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This paper examines the development tests performed at Rockwell International in Anaheim, CA on VHF meandering monopole and dipole antennas which are part of the Global Positioning System satellite. The development tests included numerous impedance measurements of individual antennas configured first in their operational positions on a full-scale mockup of the GPS satellite spacecraft and second while mounted on an indoor ground plane. The initial measurements of antennas positioned on the mockup required the mockup to be located in an exceptionally large, obstruction-free environment because of the low operating frequencies (large wavelengths) of the antennas under test, and in our case a suitable environment was an empty parking lot approximately one-half mile away from the necessary test equipment. This situation necessitated frequent transportation of fragile test equipment to and from the test site which was both impractical and time-consuming. To avoid this situation when production units are to be tested later this year, a ten-foot diameter ground plane was constructed in order to perform the antenna parameter measurements indoors, which presents a very reflective environment. To minimize and theoretically eliminate the effects of these reflections on our measurements, the time-domain gating (time filter) feature of the HP 8510 Network Analyzer was utilized at the indoor test site. The gating function removes any time-domain responses outside of the gate span, the span in this case being the radius of the ground plane. When the time-domain response is Fourier-transformed back to the frequency domain, the effect of the unwanted (gated) responses is eliminated in impedance measurements. While the gated, ground plane parameter measurements will not yield the same values as those measured on the mockup, they can be used to establish an impedance, VSWR, or return loss standard from a known “good” antenna against which production antennas can be compared to determine electrical failures.
Measurement of complex permittivity (er) and permeability (µr), both vector quantities of absorptive materials, has gained increasing importance with expanding use of the RF and microwave spectrum, particularly in communications and electromagnetic countermeasure applications. In addition, the network analyzer has seen increasing use in non-destructive measurements to determine the chemical composition of a sample dielectric material. The method described here is suited for the measurement of complex permittivity and permeability of ansorptive materials. These measurements have been made for years using numerous methods. A conventional technique involves a two-step process using a slotted line or network analyzer. First, the sample is backed up by a short circuit and the input impedance is measured. Next, the short circuit is moved ¼ ? from the sample to simulate an open circuit termination (where ? is the incident signal wavelength), and a second measurement is made. The results of these two measurements are used to solve simultaneous equations for er and µr. This procedure is repeated for each frequency of interest. Uncertainties in the measurement include test set-up frequency response, mismatch, and directivity errors, as well as the uncertainty in the physical position of the short circuit.
The receiver discussed in this paper was developed for Rome Air Development Center (RADC) under Contract F30602-81-C-0261 for testing Electronic Counter Measure (ECM) antenna systems at the Stockbridge Test Annex. This receiver, under computer control, can record ECM responses to threat radar stimuli. The ECM testing required the receiver to have a 400 kHz frequency multiplex rate in the 2-18 GHz frequency band and a 20 MHz amplitude sampling rate capability. An 80 dB interference rejection provides an accurate recording of low level signals in a multiple emitter environment. Although designed for ECM antenna testing, this receiver can have multiple uses for general antenna tests.
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.
Pulsed systems have been used for many years to eliminate unwanted clutter in RCS measurements, but have not been used much for antenna measurements, even though similar clutter problems are common to both. There are many reasons for this, such as cost, increased bandwidth requirements, lack of necessary hardware, etc. However, with the development of modern pin diode switches, one can construct a low cost pulsed measurement system that simply adds to existing CW equipment. Using the system design presented in this paper, one can eliminate unwanted clutter from antenna measurements simply by adjusting the transmit and receive pulse widths and the delay between them. For example, it can be used to range gate out the ground bounce for outdoor measurements or the backwall for an indoor facility so that one can accurately measure the backlobe of a high gain antenna. The pulsed system is presented along with several measured examples of its use.
Increased interest in antenna development at millimeter-wave frequencies has contributed to a growing need for signal sources operating to 40 GHz and beyond. The desirable features of such sources include broad frequency coverage; accuracy, stability, and resolution afforded by frequency synthesis; the ability to switch frequencies rapidly; and physical attributes which lend themselves to efficient use in the automated antenna range environment. This paper describes how a recently developed synthesizer meets these requirements. Design approaches used, engineering trade-offs considered, and applications information are presented.
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.
Millimeter wave antenna measurements are hampered by a lack of cost effective automated test equipment and the necessity of using unwieldy waveguide set-ups. This paper describes some practical considerations in using readily available test equipment to perform accurate, repeatable antenna measurements. Experimental results of gain, polarization and sidelobe level measurements will be discussed and compared with calculated results.
Paper not available for presentation.
This paper describes a digitally controlled receiver-recorder capable of time division multiplexing in the frequency domain at a 400 KHz rate and in the amplitude domain at a 20 MHz rate. Good sensitivity and interference rejection are other features of this receiver which operates over the 2-18 GHz band. It is utilized to obtain a measure of antennas performance as impacted by air frames upon which the antenna(s) are mounted.
The design concept for outdoor antenna ranges operated at frequency 50 MHz is discussed. The antenna range is designed for test of VHF antennas mounted on a full-scale satellite mockup. Due to the large size of test objects, a tradeoff between cost and test accuracy among carious range configurations is addressed. Due to near-omni directional characteristics of test antennas, the multipath interference may be severe. The interference ground reflection, surface wave and multiple scattering are quantified and evaluated.
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
The fast fourier transform capabilities of the Hewlett-Packard 8510 Network Analyzer provide the basis for an RCS measurement system covering the 50 MHz to 26 GHz frequency range. When used in the broadband mode, fine range resolution is achieved. Vector subtraction and gating capabilities permit the acquisition of accurate data in the presence of strong range reflections. Combining this instrument with a high speed data collection and analysis system yields a powerful RCS measurement capability.
This paper describes the relationship of probe polarization correction to probe-pattern corrected and non-probe-pattern-corrected spherical near-field measurements. A method for reducing three-antenna polarization data to a form useful for polarization correction is presented. The results of three-antenna measurements and the effects of polarization correction on spherical near-field measurements are presented.
This paper describes a new planar near-field measurement technique in which near-field data is collected in a hexagonal rather than a rectangular format. It is shown that the hexagonal method is more efficient than the rectangular technique in that a lower sampling density is required and the hexagonally shaped measurement surface is more compatible with most antenna apertures than the conventional rectangular measurement surface.
A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.
This paper describes a horizontal, cylindrical surface, near-field measurement facility which was designed and constructed in 1984 and is used for the determination of far field patterns from near field measurement of UHF television transmitting antennas. The facility is also used in antenna production as a diagnostic and alignment tool.
The near-field antenna testing technique is now an established testing approach. It is based on the work done over a twenty-year period by the National Bureau of Standards (Boulder, Colorado), The Georgia Institute of Technology and others. The near-field technique is used for large aperture, high frequency antennas where the antenna to probe separation necessary to test in the far-field of the antenna is prohibitively large.
Paper not available for presentation.
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.