Showing papers on "Active antenna published in 1996"

Integrated active antennas and spatial power combining

Abstract: Oscillators and Synchronization. Antennas and Arrays. Power Combining. Integrated and Active Antenna Testing. Active Antennas: Early Work Before 1987. Active Microstrip Patch Antennas and Power Combining. Integrated and Active Grids. Endfire Notches and Other Slotline Active Antennas. Integrated and Active Inverted Stripline Antennas and Other Active Antenna Configurations. Integrated Antennas with Passive Solid-State Devices. Beam Steering for Active Antenna Arrays and Spatial Power Combiners. Index.

Active frequency-selective surfaces

Abstract: Two different varieties of active frequency-selective surfaces (FSS) are described. In one type, active FSS elements incorporating switched PIN diodes are discussed. Waveguide simulation studies show that the frequency response of the surface can be electronically switched from that of a reflecting structure to a transmitting structure. In the other type, FSS are printed on ferrite substrates which are biased with a DC magnetic field. The application of this bias field to the ferrite allows tuning of the resonant frequency by several gigahertz. In addition, the frequency characteristics can be switched from transmitting to reflecting, as for the active element FSS.

A novel active antenna with self-mixing and wideband varactor-tuning capabilities for communication and vehicle identification applications

Abstract: A cavity-backed, Gunn-diode-driven, self-mixing active inverted stripline circular patch antenna has been developed. The antenna provides good radiation performance with cross-polarization levels 18 dB below copolarization at boresight. The self-mixing performance shows that the circuit has a 2 dB conversion gain for IFs up to 450 MHz and a single-sideband noise figure of 12 dB at 200 MHz. The self-mixing antenna is also capable to mix signals with its second-harmonic, providing a conversion loss of 3.7 dB. Also, a varactor diode has been incorporated with a inverted stripline circular patch active antenna to allow for electronic tuning. A 13% tuning bandwidth with a power variation of 11.0 dB was achieved. A simple equivalent circuit has been used to model the active antenna, and the calculated results agree well with the experimental results. The circuit should have many commercial applications in wireless communications, radar, and sensors, but is particularly suitable for use as a transceiver for short communications links or as a microwave identification transceiver.

Antenna microwave shield for cellular telephone

Abstract: A method and apparatus for shielding and/or redirecting radiation from a portable communication device, such as a cellular telephone is provided. In one embodiment, a conductive shield or passive antenna is positioned between the cellular telephone active antenna and the location of the user's head when the cellular telephone is in the operative position. In one embodiment, the shield is configured to reflect radiation in a pattern which is multi-directional. In another configuration, the shield is configured to reflect radiation in a preferred axial direction. Latches or other devices can be used to assure that the shield is positioned and maintained in the desired location. Insulation may be used between the shield and antenna. The shield can be made of a single unitary piece or a plurality of disconnected pieces. The shield may be reconfigurable, e.g., to accommodate a telescoping antenna.

Integrated active antenna with simultaneous transmit-receive operation

Abstract: The authors present results for a novel two element active transmit-receive array using dual linear polarisation and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that transmit and receive paths are isolated and polarisation duplexed. The array gives in excess of 55 dB transmit-receive isolation at 3.77 GHz.

Theoretical and experimental investigation on dynamic active antenna

Abstract: This paper discusses theoretical and experimental investigation, on dynamic active antenna which can detect the contact point between an insensitive flexible beam and an object through estimation of the oscillation frequency in contact with the object. We first prove that the contact position is uniquely determined if we consider every mode of natural frequencies of the beam in contact with the object, while the fundamental and the second order natural frequency, in most cases, satisfy the sufficient condition for providing the unique contact position. We also show a desirable mass distribution avoiding the estimation error for localizing the contact position. By utilising the maximum entropy method, we succeeded in experimental estimating the contact point from the fundamental and the second order natural frequencies.

