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The purpose of this paper is to detail the process used to optimize the low frequency performance of 72 inch absorber. The loading optimization was required to provide enhanced performance of a twisted 72 inch absorber which was to be used in the building of a large aircraft test facility. The chamber performance requirements are over a frequency range of 30 MHz to 18 GHz. The chamber dimensions are 30 meters x 30 meters x 20 meters high. This chamber will be used to measure a variety of fighter aircraft for many EW scenarios. The mission of this facility is to “perform radiated immunity testing of aerospace vehicles with high electromagnetic field intensity, radiated emissions measurements, EMC testing, electronic warfare testing, antenna pattern testing”. Due to the broad frequency range and the fact that the chamber is desired to test both in the low frequency EMC domain and high frequency antenna measurements, an extremely broad band absorber material had to be developed and optimized. The use of ferrite hybrids was considered. Due to the roll off at microwave frequencies and the expense of such a high volume of materials, they were eliminated for cost and due to the limited performance in the 1-2 GHz frequency range. The ideal candidate is a 72 inch twisted pyramidal geometry. The standard loading of these materials is ideal for frequencies above 150 MHz.. The performance level in the 30 MHz to 150 MHz range is less than ideal. A design for the chamber was established with specific target performances required of the 72 inch absorbers. This paper describes the effort taken to optimize the loss properties of the dielectric foam to meet the target absorber performance required for the implementation of the design. Key Words: Absorber Measurements, Absorber Performance, Computer Modeling of Absorbers, Dielectric Properties of Absorber
The measurement of the radiation patterns of the PLANCK Radio Frequency Qualification Model (RFQM) is one of the most important elements of the verification of the PLANCK telescope. PLANCK is one of the scientific missions of the European Space Agency and is devoted to observe the Cosmic Microwave Background radiation, with unprecedented accuracy. The satellite payload consists of two state-of-the-art, cryogenically cooled instruments sharing a dual reflector telescope with 1.5 m aperture and covering the frequency range from 27 GHz to 1000 GHz. As a key part of the telescope verification logic, the radiation patterns of the RFQM has been measured in the Alcatel Alenia Space Compact Antenna Test Range (CATR) at four frequencies (30, 70, 100 and 320 GHz) using representative flight feed horns of the focal plane unit. This paper presents the test logic, the measured radiation patterns, the custom-made instrumentation set-up, the correction techniques used and the final link to the Flight Model verification.
Adaptive array based antenna pattern comparison technique is presented in this paper. In the method, the antenna pattern of the antenna under test (AUT) is measured several times at different positions in the quiet-zone. The corrected antenna pattern is obtained by taking a weighted average of the measured patterns. An array synthesis algorithm is used to obtain averaging weights at the different rotation angles of the AUT. In addition, the weights are adapted specifically for the AUT. The adaptive array correction technique is demonstrated in a hologram based compact antenna test range (CATR) at 310 GHz. The demonstration is based partly on the measurements and partly on the simulations. For verification, the accuracy provided by the method is compared to the accuracy provided by the uniform weighting.
Hand-made scale models in antenna measurements have been used since the late 1940s. Today, aircraft models are fabricated using a stereolithography (SLA) process and the Computer Aid Design (CAD) for manufacturing the full size aircraft. This is the fabrication method used for the V-22 1/15th scale model. Once the SLA machine is programmed, these models are very inexpensive to produce. In this paper, antenna patterns measured on the V-22 scale model are compared with antenna patterns measured on the aircraft in-flight. Comparison of the patterns shows high correlation. Figure 1 V-22 Aircraft
The Phoenix Lander, a NASA Discovery mission which lands on Mars in the spring of 2008, will rely entirely on UHF relay links between it and Mars orbiting assets, (Odyssey and Mars Reconnaissance Orbiter (MRO)), to communicate with the Earth. As with the Mars Exploration Rover (MER) relay system, non directional antennas will be used to provide roughly hemispherical coverage of the Martian sky. Phoenix lander deck object pattern interference and obscuration are significant, and needed to be quantified to answer system level design and operations questions. This paper describes the measurement campaign carried out at the SPAWAR (Space and Naval Warfare Research) Systems Center San Diego (SSC-SD) hemispherical antenna range, using a Phoenix deck mockup and engineering model antennas. One goal of the measurements was to evaluate two analysis tools, the time domain CST, and the moment method WIPL-D software packages. These would subsequently be used to provide pattern analysis for configurations that would be difficult and expensive to model and test on Earth.
