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In this paper, considering a wireless communication network, we use the geometric-based channel modeling technique to create an innovative model for the power azimuth spectrum (PAS). Comparing the PAS model we generate (refered to as secant-square model) to the Laplacian model introduced in the literature for outdoor environments, we demonstrate that our model is a better fit to the TSUNAMI II project measurements. Specifically, our model is a simple mathematical representation, demonstrating a lower squared error when compared to measurement data, and considers effects and relationships ignored in the earlier modeling.
This paper presents the advantages of the next generation of RF Transistors and Amplifier units based on Silicon Carbide (SiC) and Gallium Nitride (GaN) materials. The use of these devices, having higher output and input impedances, allow easier matching to antenna impedances without compromises in power levels. These devices are basically wide bandgap semiconductors having superior properties to other competing technologies such as Silicon (Si) or Gallium Arsenide (GaAs). Implementation of SiC RF transistors will provide higher temperature operation than Si, higher breakdown voltages and extremely good ft operation. A typical SiC unit with a 0.7 ìm configuration will have an ft of 10 GHz.; similarly, a 0.4 ìm configuration will have an ft of greater than 20 GHz. Typical power density is up to 4.5 watts per mm. of transistor structure. In general, SiC Metal Semiconductor Field Effect Transistor (MESFET) will have up to 10 times higher impedances than a Silicon LDMOSFET (input and output). The devices are also very low noise, which allows the use of SiC as high dynamic range Low Noise Amplifiers (LNAs). The paper presents measured data on both SiC Power Amplifiers units and LNAs operating in the frequency domain between 30 to 2800 MHz.
Compact RCS measurement ranges all suffer from some level of non-ideal field illumination. Stray fields from interactions with the chamber wall and diffraction effects are major contributors to the non-uniformity of the incident field at the target. This non-uniformity gives rise to unavoidable errors in RCS measurements. We present a detailed analysis of how non-uniform illumination manifests itself into RCS measurement errors. The analysis approach is based on the plane wave spectral decomposition of the illumination. We compute the energy scattered by the planar components of the illumination and determine how much of this energy is coupled backi nto the radar antenna. We model the target as a diffuse scatterer by using a collection of point scatterers distributed within a specified volume. We present uncertainty results based on a simulation as well as field probe data collected from AFRL’s Advanced Compact Range (ACR).
Ericsson Microwave Systems (EMW) in Sweden has several outdoor and indoor test ranges in operation [1], [2], [3]. In line with future needs and requirements EMW has started building a new Compact Antenna Test Range to be used for a large range of projects and applications. The Compact Antenna Test Range will cover the frequency range of 800 MHz to 75 GHz. The test range will have the possibility for both active and passive antenna measurements at both system and subsystem / unit levels. The test zone will be 3 meters diameter. The maximum load the positioner can carry will be 700 Kg with very high position accuracy for special applications. Due to the relatively low design frequency and the desired size of the test zone, special considerations have been taken in the conceptual design of the reflector system as well as the choice of absorbers. Another important parameter in the design of the facility will be the access to the quiet zone and the time needed to change frequency bands and test objects. To accomplish this, preparations have to be made for easy alignment, very precise interfaces and a fast access to the test area.
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.
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.
Telecommunication satellites capacity growth has lead to a new generation of antennas , larger in size and with extremely sharp performance in terms of gain , cross polarization and coverage isolation (frequency re-use). In order to test such kind of antennas (the largest one is a Ku-band 3.6 m diameter and 6 m focal length reflector antenna) Alcatel Space Industries has implemented several innovations in its Compact Antenna Test Range (CATR): - a powerful and flexible machine has been invested , which provides 6 degrees of freedom (the machine has been called “6DOF Table”) in a wide range of motion to any satellite, allowing to bring any antenna of this satellite into the quiet zone - thanks to this new machine a series of accurate scanner probing has been performed , not only in the central plane of the quiet zone , but also on an eight meter range along the Angle Of Arrival (AOA) of the CATR - the quiet zone has been extended by one meter in height thanks to defocusing techniques; this extension has been modeled with GRASP 8 and tested using the vertical degree of freedom of the “6DOF Table” and a very accurate scanner. - In addition , the Cross polarization of the quiet zone has been tested with high dynamic ranges, using very high purity gridded horns . An average Cross polarization isolation better than 55 dB has been evidenced.
A 30-meter experimental outdoor RCS range designed to operate from 6-18 GHz is described. In the range, the radar antenna height is 60 cm; whereas the center of the quiet zone is 3 meters above ground. The test range, therefore, has features of many real world outdoor RCS ranges. The test range uses six R-card fences with edge taper to eliminate the ground bounce term. Using the quiet zone field probe data and backscatter measurements, it is demonstrated that the R-card fences are very effective in eliminating the ground bounce term.
