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APPROACH TO VHF GAIN MEASUREMENTS OVER SEAWATER D:\Documents and Settings\david.tonn\My Documents\Fishers Island\aerial.JPGpool3 Timothy Bolton, Dr. Stephen M. Davis, Paul Medeiros, Paul M. Mileski, D:\Documents and Settings\timothy.bolton\Desktop\Fishers Island Measurement Procedures\VHF Gain\VHF Whipcone Measurements\Pictures3\DSC00037.JPGGain at two hgtsDr. David A. Tonn, Isaac A. Wheeler D:\Documents and Settings\timothy.bolton\Desktop\Fishers Island Measurement Procedures\VHF Gain\VHF Whipcone Measurements\Pictures3\DSC00002.JPGD:\Documents and Settings\timothy.bolton\Desktop\Fishers Island Measurement Procedures\VHF Gain\VHF Whipcone Measurements\Pictures3\DSC00025.JPG-1 0 1 2 3 4 5 6 7 30 35 40 45 50 55 60 Realized Gain (dBi) Frequency (MHz) Specified Gain Measured Gain G = -106.1 + 10.594*F - 0.38865*F^2 + 6.2584E-3*F^3 - 3.6863E-5*F^4 -1 0
Tapered chambers are particularly suitable for antenna measurement at low frequencies and can provide quiet zones of up to 1.4m in a 12m range. A tapered chamber can also be used for measurement of antennas at high frequency. However, with increasing frequency, the quiet zone size reduces rapidly. For example, at a 12m distance from the feed to the turn-table, the quiet zone at 8GHz is reduced to 45cm. One possible solution to extend the quiet zone at high frequency is to use a large dielectric lens to improve the phase distribution of the field. A lightweight, broadband 2m lens was developed by Matsing Pte Ltd for this purpose. The parameters of the lens were specially customized for the tapered chamber built by ETS-Lindgren for the National University of Singapore in 2010. The lens has a focal length of 10m and weighs just 35kg. The performance of the tapered chamber with the RF lens is presented.
This paper describes the measurement campaigns carried out at P-band (435 MHz) for selection of optimum on-ground verification approach for a large deployable reflector antenna (LDA). The feed array of the LDA was measured in several configurations with spherical, cylindrical, and planar near-field techniques at near-field facilities in Denmark and in the Netherlands. The measured results for the feed array were then used in calculation of the radiation pattern and gain of the entire LDA. The primary goals for the campaigns were to obtain realistic measurement uncertainty estimates and to investigate possible problems related to characterization of the feed array at P-band. The measurement results obtained in the campaigns are compared and discussed.
A wideband scalable dual-polarized probe designed by the Electromagnetic Systems group at the Technical University of Denmark is presented. The design was scaled and two probes were manufactured for the frequency bands 1-3 GHz and 0.4-1.2 GHz. The results of the acceptance tests of the 0.4-1.2 GHz probe are briefly discussed. Since these probes represent so-called higher-order antennas, applicability of the recently developed higher-order probe correction technique [3] for these probes was investigated. Extensive tests were carried out for two representative antennas under test using the manufactured probes; the results of these tests are presented and discussed in details.
NOVEL PHASED ARRAY SCANNING EMPLOYING A SINGLE FEED WITHOUT USING INDIVIDUAL PHASE SHIFTERS Dipole Elements Reconfigurable transmission line Signal Transmission_line.bmpField mostly in air, so low ........ Field mostly in dielectric, so high ........ .... .... Nicholas K. Host, Chi-Chih Chen, and John L. Volakis Varied t .375mm Air Gap, g er=25
In 2008 and 2011 we proposed at AMTA a method of radar imagery based on Fast Fourier Transform. We demonstrated then that this method was faced with interpolation problematic (which could be almost solved) and that the obtained radar image had a poor resolution imposed by the low bandwidth used during the measurement. We saw then that because of this resolution issue, it was impossible to distinguish two scatterers when they were too close. This article presents methods allowing to improve the resolution of radar image without increasing the bandwidth of measurement but using 1D super-resolution techniques adapted to 2D or 3D measurements. More precisely, this article proposes first to explain the principle of three 1D super-resolution methods: the Capon method, the MUSIC (Multiple Signal Classification) method and the ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) method. This principle understood, these methods will be then adapted to 2D or 3D measurements in order to be used to calculate high resolution radar images. Eventually, a true target will be used in order to compare the different radar images obtained from the different super-resolution techniques.
