Showing papers on "Reflective array antenna published in 1992"

Microstrip antennas

Abstract: Microstrip antennas have been one of the most innovative topics in antenna theory and design in recent years, and are increasingly finding application in a wide range of modern microwave systems. This paper begins with a brief overview of the basic characteristics of microstrip antennas, and then concentrates on the most significant developments in microstrip antenna technology that have been made in the last several years. Emphasis is on new antenna configurations for improved electrical performance and manufacturability and on advances in the analytical modeling of microstrip antennas and arrays. >

FM radar system

Abstract: An FM radar system of more simple construction, smaller size, lower cost and improved performance is provided in which circulators of any type in the prior art are eliminated by constructing a transceiver comprised of a transmitting part and a receiving part, each formed on a common dielectric plate and having a dedicated transmitting antenna and a dedicated receiving antenna respectively The antennas comprise planar array antennas, in contrast to the solid antennas used in prior art systems The planar array antennas are also formed on the single dielectric plate The transmitting part comprises a plurality of transmission antennas and a plurality of frequency multipliers coupled to said transmission antennas The receiving part comprises a plurality of receiving antennas which are coupled to a plurality of switches through a plurality of mixers, frequency multipliers, and low noise amplifiers

Millimeter wave antennas

Abstract: Major advances in millimeter-wave antennas have been made in recent years, in particular in two areas. A new class of leaky-wave antennas based on open millimeter waveguides has been proposed and investigated, and substantial progress has been achieved in integrated antennas where active and passive circuits, possibly in monolithic form, are combined with the radiating elements in one compact unit. Interesting developments have taken place also in a third group of millimeter-wave antennas, that of microstrip antennas and printed circuit antennas in general. An attempt is made to summarize these developments. >

Reconfiguration of passive elements in an array antenna for controlling antenna performance

Abstract: Disclosed is an array antenna (10) that may be reconfigured to point in multiple directions. The array antenna includes a driven element (12) coupled to a transmission line (14) and a pair of passive elements (22) and (24). The passive elements (22) and (24) each include three antenna segments that are coupled together by a pair of optoelectronic switches (26) and (28), respectively. When the optoelectronic switches coupled to a particular passive element are closed the element functions as a reflector; when the switches are open, the element functions as a director. Other reconfigurable antennas are also disclosed, including antennas with reconfigurable gain and field pattern characteristics.

Satellite antennas

Abstract: Communication satellites have evolved from a radio relay in space to encompass other applications such as processing and meteorology. The demand for high capacity communication satellites has led in the past two decades to the development of multibeam antennas, a landmark in satellite antenna technology. Satellite antennas are classified into three categories according to function: communication; tracking, telemetry, and command (TT and C); and special satellite antennas. While the application of shaped beam antennas has been developed to its fullest extent as in INTELSAT VI and VII, an active monolithic microwave integrated circuit (MMIC) phased array will play an important role in future satellite antenna technology. Examples of each state-of-the-art satellite antenna technology and the process of space qualification are presented briefly. >

Multi-layer array antenna

Abstract: A multi-layer array antenna having high frequency band microstrip antennas formed on a surface of a first dielectric substrate, comb-shaped low frequency band microstrip antennas formed on a surface of a second dielectric substrate which is disposed on the first dielectric substrate, and through-holes for supplying microwave power to the comb-shaped low frequency band microstrip antennas through the first and the second dielectric substrates.

Method and apparatus for electromagnetic logging with two dimensional antenna array

Abstract: A two-dimensional array of slot antennas which can provide two-dimensional quantitative dielectric and conductivity images of formations in the region surrounding an earth borehole. The antennas are mounted in a wall-engaging member of a logging device that is moveable through the borehole. Selected ones of the antennas are energized at given times to transmit electromagnetic energy into the formations, the electromagnetic energy being received at other antennas for processing to obtain formation properties.

Wide field-of-view fixed body conformal antenna direction finding array

Abstract: A fixed body wide field-of-view conformal antenna array suitable for broadband precision direction finding on missile platforms. The array is configured as multiple sub-arrays of spiral antennas that cover particular regions within the desired field-of-view of the entire array. A lower cost, more reliable and more accurate direction finding solution for missile needs is provided, primarily by the elimination of conventional radomes and antenna gimbal structures. The array can be configured to include multi-mode sensors.

Optical beam forming techniques for phased array antennas

Abstract: Following an outline of established optical techniques for the generation and distribution of reference and control signals for phased array antennas, two novel approaches are put forward: (i) a ‘nondispersive prism’, controlling agile single beams or monopulse patterns, and (ii) a ‘lens fed model array’, which can control multiple, independent antenna beams. The prospects of fibre-optic transmission for other functions in the array are also considered.

