Showing papers on "Antenna (radio) published in 1970"

Support for antenna device

Abstract: A support comprising a triangular frame pivotally mounted on a tower for supporting an antenna or reflector and means for locking said frame in an adjusted position.

Stacked array of omnidirectional antennas

Abstract: A stacked vertically polarized collinear array of a plurality of independently fed omnidirectional antennas operating at different frequencies. Each antenna consists of an array of five circumferential slots in the outer conductor of a dielectric filled shorted coaxial transmission line with a hollow center conductor for feed leads to pass through.

Computer-aided radome analysis

Abstract: A procedure is presented for predicting by computer the radiation pattern of an antenna in the presence of a radome. The case of a horn antenna radiating through an actual aircraft radome is treated in detail, and a comparison is made between computed and measured antenna patterns. Good agreement between theory and experiment is noted.

Correction of near-field antenna measurements made with an arbitrary but known measuring antenna

Abstract: We describe a technique for rigorously correcting for the effects of an arbitrary but known measuring antenna (or ‘probe’) in determination of vectorial far-field antenna pattern and power-gain function from near-field measurements.

Mutual impedance between coplanar-skew dipoles

Abstract: The induced EMF formulation is employed to develop a closed-form expression for the mutual impedance between coplanar-skew dipoles, Numerical results are presented in graphical form.

On the synthesis of concentric-ring arrays

Abstract: It is shown that the radiation pattern of a circular aperture antenna can be closely approximated by a concentric ring array with sampled amplitudes. The maximum allowable inter-ring spacing is found to be about four-tenths of a wavelength if high side-lobes are to be avoided. Taylor patterns are used as examples.

Dual slot antenna device

Abstract: A dual slot antenna assembly is disclosed herein and generally includes a pair of concentrically positioned and radially spaced cylindrical conductors defining a pair of circumferential slots which are longitudinally spaced one-half wavelength apart at the anticipated operating frequency of the antenna device. An electrical signal feed assembly is connected with the conductors for exciting the slots so as to provide overlaping radiation patterns emanating in the same direction.

Direction finder system

Abstract: A high frequency radio direction finder receiver system of the over-lapping lobe switching type utilizes an array of lineal antenna elements formed of crossed multiple-element receiver antenna systems sharing one directly coupled receiver antenna element in common. Lobe switching is afforded through bias voltage control of a characteristic of the elements by semiconductor switching circuits.

Resonant slot antenna structure

Abstract: A resonant slot antenna composed of one or more elongated coaxial type radiating elements, each having an inner conductor supported within an outer conductor, the outer conductor having longitudinally spaced slots which are shaped to provide phase reversal between slots and spaced to avoid mutual coupling. This permits a coaxial or strip line antenna to be made with the desirable characteristics of a waveguide type. The antenna is particularly adaptable to construction by printed circuit techniques, with the slots and conductor elements etched in conductive plating on dielectric supporting material, making it possible to construct unitary arrays of multiple elements.

Holographic antennas

Abstract: The extension of holography to the microwave field, for the solution of problems such as antenna synthesis and construction of visible images of microwave illuminated objects, seems to be promising. In preliminary tests, the possibility of designing an antenna having any mean surface, any feeder, and any given radiation pattern by means of holographic technique, is shown. One of the practical problems which is encountered in microwave holography is the construction of the hologram, which requires the antenna to be synthesized. For this purpose, a series of holograms have been constructed and tested based on different approximations of the interference pattern. Another problem encountered is the presence of unwanted orders. Some preliminary tests on phase holograms show that this difficulty can be overcome simply by suitably varying the thickness of the hologram.

