Showing papers on "Antenna (radio) published in 1974"

Theory and application of antenna arrays

Abstract: theory and application of antenna arrays ouaps theory and application of antenna arrays theory and application of antenna arrays zaraa basic antenna theory and application theory and application of antenna arrays satcar antenna arrays antenna theory fractal antenna engineering: the theory and design of antenna theory and design john wiley & sons applications of antenna arrays to mobile communications 5. antenna types ncjrs robust synchronization of di erent coupled oscillators design of microstrip patch antenna array for wlan application session 3p3 antenna array synthesis | theory, algorithms eece 174 antenna theory and design opus college of theory and application of array coils in mr spectroscopy application of butler matrix to a tree structure of design and analysis of microstrip patch antenna arrays a study of loaded microstrip antennas and their compwnent part notice defense technical information center leaky cpw-based slot antenna arrays for millimeter-wave antenna array synthesis for suppressed side lobe level antenna theory tutorialspoint application of the neural network to the synthesis of a power wave theory of antennas e-fermat synthesis of thinned linear and planar antenna arrays fractal antenna elements and arrays university of maryland the application of the fdtd method to aperturecoupled a new definition of mutual impedance for application in array phase shifters: theory and technology origins of the digital antenna array theory slyusarev eel 4461 antenna systems eel 3472 university of florida double application of superconductor and photonic material session 2p7 antenna and array: theory and design piers course syllabus eel 4935/5462 antenna theory academics antenna array optimization using evolutionary approaches design of dielectric resonator antenna arrays for wireless planar antenna arrays for correlation direction finding design, simulation and tests of a low-cost microstrip design of microstrip antennas arrays for applications in design of antennas and antenna arrays [ d12 eth zürich design and performance analysis of microstrip array koch fractal antenna application in monopulse antenna array

Cassegrain antenna with improved subreflector for terrestrial communication systems

Abstract: A Cassegrain antenna for use in terrestrial communication systems. The antenna has the conventional subreflector including a central area which provides tapered illumination of the entire main reflector, and a peripheral area which directs spillover from the central area onto the peripheral portion of the main reflector to improve the uniformity of illumination of the main reflector, thereby improving illumination efficiency and reducing gain loss due to spillover. The central and peripheral areas of the subreflector are preferably both surfaces of revolution of conic sections of the same kind, such as hyperboloids, ellipsoids or paraboloids, although the peripheral area may be a frustoconical surface if desired. The virtual focal points of the two conic sections of the subreflector are both coincident with the phase center of the feed horn.

Optical antenna gain. 1: transmitting antennas.

Abstract: The gain of centrally obscured optical transmitting antennas is analyzed in detail. The calculations, resulting in near- and far-field antenna gain patterns, assume a circular antenna illuminated by a laser operating in the TEM(00) mode. A simple polynomial equation is derived for matching the incident source distribution to a general antenna configuration for maximum on-axis gain. An interpretation of the resultant gain curves allows a number of auxiliary design curves to be drawn that display the losses in antenna gain due to pointing errors and the cone angle of the beam in the far field as a function of antenna aperture size and its central obscuration. The results are presented in a series of graphs that allow the rapid and accurate evaluation of the antenna gain which may then be substituted into the conventional range equation.

Z slot antenna

Abstract: An improved antenna of a coaxial type utilizing Z-shaped slots disposed in the outer conductor to provide an omnidirectional antenna pattern. Current coupling to the slots is achieved by means of the transverse portion of the Z slot. Detuning effects due to the presence of a transmission line are compensated for by dielectrically loading the slots with a dielectric cover over the coaxial line and/or by lengthening the longitudinal arms of the Z. The longitudinal spacing between each slot and the length of the transverse portion of each slot are chosen while considering all line effects to obtain the required phase and amplitude relationships. The antenna consequently requires no additional coupling, tuning or phasing devices mounted within or without the coaxial line.

System and method for remote monitoring of animal temperature

Abstract: System for remotely monitoring the temperature of animals in which a capsule containing a variable length antenna which changes in length according to the animal''s temperature is embedded in the animal. Interrogating means are provided for transmitting a range of frequency signals to the capsule and for receiving reflected signals from the antenna. The system in addition has means for detecting a peak signal value from the antenna to indicate the animal''s temperature and to provide a read-out or display of the animal''s temperature.

