Polarimetric Receiver Research Articles

Development of a Polarimetric 50-GHz Spectrometer for Temperature Sounding in the Middle Atmosphere

This paper addresses the further development of the groundbased temperature radiometer TEMPERA which measures atmospheric microwave radiation in one linear polarization in order to retrieve temperature profiles up to an altitude of 50 km [1]. The latest innovation is a new polarimetric receiver, which allows observing the atmosphere simultaneously in left- and right circular polarization. In combination with an adapted inversion method, the fully polarimetric analysis can improve the accuracy and extends the vertical upper limit of retrieved temperature profiles. Comparisons between single polarization and fully polarimetric retrievals with simulated atmospheric spectra are presented and the influence of the Earth's magnetic field is analysed. In addition, we propose a simple calibration method for fully polarimetric radiometers and present first atmospheric spectra measured with the new TEMPERA-C instrument.

A 220-GHz InP HEMT Direct Detection Polarimeter

In this article, a 220-GHz direct detection polarimetric receiver is reported. This polarimetric receiver is intended for sensing of the microphysical properties of cloud ice in the earth’s upper atmosphere. In the article, we report the measured RF performance, including RF gain of approximately 35 dB per channel and integrated noise figure of the receiver. The noise figure is measured to be 5.1 dB for the horizontally polarized channel and 5.4 dB for the vertically polarized channel. The receiver measures only 1.8 cm $\times3.0$ cm $\times6.4$ cm and has a total regulated dc power consumption of 520 mW. This article represents the first 220-GHz polarimetric direct detection receiver and is enabled by an advanced 25-nm indium phosphide (InP) HEMT monolithic microwave integrated circuit (MMIC) technology.

Polarimetric receiver in the forty gigahertz band: new instrument for the Q-U-I joint Tenerife experiment

This paper describes the analysis, design and characterization of a polarimetric receiver developed for covering the 35 to 47 GHz frequency band in the new instrument aimed at completing the ground-based Q-U-I Joint Tenerife Experiment. This experiment is designed to measure polarization in the Cosmic Microwave Background. The described high frequency instrument is a HEMT-based array composed of 29 pixels. A thorough analysis of the behaviour of the proposed receiver, based on electronic phase switching, is presented for a noise-like linearly polarized input signal, obtaining simultaneously I, Q and U Stokes parameters of the input signal. Wideband subsystems are designed, assembled and characterized for the polarimeter. Their performances are described showing appropriate results within the 35-to-47 GHz frequency band. Functionality tests are performed at room and cryogenic temperatures with adequate results for both temperature conditions, which validate the receiver concept and performance.

A C-band broadband ortho-mode transducer for radioastronomy polarimetry.

BackgroundWe describe the design, the construction and performance of a narrow band ortho-mode transducer, currently used in the 5 GHz polarimetric receiver of the Galactic Emission Mapping project.ResultsThe ortho-mode transducer was designed to achieve a high degree of transmission within the 400 MHz of the GEM band around the 5 GHz (4.8–5.2 GHz). It is composed of a circular-to-square waveguide transition, a septum polarizer, a thin waveguide coupler and a smooth square-to-rectangular waveguide transition with custom waveguide bends to the output ports.ConclusionOur simulations and measurements show a very low level of cross-polarization of about −60 dB and a good impedance match for all three ports (S11; S22; S33 < −30 dB) with only 0:25 dB of insertion loss offset across the 400 MHz (4.8–5.2 GHz) of the reception bandwidth.

Q-band 4-state phase shifter in planar technology: Circuit design and performance analysis

A 30% bandwidth phase shifter with four phase states is designed to be integrated in a radio astronomy receiver. The circuit has two 90° out-of-phase microwave phase-shifting branches which are combined by Wilkinson power dividers. Each branch is composed of a 180° phase shifter and a band-pass filter. The 180° phase shifter is made of cascaded hybrid rings with microwave PIN diodes as switching devices. The 90° phase shift is achieved with the two band-pass filters. Experimental characterization has shown significant results, with average phase shift values of -90.7°, -181.7°, and 88.5° within the operation band, 35-47 GHz, and mean insertion loss of 7.4 dB. The performance of its integration in a polarimetric receiver for radio astronomy is analyzed, which validates the use of the presented phase shifter in such type of receiver.

Antenna Pattern Measurements of Weather Radars Using the Sun and a Point Source

AbstractThe sun is known to be a good target for weather radar calibration. In this paper high-resolution raster scans of the sun at high elevations will be used to derive the antenna pattern of weather radar, without being affected by beam propagation effects and reflections close to the earth’s surface. It is shown that this pattern matches well to pattern measurements using a point source. Hence, a good estimation of the real antenna pattern can be derived using the sun.Furthermore, formulas to extract undistorted antenna patterns from the sun, even at high-elevation angles, are derived. The signal processing required to achieve high sensitivity for the antenna pattern measurements will be described. Important parts of the antenna pattern—for example, sidelobes—become visible when using long integration times.The polarimetric receiver channel cross-correlation coefficient is proposed as a figure of merit of the cross-polar isolation of the antenna and hence the cross-polar pattern. The results are also compared to point source measurements. This illustrates how an unpolarized signal source like the sun can be used to derive polarimetric variables.