Electronic and automatic selector device connected to an antenna array formed by two or more antennas

Abstract: An electronic automatic selecting device has an antenna array consisting of two or more antennas pointing in different directions for the purpose of selecting and connecting to a service receiver that antenna from which the desired radio signal is best obtained. The selection is carried out by a selecting device and a search receiver having a low frequency output, from which, when receiving a frequency modulated emission, a noise signal is obtained proportional to the S/N ratio of the signal received by the receiver. This signal steers the selecting device. In accordance with the present invention the selecting device includes a noise handling unit the input of which receives the noise voltage from the search receiver and the output of which is large when the search receiver receives a signal with a poor S/N ratio and small when the search receiver receives a signal with a good S/N ratio. There is a voltage-to-frequency converter the operating frequency of which is determined by the output voltage of the noise handling circuit, whereby the output frequency is high when the output voltage is large and is low when the output voltage is small, a pulse oscillator which oscillates at a constant frequency and which gives the search command, an electronic change-over switch which upon receiving the search command from the pulse oscillator, sequentially connects, steered by the voltage-to-frequency converter, the antennas of the antenna array to the search receiver, and which after sampling all antennas returns to zero. There is also a circuit for comparing the signals obtained from the various antennas to the input of which are fed the pulses from the voltage-to-frequency converter and the output of which produces a pulse when during a search cycle an antenna giving a signal with a better S/N ratio than any other antenna previously sampled during the search cycle is connected to the search receiver, and a memory circuit to the input of which is fed from a dividing circuit constituting a part of said electronic change-over switch, the number in binary form of each of the antennas connected to said search receiver during the search cycle. This binary number moves to the output of the memory circuit only when an output pulse is obtained from the signals comparing circuit. Finally there is an electronic switch controlled by said memory circuit and connecting the service receiver to that antenna of the antenna array from which the search receiver during the search cycle has received the signal with the best S/N ratio.

The design of radially symmetric lenses

Abstract: For scanning over wide angles at millimeter wavelengths, an antenna incorporating a radially symmetric lens is an attractive solution if the lens can be realized in a practical form. It is shown that suitable lenses can be constructed very simply, from natural dielectrics if desired, and a design technique for the optimal antenna is presented. Some results are given of analytical and experimental studies of a number of actual antennas operating at wavelengths near 4 mm. These confirm that practical solutions are available. Homogeneous lenses may be used up to antenna gains of about 35 dB, and a lens consisting of a single shell and a core is sufficient for most other practical requirements.

Suppression of electrostatic noise in antenna systems

Abstract: Antenna noise reduction apparatus and method, especially suitable for airborne service, including an antenna discharging circuit for periodically grounding the receiver antenna through a switching system at a frequency substantially higher than the carrier frequency of the radio system with which the receiver operates.

Mutual Coupling Effect on Maximum-Ratio Diversity Combiners and Application to Mobile Radio

Abstract: The mutual coupling effects on an M -branch maximumratio combiner with correlated signal fading in general are considered. The results in the mobile radio case show that the average power delivered to the receiver becomes less as the antenna spacing of an antenna array decreases (i.e., the mutual coupling increases) with either an optimum load network or an optimum resistive load network connected to the antenna array at the front end of the receiver. However, there is not much effect on the power as long as the antenna spacing is equal to or greater than a certain value dependent on the number of the branches M . For M \leq 4 , the required antenna spacing is equal or greater than 0.2λ. The value for M > 4 increases gradually as M increases. It can be obtained following the same technique. The mutual coupling effect on the cumulative distribution of the signal from an M branch mobile diversity array is also small. Hence for an in-line array with M \leq 4 , the antenna spacing of 0.2λ can still provide most of the usual diversity advantage.

Dual mode rotary microwave coupler

Abstract: Microwave coupling devices having input and output rotatably mounted circular waveguide sections with a phase shifter and an orthogonal mode transducer coupled to the input circular waveguide section for converting a pair of linearly polarized input signals to counterrotating circularly polarized signals. A second orthogonal mode transducer, associated with the output circular waveguide section, provides output signals of the proper phase for dual mode transmission by a multiple feed horn antenna system.

