Showing papers on "Dipole antenna published in 1975"

Two methods for the measurement of antenna efficiency

Abstract: Two methods for measuring antenna efficiency are described. The two methods, referred to as the Wheeler method and the Q method, are used to find the efficiency of electrically small multiturn loop antennas. The principal advantage of both methods is that they can be quickly and easily applied. Further, both methods relate the antenna efficiency to the input impedance rather than a far-field pattern integration. Thus, the methods are applicable at VHF and frequencies below where the design of an antenna range or anechoic chamber becomes increasingly difficult and expensive.

Optimum element lengths for Yagi-Uda arrays

Abstract: An analytical method is developed for the maximization of the directivity of a Yagi-Uda array by adjusting the lengths of the dipole elements. The effects of a finite dipole radius and the mutual coupling between the elements are taken into consideration. Currents in the array elements are approximated by three-term expansions with complex coefficients that convert the governing integral equations into matrix equations. Array directivity is maximized by a perturbation procedure that adjusts the lengths of all array elements simultaneously and that converges very rapidly. This method can be combined with the previously developed spacing-perturbation method to form a double-perturbation procedure and obtain a Yagi-Uda array of nonuniformly spaced elements of unequal lengths. which yields a maximum directivity.

Microstrip-dipole antenna elements and arrays thereof

Abstract: Herein disclosed are antenna elements comprised of a dipole reactively coupled to a feed line on a microstrip board; and linearly and circularly polarized arrays of such elements.

Experimental study of the impedance of cavity-backed slot antennas

Abstract: The impedance of a simple open slot antenna was measured as a function of frequency and was then compared with the theoretical values obtained through Babinet's principle from the known values of the admittance of its complementary antenna, the strip dipole. A careful experimental study was then made of the impedance of the same slot with several different cavity backings. The impedance was found both as a function of frequency and of the various parameters of the cavity, namely, the cross-sectional size of the cavity, the medium filling the cavity, and the type of termination of the cavity.

Excitation of an infinite antenna above a dissipative earth

Abstract: The antenna problem consisting of exciting an infinitely long horizontal thin wire with an arbitrary distribution of impressed electric field along the axis of the wire is discussed. The special case of excitation by a delta function voltage source is solved. The current on the antenna is found as a sum of two residue (discrete) contributions and two branch integration (continuous) contributions. The far field and orthogonality properties of both the discrete and continuous modes are discussed. Finally, expressions are given for the current on the antenna. From this current the input conductance of the antenna can be obtained.

Dielectric sheet mounted dipole antenna with reactive loading

Abstract: A broadband antenna in the form of a multiple element interlaced dipole array is mounted on a thin elongated strip of dielectric material which is mechanically flexible, light weight and electrically small. Each dipole has a first tapered radiator section with an inductive loading section electrically connected to one end of the tapered radiator section. A capacitive end-loading section is connected to the inductive loading section. Second tapered radiator sections are joined to one another by a second inductive loading section. The inductive loading sections increase the effective electrical length of the first and second tapered radiators, respectively. A UHF gap filling conductor is connected to each of the dipoles to suppress grating lobes at the high-frequency end of the frequency spectrum received by the antenna. The two tapered radiator sections of each dipole are connected to one another by a pair of conductors which are tapered away from one another toward the output terminals of the antenna to provide a preselected output impedance to a receiver.

Properties of infrared cat‐whisker antennas near 10.6 μ

Abstract: Radiation patterns of 10.6‐μ infrared antennas have been obtained experimentally and interpreted by means of a simple theory. It is found that the effective antenna length is equal to the length of the etched portion of the sharpened cat‐whisker antenna. This effective antenna length appears to be caused by decoupling of the electromagnetic field across a shape discontinuity of the antenna wire. The results suggest a simple means for defining shape and size of infrared antenna structures.

A combination of linear and slot antennas for quasi-isotropic coverage

Abstract: The combination of a linear antenna and slot antenna can be used to provide a relatively isotropic radiation pattern when the dipole is perpendicular to the plane of the slot. The theoretical far-field radiation pattern of a dipole flanked by a two-element array of slot antennas is formulated. The fields for two different phasings between the elements of the combination antenna are calculated and the degree of approximation to an isotropic source in the sense of the total field noted. An experimental antenna was fabricated and the radiated fields measured with good agreement found with the theoretical formulas.

