Multilayer Effects on Cavity-Backed Slot Antennas

Spherical arrays present a natural choice if complete hemispherical coverage with nearly constant beam width is needed. In this article, circular stacked-patch antennas embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. The influence of structure radius on input impedance and radiation pattern is investigated. The results confirm the importance of rigorous analysis of curved patch antennas. Furthermore, a laboratory model is built to validate the developed program. The agreement between measured and calculated results is good

Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the reciprocity theorem. Compared to the Hertzian dipole, which is the only type of source that has been considered in the literature, the resonant dipole substantially improves the performance of periodic LWA in terms of radiated power, efficiency and bandwidth. Numerical results are given for a resonant dipole over the frequency range of 60-70 GHz and compared with those obtained from commercial softwares, FEKO ® and Ansys HFSS ® , showing an excellent agreement with considerable improvement in terms of memory usage and computational speed.

The probe-fed hemispherical dielectric-resonator antenna (DRA) with a concentric conductor is studied theoretically in this paper. Using the mode-matching method, the exact Green's functions for evaluation of the input impedance and radiation patterns are found, with the functions presented in computationally efficient forms. The moment method is used to determine the probe current and, hence, the input impedance as well as the radiation patterns. The results are verified by special cases available in the literature. In this paper, the effects of the conductor radius, dielectric constant, probe length, and probe displacement on the input impedance are investigated. The theory is very general and, by taking appropriate limits, can be used to study the solid DRA and the conductor-loaded wire antenna. To aid the DRA design engineer, the TE/sub 111/-mode characteristic equation of the DRA is also studied, from which the simple formulas for the resonant frequency and Q-factor are obtained.

In this study, a FEM-based microstrip antenna simulator, namely FEMAS, has been developed. The FEMAS allows analysis and design of three-dimensional microstrip antenna elements and outcomes the related antenna parameters such as input impedance, gain, and radiation pattern. In the paper, the FEM formulation is overviewed and the features of FEMAS are presented. Also, The return loss characteristics of a microstrip antenna achieved by means of FEMAS and Ansoft HFSS are presented.

In this article, a fast and efficient hybrid method that combines the volume-surface integral equation (VSIE) and the modified surface integration (MSI) method is proposed to evaluate the electromagnetic (EM) performance of the large-/medium-sized radome-enclosed antennas (REAs). An approximate equivalence principle is presented to formulate the physical model for the EM radiation of the REA, and then, the full-wave VSIE for the antennas and the high-frequency MSI method for the dielectric radome are coupled with each other in an iterative manner. Since mutual interactions up to the second order among the antennas and the radome are considered, the method shows good accuracy in both the near- and far-field regions of the REA system. In addition, all the computation processes involved in the method, including the method of moments (MoM) solution of the VSIE, surface integrations (SIs) in the MSI, and ray tracing for determining the local transmission matrix for the dielectric radome, are accelerated by the multilevel fast multipole algorithm (MLFMA), which makes the method highly efficient in terms of both computational time and memory requirement. Numerical results show that the proposed hybrid method can predict the EM performance, e.g., the input impedance and radiation pattern, of the REA system with good accuracy compared with the full-wave simulations.

The hemispherical dielectric resonator antenna (DRA) excited by a single-arm spiral slot is studied theoretically in this paper.The Green's function technique is employed to formulate an integral equation for the spiral slot current.The moment method with piecewise sinusoidal (PWS) basis and testing functions is used to convert the integral equation into a matrix equation by using a deltagap exciting source.The input impedance, return loss, axial ratio and radiation pattern are calculated.Numerical results demonstrate that the analysis is efficient.

A rectangular cavity backed slot antenna with two parallel parasitic slots is proposed to widen the bandwidth. The method of moments (MoM) is used to calculate the input impedance, VSWR, and radiation pattern where the effect of the cavity is taken into account. The VSWR bandwidth (/spl les/ 2) is increased from 4.6 % to 10.6 % by introducing two parasitic slots.

A slot antenna has been designed and optimized to obtain frequency reconfigurability over a wide range of frequencies. The proposed antenna has a rectangular slot with a hexagonal slot being placed in the inner conducting element. The antenna is fed through a 50Ω microstrip feed line placed on the other side of the substrate. The resonant frequency is controlled by changing the capacitance value of the varactor diode place between the two conducting elements providing a various range of resonance frequencies, frequency bands, and different bandwidths. The suggested slot antenna is simulated using the Ansys Electronics Desktop simulator (HFSS). The reflection coefficient shows the quad frequency bands cover (2.31 - 2.5), (2.9 - 3.27), (4.28 - 5.23), and (5.4 - 5.74) GHz. Other antenna parameters have been monitored to verify its performance such as gain, radiation efficiency, input impedance, and radiation patterns.