Microwave theory of phased-array antennas—A review

Abstract: The microwave theory of phased-array antennas is reviewed, emphasizing large planar arrays suitable for phased-array radar. The review looks in detail at the three major parts of the antenna, namely, the element array, the phase shifters, and the feed system. The element array is studied by first modeling it as being infinite in extent and the concept of the per element absorption cross section and gain versus angle is developed. The technique of modal analysis using plane waves is explained and used to calculate the aforementioned quantities for waveguide and dipole elements. The review proceeds first through an analysis which applies to small elements, using a single element mode, and then to a more accurate solution containing the first higher mode in addition. The author has added new research to the review which explains the blindness effect for waveguide arrays. A necessary and sufficient condition for array blindness has been derived which removes a major uncertainty about the blindness effect. A result is that a blindness angle will always occur in E and H plane scanning of rectangular waveguide elements for any waveguide size, provided the array lattice is such as to permit a grating-lobe singularity by the simple one-element-mode theory. Elements large than some critical size are not required to produce blindness but the large size has the effect of producing greater shift of the blindness angle towards broadside from the grating lobe angle. The singularity in element admittance right at the grating lobe angle, which is a well-known milestone in the analysis of elements which have been modeled to support only one mode, is in reality a fiction. When higher modes are added to the solution, as is necessary for any physical element, the grating-lobe singularity is found to disappear. Thus for any real physical element, there is no grating lobe blindness, but the blindness angle is shifted inside of this angle by an amount which depends upon the element size. A review of element design calculations using many higher element modes is presented, and element configurations are shown which produce a good impedance match over a wide scan angle as well as a wide-frequency band. The application of the aforementioned results obtained from the infinite-array model to a practical, finite array are discussed. The theory of the most useful phase-shifter types for phased arrays is discussed, including those using both ferrite and semiconductor diodes. The ferrite toroid in a waveguide is a very effective design and the results of an optimization analysis for this configuration are presented. Choices of ferrite material parameters for low loss at both small and large signal levels are discussed. A method of reducing the temperature sensitivity of phase shift by means of the driver circuit is also reviewed. Semiconductor diode phase shifters have a greatly increased potential due to an improvement in diode reliability that has produced an expected mean life of 109h. The theory of phase-shifter operation using diodes in a balanced hybrid circuit is discussed and relations are given for bandwidth, loss, and power capability. The high-power limitation of the phase shifters is due to a nonlinear loss effect in the reverse biased state and is caused by the large RF voltages. The loss can be reduced by circuit techniques and by employing the new diodes of improved design, which are discussed. Feed systems for phased arrays are synthesized from a number of basic techniques according to the antenna applications. A few of the important techniques are reviewed here. Feed systems are required to produce an optimum aperture distribution for two types of patterns simultaneously, the sum pattern (Taylor distribution) and the difference pattern (Bayliss distribution). For the constrained feed, which uses transmission line throughout, two alternatives are presented for accomplishing the aforesaid. It is shown that the feed network can prevent reflections from the element array, which are always present to some degree, from adding an error component to the desired aperture distribution by employing 4-port power dividers which are provided with a reflection absorbing termination. An approximate method of wide-band beam steering is discussed in which a small number of time delay devices are used to feed subarrays of elements steered by conventional phase shifters. The subarray feeding technique is also employed in another application with the Butler beam forming matrix to form simultaneous multiple beams in an approximate manner that reduces the size of the beam forming matrix required. The space feed is an alternative to the constrained feed and distributes energy to the elements by free-space propagation. This method possesses great flexibility and may approach the capability of the constrained feed in secondary aperture performance by using a large number of feed elements. A design method of accounting for the near-field diffraction produced by the large feed is given.

A leaky-wave antenna using an artificial dielectric medium

Abstract: A narrow-beam antenna using an artificial dielectric medium with effective permittivity less than unity has been investigated theoretically and experimentally. Complex propagation constant for a wave propagating along the structure is evaluated by solving the dispersion relation. The analysis indicates the presence of a leaky-wave mode. The radiation pattern is calculated by using Kirchhoff-Huygens integration method. Experimental results for an antenna of this type designed for operation at X band are reported and compared with theoretical calculations. Beam position varies from 17\deg to 47\deg when the frequency is changed from 8.6 to 11.5 GHz. Over this frequency range the half-power beamwidth varies from 5.6\deg to 4.8\deg . An expression for the half-power beamwidth of a leakywave antenna of finite length has been derived and discussed in the Appendix.

Plane wave spectrum-surface integration technique for radome analysis

Abstract: The purpose of this paper is to report an accurate boresight analysis for practical three-dimensional antenna-radome systems. The analysis of practical three-dimensional antenna-radome combinations has been impractical for antenna aperture areas greater than about 75\lambda^{2} . The principal difficulty encountered is the excessive computation time required for the large number of antenna near field calculations. The key feature of the approach taken by the authors is the use of the plane wave spectrum (PWS) formulation for calculation of the antenna near fields. The PWS formulation provides much improved efficiency over other nearfield analyses and makes this analysis possible. The method can also be applied to analyze other antenna distortion.