A SIMMWIC 76 GHz front-end with high polarization purity

Abstract: An integrated active antenna with a polarization purity better than 28 dB and a radiated power of 8 dBm at 75.7 GHz is presented. The linearly polarized radiator consists of a planar resonant antenna and a transit-time diode monolithically integrated on a silicon substrate. This active antenna finds various applications in low-cost multi-channel sensor systems, e.g. for object classification. Guidelines for the design are discussed. The characterization of the fabricated SIMMWIC devices includes measurements of output power, polarization purity, and far-field pattern. Moreover, the oscillation frequency of the devices has been successfully stabilized using subharmonic injection locking. The FM noise behavior of the locked oscillator has been characterized. The measured results are presented and compared to theoretical calculations.

Multifrequency microstrip antennas using alumina-ceramic/polyimide multilayer dielectric substrate

Abstract: A novel microstrip antenna using an alumina-ceramic/polyimide multilayer dielectric substrate is presented. The multilayer configuration, in which two different multilayer materials with much different permittivities and thicknesses are stacked together, can be used for designing an antenna with selective substrate thickness, thus providing the optimum substrate thickness for the desired frequency. Both 10 GHz-band and 18 GHz-band antennas are designed and fabricated on the same substrate to demonstrate this feature. They achieve perfect matching and acceptable radiation characteristics. Furthermore, for application to array antennas, power combining circuits such as a 90/spl deg/ hybrid and a four-port divider are demonstrated. Finally, the possibility of applying this technology to active antenna systems is discussed. The measurement results confirm that the proposed multilayer substrate is extremely suitable for building active array systems integrated with active devices and monolithic microwave/millimeter wave integrated circuits (MMIC), as well as for constructing multifrequency antennas.

Modified rectangular patches for self-oscillating active-antenna applications

Abstract: Two modifications to a rectangular-patch antenna, suitable for the integration of active devices, are presented. In the first modification, the impedance inverter was placed in the rectangular opening formed by removing the central part of the patch. This modification allows optimal matching of the active device by changing the position, width, and length of the impedance-line transformer. An oscillating antenna, using this modified patch and a Gunn diode, showed a high EIRP, higher spectral purity, and substantially lower cross-polarization levels, in comparison with the reference active antenna with an unmodified patch. Because of the higher overall Q, this modification is recommended for active-antenna applications with active devices that have a narrower negative-resistance bandwidth. In the second modification, an active device (Gunn diode) was integrated directly into a rectangular opening inside the patch, without the use of a line transformer. This reduced the overall Q of the antenna, thus allowing wide-band frequency tuning by changing the bias voltage. A clear spectrum, with no spurious components of the free-running oscillating antenna, was observed. Radiation patterns in the E and H planes were measured. Low levels of cross-polarization, as for the first modification, were obtained. Injection-locking properties were investigated throughout the tuning range. A relatively wide locking range, with a good locking gain, was achieved. Such a miniaturized wide-band VCO antenna is applicable for integration in injection-locked active arrays, and spatial power combiners.

Vision based active antenna

Abstract: This paper proposes the vision based active antenna (VBAA) that can detect the contact force, the stiffness of the environment, and the contact location between an insensitive elastic antenna and an environment, through the observation of the antenna's shape by a camera. We show that both the contact location and the contact force can be estimated by measuring two arbitrary points on the antenna after a pushing motion; even though the exact contact point is hidden by occlusion. By considering the geometrical relationship between. The virtual (without environment) and the real (with environment) displacements of the contact point, the stiffness of the environment can also be estimated, which our conventional active antenna can not do. We present the basic working principle of the VBAA and give experimental verification.

System and method for dynamically counteracting sway in active antenna towers

Abstract: For use with an antenna tower, the antenna tower providing a mount for an active antenna that is subject to misdirection when the antenna tower sways, a system for, and method of, dynamically counteracting sway in the antenna tower. The system includes: (1) a rotation detector that senses a rotation, relative to a fixed reference plane, of a portion of the antenna tower proximate the active antenna and develops a sway signal indicative thereof and (2) antenna beam steering logic, coupled to the rotation detector, that receives the sway signal and modifies a drive signal provided to elements of the active antenna to redirect a beam projecting therefrom, the drive signal thereby compensated for the rotation to counteract the sway in the antenna tower. The system may form a portion of a wireless communications station.

