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In a previous AMTA paper [1], we presented a firstprinciples algorithm called wavenumber migration (WM) for estimating a target’s far-field RCS and/or far-field images from extreme near-field linear (1-D) or planar (2-D) SAR measurements, such as those collected for flight-line diagnostics of aircraft signatures. However, the algorithm assumes the radar antenna has a uniform, isotropic pattern on both transmit and receive. In this paper, we describe a modification to the (1-D) linear SAR WM algorithm that compensates for nonuniform antenna pattern effects. We also introduce two variants to the algorithm that eliminate certain computational steps and lead to more efficient implementations. The effectiveness of the pattern compensation is demonstrated for all three versions of the algorithm in both the RCS and the image domains using simulated data from arrays of simple point scatterers.
A fully-functional Fresnel Zone (FZ) antenna was designed and measured using PO simulation programs and the bi-polar near-field facility. The results from these measurements and simulation are presented in this paper. First, a detailed description of an FZ antenna and its operation is given. Then, a discussion of the design and construction procedure for both the FZ antenna and supporting structure is included. The resulting far-field pattern, near-field plots, and holographic images are shown in this paper. The antenna was measured with different feed positions to observe how it affects the overall antenna performance.
A new spherical near-field probe positioning device has been designed and constructed consisting of a large 5.0 meter fixed arc. This arc has been installed in a near-field test facility located at Alenia Marconi Systems on the Isle of Wight, UK. As part of the nearfield qualification, testing was performed on a ground based radar antenna. The resultant patterns were compared against measurements collected on the same antenna on a large outdoor cylindrical near-field test facility also located on the Isle of Wight [1]. These measurements included multiple frequency measurements and multiple pattern comparisons. This paper summarizes the results obtained as part of the measurement program and includes discussions on the error budgets for the two ranges along with a discussion on the mutual error budget between the two ranges.
A Wideband Optically Multiplexed Beamformer Architecture (WOMBAt) was developed and characterized at the Crane Naval Surface Warfare Center Active Array Measurement Test Bed (AAMTB) facility. The project includes development and integration of the true-time delay (TTD) WOMBAt photonic beamformer with the Active Array Measurement Test Vehicle (AAMTV). The AAMTV is a 64-channel transmit-receive (TR) module based phased array beamformer that is integrated with the AAMTB facility 12’x9’ planar near-field scanner. The AAMTV provides phase trimming and a small amount of delay using electrical components while the WOMBAt provides longer delays using commercial-off-the-shelf (COTS) optical components typically manufactured for the telecommunication industry. By integrating the WOMBAt with the AAMTV, a highly flexible test environment was achieved that includes system calibration, multi-frequency scanning, and antenna pattern analysis. Phase I receive tests for this system were previously described and presented to AMTA[1] in 2002. This paper will describe the results of reconfiguring the AAMTV into a transmit architecture for Phase II. WOMBAt successfully demonstrated wideband TTD in both receive and transmit configurations at angles greater than the system goal of ±65º while exceeding all other system level performance goals. System level performance included a beam squint of less than 1.1º for receive and 0.5º for transmit, a worse case amplitude variation of 2.4 dB receive and 1.6 dB transmit and differential delays of less than 3.5 picoseconds.
The recent launch and successful orbiting of the EO-1 Satellite has provided an opportunity to validate the performance of a newly developed X-Band transmitonly phased array aboard the satellite. This paper will compare results of planar near-field testing before and after spacecraft installation as well as on-orbit pattern characterization. The transmit-only array is used as a high data rate antenna for relaying scientific data from the satellite to earth stations. The antenna contains distributed solid-state amplifiers behind each antenna element that cannot be monitored except for radiation pattern measurements. A unique portable planar near-field scanner allows both radiation pattern measurements and also diagnostics of array aperture distribution before and after environmental testing over the ground-integration and pre-launch testing of the satellite. The antenna beam scanning software was confirmed from actual pattern measurements of the scanned beam positions during the spacecraft assembly testing. The scanned radiation patterns on-orbit were compared to the near-field patterns made before launch to confirm the antenna performance. The near-field measurement scanner has provided a versatile testing method for satellite high gain data-link antennas.
This paper deals with different aspects of the on-ground antenna pattern characterization of the MIRAS radiometer for ESA’s SMOS mission. Various technical challenges of the project are briefly described. Special attention is given to the effect of multiple reflections between the antenna under test and the measurement probe. A series of antenna measurements of the MIRAS radiometer antennas is now on-going at the DTU-ESA Facility. The main objectives of these are to investigate the accuracy of the forthcoming antenna characterization, to find solutions to the already known problems, to identify new possible difficulties, and to establish an optimal measurement strategy, which should allow for the tight error requirements and minimize the overall time of the measurement campaign.
