AMTA Paper Archive

A strong interest exists in the commercial and military sectors for small and broadband antennas. For instance, in the automotive industry there is a need for a single antenna operating in the frequency range of 825-2500 MHz (AMPS, DAB, GPS, PCS, SDARS). For military applications, there is also a need to have a single aperture which permits operation in different communication bands and can be also used for imaging and guidance applications. These needs require wide band antennas, such as the miniaturized spiral antenna. In this paper we present the implementation of a spiral antenna situated on a ground plane that is fully functional at the size of 0.16 wavelength onward. Low profile (0.05 wavelength) and broadband operation design goals bring unique challenges, which must be confronted with multiple-front techniques. A combination of antenna geometry design and material loading results in the desired miniaturization effect. Further techniques, including the use of distributed resistors ensure good axial ratio and VSWR. Pattern uniformity and phase linearity of the antenna was also improved. In addition, we also examine the effectiveness of broadband spiral antenna miniaturization as a function of loading material’s dielectric constant.

ABSTRACT We are in the era of wireless communications and devices. The antennas that enable these technologies are electrically small and can be challenging to test and analyze. Yet, the industry is becoming more standardized, and so too are the tests and certifications being adopted to validate these antennas. These antennas must undergo “antenna measurements” to characterize such information as far-field patterns and gain. Additionally, hand-held devices, such as cell phones, must satisfy requirements of the Over-the-Air (OTA) performance tests as specified by the Cellular Telecommunication and Internet Association (CTIA). These tests require a measurement system that can accurately collect data on a spherical surface enclosing the AUT. This system also has to provide the appropriate data analysis capabilities and has to be constructed from dielectric materials to minimize reflections.

Radiation efficiency is an inherent property of an antenna that relates the net power accepted by an antenna to the total radiated power. It is especially useful for handset antennas where the radiation patterns are often of less use for comparing competing antennas. Radiation patterns though not as useful for direct comparisons, still provide one method by which efficiency can be calculated. To accurately calculate the efficiency from patterns, it becomes necessary to obtain multiple pattern measurements (cuts). A larger number of cuts whilst yielding more accurate efficiency results, significantly increase measurement time. Thus an antenna designer is often forced to trade off accuracy against measurement time since both quick and accurate measurements are desired. The focus of this paper is to quantify this trade off, in order to provide guidelines on the number of pattern measurements required for accurate efficiency results. Simulated and measured far-field radiation patterns are used and various numbers of cuts are utilized to quantify the loss in accuracy with a reduced number of cuts. The techniques outlined are geared primarily towards cellular handset antennas.

This paper presents the methodology we use to measure radiation patterns of small terminal antennas. The in-house developed measuring system is capable to record radiation patterns on the entire sphere and recorded values are not corrupted due to proximity of a large dual-axis positioner. As a feed cable had been identified as a primary factor modifying electrical properties of small antennas, we eliminated the feed cable at all by use of a built-in generator. Such generator is mounted back-to­back to the measured antenna. Most preferable the generator should be supplied with a battery, but use of a wired dc supply with a typical supplier is also acceptable in many instances. Such a concept of setup brings about many problems with providing a reference signal to an antenna receiver. Perhaps, firm operation of a reference channel is hard to accomplish without using advanced engineering means. Among them may be a switch with permanent power monitoring in its channels or an optoelectronic leg in the antenna microwave feed.

The Air Force Research Laboratory (AFRL), RF Technology Branch at the Rome Research Site, Rome NY provides a capability of far field antenna testing on full scale aircraft. A computer program, APATS – Antenna Pattern Analytical Tool Set, was developed in conjunction with the Information Systems Research Branch to provide a better way to visualize and understand the antenna pattern data taken during testing. The program is written in Java and relies on JView, developed by the Information Systems Research Branch, to process and display the 3D, three-dimensional, elements of the program.

This paper discusses the Blue Airborne Target Signatures (BATS) database. BATS is the United States Air Force central repository for US and allied signature data. It resides at and is maintained by the Signatures Element, 453rd Electronic Warfare Squadron, Air Force Information Warfare Center, Lackland AFB TX. BATS contains radar cross section (RCS), infrared (IR), and antenna pattern (AP) data, both measured and simulated. The history and background of BATS is also presented, as well as current activities.

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

OTA performance testing of active wireless devices has become an important part of evaluation and certification criteria. Existing test methodologies are extensions of traditional antenna pattern measurement techniques. A critical assumption of these methods is that the device under test utilizes a single active antenna. Advances in wireless technology continue to incorporate more complex antenna systems, starting with simple switching diversity and progressing to more advanced concepts such as adaptive arrays (smart antennas) and multiple-input multiple-output (MIMO) technologies. These technologies combine multiple antennas with various software algorithms that can dynamically change the behavior of the antennas during the test, negating the assumption that each position and polarization of an antenna pattern measurement represents a single component of the same complex field vector. In addition, MIMO technologies rely on the multipath interaction and spatial relationship between multiple sets of antennas. An anechoic chamber with a single measurement antenna cannot simulate the environment necessary to evaluate the performance of a MIMO system. New measurement methods and system technologies are needed to properly evaluate these technologies. This presentation will discuss the issues and evaluate possible solutions.

