Showing papers on "Feed horn published in 1978"

Double reflector antenna with feed horn protection

Abstract: A double reflector antenna mounted on a terrestrial mount with Azimuth and elevation shafts in which a primary field radiating and detecting horn is mounted within a housing behind a central opening of the main reflector dish so as to radiate and receive energy from a sub-reflector mounted at the focal point of the main reflector dish and such that the lead supplying energy to and from the horn can be very short and the horn can be substantially shielded from snow and rain.

Multimode dual frequency antenna feed horn

Abstract: A prime focus multimode feed horn is used to illuminate a parabolic reflector such that the reflector-horn combination produces improved performance in the E-plane and H-plane of a principal aperture. A feed assembly which includes the multimode horn also has a hub assembly that is incorporated into the reflector with support structure, a boom, supporting interconnecting waveguides and the multimode dual frequency horn. Directly coupling the horn to the feed assembly is an orthomode generator connected to a receive waveguide and a transmit waveguide. The orthomode generator is assembled to a horn body waveguide that supports a horn aperture having a circular configured principal aperture surrounded by radially displaced circular rings forming concentric channels for modification of the E-plane receive pattern. Assembled into the horn aperture is an insert having opposed shoulders in the H-plane and opposed steps in the E-plane such that for an incoming plane wave the first zeros of the focal plane Bessel Function Distribution are coincident with the effective horn aperture. Also extending into the principal aperture in the H-plane are opposed matching buttons.

Antenna structure with relatively offset reflectors for electromagnetic detection and space telecommunication equipment

Abstract: An antenna structure includes an at least partly parabolic main reflector and an auxiliary reflector of generally similar configuration, the two reflectors having confronting concave surfaces and lying respectively above and below a horizontal plane including a common focus of these surfaces. A corrugated horn illuminating the auxiliary reflector extends at the level of the latter, with a substantially horizontal axis, between vertical planes passing through the vertex of the parabolic main-reflector surface and through the common focus; in one embodiment, the horn forms with the auxiliary reflector a unitary assembly closed on all sides except for an upper aperture facing the main reflector.

Hearing aid with signals modulated onto radio waves - may include optical radiation for transmission from microphone unit to loudspeaker unit

Abstract: The hearing aid has its microphone located in a transmitter and its loudspeaker (which fits into the user's ear) located in a receiver. The transmitter and receiver are spacially separate and connected via free space. The free-space link between transmitter and receiver may be via high frequency radio waves or via light, esp. IR. Both the transmitter and receiver contain their own dc supplies such as batteries. The receiver contains a device to limit power consumption during the breaks in transmission. Alternatively, the receiver may have no dc supply of its own; in this case the transmitter transmits at a high power.

Reference signal generating apparatus

Abstract: Apparatus for generating elevation and azimuth reference signals for use in demodulating a tracking error signal to provide elevation and azimuth error components for use in adjusting the position of a tracking conical scan radar antenna, includes a template ring having a notched periphery and being attached to a rotatable nutator of the antenna such that its peripheral notches are in a predetermined angular phase relationship with a reference position on a feed horn attached on the nutator, during rotation of the feed horn with the nutator. The apparatus further includes an optical transducer and electronic circuitry coupled thereto for producing the reference signals from a signal generated by the transducer in response to rotation of the ring with the nutator. As the ring rotates with the nutator, its notched periphery makes or breaks a photon path between light beam generating and sensing elements of the transducer. The sensing element then generates the signal which is received by the electronic circuitry. In addition to the two reference signals produced by the circuitry, a sync signal is generated and used internally within the circuitry to insure that the reference signals produced are in a proper phase relationship to the reference position on the feed horn of the nutator during rotation thereof.

