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The AN/SPS-48E antenna is a three dimensional air search antenna that is currently installed on 27 US ships. Currently the 48E antenna is removed from the ship after five to seven years to be overhauled at NSWC Crane Division. The new San Antonio Class ships (LPD 17 – 25) have a new enclosed mast design, the Advanced Electromagnetic Mast/Sensor (AEM/S), in which the 48E antenna and others are installed inside the enclosed mast. The cost of removing the enclosed mast led to the decision that the 48E antenna systems (antennas and pedestals) will not be removed for overhaul and maintenance on these ships as is currently done for all other installations. As a result, new fixtures and procedures need to be developed to allow maintenance inside of the mast. The most challenging of the new fixtures is a near-field scanner, which will be used to re-tune the antenna and characterize the RF performance parameters. This paper discusses the design and development effort currently underway for this Enclosed Mast Antenna Calibration System (EMACS), most notably the mechanical design constraints placed on the scanner by the enclosed mast regarding equipment movement, installation, alignment and testing.
The groundwave correction method of measuring the gain of a vertical antenna over a lossy ground plane is an accepted means of performing a gain measurement without the need for a standard reference antenna. However, on antenna ranges where the ground plane is not uniform, this approach may not yield accurate results over certain portions of the test band due to discontinuities in the ground. This paper shall present a method for using surface impedance methods to predict the performance of an outdoor antenna test range that has a non-uniform ground. Comparison with measured data shall also be presented over the commercial HF and VHF bands.
Large ground terminal antennas for high data rate applications provide challenges to demonstrate compliance with their specified performance. Such antennas have narrow beamwidths and require evaluation of their antenna tracking performance. Terminal testing is normally performed in vendor acceptance tests that demonstrate the antenna design compliance, site installation tests that evaluate the operational compliance of the “as installed” antenna, and operational testing performed for maintenance and diagnostic purposes. The advantages and limitations of three distinct measurement techniques, radio source, satellite signals of opportunity, and boresight tower measurements are discussed.
Position uncertainty in antenna measurements is unavoidable. This is due in part to mechanical inaccuracy in the fixturing and positioning equipment. For many classes of antenna, there is also not an obvious choice of reference point, due to lack of a well-defined phase center. It has been shown [1] that a UWB transfer function measurement, taken either in the time or frequency domain, is highly sensitive indicator of antenna displacement. Extraction of the linear phase from the transfer function data results in a uniquely defined distance for any given pair of antennas in a given orientation. When a two- or three-antenna measurement using identical antennas is performed, the result is a unique reference plane for the antenna. Unlike the phase center, is not tied to a particular frequency. Here, using frequency domain measurements of monopoles, ridged horns, and an end-fed biconical antenna, we show that distances can be extracted with a high degree of repeatability. Resolution on the order of 1 part in 5,000 can be obtained in a 4-meter chamber with measurements extending to 20 GHz. Thus, variation in the extracted distance should be a highly sensitive indicator of positional inaccuracy.
In antenna measurements, the orientation of the antenna under test (AUT) is very important. The orientation here refers to the antenna placement in a plane perpendicular to the incident wavefront. For a linear polarized antenna, the antenna should be oriented parallel to the co-polarized component of the incident fields. A small error in the orientation can lead to a drop in the measured gain and an increase in the measured cross-polarization level. In the case of a circularly polarized antenna, it is not obvious how the antenna should be oriented. If the quiet zone fields (incident wavefront) have no cross-polarized component, then the orientation does not affect the measured data. However, when the quiet zone fields have a cross-polarized component, which is true for almost all test ranges, the measured gain and cross-polarized level can vary significantly with the antenna orientation. In this paper, the measured data is used to show the effects of antenna orientation on a circularly polarized antenna. The reason for the variations in the measured data with antenna orientation is discussed. A simple method to improve the measurement accuracy is presented.
