Microstrip Disk Research Articles

Microstrip-antenna design for hyperthermia treatment of superficial tumors.

Microstrip antennas have many different advantages over other RF/MW radiative applicators employed for superficial hyperthermia treatment. This is mainly due to their compact and body-conformable structure as well as to printed circuit board techniques, both of which allow a wide design flexibility for superficial tumor heating. Among the wide variety of radiator configurations, three microstrip antennas of increasing complexity with electromagnetic and heating characteristics potentially suitable as applicators for superficial hyperthermia have been designed, developed, and tested in different radiative conditions: a microstrip disk, a microstrip annular-slot, and a microstrip spiral. Electromagnetic design criteria are presented together with the determinations of the applicator return loss versus frequency and thermograms of the near-field heating pattern in muscle-like phantom. The results are in good agreement with theory and indicate that: i) the operating frequency is either single or multiple according to the applicator-mode, "resonant" or "traveling-wave," and can be chosen in the useful frequency range for hyperthermia (200-1000 MHz) according to the tumor cross-section and depth; ii) the heating pattern flexibility increases going from the simple geometry disk to the annular-slot and spiral applicators; iii) a distilled-water bolus is required; iv) the annular-slot applicator exhibits the highest efficiency, while the spiral applicator provides the best performance.

Magnetostatic wave resonators using microstrip disk

The authors propose a magnetostatic wave resonator using yttrium-iron-garnet (YIG) film with a microstrip disk. Assuming a magnetic wall at the edge of the disk, a dispersion relation is derived and solved numerically to obtain the resonant frequency. Resonant mode charts are given for various parameters of resonator. The quality factor is also given as a function of the resonator dimensions. Resonant characteristics are confirmed experimentally using 40- mu m- and 13.5- mu m-thick YIG films with 5-mm-diameter strip disk at S band.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Disk microstrip antenna with axisymmetric excitation

Disk microstrip antenna with axisymmetric excitation

Full-wave perturbation theory for the analysis of coupled microstrip resonant structures

A full-wave perturbation theory for the system of coupled microstrip disk structures is presented. The theory is based on the electric field integral equation description of the circuit, which includes all of the wave phenomena associated with the conductors and the surrounding media. This method is suitable for quantification of nearly degenerate coupling between open microstrip disks, yielding the complex system eigenmodes. For the case of two coupled disks, the perturbation theory analytically separates, though simultaneously solves for, the symmetric and antisymmetric system eigenmodes. The development of the perturbation theory leads to good physical insight for this mode-splitting phenomena. Numerical results obtained with the perturbation theory agree well with those obtained by a more accurate method of moments solution to the coupled set of electric field integral equations, as well as with experimental data. >

Analysis of biconical microstrip antennas

Biconical microstrip antennas having a conical patch over a conical substrate are investigated. Analytical expressions for the field distribution inside the conical cavity are developed in a spherical coordinate system and used to determine the eigenvalues of the resonant modes. It is found that, in addition to the axially symmetric modes, TE modes can also resonate which are asymmetric and dependent on the azimuthal angle. For coaxial probe excitation of the cavity its analytic expressions for the field components are determined and used to investigate the antenna input parameters and radiation patterns. The special case of a conical patch microstrip antenna with a planar substrate is also studied. It is shown that, in comparison with circular disc microstrip antennas, a conical patch yields a wider impedance bandwidth and higher gain.

Resonance in spherical-circular microstrip structures

The resonance problem of a circular microstrip disk mounted on a spherical surface is studied theoretically. The radiator is replaced by a surface current distribution. The effects of the dielectric substrate as well as the curvature effect are taken into account by the Green's function formulation in the spectral domain. A vector Legendre series is defined. Cavity model current distribution is used as the current basis. Galerkin's procedure is used to solve for the complex resonant frequencies. Numerical results show that the effect of the curved surface on the resonant frequency and quality factor of the microstrip patch may be significant. In general, when the radius of the sphere is decreased, the effective radius of the patch will be reduced and the radiation loss is increased. >

Patch antennas on a spherical body

The far field radiation patterns of wrap-around, circular disk and annular ring microstrip patch antennas mounted on a sphere are studied theoretically. The patches are replaced by equivalent magnetic currents based on cavity model theory. The radiation fields are then determined using the modal expansion technique in spherical co-ordinates. Results for a wraparound antenna of a half-wavelength in width, for the broadside TM11 mode of a circular disk antenna and for the TM11 and TM12 modes of an annular ring antenna are given. The accuracy of the simple theory is confirmed by a more rigorous but complicated theoretical approach based on electric surface current model.

Far field analysis of spherical-circular microstrip antennas by electric surface current models

The far field radiation patterns of a circular disk microstrip antenna mounted on a sphere are studied theoretically. The radiator is replaced by an assumed surface current distribution. The effects of the dielectric layer and the metallic sphere are rigorously taken into account by the spectral domain Green's function formulation. In the spectral domain represented by the vector Legendre series, the Green's function matrix is diagonal. The results are verified by comparison with results obtained from the cavity model theory. The cavity model agrees asymptotically with the present method for the case of a thin dielectric substrate.

Spectral domain analysis of microstrip antennas with an airgap

AbstractThe circular disk microstrip antenna with an airgap between the dielectric substrate and the ground plane is formulated using the spectral domain method. The complex resonant frequencies of the structure is determined using Galerkin's procedure. Some available experimental data are compared with the present method.

