Showing papers on "Antenna (radio) published in 1981"

Antenna theory and design

Abstract: Antenna Fundamentals and Definitions. Some Simple Radiating Systems and Antenna Practice. Arrays. Line Sources. Resonant Antennas: Wires and Patches. Broadband Antennas. Aperture Antennas. Antenna Synthesis. Antennas in Systems and Antenna Measurements. CEM for Antennas: The Method of Moments. CEM for Antennas: Finite Difference Time Domain Method. CEM for Antennas: High-Frequency Methods. Appendices. Index.

Microstrip antenna technology

Abstract: A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques. Available substrate materials are reviewed along with the relation between dielectric constant tolerance and resonant frequency of microstrip patches. Several theoretical analysis techniques are summarized, including transmission-line and modal-expansion (cavity) techniques as well as numerical methods such as the method of moments and finite-element techniques. Practical procedures are given for both standard rectangular and circular patches, as well as variations on those designs including circularly polarized microstrip patches. The quality, bandwidth, and efficiency factors of typical patch designs are discussed. Microstrip dipole and conformal antennas are summarized. Finally, critical needs for further research and development for this antenna are identified.

Antenna theory and design

Abstract: Foreword to the Revised Edition. Preface to the Revised Edition. Preface. I SOURCE-FIELD RELATIONS SINGLE ANTENNA ELEMENTS. 1 The Far-Field Integrals, Reciprocity, Directivity. 1.1 Introduction. 1.2 Electrostatics and Magnetostatics in Free Space. 1.3 The Introduction of Dielectric, Magnetic, and Conductive Materials. 1.4 Time-Varying Fields. 1.5 The Retarded Potential Functions. 1.6 Poynting's Theorem. 1.7 The Stratton-Chu Solution. 1.8 Conditions at Infinity. 1.9 Field Values in the Excluded Regions. 1.10 The Retarded Potential Functions: Reprise. 1.11 The Far Field: Type I Antennas. 1.12 The Schelkunoff Equivalence Principle. 1.13 The Far Field: Type IL Antennas. 1.14 The Reciprocity Theorem. 1.15 Equivalence of the Transmitting and Receiving Patterns of an Antenna. 1.16 Directivity and Gain. 1.17 Receiving Cross Section. 1.18 Polarization of the Electric Field. 2 Radiation Patterns of Dipoles, Loops, and Helices. 2.1 Introduction. 2.2 The Center-Fed Dipole. 2.3 Images in a Ground Plane. 2.4 A Monopole Above a Ground Plane. 2.5 A Dipole in Front of a Ground Plane. 2.6 The Small Current Loop. 2.7 Traveling Wave Current on a Loop. 2.8 The End-Fire Helix. 3 Radiation Patterns of Horns, Slots and Patch Antennas. 3.1 Introduction. 3.2 The Open-Ended Waveguide. 3.3 Radiation from Horns. 3.4 Center-Fed Slot in Large Ground Plane. 3.5 Waveguide-Fed Slots. 3.6 Theory of Waveguide-Fed Slot Radiators. 3.7 Patch Antennas. II ARRAY ANALYSIS AND SYNTHESIS. 4 Linear Arrays: Analysis. 4.1 Introduction. 4.2 Pattern Formulas for Arrays with Arbitrary Element Positions. 4.3 Linear Arrays: Preliminaries. 4.4 Schelkunoff's Unit Circle Representation. 5 Linear Arrays: Synthesis. 5.1 Introduction. 5.2 Sum and Difference Patterns. 5.3 Dolph-Chebyshev Synthesis of Sum Patterns. 5.4 Sum Pattern Beamwidth of Linear Arrays. 5.5 Peak Directivity of the Sum Pattern of a Linear Array. 5.6 A Relation Between Beamwidth and Peak Directivity for Linear Arrays. 5.7 Taylor Synthesis of Sum Patterns. 5.8 Modified Taylor Patterns. 5.9 Sum Patterns with Arbitrary Side Lobe Topography. 5.10 Discretization of a Continuous Line Source Distribution. 5.11 Bayliss Synthesis of Difference Patterns. 5.12 Difference Patterns with Arbitrary Side Lobe Topography. 5.13 Discretization Applied to Difference Patterns. 5.14 Design of Linear Arrays to Produce Null-Free Patterns. 6 Planar Arrays: Analysis and Synthesis. 6.1 Introduction. 6.2 Rectangular Grid Arrays: Rectangular Boundary and Separable Distribution. 6.3 Circular Taylor Patterns. 6.4 Modified Circular Taylor Patterns: Ring Side Lobes of Individually Arbitrary Heights. 6.5 Modified Circular Taylor Patterns: Undulating Ring Side Lobes. 6.6 Sampling Generalized Taylor Distributions: Rectangular Grid Arrays. 6.7 Sampling Generalized Taylor Distributions: Circular Grid Arrays. 6.8 An Improved Discretizing Technique for Circular Grid Arrays. 6.9 Rectangular Grid Arrays with Rectangular Boundaries: Nonseparable Tseng-Cheng Distributions. 6.10 A Discretizing Technique for Rectangular Grid Arrays. 