3:1 Bandwidth Dual-Polarized Compact Range Feeds for RCS Measurements

Authors: Jeffrey Fordham, Jacob Kunz, Edwin Barry
Publication: AMTA 2021
Copyright Owner: NSI-MI Technologies

A set of Dual-Polarized Antennas with a 3:1 operating bandwidth has been developed for use in near-field ranges as the probe or range antenna and for use as a Compact Antenna Test Range (CATR) feed. Key development parameters of the antenna are: a wideband impedance match to the coaxial feed line, E and H-plane 1 dB beam widths in excess of 30 degrees, -30 dB on axis cross-polarization, minimum polarization tilt and a phase center that varies over a small region near the aperture. To accomplish these design parameters, a family of range antennas has been developed and previously introduced. Two versions of the antenna have been manufactured and tested for performance. A 2-6 GHz version has been developed using traditional machining techniques and a 6-18 GHz version has been produced using additive manufacturing (3D printing) techniques.

These antennas provide proper illumination of the quiet zone for compact ranges used for antenna measurements as well as radar cross section (RCS) measurements. For RCS measurements, an additional requirement for time-based energy storage performance is considered. Energy storage in the feed can result in a pulse spreading or additional copies of the pulse in time, resulting in poor performances of the target characterization. This effect is called ‘ringdown’.

In this paper, we focus on the RCS ringdown performance of the 6-18 GHz antenna produced using additive manufacturing. The measured performance of the antenna will be presented and discussed. Finally, the applicability of the antenna as a CATR feed for RCS measurements will be discussed.

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A Dual-Band High Power PNF Range with Interleaved T/R and Pulse Synchronization

Authors: Bruce Williams, Eddy Park, Ryan Cutshall, Justin Dobbins, Jacob Freking
Publication: AMTA 2021
Copyright Owner: NSI-MI Technologies

Modern antenna range design is often a careful balance of several competing objectives. Some of these design parameters are defined by the antenna under test (AUT), i.e. millimeter wave (Ka-band) test frequencies, frequencyconverting and non-converting AUTs, high-power radiation requirements, pulsed RF requirements, and interleaved transmit and receive (T/R) requirements. Other parameters are driven by the AUT’s application, like requirements for providing accurate pattern, gain, EIRP, and G/T predictions based on the measurement data. Yet other parameters are driven by cost and risk considerations, like the need for all-at-once acquisitions incorporating multi-frequency, multi-port, dual-pol, and multistate measurements. Also included in the “cost and risk” category is the need to collect all these measurements in the least amount of time.

A planar near-field antenna range designed with all these parameters in mind has been realized and is currently operational. This 1 m x 1 m planar near-field range incorporates several novel electrical and mechanical features, and we illustrate these features in terms of their driving requirements and their limitations. Included in our discussion: modular T/R range “front ends,” reconfigurable probe networks, absorber cooling strategies, near-field probes for high-power measurements, interleaved single-port transmit and multi-port receive measurements, and distributed pulse mode range architectures.

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Holographic PNF Filtering Based On Known Volumetric AUT Bounds

Authors: Scott T. McBride, Pieter N. Betjes
Publication: AMTA 2021
Copyright Owner: NSI-MI Technologies

There has been much discussion in the last few decades regarding redundancy in conventional near-field sampling, and that redundancy is most pronounced in the planar geometry. There has also been much discussion regarding modal filtering of near-field data to attenuate the effects of stray signals. Both discussions revolve around the limited local spatial bandwidth that can be produced at each probe location when the antenna under test’s (AUT’s) radiating sources are all contained within a known geometric boundary.

This paper discusses a novel filtering technique that exploits the inherent sampling redundancy in conventional planar near-field acquisitions. The filtering is based solely on the known location and shape in the scanner’s coordinate system of a closed 3D boundary around the radiators of interest. The paper describes the algorithm and presents results from both measured and synthesized input. The new filter is also compared to other available filters in terms of speed, attenuation of stray signals, and preservation of AUT signals.

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Implementation and Validation of a Satellite Payload Test Suite for Planar Near Field Test Ranges

Authors: Edwin A. Barry, Pieter N. Betjes, Daniël Janse van Rensburg, Patrick Pelland
Publication: AMTA 2021
Copyright Owner: NSI-MI Technologies

Performing End-to-End testing of satellite payloads on planar near-field test ranges can greatly reduce the cost and real estate required compared to conventional far-field systems. Previous work has shown that this is theoretically possible, with limited test data showing viability. This paper provides additional validation of the technique’s ability to characterize various system-level parameters, including the equivalent isotropically radiated power , group delay, saturating flux density, system noise temperature and the gain vs. frequency response. Details of a new software satellite payload test suite is presented, along with the accompanying simulated payload that was developed for system verification and facility-to-facility comparison.

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Numerical Study of the Effects of Absorber Permittivity Variations on Quiet Zone Illumination of Tapered Chambers

Author: Vince Rodriguez
Publication: AMTA 2021
Copyright Owner: NSI-MI Technologies

Tapered chambers use the reflections from the surfaces adjacent to the range antenna to illuminate the quiet zone (QZ). Polyurethane substrate is the preferred and most widely used radio frequency (RF) absorber in these chambers, due to its ability to be cut into complex shapes to conform to the tapered sections. Unfortunately, this type of absorber always presents slight differences in permittivity related to the manufacturing process.

To analyze the effects of the permittivity of the lossy foam on the QZ illumination in a tapered chamber, a series of numerical experiments using a full wave analysis technique are executed. The results are mainly obtained for frequencies under 1 GHz. The upper frequency of the simulation is limited by the electrical size of the problem and by the available information on the material permittivity. However, frequencies below 1 GHz is where the tapered chambers are superior to other methods for indoor antenna measurements.

Magnitude and phase are recorded over a 1.82m diameter spherical QZ to show the effects of the different absorber on the illumination. Results show that a variation on the absorber around the range antenna will deviate the illumination and skew the amplitude taper across the QZ. The amplitude distribution peak can be shifted by as much as 3.5 degrees from boresight. The effect on the phase taper is smaller with a negligible change in phase.

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Near-Field Test Challenges of High Frequency Digital Phased Array Antennas

Author: Daniël Janse van Rensburg
Publication: ISAP 2020
Copyright Owner: NSI-MI Technologies

A hemispherical near-field test system that allows for the AUT to remain stationary is described. Typical structural test data is presented to illustrate the applicability of this type of test system for high frequency (mmWave) cases. Digital data rates for a typical AUT are also presented and it is shown to become restrictive in terms of the maximum throughput achievable during testing.

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