AMTA Paper Archive
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Broadband, Dual Linearly-Polarized Antenna With Controllable Beamwidth
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.
The Minimization of Spurious Radiation from the Baluns and Feed Regions of Roberts Dipole Antennas
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.
Measurement Validation of a Method for Optimizing the Array Configuration of Multimode Antenna Elements
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).
Phased Array Pattern Analysis Method for Geosynchronous Satellites
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.
Thermographic/Holographic Calibration of Phased Array Antennas
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.
Optimized VHF Antenna Measurement Test Range
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  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.
Broadband Dielectric Probe for Near Field Measurements
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.
Controlling Scattering From Near-Field Probes Without Using Absorbers
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.
Near Real-Time Spherical Near-Field Antenna Measurements
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.
Experimental Studies With Comparisons to Computational Model for Automobile Antennas
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.
3D Antenna Measurement Technique for Mobile Phone Characterization Including the User's Influence
A new 3-dimensional measurement method for the determination of the radiated power of mobile phones is presented. In contrast to usual 2D cut plane measurements, the 3D method gives the whole 3D radiation pattern. From this, insight into the detailed angular dependent radiation characteristics can be derived, which is very useful for mobile phone manufacturers and antenna developers. Furthermore, the overall radiated power as well as the directivity of the mobile phone can be post processed from the measured data. A very interesting feature is the ability of the measurement set up to carry a phantom head. With it, measurements of the whole system user and mobile phone can be performed to study the user's influence. The measurements are carried out in an EMC anechoic chamber, which has been specially optimized regarding reflection absorption. Some examples demonstrate the comprehensive measurement capabilities of the presented method.
Towards More Reduction of EMW Hazard in Mobile Telephones Using Three-Covered Monopole Array Antenna
In this paper, a three-covered monopole array antenna with 155o phase-shift and 0.1 ë spacing was suggested to give a minimum power radiation in the direction of the mobile user’s head, consequently the hazard that may the EMW inflects on the human health can be considerably reduced. Several experiments were conducted in this work to measure the power radiation pattern of the monopole, as a common antenna used in mobile telephones, and the three-element array antenna in free-space and with human head adjacent to the antenna. The frequencies were chosen to be 1800 MHz and 1985 MHz, for uncovered and covered designs, respectively, to cover the GSM-1800, PCS-1900, and DECT frequencies. A dielectric material with år = 2.33 , tanä = 0.0005 , and thickness equal to the radius of the monopole was used to cover each array element. It was found that the length of the covered monopole is about 90% of the uncovered length. A practical method was suggested in this work for attaching the adopted array to the mobile telephone.
Calibration and Verification Measurements in Compensated Compact Ranges Up to 500 GHz
Compensated Compact Ranges (CCR) represent a high standard of state-of-the-art test facilities with a fast and real time measurement capability up to the submm wave range. Future scientific and earth observation instruments of ESA/ESTEC such as MASTER, PLANCK and HERSCHEL are working within this frequency ranges and require a high measurement accuracy for large antenna apertures. Within the ADMIRALS study for ESA/ESTEC, transmit and receive modules up to 500 GHz and an appropriate large offset reflector antenna with precise surface accuracy in form of a Representative Test Object (RTO) were applied. Related tests in the CCR 75/60 of Astrium were performed in order to qualify the test facility and verify the antenna measurements with theoretical pattern calculations. The present paper shows measurement results with the highly accurate Plane Wave Scanner (PWS) of Astrium GmbH and the RTO. Through the measurements performed, the accuracy of the plane wave field as well as pattern accuracy in the quiet zone of the CCR 75/60 have been qualified up to 500 GHz.
Modeling of the Antenna-to-Range Coupling for a Compact Range
Two ways of modelling a compact range design are presented, and the coupling to a given antenna under test (AUT) is determined and compared to the AUT far field. The compact range models are both based on physical optics (PO). The first model applies a simple presentation of the serrations of the range reflector while the second model is based on a new feature of GRASP8, which allows a detailed description of the triangles of the range serrations. The AUT measurement is modelled by an accurate coupling analysis between the current elements on the compact range reflector and the antenna under test. This coupling pattern is compared to the real far-field pattern and the differences are discussed. By including known range imperfections in the AUT-torange coupling a better agreement to the measured patterns may be obtained. All computations are carried out by GRASP8.
RCS Measurements in an Anechoic Chamber in V/UHF Band: Ray Tracing Model and Exact Simulation
CAMELIA is a large RCS measurements facility (45m.12m.13m in dimensions) that is operated at both SHF and V/UHF frequencies. In the V/UHF band, coupling between the target and the walls can be exhibited, due to non directive transmitting/receiving antenna, and low efficiency absorbers, that must be eliminated to derive the intrinsic response of the target To this aim, we have first developed a 1:10 small scale model of the chamber, that is operated in the SHF band. It enables the experimental simulation of RCS measurements in the V/UHF band, and confirmed the interpretation of the electromagnetic phenomena in the large scale facility ([l]). Then, two theoretical algorithms were developed, modeling these coupling phenomena. The first one is a simple ray tracing model, requiring as input data the measured reflection coefficient of the walls, the radiation pattern of the transmitting/ receiving antenna and the bistatic RCS of the target. The second one introduces an analytical model for the antenna and its images with respect to the walls, and calculates the near field scattered by the target. The measurement of several targets bas been modeled, and a good agreement bas been obtained. The advantages and drawbacks of each method are discussed.
