Showing papers on "Radiation pattern published in 1985"

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Optimising the synthesis of shaped beam antenna patterns

Abstract: A technique is introduced which uses the conventional polynomial representation of the antenna pattern produced by an equispaced linear array. Certain roots are displaced from the unit circle radially, to fill a portion of the pattern, which before this displayed lobes interspersed by deep nulls. The angular and radial positions of all the roots are simultaneously adjusted so that the amplitude of each ripple in the shaped region and the height of each sidelobe in the nonshaped region are individually controlled. Applications to a cosec 2 θ × cos θ pattern and to a flat-topped beam are presented. Experimental validation is also offered.

Dipole and slot elements and arrays on semi-infinite substrates

Abstract: The printed dipole or slot antenna on a semi-infinite substrate and infinite phased arrays of these elements are investigated. The solution is based on the moment method in the Fourier transform domain. The generalized impedance or admittance matrix can be expressed in rapidly converging infinite-integral or infinite-summation forms, allowing the accurate determination of the current distributions. Using the present formulation, the input impedance, resonant length, and radiation pattern for the isolated antennas, and the reflection coefficient for infinite phased arrays, are calculated.

Directly coupled multiple resonator wide-band microstrip antennas

Abstract: Three new configurations for increasing the impedance bandwidth of the microstrip patch antennas are described. In these configurations, additional resonators are directly coupled through short sections of microstrip line to the radiating edges, nonradiating edges, and all the four edges of the rectangular patch antennas, respectively. Green's function approach and segmentation method are used for the analysis. The experimental results are in reasonable agreement with the analysis and impedance bandwidths of 548 MHz, 605 MHz, and 810 MHz are obtained for these three configurations, respectively in S -band (substrate thickness = 0.318 cm and \epsilon_{r} = 2.55 ). The variation in the radiation pattern over this impedance bandwidth is discussed.

Electric surface current model for the analysis of microstrip antennas with application to rectangular elements

Abstract: An approach to the analysis of microstrip antennas which is applicable also to relatively thick substrates using the relevant Green's function is presented. The Green's function is derived and closed form expressions for various antenna characteristics which explicitly take into account the presence of the dielectric material are obtained in terms of the electric surface current density. For rectangular microstrip elements near resonance the current distribution is approximated using lossless transmission line analysis, thus enabling the complete evaluation of the characteristics of the element near resonance. The results obtained in this approach for the radiation resistance, surface wave resistance, radiation pattern, directivity, and bandwidth are presented in a detailed set of graphs for a representative set of parameters.

The receiving antenna as a linear differential operator: Application to spherical near-field scanning

Abstract: The general receiving antenna is represented as a linear differential operator converting the incident field and its spatial derivatives at a single point in space to an output voltage. The differential operator is specified explicitly in terms of the multipole coefficients of the antenna's complex receiving pattern. When the linear operator representation is applied to the special probes used in spherical near-field measurements, a probe-corrected spherical transmission formula is revealed that retains the form, applicability, and simplicity of the nonprobe-corrected equations. The new spherical transmission formula is shown to be consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.

Broadband circularly polarised planar array composed of a pair of dielectric resonator antennas

Abstract: A new type of planar array composed of a pair of dielectric resonator antennas has been devised and tested. Both the radiation patterns and ellipticity properties are presented. The 2 dB ellipticity bandwidth obtained was approximately 15% at X-band.

Rectangular ring and H-shaped microstrip antennas—alternatives to rectangular patch antenna

Abstract: H-shaped and rectangular ring microstrip antennas have been compared with the commonly used rectangular patch antenna. It has been found that the H-shaped patch antenna is smaller in size (about half), and is broadbeam but with narrow bandwidth. On the other hand, for larger bandwidth and/or narrow beamwidth applications a rectangular ring antenna is better than a rectangular patch antenna. Because of size reduction the H-shaped patch looks attractive for UHF applications.

Parasitically coupled, complementary slot-dipole antenna element

Abstract: A parasitically coupled, complementary slot dipole antenna element includes a driven, cavity-backed slot antenna element and a parasitic dipole element transverse to the slot of the cavity-backed slot antenna element. The cavity-backed slot and parasitic dipole antenna elements resonate at about the center frequency of the excitation signals supplied to the cavity-backed slot antenna element in order to generate a relatively symmetrical electromagnetic signature and an increased bandwidth.