Microwave moisture indicator and control

Abstract: A moisture indicator and control device for measuring the moisture content of a moving web includes a modulated signal microwave generator, directional microwave transmitter and receiver antenna horns which are angularly mounted with respect to each other on one side of a moving web of material whose moisture content is being monitored. The transmitter and receiver horns are mounted within an enclosure with their adjacent edges in physical contact and with a selected optimum angle between them to minimize residual energy transfer from the transmitter horn into the receiver horn. Sine wave modulated microwaves are transmitted by the transmitter horn toward the web at a selected angle of incidence thereto. A portion of the modulated microwave signal is reflected by the web and is received by the tranmsmitter horn. The microwave detector in the base of the receiver horn detects the reflected microwave signal and produces a sine wave output, the amplitude of which is directly proportional to the amount of moisture present in the web. The moisture indicator circuit includes in connected series an operational amplifier whose gain is adjustable over a wide range for amplifying the detected signal, an a-c to d-c convertor for converting the a-c detected signal to d-c, a d-c amplifier whose gain is controlled by a range potentiometer and a microammeter moisture meter. The device further includes a special offsetting circuit to offset any signal present when no material is in front of the transmitter horn, an over range indicator, and moisture control circuit for providing correctional control signals for restoring the moisture content of the web to a selected level.

Duplex-transmitter receiver arrangement

Abstract: A duplex-transmitter-receiver arrangement wherein only a single oscillator is utilized for the transmitter and receiver for a digitally modulated radio communication system wherein each location has a transmitter and receiver and a single oscillator is used for both the transmitter and receiver with a circulator switch connected respectively to the antenna, the receiver and the transmitter with the oscillator in the transmitter coupling through to the branch for the receiver so as to serve as a mixing frequency for the receiver.

A dual doubly curved reflector antenna having good circular polarization characteristics

Abstract: A new type of shaped-beam radar antenna having good polarization characteristics is described. This antenna is composed of a dual doubly curved reflector system and a feed horn with good axial ratio, such as a dual-mode horn. The rotationally symmetrical beam of the feed horn can be converted into a shaped beam by the reflector system without degradation of the axial ratio. The design of this type antenna is discussed and the experimental results of a model antenna with a cosecant squared beam are shown. Integrated cancellation ratio of the model was 22 dB.

Erratum: Optimisation of feed position and improved profile mapping of a reflector antenna from microwave holographic measurements

Abstract: A method for optimising the feed position of a prime focus reflector antenna from phase and amplitude recordings of the radiated field is given. Experimental results illustrate the improved radiation pattern and the detailed profile map of the reflector attained after feed position correction.

Reflector antenna with plural feeds at focal zone

Abstract: An antenna assembly with a curved reflector and feed means at one side of the focal axis of such reflector. The feed means includes a number of relatively-fixed-position feed elements spaced apart unequally to obtain signals of different phase at the reflector for forming a composite reflected beam with minimized sidelobe content.

A computer program to calculate radiation properties of reflector antennas

Abstract: A computer program to calculate the radiation properties of the reflector antennas is presented It can be used for paraboloidal, spherical, or ellipsoidal reflector surfaces and is easily modified to handle any surface that can be expressed analytically The program is general enough to allow any arbitrary location and pointing angle for the feed antenna The effect of blockage due to the feed horn is also included in the computations The computer program is based upon the technique of tracing the rays from the feed antenna to the reflector to an aperture plane The far field radiation properties are then calculated by performing a double integration over the field points in the aperture plane To facilitate the computation of double intergral, the field points are first aligned along the equispaced straight lines in the aperture plane The computation time is relatively insensitive to the absolute size of the aperture and even though no limits on the largest reflector size have been determined, the program was used for reflector diameters of 1000 wavelenghts

The effect of slowly varying surface errors in large millimeter wave antennas: A practical verification in the Itapetinga 45-ft reflector

Abstract: The aperture efficiency of the 45-ft Itapetinga reflector was found to be about 50 percent at \lambda = 7 mm. The reflector surface panels were mechanically measured in 2664 points displaying the presence of slowly varying errors that negligibly effect the aperture efficiency. We confirm that the reflector's aperture efficiency seems to be predictable from mechanical measurements of the surface when the distribution of errors is non-Gaussian, when the surface is only slightly rough in terms of a wavelength, and when the slowly varying errors across the surface are known [1], [2].

An equivalent focused reflector feed in place of any generalised defocused or extended feed

Abstract: A procedure is presented whereby generalised reflector feeds with near-field and/or defocused properties can be replaced by an equivalent point-source feed located at the origin. The equivalent feed induces identical reflector currents and consequently yields identical scattered fields. Thus all physical optics reflector analysis can be carried out in terms of a focused point-source illumination function.

