Showing papers on "Active antenna published in 1997"

Microstrip antennas on synthesized low dielectric-constant substrates

Abstract: Micromachining techniques using closely spaced holes have been used underneath a microstrip antenna on a high dielectric-constant substrate (/spl epsiv//sub r/=10.8) to synthesize a localized low dielectric-constant environment (/spl epsiv//sub r/=2.3). The measured radiation efficiency of a microstrip antenna on a micromachined 635-/spl mu/m thick /spl epsiv//sub r/=10.8 Duroid 6010 substrate increased from 48/spl plusmn/3% to 73/spl plusmn/3% at 12.8-13.0 GHz (including 3.3-cm feed line losses). We believe that this technique can be applied to millimeter-wave antennas (microstrip, dipoles, slots, etc.) on silicon and GaAs substrates to result in relatively wideband (3-6%) monolithic microwave integrated circuits (MMIC) active antenna modules for phased-arrays and collision-avoidance systems.

High-efficiency power amplifier integrated with antenna

Abstract: Two class B GaAs field-effect transistor (FET) power amplifiers integrated with patch antennas have been designed and fabricated at 2.48 GHz. Both amplifiers are integrated with patch antennas, which serve as load and radiator. In one case, a standard patch design was used with random harmonic termination. In another case, a modified patch design was used, which allows the tuning of the second harmonic. In this case the antenna has an additional function of a filter. An increase of 7% in the power-added efficiency (PAE) and 0.5 dB in the output power was achieved through the second harmonic tuning.

Communication system comprising an active-antenna repeater

Abstract: An indoor wireless communications system using two-way active-antenna repeaters to distribute signals received from external signal sources within an office, and to extend the range of cordless phone units in use there, is disclosed. The repeaters provide menu-selectable phase-shifting, selectable receiver sensitivity and transmitter power, and selectable signal format conversion to provide added privacy and to prevent interference with communication links in use by third parties within the building. Pattern selection is done by empirical adjustment of an antenna pattern suited to the general floor plan of the area served.

Compact antenna for circular polarization

Abstract: A compact antenna for circular polarization comprises a substrate of a dielectric material which is formed on its bottom surface with a ground plane and on its top surface with four planar rectangular patches of an electrically conductive material. The four patches are mounted in a coplanar relation on the top surface of the substrate, and arranged along four sides of a square pattern with the length of each patch angled at 90° with respect to the length of the two adjacent patches. Each of the four patches is short-circuited to the ground plane at a shorting point located at a corner of the square pattern. A 90° hybrid circuit is connected to directly feed only the two adjacent patches with a phase difference of 90° to thereby define these two patches as active antenna elements which are fed with 0° and 90° signals, respectively. The other two adjacent patches are not fed from the hybrid circuit to define parasitic antenna elements each coupled with the adjacent active antenna element to provide a signal which is 90° out of phase with a signal on the adjacent active antenna element. Thus, the active and parasitic antenna elements arranged in one direction around the substrate are fed at 0°, 90°, 180°, and 270° phases for circular polarization only with the use of a single hybrid circuit.

Integrated active antenna with full duplex operation

Abstract: This paper discusses the design and implementation of a novel two-element active transmit-receive array using dual linear polarization and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that the transmit and receive paths are isolated and polarization duplexed. The array gives in excess of 45-dB transmit-receive isolation with an output power of 5.4 dBm and a receive gain of 8.2 dB at 4.05 GHz. Link budget calculations are used to show expected system performances. These active antennas have potential uses in both short-range communication and radar systems.

Active micropatch antenna device and array system

Abstract: An active microwave antenna device includes a two-port micropatch antenna which receives signals having a first circular polarization and transmits signals of opposite circular polarization. The device includes an integrated active circuit for amplifying and, optionally, filtering the signal. An array of such devices can be formed on a single substrate, each device being an independent active antenna, thus eliminating the need for RF or IF feed networks between the devices. Such arrays are believed to be particularly suitable for spatial power combining, rapid beam scanning, microwave imaging, frequency-polarization selective processes, and other related applications. The arrays may be either reflective or transmissive.

Spacecraft with active antenna array protected against temperature extremes

Abstract: A spacecraft carries a deployable active antenna array panel(s) and a deployable solar array panel(s). In the stowed condition, the antenna array panel(s) is sandwiched between a side of the body of the spacecraft and the solar array panel(s). This stowed state prevents the antenna panels from becoming too cold by radiation, or too hot by insolation, in an intermediate orbit. The outermost solar panel preferably has its active surface facing outward, so that it can generate electricity in the intermediate orbit.

