Showing papers on "Active antenna published in 1989"

Experiments on injection locking of active antenna elements for active phased arrays and spatial power combiners

Abstract: Two types of active antenna elements have been studied experimentally. One type uses a microstrip antenna with an active device mounted directly on the antenna. The other uses an active device coupled to a microstrip patch antenna through an aperture. Microstrip active antenna elements and two-element arrays have been demonstrated for both types of circuits. Injection locking of the antenna elements has been achieved through space and mutual coupling. The circuit Q factor was calculated based on the locking gain and the locking bandwidth. The power output from two elements has been successfully combined in free space with a combining efficiency of over 90%. For a single active antenna with a Gunn diode mounted directly on the patch, an electronic tuning range exceeding 9% has been achieved by varying the DC bias. The results should have many applications in low-cost active arrays, active transmitters, and spatial power combiners. >

Active array element amplitude stabilization

Abstract: An amplitude control system particularly suitable for an active antenna array includes a power detector (18) for generating a power level signal representative of a level of radio frequency (RF) energy radiated by an antenna element (10), or groups of elements, in a phased antenna array. A reference signal (R) corresponding to a desired value for the radiated level of RF energy is set by a control device (20), and the power level signal and the reference signal are compared with one another. Depending on the comparison result, an attenuator (14) associated with an RF amplifier than drives the antenna elements, is adjusted to maintain the radiated RF energy at the desired value set at the control device.

MMIC phase shifters and amplifiers for millimeter-wavelength active arrays

Abstract: The development of MMIC (monolithic microwave integrated circuit) phase shifters and amplifiers at 20 and 44 GHz for application in space-based active antenna arrays is described. Radio frequency probing to characterize the active elements at these frequencies is shown to provide a good basis for the MMIC design. Measured performance results are presented for a 44-GHz phase-shifter switching element, all 16 states of a 4-b 20-GHz MMIC phase shifter, a 180 degrees 44-GHz phase shifter, and a three-stage 20-GHz amplifier. >

Gain of active Antenna Systems: Antenna Standards committee requests input

Abstract: The major topic of discussion at the Antenna bers on the subject, on how their organizations are posium was how to define the gam of active antenna antenna systems, and on what definitions would prove systems. (BY the term "active antenna system", what useful to the antenna community. In the end, the job is meant is an antenna system in which active devices of the committee is to develop standard definitions such as amplifiers, receivers, oscillators, Or 0 t h that are not only precise and correct, but are also active devices are embedded, so inextricably that the useful. passive antenna gain cannot be directly measured. An example is a phased array with individual transmitrecelve modules attached to each element in the Please send comments to the committee chair, array.)

Process for producing vias in semiconductor

Abstract: An improved phased-array active antenna transmit-receive means utilizing a multiplicity of individual transmit-receive cells positioned in an array format upon a common wafer of semiconductor material. Each transmit-receive cell, comprises a multiplicity of redundant, integrated circuit, electronic devices implanted upon the common semiconductor substrate. The transmit-receive cells utilize novel mitered mechanical switches to permanently interconnect individual electronic devices into either transmit or receive circuits during the fabrication and test of the transmit-receive cells. Radio frequency and direct current input and output vias formed from a novel metal evaporation technique connect the devices upon the surface of the common semiconductor wafer to underlying, insulated direct current distribution circuits and a radio frequency manifold. This array of improved phased-array active antenna transmit-receive means comprised of transmit-receive cells sharing common central processing means, logic control and heat dissipation means results in a significant reduction in the size and weight of the standard phased-array active antenna system. This significant reduction in antenna system size and weight is very important in broad band electronic countermeasure systems or narrow band phased array active antenna radar systems as used in advanced tactical fighters, or space applications.

A Microstrip Based Active Antenna Doppler Transceiver Module

Abstract: We present the design and test of a microstrip active transceiver element suitable for use as a CW Doppler module. The circuit consists of a microstrip annulus from which a small section has been removed, resulting in a two-port antenna. This antenna is then coupled to the drains of two FETs through a short section of microstrip line. By adjusting the length of this section of line, the oscillation condition is satisfied, the two FETs oscillate in the odd mode, and a microwave signal is radiated from the circuit. The Doppler-shifted return signal which is picked up by the antenna is applied back to the drain ports of the FETs, which also function as self-oscillating mixers. The IF signal is coupled out using audio transformers. By measuring the in-phase and out-of-phase IF signals, we can determine the co-polarized and cross-polarized components of the reflected signal.

Mitered mechanical switches

Abstract: An improved phased-array active antenna transmit-receive means utilizing a multiplicity of individual transmit-receive cells positioned in an array format upon a common wafer of semiconductor material. Each transmit-receiver cell, comprises a multiplicity of redundant, integrated circuit, electronic devices implanted upon the common semiconductor substrate. The transmit-receive cells utilize novel mitered mechanical switches to permanently interconnect individual electronic devices into either transmit or receive circuits during the fabrication and test of the transmit-receive cells. Radio frequency and direct current input and output vias formed from a novel metal evaporation technique connect the devices upon the surface of the common semiconductor wafer to underlying, insulated direct current distribution circuits and a radio frequency manifold. This array of improved phased-array active antenna transmit-receive means comprised of transmit-receive cells sharing common central processing means, logic control and heat dissipation means results in a significant reduction in the size and weight of the standard phased-array active antenna system. This significant reduction in antenna system size and weight is very important in broad band electronic countermeasure systems or narrow band phased array active antenna radar systems as used in advanced tactical fighters, or space applications.