6.11 Circular Bayliss Patterns. 6.12 Modified Circular Bayliss Patterns. 6.13 The Discretizing Technique Applied to Planar Arrays Excited to Give a Difference Pattern. 6.14 Comparative Performance of Separable and Nonseparable Excitations for Planar Apertures. 6.15 Fourier Integral Representation of the Far Field. III SELF-IMPEDANCE AND MUTUAL IMPEDANCE, FEEDING STRUCTURES. 7 Self-Impedance and Mutual Impedance of Antenna Elements. 7.1 Introduction. 7.2 The Current Distribution on an Antenna: General Formulation. 7.3 The Cylindrical Dipole: Arbitrary Cross Section. 7.4 The Cylindrical Dipole: Circular Cross Section, Hallen's Formulation. 7.5 The Method of Moments. 7.6 Solution of Hallen's Integral Equation: Pulse Functions. 7.7 Solution of Halle'n's Integral Equation: Sinusoidal Basis Functions. 7.8 Self-Impedance of Center-Fed Cylindrical Dipoles: Induced EMF Method. 7.9 Self-Impedance of Center-Fed Cylindrical Dipoles: Storer's Variational Solution. 7.10 Self-Impedance of Center-Fed Cylindrical Dipoles: Zeroth and First Order Solutions to Hallen's Integral Equation. 7.11 Self-Impedance of Center-Fed Cylindrical Dipoles: King-Middleton Second-Order Solution. 7.12 Self-Impedance of Center-Fed Strip Dipoles. 7.13 The Derivation of a Formula for the Mutual Impedance Between Slender Dipoles. 7.14 The Exact Field of a Dipole: Sinusoidal Current Distribution. 7.15 Computation of the Mutual Impedance Between Slender Dipoles. 7.16 The Self-Admittance of Center-Fed Slots in a Large Ground Plane: Booker's Relation. 7.17 Arrays of Center-Fed Slots in a Large Ground Plane: Self-Admittance and Mutual Admittance. 7.18 The Self-Impedance of a Patch Antenna. 8 The Design of Feeding Structures for Antenna Elements and Arrays. 8.1 Introduction. 8.2 Design of a Coaxially Fed Monopole with Large Ground Plane. 8.3 Design of a Balun-Fed Dipole Above a Large Ground Plane. 8.4 Two-Wire-Fed Slots: Open and Cavity-Backed. 8.5 Coaxially Fed Helix Plus Ground Plane. 8.6 The Design of an Endfire Dipole Array. 8.7 Yagi-Uda Type Dipole Arrays: Two Elements. 8.8 Yagi-Uda Type Dipole Arrays: Three or More Elements. 8.9 Frequency-Independent Antennas: Log-Periodic Arrays. 8.10 Ground Plane Backed Linear Dipole Arrays. 8.11 Ground Plane Backed Planar Dipole Arrays. 8.12 The Design of a Scanning Array. 8.13 The Design of Waveguide-Fed Slot Arrays: The Concept of Active Slot Admittance (Impedance). 8.14 Arrays of Longitudinal Shunt Slots in a Broad Wall of Rectangular Waveguides: The Basic Design Equations. 8.15 The Design of Linear Waveguide-Fed Slot Arrays. 8.16 The Design of Planar Waveguide-Fed Slot Arrays. 8.17 Sum and Difference Patterns for Waveguide-Fed Slot Arrays Mutual Coupling Included. IV CONTINUOUS APERTURE ANTENNAS. 9 Traveling Wave Antennas. 9.1 Introduction. 9.2 The Long Wire Antenna. 9.3 Rhombic and Vee-Antennas. 9.4 Dielectric-Clad Planar Conductors. 9.5 Corrugated Planar Conductors. 9.6 Surface Wave Excitation. 9.7 Surface Wave Antennas. 9.8 Fast Wave Antennas. 9.9 Trough Waveguide Antennas. 9.10 Traveling Wave Arrays of Quasi-Resonant Discretely Spaced Slots [Main Beam at theta0= arccos(beta/k)]. 9.11 Traveling Wave Arrays of Quasi-Resonant Discretely Spaced Slots (Main Beam Near Broadside). 9.12 Frequency Scanned Arrays. 10 Reflectors and Lenses. 10.1 Introduction. 10.2 Geometrical Optics: The Eikonal Equation. 10.3 Simple Reflectors. 10.4 Aperture Blockage. 10.5 The Design of a Shaped Cylindrical Reflector. 10.6 The Design of a Doubly Curved Reflector. 10.7 Radiation Patterns of Reflector Antennas: The Aperture Field Method. 10.8 Radiation Patterns of Reflector Antennas: The Current Distribution Method. 10.9 Dual Shaped Reflector Systems. 10.10 Single Surface Dielectric Lenses. 10.11 Stepped Lenses. 10.12 Surface Mismatch, Frequency Sensitivity, and Dielectric Loss for Lens Antennas. 10.13 The Far Field of a Dielectric Lens Antenna. 10.14 The Design of a Shaped Cylindrical Lens. 10.15 Artificial Dielectrics: Discs and Strips. 10.16 Artificial Dielectrics: Metal Plate (Constrained) Lenses. 10.17 The Luneburg Lens. APPENDICES. A. Reduction of the Vector Green's Formula for E. B. The Wave Equations for A and D. C. Derivation of the Chebyshev Polynomials. D. A General Expansion of cosm v. E. Approximation to the Magnetic Vector Potential Function for Slender Dipoles. F. Diffraction by Plane Conducting Screens: Babinet's Principle. G. The Far-Field in Cylindrical Coordinates. H. The Utility of a Csc2 theta Pattern. Index.