A self-mixing active antenna for communication and vehicle identification applications

Abstract: A cavity backed, Gunn diode driven, self-mixing active inverted stripline circular patch antenna has been developed. The active antenna provides good radiation patterns with cross-polarization levels 18 dB below copolarization at boresight. The self-mixing performance shows that the circuit has a 2 dB conversion gain for IFs up to 450 MHz and a double sideband noise figure of 15 dB at 200 MHz. The antenna is suitable for use as a transceiver for short communications links or as a microwave identification transceiver.

Antenna research at the Communications Research Centre

Abstract: An overview is presented of the antenna research carried out by the Directorate of Antennas and Integrated Electronics (DAIE) of the Communications Research Centre (CRC). The antenna research within the DAIE can be categorized into two groups: antenna-hardware development and electromagnetic-software development. Research in antenna hardware has focused on printed multi-layer arrays, dielectric-resonator antennas, ferrite antennas, active-circuit integration, and low-loss feed networks. Research in electromagnetic software includes the development of three-dimensional transmission-line-matrix (TLM) code, and the application of cellular automata (CA) techniques for the analysis and modeling of antennas, microwave circuits, and general electromagnetic phenomena, such as scattering. This article concentrates on the antenna-hardware research and development within the DAIE. Radiation patterns are considered.

Angle measuring instrument and composite guiding device

Abstract: PURPOSE:To obtain a composite guiding device which has a highly accurate angle measuring ability over a wide band and an ability equal to that of an active radio guiding device by arranging passive antennas so that the performance of an active antenna cannot be deteriorated and using an algorithm with which a sufficiently high angle measuring accuracy can be obtained. CONSTITUTION:Antennas for passive radio waves are constituted by annularly arranging element antennas 14-1 to 14-n on the outer periphery of the aperture 2C of an antenna for active radio waves. The phase difference between received signals of each two adjacent ones of the element antennas 14-1 to 14-n is measured (n) times and the primary solution of the phase differences is found by applying the method of least squares. Then the phase difference of received signals at (n) pieces of element antennas and (m) pieces of secondary solutions are found by applying the method of least squares at every block of (m) pieces and the secondary solution which is the closest to the primary solution is used as the final solution of the arriving angle of radio waves. Therefore, a highly accurate radio wave arriving angle containing no ambiguity is obtained.

Use of direct-modulated/gain-switched optical links in monopulse-type active phased array systems

Abstract: With the advance of high speed laser technology, optical interaction with microwave circuits has become highly viable. Such interaction is advantageous as the fiber is low-loss, lightweight, and immune to electromagnetic interference. In this paper, interaction of direct-modulated and gain-switched optical links with active antenna phased array systems is demonstrated. In the direct-modulated optical system, the RF signal directly modulates the DFB laser. In the gain-switched optical system, the laser is gain-switched to function as a RF frequency doubler. The modulated signal is transmitted via an optical fiber and recovered at the receiving end by a high-speed photodetector. The recovered RF is then injected into the active antenna phased array systems as an injection-locking reference signal. Two active antenna systems are used for this demonstration: beam-switching and Doppler transceiver.

Integrated active antenna with simultaneous transmit-receive operation

Abstract: This paper presents results for a novel two element active transmit-receive array using dual linear polarisation and sequential rotation. Each element includes an integrated (MESFET) oscillator and amplifier mounted on orthogonal edges of a square patch, such that transmit and receive paths are isolated and polarisation duplexed. The array gives in excess of 55 dB transmit-receive isolation at 3.77 GHz.