Antenna pattern and isolation measurements for the B-1 Fully Integrated Data Link (FIDL) Program have been completed at the US Air Force Research Laboratory (AFRL) Antenna Measurements Facility located near the AFRL Rome Research Site (RRS), Rome, NY. This combined satellite and airborne communications upgrade has been performed under the supervision of the B-1 Systems Group, Wright Patterson AFB, Ohio. One eighth scale antenna patterns were collected on a far field range for new Link-16 antennas, a relocated VHF/UHF2/L-Band antenna and the new Satcom transmit antenna, while on a one eighth scale B-1 model. Antenna to antenna isolation measurements were performed with antennas mounted on a full scale front section of the B-1 airframe. The RF Technology Branch (IFGE) has developed techniques for evaluating the effects of airframe and external stores on the radiation pattern characteristics of antenna systems in a simulated flight environment. Data obtained in this manner is used to evaluate antenna radiation characteristics of antenna/systems without the requirement of an extensive flight test program. Using similar techniques, AFRL has developed procedures whereby precision measurements of isolation between aircraft mounted antennas can be accomplished. This paper will present how the measured data was obtained for the antennas involved in the FIDL upgrade.
Using software and measured receive power data from aircraft during flight test, the pattern of the installed antenna is derived and validated. During the test flight, data packets were continuously transmitted from an aircraft using the antenna under test. The aircraft flew a designated pattern having straight legs oriented at specific angles to the ground station. Throughout each of these legs the aircraft performed appropriate maneuvers to provide elevation pattern data. A ground station recorded the received data packet signal strength with GPS time tags. Position data of aircraft (latitude, longitude, and altitude) and attitude (roll, pitch, and yaw) was recorded with time tags. Satellite Tool Kit, (STK™), by Analytical Graphics Inc. [1] reproduces flight test conditions and calculates the predicted ground station receive power based on vector direction, range, and a theoretical pattern for the antenna under test. The result is a dynamic link budget and a graph plotting predicted received signal strength versus time. Overlaying the recorded ground station received signal strength with the predicted signal strength allows the correlation of the measured data to that calculated using the theoretical antenna pattern. Curves are presented which show correlation sufficient to validate pertinent portions of the theoretical antenna pattern.
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 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.
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.
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.
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.
Abstract. Scientists at the National Institute of Standards and Technology (NIST) have measured the gain of several antennas using two different methods. The first method is the three-antenna extrapolation method developed at NIST in the early 1970s. The second method is the far-field pattern integration method. We compare gain results and gain uncertainties for several antennas using these two methods.
ABSTRACT A design of a spherical two-arch multi-probe antenna measurement system for measuring radiation patterns of mobile phones is presented. The proper functioning of the designed system is shown partly by computer simulations and partly by practical measurements with Rapid Antenna Measurements System (RAMS) at Helsinki University of Technology.
A method is presented to measure the antenna pattern of an AUT where the antenna port is inaccessible. That means that it is not possible to connect a test cable, nor can the termination be changed physically. In some cases there is no test port at all. The only variation possible is to change the input impedance of the first receiver or LNA by switching it on and off. An RCS-technique can be used to retrieve the radiation pattern. By experimental comparison between the conventional pattern measurement technique and the RCS-technique it is shown that pattern determination via RCS-measurements is feasible. In addition, the measurement method offers the advantage of directly reducing the influence of systematic measurement errors. On the other hand, the penalty is put on power efficiency and a subsequent limited dynamic range.
