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This paper describes a unique three axis gimbal assembly used to test the performance of small radomes. The gimbal assembly supports thin, low profile antennas within the radome, and achieves the correct orientation of the antenna relative to the radome as the entire radome/antenna assembly is rotated for measurement of parameters such as transmission loss and boresight error. The gimbal provides roll, elevation, and azimuth compensation for the antenna within the radome using a small package, with the gimbal point located very close to the rear of the antenna. The axes are equipped with high resolution encoders to provide the very accurate antenna positioning required to demonstrate compliance with tight boresight error tolerances for the radome under test. The entire assembly is removable from the master positioning system for the purpose of switching the test range configuration from radome testing to standard antenna pattern testing.
This paper refers to a special type of antenna, called frequency independent antenna, used in Stepped Frequency Continuous Wave (SFCW) radar employed for humanitarian demining. The radar transmits 128 frequencies within the frequency range from 400 MHz to 4845 GHz, in groups of 8 simultaneously transmitted frequencies. It has been built at the International Research Center for Telecommunications transmission and Radar (IRCTR), Delft University of Technology. Two Archimedean spiral antennas with opposite sense of rotation, in order to decrease coupling signal below –55dB, have been chosen. Precise antenna behavior characterization is needed because SFCW radar is phase sensitive. The paper is focused on antenna footprint measurements, translating data from frequency domain to time domain and gating in order to remove any unwanted signals. Some phase and amplitude pattern using gating measurements are presented.
As the demands on the RF spectrum increase, there is a growing need for antenna test capability at ever higher frequencies. To support our current needs and to accommodate future growth, Ball has outfitted its’ antenna ranges for antenna test from 100MHz through 210GHz. This paper will discuss the considerations and techniques used in extending Ball’s antenna test capability up to 210GHz. The final setup will be discussed and measured pattern data will be presented.
From the earliest days of antenna development, the need for measurement of performance and function has been present. Some characteristics of antennas, such as radiation pattern, are measured by moving one antenna with respect to another. In early antenna testing, outdoor ranges were used to provide a close approximation to the pattern. However, due to the challenges of weather and other environmental effects, antenna testing moved indoors with a number of methods used to compensate for the lack of available space. This paper presents an overview of the history of testing at BATC, from the early days of outdoor testing to the transition to conventional anechoic chambers and nearfield probe facilities. During this time, a variety of techniques have been used to augment standard methods for special requirements, and this paper seeks to communicate some of these methods to the testing community as well as providing a general history of antenna measurement.
A system has been developed for acquiring an antenna’s complete (3D) radiation pattern and radar cross-section (RCS) measurements. The system consists of a motion controller, a network analyser and tower assembly. The tower assembly is in an anechoic chamber. The tower has a novel design. It uses three motors in a special configuration, thereby allowing 2 ½ degrees of freedom. This freedom gives the ability to run complete antenna or RCS measurements automatically. Another advantage stemming from the degrees of freedom is expansion of the range of measurements. This is enabled by a variety of possible positions inside the chamber. Tests have also been carried out on system performance. The data acquisition rate becomes crucial when dealing with 3D pattern measurements. The performance of an HP 8720 or 8753 network analyser series can be dramatically increased by using the power sweep mode for data acquisition. Together with the “external trigger-on-point” mode, this gives the best positioning accuracy. The six-month experience has demonstrated the flexibility and reliability of the set up and ideas.
It is a very common practice to over specify the Quiet Zone performance requirements for an anechoic chamber. Very often what is done is a person who is in need of a chamber contacts someone with a similar facility, often a supplier or a customer, and simply patterns their performance requirement after what the other guy has done. This often results in a chamber, which is specified to a tighter performance requirement than is actually needed to perform the particular measurements required and can cost thousands of dollars more than is necessary. Qualcomm had a requirement to build a chamber for the evaluation of various antenna designs for mobile communication equipment. Due to building and space limitations the “ideal” size for a chamber operating in the 800 Mhz to 6.0 Ghz was not available. Qualcomm worked with AEMI to define the performance parameters to provide them with the best performing chamber that could be built within the restricted space available. Once the design parameters were defined adequately the chamber deign was developed and the chamber was built. Once the chamber was built Qualcomm went about defining the best test methods and parameters that could be achieved given the performance limitations that were evident in the design due to the compromises that had to be made in the limited space available to accommodate the chamber. This paper will discuss the design process, the design limitations and the methods used to overcome the performance compromises made in the development of the chamber and its intended purpose.
While there are standard test methods to characterize the performance of passive antennas, active antennas (with integrated amplifiers) and more complex systems with adaptive functionality create new testing challenges, both in definition and approach. Active antenna gain is a combination of the antenna gain and the embedded amplifier gain. Since these amplifiers may be distributed throughout the array with gain variations between amplifiers, there is a challenge in performing measurements that separate the two gain components. For adaptive antennas, the pattern changes with the incident angle of the test signal, so the adaptive function is often disabled to provide a snapshot of the system, like antenna patterns, for a particular set of conditions. In other cases of adaptive antennas, the composite system performance is measured for angular changes while the system adapts. This paper presents an overview of the testing of both active antennas and adaptive antenna combining systems. Examples of the types of test metrics and errors will be given.
