Showing papers on "Coaxial antenna published in 1973"

Determination of far-field antenna patterns from near-field measurements

Abstract: In many cases, it is impractical or impossible to make antenna pattern measurements on a conventional far-field range; the distance to the radiating far field may be too long, it may be impractical to move the antenna from its operating environment to an antenna range, or the desired amount of pattern data may require too much time on a far-field range. For these and other reasons, it is often desirable or necessary to determine far-field antenna patterns from measurements made in the radiating near-field region; three basic techniques for accomplishing this have proven to be successful. In the first technique, the aperture phase and amplitude distributions are sampled by a scanning field probe, and then the measured distributions are transformed to the far field. In the second technique, a plane wave that is approximately uniform in amplitude is created by a feed and large reflector in the immediate vicinity of the test antenna. And in the third technique, the test antenna is focused within the radiating near-field region, patterns are measured at the reduced range, and then the antenna is refocused to infinity. Each of these techniques is discussed, and the various advantages and limitations of each technique are presented.

Probe compensated near-field measurements on a cylinder

Abstract: A new method is developed for determining the farfield pattern of an antenna from probe compensated near-field measurements over the surface of a right circular cylinder enclosing the antenna. The method is derived by first expanding both the field radiated by the antenna and the field radiated by the measurement probe, when it is used as a transmitter, into cylindrical wave expansions. The Lorentz reciprocity theorem is then used to solve for the field radiated by the antenna from the probe output voltage. It is shown rigorously that the antenna pattern can be determined independently of the characteristics of the measurement probe provided that certain calibration data are known. A method for determining these data from the measured far field radiated by the probe is described. It is shown that the necessary numerical integration can be performed with the fast Fourier transform algorithm. Experimental results are presented to validate the theory and to demonstrate its practicality from a measurement and computational viewpoint.

Linearly polarized phased antenna array

Abstract: There is disclosed herein a linearly polarized mat-strip phased antenna array wherein the antenna array is phased by incorporating in series relationship one or more mat-strip loaded line type phase shifters in the mat-strip power division distribution network for the mat-strip dipole elements and/or a combined mat-strip dipole element and phase inverter. Two embodiments are illustrated.

Coaxial feeds for high aperture efficiency and low spillover of paraboloidal reflector antennas

Abstract: Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H 11 modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of 100\deg to 160\deg . Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.

Stripline slotted balun dipole antenna

Abstract: A stripline slotted balun dipole antenna, suitable for use as a single antenna or as an array antenna element, is fabricated from two metal-clad dielectric sheets, from which metal has been removed in predetermined patterns, and then the sheets are sandwiched together to form both the slotted balun dipole antenna and its stripline feed. The metal remaining on the exterior of the laminated structure constitutes a slotted balun dipole and the metal remaining between the dielectric sheets constitutes the center conductor of the stripline feed. The structure obviates the need for metallic connections in the antenna area.

Optically operated microwave phased-array antenna system

Abstract: An optical processing technique is employed to optically generate a set of properly phase-controlled signals that are appropriate to forming and steering, in space, a beam from a two-dimensional phased array antenna

Antenna for direction finders

Abstract: This invention relates to an antenna for direction finders presenting a high sensitivity in a narrow band by making a loop antenna and a shielding tube resonate at any two desired frequencies.

Circularly polarized phased antenna array

Abstract: This relates to a mat-strip dual circularly polarized phased antenna array with independent steering of both right hand circularly polarized and left hand circularly polarized antenna beams. This is obtained by superimposing in a common aperture two linearly polarized phased arrays with their dipole element axis in space quadrature and by setting one polarizer over both linearly polarized arrays. The two circularly polarized antenna beams can be independently and simultaneously scanned, operated in transmit or receive, operated at different frequency and be designed for different bandwidth, gain and slidelobe characteristics. The beams are oppositely polarized through the use of a single polarization device interposed over orthogonal linear arrays. The linearly polarized arrays are phased by a separate phase shifter coupled to the mat-strip power division distribution network of each of the arrays, by providing one or more mat-strip phase shifter which can be controllably connected into the distribution network and/or by controlling the manner in which the distribution network is connected to the mat-strip dipole elements of the array.

Scanning lens antenna

Abstract: An improved microwave antenna for use in aircraft guidance in which respective azimuth and elevation antenna are fed through dielectric lenses by respective rotating scanners to result in scanned planar beams without physical antenna rotation. The respective scanners are mechanically coupled to thereby insure synchronization so that radiation is fed to only one antenna at a time.

Coaxial horn antenna

Abstract: A wide band, multi-mode antenna having a plurality of coaxial, independently fed, radiating horns. Each horn has multiple feeds which can be energized in various phase relationships to control polarization. The antenna can be used as a direct radiator, or to illuminate a reflector, has transmit or receive capabilities, and is adaptable to monopulse operation. The antenna is a compact rigid unit of very simple construction.