Fundamental limitations in antennas

Abstract: Four fundamental limitations in antennas have been identified in the areas of: electrically small antennas, superdirective antennas, superresolution antennas, and high-pin antennas. All exhibit roughly exponential increase in cost factors with performance increase beyond the robust range. This paper reviews these limitations. Electrically small antennas are analyzed via spherical mode theory, with the antenna enclosed in a virtual sphere. Minimum Q varies inversely as the cube of sphere radius in radian wavelengths when the radius is much less than the latter. This limits the achievable bandwidth. Superdirective apertures require a constraint; the optimization is generally intractable except for line sources. Superdirective arrays have spacing below half-wavelength, and for small spacings a constraint is desirable to limit Q, tolerances, efficiency, sidelobes, etc. This is accomplished by expressing constrained directivity as a ratio of two Hermilian quadratic forms, for which a solution exists. Array Q varies exponentially with directivity so only modest increases are practical. Superresolution arrays use maximum entropy processes to improve spatial frequency resolution for short samples (short arrays), analogous to spectral analysis processing. An amplitude-tapered autocorrelation function is extended by linear least square prediction and autoregression; the latter contributes filter poles. This extension is with minimum added information, hence maximum entropy. In contrast to superdirective arrays which are all zero functions, superresolution maximum entropy uses an all pole function. Results are dependent upon the sampling subarray size and upon signal/noise (S/N). Required S/N increases exponentially with inverse angular resolution. Achievable gain of high-gain reflector antennas is limited by cost of the structure. For random surface errors maximum gain is proportional to the mechanical tolerance ratio (antenna diameter/1σ tolerance) squared. Since cost increases rapidly with diameter and with tolerance ratio this comprises a gain limitation. Current best reflectors have maximum gain in the range of 90 to 100 dB.