Anti-collision apparatus for vehicles

Abstract: A safety apparatus or anti-collision device to be installed on motor vehicles for detecting and indicating obstacles encountered on a road during conditions of poor or reduced visibility. The apparatus includes wave propagation means to emit a continuous periodically frequency modulated wave with, for example, a triangular pattern. The wave is emitted by an antenna and echo waves reflected by obstacles are received and mixed with a portion of the transmitted wave to obtain a raw signal which is passed through filters to activate one of a plurality of transducers including, for example, light bulbs which are illuminated to indicate the presence and distance of the obstacles. Arrangements are made to limit the number of light bulbs which are illuminated.

Multi-purpose antenna employing dish reflector with plural coaxial horn feeds

Abstract: A microwave antenna useful on a spacecraft, which utilizes a single dish reflector and single coaxial horn structure to transmit at two frequencies, and to receive signals at a third frequency that allow tracking. The horn structure includes a coaxial wave-guide with an inner pipe for transmitting X-band waves, an intermediate pipe, surrounding the inner pipe for transmitting S-band waves through the space between it and the inner pipe, and an outer pipe surrounding the intermediate pipe for receiving S-band tracking signals. An outer horn flares from the outer pipe and an inner horn flares from the inner pipe, to efficiently illuminate the dish reflector at both X and S bands.

Miniature tv antenna

Abstract: An antenna for TV reception predominantly in the low band and high band VHF ranges having dipoles of significantly reduced physical length as compared with conventional dipoles for reception of signals respectively in the low and high band VHF ranges. Inductive elements are employed to form a portion of the dipole length to permit significant reduction in the physical length of the dipole. The dipoles are electrically isolated from one another by suitable trap circuits to isolate high band VHF operation from low band VHF operation. Lossy components are deliberately added to the dipole section of the antenna to provide significantly improved noise matching and power transfer between antenna and amplifier. The inductive elements further provide good impedance matching between antenna and amplifier to optimize power transfer. The antenna is provided with end loads of the capacitive-type for improving both current magnitude and current distribution across the dipole in both low band and high band VHF operation. Separate amplifier channels are provided for low band and high band VHF signals to improve gain and reduce intermodulation and cross modulation effects, among other. A passive UHF section may be integrated into the array.

Bistatic passive radar

Abstract: A radar system for determining the position of a target using a radio frequency source of opportunity. The system uses an interferometer antenna and cross-correlation techniques to measure the time delay in receiving a reflected signal from the target as compared to receiving a direct signal from the signal source. Thereby, the distance from the RF source via the target to the antenna is determined. Additionally, the system uses a plurality of interferometer antennas and cross-correlation techniques to measure the relative phase difference between the signals received by the antennas. Thereby, the angle of arrival of the reflected signals from the target is determined. Combining the range and angular information locates the target.

Radiation Characteristics of Longitudinal Waves From an Antenna in a Plasma

Abstract: This paper describes experiments designed to measure the radiation patterns of a longitudinal wave excited in a warm plasma by both monopole and dipole antennas. The longitudinal wave used in this experiment is the low-frequency ion acoustic wave that propagates with a phase velocity [γkTe/M/i]½. Experimental results agree well with the theoretical predicted radiation pattern.

Dual base line interferometer antenna

Abstract: A radar system for determining the position of a target using a radio frency source of opportunity. The system uses an interferometer antenna and cross-correlation techniques to measure the time delay in receiving a reflected signal from the target as compared to receiving a direct signal from the signal source. Thereby, the distance from the RF source via the target to the antenna is determined. Additionally, the system uses a plurality of interferometer antennas and cross-correlation techniques to measure the relative phase difference between the signals received by the antennas. Thereby the angle of arrival of the reflected signals from the target is determined. Combining the range and angular information locates the target.

Tethered airborne communications and information transfer system

Abstract: A tethered balloon including means for controlling the height thereof is utilized as an airborne platform for transmitting and receiving apparatus including a multiple antenna assembly. The antenna assembly is suspended from a gimbal or ball joint configuration attached to the balloon so that it is gravity stabilized in the vertical plane. The antenna assembly itself is comprised of a plurality of independently rotatable coaxial shafts having respective antenna means coupled thereto. The shafts are hung from a pendulum arm member which is freely moveable within a vertical cone angle limit of 45* and maintains vertical orientation to within + OR - 2*. The rotation of each of the coaxial shafts is independently controlled from a ground station by means of a control signal to selectively point each antenna means in a predetermined compass direction. Additionally, each coaxial shaft couples respective transmitter-receiver means to its antenna means in order to provide selective signal transfer between the ground station and/or other similar airborne systems.