Nonlinear two element active antenna array stability analysis

Abstract: Closed form analytical equations for the stability condition for the two modes available within a two element active antenna linear array as the element separation is increased are presented for the first time. A mathematical explanation to the mode swap characteristics first reported by Stephan and Young (1988) is given with a prediction of within which mode the array will operate as a function of element separation. This knowledge is imperative since the array far-field radiation pattern is different depending on the operating mode, and so a prediction method is desirable (i.e. boresight null or peak). The identical element case is considered, although the analysis can be extended to incorporate similar though non-identical elements.

An active inverted patch antenna with wideband varactor-tuned capability

Abstract: A varactor-tuned inverted circular patch antenna has been developed with a power variation of /spl plusmn/1.0 dB over a 13 percent tuning bandwidth. A simple equivalent circuit has been used to model the active antenna, and the calculated results agree well with the experimental results. The circuit should have many commercial applications in wireless communications, radar, and sensors.

Eigenvalue mode confirmation in a mutually coupled active antenna chain array

Abstract: Arrays of coupled active antenna oscillators can be used for power-combining at microwave and millimetre-wave frequencies. It is known that the relative phase angle between active antenna oscillators placed in an array and hence their far-field radiation pattern can have certain discrete values depending on the separation distance between elements. Thus in order to characterise an active array an accurate method of evaluating the coupling between oscillators and a knowledge of the available modes that exist within the array are required. In this paper the available modes for an array of mutually coupled active antenna elements are evaluated by examination of the eigenvectors of the impedance matrix of the passive element components in the active array. Time domain numerical simulations are performed and the resulting predictions compared to those obtained by experiment and by the eigenvalue approach.

Vision based active antenna-basic considerations on two-points detecting method

Abstract: This paper is an extended version of the vision based active antenna (VBAA) that can detect the contact force, the stiffness of the environment, and the contact location between an insensitive elastic antenna and an environment, through the observation of the antenna's shape by a camera. If measured points are on the antenna, two arbitrary points are sufficient for computing the contact location and the contact force uniquely. In a practical application of VBAA, however, the measured points are not always on the antenna. In this paper, we show the condition for uniquely obtaining both contact location and contact force under the situation that the measured points are not always on the antenna. We also show a new compensation method to improve the sensing accuracy. We further verify our idea experimentally.

Microstrip antennas on localized micromachined dielectric substrates

Abstract: Micromachining techniques using closely spaced holes have been used underneath a microstrip antenna on a high dielectric constant substrate (/spl epsiv//sub /spl gamma//=10.8) to synthesize a localized low dielectric constant environment (/spl epsiv//sub /spl gamma//=2.3). The bandwidth of a 12.8 GHz microstrip antenna, was improved from 0.8% to 7.8%, and the measured radiation efficiency increased from 40% to 70%. We believe that this technique can be applied to millimeter-wave (30-100 GHz) microstrip antennas on GaAs substrates to result in relatively wideband (4-6%) MMIC active antenna modules for phased-arrays and collision avoidance systems.

Noninvasive experimental determination of charge and voltage distributions on an active surface [active antennas]

Abstract: Optical sampling has been employed to obtain the charge and voltage distributions on both a self oscillating active antenna and a power combining oscillating array of such active antennas. Various oscillating arrays have been fabricated on GaAs substrates, and the microwave characteristics of these active structures were tested before the optical sampling measurements were performed. The results of optical sampling measurements have revealed some interesting characteristics of both the individual antenna and array operation. It was noted that the charge and voltage distributions of a single isolated oscillating antenna were quite similar to those measured on an oscillating antenna in an array. Along with this, no edge effects were observed in the finite arrays. The charge and voltage distributions repeated smoothly in periods less that a wavelength with the excess phase necessary to achieve 180 degrees per cell being taken up by a large phase jump across each transistor, despite the fact that each transistor has dimension much smaller than the free space wavelength of the oscillation. Some analytical modeling results are presented to try to put the results into perspective.