Properties of mobile radio propagation above 400 MHz

Abstract: This paper begins with a discussion of multipath interference. The spatial description of the field impinging upon a mobile radio antenna is derived and the power spectrum and other properties of the signal envelope are considered. Next, large scale variations of the average signal are discussed. Measurements of observed attenuation on mobile paths over both smooth and irregular terrain are summarized. The paper concludes with a discussion of methods of predicting the area of coverage from a base station.

Optical antenna gain. II ; Receiving antennas

Abstract: Expressions are developed for the gain of a centrally obscured, circular optical antenna used as the collecting and focusing optics in a laser receiver, involving losses due to (1) incoming light blockage by central obscuration, (2) energy spillover at the detector, and (3) the effect of local oscillator distribution in the case of heterodyne or homodyne detection. Numerical results are presented for direct detection and for three types of local oscillator distribution (uniform, Gaussian, and matched).

Mechanism and properties of point‐contact metal‐insulator‐metal diode detectors at 10.6 μ

Abstract: Detection mechanisms of point‐contact MIM diodes at 106 μ wavelength have been studied Detailed measurements of the static current‐voltage characteristic and its first and second derivatives as functions of bias voltage were made simultaneously with infrared sensitivity measurements The results indicate that the static current‐voltage characteristics extend to infrared frequencies We find that thermal effects do not contribute significantly to detection at this wavelength, and that the tungsten whisker acts as a rather efficient receiving antenna The antenna and its shunting capacitance apply a 3×1013‐Hz ac voltage to the diode which in our experiment has amplitude 124 mV, through an impedance which is much less than the junction impedance The diode nonlinearity d2I/dV2 varies from 65×10−5 to 67×10−3 A/V2 as dc bias increases from 0 to 300 mV None of these conclusions apply to detection at 6328 A; it is found that detection in the visible is dominated by thermal or photoconductive effects

Insulated linear antenna: Theory and experiment. II

Abstract: The applications and theories of the insulated dipole and monopole are reviewed. A recent analysis of the insulated antenna in a relatively dense ambient medium is summarized and its predictions are shown to be in good agreement with an extensive new set of measurements of the distributions of current and charge and the driving‐point admittances of air‐insulated antennas in fresh and salt water. Four different thicknesses of insulation and lengths up to one wavelength are used. The attenuation due to radiation into fresh water is comparable with and even exceeds the attenuation due to dissipation in salt water. It increases with decreasing radius of the insulating cylinder. The effect of the junction between the feeding coaxial line and the insulated antenna is discussed.

Radiation and scattering by thin-wire structures in the complex frequency domain

Abstract: Piecewise-sinusoidal expansion functions and Galerkin's method are employed to formulate a solution for an arbitrary thin-wire configuration in a homogeneous conducting medium. The analysis is performed in the real or complex frequency domain. In antenna problems, the solution determines the current distribution, impedance, radiation efficiency, gain and far-field patterns. In scattering problems, the solution determines the absorption cross section, scattering cross section and the polarization scattering matrix. The electromagnetic theory is presented for thin wires and the forward-scattering theorem is developed for an arbitrary target in a homogeneous conducting medium.

Antenna pattern generator and switching apparatus

Abstract: A variable pattern antenna system including a plurality of radiating elements, a switching circuit for selectively applying signals to various ones of the radiating elements, a phase shifting circuit for shifting the phase of the signals applied to the elements, and a control circuit for operating the switching circuit and phase shifting circuit to cause variable phase signals to be applied to predetermined radiating elements for changing the pattern of the antenna, and a drive wave-shaping circuit to prevent abrupt switching and the spectrum spreading interference commonly known as ''''splatter'''' that would occur.

Personal paging receiver with swivel clip and distributed antenna

Abstract: A personal paging device is housed in a case which has one dimension (length) longer than its width or thickness, and a clip is affixed to a side on a swivel between the ends of the length dimension, which allows the device to be worn on the person in a vertical or a horizontal posture. A radio receiving antenna is carried on a flexible dielectric sheet within the casing, and radio components are enclosed within that sheet. A pair of orthogonally-related antenna loops can be provided on the dielectric sheet. The swivel clip can be arranged to cooperate with these or other antennas in a circular-polarization antenna system, such that in one orientation one or the other of the antennas will be detuned.

Microwave radiometric measurements of the temperature inside a body

Abstract: Temperatures inside a body have been measured by a radiometer at 0.9 to 1.2 GHz with an antenna on the surface of the body. This technique to measure depth temperatures may have both industrial and medical applications.