Accurate Gain Calibration With Corrugated Horns
A method is presented for calculating the gain of corrugated conical horns. It is based on basic symmetry conditions of circular or conical waveguide mode fields. This formulation allows to derive the radiation pattern over a complete sphere form two principal polarization patterns (E- and H-plane patterns). This method can be applied for both theoretical or experimental patterns, respectively. The theory has been verified experimentally with measurements carried out on two different ranges. The results agreed within 0.05 dB or less in all situations.
Determination of the Phase Center Loci of H-plane Arrays of LPDAs
Log Periodic Dipole Arrays (LPDAs) are widely used for certain metrology applications including site attenuation measurements. To accurately make such measurements, the location of the phase center of the antenna is required. However, the LPDA does not, in the strictest sense, exhibit a phase center. Approximate phase centers can be defined by computing the local curvature of a far-field constant-phase surface on the antenna’s principal lobe. However, because the E- and H-plane patterns are different, the phase centers computed from each pattern (or any two-dimensional cut) are not co-located at a given frequency and, moreover, track differently with frequency. An H-plane array of LPDAs with an appropriate taper can be made to exhibit very similar E and H plane patterns over a very broad frequency range. Such an antenna exhibits a much better defined phase center (the phase center still moves as a function of frequency) and is therefore much better suited for metrology applications. Here we present phase center calculations and measurements for two different H-plane arrays of LPDAs. One array is composed of two highly compressed LPDAs (ô=.88, ó=.05) fed with a corporate feed network, while the other is composed of two high gain LPDAs using the so-called “optimum” parameters (ô=.88, ó=.16) and fed with a hybrid feed network. Numerically predicted and experimentally measured results for the phase center loci are presented and compared with those of the component LPDAs.
Correcting for Range Measurement Errors Using Quiet Zone Synthesis
A method is presented for correcting for range measurement errors resulting from non-uniform quiet zone illumination in indoor tapered antenna chambers. The interaction of the source antenna with the throat of the chamber causes undesirable amplitude and phase variations over the quiet zone, the region where the antenna under test (AUT) is located. These variations can impact the accuracy of the antenna pattern measurements, especially when the AUT has a significant aperture. These quiet-zone anomalies can be measured and removed from the antenna patterns by quiet-zone probing. The quiet zone can be probed planar, cylindrical, or spherical quiet zone probe configurations. A planar quiet-zone probe is used here. This process of calibrating the antenna pattern measurements for quiet-zone range errors is called quietzone synthesis (QZS) and is implemented here using MATLAB .
Combined Side Lobe Measurement Errors for Frequency Re-Use Multi-Beam Antennas
A transmitting multi-beam frequency-reuse antenna on an orbiting satellite has N co-polarized spot-beams with each beam driven by a separate transmitter (all transmitters sharing a common band) and each pointed in a different azimuth and elevation direction. The interference effect of N-1 beam side-lobes falling simultaneously on any receiving ground user in a satellite main beam can be estimated by combining the N-1 radiation pattern side-lobe levels which coincide on each user. To predict this effect, the radiation pattern of each beam can be measured in a near field pattern range (NFR) on the ground. When this is done, the measurement error (uncertainty) of each side-lobe falling in the direction of a given main beam ground terminal can also be obtained by a series of special error measurements. The measured error terms for a given side-lobe can be combined in an NFR error table to obtain the measurement error for that side-lobe in the direction of the given terminal location. This process can be repeated for each of the N-1 side-lobes. In this paper we present a method for combining the measured errors of the N-1 side-lobes to yield a combined uncertainty for the combined interference level of the N-1 side-lobes. This process can be repeated for each main beam terminal location. Several tables are presented showing how the combined side-lobe error varies as a function of the levels of the individual side-lobes and the measurement uncertainty of each side-lobe.
Quasi-Optical Waveguide Modeling Method for Scattering Matrix Measurements in the Near Millimeter and Submillimeter Wave Regions
Earlier (AMTA'97, AMTA'98), we have proposed a new low-cost laboratory method named the quasi-optical waveguide modeling (QWM) method to study power and amplitude-phase scattering characteristics of objects, in particular the RCS of targets or their scale models, in the near millimeter (NMM) and submillimeter (SMM) wave regions. A specific feature of this technique in that an investigated object (or its scale model) is mounted inside a quasi-optical waveguide structure in the form of a hollow dielectric waveguide (HDW), in which the scattering characteristics of the waveguide dominant HE11 mode are determined. These characteristics are related to the wanted scattering characteristics of the test object in free space by definite relationships. At the same time the HDW serves several functions: it forms a quasiplane incident wave within the scattering area where test object is placed, performs the low-loss and low-distortion transmission of the scattered wave carrying information of the object being tested to the receiver, effectively filters the unwanted modes arising at the scattering on the test object, and insulates the measurement area from the ambient conditions containing parasitic sources. In this paper we consider the possibility of using the QWM method to study polarization backward scattering characteristics of physical objects, in particular the complex elements of the scattering matrix with relative phase (SMR). A quasi-optical polarimetric micro-compact range (PMCR) based on the circular HDW and quasi-optical devices has been developed and built. The measurement results of the SMR and backward scattering patterns of a reference object as a square metallic cylinder obtained in the PMCR for the different linear polarization basic sets at the 4-mm wave band are presented. The comparison between the experimental results for the reference object and the theoretical data calculated by the geometrical theory of diffraction have shown a good agreement, and demonstrated the possibilities of the QWM method, and its good perspectives for backward scattering polarization characteristics modeling in the NMM and SMM wave regions.
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