A usual way of performing pattern-measurements on circularly polarized antennas is by measuring the linear components of the field and mathematically converting those to the left-hand and right-hand circular components. These synthesized circular components are sensitive for a number of factors: The exact orthogonality of the measured linear components, the measurement-accuracy of both phase and amplitude of the measured linear components, the polarization-pureness (or the accuracy of the description of the polarization-characteristics) of the probe, etc. This paper analyzes these factors, using a computer-model. An indication on the requirements to be imposed on the measurement-equipment is provided.
Holographic back-projections of planar near-field measurements to a plane have been available for some time. It is also straightforward to produce a hologram from cylindrical measurements to another cylindrical surface and from spherical measurements to another spherical surface1-7. In many cases the AUT is approximately a planar structure and it is desirable to calculate the hologram on a planar surface from cylindrical or spherical near-field or far-field measurements. This paper will describe a recently developed spherical hologram calculation where the farfield pattern can be projected on any plane by specifying the normal to the plane. The resulting hologram shows details of the radiating antenna as well as the energy scattered from the supporting structure. Since the hologram is derived from pattern data over a complete hemisphere, it generally shows more detail than holograms from planar measurements made at the same separation distance.
Future scientific and earth observation instruments as MASTER, PLANCK and HERSCHEL of ESA/ESTEC are working in the sub-millimeter wave range. For measurement of the instruments, a study named ADMIRALS was performed, mainly to identify the most suitable test facility, procure transmit and receive modules and perform measurements up to 500 GHz. The CCR 75/60 of Astrium GmbH, Ottobrunn, was selected for the facility calibration and the pattern verification with an Representative Test Object (RTO). The measurements were performed in three different frequency bands between 200 and 500 GHz. The mmwave transmit and receive modules were designed, manufactured and tested by Radiometer Physics GmbH (RPG). A cost efficient design was achieved by a modular concept. Within this paper, the design and realization of the modules as well as most characteristic performance parameter will be presented.
The OSU/ESL has been developing a broadband, dual-polarized dielectric horn antenna (DHA). This antenna has some attractive characteristics such as dual-polarization, good antenna isolation and stable beamwidth. By adjusting the geometry, the beamwidth of the E- and H-plane patterns can also be controlled independently. Critical design issues that affect the DHA performance include launch structure, lateral-wave elimination and dielectric constant will be addressed. A design example will be provided with a prototype DHA antenna constructed and tested for 2~14 GHz frequency range with a 110o beamwidth in both Eand H-planes. The antenna isolation was found to be greater than 30 dB for this prototype. The new DHA antenna could have wide applications in which broadband, dual-polarization operation, independent E- and H-plane beamwidths are desired.
Linear dipoles are universally employed as low-gain metrology antennas. At shorter wavelengths it becomes difficult to implement linear antennas for which the feed regions comprise an insignificant fraction of the entire structure. Thus, at shorter wavelengths, radiation from the feed region itself and base loading are important issues. Moreover, if an open balun is employed, radiation from the balun can occur. The combination of a linear dipole with a detachable, shielded balun having a coaxial input and two coaxial output ports as called for in CISPR 16-1 has become the preferred approach for site attenuation and path loss measurements below 1000 MHz. Such a design can effectively eliminate the possibility of radiation from the balun. However, the Roberts dipole with its integral Marchand balun can provide superior balance to that obtained using most commercial off-the-shelf 180-degree hybrid networks. Furthermore, at shorter wavelengths, it is difficult to implement a detachable, shielded balun small enough to ensure scattering from the balun housing is negligible. Thus, for metrology dipoles at higher frequencies, the Roberts dipole topology is most appropriate. Because the balun in this antenna is open, it can contribute to the radiation from the antenna. Radiation from the balun distorts the radiation pattern and can displace the phase center of the antenna. However, radiation from the balun can be minimized through careful design. The guidelines for minimizing radiation from the balun differ from those previously published concerning maximizing bandwidth. Here we present gain and radiation pattern measurements for two sets (representing two different design approaches) of linear dipoles employing Marchand baluns. While the experimental effort in this paper focuses on a 900 MHz implementation of the dipoles, the design concept has been shown to work well over a frequency range of 400 MHz to 2.5 GHz. We show how radiation from the balun and feed region can be minimized to provide a dipole with performance very close to that of an idealized linear dipole.