Microwave array antenna having sources of different widths

Abstract: A microwave array antenna comprises a plurality of like unit sources whose width increases progressively from the center of the array towards its ends and which are disposed relative to each other in such a way that substantially no illumination gaps are created in the array.

A fault correction technique for phased array antennas

Abstract: The application of R.A. Shore's (1985) sidelobe sector nulling method to fault correction of a phased array radar antenna has been developed under the smart skins program. This fault correction technique can reshape the beam pattern of a partially failed array to maintain low sidelobe characteristics. If a faulty element is discovered, then the fault correction method is used to compensate for the failed element by readjusting the complex weights of the remaining operating elements. Several algorithms such as adaptive array methods, the null displacement technique, the gradient search algorithm, the pattern search algorithm, and the sector nulling algorithm have been investigated for deriving the proper complex weights for maintaining low sidelobe levels. Because the column array is linear, Shore's sidelobe sector nulling algorithm has been selected for its simplicity and effectiveness. The sector nulling method can be extended to reduce the overall sidelobe level of a 20-element array with no failed element. >

Method and apparatus for determining antenna radiation patterns

Abstract: A compact range for the determination of the radiation pattern of a first antenna (1), comprises a focusing system (3) and apparatus (2) supporting the first antenna in the quiet zone of the focusing system. For that purpose, the base comprises a modulated-retransmission probe array (6, 16) mounted in the focal plane (7) of the focusing system, a second antenna (10, 17) mounted near the probe array, apparatus (13) to determine, from the electromagnetic radiation retransmitted by the probe array and collected by one of the antennas during the transmission of electromagnetic radiation by the other, a signal SI representing the field at each point of the probe array, and a display (14) for displaying the signal.

Antenna and diversity techniques for broadcast reception in vehicles

Abstract: In recent years, powerful active windshield antennas have been developed, and different design principles of active rear window antennas including the use of the heater structure have been realized. With these basic antenna principles an equivalent or even superior performance compared to the rod antenna is obtained both for horizontally and vertically polarized FM waves. Multiple antenna diversity techniques for FM reception are also discussed, with attention given to a fast operating diversity processor for all kinds of distortions and multiple diversity antennas densely packed on a window. Finally, TV reception in the VHF range and UHF range is discussed. >

True time-delay beam forming using acousto-optics

Abstract: Wide aperture arrays for transmitting and receiving wideband signals suffer beam broadening when steered away from array normal with phase delays between the array elements. This beam dispersion is eliminated if the signal is time delayed between antenna array elements. This paper describes an acoustooptic signal processing architecture that generates and controls, with the frequency of a single signal, a set of the time delays required for linear antenna array beam forming. This acousto-optic architecture allows an array to scan a beam rapidly over a continuum of angles. Results of analysis are presented showing that a narrow beam can be formed and maintained as it is scanned over a wide range of angles.

A dual-beam microstrip array antenna

Abstract: The dual-beam antenna concept is presented, along with theoretical and measured results. To meet the requirements given by the radar system, an array composed of 76 microstrip patches has been designed and fabricated at 5.29 GHz. It is a long rectangular array with elements arranged in two rows of 38 each. By using the conventional array theory, the far-field pattern cut along the long dimension of the array is calculated and presented. It is concluded that a relatively simple technique to generate two symmetrically squinted beams from a single array has been demonstrated. >

GaAs optical time-shift network for steering a dual-band microwave phased-array antenna

Abstract: A monolithic optical time-shift network is described which is designed to steer a dual-band microwave phased array antenna at 2 and 10 GHz The advantages of using cascade type network architectures to achieve the desired resolution are demonstrated The implementation of different delay times in this optical time-shifter via bias control of detectors integrated monolithically on a GaAs wafer is described

Analysis of phase-focused near-field testing for multiphase-center adaptive radar systems

Abstract: Airborne or spaceborne radar systems often require tests before deployment to verify how well the system detects targets and suppresses clutter and jammer signals. The radar antenna diameter can be large and thus the conventional far-field test distance is impractical to implement. The theory and simulations of phase-focused near-field testing for adaptive phased array antennas is discussed. With near-field source deployment, standard phased-array near-field phase focusing provides far-field adaptive nulling equivalent performance at a range distance of one aperture diameter from the adaptive antenna under test. Both main beam clutter sources and sidelobe jammer sources are addressed. The phased array antenna elements analyzed are one-half wavelength dipoles over the ground plane. Bandwidth, polarization, array mutual coupling, and finite array edge effects are taken into account. Numerical simulations of an adaptive antenna that has multiple displaced phase centers indicate that near-field and far-field testing can be equivalent. >

