Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completeness. Good correlation between the computed results and measurements is observed.

Patch antennas on externally perforated high dielectric constant substrates

A new heuristic UTD diffraction coefficient for non-perfectly conducting wedges is proposed. The coefficient is an extension of the heuristic one given by Luebbers (1984) and as simple as that to compute. In the case of forward-scattering and neglecting the surface wave effects, the new coefficient gives a result close to Maliuzhinets's (1958) solution, also deep in the shadow region where the previous one fails. Moreover, it makes the special care used by Luebbers to deal with grazing incidence unnecessary.

A new heuristic UTD diffraction coefficient for nonperfectly conducting wedges

The Japan Aerospace Exploration Agency will launch the Engineering Test Satellite VIII (ETS-VIII) in 2006 to support the next generation of mobile satellite communications covering the area of Japan (beam coverage El=38/spl deg/ to 58/spl deg/). In this paper, a satellite-tracking left-handed circularly polarized triangular-patch array antenna is developed for ground applications. The targeted minimum gain of the antenna is set to 5 dBic at the central elevation angle (El=48/spl deg/), in the Tokyo area, for applications using data transfer of around a hundred kbps. The antenna is composed of three equilateral triangular patches for both reception and transmission units operating at 2.50 and 2.65 GHz frequency bands, respectively. The antenna was simulated by method of moments (MoM) analysis, and measurement of the fabricated antenna was performed to confirm the simulation results. The measurement results show that the frequency characteristics and the 5-dBic gain coverage in the conical-cut plane of the fabricated antenna satisfy the specifications for ETS-VIII. A prototype of the proposed antenna system is employed in outdoor experiments using a pseudosatellite and shows good performance from El=38/spl deg/ to 58/spl deg/.

Dual-band circularly polarized equilateral triangular-patch array antenna for mobile satellite communications

The Malyuzhinets theory for scattering from wedge boundaries: a review

For a low base-station (BS) antenna located on one street, signals propagate into crossing and parallel streets by reflection and diffraction at corners of buildings. Therefore, in order to accurately predict the received signals, it is necessary to properly model the diffraction coefficient at the building edge and to accurately represent the shape and the electrical properties of the building near the corner. This paper compares ray-tracing predictions to measurements of received power and root mean square (rms) delay spread and shows the need for a diffraction coefficient having larger values than suggested by the commonly used heuristic diffraction coefficient. A new heuristic diffraction coefficient is proposed that has higher diffracted field strength in the deep shadow region and in the region between the two shadow boundaries. The proposed diffraction coefficient shows better agreement with measurements of both received power and delay spread compared to the commonly used heuristic diffraction coefficient. The influence of building shape near the corner and its electrical properties on the ray-tracing predictions are also presented. The shape is shown to have an important role in accurately predicting both received power and delay spread.

Influence of diffraction coefficient and corner shape on ray prediction of power and delay spread in urban microcells

Microstrip antennas have many applications on structures where size and weight constraints are critical. Because of their low profile and conformal nature, they are especially useful for airborne and spacecraft systems. When designing these antennas, it is often assumed that the microstrip elements are mounted on infinitely large ground planes so that the diffraction from the edges of the ground plane are neglected. In practical applications, however, the diffraction from these edges can have a significant affect on the radiation pattern. It would be desirable to have an analytical model that can be used to understand exactly how great this affect is. Treatment of these edges may be necessary to control their effect on the radiation pattern, which can often be accomplished by placing lossy materials in the vicinity of the edges to minimise the fields which diffract from them. Such a technique has been previously successfully applied to control the scattering from the vertex of a wedge using resistive cards, and will be extended here for the problem of controlling radiation patterns.

Analysis and treatment of edge effects on the radiation pattern of a microstrip patch antenna

The solution for the two-dimensional (2-D) Green's function for a wedge with impedance faces is presented. The important feature of this Green's function is that there are no restrictions on the locations for the source and observation points-they can be anywhere. Its development proceeds along two separate lines: one for when the source or observation point is far from the wedge vertex and another one for when it is close. Much of the effort that has been expended in these formulations has been in obtaining forms for the Green's function which are efficient to evaluate numerically. This involved deforming the various contours of integration so that they are rapidly convergent and separating the contributions from the numerous singularities that occur in the integrands and evaluating them in closed form. The formulations that are employed here allow for the individual field components such as the diffracted, geometrical optics, and surface wave components to be identified and studied individually so that a physical understanding for the various scattering mechanisms for the impedance wedge can be appreciated.

Two-dimensional Green's function for a wedge with impedance faces

The high frequency electromagnetic diffraction by a finite length resistive strip attached to a wedge with equal impedance faces is presented. The problem considered is two dimensional where the in...

EM Diffraction by a Resistive Strip Attached to an Impedance Wedge

Microstrip antennas have been employed in airborne and spacecraft systems because of their low profile and conformal nature. Recently, they are being used for other commercial applications such as GPS. Most of the antenna design schemes assume that the microstrip elements are mounted on an infinitely large ground plane, therefore, the diffraction from the edges of the ground plane is usually neglected. However, there are applications where the effect of the edges can become very significant because these edges distort the far-field pattern and also the phase center of the antenna. Attaching resistive cards to the edges of a scatterer is a well known technique for reducing the edge diffracted fields, and was successfully applied to reduce the echo width of a semi-infinite PEC half plane. In this paper, we introduce simple two dimensional (2-D) E- and H-plane models for the microstrip antenna, and study the effect of attaching resistive strips to both ends of a metal ground plane on the radiation pattern as well as the phase center. Note that in general, the edges have a more significant impact in the E-plane pattern. Our main goal is to find an optimum resistive profile which yields the desired radiation pattern and phase center. A nonlinear optimisation algorithm is used where the cost function, which depends on the desired antenna pattern, is minimised to determine the resistive profile which gives the best results. Different types of resistive profiles (piece-wise constant, linear, exponential, quadratic) have been optimized by using two gradient type non-linear optimization techniques, namely, conjugate gradient and Fletcher-Powell algorithms. Numerical and experimental results for the radiation patterns in the E-plane as well as the H-plane are found to be in good agreement.

https://ieeexplore.ieee.org/iel3/3934/11385/00530240.pdf

Synthesis of tapered resistive ground plane for a microstrip antenna

A novel approach to synthesize the frequency response of a scatterer is proposed. A cost function which can be optimized by a number of optimization techniques is obtained in terms of the field scattered by the body under study and the desired frequency response. The field diffracted by the scatterer is obtained by means of the uniform geometrical theory of diffraction. This is done in order to minimize the time spent in calculating these fields, since optimization is an iterative process where the scattered field must be calculated many times. Using this approach, multisection transformers have been designed which substantially reduce the echo width of a perfectly electrically conducting half-plane scatterer for both a wide range of frequencies and over a broad range of backscatter angles. >

M.F. Otero

Papers

Analysis and treatment of edge effects on the radiation pattern of a microstrip patch antenna

Two-dimensional Green's function for a wedge with impedance faces

EM Diffraction by a Resistive Strip Attached to an Impedance Wedge

Synthesis of tapered resistive ground plane for a microstrip antenna

Synthesis of the frequency response of an inhomogeneous resistive strip