The use of multimode antennas to aid problems of direction finding (DF) has been examined and shown to provide benefit over standard interferometric techniques [3, 5]. In this work, we consider the issue of managing the configuration of multimode antennas on a standard platform to optimize the robustness of the system DF capability. The Fisher Information Matrix (FIM) and corresponding Cramér Rao Lower Bound (CRLB) for a given antenna steering vector size leads to a normsquared maximization problem for steering vector optimization. This, in turn, drives the array configuration for a given element pattern vector. The optimization is developed based on desired performance, using a cost function over elevation. An optimized design is found using both theoretic element pattern calculations and measurements collected at the Radiation and Scattering Compact Antenna Laboratory (RASCAL).
Analysis of in-orbit phased array antenna patterns measured from earth station requires a considerable examination of the in-orbit antenna operation. The antenna analysis should take into account the constant change of both observation angles and scan angles. The in-orbit phased array antenna pattern characteristics are mathematically analyzed. The coordinate transformation technique to calculate the time-varying trajectory of the observation angle in the antenna coordinate system is presented. The technique also encompasses the satellite track angle calculation as seen from the ground antenna. Data processing procedure of the dynamic antenna patterns and several test issues are discussed.
A thermal technique for the remote calibration of phased array radar antennas is proposed in this paper. The technique is based on infrared (IR) measurements of the heat patterns produced in a thin planar detector screen placed near the antenna. The magnitude of the field can be measured by capturing an isothermal image (IR thermogram) of the field with an IR imagining camera. The phase of the field can be measured by creating a thermal interference pattern (IR/microwave hologram) between the phased array antenna and a known reference source. This thermal imaging technique has the advantages of speed and portability over existing hard-wired probe methods and can be used in-the-field to remotely measure the magnitude and the phase of the field radiated by the antenna. This information can be used to calibrate the individual elements controlling the radiation pattern of the array.
In practice, accurate VHF Antenna radiation patterns are usually difficult to achieve due to high level multipath present in the measurement test range. Special range geometry’s and source arrangements have been devised over the years [1] to mitigate the measurement errors produced by test range multipath. In this paper we will describe a new illumination source method designed to accurately control the influence of ground path illumination and in turn reduce quiet-zone amplitude ripple. An array of VHF elements with adaptive complex weights will be used to produce a controlled illumination line source for a given range geometry. Simulated quietzone performance will be shown.
A novel broadband dielectric rod probe design that has the characteristics of broad bandwidth; symmetric probe pattern; low RCS; low antenna clutter and dual polarization operation is discussed. The RCS level reduces the interaction between the probe and antenna under test (AUT). The lower antenna clutter level improves the sensitivity in detecting responses from wide angles with greater time delays. During the transmission mode, the rod is excited with a broadband microwave launcher from one end. The radiation then occurs at the other terminal of the rod. Measurement results of the far-field patterns, RCS and reflection coefficient for a prototype rod probe (DRP) are presented.
The level of multiple reflections in near-field antenna measurements is an important issue in a measurement error budget. Traditionally, the interactions between the test antenna and the measuring probe have been reduced by covering the probe mounting structure with absorbing material. In this paper, a novel approach to alleviating the problem is discussed. This implies the use of a skirt to act as a shield against the mounting structure behind the probe, thereby eliminating the need for an absorber, which is a fragile material when exposed to wear and tear. This also has the added advantage that probe calibration data will not depend on a particular absorber that must be considered as an integral part of the probe. With a suitable design of the skirt, the level of multiple reflections can be reduced, whilst at the same time maintaining the pattern of the probe in the boresight direction unchanged. Prototypes of probes for 20 GHz and 30 GHz have been manufactured and tested, and excellent agreement between experimental results and theoretical predictions has been observed.
High growth in the mobile telephone industry is forcing the development of new terminal antennas at an everincreasing pace. The future multi-standard telephones demand antennas that need to be designed and tested for a variety of radiation and bandwidth specifications. New wireless communications devices, such as those using the new Bluetooth and IEEE 802.11 standards, will require testing of a whole range of new products containing antennas, such as computers, household appliances and consumer electronics. The radiation characteristics of the small antennas used in such devices are strongly dependent on the environment into which they are radiating. For example, the presence of the operator or the mounting and positioning equipment of a test set-up can severely change their radiation characteristics. etenna Corporation addresses this problem by employing a Satimo spherical near-field test system. This system allows for rapid, and in some cases, real-time observation of in situ antenna patterns. A brief description of the test facility is presented in this paper along with sample data.
A series of experimental and theoretical tests designed to develop techniques for reliable computational modeling of automobile antenna performance is presented. The results from the experimental measurements are compared with the results of computational techniques to verify their accuracy and reliability. The Electromagnetic Surface Patch (ESP5) code, a theoretical Method of Moment (MoM) general-purpose code developed at the Ohio State University, is used for computational modeling. We progress from the simple geometry of a single square plate and a monopole, to the more complex structure of a small copper-coated plastic model of an automobile. The computational simulation and measurements are configured with both a monopole antenna mounted at the center of the automobile roof and a backlite heater grid FM antenna. The input impedance, pattern, and polarization are all measured. Comparisons between the results of the computational simulations are presented, as well as the procedures used to measure the antenna characteristics and compare the experimental data with the measured data.