The CTIA (The Wireless Association – www.ctia.org) were the first to publish a widely accepted test plan for antenna performance testing of “live” mobile phones[1]. The test plan describes the use of phantom heads and involves recording transmitted power and receiver sensitivity information over a full sphere to derive parameters such as Total Radiated Power (TRP) and Total Integrated Sensitivity (TIS). The test plan, has until now, assumed that testing is performed in the far-field at test distances greater than 2D2/.. For typical mobile phone frequency and device test diameters (assumed 300mm in the CTIA test plan), this has not been a constraint. However, as such testing evolves to include the various versions of IEEE 802.11 combined with new devices such as larger laptops and other consumer electronics, a far-field test requirement would lead to very large test facilities. Using experiments and rigorous simulations, this paper will show that for the commonly accepted performance criteria, the far-field requirement is unnecessarily strict. A minimum distance requirement based on the geometry and probe pattern is proposed which will ensure that the performance parameters (TRP, TIS, and others) are obtained with insignificant loss of accuracy.

In this paper a circular planar near-field scan region is considered as an alternative to the commonly used rectangular boundary. It is shown how the selection of this alternative boundary can reduce test time and also to what extent the alternative truncation boundary will affect far-field accuracy. It is also shown how well known single dimensional filter functions can be applied over a two-dimensional region of test and how these attenuate the truncation effect. The boundary and filter functions are applied to measured data sets, acquisition time reduction is demonstrated and the impact on far-field radiation pattern integrity in assessed.

ABSTRACT An efficient probe compensated NF–FF transforma­tion technique with spherical scanning requiring a minimum number of irregularly spaced data is pro­posed in this paper. The Singular Value Decompo­sition method is applied for recovering the uniformly distributed samples from the irregularly spaced ones. The positions of the uniform samples are fixed by a nonredundant sampling representation of the electro­magnetic field. It is so possible to efficiently recon­struct the near-field data required by one of the avail­able NF–FF transformation techniques with spherical scanning. Many numerical tests have been performed to assess the effectiveness of the proposed technique.

A dual-polarization ultrawide bandwidth (UWB) dielectric rod antenna containing two concentric dielectric cylinders was developed for near field probing applications. This antenna features more than 4:1 bandwidth, dual-linear polarization, stable radiation center and symmetric patterns. The antenna begins with a tapered wave-launching section consisting of shaped conducting plates and resistive films. This launcher section is followed by a guided section where the excited HE11 modes are transported to the radiation section. The radiation section contains specially shaped dimensions and materials to generate similar E and H plane patterns with 3-dB beamwidths greater than 55° over 4:1 bandwidth (2 to 8 GHz).

This paper will present techniques used to simulate semi-hemispherical spiral antennas with measured VSWR and antenna pattern data for performance verification. Previous work on semi-hemispherical spiral antennas has been done by Lobkova, Protsenko, and Molchanov [1]. GTRI researchers have built on this work by developing a MATLAB computer model to create a general semi-hemispherical spiral antenna pattern model. Parameters that can be adjusted include the radius of the sphere, the number of turns of the spiral, the creation of a 1-arm or 2-arm spiral, and the inclusion of dielectric material between the spiral and ground plane. In creating the MATLAB computer model, GTRI researchers found errors in the notation of the elliptical integral in [1] and added additional details for the calculation of the antenna pattern. The paper will then present the characterization of a specific example of a semi-hemispherical spiral antenna. First, the VSWR of a single antenna was measured using a standard HP8510 Network Analyzer setup. Next, antenna pattern data was measured for a single spiral antenna and a pair of spiral antennas on both the GTRI planar near-field range and the GTRI anechoic chamber. The paper will conclude with the presentation of the modeled and measured antenna pattern data for the single antenna case.

This paper discusses the process of optimization of a spherical near-field range for measurement of large UHF antennas used in space applications. Results of a study undertaken to understand and optimize range performance in presence of multi-path errors and mutual coupling are presented. Data is presented showing variation in measured patterns of a generic UHF antenna as a function various parameters such as a) use of probes of different gains, b) separation distance between the probe and the antenna and c) absorber rearrangement. Use and effectiveness of software post processing approaches such as spherical mode filtering, time domain gating and use of proprietary algorithms (e.g. “MARS processing” developed by NSI Inc.) is illustrated. Practical implementation of these approaches and corresponding impact on data density, test duration and computational effort are also discussed.