Asymmetrically fed electric microstrip dipole antenna

Abstract: An asymmetrically fed electric microstrip dipole antenna consisting of a n electrically conducting, rectangular-shaped element formed on one surface of a dielectric substrate, the ground plane being on the opposite surface The length of the element determines the resonant frequency The feed point is located along the centerline of the antenna length and the input impedance can be varied by moving the feed point along the centerline from the center point to the end of the antenna without affecting the radiation pattern The antenna bandwidth increases with the width of the element and spacing between the element and ground plane

The dipole antenna with eccentric coating in a relatively dense medium

Abstract: In a medium of high permittivity or conductivity, such as sea water, lake water, or wet earth, a dielectric coated antenna can produce a directional radiation pattern when the coating is eccentric. The current distribution on a finite or infinite dipole with such a coating is obtained. Formulas for the directivity and the radiation pattern of an infinitely long dipole with eccentric coating are also derived.

Modeling and Computer Simulation of a Microwave-to-DC Energy Conversion Element

Abstract: A microwave-to-dc energv conversion element consisting of a dipole antenna, a low-pass filter, a Schottky-barrier diode, and a dc filter has been modeled using a distributed transmission-line modeling technique that includes skin-effect losses. Computer simulation has shown 80-percent conversion efficiency and has indicated that the diode generates significant power at higher harmonics due to a resonance effect.

Limited scan array antenna systems with sharp cutoff of element pattern

Abstract: Disclosed are array antenna systems wherein the effective element pattern is modified by means of coupling circuits to closely conform to the ideal element pattern required for radiating the antenna beam within a selected angular region of space. Use of the coupling circuits in the embodiment of a scanning beam antenna significantly reduces the number of phase shifters required as compared to prior art array antennas.

Interference rejection antenna system

Abstract: Interference from polarized signals is minimized by controlling the polarization of antennas having orthogonal dipole radiating elements. The antenna system utilizes microwave hybrids and phase shifters in a coaxial cable feed circuit that divides the power between horizontal and vertical dipole radiating elements. The circuit provides a variable antenna polarization that can be controlled to discriminate against interfering signals having any given polarization characteristics. Coaxial double folded baluns connect feed circuits to the dipole radiating elements and provide proper phasing and impedance transformation for efficient dipole operation.

An Improved Element for Use in Array Antennas

Abstract: A new element is described which is useful in array antennas. This element has a circular symmetric radiation pattern, controllable beamwidth, and exhibits extremely low mutual coupling between elements in the array. A modification of this antenna element results in a single antenna having equal E- and H-plane patterns, no side lobes and extremely low back radiation.

The trap-loaded cylindrical antenna

Abstract: The trap-loaded cylindrical antenna is a cylindrical antenna having one or more traps located in its arms. The traps are either parallel inductor-capacitor circuits or short-circuited transmission line stubs that are designed to be antiresonant (having essentially an infinite input impedance) at some particular frequency. The location and the antiresonant frequency of the traps are selected to enhance the radiation pattern or input impedance of the antenna. This study is confined to the properties of trap-loaded cylindrical antennas that contain only one trap in each arm. The effect of the length of the outer section, length of the inner section, diameter of the cylinder and characteristic impedance or inductance-capacitance ratio of the trap on the input impedance, radiation pattern, and current distribution were studied both experimentally and with the aid of two numerical solutions of an integral equation for the current distribution. The conclusions drawn from this study are that the design procedure for the multiband trap antenna described by Greenberg [1], adjusting the antiresonant frequency of the trap to control the upper resonant frequency, is indeed valid. Graphs suitable for designing trap antennas using this procedure are available in this paper. Furthermore, it is shown that the characteristic impedance or inductance-capacitance ratio of the trap can also be adjusted to vary the lower resonant frequency of the antenna. Design graphs using this procedure are also available in this paper. This study also showed that a relatively wide range of upper to lower antenna resonant frequency ratios can be obtained while still maintaining radiation patterns and input impedances close to those of a half-wave dipole at both frequencies. Graphs are available showing the tradeoff in pattern shape and input impedance that must be made to obtain resonant frequency ratios other than 2 to 1. It was discovered that the trap antenna, sometimes called a Franklin array, must be operated somewhat below the nominal design frequency or have the spacing between traps shortened somewhat, for it to have a radiation pattern similar to a collinear array of half-wave dipoles. Furthermore, the thicker the antenna, the more pronounced this effect is. While the nominal design was discovered to give an input impedance nearly resistive and near 70\Omega (for a dipole), any of the aforementioned modifications resulted in a nonresonant highly capacitive input impedance.