Directivity optimization of a reflector antenna with cluster feeds: A closed-form solution

Abstract: The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of a single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 \lambda parabolic reflector scanning 10 beamwidths, the optimum-directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 \lambda , it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d , the optimum design may exhibit the supergain phenomenon, namely, extremely high directivities achieved by an oscillatory cluster excitation.

Radiation from a dipole in the proximity of a general anisotropic grounded layer

Abstract: The radiation from a dipole in the presence of a grounded general gyromagnetic-electric (gyrotropic) layer is investigated. The use of matrix methods in conjunction with Fourier transformation techniques greatly facilitates the formulation of the boundary-value problem, reducing the algebraic complexity to a minimum, and provides a closed-form representation of the electromagnetic field over the anisotropic region. Numerical results in plots, related to the radiation pattern of the structure, are also included for various cases.

Microwave holography of large reflector antennas--Simulation algorithms

Abstract: The performance of large reflector antennas can be improved by identifying the location and amount of their surface distortions and then by correcting them. Microwave holography techniques are finding considerable applications as viable tools for performing this task. In these techniques, the complex (amplitude and phase) far-field pattern of the antenna is measured, using a reference antenna. Then, the Fourier transform relationship, which exists between the far field and a function related to the induced current, is invoked to result in the identification of the surface distortions. To critically examine the accuracy of the constructed surface profiles, simulation studies are required to incorporate both the effects of systematic and random distortions, particularly the effects of the displaced surface panels. In this paper, different simulation models are investigated with emphasis given to a model based on the vector diffraction analysis of a curved reflector with displaced panels. The simulated far-field patterns are then used to reconstruct the location and amount of displacement of the surface panels by employing a fast Fourier transform (FFT)/iterative procedure. The sensitivity of the microwave holography technique based on the number of far-field sampled points, level of distortions, polarizations, illumination tapers, etc., is also examined. In addition, the relationships between Az-El and u-v spaces are addressed in the Appendix. Most of the data are tailored to the dimensions of the NASA/JPL Deep Space Network (DSN) 64-m reflector antennas for which the result of a recent measurement is also presented.

Coupled-mode analysis of gain and wavelength oscillation characteristics of diode laser phased arrays

Abstract: The lasing wavelengths and gain characteristics of the modes of phase-locked arrays of channel-substrate-planar (CSP) lasers are presented. The gain values for the array modes are determined from complex coupling coefficients calculated using the fields of neighboring elements of the array. The computations show that for index guided lasers which have nearly planar phase fronts, the highest order array mode will be preferred. The "in phase" or fundamental mode which produces only one major lobe in the far-field radiation pattern, has the lowest modal gain of all array modes. The modal gain differential between the highest order and fundamental modes is less than 10 cm-1for weak coupling between the elements.

Electronically rotated antenna apparatus

Abstract: An antenna of the type having a central driven element and a plurality of surrounding parasitic elements is shown. Further, there is circuitry for modifying the basic omnidirectional pattern of said antenna to a directional pattern by normally capacitively coupling the parasitic elements to ground but on a selective basis changing some of the parasitic elements to be inductively coupled to ground whereby they act as reflectors and provide an eccentric signal radiation pattern. By cyclically altering the connection of various parasitic elements in their coupling to ground, a rotating directional signal is produced.

Antenna apparatus for scanning hyperthermia

Abstract: An arrangement for heating includes an antenna which has at least one convolution of conductor centered on an axis. The antenna is adapted for receiving electrical power for heating a surface. A noncontacting temperature sensor is centered on the axis of the antenna with its field of view directed along the axis.

Dual offset reflector multibeam antenna for international communications satellite applications

Abstract: Dual offset reflector antenna systems offer exciting possibilities for achieving both low scan losses and low cross polarization in geosynchronous communications satellite antennas providing narrow ( 100 \leq D/\lambda \leq 400 ) and multiple beam frequency reuse coverages over an 18\deg conical field of view. Novel geometrical configurations for the reflectors are characterized by simultaneously achieving: 1) blockage free apertures for all element beams within the 18\deg conical field of view, 2) compatibility with large planar feed arrays, 3) additional degrees of design freedom by orientation and shaping of reflector surfaces for depolarization and scan loss optimization, and 4) large effective f/D ratio achieved in compact and foldable geometries. A comparison of new front-fed offset Cassegrain (FFOC) and side-fed offset Cassegrain (SFOC) systems is made.