Microstrip Antenna Theory and Design

Abstract: * Chapter 1: Flat-plate antenna techniques and constraints on performance * Chapter 2: Microstrip design equations and data * Chapter 3: Radiation mechanism of an open-circuit microstrip termination - fundamental design implications * Chapter 4: Basic methods of calculation and design of patch antennas * Chapter 5: Linear array techniques * Chapter 6: Techniques and design limitations in two-dimensional arrays * Chapter 7: Circular polarisation techniques * Chapter 8: Some manufacturing and operational problems of microstrip antennas * Chapter 9: Recent advances in microstrip antenna analysis * Chapter 10: Other trends and possible future developments

Miniature Interferometer Terminals for Earth Surveying: Ambiguity And Multipath with Global Positioning System

Abstract: With the recent launching of several satellites of the global positioning system (GPS), a variety of schemes based on radio interferometry have been proposed for the accurate determination of relative positions of receiving terminals on the ground. Provided that the integer-cycle ambiguities of the interferometric phase observations can be correctly resolved, the baseline vector extending from the antenna of one terminal to that of another should be determinable with uncertainty much smaller than the 19-cm wavelength of the GPS transmissions. We propose a method of ambiguity resolution that is suitable for observations made with antennas of low directive gain. Such antennas are compact, but the feasibility of their use has been questioned because observations with them are susceptible to multipath interference. For short-baseline interferometric observations of GPS our method yields correct ambiguity resolution despite severe multipath interference and significant sky blockage, even when instability of the frequency standards governing the separate receiving terminals limits the time span of coherent integration to five minutes.

Antennas in Matter: Fundamentals, Theory, and Applications

Abstract: The volume provides an introduction to antennas and probes embedded within or near material bodies such as the earth, the ocean, or a living organism. After a fundamental analysis of insulated and bare antennas, an advanced treatment of antennas in various media is presented, including a detailed study of the electromagnetic equations in homogeneous isotropic media, the complete theory of the bare dipole in a general medium, and a rigorous analysis of the insulated antenna as well as bare and insulated loop antennas. Finally, experimental models and measuring techniques related to antennas and probes in a general dissipative or dielectric medium are examined.

Battery operated access control card

Abstract: An access control card for use in an access control system. A battery, a wireless signal sensor such as an antenna for receiving coded wireless signals such as coded radio frequency signals generated by a card reader, a clock connected to the battery and including a receiver are connected to the antenna for supplying a received signal based upon the coded radio frequency signal. A memory for stores first and second stored codes, and a transmit circuit connected to the antenna, to the clock and to the memory compares the first stored code to the received signal and transmits the second stored code when there is a match between the received signal and the first stored code.

Phased array antenna employing linear scan for wide angle orbital arc coverage

Abstract: The present invention relates to phased array antenna arrangements which comprise a linear array of feed elements where the array has an aperture which is out at a bias angle along the minor axis of the array to produce a fixed linear phase taper along the minor axis by all elements Then by linearly scanning the array along the major axis of the aperture of the array, a beam is scanned along an arc which can be made to correspond to an orbital arc segment around a celestial body and within the field of view of the antenna arrangement when the bias angle is properly chosen The feed elements can comprise long feedhorns or horn antenna configurations which can be used in a separate array or disposed in an array on a conjugate plane of a main cylindrical reflector when used in multiple reflector phased array antenna arrangements

360-Degree scanning antenna with cylindrical array of slotted waveguides

Abstract: A 360 degree scanning antenna is disclosed which includes a mechanism for anning the main beam of a cylindrical array in azimuth and over a limited angle in elevation in which a primary feedhorn illuminates a geodesic lens which in turn illuminates the cylindrical array structure. Energy is coupled from the parallel plate structure of the feedhorn assembly into the individual waveguides of the array via dielectric wedges extending from the waveguides. Scanning in elevation is accomplished by changing the transmitter frequency and in azimuth by rotating the primary feedhorn assembly.

