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A 400 element phased array antenna has been constructed at the GEC-Marconi Research Centre. Each radiating element is fed from its own phase shifter. The radiation patterns of this array have been measured using a recently constructed Cylindrical Near Field Test Facility. The radiation pattern is obtained on a two dimensional grid and contains both amplitude and phase information. It is therefore possible to transform these data back to the array aperture to obtain the array excitation amplitudes and phases. The spatial resolution obtained in the aperture is a function of the angular coverage of the radiation pattern used. The effect of deliberately introduced phase errors on the calculated aperture data is shown.
Separation of the Antenna from the remainder of the system is not possible with a fully active phased array such as MESAR, since each array element has an associated electronic module which contains amplifiers (separate for transmit and receive), phase shifters, switches, etc. The "antenna" is therefore not reciprocal and it also requires a control system. As a result, the system used for pattern acquisition is considerably more complex than that used for testing conventional antennas and some of the traditional parameters are either not obtainable or require redefining. The methods used for testing the MESAR antenna are given together with details of the range equipment involved.
A flexible near-field antenna test-facility is presented. This system gathers all that is necessary to design, to debug and to validate the high performance antennas which are made by ESD. ARAMIS has been operational since January 1988. Its applications are: - Near-field measurements (for diagrams): * planar, * cylindrical. - High speed field mapping (for default analysis): * planar radiating surface, * cylindrical radiating surface. - Generation of element excitation (active phased array testing): * planar antennas, * cylindrical antennas. - Direct far-field measurements (probes, small antennas), - Circuit measurement (S parameter). The facility features a specially designed scanner. Thanks to its six degrees of freedom, this positionner allows the differents types of measurements to be made. The instrumentation is based upon the HP 8510 B network analyzer. A single computer performs the measurements, transforms the data and presents the graphics (linear diagrams, color maps, three-dimensional colored projections). In order to grant a high scan speed, the system uses the FAST CW mode of the HP 8510 B. An external trigger is provided during the motion process of the probe. A rate of 500 measurements/sec. has been proved. This on-the-fly process is clearly depicted. Experimental results are presented which include: - Low sidelobe (-38 dB) antenna diagrams. - Default analysis through: * Amplitude mapping (leakage short-circuit in a microstrip antenna). * Phase mapping (out-of band comparison between two radiating element technologies). * Measurement of excitation laws. * 3-D transformation. - Simultaneous on-the-fly acquisition of up to three antenna outputs.
This paper describes techniques for coherently suppressing multipath and other error sources in planar near-field measurements. Of special interest is a simple, yet effective technique of suppressing axial multipath and mutual coupling between the nearfield probe and an antenna. This is of particular value in the testing of low sidelobe antennas. Traditionally, self comparison tests with different separations between the probe and the antenna under test are used to identify the magnitude of multipath errors. What is not generally realized is that these tests can be used to produce a coherent estimate of the induced error, which can often be suppressed. A series of tests was performed with a small X-band phased array antenna, resulting in a reduction of the sidelobe noise background from a 25 dB level to better than 50 dB.
This paper describes the measurement requirements of a phased array comprised of three sub-arrays and the test system built to measure it. To evaluate the performance of the array, it is necessary to measure the radiation patterns of all three outputs at various azimuth scan angles. Because the relative phase and amplitude between the elements is an important performance parameter, if data is to be taken "on the fly", then high speed measurements are required. In addition, when taking elevation patterns through the peak of the beam, which has been scanned in azimuth, the polarization of the antenna under test changes with elevation angle. Consequently, since the patterns are to be measured to matched polarization, the transmit antenna polarization must be varied as a function of elevation angle. To complicate matters, this is a non-linear relationship. The test system architecture and resultant performance capabilities are presented.
Near-field testing of a very low sidelobe, L-band, 32-element, linear phased array antenna was conducted. The purpose was to evaluate testing and calibration techniques which may be applicable to a much larger, space borne phased array antenna. Very low sidelobe performance in a relatively small array was achieved by use of high precision transmit/receive modules. These modules employ 12-bit voltage controlled attenuators and phase shifters operating at an intermediate frequency (IF) rather than at RF. Three array calibration techniques are discussed. One technique calibrates the array by means of a movable near-field probe. Another method is based on mutual coupling measurements. The last technique uses a fixed near-field source. The first two calibration methods yield substantially the same results. Module insertion attenuation and phase can be set to 0.02 dB and 0.2 degrees, respectively. Near-field measurement derived antenna patterns were used to demonstrate better than -20 dBi sidelobe performance for the phased array. Application of increasing Taylor array tapers showed the limitations of the measurement systems to be below the -35 dBi sidelobe level. The effects of array ground plane distortion and other array degradations are illustrated.
Electronic scanning phased arrays are being used more and more in radar, EW and communication systems. The development of such an array can be divided into two separate parts: development of the radiating elements and development of the beam forming network. The development of these two parts is often done in parallel and the radiating elements should always be developed taking into consideration the whole array and not only single elements.
An investigation of the use of array mutual coupling measurements, to evaluate displaced phase center antenna (DPCA) performance, is made. The details of a subscale space based radar (SBR) DPCA phased array and the array mutual coupling technique are discussed. DPCA results are quantified experimentally under a number of test conditions. It is shown that the test array beam decorrelation computed from array mutual coupling data, is in good agreement with both theoretical predictions, planar near field measurements and direct far field measurements.
This paper describes a receiver and exciter built by Texas Instruments for automated testing of electronic-scan antennas. The equipment is suitable for both near-field and far-field testing, and is programmable through a General-Purpose Interface Bus (GPIB) conforming to IEEE Standard 488. A two-channel design is described, but the technology is equally applicable to receivers from one to three (or more) channels. The receiver outputs are digitized as 10-bit I and Q (In-phase and Quadrature) components.
End-to-end testing of electronic warfare (EW) equipment at the organizational or flight lines level is accomplished by use of an antenna coupler which is placed over the EW system antenna. The coupler is used to inject a stimulus signal simulating a signal emanating from a distant radar, and to receive and detect the EW system response (EW transmit) signal. The coupler is used to determine the EW receiver sensitivity over a swept frequency coverage and the EW transmit gain and effective radiated power (ERP) versus frequency characteristics, as well as to determine the operating integrity of the EW antenna and transmission lines.
An 80 element linear phased array antenna was measured in the nearfield. The insertion phase and amplitude for each element were measured while the 8-bit ferrite phase shifters were individually stepped through their degrees for freedom.
Acceptance testing of the AN/SYR-1 Electronically Steered Phased Array (ESPA) antenna in a Compact Antenna Range is described. Unique to the testing described are (1) generation of the beam steering commands to the phased array as well as control of the positioner and recording equipment by a single desktop computer and (2) the recording of S-band antenna patterns after down-conversion to a 300 MHz IF. Modifications and interfaces to the standard Compact Antenna Range equipment for testing of the multi-element planar phased array are described.
The AEGIS AN/SPY-1A antenna system is an S-band monopulse phased array system designed for monopulse operation. Its high performance and manifold capabilities have placed stringent demands on the test system used in its evaluation. This paper will describe the AEGIS Near-Field Antenna Test Set (ANFATS) currently being implemented for acceptance testing production models of the antenna, a system designed for operation by manufacturing test personnel