Payload testing is the only measurement where the real Significant reductions in the overall test time radiated end-to-end performances of the satellite are requirements for satellite EIRP/IPFD measurements measured and compared with respect to predictions. These are achievable if the traditional single polarization or critical measurements are performed in the ALCATEL narrow band dual polarization illuminators are ALENIA SPACE Compact Antenna Test Range in substituted with efficient wideband probes in dual Cannes as shown in Figure. 1. polarization. For C-band payload testing, the frequency bands of interest cover more than an entire octave: 3.4-4.8GHz (Tx) and 5.6-7.1GHz (Rx). The cross polarization and taper requirements on the field of view are such that a flared aperture horn can satisfy the requirement but the polarization purity places rather stringent requirements on the orthomode transition in terms of on-axis cross polarization levels and port to port coupling. A suitable probe for this application consists of two components: orthomode transition and radiating aperture. A flared aperture horn, including a stepped matching section, has been designed by ALCATEL ALENIA SPACE to satisfy the illumination Fig 1: ALCATEL ALENIA SPACE Compact Antenna specification. A wide-band dual polarized orthomode Test Range in Cannes. transition covering the entire C-band Tx and Rx During payload testing the antenna pattern measurements ranges has been developed by SATIMO to feed the and other systems tests are carried out. Two of the key horn. The effective bandwidth of the orthomode payload tests are the Equivalent Isotropic Radiated Power transition more than exceeds the specification and it is (EIRP) and Input Power Flux Density (IPFD) of the usable even throughout the Ku band. The final spacecraft [14]. illuminator has been manufactured by SATIMO and delivered to ALCATEL ALENIA SPACE for test in The EIRP is an indication of the power level capability of the Compact Antenna Test Range in Cannes. the telecommunication satellite within a given coverage This paper describes the definition of the performance on the earth surface. This performance is directly linked to specifications, the baseline horn and applied OMT the power budget of the satellite and to the requirements technology and final validation measurements. on the end user parabola diameter. The IPFD is a useful parameter to determine the needed power on the earth
This paper presents measurements of the CloudSat Collimating Antenna (CA) as fabricated for the 94.05 GHz CloudSat radar, which is to be used to measure moisture profiles in the atmosphere. The CloudSat CA is a 3 reflector system consisting of the 3 "final" (relative to the transmitted energy) reflecting surfaces of the CloudSat instrument. This assembly was fed by a horn designed to approximate the illumination from a Quasi-Optical Transmission Line (QOTL). This same horn was employed as a "standard" for measurement of the CA gain via substitution, and its patterns were also measured (this substitution represents a departure from the standard insertion loss technique in the near field range). The CloudSat CA presented a substantial measurement challenge because of the frequency and the electrical size of the aperture is approximately 600 wavelengths in diameter, with a nominal beamwidth of 0.11 degrees. In addition, very high accuracy was needed to characterize the lower sidelobe levels of this antenna. The CA measurements were performed on a 3122-ft outdoor range (this distance was 41% of the far field requirement), which were immediately followed by measurements in an indoor cylindrical Near Field (NF) range. The instrumentation challenges, electrical, mechanical, and environmental are described. Comparison of the outdoor vs. indoor pattern data is presented, as well as the effect of the application of tie-scans to the near field data.
The performance of modern Satellites Antennas and Payloads is characterized by physical parameters like e.g. Antenna Pattern and Gain; EIRP, Flux Density, G/T and the overall PIM-performance. The available time frame for measurement of these parameters is getting constantly shorter. The EADS Astrium GmbH Compensated Compact Range (CCR) allows a time efficient measurement of all payload parameters with high accuracy under controlled environmental conditions. In addition to an efficient measurement facility high-performance measurement equipment is required. The economical budgets of most space programs demand the application of well-known measurement techniques in a cost efficient way. EADS Astrium GmbH supported by Agilent Technologies GmbH has developed an easy to handle and therefore cost optimized measurement platform for Satellite Payload Measurements. This platform consists mainly of a generic Agilent switch matrix operating up to 40GHz which can be connected to a wide range of measurement equipment. The matrix allows a highly flexible routing of the RF uplink and downlink signals including reference paths. Integrated and/or external RF components, like amplifiers, attenuators, and hybrids can be added to the paths, depending on the required test configuration. Starting from a minimum configuration the system can be modularly upgraded to satisfy any further test requirements. The software interface utilizes standard protocols and can be therefore easily addressed by any user specific measurement software. The EADS Astrium GmbH Advanced Antenna Measurement System (AAMS) includes an optional payload toolbox which provides a modular concept expandable for additional test functions.