A mobile base station phased array antenna

Abstract: A mobile communications base station antenna, which utilizes a cylindrical array design, is presented. A scanning antenna beam can be achieved by arranging a number of travelling wave patch antennas in a cylindrical array configuration. Using a switching matrix, different subsets of antenna elements, in the array, can be excited, thus producing a narrow steerable beam. Narrow scanning beams allow these base station antennas to retain both the high gain characteristic of directional antennas as well as the multidirectional characteristic of omnidirectional antennas. For a given transmit power such base station antennas can broadcast greater distances while still being able to communicate with users in a 360 degrees radius (at different time intervals). An alternative perspective is that scanning antennas can be placed in much closer proximity with the same co-channel interference. This decrease in cell size means that a larger number of mobile users can be concentrated in a smaller area without increasing spectrum allocation. >

Broadband gap-coupled microstrip antenna arrays

Abstract: In order to increase the bandwidth of microstrip antennas, an antenna array using gap-coupled patches as the elements is proposed. The input impedance characteristics of gap-coupled patches are analyzed by the dyadic Green's function for a grounded dielectric slab and the moment method. The input impedance of gap-coupled patch arrays is by combination with the antenna elements and the feed network that consists of divider tees, bends and feed line. In addition, considering the surface currents solved from the integral equation, the far field patterns of gap-coupled patch arrays are calculated. Comparison with the ordinary rectangular patch arrays is made. It turns out that the impedance bandwidth for a voltage standing wave ratio of less than 2 of the two-element gap-coupled patch array is much wider than that of the ordinary patch antenna array. All microstrip antennas have been designed and fabricated on substrate with in /sub r/=2.86, h=1.5 mm. >

Spherical array antenna using digital beamforming techniques for mobile satellite communications

Abstract: Problems arise in providing excitation phases and amplitudes to individual antenna elements for wide-angle scanning by applying spherical array antennas for mobile satellite communications for ships, automobiles, and aircraft. These antennas do not have many antenna elements. Thus, emphasis is on obtaining the maximum gain rather than realizing the characteristics of low sidelobe levels. This paper considers the application of spherical arrays for antennas of mobile satellite communications. An adoption of a control method is assumed which regulates the phases and amplitudes freely and accurately for individual antenna elements for the beamforming circuits of digital beamforming antennas. A beamforming method is examined for spherical arrays. First, a selection of necessary antenna elements is proposed utilizing the received signals and an adjustment of their phases and amplitudes. This method is applied to a 16-element spherical array which had circular micro-strip antennas. Their radiation characteristics are calculated. As a result, it was clarified that the maximum directive gain could be obtained almost without being influenced by the properties of individual antenna elements. Next, circuits are designed for the reception of binary PSK signals of constant envelope modulated waves. Carrier recovery circuits are established for individual antenna elements for spherical arrays, and a method is used to detect their phases and amplitudes. The method shows the effectiveness in obtaining the amount of gain reduction due to the detected phase and amplitude errors.

Reconstruction of the Excitation of Array Antennas from the Measured Near-Field Intensity using Phase Retrieval

Abstract: A technique is described to reconstruct the source distribution on an array antenna from the measured radiated intensity and the configuration of the elements. The reconstruction algorithm has been evaluated with measured data from a near-field planar scan of a slotted waveguide array and validated by comparison with the deconvolved holographically reconstructed source distribution. Results are also presented for the phase retrieval diagnosis of a commercial SSR array antenna from 1-dimensional cylindrical near-field measurements.

The Millimeter Array

Abstract: A brief review of the purpose and the design of the Millimeter Array, (MMA) is given Particular attention is paid to the effects of the atmosphere and to millimeter-wavelength components, which are the antennas, the low-noise input stages, and the local oscillator system The MMA is a radioastronomy instrument planned for construction at the National Radio Astronomy Observatory in the 1990s It will consist of 40 antennas working in the range 30 to 350 GHz for imaging cosmic sources with an angular resolution as fine as 006 arcseconds The antennas are to be movable between sets of foundations so as to provide four two-dimensional configurations in which the overall size of the array can be varied from 70 m to 3 km The angular resolution can thereby be selected to match a wide range of astronomical requirements >

