On the aperture field of a solid cylindrical antenna

The situation of a solid cylindrical antenna excited by a narrow circumferential gap is considered, and an approximation which is realistic, simple, and very accurate is obtained for the aperture electric field.     

Analysis of an aperture coupled microstrip antenna

A microstrip patch antenna that is coupled to a microstripline by an aperture in the intervening ground plane is analyzed. Coupled integral equations are formulated by using the Green's functions for grounded dielectric slabs so that the analysis includes all coupling effects and the radiation and surface wave effects of both substrates. A Galerkin moment method solution of the coupled integral equations agrees quite well with measured data. Design data are contained in parameter studies, many of which are verified by experimental results.     

Transient response of an infinite cylindrical antenna

A simple analytical formula derived from Wu's exact solution for the transient response of an infinite cylindrical antenna is found to be extremely accurate. Existing results from other numerical schemes are also compared to Wu's solution and found to be in good agreement.     

Wide-band microstrip antenna with an H-shaped coupling aperture

Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite-difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than 23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed     

Transient response of an infinite cylindrical antenna in a dissipative medium

The transient solution of an infinite cylindrical antenna in a dissipative medium caused by an impulse excitation at a delta gap is obtained via an exact solution in the form of definite integrals and a simple asymptotic formula. This formula is used to obtain an integral for calculating the antenna current caused by a double exponential input voltage at the gap; furthermore, the resulting integral reduces to Sunde's classic result under the diffusion limit. These results are applied to the transient response of a buried wire subject to an electromagnetic pulse (EMP) or nearby lightning incident wave.     

Analysis of a folded dipole antenna mounted on a cylindrical metallic mast

A numerical technique has been presented for analysis of practical folded dipole antennas mounted on metallic masts. Results have been compared against experimental results and excellent agreement obtained demonstrates the capability of this method.     

Current waves on an infinite cylindrical antenna in a warm plasma

The current waves on the outside wall of an infinite cylindrical antenna, fed by a delta-function generator and immersed in a warm isotropic plasma, which is in direct contact with the antenna, is separated into its components: the familiar e.m. wave, the `transverse-plasma? wave and the slow surface wave.     

Properties of a cylindrical antenna in an infinite planar or collinear array

A solution is given for the active impedance and current distribution on a cylindrical antenna in a uniform, infinite, planar, or collinear array. The analysis is applicable to the case in which the distance in the collinear direction between the ends of adjacent elements is small. The current distribution on the collinear array is found by relating the antenna current and electric-field variation on the cylindrical surface of infinite length which contains the array. This analysis is then extended to consider a planar array. Results obtained are applicable to any combination of element length and array phasing, for arrays with or without a ground plane. Comparisons with other investigations based upon sinusoidally distributed currents reveal substantial discrepancies for some configurations.     

Driving-point impedance of a linear cylindrical antenna

A new approach is presented for evaluation of driving-point impedance, requiring only one component of the dyadic Green's function through replacement of the equivalent surface magnetic current at the aperture by an equivalent volume polarisation current. The analysis is applied to a cylindrical antenna at a general position between parallel plates.     

Full-wave aperture coupled patch antenna

An aperture coupled patch antenna with a dual-lobed (cavity mode TM/sub 200/) radiation pattern is described. The antenna employs a full-wavelength long patch fed via a butterfly-shaped aperture and a stripline feed network. This configuration provides high patch to feed network coupling and reduced back radiation. Measured return loss and pattern data are presented with proposals for several potential applications of this element.<>     

Single aperture monopulse horn antenna

This paper describes the design and performance of a conical Potter horn antenna which can generate sum or difference far field patterns suitable for monopulse tracking applications. The antenna consists of a horn antenna fed with a metal post loaded polarizer which is energised by suitably phased 50-/spl Omega/ matched coaxial probes. The prototype demonstrator designed here operates in the frequency range 8-8.6GHz with sum and difference patterns obtained by using a very simple phasing circuit. At 8.5GHz, the gain of the sum pattern is 18.6dB and the in the difference pattern is 26dB at boresight.     