As known, spacecraft antenna design is an everdemanding task, due to the tight requirements on performance and the small available space. Moreover, the trend of installing array antennas onboard makes this task even more complex. For this reason, every antenna design must be verified against its installation constraints, in term of pattern distortion, due to interaction with spacecraft structure, inter-antenna coupling with nearby antennas, which can be remarkable due to the reduced available space, and generation and propagation of passive inter-modulation products (PIM), that can seriously affect the performance of transponders. For the above reasons, a Design Framework has been developed in the frame of an ESA contract. In this activity, European universities, industry and research centers cooperated in order to integrate within a single environment different prediction codes providing the required modeling capabilities. The system is able to guide the user from the antenna design phases through antenna installation simulation. The framework also allows for storage and management of experimental data in the more common formats or in user-defined ones, making able the designer to validate its numerical models with measured data obtained from intermediate breadboards. A validation activity is in progress and comparisons between simulation and measurements are reported, together with main characteristics of the design system. The system has been applied, among others, in the design and compatibility analysis, of Galileo antennas.
We have developed the spherical near-field measurement system using a photonic sensor as the probe of the spherical scanning. Because the photonic sensor is a few gram of weight and a few mm in length, the measurement system can be compact and simple. The probe compensation is not needed because the photonic sensor can be considered as an ideal infinitesimal electric dipole antenna in the spherical near-field measurements as well as the planar near-field measurements as shown before. To demonstrate the validity of the system, we have measured the antenna patterns of a microstrip antenna on a finite printed board at 5.85 GHz. The measurements by the photonic sensor agreed with the one by the far-field method.
While probe arrays are now recognized to allow rapid and accurate near-field measurements, the interaction with the Antenna Under Test (AUT) is still sometimes considered as a potential limitation, especially for electrically large directive antennas [1]. Based on numerical simulations, this paper reports the results of a thorough investigation of the interaction mechanism and analyses its impact on the far-field pattern accuracy. The most often, interaction effects can be maintained at an acceptable level, thanks to an appropriate design of the probe array element and structure. However, the efficiency of a posteriori compensation schemes has also been investigated. The Pattern Coherent Averaging Technique (PCAT) [2], which is well known for compensating plane wave deviations in the quiet zone of antenna far-field test ranges or interactions from single probe near-field facilities, also proved very efficient to reduce the interaction effects with a probe array.
One basic Direction Finding (DF) technique for Radar is Amplitude Based Comparison DF. Multiple directional antennas are placed around an aircraft to get a 360 deg view of the area. By placing these antennas on the aircraft, the antennas are subjected to reflections from the aircraft, which distorts the antenna characteristics. This antenna distortion causes errors in the measurement of the angle of arrival. The work presented here describes the measurement of the antenna characteristics of a cavity backed spiral antenna both by itself and attached to the nose of an MH- 47A helicopter nose measured in an anechoic chamber. The spiral antenna’s pattern was changed when it was measured on the helicopter. The effect this change in pattern has on the DF accuracy is discussed.
A compact range was recently constructed at the Applied Physics Laboratory to measure broad-beam, fan-beam, and pencil-beam antennas (max aperture: 1 meters). Chebyshev absorber treatments, lightweight composite reflector, foam column mount for light-weight antennas, automated measurement software, and a novel feed spillover rejection algorithm are the technology elements implemented in this compact range measurement facility. This paper will describe a trade study that APL performed before the compact range antenna facility was built. Solutions to some of problems that were encountered during the construction will be discussed as well as the overall performance of the facility. The measurement of a broad-beam antenna will be compared to calculated pattern. This measurement will highlight the advantages of using a software range gate that was recently developed.
When a dual port probe is used for near-field measurements, the amplitude and phase difference between the two ports must be measured and applied to the probe correction files so that the measurements and calculations will have the same reference. For dual port linear probes, the measurement of this “Port-to-Port” ratio is usually accomplished during the gain or pattern measurements by using a rotating linear source antenna.1 When a dual port linear probe is used to measure a circularly polarized antenna, the uncertainty in this Port-to-Port ratio can have a significant effect on the determination of the cross polarized pattern. Uncertainties of tenths of a dB in amplitude or 1-3 degrees phase can cause changes in the cross polarized pattern of 5-10 dB.2 3 The paper will present a method for measuring the Port-to-Port ratio on the near-field range using a circularly polarized antenna as the AUT (Antenna Under Test). The AUT does not need to be perfectly polarized nor do we need to know its correct polarization. The measurements consist of two separate near-field scans. In the first measurement the probe is in its normal position and in the second it is rotated about the Z-axis by 90 degrees. A script then calculates the Port-to-Port ratio by comparing the crosspolarization results from the two measurements. Uncertainties in the Port-to-Port ratio can be reduced to hundredths of a dB in amplitude and tenths of a degree in phase. Measurements were taken at TRW’s Large Horizontal Near-field Antenna Test Range.
Single-beam and composite-beam performance of a 4-port X-band waveguide Butler matrix was measured on the Georgia Tech Research Institute planar near-field range for wideband frequency performance. The techniques necessary to perform accurate measurements on a broad-beamed antenna in a near-field range will be discussed, and measured far-field pattern data collected at the design frequency of 9.3 GHz are presented and compared with predicted results of the Butler matrix. In cases where the measured data and the expected results do not compare well, aperture amplitude and phase data, transformed from the near-field data, are shown as a diagnostic tool for corrections. After correction, new data at 9.3 GHz are presented for comparison with predicted results, and selected farfield pattern data collected at 8.6 GHz and 11.0 GHz are presented.
