AMTA Paper Archive

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 method for detecting a single faulty element in a linear array using neural networks is presented. A feed forward back propagation neural network is trained to detect the faulty element. Given the error patterns due to the faulty array, the network can predict the number of faulty element. A linear array of 21 elements with uniform excitation and uniform spacing is considered. Indexing Terms: Array, Neural Networks, Feed Forward, Back Propagation.

Doing EIRP measurements in a nearfield facility is a known procedure. However, if the transmitted power is relative high, options are limited and care must be taken to prevent damage on equipment and absorbers. This paper describes how EIRP and pattern measurements for high power antennas and transmitters can be done in an indoor facility, and describes various considerations, choices and practical aspects. An example shows that even high power wide-band systems can be measured in near-field facilities.

The KRISS is in the process of completing the construction and installation of a planar near-field antenna test facility in the frequency range of 2 GHz to 50 GHz. This paper describes the planar near-field antenna test facility. Comparison of the far-field pattern, for verifying the antenna test facility, using a parabola antenna as artifact is also described. The patterns were measured by using the installed antenna test facility and a method developed by our group and showed good agreement.

In this paper two planar near-field scan plane reduction techniques are considered and results are presented. It is shown how truncation based on field intensity contours, instead of simple geometric truncation can in some cases improve the efficiency of the truncation process. Both techniques are applied to measured data sets and it is shown how these methods can be used to reduce data acquisition times while also assessing the impact of the total acquisition surface reduction on the far-field radiation pattern integrity.

At the Fraunhofer IIS many antenna design and measurement problems deal with electrically small antennas for different wireless communication links. Therefore we want to establish a meaningful procedure to measure the pattern and also the gain of these antennas quite exactly.

This paper describes a Composite Near-Field Scanning Antenna Range for frequency bands that extend from X- Band in the microwave frequency regime through W- Band in the millimeter-wave regime – i.e. 8.2 through 110 GHz. We show some of the initial checkout data using pyramidal standard gain horns and compare the patterns to theory.

The gain patterns of VHF/UHF antennas on ground structures and vehicles are influenced by the characteristics of the ground. The measurement of the performance of such antennas is more accurate with a test chamber that incorporates a realistic ground surface. This paper will discuss the near field to far field transformation process for the case where there are reflections from a ground surface outside the probing hemisphere. We will show that the ground reflection term in the transformation must be based on the characterization of the ground outside the probe region.

The frequency band 3.1 – 10.6 GHz has been opened for commercial use. Design and measurement of Ultra Wide Band (UWB) antennas in UWB communication systems are growing rapidly due to difficult requirements of UWB antennas such as small size, non-dispersiveness and ultra wide-band characteristics. In this paper, a CPW-fed planar ultra-wideband antenna is presented. Measurement results show that the radiation gain patterns are strongly influenced by the interaction signals between the antenna and the cable, especially at low frequency band. The performance of this antenna is also dependent on the leakage current along the cable. The antenna is mounted on various rectangular metal electronic devices such as DVD players or digital camcorder to investigate the interaction between the antenna and nearby metal objects. The antenna proves to be a good UWB antenna with broad radiation pattern, consistent gain and small group delay variation. The experiment shows that the performance of this antenna depends heavily on the cable interactions and the object that it is mounted on.

It is well known that a microstrip transmission line can radiate if it is excited in its first higher order mode (with the fundamental or dominant mode suppressed). A new microstrip configuration is proposed that supports the first higher order mode while suppressing the fundamental mode. To quantify the leakage constants in the two cases for comparison purposes, several experimental means are considered to determine the source amplitude distribution from which the leakage constants may be deduced. First, an approximation to the source distribution is determined from the far field patterns themselves. Second, the source distribution is determined by carefully probing the near field. This paper uses these techniques to verify the performance of a new leaky wave antenna design.

The Fresnel zone plate lens antenna has seen extensive investigation in the recent past, and has been used at frequencies from the microwave range through the millimeter-wave region to terahertz frequencies. For the usual zone plate antenna employed at these frequencies, path correction (i.e. phase adjustment) is accomplished by cutting different depths (grooves) in a dielectric plate or by using two or more dielectrics having different dielectric constants. Usually the focal length and aperture diameter are comparable, unlike the Fresnel zone plates which have been used at optical wavelengths. The planar configuration offers advantages of low cost, low loss, low weight, and ease of fabrication, while providing better performance, in some cases, than a true hyperboloidal or spherical lens or reflector antenna. Although the gain of the zone plate is normally less than that of a true lens, the reduced attenuation gives a greater overall system gain for the zone plate. Many measurements have been made to determine the antenna patterns (including beamwidth and sidelobe level), gain, efficiency, frequency dependence, focal behavior, aberrations, and bandwidth for both transmission and reflector designs. The major area of current debate is the question of efficiency as understood from analysis compared with actual measurements. This paper summarizes the parameters of zone plate antennas, and defines areas where more measurements are needed to fully describe their characteristics.