Radar Cross Section (RCS) and Antenna measurement ranges share many common features and are often used for both purposes. Calibration of these dual-purpose ranges is typically done using the substitution method for both RCS and antenna testing, but with separate RCS and antenna standards. RCS standards are typically based on a geometric shape having a well known theoretical value – and corresponding small uncertainty. By contrast, antenna standards typically must be “calibrated” in a separate antenna calibration system to be used as a gain standard, often yielding higher uncertainties. This paper presents an efficient method for transferring an RCS measurement calibration to an antenna measurement range configuration, allowing a range to be used for both purposes with a single calibration. Insight into the best ways to re-configure the instrumentation between RCS and antenna testing is included. Validation measurements from a compact range are included along with an uncertainty analysis of the method.
Many modern antennas are incorporating LNAs into the aperture to maximize system receive performance. G/T (Gain over Temperature) quantifies the performance of these antenna systems. Historically, G/T measurements needed knowledge of absolute effective temperature of multiple noise sources, which is not practical in an anechoic chamber. A Y-factor method is presented which uses a reference antenna system with a known G/T to determine the G/T of the Antenna Under Test (AUT). This paper will review G/T, describe the measurement process, cover calibration of the reference antenna system and discuss error sources and their mitigation.
The speed of spherical near-field scanning is increased significantly when measurements are not restricted to standard measurement locations, i.e., the locations that are equidistant in theta and in phi. Measurement positions can be chosen so that mechanical positioners perform scans with a continuous motion; this will decrease the time it takes to acquire data for near-field measurements. The issue then becomes transforming the data acquired with non-uniform spacing. This paper describes the development of a spherical near-field to far-field transform that can efficiently process data acquired on a non-uniform grid.
A dielectric rod feed with a special radiation pattern of a tabletop form used for the compact range reflector is developed and analyzed. Application of this feed increases the size of the compact range quiet zone generated by the reflector. The feed consists of the dielectric rod made of polystyrene; the rod is inserted into the circular waveguide with a corrugated flange. The waveguide is excited by the H11-mode. The rod is covered by the textolite biconical bushing and has a fluoroplastic insert in the vicinity of the bushing. Mathematical modeling was used to obtain the parameters of the feed for the optimal tabletop form of the radiation pattern. The problem of the electromagnetic radiation was solved for metal-dielectric bodies of rotation by method of integral equations with further solving of the problem of the synthesis for feed parameters. The dielectric rod feed was fabricated for the X-frequency range. Feed amplitude and phase patterns were measured in the frequency range 8.2-12.5 GHz. Presented results of mathematical modeling and measurements for X-range radiation patterns correlate well. It is shown that this feed increases by 20-25% the quiet zone of the compact range with reflector in the form of nonsymmetrical cutting of the paraboloid of revolution 5.0 . 4.5 m in size in the frequency range 8.5-10.0 GHz as compared to a conical horn feed.
The RF electromagnetic spectrum, extending from 2 MHz to 94 GHz, can be considered an evolving, but finite resource. This span of spectrum is used for a multitude of purposes including communications, radio and television broadcasting, radio navigation, sensing and radar. The portion of the spectrum from 2-4 GHz has become particularly problematical due to the influx of wireless systems such as WiMAX into a region which has traditionally been associated with radar systems. This paper will discuss the different types of measurements made on radars and other non-radar users of this spectrum. First, the propagation physics of why different types of radars reside in selected frequency bands and why other non-radar systems seek and have gained entrance to these bands is reviewed. The unique spectral characteristics of radars, not generally found in communications systems will be addressed. The trade-offs in using conventional superheterodyne and FFT based spectrum analyzers versus the newer real time spectrum analyzers will be discussed in terms of their capability in evaluating radar spectrum. The spectral characteristics of a variety of communications waveforms will be explored, such as OFDM, and how they can complicate the process of measuring radar type signals in a radiated test. The types of antennas that are used in these radar systems will be discussed and how these antennas influence the reliability of these measurements. Finally, some of the issues associated with separating out antenna effects from waveform effects in legacy & future radars will be discussed. The need for improved measurement techniques and systems will also be addressed.