In the early 1990's, Georgia Tech Research Institute (GTRI) was able to acquire an unclassified phased-array antenna from the former Soviet Union. Since that time, GTRI personnel have analyzed the antenna for design features that enabled the production of low-cost phased-array antennas. Antenna pattern data collected on the GTRI planar near-field range of a working and errored antenna will be presented. Also, modeled antenna pattern data will be presented as a comparison to show the particular effects of the low-cost design versus an ideal antenna. Finally, the original control mechanism of the phased-array antenna will be analyzed and compared with a modern control mechanism developed by GTRI researchers. Control data for the original and new control systems was captured with a logic analyzer and will be presented for comparison.
The time delay behavior of antennas is of high importance for high accuracy localization and navigation systems. Next to the investigation of the receiving antennas, the transmitting antennas are of substantial interest, too. In the application envisioned these antennas are small dipoles integrated in a battery powered miniaturized transmitter system. The method described in this paper is based on the measurement of the time difference of arrival of a broadband signal in a synchronized setup. This setup consists of the transmitter under test which transmits a bursted sequence of the localisation waveform. The receiving side of the measurement system consists of two antennas, where one works as a reference antenna (with fixed position in relation to the transmitter) and the other works as “classical” probe antenna. Two synchronized tuners and data acquisition systems determine the time difference of arrival of the signal. Detailed measurements of different transmitters have been performed in the 2.45 GHz ISM band and will be presented.
The UWB radar operates simultaneously over large bandwidth and the antenna parameters must refer to simultaneous performance over the whole of the bandwidth. Conventional frequency domain (FD) parameters like pattern, gain, etc. are not adequate for UWB antenna. This paper describes an UWB radar antenna planar near field (PNF) measurement system under construction to get the impulse response or transient characteristic of the UWB antenna. Unlike the conventional antenna or RCS time domain test system, the UWB radar signal instead of the carrier-free short time pulse was used to excite the antenna that can avoid the decrease of the dynamic range and satisfy the needs of SAR and the other UWB radar antennas measurement. In order to demonstrate the data analysis program, FDTD simulation software was used to calculate the E-field of M×N points in a fictitious plane at different times just like the actual oscilloscope’s sampling signals in the time domain planar near field (TDPNF) measurement. The calculated results can be considered the actual oscilloscope’s sampling output signals. Through non-direct frequency domain near field to far field transform and direct time domain near field to far field transform, we get the almost same radiation patterns comparing to the FD measurements and software simulation results. At last, varied time windows were used to remove the influences of the non-ideal measurement environment.
This paper presents an overview of work carried out in developing the probe-corrected, poly-planar near-field antenna measurement technique [1, 2, 3, 4, 5]. The poly-planar method essentially entails a very general technique for deriving asymptotic far-field antenna patterns from near-field measurements taken over faceted surfaces. The probe-corrected, poly-planar near-field to far-field transformation, consisting of an innovative hybrid physical optics (PO) [6] plane wave spectrum (PWS) [7] formulation, is summarised, and the importance of correctly reconstructing the normal electric field component for each of the discrete partial scans to the success of this process is highlighted. As an illustration, in this paper the poly-planar technique is deployed to provide coverage over the entire far-field sphere by utilising a small planar facility to acquire two orthogonal tangential near electric field components over the surface of a conceptual cube centred about the antenna under test (AUT). The success of the poly-planar technique is demonstrated through numerical simulation and experimental measurement. A discussion into the limitations of the partial scan technique is also presented.
Hemispherical Near-Field (NF) antenna measurement technique has been applied for automotive antenna testing within a chamber dedicated to EMC tests. An existing turntable was used for azimuth rotation of a vehicle and a new portable 90°arch was added for elevation scanning of the radiated NF of the Device Under Test (DUT - vehicle with the antenna). Two antenna types were tested during chamber commissioning, one for GPS and another for XM satellite radio applications at frequencies 1.57 and 2.33 GHz respectively. Test results have shown that the EMC chamber can be successfully used for automotive antenna measurements as well, with accuracies acceptable for automotive applications. For higher operating frequencies, the EMC absorbers must be changed to less reflective material. In the paper, the measurement system is described, and the test results are presented, as well as some considerations on far-field pattern restoration based on measured hemispherical NF data.