Effects of deterministic surface distortions on reflector antenna performance

Abstract: Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector

Antenna with radial and edge slot radiators fed with stripline

Abstract: An antenna suitable for the generation of a circularly polarized annular radiation pattern comprising a substrate spaced apart from a ground plane by a layer of dielectric material, the substrate being arranged to carry on one side thereof a conductive layer in which a plurality of radial slots is defined equiangularly disposed to extend outwardly from a central region of the substrate, and on the other side thereof a microstrip feed line arrangement via which the radial slots are arranged to be fed with microwave energy for the generation of a horizontally polarized radiation pattern and via which an edge slot defined between the peripheral edge of the layer and the ground plane is arranged to be fed with microwave energy for the generation of a vertically polarized radiation pattern whereby the horizontal pattern and the vertical pattern in combination afford the circularly polarized annular radiation pattern.

Polarization properties of the axial mode helix antenna

Abstract: The helix is considered as a surface wave antenna. A network model of the infinite structure provides a simple vehicle to view the fields behavior. The far-field polarization properties are examined in detail, and it is shown how they depend on the surface wave structure and the open and feed end configurations. By suitably arranging the antenna ends, perfect endfire polarization purity can be produced independent of antenna length (i.e., number of turns). Inclusion of a dielectric core decreases the cross polarized radiation in off-axis directions. Theoretical and experimental patterns illustrate these results.

Radiation pattern analysis of reflector antennas

Abstract: A method is proposed for accurately calculating the radiation pattern of reflector antennas in the entire angular range from the main beam direction to the off axis region. The principle of the method is similar to the physical optics diffraction theory, and consists of the result obtained by conventional physical optics corrected with the contribution from the edge current calculated by the geometrical theory of diffraction. However, the edge current is expressed in a simple form by means of a local coordinate system defined by the peripheral line and the mirror normal at each edge point and of the incident electromagnetic vector components in reference to this coordinate system. Therefore, it is possible to treat an arbitrarily shaped mirror surface and an antenna with a primary radiator using an arbitrary pattern. It is confirmed that the results obtained by the present method approach those obtained by the physical optics method near the main beam and those obtained by the geometrical theory of diffraction at the off axis. Accuracy is tested by applying the present method to the problem of diffraction from a circular disk for which a rigorous solution exists. The present method makes unnecessary the distinction of the use of physical optics (main beam) and the geometrical theory of diffraction (off axis) performed so far, in an empirical manner. It is possible systematically to obtain the pattern near the first-third side lobes where two methods may be connected.

Theoretical and experimental study of monopole phased array antennas

Abstract: A theoretical and experimental investigation of the mutual coupling in large two-dimensional periodic planar phased arrays of thin cylindrical monopoles is addressed. A plane wave representation of the active input impedance is used to analyze an infinite array of monopoles. A finite array analysis is used to compute the center element gain pattern and input impedance as a function of the array size and element position. The center element gain pattern is shown to have omnidirectional vertical polarization with a null on-axis and peak gain in the vicinity of 50\deg from broadside. Measurements of the element gain pattern and mutual coupling for a 121-element passively terminated monopole square lattice array are shown to be in good agreement with the theory. The results of the infinite array analysis are compared to theoretical and experimental data in the literature for hexagonal lattice arrays.

Fundamental surface-wave effects on microstrip antenna radiation

Abstract: The spectral domain approach is used to determine the influence of surface waves on the radiation efficiency of a rectangular patch antenna. The effects on the radiation patterns due to the dielectric truncation are computed and compared with experiment.

Antenna assembly for microwave reflection survey equipment

Abstract: An antenna assembly is provided for use in locating buried objects, particularly long thin objects such as pipes can be located, determining the position, and ascertaining the pipe direction by taking measurements from a single point, without mechanical movement of the antenna, and allowing a better suppression of spurious signals and reduction in false indications; which assembly has a plurality of antenna arms adapted and arranged to transmit and receive radiation into the ground and is characterized in that the arms have, on at least the surface nearest the ground, a cladding of a substantially lossless dielectric material, the relative permitivity of said dielectric being at least 3.5 and the thickness of said coating being at least λ d /20 where λ d is the wavelength of lowest frequency of the radiation to be transmitted from the antenna.

