrical theory of diffraction (GTD) (R.G. Kouyoumjian and P.H. Pathak, Proc.IEEE, vol. 62, pp. 1448-1461, 1974) is employed to examine the finite ground plane effect for circularly polarized patch antennas. It is shown that a finite ground plane has a small effect on the radiation patterns of circularly polarized microstrip antennas in the forward direction. However, the effect on backside radiation and axial ratio in the forward radiation is noticeable when the four ground plane edges are asymmetric. This effect should be taken into consideration in designing circularly polarized microstrip antennas, and arrays, since their axial ratio bandwidth is generally very narrow.

An Anti-Jamming 5-Element GPS Antenna Array Using Phase-Only Nulling

This paper describes a GPS antenna array that is able to reject jamming signals from two different directions. The GPS array consists of five antenna elements of equal amplitude and different phases. The 5-element GPS array can produce two nulls using the phase-only technique. Ceramic substrate of high dielectric constant is used to realize a miniaturized GPS antenna element. Due to the narrow bandwidth of microstrip patch antennas printed on ceramic substrates, mutual coupling effect must be taken into account in the design of the 5-element GPS array. Closed-form solutions of the required phases to produce two nulls are obtained and given. Simulation results of the GPS antenna elements and arrays by Ansofts HFSS are also presented and discussed

Design of a wide-band high-gain linear array antenna

This paper presents a novel design of wide-band high-gain linear array antenna. The operating frequency of the array antenna is from 890MHz to 2500MHz. The antenna radiates or receives vertically polarized waves and can cover a sectored range of 120° in the azimuth plane. The minimum gain of the array antenna is 10dBi over the entire frequency range covering the whole sector. Measured results for a two-element array are in excellent agreement with simulated ones. This array antenna should be very useful for base stations serving wide-range mobile users and can be readily scaled to other ultra-wideband applications.

Shielding effectiveness of cylindrical enclosures with rectangular apertures

This paper presents an efficient numerical method to predict the shielding effectiveness of a cylindrical enclosure with a rectangular slot. The problem is initially divided into two parts using the field equivalence principle: one is the half free space with a plane wave illumination and a magnetic current on the aperture surface and the other is the rectangular-to-circular waveguide junction with one end of the circular waveguide being shorted. The reflection coefficient of the waveguide junction is calculated by the mode-matching method and the magnetic field in the exterior region is modelled using a mixed potential integral equation. The unknown coefficients of the electromagnetic field are obtained by matching the tangential magnetic field along aperture surface. Numerical results are presented and compared to those obtained by Ansoftpsilas high frequency structure simulator (HFSS). Parametrical studies are also conducted for the effect of the location and size of the aperture on the shielding effectiveness.

Effect of a Finite Ground Plane on Rectangular Waveguide Slot Antennas' Radiation Patterns

This paper examines the effect of a finite ground plane on the radiation patterns of waveguide slot antennas. A hybrid geometrical theory of diffraction (GTD) method is presented to calculate the radiation patterns of slot antennas on both air-filled and partially dielectric-loaded rectangular waveguides with a finite wall size. The electric field distribution along the slot is obtained by a full-wave mode-matching method and then employed to calculate the geometrical optics (GO) field. The GTD is then applied to evaluate the diffraction from all the waveguide wall edges. Radiation patterns are finally obtained by the vectorial summation of the GO field and the diffracted fields. Numerical results obtained by our method are compared with measured data and those simulated by Ansofts high frequency structure simulator (HFSS). Good agreement is observed for all the cases considered. The backward radiation is also examined for different sizes of waveguide wall on which the slots are cut.

Full-wave analysis of dielectric-loaded waveguide slot antennas including internal and external mutual coupling

A hybrid full-wave technique is proposed to analyze the structure having two slots cut in the wall of a rectangular waveguide partially filled with a dielectric slab. Each slot element is decomposed into two parts: a dielectric-loaded waveguide T-junction and an open-ended waveguide. A four-port network is composed in the T-junction cascading and the internal mutual coupling between the two slots is included automatically. The external mutual coupling is calculated by a full-wave integration method. Combining the scattering parameters of the four-port network and the external mutual coupling solves the whole waveguide slot structure. Numerical results obtained by our hybrid method are presented and compared with simulated data by Ansofts HFSS. Good agreement is observed for all the cases considered.

A Dual-band Microstrip-fed Cavity-backed Subarray

A compact dual- and wide-band cavity-backed slot antenna subarray has been presented in this paper. Ridged slots have been employed in the design to shorten the slot length. Four slots are fed by two feeding networks printed on the upper layer of a substrate for great design flexibility. The designed antenna has been measured and experimental results have shown that the 10 dB return loss bandwidth is 7.5% for 900 MHz band and 26% for 1800 MHz band, respectively. Because of its compact size and good radiation patterns at both frequency bands, this described subarray can be very useful for dual-band array applications