The horizontal wire antenna over a conducting or dielectric half space: Current and admittance

Abstract: The wave number, the distribution of current, and the admittance of a horizontal wire antenna over a homogeneous isotropic half space are determined when the complex wave number characteristic of the half space is large in magnitude compared with the real wave number of the air. The axial electric field at the surface of the half space is described. The properties of the antenna are obtained from those of the eccentrically insulated dipole in a general medium in the limit as the radius of the insulation is increased without limit while the distance of the dipole from the boundary is kept constant. Application of the new theory to the Beverage or wave antenna is discussed.

Antenna with rotatable sensitivity pattern

Abstract: Antenna having a selectively rotatably extendable sensitivity pattern provided by an array of three or more dipole antenna units, each of substantially equal mechanical length and located at the corners of a substantially regular polygon having the same number of sides as the number of units in the array and switching means having connections to each dipole unit to selectively energize at least one of said units and interpose an electrically-lengthening inductive reactance in at least two other units located, with respect to the direction in which the sensitivity is to be extended, behind and on either side of an energized unit to serve as parasitic reflectors extending the lobe of sensitivity of an energized unit in the selected direction.

Aberration correcting subreflectors for toroidal reflector antennas

Abstract: The correction of aberration in toroidal reflector antennas by a novel type of subreflector is disclosed. The specific shape of the subreflector ultimately depends on the geometry of the toroidal reflector. However, in any case, the effect of the subreflector is to achieve a point focus in a system which, without the subreflector, does not focus at a point. Considering the antenna system from a radiation point of view, this is equivalent to turning a non-planar equiphase surface in the aperture into a plane thereby eliminating the phase error about the aperture plane perpendicular to the desired direction of propagation. This is achieved while preserving the wide field of view characteristic of the torus antenna by designing the subreflector so that all pathlengths from a reference plane are constant and equal to a desired reference pathlength. In a practical case, the design of the subreflector is accomplished by developing a heuristic geometric optics model of the focusing properties of the toroidal reflector and using a programmable general purpose digital computer to generate the subreflector shape by numerically computing points on the surface of the subreflector for separate, individual rays intercepted by the toroidal reflector, for a bundle of rays incident from the desired direction. These points may then be used to machine the subreflector surface using well-known numerically controlled milling machines. Of special significance is an optimum antenna configuration using what may be termed a ''''Cassegorian'''' subreflector designed according to the principles of the invention having similarities to both Cassegrain and Gregorian subreflectors.

VLF Antarctic antenna: Impedance and efficiency

Abstract: A 21-km horizontal very-low frequency (VLF) antenna has been constructed at Siple Station, Antarctica. This antenna is to be used to inject VLF waves into the magnetosphere in order to perform wave particle interaction experiments. In the present paper, the properties of this antenna are analyzed and its impedance and efficiency calculated. The electrical properties of the ice layer beneath the antenna are modeled. The ice is represented by several layers, each with a different dielectric constant and conductivity. A variational method due to Galejs [2] for an antenna in a stratified dielectric is used. In this method the cylindrical antenna is replaced by an equivalent strip antenna so that the entire geometry is planar. The efficiency is calculated as a function of frequency for different lengths of the antenna. It is found that the antenna is most efficient near its antiresonant frequency. The optimum length for efficient operation at a given frequency is discussed. It is shown that the antenna has an efficiency greater than 2 percent over more than a 2 to 1 frequency range. Some advantages of the Siple antenna, as compared with other horizontal and vertical antennas, are pointed out.

The French quadristatic incoherent scatter facility

Abstract: The original Nancay-St. Santin incoherent scatter facility based on the radio astronomy antenna at Nancay and a CW transmitter located at St. Santin (300 km south) was improved in many ways between 1965 and 1970: doubling of the transmitted power to 140 kw, lowering of the receiver noise level down to 100 K, monitoring of the antenna and data acquisition through the use of a computer, rejection of the parasitic tropospheric echoes. However, the most important improvement brought to the system is the addition of two new receiving stations 100 km east and west of the transmitter. Each of the new stations is equipped with a three-beam Cassegrain antenna (25-m parabola) aimed to simultaneously intersect the vertical transmitted beam at three different heights. Both new receivers have wide band (38 MHz at 3 db) gaseous helium cooled parametric amplifiers and on-line computers. While one of the two new stations is equipped with filter banks for the purpose of spectral analysis, a different choice has been made for the other station. For the latter the data acquisition will imply multibit correlators, for both the ionic spectrum and plasma line measurements. Most of the improved electronic equipment designed for the new stations has also been implemented in the Nancay receiver. The frequency and time synchronization between the four sites is now accomplished by employing a single 5-MHz frequency standard in each station monitored by standard time and frequency signals from MSF and/or HBG stations. The observation procedure consists of tilting the different receiving antennas so as to gather the signal scattered from the ionospheric vertical column illuminated by the transmitter. For calibration purposes a standard ionosonde is operating at St. Santin. The main objective of the quadristatic system is to determine completely the ion drift vector in order to study the electric fields and the neutral tidal winds. Other capabilities offered by the new system are a determination of the plasma line and a higher data acquisition rate. The first observations with one of the new stations were performed in December 1972.