Quasi-optical phase modulators

Abstract: Three X-band quasi-optical transmission type phase modulators are presented: a varactor loaded grid with 25/spl deg/ continuous phase shift; a p-i-n diode loaded grid with digital phase shifts of 0/spl deg/ and 90/spl deg/; and a transistor antenna array with 0/spl deg/ and 180/spl deg/ phase states. All of the modulators operate in transmission mode and are suitable for cascading with other quasi-optical components. Relative amplitude and phase change of the transmission coefficient as a function of frequency is presented for the two digital modulators. Antenna patterns for the BPSK active antenna array modulator are also presented.

Injection-locked 28-GHz oscillator array with disk-cylinder reflector

Abstract: A 28-GHz endfire (modified Vivaldi) active antenna is described that contains a secondary, circularly polarized patch antenna for reception of an external injection-locking signal. Three of these devices are used to characterize an octagonal cylindrical reflector designed for creating an omni-directional transmitter suitable for use in point-to-multipoint communication systems. The experiments provide data that validates the approach used to simulate the azimuthal radiation patterns. These simulations are then extended to predict the patterns from a full eight-element array.

AMSAR: a European active antenna radar programme

Abstract: AMSAR is a tri-national programme being undertaken by GEC THOMSON DASA Airborne Radar (GTDAR EEIG, a joint venture set up by the above companies) and supported by the governments of France, UK and Germany. This active array antenna radar demonstrator programme includes the development of X-band transmit/receive modules based on European GaAs MMIC technology, a multiple channel receiver chain and real-time adaptive digital beamforming. These features will allow the demonstration of electronic scanning, multiple jammer cancellation, and environmentally reactive radar operation, all in real airborne conditions. The risks associated with the use of a new technology in an airborne environment are reduced by a progressive approach. In the first stage primary feasibility issues are being addressed in an antenna demonstrator. In the second stage, demonstration of a complete radar system with full real time functionality will be performed on a trials aircraft. Finally, experimental results are compared and integrated with a full system global simulation model to permit reliable prediction of operational characteristics.

Antennas for safer hand-held radios

Abstract: An antenna for a personal communication device designed for reducing RF emissions to a user's head and body comprises a single half-wave dipole antenna element (20) mounted on the top of a telescoping rod (22) such that the antenna element (20) is raised above the user's head (18) when the rod (22) is extended. The rod (22) is completely inactive and serves only to elevate the active antenna element (20) above the user's head and away from the body. A built-in switch (30) is provided which reduces the transmission RF power when the rod (22) is retracted to further protect the user. In a second embodiment, a co-linear array of dipole antenna elements (38) is used. The full array is active for reception. However, a proximity detector (50) senses the proximity of a human body, and lowers the RF transmission power to those antenna elements (38) in the array that are closest to the user's head.

Active and semi-active array antennas for mobile communications satellites

Abstract: The latest generation of mobile link antennas for mobile communication satellites are characterised by the requirement to generate a lattice of similar pencil beams with good mutual isolation. To satisfy this requirement complex antennas with distributed amplification are necessary. The optimum antenna solution in any particular case may be either a direct radiating array or a reflector system, depending on various system characteristics. The paper focuses on direct radiating arrays for the mobile link transmit function and examines the application to such antennas of the latest developments in semi-active architectures. Some fundamental issues concerning beamforming, frequency reuse and grating lobe structure are addressed. A typical active antenna design is introduced for comparison, a semi-active solution for the same example is derived, and preliminary pattern plots are given.

A combination of piecewise harmonic balance technique and neural network for analyzing active antenna

Abstract: Active antenna which offers much potential as useful circuits for future applications are a newly developing area. Several methods for analysing active antennas are presented. The first method relies on the FDTD technique. In this approach the time domain model of active devices is introduced into the FDTD frame. The large signal characteristics of active devices and the behaviour of antennas are both taken into account. This is considered to be the most rigorous method. This paper presents a simple method for analysing active antennas. The method is based on the piecewise harmonic balance technique. A neural network is used to speed up the optimization by replacing repeated circuit simulation. Therefore, the new approach is much faster than the traditional optimization technique. Compared with the data obtained from FDTD, the results also agree well.