Showing papers on "Active antenna published in 1990"

Local compensation of failed elements of an active antenna array

Abstract: Compensation for a failed element of an active antenna array is acheived by turning the failed element off and selecting a plurality of adjacent, properly working elements as local compensators. A selected voltage and phase increment is then added to the complex output voltage which each local compensator would normally produce. The magnitude of the voltage increment is selected by dividing the magnitude of the failed element's voltage, were it not failed, by the number of compensators. The phase increment is selected to scan the associated voltage increment at a depression angle of about 30 degrees below the horizon.

Synthesis procedure for active integrated radiating elements

Abstract: This letter demonstrates a technique for the synthesis of a new integrated active radiating element topology. The approach adopted uses a microwave MESFET operating in large signal mode as the active device in an oscillator configuration. The oscillator has as its parallel feedback element and load element a microstrip patch antenna. The synthesis approach developed in this paper uses numerical optimisation to find the optimum terminal voltages for a given MESFET at a specified frequency. A set of explicit equations are presented in terms of these optimum terminal voltages. These allow the active radiating element terminations to be realised analytically. An NE71000 chip is used as the active device in the active radiating element circuit. Construction is on RT Duriod 5880 and the circuit operated at 10.2 GHz with 30mW power delivered to the antenna.

GaAs MMIC control functions for 3.7-4.2 GHz band active antenna

Abstract: This paper describes the realization of gain and phase control function in GaAs microwave monolithic integrated circuit (mmic.). The measured performances are successfully compared with simulation results. The attenuator uses a dual-gatefet in order to adjust the level of the transmitted signal. The obtained dynamic range is 27 dB. The phase-shifter is made up of T and π networks connected in series and makes use of the capacitance variation of Schottky diodes to change the transmission phase. The phase shift reaches 115° at its maximum. Both circuits have been developed for a C-band beam forming network project for space communications.

Split-phase technique for eliminating pattern nulls from a discrete guard antenna array

Abstract: A guard for an active antenna array is formed from first and second subarrays of the elements of the antenna, the first and second subarrays each being quadrant symmetric and having respective center phases which are 90 degrees apart. This arrangement greatly reduces nulls in the resultant guard pattern.

Fiber Optic Feed

Abstract: : This report details a Fiber Optic Feeding (FOF) concept for beamforming in phased arrays. Experimental data is presented which validates the basic underlying assumptions. Elaborations on this basic concept are presented which illustrate the power of this new approach to beamforming. All radar and communications functions have a realization in the architecture, including monopulse, multiple beams (on same or different frequencies), beamspace adaptivity (open or closed loop), and wide-band beam and null forming. It presumes an active antenna aperture but uses TR modules containing no phase shifters. Identical TR modules are used at each of the antenna elements and which require a minimum of digitally controlled components. The architecture is appropriate for arrays on any platform and accommodates sparse and/or conformal designs without the necessity of introducing significant microwave modifications. The approach can use existing state-of-the-art components to affordably implement high performance arrays. Of particular importance is the capability of forming time delay beams from an array without the use of phase shifters. (rh)

On the Design of Optimized Microstrip Radial Line Power Dividers

Abstract: The planar realization of beam forming networks for active antenna systems in satellite communication requires small and high performance power splitters. The microstrip radial line power divider seems to be a suitable structure for this purpose, because, under certain hypothesis, insures an equiphase and equiamplitude power splitting. A design procedure which assures the realization of optimized n- way radial line dividers is proposed and the corresponding design charts are given. Moreover good agreement between experimental and theoretical data from different sources is demonstrated.

Method and device for generating at the same time many antena patterns capable of being controlled at real time

Abstract: PURPOSE: To attain antenna control of a multi-channel antenna by using an antenna consisting of an active microwave radiation device conducting direct radiation and controlling the microwave radiation device with an optical beam forming circuit network. CONSTITUTION: The optical beam forming circuit network is placed between a microwave channel and amplifiers being components of an radiation device, and the optical beam forming circuit network is made up of an antenna control section, a distribution circuit network, a phase shift setting section and an amplitude adjustment section, and the antenna control section calculates for the phase shift setting section and the amplitude adjustment section. Furthermore, the distribution circuit network and the phase shift setting section are configured by using microwave components and optical and electrooptic components, a microwave signal is converted into an optical signal at an input terminal of the beam forming circuit network and the optical signal is converted again into the microwave signal at an output terminal of the beam forming circuit network. Thus, an active antenna whose phase is controlled is used and sends/receives lots of channel is different directions or in the same direction. Thus, lots of antenna axes able to be controlled in real time are generated.

Integrated active antenna module for space station multiple access communication

Abstract: The development of an integrated module applicable for use on the multiple access communication system (MACS) of the space station Freedom is presented. The design is innovative in its ability to merge the three key functions of circuitry, feed network and antenna element into a common unit capable of being mounted on a MACS user platform. The design utilizes a broadside suspended-stripline and balun to feed a balanced antenna element and still allow the active circuitry to be implemented in MMIC (monolithic microwave integrated circuit) or hybrid-MIC (microwave integrated circuit) technology. >

An Advanced Sar For A European Polar Platform

Abstract: The feasibility of a spacebome SAR in C-band using a phased array antenna with active Transmit/Receive modules was demonstrated. An active antenna was selected to enable electronic beam forming while maintaining a good RF/DC power ef6ciency. Further advantages are the avoidance of high power concentrations and high power supplies, and an inherent redundancy in the case of module failures. Orthogonal transmit and receive channels are used, so that horizontally and vertically polarized signals can be transmitted and simultaneously received for polarimetry measurements. This flexible and fully programmable design allows many different modes to be applied. Resolutions from 15 m by 15m (4 looks), swath widths up to 500km, incidence angles between 200 and 500 and polarimetric measurements are possible. Performance requirements can be satisfied within the tight instrument power and mass allocations on the polar platform.

Ku-Band MMIC's for Space-Borne Active Antenna

Abstract: A full set of Ku-Band monolithic integrated circuits designed for a spatial telecommunication active antenna is presented. Low Noise Amplifier, Medium Level Amplifier, Mixer, Attenuator and Digital Phase-Shifter are detailed and the measured results are discussed. This is completed with the design and simulation of Digital and Analog Phase-Shifter whose processing is in progress.

Recent developments of microwave/millimeter-wave integrated active antenna elements

Abstract: Recent developments in solid-state devices and microwave integrated circuits have made it possible to integrate the active devices with planar antennas to form active antennas. This paper presents the recent technology advances at Texas A&M University in active antenna elements using patch, notch and circular ring antennas integrated with Gunn or FET devices.