Apparatus for scanning and measuring the near-field radiation of an antenna

Abstract: Apparatus for measuring the near-field radiation of an antenna such that its far-field radiation characteristics can be determined. The invention utilizes the principle of the Foucault pendulum. It uses a bob attached to a long pendulum arm that is free to rotate. Rotation of the earth causes an apparent rotation of the swing plane of the pendulum with a period of T=24/sin (latitude). By attaching a field sensing probe to the pendulum bob and mounting the antenna under the Foucault pendulum, the entire antenna aperture can be scanned without moving the antenna. The motion of the probe covers part of an external sphere centered at the pivot point of the pendulum and having a radius equal to the length of the pendulum. Appropriate transformation of the measured near-field data gives the far-field radiation pattern.

Optimization of the transient radiation from a dipole array

Abstract: The optimum solution for the transient radiation from a dipole array is derived in terms of the time-domain voltages which are required at the input terminals of dipoles in an array so that the amplitude of the transient radiated field at a specified time t_{0} and far-field position r_{0} , \theta_{0}, \phi_{0} is maximized. Constraints are placed on the energy and bandwidth of the input signal voltages with current restricted by Pocklington's equation. Further constraints on the sidelobe level are used to obtain a modified solution for suppressed sidelobes in the radiation pattern. Results of numerical optimization are presented, and the effects of scan angle, element spacing, and a sidelobe constraint on the optimization are discussed.

Theory and experiment on the annular-ring microstrip antenna

Abstract: This paper presents a critical and comprehensive account of the theory of the annular-ring microstrip antenna based on the cavity model and compares the theoretical results with measurements. It is found that in the theory, the physical radii must be modified to account for the fringing fields along the edges of the ring. The modifications are necessary not only for improving accuracy but also for the correct identification of the modes. Detailed theoretical and experimental results are given on resonant frequencies, radiation patterns and input impedances. Our results also confirm the various features of thetm11andtm12modes predicted previously by the vector Hankel transform analysis.

Study of element patterns and excitations of the line feeds of the spherical reflector antenna in Arecibo

Abstract: The element patterns of the circularly polarized line feeds for the spherical reflector in Arecibo are calculated, showing strong endfire radiation. The radiation fields of the line feeds are then obtained by adding up the contributions from all elements. The optimum excitation of the feed is found by an approximate stationary-phase solution of the radiation field. This shows that the element pattern gives a large phase contribution to the excitation, because of the finite diameter of the feed. If not corrected for, this phase error can cause losses up to 1.5 dB. The excitation is optimized further by cutting and trying. The validity of the analytical models is checked by calculation of the radiation pattern of the existing 96.6 ft 430 MHz feed. The excitation is modeled from measured phases along the feed. The calculated radiation patterns show good agreement with the measurements, including the phase errors and the dip in the center. By using the proposed new excitation it should be possible to increase the efficiency of the 96.6 ft feed by 0.7 dB and to increase the efficiency of the 40 ft feeds at higher frequencies by even more.

Monitoring techniques for phased-array antennas

Abstract: The problem of monitoring phased-array antennas in general and microwave landing system (MLS) in particular is considered. Various methods of monitoring phased-array antennas are suggested. One is based on changes in the far-field radiation pattern arising from defects in the array. Another method uses the near-field to far-field transformation, based on the concept of the plane-wave spectrum, for the detection of defects in the antenna. A third method is based on near-field measurements and uses the properties of the Fresnel integral. The methods were simulated on the computer and, where possible, were tested by experiment. A comparative assessment of the methods is given, and an operational monitoring system is suggested for the MLS phased army.

An aperture-matched compact range feed horn design

Abstract: The moment method and the uniform geometrical theory of diffraction are used to obtain two separate solutions for the E -plane far field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate the E -plane pattern and voltage standing-wave ratio (VSWR) of the antenna. However, at higher frequencies, the moment method requires large amounts of computation time. On the other hand, the uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for the E -plane field pattern. In fact, the uniform geometrical theory of diffraction may be used to initially design the antenna; then the moment method may be applied to "fine tune" it. In both methods, a two-dimensional E -plane model of the antenna is used, but these two-dimensional solutions yield excellent agreement with measured data of the actual three-dimensional antenna. This procedure has been successfully applied to design a compact range feed horn.