Hollow metallic aluminum spheres have been used for years for calibrating RCS measurement systems both indoors and outdoors. While many previous papers have identified the RCS calibration shortfalls associated with spheres [1,2], most of these papers have concentrated on indoor RCS measurement systems, where there exist a number of accurate calibration alternatives to spheres, including the so-called "squat cylinder" [3,4]. For outdoor free space RCS measurement systems, especially those designed to measure dynamically moving or changing targets, (i.e. the NASA Shuttle C-Band Debris Radar), calibration is a much tougher problem. Frequently, spheres are used to calibrate such systems, by releasing and tracking a sphere attached to a lighter-than-air balloon, or by tethering a sphere to a lighter-than -air balloon and allowing it to float through a fixed radar beam. Recently, the Air Force Research Laboratory Mobile Diagnostic Laboratory (MDL) had the opportunity to measure the clutter and uncertainty associated with balloon tethered Sphere RCS calibrations. Two spheres were measured suspended by various string types and a line under an 8 ft. diameter tethered Helium filled balloon. We will provide design guidance, signal processing techniques and measurement uncertainty to help minimize the clutter and error induced by balloon borne RCS calibration spheres.
Abstract. We present new RCS measurements from an 8-foot square flat plate for frequencies from 0.15 to 5.5 GHz. Guided by the theory, we study the peak RCS at normal incidence, the principal plane pattern, and the 3-dB beam-width in detail. The broadside echo from the plate is found to be extremely narrow at higher frequencies. From the errors, we estimate that the wave-field experienced by the plate is reasonably uniform to within +0.3 dB, over a wide dynamic range of 60 dB.
Three methods are described to characterize ground antennas in frequency bands where satellite beacons exist. This measurement method is useful when the antenna to be tested cannot be easily measured using conventional general purpose facilities or radio source measurement techniques. The measurement methods are described, and the factors that result in measurement uncertainties are discussed. Key Words: Antenna Measurements, Gain Calibration, Ground Terminals
The calibration of a prototype system to monitor the on-orbit performance of heritage and modernized GPS satellites is described. While the monitor can measure other GPS parameters of interest, the calibration to accurately determine the received signal levels is described here. The calibration determines the monitor’s receive antenna gain and relates the received power at the antenna terminals to the indicated output of the monitor’s receiver. Key Words: System Calibration, Error Budgets, Satellite Measurement
This paper presents results of planar near-field measurements at 16, 35 and 94 GHz using probe position correction algorithms. The algorithms correct for position errors of the probe near the scan plane. The probe’s actual position is measured using a laser tracker integrated into the planar-near-field scanning system at NIST. The laser tracker simultaneously obtains probe-position information at each point where amplitude and phase data are acquired during planar near-field antenna measurements.
This article will focus on some of the Modern high-performance antenna measurement technologies and techniques incorporated inranges demand enhanced performance from the ORBIT/FR’s new positioner controllers in orderpositioning systems, for both static and dynamic to achieve the positioning accuracies andaspects of the required test scenario. Accurate performance required in current antenna static and dynamic positioning, as well as measurement systems.
A technique is proposed to measure the propagation constant of surface waves on a periodic dipole array using a waveguide simulator. Due to the slow wave characteristic of surface waves, it is necessary to present an evanescent waveguide mode to the plane containing the elements. Two techniques for sensing the element currents are outlined.
This paper describes the use of a two-dimensional chirp z-transform (2D-CZT) to efficiently concentrate a large number of sample points in a single portion of the far zone without interpolation. This work presents the equivalence of transforms calculated from measured near-field data using both the 2D-CZT and 2D-fast Fourier transform (FFT). The paper also shows that the 2D-CZT is computationally more efficient than a zero-padded FFT when one requires a high resolution over a small area of the pattern.
ABSTRACT An iterative probe correction technique for spherical near-field antenna measurements is examined. This technique has previously been shown to be ideally-suited for non-ideal first-order probes. In this paper its performance for other probes is examined.
This paper will discuss the development of a VHF/UHF near field test range for the case where there are reflections from a realistic ground surface. We will show the results of a direct computation algorithm where a far field pattern is computed using plane wave synthesis. The performance of a C++ program that implements this algorithm will be discussed.