The impedance of a dipole antenna in the ionosphere: 2. Comparison with theory

Abstract: The interpretation of the experiment EIDI I, described in a companion paper, is undertaken. A relatively complete calculation of the impedance is done including the effect of the temperature of the plasma by using the Vlasov equation and hydrodynamic equations, the structure of the sheath using a simple model of it, the collision frequency computed for an equilibrium plasma, and an estimation of various other small effects (wake, ionospheric gradient, motion of ions, …). The result so obtained is in very good agreement with the experiment for the most part but a strong discrepancy appears in the resistance when X > 1. This indicates that the main features of the theory are correct except that a loss mechanism is missing; some hypothetical ones are discussed.

Integrated Diode Phase-Shifter Elements for an X-Band Phased-Array Antenna (Short Papers)

Abstract: The design and production of 502 X-band P-I-N diode phase-shifter elements for a transmissive phased-array RADAR are presented. These elements consist of three phase-shifter states and two integrated dipole radiators formed using microwave integrated circuit techniques. The detailed design of loaded-line phase shifters and effects of circuit variations during production are examined in terms of measured performance. Finally, the performance of the phase shifters in the phased array is demonstrated through computed and measured antenna patterns giving quantitative results.

Interleaved antenna array for use in a multiple input antenna system

Abstract: An interleaved antenna array is disclosed in conjunction with an improved multiple transmitter antenna system for simultaneously generating two independent groups of composite radiation patterns for two separate pluralities of independent radio devices. A first plurality of isolated independent radio transmitters is coupled, without any signal cancellation, to each and every one of a first plurality of independent antenna elements which form a first group of composite radiation patterns for these transmitters. A second plurality of transmitters is likewise coupled to a second plurality of antenna elements which create a second group of composite patterns for these transmitters. The antenna elements of the first and second pluralities are alternately circumferentially disposed about a central axis and each produces a 90° half power beam width radiation pattern which is directed radially away from the central axis. First and second combining networks produce 90° electrical phase shifts between the adjacent radiation patterns produced by the elements in each of the two pluralities, respectively. By providing such an interleaved antenna array for first and second pluralities of independent transmitters, a single multiple input antenna system is provided which has a small size and produces a uniform omnidirectional pattern for each of the transmitters while maintaining isolation between each transmitter.

Conformal radar antenna

Abstract: A conformal electronically scanned antenna array system utilizing an inve Butler matrix in combination with directive antenna elements. The system provides a simple and inexpensive device for scanning an elemental array without the problems of output frequency shift or mutual coupling between antenna elements.

Efficiency and Matching Tradeoffs for Inductively Loaded Short Antennas

Abstract: Efficiency and input resistance of short monopoles (or dipoles) may be significantly improved through use of a loading coil in series with the monopole wire. The piecewise sinusoidal moment method is used to analyze the loaded monopole. When loaded to resonance, the current rises from the feed value to a peak slightly beyond the load point with decay to zero at the end. Radiation resistance improvement factors as large as 5 have been calculated. The resonant loading reactance is shown to vary inversely with the antenna length for most lengths. Efficiency varies slowly with load point and peaks at roughly 0.4 from the feed, in contrast to earlier approximate theory that predicted higher efficiency for loads farther out toward the end. The curves allow a tradeoff between slightly reduced efficiency and larger input resistance (to allow easier matching) to be made. For this case, a 2/3 loading point may be a good compromise. The length for which efficiency is 50 percent is a useful design guide. This length varies slowly with Q and h/a and is in the range 0.06 to 0.09 λ. Thus shorter monopoles will have low efficiency. Bandwidth is improved due to loading coil losses at the expense of efficiency; lossless loading bandwidth is unchanged over the unloaded monopole as the radiation resistance and reactance slope increase commensurately. Extensive graphical data are presented.