Dual polarization spiral antenna

Abstract: An element antenna for use with a plurality of similar element antennas in an array. The element antenna receives and reradiates circular polarized electromagnetic energy such that the reradiated energy is of the same polarity as the received energy, independently of the geometric polarization element antenna. The element antenna includes a plurality of elongated, electrically conductive arms, each having an intermediate portion located in an annular active antenna region where circular polarized electromagnetic energy is received and reradiated. The arms of the element antenna are configured so that they define a geometric polarization element antenna of a given circular polarity so that currents induced in the respective intermediate arm portions from received energy, flow towards specific arm ends in dependence upon the polarity of the received energy. The currents are acted upon so that they re-enter the active region having their relative phases controlled in such a manner that the reradiated energy is of the same circular polarity as the received energy.

Thin sandwich telemetry antenna

Abstract: A thin sandwich slot antenna is provided which produces a cardiod shaped antenna pattern. The antenna structure requires no antenna cavity or other remote structure behind the antenna. A thin-film antenna is supported by a thin dielectric strip and contoured to the shape of support structure. A metallic support structure becomes the ground plane for the antenna otherwise a metallic ground plane is placed behind the radiating element.

Electrically small dipolar antenna utilizing tuned lc members

Abstract: A miniaturized dipolar antenna having high radiation efficiency includes two parallel spaced capacitor plates shunting an inductance which is connected in a perpendicular orientation to the plates. In a first embodiment for VHF operation, the inductance is a coil having an adjustable ferrite slug core which permits tuning of the antenna. In lieu of the slug, a coaxial variable capacitor may be connected in series with the plates. In a second embodiment for UHF operation, the inductance consists of parallel positioned conductor rods perpendicularly connected between the capacitor plates. A coaxial variable capacitor connected in series with the plates permits tuning of the antenna.

Dual-band array antenna

Abstract: A unitary antenna comprising two different arrays. The first is a group of waveguide antenna elements in alternately displaced rows forming a triangular grid structure and the second is another group of waveguide antenna elements forming a triangular grid structure within the first grid structure. The two groups of elements are dielectrically loaded, are polarized to radiate orthogonally to each other, and are designed to radiate at different frquency bands.

Computer design of antenna reflectors.

Abstract: Performance of paraboloidal antenna reflectors is adversely influenced by surface distortions from a perfect paraboloid, which cause pathlength variations of the RF energy beam. The structural design objective for the surface backup structure is to minimize the rms pathlength deviations for gravity loading. Two design approaches are illustrated and applied to sample antenna structure designs. These are a sectional search method and a virtual work/Lagrange multiplier method. Both are shown to provide useful performance improvements. The second, however, appears to be more suited for application to design of large antenna structures.

Low-frequency loop antenna arrays: Ground reaction and mutual interaction

Abstract: An investigation is presented dealing with the ground reaction and the mutual interaction of horizontally and vertically oriented loops in antenna arrays of arbitrary configuration located above the ground and contains the calculation of appropriate reaction coefficients. Because of the similarity of the derivations for systems of vertical and horizontal loops, only the calculation technique for systems of vertical loops is performed in detail.

Hybrid scan antenna

Abstract: A hybrid antenna system comprises two or more wave guide antenna sections which are physically separated and separately fed with radiant energy from a single source by dividing up energy from the source and feeding it into first ends of the various sections. Phase shifters are provided such that the radiant energy fed to successive sections is shifted in phase in such a manner that the overall radiated output beam from all of these sections constitutes a single beam which may be scanned in the same manner as though all of the sections were connected together to form a single elongated wave guide antenna. The provision of the antenna in sections makes it more convenient to locate the antennas on various portions of an aircraft to realize the same effect as an elongated single waveguide type antenna.

Radar antenna scan apparatus

Abstract: A radar antenna scan drive employs a planetary type drive. An RF antenna is fixed to rotate with a planet gear while the planet rotates around a sun gear. The swept volume of the RF antenna, as it scans, is shaped to be noncircular by the ratios selected for the planetary drive. The swept volume shape is utilized to package a larger RF aperture antenna in a fixed available space that is not circular.

Shipboard yardarm half-wave antenna

Abstract: Two frequency-adjustable antennas of the type having a helix and cylinder coaxially arranged end-to-end are themselves arranged inversely end-to-end in a 1/2-wave dipole antenna arrangement that is entirely ground plane independent. The end-to-end radiators are arranged about a common drive means which, while providing the main structural support of the antenna arrangement, provides simultaneous synchronous tuning of each leg of the antenna arrangement.

Built-in FM dipole antenna

Abstract: A component type of FM stereo broadcast receiver is provided with a built-in dipole antenna by making use of the cables that connect the left and right speakers to the receiver. Since these speakers are usually placed at least one half wavelength apart at the received carrier frequencies, the system lends itself to efficient dipole antenna operation. By using an r-f impedance raising circuit at the amplifier output, and a frequency selective coupling system between the speaker jacks and the antenna terminals, a high performance ''''built-in'''' antenna is achieved.