The plasma wave and quasi-static electric field instrument /PWI/ for dynamics Explorer-A

Abstract: It is explained that the Plasma Wave Instrument (PWI) on Dynamics Explorer-A measures both plasma wave phenomena and quasi-static electric fields. The quasi-static electric fields are measured parallel to the spin axis of the spacecraft in a range of 2 mV/m to 2 V/m and perpendicular to the spin axis 0.5 mV/m to 2 V/m at 16 samples/s. The ac electric field sensors include a 200-m tip-to-tip long wire antenna and a 0.6-m short electric antenna, both of which are perpendicular to the spin axis, and a 9-m tip-to-tip tubular antenna parallel to the spin axis. AC electric wave fields are measured over a frequency range of 1 Hz to 2 MHz and over an amplitude range of 0.03 microvolt/m to 100 mV/m.

The elliptical microstrip antenna with circular polarization

Abstract: A theoretical analysis of an elliptical microstrip antenna is presented. It is shown that radiation from this antenna is left-hand or right-hand circularly polarized in a narrow frequency band when the eccentricity of the ellipse is small. The theoretical result agrees with the experimental data.

Preliminary design of large reflectors with flat facets

Abstract: A concept for approximating curved antenna surfaces using flat facets is discussed. A preliminary design technique for determining the size of the reflector surface facets necessary to meet antenna surface accuracy requirements is presented. A proposed large microwave radiometer satellite (MRS) is selected as an application, and the far-field electromagnetic response of a faceted reflector surface is compared with that from a spherical reflector surface.

Monolithic microwave integrated circuit with integral array antenna

Abstract: A monolithic microwave integrated circuit including an integral array antenna. The system includes radiating elements, feed network, phasing network, active and/or passive semiconductor devices, digital logic interface circuits and a microcomputer controller simultaneously incorporated on a single substrate by means of a controlled fabrication process sequence.

Radar imaging from a distorted array: The radio camera algorithm and experiments

Abstract: High angular resolution radar imaging may be achieved with a large-aperture antenna even if the aperture is distorted, provided that adaptive signal processing compensates for the distortion. The radio camera is an instrument designed for this purpose. Its algorithm for imaging ground-based targets is described and experimental results are given for a 3 cm wavelength demonstration system using a distorted 27-m random sparse array. The measured beamwidth of 1 mrad conformed to theory, confirming the validity of the technique. Extension of the algorithm to accommodate isolated targets such as aircraft and ships also is discussed.

Low profile circular array antenna and microstrip elements therefor

Abstract: An antenna element is comprised of two rectangular microstrip patch dipoles spaced by dielectric a predetermined distance above a ground plane conductor. One edge of each dipole is electrically shunted to the ground plane conductor. The dipole feedpoints are separated by a quarter wavelength of the antenna resonant frequency. An isolated power splitter and phase shifter connects an antenna element port with the dipole feedpoints so that the signal at one feedpoint lags the signal at the other feedpoint by 90°. The antenna element will end fire through the dipoles in the direction of the lagging signal feedpoint. A low profile circular array antenna is comprised of eight such antenna elements arranged on the ground plane conductor equally spaced with their phase centers on a common phase center circle.

An experimental study of the circular-polarized elliptical printed-circuit antenna

Abstract: Elliptical-shaped printed-circuit antennas were fabricated with varying eccentricities, and their impedance and radiation patterns were measured. Special attention was devoted to investigating the design criteria which produced the best circular polarization.

Coherent, frequency multiplexed radar

Abstract: Coherent, frequency multiplexed radar is a new generic type of continuous wave radar architecture wherein contiguous pulses of discrete frequency segmented signals are serially transmitted from an antenna, and after reflection from radar targets, signals from the same antenna are coherently processed in a parallel manner to provide correlated measurements of target's pulse compressed range and radial velocity. Simultaneously transmitted and received signals are separated by frequency multiplexing.