Time dispersion measurements using a SSFIP base station antenna

Abstract: A novel type of base station antenna using strip-slot-foam-inverted-patch (SSFIP) arrays is proposed. The SSFIP configuration offers many advantages. The microstrip technology used in the feed network allows to tailor the antenna pattern to a wide range of applications. The antenna is very flat (about 4 cm thick), and thus can be unobtrusively mounted on a wall. Unlike conventional microstrip antennas, the SSFIP antennas have a broad bandwidth ( approximately 13%) suitable for mobile radio and personal communications applications. Measurements in cellular radio environments with a seven-element SSFIP array are compared to other conventional dipole array antennas. It is shown that the SSFIP array offers an alternative to conventional base station antennas. >

Current status of integrated submillimeter-wave antennas

Abstract: The author presents a summary of the development status for recent high-efficiency integrated antennas that are suitable for low-noise submillimeter-wave receivers. The use of these antennas in planar receivers will result in very-low-noise receivers for frequencies above 100 GHz. The antennas presented here are the quasi-monolithic integrated horn antennas, the substrate-backed spiral and log-periodic antennas, the endfire slot-line antennas on thin membranes, the double-dipole integrated reflector antenna, and the dielectric-filled parabola. >

Antenna array with system for locating and adjusting phase centers of elements of the antenna array

Abstract: In an antenna array consisting of a plurality of antennas, an antenna may behave as if its transmitted radiation emanates from a position, phase center, disposed away from the actual location. Probe antennas are used with a processor to locate the phase center of respective antennas at a selected frequency of transmission and to adjust the phase center to a desired location, thereby calibrating the antenna array for the selected frequency.

Radio wave propagation in urban microcellular environment

Abstract: Extensive experimental test results from lamppost antennas in Manhattan are presented. There are various problems with such a nonuniform coverage area, including inefficiency in coverage, frequency handoffs, frequency planning, and dynamic power control. A more uniform coverage area can be obtained by strategic placement of antennas for microcells and the use of directional antennas. Experimental test results are presented to support this result. >

Linear-sum mode arrays and beam forming

Abstract: In conventional phased arrays, antenna elements are usually simple radiators, such as dipoles, slots, dominant mode horns and microstrip patches, etc., that generate broadbeam, low gain and radiation patterns with a desired polarization property. The array beam is then formed and scanned by introducing phase shifts between the elements and modifying the phase shift values. The simplicity of array elements facilitates the design and then the fabrication. Also, because the element patterns are broad and often symmetric, with respect to the array axis, the beam scanning and its associated algorithm are easy to implement. In addition, this method of array design and beam scanning is general and can be used with different array configurations and electrical performance. However, a number of difficulties are often faced in such array implementations. Since each element, or each sub-array, needs a separate phase shifter, the array complexity and cost increases with its size and gain requirements. Also, the mutual coupling and array element pattern role off decrease the array gain for excessive scan. Furthermore, assuming array design can be achieved and implemented satisfactorily, the phase shifter insertion loss introduces an additional difficulty. Normally, this insertion loss limits the array performance in G/T, i.e. the gain to noise temperature ratio, for receive systems and the power efficiency for transmit systems. With microstrip arrays this phase shifter loss is accompanied by the feed line loss to further deteriorate the array performance.

Fiber optic fed C-band active phased array antennas

Abstract: Experimental results are presented demonstrating the operation of optically controlled phased array antennas at C-band. More specifically, experimental results on optically controlled 2*4 MMIC (monolithic microwave integrated circuit) based active T/R (transmit/receive) modules over the frequency of 5.5 to 5.8 GHz are presented. Custom-designed fiber-optic links have been used to provide distribution of data and frequency reference signals to phased array antennas used in the T/R Level Data Mixing architecture system. >

A review of current ground penetrating radar concepts

Abstract: Ground penetrating radar concepts are reviewed, with particular attention given to the focused spot antenna. It is noted that an antenna array can be designed based on either the focused antenna or the uniform aperture (focused at infinity). A solid-state pulser can be placed at the terminals on each transmitting antenna and triggered so that the pulse from each element arrives at the desired target position at the same time. The receive array can be connected by means of a corporate harness to a single sampling system to reduce signal-to-noise and signal-to-clutter problems. This may introduce excessive ringing in the harness itself, since near-perfect matching is required. Alternatively, a sample-and-hold circuit could be placed at the terminals of each receive antenna and their output voltages combined. This has several advantages and can be used as long as the dynamic range of the sampler is adequate. >

Some considerations for microstrip coplanar-waveguide antennas

Abstract: The CPW (coplanar waveguide) antenna element is shown to be an effective antenna element, whether used singly, as a two-element array, or as an eight-element array. It is also demonstrated that the finite-difference time-domain technique is a very effective diagnostic tool for designing array antennas. A very inexpensive technique for building phased-array antennas was developed. No evidence of the unwanted propagation mode was found. >