Antennas that are used aboard next generation airborne, maritime and ground vehicles are increasingly required to satisfy both conventional radiation pattern and gain requirements as well as new radar cross section (RCS) requirements. In response to these requirements, Nurad and ORBIT/FR recently completed design, installation, and verification of a high performance, multi-purpose antenna and RCS measurement facility at the Nurad site in Baltimore, Maryland. This compact range facility features a 60x36x26 foot shielded anechoic chamber and a precision machined, serrated edge, offset-fed reflector system that produces a 5.3’H x 8’W x 8’L quiet zone over the 2-50 GHz frequency range. The facility includes a unique feed room structure that positions the primary radar components close to the feed mount for RCS measurements, and allows for easy change of compact range feed antennas. A removable pylon assembly is used for test body support during RCS testing, and a unique add on section to the pylon rotator allows for inclusion of a roll axis that enables measurement of small and medium size antenna assemblies without removing the pylon. Measurements performed on low RCS standard targets and antennas made in the chamber demonstrate that the chamber provides a high performance measurement environment while providing ease of use and rapid configuration and target changeover.

It is vital for many future scientific remote sensing satellite missions to develop accurate measurement techniques for high-gain sub-mm wave antennas. At microwaves and longer millimeter wavelengths, the measurement techniques are well established and several error compensation methods have been introduced. This paper proposes a novel error compensation technique suitable for compact antenna test ranges (CATRs) at sub-mm wavelengths. The method is based on antenna pattern comparison (APC). In the APC-technique, several antenna patterns are recorded at different positions in the quiet-zone field and the corrected pattern is obtained by averaging the measured patterns. In the proposed technique, the relatively small feed antenna of the CATR is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. This is much easier to accomplish. The applicability of the proposed method is studied and the method is demonstrated by a combination of quiet-zone measurements and simulations of the antenna measurements in a hologram based compact antenna test range at 310 GHz. For verification purposes the results with this method is compared to the results with the conventional APC-technique.

We have constructed a hologram based compact antenna test range (CATR) and tested its performance at 650 GHz. A hologram of 0.93 meter in diameter was used as the focusing element of CATR. The test was done to demonstrate the feasibility of the hologram based CATR at high submillimeter wave frequencies. A suitable substrate material was found for the hologram. Direct laser writing of the hologram pattern combined to chemical wet-etching was used as the manufacturing method. The quiet-zone field was probed using a planar scanner. For an adequate dynamic range, a backward-wave oscillator (BWO) was used as the transmitter and a Schottky diode harmonic mixer as the receiver. The results from the quiet-zone testing are good. The applicability of the hologram based CATR for high sub-millimeter wave frequencies is considered on the basis of the results of this work.

Computer generated holograms can be used as collimating elements in compact antenna test ranges (CATRs). Recently, a 1.5 m parabolic antenna, the ADMIRALS representative test object (RTO), was tested at 322 GHz using a hologram based CATR that was built specifically for these tests. In this paper, the construction of the compact range is discussed. A 3­meter hologram was used to realize a 1.8 meter diameter quiet-zone. The measured quiet-zone field amplitude and phase and the measured H-plane radiation pattern cut of the RTO are presented. The measured -3 dB beam width of the antenna was 0.050º in the H-plane.

An internal research and development project at the Georgia Tech Research Institute (GTRI) focused on cohering multiple apertures into a single distributed aperture. Cohered distributed aperture antenna patterns were collected on the GTRI far-field range for a 1.5 GHz bandwidth at X-band frequencies. Both 1-way and 2-way antenna patterns were measured, with the 1-way antenna pattern measurement requiring coherence on receive only and the 2-way antenna pattern measurement requiring coherence on transmit and receive. The resulting data were compared with the ideal angular resolution and power-aperture gain product improvements from a perfectly cohered distributed aperture, and the results are presented. As measurement techniques were developed for collecting 1-way and 2-way antenna pattern data, sources of potential errors in measurement collection and aperture coherence were identified, with potential methods of error mitigation outlined.

In this paper the electrical displacement of phased array elements along the axis of a linear array, and in the direction normal to the array are examined. A closed-form solution is presented for determining the location of phased array elements from the first and second derivatives of the phase measured on a near-field antenna range. The technique is applied to swept CW measurement patterns of a 20-element, S-band array of open-ended waveguides. It is shown that the electrical location of edge elements differs significantly from the physical location in both x-dimension and z-dimension. The effects of wide array bandwidth on the phase center displacement are illustrated.

Phased arrays antennas are designed to control their radiation characteristics by accurately setting the phase and amplitude distribution of the elements. Inaccurate control of the phase and amplitude can significantly alter the radiation pattern of an array. In fact, the operating principle of scanning arrays of elements for applications such as target tracking or mobile satellite communications, where the requirements for low side lobes and high gain are of very high importance, is primarily based on precise control of the phase and amplitude of the elements. For these reasons, the complexity of antenna measurement system design for phased array antennas measurements involves high accuracy and precise time synchronization between all the components of the system. This paper presents a comprehensive solution for accurate and reliable measurement of very large phased array antennas at high frequencies. The presented solution addresses the following issues: • Accurate positioning of the RF sensor / probe. • High-speed multi – frequency data collection. • High-speed multi - port data collection. • Programmable and real-time TTL position event triggers. • Pulse measurement. • Multi beam measurement. • Synchronization with the radar computer.