Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
Two types of cellular handset testing are presented. The first studies models of a cellular handset near the human head. A comparative analysis is done between simulation and measurement of an inexpensive head mockup compared to a more expensive head mockup. Peak gain values have good agreement within about 1 dB. The second type of cellular handset testing is for a PCS band PIFA antenna integrated to a cellular handset. This paper describes the design and experimental study of the radiation patterns of a PCS band (1850-1990MHz) cellular handset with an internal PIFA. The PIFA described in this paper has good gain, impedance matching, and reduced sensitivity to human body interaction. This PIFA is a good cellular internal antenna.
Errors arising in the measurement of reflection coefficient are identified and analyzed. The presence of multiple reflections due to poor connectors, transmission line discontinuities, and terminal loads is described, modeled and applied. Various measurement scenarios are analyzed, and measured results are presented as a guide for laboratory troubleshooting and as a validation of the measurement models. Improvements to Vector Network Analyzer calibration methods are proposed, including computer corrected calibration for one-port radiating elements and elementary improvements to two-port TRL calibration. An extensive error evaluation of the somewhat forgotten slotted line measurement is finally presented as a robust alternative, and computer automation, acquisition, and calibration of this measurement is outlined.
This paper is concerned with the measurement and analysis of a circularly polarized, flat plate patch array receiving antenna at 12.5 GHz. Input impedance and far field pattern measurements of the antenna over the frequency band from 10 to 15 GHz were performed. The small Compact Range (CR) facility of the Ohio State University Electro Science Laboratory OSU/ESL was used to measure the gain pattern. Gain pattern measurement of the antenna was done by using the gain comparison method. A broadband (2-18 GHz), constant phase pyramidal horn antenna was used as a reference. The data were analyzed to determine the radiation efficiency of the antenna.
Bowtie dipole antennas have been widely used for surface-based ground penetrating radar ( GPR) applications. This type of GPR antennas share common problems such as low directivity, antenna ringing, unstable characteristic impedance, RFI and large size. Special treatments have been used to improve their performance. Resistive terminations have been used to reduce the antenna ringing at t he price of efficiency. Some use reflectors to increase directivity at the price of bandwidth and the risk of cavity ringing excitation. Absorbing material is also used to shield RFI with increased size and weight. Some people use horn antennas because of bet ter gain. However, they are limited to high frequency applications where their size are still reasonable to handle. This means they can only do shallow target measurements. Horn antenna approach also faces the strong reflection arising at the air-ground interface. A new type of GPR antenna design presented in this paper has been developed to overcome the above difficulties.
Until now the mobile phones have been qualified by power measurement at the RF-connector of the handset without any regard to the antenna characteristic and the losses caused by the mismatch of the impedance matching network. IMST is exammmg, via measurements, the user's influence on the antenna pattern of the mobile phone. These measurements were performed in the transmit situation and in the receive situation of the mobile phone at different elevation angles and for different channels of the German E Plus-Network. Due to the differences between human bodies and due to the body's movement during a measurement, the emphasis of this investigation was on the development of a model with dimensions and electromagnetic characteristics similar to those of the average human body. By comparing measurement results using different test persons and the model, the validity of the model has been evaluated.
At high frequencies, the scattered fields from a radar target can be modeled as a sum of contri butions from a finite number of scattering centers. We use a parametric model based on the Geometric Theory of Diffraction (GTD) to estimate the location and type of scattering centers present in a frequency domain data set. The parameters of the model are estimated using a modified MUSIC algorithm that incorporates the GTD model. A new spatial smoothing algorithm is also introduced.
Several approaches are known for the identification of noncooperative air-borne targets with radar. Assuming that the tar get can be tracked during a certain flight path, observations from different aspect angles will be obtained. High-resolution radar (HRR) systems use these observations to create one-dimensional range profiles. With Inverse Synthetic Aperture Radar (ISAR) the data from all observed aspect angles are combined to obtain two-dimensional images. In recent years, techniques for resolution enhancement have been developed for both techniques. The choice for one of the two approaches should depend on the applicability of the target representation for identification. ISAR is the most suitable for reproduction on a display and identification by human observers. In case of identification by a machine, for example an algorithm on a computer, the choice is not straight forward. In this paper an overview of the influence of several errors on the performance of HRR and ISAR will be given. The error sources that will be evaluated are: • uncertainty of the absolute distance of the target; • errors in the mutual alignment of observations; • additive noise. The errors are generated numerically and applied to data from simulations and low-noise measurements. The influence of the bandwidth and angular span on the quality of the target reconstruction will be regarded as well as the performance of some high-resolution techniques. Finally, conclusions are drawn concerning the applicability of ISAR and HRR.