Large dual reflector compact ranges are typically designed for antenna and payload testing of spacecraft antennas and payload units. Astrium's Compensated Compact Ranges have two major advantages for such measurements: (a) A very small cross-polarization (< -40 dB over the entire test zone) for frequencies = 3 GHz due to the compensating reflector design, (b) A scanning capability of the test zone due to the short effective focal length of the reflector system. The first item is a necessary condition for precise spacecraft antenna measurements at which the cross-polar performance is an important requirement and was subject to multiple publications in the past. The second one, the scanning capability, is an additional feature that was addressed in the past, but has not been analyzed in detail so far. This paper addresses practical implementations, achieved performance figures of the latest installations and inherent limitations by the utilization of the scanned quiet zones at a CCR test facility for antenna and payload testing.
An improved system for antenna gain extrapolation measurements is proposed. The improved method consists of a vector network analyzer, a pair of RF optical links, and a pair of waveguide mixers. This change in hardware equates to a system with better dynamic range and a simplified reference measurement. We present a detailed description of the new extrapolation measurement setup, discuss the advantages and disadvantages, and validate the new setup by measuring the gain of an antenna previously measured with a traditional extrapolation setup. After presenting the comparison, we will discuss applications of this measurement system that extend beyond extrapolation gain measurements (e.g., spherical near- and far-field pattern measurements).
A desired feature of modern field probes is that the useable bandwidth should exceed that of the Antenna Under Test (AUT) [1]. Recent developments in probe and orthomode junctions (OMJ) technology has shown that bandwidths of up to 4:1 are achievable [2-5]. The probes are based on inverted ridge technology capable of maintaining the same high performance standards of traditional probes However, in typical Spherical Near Field (SNF) measurement scenarios, the applicable frequency range of the single probe can also be limited by the content of µ.1 spherical modes in the probe pattern [6-7]. This is because the traditional NFtoFF software applies probe correction under the assumption that the probe pattern is fully specified from knowledge of the E-and H-plane patterns only [8]. While this condition is guaranteed for virtually any type of probe for small illumination angles of the AUT and/or a long probe/AUT distance this assumption may lead to unacceptable errors in special cases. This paper describes the design and experimental verification of a Ka-band probe based on the inverted ridge technology. The probe is intended for high precision SNF measurements in special conditions that require less than -45dB higher order spherical mode content. This performance level has been accomplished through careful design of the probe and meticulous selection of the components used in the external balanced feeding scheme. The paper reports on the electrical and mechanical design considerations and the experimental verification of the modal content.
Ideally, a spherical-scanning probe should be uniformly sensitive to the spherical-wave modes that are superimposed to represent the transmitted .elds of a test antenna. We consider several actual and simulated probes, calculate their sensitivities, and discuss their best use in spherical-scanning measurements. We recommend evaluating probe sensitivity prior to measuring a test antenna.
There are a number of near-field measurement situations where it is desirable to use a broad band probe to avoid the need to change the probe a number of times during a measurement. But most of the broad band probes do not have low cross polarization patterns over their full operating frequency range and this can cause large uncertainties in the AUT results. Calibration of the probe and the use of probe pattern data to perform probe correction can in principle reduce the uncertainties. This paper reports on a series of measurements that have been performed to demonstrate and quantify the cross polarization levels and associated uncertainties that can be measured with typical log periodic (LP) probes. Two different log periodic antennas were calibrated on a spherical near-field range using open ended waveguides (OEWG) as probes. Since the OEWG has an on-axis cross polarization that is typically at least 50 dB below the main component, and efforts were made to reduce measurement errors, the LP calibration should be very accurate. After the calibration, a series of standard gain horns (SGH) that covered the operating band of the LP probe were then installed on the spherical near-field range in the AUT position and measurements were made using both the LP probes and the OEWG in the probe position. The cross polarization results from measurements using the OEWG probes where then used as the standard to evaluate the results using the LP probes. Principal plane patterns, axial ratio and tilt angles across the full frequency range were compared to establish estimates of uncertainties. Examples of these results over frequency ranges from 300 MHz to 12 GHz will be presented.