Dual frequency anti-theft system

Abstract: An anti-theft tag (34) containing a semiconductor diode (36) connected to a metal antenna loop (38) is configured to receive two distinct radio frequency transmissions. The diode (36) bridges a closed loop at one end of the antenna (38), forming a tank circuit resonant at twice a selected center frequency. A first transmitter (26) generates a tone modulated radio frequency (f) displaced on one side of the center frequency, and a second transmitter (30) generates a continuous wave radio frequency (f) displaced on the other side of the center frequency. Both signals are fed separately to respective dipole radiating antenna strips (18, 19, 20, 21) on opposite sides of a surveillance area. The dipole strips for the different frequencies are at right angles to each other on each side; those for the same frequency are at right angles to each other on opposite sides. This produces cross polarized transmission of both frequencies within the area. Diode (36) of tag (34) mixes the two frequencies received by the antenna loop (38), causing the tank circuit to resonate at the sum of the two frequencies (double the center frequency). That resonant frequency is reradiated to receiver antennae (22, 24) on each side for detection by a very narrow band receiver (42) responsive to the sum frequency. The modulating tone is derived from the received signal and processed to trigger an alarm (44) when the detected signal is of sufficient strength and duration.

Circularly polarized microstrip line antenna

Abstract: A circularly polarized microstrip line antenna for receiving or transmitting a signal of a particular wavelength includes a dielectric substrate having a ground plate provided on one surface thereof and having a microstrip line formed on another surface thereof. The microstrip line has an omega shaped fundamental portion composed of a loop portion and a pair of straight portions. The loop portion is one of either a regular polygon or a continuous closed curve having a length equal to the particular wavelength. The loop portion is symmetric about an axis which is on one of the surfaces of the substrate and is at right angles to the straight portions of the microstrip line.

A spectral domain approach for computing the radiation characteristics of a leaky-wave antenna for millimeter waves

Abstract: A new method for evaluating the complex propagation constant \beta in a leaky-wave structure comprising thin metallic rectangular strips etched on a dielectric rod of rectangular cross section is described. The radiation pattern of the leaky-wave antenna can be determined once \beta is known, since Re( \beta ) governs the direction of the main beam and Im( \beta ) accounts for the beamwidth and aperture efficiency. In addition the knowledge of the dependence of \beta on frequency allows one to design the antenna for frequency-scanning applications. The method employed in this communication is based on the spectral domain approach that formulates the eigenvalue problem in the Fourier transform domain. Computed results are shown to be in very good agreement with experimental measurements.

Quasi‐thermal noise in a stable plasma at rest: Theory and observations from ISEE 3

Abstract: The noise voltage found at the terminals of an electric dipole antenna immersed in a hot plasma is calculated. The plasma is assumed stable and at rest. It is described as made of two maxwellian electron populations. A grid of calculated noise spectra is presented in normalized coordinates, and we give analytical expressions valid for frequencies much lower or larger than the plasma frequency fp or close to the noise peak. The antenna impedance is also calculated; in contrast to the noise spectrum, it is found to be very weakly dependent upon the hot population parameters. From these results one can calculate the response of a receiving system, thus enabling the actual measurement of the plasma parameters from the noise spectrum. Using ISEE 3 SBH experimental data, it is shown that the observations do fit the theoretical predictions over most of the frequency range. Plasma parameters are obtained and found in good agreement with results from the Los Alamos plasma analyzer on the same spacecraft. It appears that the high energy tail of the particle distribution function accounts for the peak noise voltages of several times 10−12 V²Hz−1 found at the terminals of a 45-m half-length dipole. The interpretation of these observations does not therefore require an unstable plasma. We discuss these results and show that more work should be done to explain an unpredicted increase of the spectrum below fp and to explain the weak spin modulation. Solving these remaining problems requires the introduction of ions and of the bulk and/or drift velocity into the calculations. Appendix A contains a partial justification of the assumption of a triangular current distribution on the antenna. The calculations are presented in appendix B.

Adaptive steerable null antenna processor with null indicator

Abstract: An adaptive antenna array system steers a plurality of antennas to direct e null toward an undesired source of interference to reduce noise and enhance detection of desired signals. A null indication processing system adjusts the phase and amplitude of the antenna branches to steer the null and provide a null angle indication and display. Digital controller and memory circuits provide automatic operation.