The characteristics of a wire biconical antenna that determine its antenna factor were computed by using the method of moments code NEC-2. A fairly extensive validation exercise was conducted from which a suitable computer model was derived. The input impedance, gain, and radiation patterns of the antenna were computed for special cases where the biconical antenna is used above a conducting ground plane for open-field EMC (electromagnetic compatibility) testing. The effects of height above the ground plane and polarization of the antenna on these parameters were found and the antenna factor was corrected for them. The current distribution along the antenna elements was also examined, and it was found that significant pattern distortion can occur at some frequencies when a horizontal wire biconical antenna is used close to the ground. These results will allow this broadband antenna to be used with confidence in applications where previously only resonant dipoles were specified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The ability of the finite-difference-time-domain (FDTD) method to calculate radiation patterns, input impedance, and gain for a monopole antenna on a conducting box is demonstrated. Results are given for the bare box and with the box coated with a dielectric layer. Radiation patterns are compared with measurements and with the method of moments for the bare box. Radiation patterns for the dielectric-covered box and all impedance and gain results are compared with measurements only. Good agreement is obtained in all cases. The FDTD approach includes a dielectric covering quite easily, while this would be quite difficult for a method of moments approach. The FDTD method requires similar computer time as the method of moments for a single-frequency result, but produces wide-bandwidth impedance and gain results with much less computer time. >

A cavity-backed slot antenna is thought to be one of the most suitable elements for the wireless transmission of microwave energy. A design technique is developed for the cavity-backed slot antenna using the finite-difference time-domain (FDTD) method. The technique is effective in characterizing antenna performance such as the input impedance and the far-field pattern since it takes into account the geometry of the feeder as well as the cavity. We present a method that overcomes difficulties when the FDTD method is used to design the antenna. Moreover, we discuss how to determine the calculation parameters used in the FDTD analysis. Several numerical results are presented, along with measured data, which demonstrate the validity, efficiency, and capability of the techniques. The paper proposes a new prediction method for the frequency characteristics of the cavity-backed slot antenna, which applies computational windows to time-sequence data. It is emphasized that windowing the slow decaying signal enables the extraction of accurate antenna characteristics. We also discuss how to estimate the antenna patterns when we use a sinusoidal voltage excitation.

In this paper, a high-gain L-probe antenna array, which also has a broadside radiation pattern, is presented. To demonstrate the design idea, three L probes are placed along the vertex of a V-shaped ground to form a 3×1 antenna array. In this structure, the ground plates also act as a corner reflector. The proposed antenna array is simple and can be easily constructed by only using wires and metal plates. In this paper, the input impedance, antenna gain, and radiation patterns of the proposed antenna are studied.

An eigensolution expansion of dyadic Green's function for cylindrical sector structures is presented. The cylindrical structure is limited in azimuthal direction by electric or magnetic walls. Due to orthogonality of the eigensolution functions between the walls, the derivation of the dyadic Green's function can be done in spectral domain. The Green's dyad is used to set up an electric field integral equation for the microstrip structure. The solution is carried out with the method of moments. Numerical results for input impedance and radiation pattern are shown.

In this research work a Circular Microstrip Patch Antenna designed and the circular patch of the antenna slotted with U-slots, that enabled it to generate five resonant bands for penta band application. The antenna had exited using coxial probe with proper probe position. From IGHz to 5GHz frequency range over which the designed antenna had been investigated and within this frequency range the antenna generated multiple resonant bands with center frequencyl.02GHz, 1.66GHz, 2.55GHz, 3.7GHz and 4.93GHz. HFSS commercial software used to simulate the above said antenna for evolution of input impedance, Sn, Gain and Radiation Pattern.

This paper first examines and corrects Storer’s theory of circular loop antennas, and then investigates theoretically the proposed Ω-shaped loop-dipole antenna. Special emphasis is given to the analysis of the effect of the higher-order terms of the Fourier series as a remainder on the current distribution, input impedance, and radiation patterns of the thin-wire circular loop antenna. It is found that the remainder must be included in the calculation of the current distribution and input impedance but can be neglected to simplify the calculation of far-field radiation. Then, a theoretical model is proposed to analyze the radiation fields, directivity, and input impedance of the proposed Ω-shaped loop-dipole antenna based on the loop and dipole antennas’ theories. Analytical expressions for the radiation fields, directivity, and input impedance of the Ω-shaped loop-dipole antenna are derived. The theoretical and numerical results are compared for the Ω-shaped loop-dipole antennas of practical interests. They are in good agreement.