The numerical analysis used for efficient processing of spherical near-field data requires that the far-field pattern of the probe can be expressed using only azimuthal modes with indices of µ = ±1. (1) If the probe satisfies this symmetry requirement, near-field data is only required for the two angles of probe rotation about its axis of . = 0 and 90 degrees and numerical integration in . is not required. This reduces both measurement and computation time and so it is desirable to use probes that will satisfy the µ = ±1 criteria. Circularly symmetric probes can be constructed that reduce the higher order modes to very low levels and for probes like open ended rectangular waveguides (OEWG) the effect of the higher order modes can be reduced by using a measurement radius that reduces the subtended angle of the AUT. Some analysis and simulation have been done to estimate the effect of using a probe with the higher order modes (2) – (6) and the following study is another effort to develop guidelines for the properties of the probe and the measurement radius that will reduce the effect of higher order modes to minimal levels. This study is based on the observation that since the higher order probe azimuthal modes are directly related to the probe properties for rotation about its axis, the near-field data that should be most sensitive to these modes is a near-field polarization measurement. This measurement is taken with the probe at a fixed (x,y,z) or (.,f,r) position and the probe is rotated about its axis by the angle .. The amplitude and phase received by the probe is measured as a function of the . rotation angle. A direct measurement using different probes would be desirable, but since the effect of the higher order modes is very small, other measurement errors would likely obscure the desired information. This study uses the plane-wave transmission equation (7) to calculate the received signal for an AUT/probe combination where the probe is at any specified position and orientation in the near-field. The plane wave spectrum for both the AUT and the probe are derived from measured planar or spherical near-field data. The plane wave spectrum for the AUT is the same for all calculations and the receiving spectrum for the probe at each . orientation is determined from the far-field pattern of the probe after it has been rotated by the angle .. The far-field pattern of the probe as derived from spherical near-field measurements can be filtered to include or exclude the higher order spherical modes, and the near-field polarization data can therefore be calculated to show the sensitivity to these higher order modes. This approach focuses on the effect of the higher order spherical modes and completely excludes the effect of measurement errors. The results of these calculations for different AUT/probe/measurement radius combinations will be shown.
Total radiated power (TRP) and total isotropic sensitivity (TIS) are two metrics most commonly used to characterize the performance of a wireless device. These integrated measurement parameters are not as sensitive to the measurement distance as a single point measurement such as an antenna gain measurement, but it is difficult to accurately quantify the effects of measurement distance on these two parameters. This paper presents a simple approach to quantifying the effects of measurement distance using spherical near-field transforms. Data is taken on a typical wireless device at different range lengths and transformed to the far-field using a spherical near-field transform. The total radiated power is then calculated for both the measured data and the transformed data. The difference in the two calculations shows the effect of a finite range length on the measurement. Measured results are presented for three different range lengths. For each of these range lengths the data is transformed to the far-field and the TRP is calculated.
A four arm sinuous antenna able to sustain an order of magnitude higher continuous wave (CW) power than commercially available sinuous articles is presented. The wide bandwidth performance from 550MHz to 2.5GHz of the sinuous was preserved with the use of dielectric lens loading and ferrite-tiled cavity backing. The conducted tests show the antenna capability to radiate at least 200W of input CW power. A high power beamformer network built using commercial of the shelf (COTS) components was also characterized. The integrated antenna and beamformer configuration shows excellent thermal and electromagnetic behavior across the frequency band. Presented results may pave the way for use of the sinuous antennas in relevant wideband high power applications.
In this paper application of quasi-planar near-field measurements to characterize the radiation from a test object with the purpose of electromagnetic compatibility (EMC) will be described. First a brief description of an EMC radiated emission Open Area Test Site (OATS) and the setup of a typical EMC quasi-planar table top near-field scanner will be presented. Then the challenges of adapting the near-field scanning technology used for antennas to near-field scanning of EMC test objects will be discussed. Specifically the challenges of 1) Obtaining phase from active equipment under test (EUT) with a radiation caused by quasi stationary random processes. 2) Challenges in probe design and construction that yields satisfactory sensitivity, cross polarization rejection and field disturbance. 3) Measurement in the reactive near-field region and analysis of the probe impact on the measured data. 4) The problems of characterization of non-planar EUT geometry that violates the equivalent surface theorem due to cables leaving the box enclosed by the surface. 5) Near-field measurements on non-directionally radiating test objects 6) Post processing of EMC near-field data: combining of several measurement data sets and taking multiple reflections into account when inserting measured near-field in a CAD model of the full apparatus. 7) Current status in predicting the absolute radiation level in dBuV/m, as measured in OATS, from a near-field measurement