Low noise lumped parameter active receiving antenna

Abstract: A small, relatively wide-bandwidth, active antenna is usable in a wide range of applications spanning the VLF and SHF bands The antenna is capable of receiving relatively weak radio frequency signals having a signal strength below that detectable using conventional passive antennas The antenna includes a lumped constant element forming an electric wave receiving part, and a high impedence amplifier having input terminals connected via leads having a short electrical wavelength at the design frequency, to corresponding ends of the lumped constant element Output terminals of the antenna are connected to a receiver to provide a small, high sensitivity, active antenna

A multibeam active antenna for an European contiguous coverage at Ku-band

Abstract: An active multibeam antenna has been studied with the aim of providing multispot European coverage at Ku-band according to ESA study requirements. The coverage characteristics have been optimized to meet the required directivity, and a compromise has been reached between antenna and payload complexity. The impact of the active concept on system performance and reliability has been evaluated, considering both uniform and unbalanced traffic distribution among the coverage beams. The possible adoption of frequency reuse has also been investigated. >

System Design Considerations in Fiber-Optic Networks for Active Array Satelite Antenna

Abstract: Multiple pencil-beam scanning/hopping antenna systems provide a powerful approach to increase the satellite's capacity by the frequency reuse, the increased e.i.r.p. and G/T of each of the pencil beams, and also by the efficient satellite resources utilization through matching the antenna beams' dwelling times to the traffic and connectivity requirments. Since this permits also to use very small and inexpensive earth stations, a significant reduction in cost per communication channel can be obtained. One of the problem areas still existing and requiring an innovative solution is the distribution of the broadband microwave communications and control signals to the very large number of the active antenna moduls. Each module consists of a digital phase shifter and gain control, amplifier, and a radiating element. Recent advances in fiber optics technologies for microwave applications in the over-l0-GHz region, make it a very attractive candidate for signal distribution networks in large satellite antenna arrays. The main advantages of a fiber optic network are the very small size and weight, the capabillity to be integrated with MMIC devices, and immunity to electromagnetic interference, while the main disadvantages are the high insertion loss and high noise figure. In this paper some system design considerations are evaluated, in applying the fiber optic technologies and techniques to multibeam scanning Ku-band satellite antenna signal distribution and control networks. It is demonstrated that the fiber optic links can provide a feasible solution.

Array antenna system with direction finding capability

Abstract: An array antenna system having a predetermined electric current distribution on an antenna aperture to form a desired shape of antenna beam. Active antenna elements arranged on the aperture transmit a signal for electronically scanning a predetermined region to detect a target and receive a signal reflected by the target. Passive antenna elements are also arranged on the aperture. The antenna system further includes a direction finding section including reception antenna elements which receive an incident signal. The active, passive and reception antenna elements are positioned to allow a predetermine electric current distribution to be established on the antenna aperture.

Concept for a Spaceborne Synthetic Aperture Radar (SAR) Sensor Based on Active Phased Array Technology

Abstract: : For surveillance with spaceborne remote sensing systems quite often a spatial resolution of 1 m or less is requested In the paper a SAR concept is presented for a low flying satellite Assuming a peak power of 5 kW and using active phased array technology a swath width of about 30 km at an off nadir angle of 35 deg is considered to be reasonable A wide swath width combined with a high resolution can only be achieved if we use a fixed antenna beam for transmitting which illuminates the whole swath width, while a very narrow antenna beam scans the swath in the manner as the reflected pulse travels from the near range to the far range across the swath width For the active antenna system a high efficiency of the transmit/receive-moduls, low losses in the feeding network and doubly polarized radiating elements with high polarization purity are considered of utmost importance

Single antenna receivers for advanced satellite T/R systems

Abstract: Three active antenna systems have been synthesized for 14-spot European coverage in the down-link range 12.5-12.75 GHz: far-field multibeam antenna, a near-field multibeam antenna, and a direct radiating phased array. The block diagram for all the three antenna systems is shown, assuming that a single antenna is utilized for both transmission and reception. Through a set of diplexers, both receiver and transmitter modules use the shared feeds. The use of a single antenna for both transmission and reception has been shown to be attractive in terms of size and weight reduction. These features conflict, however, with the thermal and interconnecting issues that can arise in practical systems. The transmitter topology and complexity seem important points in the feasibility of the integration with the receiver. In particular, the number and allocation of the power amplifiers are quite critical. >

Further comments on the definition of antenna gain

Abstract: [Editor's note: Three short articles concerning the definition of the gain of active antenna systems and planar arrays appeared on pages 62-64 of the October, 1989, Newsletter. The following comments were solicited by Antoine Roederer as a part of the questions he raised in the October issue, but unfortunately arrived a few da s too late to include in that issue. Alan J. Simmons ($0 Box 103, Winchester, MA 01890) and Donald G. Bodnar (GTRI/CCRF/STL/ATD-Room 4-138, Georgia Institute of Technology, Atlanta, GA 30332 also solicited input from M - S regarding the gain o d active antenna s stems, as a result of discussions at an Antenna StandYards Committee meeting during the San Jose symposium. This later input was sollcited on behalf of the Committee. Those wishing to contribute to this discussion are requested to send their comments to the appropriate author, with copies to Alan Simmons or Donald Bodnar, who will act as coordinators for these discussions. WRS]