Active SIMMWIC-antenna for automotive applications

Abstract: An active SIMMWIC-Antenna (Silicon Monolithic Millimeterwave Integrated Circuit) for vehicular technology in the frequency range around 76.5 GHz is presented. This active antenna acts as a transceiver and is well suited for low-cost integrated sensor systems for automotive applications. The monolithic active antenna embedded in a synchronization network requires only 3.2/spl times/2.6 mm/sup 2/ chip size. Using subharmonic injection locking frequency tuning and stabilization is realized. With an injection power of 0 dBm we measured a tuning range of 300 MHz. To our knowledge, this is the first synchronizable monolithic integrated active antenna suited for automotive applications in the frequency band around 76.5 GHz.

Antenna system for enhancing the coverage area, range and reliability of wireless base stations

Abstract: An active antenna system which has a plurality of antenna elements arranged in a column with each element or subarray of elements integrated with an amplifier and other beam forming components. A separate amplifier and filter are disposed immediately adjacent and connected to each of the antenna elements or a subarray of antenna elements and a separate combiner/divider is connected to each of the amplifiers. The antenna elements, amplifier and filter are disposed on a common support. A base station is connected by the feed cables and is remote from each amplifier. A first group of the antenna elements with low power amplifiers forms a transmitting antenna system and/or a second group of the active antenna elements with low noise amplifiers forms a receiving antenna system. A variable attenuator and a variable phase shift circuit can be integrated with each amplifier and can be used for beam shaping and electronic beam pointing. For diversity combining, spatially separated or polarization diverse active antennas are used. For polarization diverse active antennas, implementation involves a shared column or two colocated orthogonally polarized columns.

An integrated active circulator antenna

Abstract: An active circulator is integrated with a quarter-wave short-circuited microstrip patch antenna to produce a fully duplexed transceiver with transmit and receive operation at the same frequency and with the same polarization. The active circulator antenna is shown to have 14-dBi transmit gain and 7.4-dBi receive gain with a transmit-receive isolation of 26.9 dB at 3.745 GHz. This active antenna has potential uses in both short-range communication and radar systems.

A low-noise active receiving antenna using a SiGe HBT

Abstract: A low-noise active receiving antenna based on a printed dipole and a Si-SiGe HBT in the 5.8 GHz band is presented. A power gain of 8.3 dB compared to the respective passive antenna and a noise figure of 1.4 dB at center frequency were achieved. To improve the antenna gain, two of these components were combined with a small array with reduced beamwidth and comparable noise figure.

Frequency offset retrodirective antenna array

Abstract: A new architecture for the Van Atta self-steering array is presented. Active antenna techniques are used to realise a compact self-steering array with enhanced retrodirective properties. The experimental performance of the array is demonstrated and a technique is described which compensates for the beam pointing error induced by antenna array element directivity.

A tunable second-resonance cross-slot antenna

Abstract: Second-resonance slot antennas, due to their ability to transmit and receive on both sides of a microstrip ground plane, are often employed in planar active antenna arrays. For example, in an amplifier array, the input and output of an amplifier circuit are connected to orthogonally polarized antennas. The purpose of using orthogonal polarizations is to ensure amplifier stability. We present a 7 GHz cross-slot antenna designed to be used in a mixer/phase detector active antenna. By incorporating a varactor diode into the microstrip feed line, the cross-slot resonance can be electronically tuned over a 10% bandwidth. By mechanically varying the feed line (tuning stub) length, a 45% 2:1 VSWR bandwidth is possible.

Electronically scanned millimeter wave antenna using a Rotman lens

Abstract: Georgia Tech developed a Ka-band (33 to 37 GHz) millimeter wave Rotman lens that is being integrated with a beam switching system and horn array to produce a low cost electronically scanned antenna system. The MMW lens was designed and analyzed by generating various lens configurations as input into a mathematical model. This model uses a contour integral equation formulation to obtain the scattering matrix associated with a particular lens design. The optimized lens configuration was fabricated, and the S-matrix of the device was measured and processed to obtain the beam patterns and insertion loss. Maximum sidelobe levels -30 dB were achieved by applying an ideal -40 dB Taylor weighting function to the measured data. The measured insertion loss (Taylor weighting loss not included) ranged between 0.8 and 2.3 dB depending on the particular beam port that was excited and the frequency that was used. The lens has 32 active antenna element ports, and 17 active beam ports. Although the maximum scan angle for the present design is only ±22.2 degrees, greater scan angles up to ±45 degrees as well as frequencies up to 95 GHz are possible with different lens designs.

Multiple beam planar array with parasitic elements

Abstract: A multiple beam antenna array utilizing strategically placed parasitic elements to control side lobe levels is disclosed. Two specific arrangements of such parasitic elements are taught. A first preferred arrangement of parasitic elements provides for their placement between a ground plane and a plane of active antenna elements. An alternative preferred arrangement of parasitic elements provides for their placement both between a ground plane and a plane of active antenna elements, as well as in front of the active antenna elements. Both such embodiments provide improved side lobe control over a similar antenna system without parasitic elements. Moreover, the characteristics of the main lobe are improved by both embodiments.