Adaptive steerable null antenna processor

Abstract: According to the invention, a receive-transmit steerable null antenna prosor includes incrementally adjustable delay lines and a variable ratio power network (amplitude balance control) for adjusting the relative phase and amplitude in two or more antenna branches to steer a null on an interference source. A digital controller compares a signal which includes a representation of the interference level to a previously sampled value to note improvement or not and adjusts the delay lines and amplitude balance accordingly.

Antenna with P.I.N. diode switched tuning inductors

Abstract: A tuned radio antenna for a frequency agile communication system has a plurality of tuning inductors in series with a short-circuiting switch for each inductor, each switch being formed by a pair or a plurality of pairs of P.I.N. diodes, control means being provided for applying biasing potentials to the diodes to effect switching of the antenna tuning.

Computer modeling of antennas near the ground

Abstract: An accurate and efficient numerical method based on the rigorous Sommer-feld theory is described for modeling antennas near an interface such as the ground. The Sommerfeld integrals are evaluated by numerical integration along contours in the complex plane and two-dimensional interpolation is used subsequently to obtain the many Sommerfeld integral values needed for the moment-method solution of an integral equation. These methods permit modeling an antenna within 10-6 wavelengths of the ground for about two to four times the computation time for the same antenna in free space. Results showing currents and radiation patterns are included.

Helmet metal mass compensation for helmet-mounted sighting system

Abstract: An electromagnetic system for determining the orientation including position of a helmet worn by a pilot is disclosed having a transmitting antenna for transmitting electromagnetic field vectors, a receiving antenna for sensing the electromagnetic field vectors generated by the transmitting antenna, and a control apparatus responsive to the sensed electromagnetic field vectors and the transmitted electromagnetic field vectors for determining the compensated orientation of the helmet, the compensated orientation relying upon the rotation matrix determined by a previous solution for the orientation of the helmet.

Microstrip antennas for millimeter waves

Abstract: Proof of the feasibility of low-cost conformal printed circuit board antenna arrays at millimeter wave frequencies is presented It has become apparent that present day trends in microwave systems are indicating extensive design efforts in the millimeter wave region Many proposed systems will be seriously hindered by a lack of readily available inexpensive components Microstrip conformal antennas have distinct advantages in cost, variety of field pattern, and reproducibility for microwave system design It is felt that similar advantages could be realized at millimeter wave frequencies The results obtained with actual experimental hardware are described Discussed are 4 \times 4 element arrays operating in the 35- and 60-GHz regions and a 32 \times 32 element array operating near 38 GHz

Theft detection apparatus using saturable magnetic targets

Abstract: An electronic theft detection apparatus for detection of saturable magnetic targets has transmitter and receiver antennas formed of single turn loops of rigid metal pipe. The antennas are rectangular and have a width, in the direction of passage, through the interrogation zone, less than the length of a shopping cart. The transmitter antenna is in the form of a rectangular loop and the receiver antenna is of the same overall size and configuration but is bisected with a conductor to form two balanced loops. The antennas are purely inductive and a series resonant circuit is inductively coupled into the transmitter antenna and a parallel resonant circuit is inductively coupled out of the receiver antenna. Special circuits are also provided for temporarily disabling the apparatus when a related lower harmonic frequency signal decreases in amplitude.

Some aspects of optimization of an invasive microwave antenna for local hyperthermia treatment of cancer

Abstract: Hyperthermia has emerged as a promising alternative or adjunct to other forms of cancer therapy. In order to utilize hyperthermia in very localized volumes immersed in regions of vital normal tissue, an invasive microwave coaxial monopole antenna has been developed. An experimental approach has been taken to characterize and optimize the electromagnetic properties and heating capabilities of bare and insulated antennas imbedded in tissue equivalent phantoms and dog brain. Four methods have been used to visualize the thermal profiles of the microwave probes: the liquid crystal technique, the gelatin technique, and the direct measurement of temperature with thermistor probes in phantom and dog brain. Among the parameters studied are: antenna impedance, insertion depth, antenna insulation (dielectric constant and thickness), shaft insulation, and frequency.