The impedance of a dipole antenna in the ionosphere: 1. Experimental study

Abstract: The impedance of a short electric dipole antenna has been measured from rockets in the ionosphere. The EIDI I experiment was launched in conditions where the plasma was expected to be nearly isotropic (operating frequencies 4.48 and 6.09 MHz, f0F2 ⋍ 9 MHz, fH ⋍ 1 MHz). It was designed to detect and measure or to eliminate most of the unwanted effects which complicated the data reduction of previous experiments: outgassing, telemetry radiation, etc. The number of parameters measured simultaneously on board (impedances with variable bias and RF excitation level, resonance frequencies, Te, dc current drawn by the antennas, vehicle potential) and from the ground or an overhead satellite was large enough to provide numerous cross checks and to determine the sheath dimensions. The impedance is very weakly spin-modulated over most of the flight; the collision frequency is very low (v/ω ⋍ 10−5) unlike some of the previous experiments where collision losses were dominant. The measured values of the impedance are given as a function of X=f2p/f2 where the other parameters are known.

Notch fed electric microstrip dipole antenna

Abstract: A notch fed electric microstrip dipole antenna consisting of a thin electally conducting, rectangular-shaped element formed on one surface of a dielectric substrate, the ground plane being on the opposite surface. The length of the element determines the resonant frequency. The feed point is located in a notch along the centerline of the antenna length and the input impedance can be varied by moving the feed point along the centerline of the antenna without affecting the radiation pattern. Of all the many types of microstrip antennas built to date, this antenna offers the best advantages as far as arraying of the elements are concerned. The notched antenna can be arrayed using microstrip interconnecting transmission lines. The corner losses in the clad material and the width of the notch determines how narrow the element can be made. The purpose of the notch feed system is to interconnect any array of elements at the elements' optimum feed point using microstrip transmission lines.

Travelling wave meander conductor antenna

Abstract: A travelling wave conductor antenna including a ground plane. The antenna consists of meander-structure conductors made of a conductive material, zigzagging at right angles or at almost right angles. The conductors are placed above an even or deformed ground plane and they alternately comprise portions parallel with the longitudinal axis of the antenna and portions perpendicular or almost perpendicular to said longitudinal axis so that the number of the conductors is even. The conductors are at their ends connected to an antenna feed point by means of electrically equally long or almost equally long conductors.

Broadband ferrite transformer-fed whip antenna

Abstract: The feed point of a whip antenna having a length less than one quarter-wavelength at the lowest frequency of operation is raised above a counterpoise ground plane by a short base sleeve. Gain over a 2.5:1 bandwidth of radio frequencies closely approaches the gain of a standard quarter-wavelength antenna without requiring use of power-dissipating resistance loading. A ferrite transformer at the whip antenna feedpoint is utilized to reduce the high anti-resonance impedance of the broadband whip antenna to the characteristic impedance of a coaxial cable transmission system and to minimize the VSWR thereof. The base sleeve raises the antenna resistance at the resonant frequency near the lower end of the bandwidth to make the transformer effective as an impedance matching element over the entire radio frequency band. A pair of the whip antennas are axially aligned and electrically coupled in series to realize a broadband dipole having increased gain. A pair of dipoles are energized in phased relationship to realize even higher gain and directivity.

Radio telescopes of large resolving power.