This paper describes two methods that can be used to measure the leakage signals in quadrature detectors, predict the effect on the far-field pattern, and correct the measured data for leakage bias errors without additional near-field measurements. One method is an extension and addition to the work previously reported by Rousseau1. An alternative method will be discussed to determine the leakage signal by summing the near-field data at the edges of the scan rather than summing below a threshold level. Examples for both broad-beam horns and narrowbeam antennas will be used to illustrate the techniques.
In this paper, techniques are presented for the measurement of element radiation patterns of a belt-like C-band conformal array of microstrip patch elements, which wraps completely around the cross-section of an aircraft wing. The element patterns were measured, in situ, then analyzed in terms of phase and amplitude ripple versus element location around the wing. These results indicated trends in interference due to the experimental environment and the geometry of the wing itself. Experiments were conducted which minimized interference effects due to the environment, resulting in the true element patterns in the presence of wing platform interference. In an effort to identify platform-induced interference, anechoic absorber was used to minimize pattern ripple attributed to the edges of the wing, enabling validation of the measured element patterns against simulated data, which did not include platform interference. Thus, determining whether to include the platform effects in the measured data is dependent on the intended use of the results.
An error detection technique was developed for culling large masses of measured antenna pattern data by first removing information that is likely to be associated with the antenna. Since the maximum spatial frequency of radiation from the antenna can be determined by its electrical size, any energy outside that spatial band is not considered to be valid and may be used to flag suspicious data. This analysis can be accomplished rapidly and can be used to cull patterns containing such anomalies as spikes, notches, non-closures and multipath effects. This paper describes the method with examples from simulated and measured patterns.
We present and analyze a procedure for performing relative, ultra-wideband antenna pattern measurements in a non-ideal EM facility. Ultra-wideband, shortimpulse, TEM horn transmission measurements were performed and compared with computer-modeled radiation pattern results. These measurements allowed us to analyze radiation lobes and nulls in both boresight and off-axis antenna positions. The results show that the measurements performed in this testing environment agreed well with computer models.
New automobile antennas must be developed to satisfy the growing requirements of the automobile industry. The uses of GPS band antennas for vehicle applications are growing very rapidly in the modern telecommunication area. In automobile antenna design, there exists geometrical constraints and several requirements for antenna specifications, for example, a Right-Hand Circular Polaization (RHCP) for a GPS antenna. In this paper, a new antenna for the automobile applications is designed using a Genetic Algorithm. It is well known that the GA can be used efficiently in the designing of various antennas. The GA searches the solution space of the possible antenna geometries satisfying the design goals. The design goals are RHCP with low cross polarization, a low SWR, and an omni-directional gain pattern in the upper-half plane. These design goals will be included in the cost function. The GA produces a set of new optimal antenna geometries. A series of experimental tests of the new antennas is presented, and the results are compared with the theoretical prediction. The ESP 5, a theoretical Method of Moment (MoM) general-purpose code developed at the Ohio State University, is used for an analysis tool.
Requirements for pattern measurement of antennas with low directivity continue to increase. The wireless communications industry is a significant driving force behind this change, but other fields such as electromagnetic compatibility (EMC) have an emerging need of low directivity antennas that work well to microwave frequency ranges. Traditional microwave techniques used for highly directional antennas are not suitable for testing more broad-beamed or omnidirectional antennas. Spherical pattern measurement systems using dielectric support materials with low permittivity are required to obtain acceptable results. This paper will review several different spherical pattern measurement techniques proffered by the Cellular Telecommunications & Internet Association (CTIA) for testing cellular handsets. It will present a benefit analysis of each method and provide useful information for both the novice and experienced antenna user. It can be shown that with appropriate care, several different techniques can generate the same resulting data, but each method has its own unique benefits and drawbacks. Spherical surface plots of measured data will be provided to illustrate some of the pitfalls related to this type of pattern measurement, and results from a certified test site will be presented.
A Wideband Optically Multiplexed Beamformer Architecture (WOMBAt) was developed and characterized at the Crane Naval Surface Warfare Center Active Array Measurement Test Bed (AAMTB) facility. The project included development and integration of the WOMBAt photonic beamformer with the Active Array Measurement Test Vehicle (AAMTV). The AAMTV is a 64-channel transmit-receive (TR) module based phased array beamformer that is integrated with the AAMTB facility 12’x9’ planar near-field scanner. The AAMTV provided phase trimming and a small amount of electrical delay while the WOMBAt provided longer optical delays using commercial-off-the-shelf (COTS) components typically manufactured for the telecommunication industry. By integrating the WOMBAt with the AAMTV, a highly flexible test environment was achieved that included system calibration, multi-frequency scanning, and antenna pattern analysis. This paper presents antenna pattern results showing less than 0.7 dB of amplitude variation over the frequency range from 9 to 10 GHz at each of the measured nominal steering angles. The beamformer was steered to greater than ±69 degrees with an observed beam squint from 9 to 10 GHz of less than 1 degree.