Dual polarized probes for modern high precision near field measurement systems have stringent performance requirements in terms of pattern shape, on-axis and off-axis polarization purity, return loss and port-to-port isolation. A further requirement to the probe is that the useable bandwidth should exceed the antenna under test. As a consequence, the probe design is often a trade-off between performance requirements and the usable bandwidth of the probe. Current high performance designs are based on corrugated horns with balanced capacitive orthogonal excitation achieving close to 25% bandwidth [1]. This technology is well suited for near field probes in the L to Ka band range. Although attractive for compactness, simplicity and excellent performance, probes with external balanced feeding require high precision couplers and manual tuning that impact the overall complexity and manufacturing cost of the final probe. A reduction in cost and complexity can be achieved while maintaining the high performance standards. SATIMO has developed an innovative near field probe with self-balanced feeding maintaining high performance on a wide bandwidth. The overall simplicity makes the new technology very attractive for probe designs in the L to Ka band range.

Nowadays near-field measurement techniques are widely used for detecting the characteristics of the radiated pattern for a large variety of antennas. The core of any near-field measurement is the near-field to far-field transformation. Such transformations use different coordinate systems, like planar, cylindrical, or spherical, and may utilize special solutions. They are already well known for many years. The common feature of all mentioned near- to far-field transformations is the usage of regular measurement grids on planar, cylindrical, or, respectively, spherical surfaces. Future applications, like the Airborne Near-Field Test Facility (ANTF) are expected to lack this characteristic of regular measurement grids, since the flying or floating probe platform cannot be guided sufficiently accurate. This requires the utilization of advanced data processing methods for interpolating measured data on an arbitrary irregular grid to a nearby regular grid, or direct transformation to the far-field. It will be shown that this data processing can be performed by using the Stratton-Chu representation formula utilizing equivalent currents on a well-chosen artificial surface or the classical mode expansion method with additional pre-processing. This paper describes briefly the principles of the ANTF, discusses the application of the equivalent current method and compares it with the widely used mode expansion method. Measured and processed data examples will be presented.

A transmission line system has been developed for an electromagnetically transparent antenna array. The goal was to provide equal signal distribution to the array elements while maintaining the transmissivity of the antenna. The transmission lines consist of microstrip directional power couplers which are fed in series. This reduces the transmission line length needed. The transmission line was built, tested, and integrated with an array of circular polarized array elements mounted over a frequency selective surface (FSS) ground plane. Preliminary bench tests performed on the integrated array with a small test dipole indicated that the transmission lines provided uniform signal distribution. Outdoor far field measurements of the integrated antenna indicated that the antenna performance was satisfactory. The integrated antenna array was tested in the compact range located at the ElectroScience Laboratory at The Ohio State University. These tests were used to accurately characterize the antenna performance at S band and the transmissivity properties of the integrated array at L band. The measured antenna pattern and beamwidth were consistent with predictions. Transmissivity of the antenna as viewed by a second antenna was also consistent with predictions.

A probe station based antenna measurement setup is presented. The setup allows for measurement of complex impedance and radiation patterns of an on-wafer planar antenna, henceforth referred to as the device under test (DUT), radiating at broadside and fed by a coplanar waveguide (CPW). The setup eliminates the need for wafer dicing and custom-built test fixtures with coaxial connectors or waveguide flanges by contacting the DUT with a coplanar RF probe. In addition, the DUT is probed exactly where it will be connected to a transceiver IC later on, such that no de-embedding of the measured data is required. The primary sources of measurement errors are related to calibration, insufficient dynamic range (DR), misalignment, scattering from nearby objects and vibrations. The performance of the setup will be demonstrated through measurement of an on-wafer electrically short slot antenna (.0/35 × .0/35, 5 mm2) radiating at 2.45 GHz.

Double-ridged waveguide horns can provide better than 10:1 relative frequency bandwidth over which they exhibit excellent impedance match and power transfer characteristics. However, the radiation pattern of such an antenna generally becomes more complex at the high end of its operating frequency range. That is, the pattern degenerates from being predominantly single-lobed at lower frequencies to a more complicated pattern exhibiting four gain maxima around the principal axis, all of which are greater than the gain on the principal axis. Here, we present some numerical simulations that appear to indicate that this behavior might not be directly related to higher order modes in the feed region and is not due to manufacturing imperfections, but rather is simply due to the overall taper of the horn itself.

This paper presents a generalized nonlinear interpolation technique for generating 3D antenna radiation patterns from 2D cross sections. The motivation for this work is that most of the patterns provided by antenna manufacturers are only available as vertical and horizontal cross sections. Accurate propagation calculations, however, require gain values at arbitrary orientations, corresponding to points on a 3D gain surface. After reviewing the current methods of generating such a gain surface, we find that linear interpolation algorithms seem the most promising, even though they can often lead to pronounced mathematical artifacts. To overcome these shortcomings a new nonlinear algorithm is proposed. The new approach mitigates, and in most cases eliminates, the artifacts produced by linear interpolation weights. The new method is fast, yields smooth, more realistic surfaces that are consistent with the vertical and horizontal cuts, exhibits diminished mathematical artifacts, and improves the accuracy of propagation calculations of radio frequency signals. Representative examples from the application of the new algorithm to cellular base station antenna patterns will be presented.