Fuzzy-Fusion Classifier for MMV Full-Polarization Radar Target Recognition Using One-Dimensional Scattering Centers

One-dimensional (1-D) scattering centers on a target can be used for radar target recognition purpose. In this paper, a new classifier based on fuzzy techniques is proposed, which is very much suitable for target recognition using 1-D scattering centers. Furthermore, information fusion techniques for full polarimetric receiver data are utilized at the decision level. The performance of the proposed fuzzy-fusion classifier is evaluated using a dataset of five aircraft models measured by millimeter-wave (MMW) full-polarization stepped-frequency radar in the compact range facility.

The COBEAM-1/96 experiment

Today more than 8,700 objects larger than 10 cm are on Earth orbits. Most of them are frequently measured and cataloged, and only about 6% are operational satellites. The number of objects larger than 1 cm is between 70,000 and 200,000. A 1 cm fragment can damage and a 10 cm sized object can destroy a satellite. Despite the fact that in 1996 an operational satellite was hit by a cataloged debris object and that in 1997 an ESA satellite has carried out a collision avoidance manoeuvre, experts agree that today space debris pose only a small threat to operational satellites or to constellations of communication systems like Iridium or Globalstar. Experts disagree, however, how severe the space debris situation might be in future years, because this depends on assumptions with respect to future space activities, generation of debris, and effectiveness of adopted mitigation measures. This problem can be analysed by simulations using an appropriate space debris environmental model. But such models have to be validated with measurement data. Within the bistatic coordinated beam-park experiment COBEAM-1/96, involving FGAN's Tracking and Imaging Radar system and the 100-m telescope of the Max-Planck-Institute of Radio Astronomy as secondary, polarimetric receiver, a 24 hour snapshot was taken of the existing space debris population in a predefined space volume. Cataloged objects and unknown space debris as well as two subpopulations generated from leaking RORSAT reactor cores and from a Pegasus upper stage explosion were detected.

Theoretical analysis of coupling and cross polarization of perpendicular slot antennas on a dielectric half-space

In this paper, design curves are given for minimizing the coupling between two perpendicular slot antennas on a dielectric half space. Such antennas may be utilized in polarimetric receivers in which coupling must be minimized to ensure polarization purity and in polarization diplexed quasi-optical receivers in which the local oscillator (LO) is received in a polarization perpendicular to that of the RF signal. For this analysis, Galerkin's method in the spectral domain is applied along the length of the slots and point matching across their widths. At the second resonance, for equal length slots and for constant width/length (w/L) of the slots, there is a decrease of about 2-dB coupling for a factor of three increase in dielectric constant (/spl epsiv//sub 1/=1.0/spl rarr/3.8 and /spl epsiv//sub 1/=3.8/spl rarr/12.8). For fixed dielectric constant there is a 1-2-dB increase in coupling for a factor of two increase in w/L. For slots of unequal length (L/sub 2/=L/sub 1//2), the changes are even smaller. Design curves are shown for various relative positions of the slots in two dimensions. A strong correlation between coupling levels and peak cross-polarization levels is found.

IF-based polarimetric receivers

A low-cost low-power polarimetric receiver has been developed based on the idea of IF processing. This architecture allows accurate measurement of the incident wave polarization and greatly reduces the cost and size of the receiver. An X-band polarimetric receiver with a dual-polarized microstrip antenna has been designed and tested. The results show a maximum /spl plusmn/5/spl deg/ polarization error using low-cost IF components and demonstrate the feasibility of performing inexpensive polarimetric processing at IF frequencies.

Polarization of auroral backscatter at 50 MHz

Auroral backscatter from the lower E region was studied using two 50 MHz bistatic, continuous wave radar links which shared a common polarimetric receiver. The polarization parameters were defined in terms of the polarization ellipse, which is described by the ellipticity angle χ orientation angle ψ, and polarization ratio m. Spectral analysis was applied to the intensity measurements and its corresponding polarization parameters. Observations of typical auroral spectral types 1, 2, and 3 indicated that the scattering of a linearly polarized incident wave produced an essentially linear and highly polarized scattered wave. These results imply a small scattering volume and/or a small number of discrete scatterers located close to one another, “scatterer” referring to a volume where radar waves are scattered according to weak coherent scattering theory, and also reaffirms that the scattering process is a weak coherent one. These results are typical of most observations, but not all; an otherwise typical intensity spectrum may also exhibit variable polarization parameters with an appreciable reduction in the polarization ratio and/or signals of significant ellipticity. These anomalous properties can be explained as scatter coming from a number of individual scattering volumes within the scattering region (i.e., the effective radar viewing region), which are each influenced differently by Faraday rotation to and from the scattering region.

92 GHz dual-polarized integrated horn antennas

A dual-polarized two-dimensional imaging array was designed for millimeter-wave applications. The dual-polarized design consists of two dipoles perpendicular to each other and suspended on the same membrane inside a pyramidal cavity etched in silicon. The dual-polarized antenna is fully monolithic with room available for processing electronics. The IF or video signals are taken out through a novel bias and feeding structure. The measured polarization isolation is better than 20 dB at 92 GHz, and the orthogonal channels show identical far-field patterns. The antenna is well suited for millimeter-wave polarimetric synthetic aperture radars (SARs) and high-efficiency balanced-mixer receivers. >