New variational principle in electromagnetics

Abstract: A new variational principle that applies to a wide class of electromagnetic problems is presented. This principle has the distinctive characteristic of always producing linear algebraic equations when the Rayleigh-Ritz procedure is applied using a trial field composed of a linear combination of variational parameters. The new technique is applied to a general class of antenna problems, and is specialized to the case of a dielectrically coated slot antenna. Experimentally observed admittance values at X band are presented and compared with theoretical predictions.

Recent experimental results in near-field antenna measurements

Abstract: Recent experimental results on determination of antenna pattern and power gain from near-field measurements are described. Two new antenna measurement theorems were applied. Measurements were made on an electrically large horn lens, a standard-gain horn and a nominal duplicate of the measuring antenna. Some comparisons with direct far-field measurement results were made.

Dependence of very-low-frequency electric field antenna impedance on magnetospheric plasma density

Abstract: Data from a VLF electric field antenna on board the spacecraft OV3-3 show that the antenna response depends upon the local plasma density. Antenna impedances, calculated on the basis of a cold, magnetized plasma model and a warm, nonmagnetized, collisionless plasma sheath model, are compared with the data, showing that the sheath model is more appropriate. The response of the electric field antenna to constant onboard sources of electromagnetic interference is used with the antenna sheath impedance model to calculate plasma densities. The resulting densities are similar to those obtained from OGO 2 plasma density data scaled to the OV3-3 orbital parameters. The impedance of the TRW Systems Group VLF electric field antenna, also on board OV3-3, is calculated and compared with the data. It is shown that the sheath antenna impedance model applies equally well to both antennas even though they were quite dissimilar. Much of the signal variation observed by the Aerospace and TRW electric field antennas is caused by antenna impedance changes as a function of local plasma density.

The cylindrical antenna as a probe for studying the electrical properties of media

Abstract: When a base-driven cylindrical monopole (or center-driven dipole) is immersed in an arbitrary medium, the electric and magnetic fields on its surface depend not only on its length and radius but also on the effective conductivity and permittivity of the medium. These fields can be explored and measured with small probes designed to travel along the cylindrical surface of the antenna. The interpretation of the observations depends on the availability of a general theory that correctly describes the distributions of current and charge on the conductor. The results of a new theory that is valid for electrically thin monopoles up to 5\lambda/8 (dipoles up to 5\lambda/4) in length over all practical ranges of conductivity and permittivity of the ambient medium, including those characteristics of under- and overdense cold plasmas, are described together with their experimental verification.

Radiation patterns for two monopoles on a perfectly conducting sphere

Abstract: A general numerical technique for analyzing monopole antennas protruding from a conducting sphere is suggested. Computed results for special cases of antenna locations are compared to known and approximate solutions showing that the method is practical and accurate.

Microwawe Power Transmission from an Orbiting Solar Power Station

Abstract: The paper considers the problem of microwave power transmission from an orbiting solar power station to the earth. In particular, questions such as the optimum frequency range, antenna dimensions and mechanical tolerances, phasing and directional control, and attainable transmission efficiencies are discussed.

Antenna mounting structure

Abstract: A limited motion antenna mounting structure for use with synchronous satellites. The structure is a modified polar mount constructed of aluminum and steel having the advantage of being rigid, light-weight, of low cost, highly transportable, of simple design, self-erecting and aligned without use of special tools, equipment or techniques. The structure includes a base assembly, an antenna supporting assembly pivotably secured to the base assembly and adjustably secured to the antenna assembly to enable hour angle fine adjustment of the antenna assembly and a hydraulic jack or electric motor driven worm gear to perform the combined functions of self-erection and elevation angle adjustment pivotably secured to the base assembly and the supporting assembly.