Static RCS ranges typically generate RCS imagery using ISAR imaging techniques. This provides a twodimensional image of amplitude plotted within some down-range and cross-range extent. The down-range resolution is a function of the bandwidth of the radar system while the cross-range resolution is a function of the target motion between consecutive measurements. A radar look down angle of 0-degrees provides the maximum cross-range information because the target’s movement is normal to the transmitted wave front. As the radar look down angle is changed from 0-degrees to 90-degrees less cross-range information is gathered as the target movement becomes more coplanar to the transmitted wave front. At a radar look down angle of 90 degrees no cross-range information can be discerned. To collect 3-dimensional data for imagery at a look down angle of 90-degrees a raster scan type process can be used. In this implementation the beamwidth of the radar antenna was changed to produce a 6-inch spot on the target rather than fully illuminating the target as is typical with ISAR imaging. A rail was built over the target to support a linearly scanned reflecting plate to direct the transmitted pulse down onto the target to simulate a radar look down angle of 90-degrees. The target was rotated 370-degrees (10-degree overlap) beneath the stationary reflecting plate providing a circumferencial scan i.e. a ring. After each rotation, the reflecting plate was moved a fixed interval radially and another ‘ring’ of data was collected. This procedure was repeated until the entire target was measured. This method of scanning provided two-dimensional information of the target’s length and width with height information obtained by using a 256-stepped-frequency waveform over a bandwidth of 1.6 GHz providing complete three-dimensional imagery.
Translating pylon terminations are often used in narrowband RCS background measurements as means of separating the returns of the termination from those of the pylon itself. Typically, this is done by measuring the pylon while the fixture continuously translates in the range direction through a distance of at least half a wavelength. This paper describes a translated target processing (TTP) algorithmw hich is an extension of this technique to RCS measurements of rotating targets. The technique is applicable to both narrowband and wideband measurements. The algorithm is applied to the problemof mitigating multipath and ground interaction contamination in indoor and outdoor RCS measurements, respectively. Its performance was evaluated as a function of signal-to-noise ratio, target-tocontamination ratio, and translation distance and accuracy using point target simulations. We conclude with a demonstration of the TTP algorithm using actual measurements from the Boeing 9-77 compact range.
When making RCS measurements on a ground bounce range, EPS foam columns are frequently used as target supports for testbodies and air vehicles. Since background subtraction is rarely used to suppress foam column scattering in large scale RCS measurements, the columns must be structurally sound while maintaining a minimized RCS signature over the aspect angles and radar frequency band of interest. The goal is to devise a column that is unnoticeable in the measured data yet strong enough to support a specified weight. The major factor that contributes to EPS foam column scattering is shaping, and finding the optimal shape for a particular test is not trivial. This paper describes methods in the design and construction of EPS foam columns. Subjects include determination of EPS material properties, mathematical specification of column geometries, accurate and efficient computation of column mechanics and scattering, and effective optimization of column parameters.
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.
Usually, a plane wave is approximated by increasing the distance between the transmit antenna and the antenna under test. The phase error across the test aperture increases from zero at the center to a maximum at the edges. Sometimes it is difficult to separate the transmit antenna from the test antenna enough to keep the phase error within acceptable tolerances. In these cases, it would be useful to be able to generate a plane wave across the test aperture at the closer distance. This paper presents an approach to generating a plane wave across an antenna under test that is at an arbitrary distance from a linear array of line sources. The placement of the line sources, as well as the phase and amplitude of each element is optimized to create an approximate plane wave over a specified area.
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.
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.
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 [1].
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.
A number of Australian satellite pay-television companies have engaged CSIRO to measure the performance of their domestic reception antennas. These reflector antennas have their feed integrated with a low-noise block-down-converter (LNB), which converts 12.25-12.75 GHz to 0.95-1.450 GHz. We calculate the LNB noise temperature and gain by using a hot/cold-load Y-factor technique and a known noise source. For the cold load, we use absorber soaked in liquid nitrogen and ambient-temperature absorber for the hot load. The system noise temperature is calculated from another Y-factor measurement where the antenna is pointed at the sky for the cold load and ambient temperature absorber placed in front of the feed for the hot load. The gain is measured on an antenna range and we use a Fresnelzone gain correction, as the range is too short for farfield measurements. We have identified the major sources of uncertainty and estimated the overall uncertainty.
This paper describes a large aperture, 650 GHz, planar near-field measurement system developed for field of view characterization of the Earth Observing System Microwave Limb Sounder (EOS MLS). Scheduled for launch in 2003 on the NASA EOS Aura spacecraft, EOS MLS is being developed by the Jet Propulsion Laboratory to study stratospheric chemistry using radiometers from 118 to 2500 GHz. The combination of a very high operating frequency and a 1.6-meter aperture, coupled with significant cost and weight restrictions, required a new look at near-field scanner design approaches. Nearfield Systems Inc. (NSI) developed a planar scanner that provides a planar accuracy of 4 microns RMS over the entire 2.4 x 2.4 meter scan area. This paper presents an overview of this system including the sub-millimeter wave RF subsystem and the ultrahigh precision scanner. Representative measurement results will be shown.
The design of an integrated microstrip probe performing phaseless near-field measurements on a plane-polar geometry is presented. Amplitude data collected by the probe are processed for obtaining the unknown near-field phase, which is provided by an interferometric algorithm used in conjunction with a minimization procedure. Numerical simulations on an array of dipoles are presented and experimental results are also shown on a microstrip patch antenna for SAR applications.