In this paper, we present a new technique for measuring the input impedance of balanced antenna systems. The process uses standard two-port scattering parameters for balanced antennas, feeding each of the balanced input ports as the port of a two-port. The scattering-parameters will be related to the designed input impedance which may be obtained by post-processing the data. In addition, the scattering-parameters may be used to check for the assumed balance of the system. Both experimental and simulated results will be presented to validate the technique.
Finite-Difference Time-Domain (FDTD) is prov ing to be a practical and accurate technique for an alyzing and predicting the performance of anten nas mounted on complex structures. As part of an effort to develop and validate an FDTD code, the impedance and radiation patterns of helicopter mounted loop antennas are predicted and compared to full-scale and 1:10 scale measurements. The input impedance and coupling of HF loop an tennas on the scale model helicopter are measured in the ElectroMagnetic Anechoic Chamber facility at Arizona State University. Although made difficult by the large mismatch between the highly reactive HF antennas and the instrumentation, the scaled impedance measurements agree well with the full scale measurements and predictions. In addition, ro tor blade modulation effects on the input impedance are examined.
Due to the limited size of modern helicopters, airborne antennas must be physically small and lightweight. Slot antennas have been widely used by the aerospace community to meet the size, weight, and aerodynamic requirements when flush-mounted to a platform surface. Having these characteristics, a ferrite-loaded cavity-backed slot (CBS) antenna is an excellent choice for as a tunable low-frequency antenna. Excitation of a magnetostatic mode in the ferrite results in resonances at frequencies below those of the dynamic modes of dielectric-loaded CBS antennas. Frequency agility is achieved by varying the applied DC magnetic bias. Two ferrite-loaded CBS antennas were built and their impedances and radiation patterns were measured. Reasonable (0-6 dBi) with dynamic 3 dB bandwidths in excess of 20% were measured in the UHF band. Air-filled versions of these antennas agree well with Method of Moments (MoM) predictions, but non-uniformity of the magnetic field in the ferrite violates assumptions made in the theoretical model, resulting in discrepancies.
This paper will describe a new type of automotive AM/FM conformal antenna. The slot formed between the body of the automobile and a metal solar heat reduction film imbedded in the front windshield of the automobile is used to form an annular slot. Such partially conducting (4 to 12 ohms per square) metal films represent an opportunity to incorporate an antenna in the overall design at only marginal costs. The characteristic impedance and gain patterns will be described and techniques for improving the impedance match will be shown. A mobile measurement system will be described along with an on-road system to characterize the performance of a number of difference vehicle antenna systems in urban and suburban environments. The application of this system to the measurement of calibrated fain patters will be demonstrated.
A modern outdoor test facility has been designed for comprehensive evaluation of antenna systems on full scale aircraft. The aircraft are mounted to a positioner/tower assembly in an underground handling facility, and are raised to a height of 25 meters by a hydraulically activated lift. A source site 1000 meters downrange provides illumination of a 7 meter radius test zone over a 0.1-18 GHz band. All source site functionality is remotely controlled from the operations center located near the aircraft support tower. The range is designed to provide the capability not only for conventional automated antenna pattern measurements, but also for the support of ECCM testing. This is accomplished by activating both fixed and mobile jamming transmitters available to illuminate the test zone using either CW or modulated waveforms. The FR Model 959 Automated Antenna Measurement Workstation is being enhanced to allow for control of the jammer sites as well as the primary range sited. The system design and operation is described.
The antenna analyzer is specifically designed to make use of measurement techniques that have been difficult to use until now The analyzer is an original vectorial receiver design, based upon the analysis of one of the sidebands of the marked RF measurement signal. Thanks to the RF marking process, the antenna analyzer is not the only equipment that allows characterization (in amplitude, phase or return loss) of all devices in a transmitting chain, including the high power elements, without cutting off the transmission. Originally introduced for the analysis of wired antennas in UHF-VHF bands, its use is now extended to microwave antenna measurements, especially printed circuit antennas. A special characteristic of the new analyzer, ESTAR 2110 is its capacity to measure the phase of RF signal with power levels as low as -120dBm. The analyzer is ideal for elaborate analysis of fundamental antenna parameters such as RF current distribution, close field, antenna pattern, impedance and phase balance of antenna network. The paper describes the marking principle and its use in making antenna parameter measurements.