Abstract: It was not until 1958 that It could be shown with some certainty that most of the radio sources were powerful extragalactic objects, but the possi­ bilities were so exciting even in 1952 that my colleagues and I set about the task of designing instruments capable of extending the observation to weaker and weaker sources, and of exploring their internal structure. Early observations of radio sources were severely limited both by the poor angular resolution and by the limited sensitivity. It was usually impossible to obtain any information about the structure of a source, and adjacent sources could often not be properly separated, whilst attempts to relate the radio sources to optically visible objects were often prevented by the poor positional accuracy. The use of interferometers allowed better posi­ tions to be obtained, and sometimes made it possible to derive simple models for the source structure. Few of the sources were found to have an angular size greater than 2-3’ arc. The problem of making detailed maps of such sources arises simply from the fact that the wavelengths used are some million times greater than optical wavelengths — so that even to obtain a radio picture with the same resolution as that of the unaided human eye (~1’ arc) a tele­ scope having a diameter of about 1 km operating at a wavelength of 50 cm would be needed. At the same time the instrument would be effective only if the surface accuracy was good enough to make a proper image, corresponding to errors of ≤ λ/20 or a few cm; the engineering problems of building such an instrument are clearly enormous. An entirely different approach to the problem is to employ small aerial elements which are moved to occupy successively the whole of a much larger aperture plane. The develop­ ment and use of “aperture synthesis” systems has occupied much of our team in Cambridge over the past 20 years. The principle of the method is ex­ tremely simple. In all methods used to obtain a large resolving power, that is to distinguish the wavefront from a particular direction and ignore those from adjacent directions, we arrange to combine the field measur­ ed over as large an area as possible of the wavefront. In a paraboloid we do this by providing a suitably shaped reflecting surface, so that the fields incident on different parts of the sampled wavefront are combined at the focus (Fig. 1a); the voltage pro­ duced in the receiving dipole repre­ sents the sum of these fields. We can achieve the same result if we use an array of dipoles connected together through equal lengths of cable (Fig. 1b). Suppose now that only a small part of the wavefront is sampled, but that different parts are sampled in turn (Fig. 1c); could we combine these signals to produce the same effect? Since in general, we do not know the phase of the incident field at dif­ ferent times this would not normally be possible but if we continue to measure one of the samples while we measure the others we can use the signal from this one as a phase refer­ ence to correct the values measured in other parts of the wavefront. In this way, by using two small aerial ele­ ments, we can again add the fields over the wavefront — the area of which is now determined by the range of relative positions taken by the two aerial elements. It might be thought that this method would be extremely slow, for if we are Energy and Physics

The insulated monopole: Admittance and junction effects

Abstract: Recent theoretical and experimental studies of the insulated linear antenna in a relatively dense ambient medium are reviewed briefly. Attention is then directed to a description of the admittance and impedance of air-insulated monopoles as determined by theory and by measurements when two quite different junctions between the antenna and the feeding coaxial line are used. Graphs of the admittances of antennas with three different thicknesses of the insulation and lengths up to a wavelength are shown. No theory of the junction effects or simple corrective network is provided, but it is shown that with proper design of the junction region, the uncorrected (ideal) theoretical admittances are satisfactory approximations of measured values.

Analysis of the log-periodic V-dipole antenna

Abstract: The log-periodic V-dipole antenna (LPVA) operating in the 3\lambda/2 mode is analyzed numerically using the projective technique. The antenna is treated as a parallel connection of an array of V-dipoles and a feeder transmission line. This decoupling of the circuits enables one to obtain the dipole currents simply by considering the array of V-dipoles as a boundary value problem and solving the necessary integral equations. The currents can then be used to give the various properties of the antenna. Effects on the antenna behavior obtained by changing its parameters are illustrated, and general characteristic curves presented.

Adjustable yagi antenna

Abstract: A yagi antenna having a director element, a half-wave active dipole element, and a reflector element mounted on an antenna boom. All antenna elements are rods that are telescopically adjustable in length from a collapsible position to an operating length for a predetermined frequency of operation, and removable from threaded mounting for storage. The director element and reflector element are slidably adjustable on the antenna boom for independent spacing with respect to the half-wave active dipole element. The antenna boom has two mast support holes; one for horizontal polarization and the other for vertical polarization. A ferrite core member surrounds a coaxial cable connecting the half-wave active dipole element to a coaxial connector, and provides balun action between the coaxial cable and a balanced antenna feed point.

The far-field response of a step-excited linear antenna using SEM [singularity expansion method]

Abstract: Previous investigation of the use of the singularity expansion method (SEM) for analyzing antennas or scatterers has concentrated on the behavior of currents and charges on a conducting body. In this paper the previous work is extended by defining the far-field natural modes for the linear antenna. The transient radiation pattern is then computed for a step-excited center-fed linear antenna.

Interferometric doppler guidance system

Abstract: A means for identifying a particular range and Doppler shift signal in the field of view of a moving radar antenna which determines azimuth angle to this range-Doppler signal relative to the antenna by determining the phase difference between said signal as processed through two channels each fed by antennas displaced in a horizontal direction with respect to the axis of the antenna system.