Steerable antenna null combiner system

Abstract: A system employing broadband radio frequency vector multipliers in a balang process for nulling out unwanted radio frequency signals. The nulling is achieved by adjustment of both the desired and interference signals as they pass through the system. The adjustment is accomplished by using vector multipliers which shift the phase by equal amounts and vary the amplitude by proportionate amounts of one or more radio frequency signals in response to separate phase shift and amplitude control forces. To obtain a desired phase shift, an incoming radio frequency signal is split into 0° and 90° components. By multiplying the 0° component by the cosine of the desired phase shift angle, multiplying the 90° component by the sine of the desired phase shift angle, and then summing the results, the signal can be phase shifted by any amounts through all four quadrants. The phase shift and amplitude control forces may be operator initiated or may be initiated through control processing to maximize the relative strength of the desired signal with respect to the interference signal.

Antenna arrays of internally phased elements

Abstract: An antenna array which receives radio waves and reradiates them in a controllable direction. Direction of the reradiated wave is controlled by controlling the phase relationship between waves reradiated from individual antennas which are elements of the complete array assembly. Phase control of the individual element antennas is effected by altering the relative phase between the received wave and the reradiated wave for each individual element antenna. The phase of the received signal is controlled at terminals on the individual antennas at which that received signal arrives. The phase-altered signal is reapplied to those terminals to serve as an excitation signal for the antenna for causing a reradiated wave to be emitted. The difference between the direction of the reradiated wave and the direction of the received wave is controlled by diode switches or by varactor diodes (or by both) which can be mounted integrally with the individual element antennas of the array assembly.

Receiving loop antenna system

Abstract: In a receiving loop antenna especially adapted for use as a built-in antenna of a portable wireless set and of the type wherein the antenna output terminals are so tapped that power matching impedance of the wireless set may be attained, a circuit having series resonant circuit characteristics and a transmission line connected in series with the circuit and having such a length that impedance matching may be obtained, which may minimize the noise at or in the proximity of the center frequency of the frequency band of the series resonant circuit, are inserted between the antenna output terminals and the input terminals of the wireless set.

Circularly polarized helix and spiral antennas

Abstract: An antenna including a support having a conductive outer surface serving to support one or more bays of multifilar helical or spiral conductors with the conductors of each bay fed from the same end and serving to radiate substantially circularly polarized radiation broadside to the antenna.

Combined window heater and antenna

Abstract: A heater grid and antenna for defogging a window such as the windshield of an automobile comprises a plurality of resistive conductors and bus bands for the supply of heating current thereto, at least one of said bus bands having an extension beyond its connection to said resistive conductors, by means of which the resistive conductors and bus bands may be tuned for improved radio reception in the frequency modulation band.

Theoretical and experimental study of the effect of the sheath on an antenna immersed in a warm isotropic plasma

Abstract: A new approach to the problem of electromagnetic wave propagation through a vacuum‐plasma interface is formulated and used to solve two simple antenna problems. First, the impedance of a spherical body covered by a vacuum sheath and immersed in a plasma is calculated. The result is found to coincide with the empirical formula commonly used so far. Second, a cylindrical antenna also isolated from the plasma by a sheath is studied. The antenna can support guided modes whose dispersion relation is derived. An experiment has been performed in order to verify this dispersion relation. Experimental results are found to be in favor of the present approach.

Numerical methods for antenna problems

Abstract: An account is given of some of the integral equations that can be devised for an antenna on whose surface the tangential electric intensity is prescribed. Some of the problems that can arise in numerical work from the formulation of the integral equations and their possible lack of uniqueness are described. Numerical methods of tackling integral equations are given, together with a survey of their advantages and disadvantages from the point of view of electromagnetism. Whip antennas merit separate consideration because of their special structure. There are also a few remarks on modelling surfaces by wire grids. The differing requirements of pulse and harmonic excitation are compared. Finally, the problems of error analysis are briefly mentioned.