Radiation of an aperture antenna covered by a spherical-shellchiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE₁₁ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically     

AVERAGE BRIGHTNESS TEMPERATURE OF ANTENNA APERTURE

This paper presented an idea for the average brightness temperature of lossless antenna aperture, gave its expression for matched and dismatched noise source. This expression showed that the average brightness temperature of antenna aperture related with three factors: the noise temperature of noise source, the reflection coefficient of noise source, and the aperture efficiency.     

Radiation characteristics of a cavity-backed cylindrical gap antenna

The input impedance and the equatorial radiation patterns of a VHF cavity-backed cylindrical gap antenna are derived and compared with experiments. The experiments generally support the computations, provided that the gap dimension is neither larger than about 1/100 of a wavelength, nor so thin that mechanical tolerances in the feed design become important. The results show that the tuning, impedance bandwidth, and the radiation patterns of this antenna can be controlled very accurately by adjusting the internal radius and height of the cavity. Salient points of this antenna are its wide-band characteristics (10-percent bandwidth), its pattern circularity, and particularly the fact that it can be made an integral part of a space vehicle.     

Admittance of an infinite cylindrical antenna with realistic gap field

A numerical comparison is made between the admittance of an infinite cylindrical antenna excited by a realistic electric field across a finite gap, and the admittance found by assuming a constant electric field in the same gap. A simple approximate relation between the two is derived, while a second simple expression shows how the admittance changes as the gap width is varied.     

Waves along a cylindrical "Grid-like" antenna in an anisotropic compressible plasma

In an anisotropic compressible homogeneous plasma, the dispersion equation of waves along an infinitely long cylindrical "grid-like" antenna is obtained analytically. Numerical solutions of this equation show that an external static magnetic field has great influence upon the anomalously dispersive region of the dispersion relation around the plasma frequency.     

Feed gap aperture field and input admittance of an infinitely longinsulated antenna

Expressions are derived for the input admittance and aperture electromagnetic fields in the feed gap of a solid insulated antenna of infinite extent. This is done by solving the boundary value problem where the fields are represented by Fourier series built up by superposition of basic sets of φ-independent cylindrical waves. Such waves are obtained from the solution of the Helmholtz equation governing the z-directed electric Hertzian potential. The axial aperture electric field in the gap is in the form of a Fourier-Bessel series and is used to find the input admittance. Results are plotted for the aperture fields and tabulated for the input admittances at different radii, insulating shell dielectric constants, and gap widths     

The resolution limit of a variable baseline synthetic aperture antenna

The resolution capabilities of a variable baseline correlation interferometer are analyzed using a maximum likelihood estimator algorithm for the output data. Optimum estimates (in the Cramer-Rao sense) for two sources of both equal and unequal strengths, for different levels of receiver-background noise, and for finite integration (averaging) times are obtained. A likelihood probabilityp_{n}(n = 0, 1, 2, 3, ...)is also obtained from the measured data, and the resolution limit is defined to be that for which the probabilitiesp_{1}andp_{2}are equal (on the average). It is shown by a computer simulation that the average resolution limit improves (decreases) with increased integration time, exceeding the traditional Rayleigh limit by an arbitrary amount even for quite unequal source strength ratios and large levels of receiver-background noise.     

A reactively loaded aperture antenna array

The use of variable reactive loads to control the beam direction of an antenna array consisting ofNclosely spaced waveguide-backed dielectric-filled rectangular slots is considered. Only the center waveguide is driven (no complex feed network is required for the array), and the other waveguides are short circuited at specified distances to provide reactive loading. The solution uses the method of moments applied to the integral equation for the equivalent magnetic current in the aperture region. The initial, design of the array is obtained by resonating the complex excitation voltages required for maximum gain with all of the elements driven. This is then improved by an optimum seeking univariate search method. Computed results are given for seven- and fifteen-element aperture arrays.