Millimeter-wave antennas

Abstract: With the continually increasing demand for bandwidth, and the development of components for higher and higher frequencies, millimeter-wave systems are finding numerous applications of a commercial nature rather than being limited to military and scientific applications only. Since active device performance deteriorates with increasing frequency, the performance of the antenna becomes critical as we go higher into the millimeter-wave band. This paper presents a review of some of the recent developments in the field of millimeter-wave antennas. Finally, some details of a specific antenna for imaging are given, illustrating the benefits and challenges of fabricating such antennas.

System and method for the acquisition of a non-geosynchronous satellite signal

Abstract: An antenna having multiple antenna elements that are selectively activated performs an initial acquisition of a satellite signal by activating only a few of the antenna elements. This results in a broad beam width and increases the likelihood of detecting the signal from the satellite. When the satellite signal is initially detected, the system increases the number of active elements to narrow the beam width. The system incrementally increases the number of active antenna elements until the detected signal from the satellite exceeds a predetermined threshold. At that point, the location of the satellite may be precisely determined and all antenna elements activated to lock onto the satellite signal. If the antenna loses acquisition of the satellite signal, the reverse process may be implemented whereby some elements are selectively deactivated to broaden the beam width of the antenna in an effort to reacquire the satellite signal. When the satellite signal is reacquired, the antenna elements are incrementally reactivated until all antenna elements are active.

Measurement and modeling of a microwave active-patch phased array for wide-angle scanning

Abstract: An active antenna consisting of an integrated oscillator with a passive radiator has been arrayed and beam-scanned using a new principle for phase shifting. The radiating elements consist of a transistor oscillator whose frequency is controlled by a rectangular microstrip patch antenna. Each oscillator is injection locked to an external source. The phase control of the radiated wave is achieved by varying the bias on the transistor. Individual element performance has been characterized for potential use as an array element and is comprehensively reported. Methods used to achieve configurations with full 360/spl deg/ phase control have been investigated utilizing novel configurations and cascaded oscillator pairs. Close to 360/spl deg/ of radiated phase control from each element has been achieved. Measured results on an experimental four-element S-band array indicate that beam scanning in excess of /spl plusmn/60/spl deg/ can be achieved. Mutual coupling effects on this new form of array are studied both experimentally and theoretically. A van der Pol (1934) model for the weak coupling that is occurring on the array is developed and used to qualitatively predict the phase offsetting on array elements. Reasonable agreement between theory and experiment is obtained and it is observed that good control of the coupling mechanism is essential to array performance within this new form of active integrated phase shifterless array.

Electrically small, wideband, high dynamic range antenna having a serial array of optical modulators

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

Use of an active retrodirective antenna array as a multipath sensor

Abstract: The use of an active retrodirective antenna as an indicator of multipath propagation effects is investigated by the authors. It is shown that the flat azimuthal gain response normally associated with a retrodirective antenna array can be significantly modified by the presence of multipath signals. These signals act as secondary sources impinging on the retrodirective antenna array and give rise to amplitude perturbations in its azimuthal gain response. Using a retrodirective antenna array, the relative amplitude and phase components for the multipath signals can be recovered. In this way, the retrodirective antenna can be used as a low-cost multipath sensor.

Integrated active antennas on silicon

Abstract: Integrated active antennas have been designed, fabricated, and used as low-cost front-ends for sensor and communication applications in the frequency bands around 61 and 76.5 GHz allocated for industrial and vehicular applications. The active antenna concept, i.e. the spatial integration of antenna and active element, results in minimization of the required chip size, high reproducibility, and, thus, low costs. The design of active millimeter wave antennas with respect to the impedance matching of antenna and active element as well as the radiation characteristics is discussed. The fabrication process on high resistivity silicon substrates is presented. Application of these front-ends in radar and communication systems is demonstrated.

A three-dimensional active antenna for a high-speed wireless communication application

Abstract: This paper proposes a three-dimensional active antenna configuration for a front-end module of a high-speed wireless communication system at millimeter and quasi-millimeter-wave frequencies. The active antenna is integrated with a microstrip antenna array on multilayer alumina-ceramic, individual MMIC chips including transmit/receive amplifiers, time division duplex switches, and a filter on multilayer polyimide. The three-dimensional structure achieves an unrestricted RF-circuit design on multilayer polyimide.