Composites of the electrically conducting polymer polypyrrole with paper, cotton cloth and polyester fabrics have been evaluated for use in radar absorbing structures. Reflectively measurements on the composites in the range 8-18 GHz and transmission line modelling have revealed impedance characteristics with a common transition region. Relationships between substrate material, polymer loading and electrical performance have been explored. Polarization characteristics have also been measured. The electrical model has been successful in predicting the performance of Salisbury screen and Jaumann multi-layer designs of RAM.
Implementation of a two-ring array for feeing a compact range reflector is investigated. The array is designed to produce a shaped beam with a null at the angle corresponding to the rim of a circular-aperture offset paraboloid. Therefore fields diffracted from the reflector rim are reduced and no reflector edge treatment is necessary. The advantages and disadvantages associated with various feed systems are discussed. A dielectric-filled radial transmission line is proposed as a simple, cost effective implementation of the array beam-forming network. Curves for determining the required dielectric constant for null placement at a desired angle are presented. System bandwidth is examined. Methods for impedance matching and suppression of higher order modes in the beam-forming network are proposed.
This paper describes new developments in broadband Microwave power amplifiers for compact RADAR Cross Section (RCS) Ranges. The RF Power level of transmitters used in compact RCS ranges for the most part has been limited to a watt or two. This is due to the limitations of the power available from solid state RF amplifiers and the power handling capabilities of PIN diode switches, used to pulse modulate the RF amplifier output. Inherent impedance mismatches of the PIN diode switch, RF amplifier and RF output circuits produce reflections of RF energy. The reflected RF energy reverberates between the output circuits of the RF amplifier and the antenna. Reverberation of RF energy between mismatches continues until circuit losses reduce the energy to zero. These reverberations manifest as deterioration of the RF output pulse fall time waveshape. The radiated pulse fall time is extended and damped rather than abrupt. This deterioration of pulse waveshape, due to reverberations, is ring down time. RF pulse ring down deteriorates the resulting RCS measurements. New broadband microwave Traveling Wave Tube (TWT) technology, combined with extremely quiet power supplies and modulator, provide increased power, low noise floor and reduced ring down time resulting in improved RCS measurements.
To improve measurements at lower signal levels and/or reduce the size of the compact range chamber, absorber with much better scattering performance is required. This high performance absorber can be realized by introducing multiple layers to obtain a better impedance transition from air to the absorber. The inhomogeneity leads to the use of the Moment Method. However, the truncated ends of a finite absorber panel produce a scattering so strong that the edge and valley diffractions from a typical wall of absorber cannot be recovered. Thus, an approach to solve and infinite wall of identical wedges has been developed for the TM case using the Periodic Moment Method (PMM). In this paper, PMM will be briefly discussed. Then, some interesting designs will be presented, including ordinary wedge absorber with different dopings, wedge widths and wedge heights, wedges with curves surfaces, and multi-layer wedge absorber designs.
A novel and very powerful measurement technique is presented which allows the determination of antenna radiation and scattering by radar-cross-section (RCS-_ measurements. The antenna under test is treated as a loaded scatterer using a polarization dependent network model that allows a complete antenna description in terms of scattered, radiated and absorbed waves. A load variation principle is used to determine the network model parameters and all commonly used antenna parameters like gain, antenna polarization, axial ratio, polarization decoupling, input impedance and also structural scattering can be derived from the backscatter measurement without using any additional standard antenna. With the antenna network description it is furthermore possible to examine the antenna behavior for arbitrary excitation or loading on their waveguide or radiation port.
The Synthetic Aperture Radar Antenna for the European Remote Sensing Satellite ERS-1 is a 10 by 1 metre deployable slotted waveguide array operating at 5.3 GHz. Electrical performance of the complete antenna is derived at the end of the environmental test programme from near field measurements on a planar NF scanner. In order to obtain very early information on electrical integrity of the flight model antenna, suitable for pre- and post-environmental comparison, a fast electrical functional test was implemented in the total test sequence. It basically consists of a 2D slot probing of a well distributed number of slots in combination with complex input impedance measurements. The paper describes the method and presents results of different test steps. The data of pre-/post-environmental measurements are compared.
At the National Bureau of Standards (NBS) we have examined the out-of-band response of array antennas from both a theoretical and experimental point of view. Theory shows that the out-of-band response of an antenna depends primarily on two factors: the antenna's input impedance, and its directivity. Experiment shows that, for most practical purposes, the out-of-band response of an antenna can be estimated from a measurement of the antenna's input reflection coefficient alone. If the reflection coefficient is low, the antenna response will be good; if the antenna coefficient is high, the antenna response will be poor.