Telescope surface measurement with two feeds

Abstract: A method is suggested where a reference feed is fixed at the telescope focus, and a second feed has a lateral offset and scans the focal plane The telescope tracks a celestial radio source, and the receiver measures the phase difference at the two feeds and their (voltage) amplitude ratio A set of coordinate transformations is applied, after which the surface deviations \sigma from a paraboloid can be obtained by a Fourier transform The measuring error is discussed, and the best wavelength is found to be between 14 and 21 rms \sigma

Antenna having low side-lobes and high polarisation purity

Abstract: The antenna is produced using an isotropic dielectric lens (1), a solid, flat reflector (3) and a horn (2). The horn (2) which is offset relative to the axis (XX) of the lens (1) radiates a spherical wave. The reflector (3) provides from the horn (2) an image situated at the focus (F) of the lens (1). Having crossed the lens (1), the spherical wave emitted by the horn (2) is transformed into a plane wave. Use of the antenna in high-density radiolinks.

Feed network for dual beam reflector antennas

Abstract: A primary feed network for doubly curved shaped-beam reflector antennas is described which allows simultaneous signal reception on two distinct elevation plane patterns such that the underside falloff separation between a fixed lower beam and a higher beam can be substantially varied in a lossless manner. A three-element feed array is employed wherein two elements of the array are interconnected by means of a sum-difference hybrid. The sum port generates the fixed low beam while the difference port generates an orthogonal beam pattern suitable for RF combining with an independent high beam generated by the third array element. Adjustment of the combining amplitude and phase relationships permits the variation of the underside falloff separation. The fixed low beam is, of course, also used for transmission at high power. Design parameters for a typical surveillance radar application axe discussed for a linearly polarized case. Calculated antenna patterns and free-space coverage diagrams are presented. The complexities of extending the feed network concept to handle switchable linear/circular polarization cases and an integral directional beacon pattern for L band systems are indicated.

Method for testing metal detectors

Abstract: An apparatus and method for testing low-power, low-band radio frequency metal detectors of the type employing a radio transmitter alone or a transmitter and a receiver. The apparatus is characterized by a variable voltage power supply, a transmitter, an antenna, a voltmeter, a rectifier connected to the voltmeter, a switch for connecting the rectifier to either the antenna or the power supply and for selectively energizing the transmitter, and a surface placed in a fixed position relative to the antenna and defining the proper position for placement of the equipment under test.

Directional properties of nonplanar aperture-type antennas

Abstract: Theoretical analysis of the directional properties of a large nonplanar aperture-type antenna and experimental results thereon are given and discussed. Two kinds of nonplanar parabolic cylindrical apertures have been considered: one having a curvature in the E - plane and the other in the H -plane. In the experiments, such nonplanar apertures were cut at the mouth of a suitable sectoral horn. Good agreement between experimental and theoretical results has been obtained. It is concluded that the curvature of a nonplanar aperture could be taken as an additional parameter in the design of microwave antennas.

The Measurement of Echo Direction in a Phased-Array Radar

Abstract: For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm.

Performance of a reflector antenna incorporating a filtering Cassegrain mirror

Abstract: Radiation patterns have been measured at 20.0, 22.0 and 25.2 GHz for a parabolic reflector illuminated from the prime focus by a linearly polarised feed radiating through a sub-reflector built from a stack of dielectric filled waveguides. The influence of the intervening guides on the radiation patterns is discussed.

Radiation properties of microwave reflector antennas covered with a water film

Abstract: Using simple models, first-order effects of a thin water film over the reflector surfaces of symmetrically fed microwave reflector antennas on the antenna radiation pattern and cross-polarisation in the frequency range 10–15 GHz are investigated. It is shown that the influence of the water film on cross-polarisation and the main-mode radiation pattern can usually be neglected, but that the minimum in the tracking mode can be substantially deteriorated. In addition, it was found that, in the frequency range 11–15 GHz, under certain circumstances the antenna gain can be reduced by as much as between 1 and 2 dB.