Antenna system for radiating doppler coded pattern using multiple beam antenna

Abstract: ANTENNA SYSTEM FOR RADIATING DOPPLER CODED PATTERN USING MULTIPLE BEAM ANTENNA ABSTRACT OF THE INVENTION Disclosed is an antenna system for radiating a frequency coded or "Doppler" pattern of wave energy into a region of space using a multiple-beam antenna unit. The system radiates a pattern in which the radiated frequency varies as a function of angular direction from the antenna unit. The system uses an antenna unit capable of radiating simultaneous multiple beams and having a separate input port associated with each beam. The frequency coded pattern is achieved during each of a plurality of successive time periods by supplying wave energy to each of the input ports of the antenna unit from a common source via controllable phase shifters.The phase shifters are controlled such that the wave energy signal supplied to each port of the antenna unit has a phase, measured with respect to the phase of the wave energy signal supplied to the port corresponding to an adja-cent antenna beam, which varies during each time period between a predetermined pair of values, with the variation being less than 360° and the sense of the variation being alike for pairs of input ports corresponding to similarly adjacent beams.

Wide scan angle antenna utilizing surface wave and multiple element array modes of operation

Abstract: An antenna capable of 180.degree. scan with improved gain characteristics at end-fire is realized by combining multiple element array and surface wave antenna structures. An end-fire feed element is positioned to radiate along a column array of antenna elements. A transmitter is switched to feed either the end-fire feed elements or the column array of antenna elements and the column array antenna elements are short circuited during end-fire operation.

Reentry vehicle stripline slot antenna

Abstract: A reentry vehicle antenna which is comprised of a stripline slot antenna with the antenna element including a stripline circuit board with a radiating aperture fed by a conventional strip transmission line. A feedback circuit is provided to control the input impedance of the antenna while operating into an RF transparent window as the window depth varies due to erosion upon reentry.

Thin monopole antenna: finite-size belt-generator representation of coaxial-line excitation

Abstract: The real system of a vertical monopole, obtained as a simple protrusion of the inner conductor of a coaxial line through the ground plane, is approximated by a monopole base driven by a finite-size belt generator. A simple formula is derived for determining the size of the belt generator so that it is equivalent to the coaxial-line excitation. The integral equation for current obtained with the finite-size belt generator is similar to the well known equation for the delta-function generator. However, the new equation has an integrable solution, convergent at all points. In particular, the monopole admittance obtained from the modified integral equation closely approaches, in the limit, the apparent admittance of the monopole, as measured by reflection measurements on the coaxial line and referred to the ground plane.

Broad-band antenna having folded dipoles with hairpin transformers

Abstract: A broad-band antenna characterized by having a folded dipole that includes first and second open center portions with a broadband transformer element spanning one of said open center portions while transmission line feed points are located at the opposed sides of the other open center portion, with this arrangement permitting the transformer element to electrically lengthen the antenna into half-wave folded dipole antenna for the reception of low-band signals while also simultaneously electrically opening the antenna into a full-wave dipole antenna for high-band reception. By the use of a single antenna to receive two bands from a broad-band spectrum, size and weight are reduced while simultaneously achieving a greater gain in decibels than would otherwise occur absent the use of the arrangement above-described.

Dual polarized antenna with triangular wire reflector

Abstract: A citizens band antenna has two or more units made up of horizontal, vertical and twin duty elements supported by a mast and a boom, at the rear of which is a triangular reflector connected at the rear of the antenna to the nearest array.

Optimization of the loop-coupled log-periodic antenna

Abstract: Varying the spacing between the transposed transmission line feeder and the radiating elements of the loop-coupled antenna is investigated experimentally using far-field swept-frequency techniques. An optimum spacing is found in the sense that anomalous frequency performance is minimized. A theory using dispersion relationships is developed and used to explain some of the experimental phenomena observed.

Dipole antenna coaxially mounted on a conducting cylinder

Abstract: The problem of a cylindrical dipole antenna symmetrically mounted on a conducting coaxial cylinder is analyzed both theoretically and experimentally. The theoretical approach is based on the Fourier transform solution for thin wire antennas, equivalence and image principles, point matching, and numerical optimization. The basic idea is that the modified dipole structure can be replaced by an equivalent system (as far as exterior fields are concerned) consisting of a simple perfectly conducting rod excited by an array of magnetic ring sources. The coefficients of these sources are then adjusted to match boundary conditions on the cylindrical modification surface. For the locations of the match points and sources, three gauges involving weighted integrals of the tangential electric fields are used to optimize the solution. Good agreements between measurement and theory have been obtained for the input admittances, resonance properties, and radiation patterns. Results are also presented for a dipole on a sphere to contrast effects due to change in modification shape.

Radiation symmetries of antenna arrays

Abstract: A new class of antenna array lattices is examined and classified by using the formalism of the space point groups. The space symmetries of the current excitations and their resulting patterns are investigated. A new procedure for designing orthogonal antenna field patterns is developed.