No abstract

No abstract

The statistical behavior of instrument-limited phased m a y angular measurement errors has been examined with the aid of a specially developed computer program which simulates the effect of 1) beam steering computation accuracy, 2) truncation of beam steering commands, and 3) differential phase errors.The following conclusions were reached for a typical array configuration (1891 elements) : 1 ) A beam split ratio, neglecting bias errors, in excess of 300: 1 can be achieved with only 3-bit phase shifters.2) Truncation of row and steering commands to four 3) Differential phase errors of 10' (one sigma per bit) only increased measurement errors about 20 percent. 4) A steering angle of approximately 2 ms in any direction will cause a 50 percent drop in the autocorrelation of the angular errors. The shape of the -central peak of the two-dimensional autocorrelation funct,ion does not show strong "preferred" correlation directions.5) The phase dithering technique was shown to be completely effective in annihilating all angle measurement error correlations. Results were presented for a typical sector scan, but beam steering is not required to achieve decorrelation. The phase dithering technique is very easy to implement. Frequency and beam dithering were also found to be effective decorrelation techniques, bits reduces the beam split ratio to below 100: 1.nearly as effective as phase dithering, but involve compromises which could make them unacceptable for certain applications.ACKNO~LEDGMENT A number of people were consulted during the course of this work; they provided the authors with valuable help and suggestions. In particular, the assistance of L. J. Cantafio, Radar and Communications Department, and C . Crummer, Information Processing Dipision, both of the Aerospace Corporation, are gratefully acknowledged.We acknowledge helpful discussions with J. Walsh, D. K. Barton, a.nd others at the Raytheon Company, and L. Schwartzman and P. M. Liebma.n and others at the Sperry Gyroscope Company. REFERENCES [l] D. K. Barton and H. R. Ward, Handbook of Radar M m r e m e n t . [2] W. J. Alberaheim, "Reduction of side lobes and pointing errom Englewood Cliffs, N. J.: Prentice Hall, 1969. in phased array radars by randomizing quantuation steps," the Mitre Corp., Bedford, Mass., Rep. TM-3435, AD 402953, Apr. 1963. [3] C. J. Miller, "Minimizing the effects of .phase quantization EbctronicQlly Scanned Array Techniques and Applications, errors in an electronically scanned array," m Proc. 1964 S m p .Abstracf-The absolute gain of wide-beam antennas may be accurately measured using the method described. Both the theoretical and practical aspects of gain calibration on a ground reflection antenna range are presented. The measurement procedures developed were used to calibrate a log-periodic antenna at selected frequencies from 250 to 400 MHz. Measured data at 300 MHz is tabulated and error contributions are analyzed, yielding a measurement accuracy of f0.27 dB with a 95 percent confidence interval.He is now with the Bishop Company, Hun...

the instrumentation for antenna measurements has kept pace to provide increased capability for the measurement of important antenna characteristics. Pattern recorders, receivers, signal sources and positioners have been developed to provide greater dynamic range, improved accuracy of measurements and ease of operator use. Economic considerations and the measurement demands created by new antenna techniques and severe performance measurements. These trends can be catagorized as follows:specifications have brought about some definite new trends in antennaAs antenna technology has advanced over the past twenty years, 1) Automation to reduce time and manpower requirements2) Indoor measurements on compact or near field ranges for increasingly complex measurements;to eliminate real estate requirements and permit 3 ) Greater stability of signal sources and receivers and operation in inclement weather; precision in positioners for verification of severe antenna specifications; mental effects, 4) M e a s u r e m m t s of antennas a s functions of environautomated anteMa measurement system. A l l functions of the ment are automated using programmable instrumentation and softsystem, including positioning, frequency control and data measureware designed specifically for the acquisitions analysis and display listed in Table 1. of antenna data. Tpical measurement performance capability is Figure 1 shows a block diagram of a commercially available The proliferation of m i c r o p r o c e s s o r s i s a l s o having a significant impact on antenna measurement instrumentation, increasing both capability and flexibility. A new generation of instruments and measurement systems will result.The compact range which was originally developed at Georgia Tech, Reference 1. is a system that is now available off the shelf.feet. The basic principle of a compact range is to generate a Measurements can be made indoors on antennas as large as 5 to 6 uniform plane wave, using a very accurately machined section of a paraboloidal reflector.A s shown in Figure 2, serrations on the edges of the reflector reduce effects of edge diffraction. Reference 2 gives plots of amplitude and phase in the active zone to indicate the uniformity of the plane wave illumination. Antenna measurements up to 30 GHz have been made on compact ranges with excellent results.academic and research institutions for many y e a r s (e.g. Ref. 3 and 4). Near field measurement techniques have been investigated by 268