Millimeter wave Rotman lens

Abstract: A millimeter wave Rotman lens was developed that operates at frequencies between 33 GHz and 37 GHz with the potential of being implemented in metallized plastic. Various lens designs were evaluated with a computer model based on the contour integral method. The best lens design was manufactured and characterized by measuring the scattering parameters between the beam and array ports within the frequency interval of interest. The measured S-parameters were processed to determine beam sidelobes and insertion loss. Maximum sidelobe levels /spl les/-30 dB were obtained. The insertion loss of the lens was between 0.8 and 23 dB depending on the particular beam port that was excited and the operating frequency. The current lens design has 32 active antenna element array ports, 17 active beam ports, and a maximum scan angle of /spl plusmn/22.2.

Method using squid array for improving the sensitivity of a slot antenna

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

Method for using a wideband, high linear dynamic range sensor

Abstract: A magnetic field sensor which can be used as an active antenna is disclosed that is capable of small size, ultrawideband operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators, that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.

The trinational AMSAR programme: CAR active antenna architecture

Abstract: The work described is being carried out on the European AMSAR programme for an Airborne Multi-role, Solid-state Active array Radar undertaken by GTDAR (GEC Thomson Dasa Airborne Radar, EEIG) under contract to the French Authorities acting on behalf of the United Kingdom, France and Germany Ministries of Defence. It was undertaken by the three Industrial Members of GTDAR, GEC Marconi Avionics, Thomson-CSF Radars & Contre-Mesures and Daimler-Benz Aerospace/Sensor Systems. One main stage of the programme is the definition, manufacture and flight trials of the CAR Radar Demonstrator. The CAR (core antenna radar) active antenna is a full size, fully functional X-band airborne equipment; it includes new generation (Mark 2) transmit/receive modules (TRMs) and air-capable technology. The antenna architecture, based on proven and advanced principles, complies with all the mechanical, thermal and functional stringent requirements of an active array dedicated to advanced multi-PRF airborne radar. It represents a cost effective definition capable of providing a generation of high performance and affordable systems. The article gives the main principles behind the AMSAR antenna architecture, applied to the airborne demonstrator, the rationale which lies behind the options and the predicted benefits.

Dynamic Active Antenna Considering with Multi Oscillation Modes

Abstract: This paper discusses a new sensing strategy for the Dynamic Active Antenna which can estimate the contact point between an insensitive flexible beam and an object by using multiple mode of natural frequencies of the beam in contact with the object. We first prove that the contact position is uniquely determined if we can consider every mode of natural frequencies of the beam in contact with the object. We also show that the use of the fundamental and the second order natural frequencies is sufficient for uniquely determining the contact point if the beam has uniform mass and stiffness distribution. The strategy is composed of two steps. In the first step, the fundamental and the second order natural frequencies of the beam in contact with the object are evaluated by utilizing a Maximum Entropy Method. Then by using the mapping diagram from those two frequencies into the contact point, we can obtain the contact point. Experimental results are also shown to verify our idea.

Novel retrodirective beam formation techniques

Abstract: This paper presents two novel active antenna architectures for retrodirective beam formation which rely on heterodyne phase techniques for their operation. Both the methods use the phase conjugate properties of a mixer driven with f0 and 2f0 signals for retrodirective beam formation. In the first approach frequency diversity, coupled with power divider circuits is used as a quasi circulator to provide isolation between incident and retransmitted signals. In the second method a dual linearly polarised microstrip patch antenna provides the complementary function of radiator and isolation element by virtue of its polarisation diversity response. Two element arrays using both approaches were made for 1 GHz operation. Results and theoretical performance figures for the retrodirective antenna architectures are presented in the paper and are compared to a passive 2 element array which is used as a reference for discussion.

Spectral control of integrated active antennas

Abstract: Integrated active antennas are of increasing interest as system designers require more complex functions to be implemented in reduced space. Many of these systems require very low levels of harmonic and spurious radiation in order to meet electromagnetic compatibility specifications. Active antennas introduce nonlinear devices directly into the antenna and thus they can exhibit high levels of harmonic radiation, moreover, due to size constraints, filters can not be easily added as in conventional systems. In the case of active receiving antennas it seems that by suppressing the harmonic resonances of the antenna the harmonic reception problem can be reduced. However, with patch oscillators, due to the interdependence of the active device and the patch, the solution to the problem of harmonic radiation is more complex. This work aims to investigate these problems, especially in the case of the patch oscillator since these devices seem to pose the greatest challenge. The final goal is to obtain closed form expressions for the level of harmonics in terms of physical circuit parameters. Although numerical methods could be used to solve this problem it is felt that greater physical insight can be obtained from closed form expressions, allied to this they will be useful for CAD of patch oscillators. Closed form expressions would allow designers to realise low levels of harmonic radiation either by modifying the patch geometry or by altering the active device configuration.