Hankel transform domain analysis of dual-frequency stacked circular disc microstrip antenna

This paper presents an accurate and efficient method for the computation of resonant frequencies and radiation patterns of a dual-frequency stacked circular microstrip antenna. The problem is first formulated using the Hankel transform domain approach and expressions are obtained for the Green's function in the Hankel transform domain, which relates the electric surface currents on the circular disks and tangential electric field components on the surfaces of the substrates. Then Galerkin's method together with Parsebal's relation for Hankel transformation is used to solve for the unknown currents. In the derivation process, the resonant frequencies are numerically determined as a function of the radii of two circular disks and thicknesses and relative permittivies of two substrates. Finally, the far-zone radiation patterns are directly obtained from the Green's function and the currents. The numerical results for the resonant frequencies and radiation patterns are in excellent agreement with the available experimental data corroborating the accuracy of the present method.

A ring cavity antenna of wide beamwidth

AbstractMobile telecommunication systems by satellite meet the requirement of antenna radiation pattern of wide beamwidth. The wide beamwidth of the circular microstrip disk antenna is obtained by high dielectric constant substrate. However, the dielectric losses and difficulty in manufacturing are problems for high dielectric constant materials.Wide beamwidth is obtained also using the antenna with an electrically small magnetic current loop.This paper presents the ring cavity antenna without dielectric materials. It also has electrically small magnetic current loop. Antenna characteristics calculated by the cavity model showed that the ring cavity antenna has wide beamwidth. Theoretical values are verified also by the measured radiation pattern and the input impedance.

Moment-method solution of the center-fed microstrip disk antenna invoking feed and edge current singularities

The problem of a microstrip disk antenna excited by a probe at its center is studied using a moment-method approach for the evaluation of the surface current on the disk. The novelty of the work is a careful treatment of the singular effects of the probe and of the disk edge on the surface current on the disk. This is done by including in a proper way an attachment-mode current and an edge current in the surface current on the disk. The inclusion of these two currents accelerates the convergence of the moment-method solution and enables the input impedance to be obtained in a broad frequency range, including the zero-frequency limit. The influence of the probe on the input impedance is taken into account in a correct and accurate way. A comparison between measured and computed results is given, and good agreement is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Technical memorandum: Analysis of reactively loaded microstrip disk antenna

The moment method solution to the problem of a reactively loaded circular patch is presented. Using the reaction integral equation in conjunction with the method of moments, parameters of the Thévenin&apos;s equivalent network for the loaded patch are obtained. From the equivalent network parameters an expression for the input impedance of the loaded patch is derived. A design procedure for a circularly polarised disk antenna is presented. Computed results are compared with the experimental data.

New determination of resonant frequency of circular disc microstrip antenna: application to thick substrate

An analytical expression is presented for the resonant frequency of a circular disc microstrip antenna with a thick dielectric substrate. It shows explicitly the dependence of the resonant frequency on the characteristic parameters of a patch antenna. The theoretical results are in good agreement with experimental data.

Multiple-Port Power Divider/Combiner Circuits Using Circular Microstrip Disk Configurations

A generalized method for evaluating the scattering parameters of a multiport center-fed circular microstrip disk power divider/combiner circuits is presented. The method is based on the planar circuit approach in which the two-dimensional Green's function of a circular segment is used. Various symmetrical power divider/combiner circuits have been designed and tested. The effect of introducing additional shorted ports between the circumferential output ports on the reduction of spurious radiation losses is discussed. Experimental results verifying the design methodology are given.

Resonance and radiation of the elliptic disk microstrip structure, part I: Formulation

The analysis of resonance, input impedance, and radiation of the elliptic disk microstrip structure is rigorously formulated, using the scalar and vector Mathieu transforms. With the help of these transforms, the resonance frequencies of the structure can be derived exactly using Galerkin's method and approximately using a perturbational approach. Expressions for the input impedance and the radiation pattern are also obtained.

Mutual coupling between circular disc microstrip antennas

The mutual coupling between microstrip antennas is studied by applying the reaction theorem and the cavity model. A semianalytic formula is derived for disc antennas which takes into account the dependence on the relative angular position of the antennas, as well as on the angular feeding point poisition. Theoretical results are in good agreement with measurements.

Numerical analysis of circular disk microstrip antennas with parasitic elements

Efficient numerical analysis of double tuned circular disk resonators/radiators is described. This method is based upon the Hankel transform domain analysis. Several numerical examples of input voltage standing-wave ratio (VSWR) characteristics and radiation patterns are compared with available experimental data.

Input impedance of a circular microstrip disc antenna using mode matching

A model is developed to calculate the input impedance of a coaxially fed circular microstrip disc antenna. A mode-matching approach is used, which makes it possible to include the effects of modes other than the dominant mode. Comparison is made with measured results taken over the frequency range 8 GHz to 11 GHz.

Spectral Domain Analysis of an Elliptical Microstrip Ring Resonator (Comments)

Along with the above paper several other papers have been published recently by Sharma and his co-workers [2]-[3] on the analysis of the resonant frequencies of a microstnp disk using the quasi-static approach. The quasi-static approach has been proven to be incorrect in [4] and [5]. The quasi-static argument on the correction to the resonant frequencies of a microstrip disk is based on some intuitive arguments that are not rigorous. The only thing it predicts correctly is that the resonant frequencies of a microstrip disk should decrease compared to that of a magnetic-wall model. The author may argue that since the correction to the magnetic-wall model is small, any approximate method is viable. However, we have found that the quasi-static correction could be as much as 50 percent in error. Even when this correction is small, if we bother to caIculate it, I think we should calculate it correctly. The author's quasi-static correction has a new twist compared to earlier authors, but when epsilon/sub r/ = 1, it does not differ from the quasi-static correction of earlier work.