C-band Antenna Research Articles

Combined-Phase-Shift Waveguide Polarizer

A waveguide polarizer exploiting two different phase shift phenomena is presented in this letter. Iris-type discontinuities are in fact introduced in a waveguide structure having different propagation constants for the two principal polarizations. In this way, the required 90 differential phase shift is obtained combining the iris phase shift with the waveguide one. Several operative conditions arise from the combination of the two contributions. This approach has been used to design a broadband waveguide polarizer for the C-band antenna feed system of the Sardinia radio telescope with -40 dB reflection coefficients and a -35 dB cross polarization level in a 30% bandwidth.

Accuracy assessment of interferometric digital elevation models derived from the Shuttle Radar Topography Mission X- and C-band data in a test area with rolling topography and moderate forest cover

In February 2000, the Shuttle Radar Topography Mission (SRTM) mapped large areas of the global landmass using two radar systems operating simultaneously in X and C band. The radar mapping instrument consisted of modified versions of the SIR-C C-band and X-band radars flown on the shuttle in 1994. Modifications included a 60-m retractable boom, with C-band and X-band receive-only antennas attached to the boom's end. High-accuracy metrology systems were added to measure position and attitude of the shuttle and the positions of the boom antennas. The dual apertures at each band form radar interferometers suitable for making high-accuracy topographic maps of the Earth. The C-band data set is being processed by JPL for the archives of the National Imagery and Mapping Agency and the National Aeronautics and Space Administration. The X-band data set is processed and distributed at DLR, Germany. This paper deals with the accuracy assessments of the interferometric DEMs derived from the X- and C-band synthetic aperture radar systems over a testfield with rolling topography and moderate forest cover using the reference DEM digitized from the topographic maps of 1:25,000 scale. Obtained results for the two interferometric DEMs are similar and lie in the range of 10–11 m. The accuracy of SRTM X- and C-band DEMs was also checked against ground control points measured by differential GPS, and the rms height errors were found to be about 9 m, which confirms the results based on the reference DEM.

The Shuttle Radar Topography Mission–a new source of near-global digital elevation data

The Shuttle Radar Topography Mission (SRTM) has generated a homogeneous near-global digital elevation model (DEM) of the Earth using single-pass radar interferometry. The crew of Space Shuttle Endeavour (STS-99) operated the modified dual-antenna synthetic aperture radar systems for 11 days in February 2000. SRTM acquired both C-band and X-band synthetic aperture radar data, collecting 3D data using a 60-metre mast extending from the shuttle payload bay, containing additional C-band and X-band receiver antennas. SRTM DEM data have a horizontal resolution of 1 arc second (30 m at the equator) and vertical resolution of 10 m (C-band radar). SRTM-1 (1 arc second) data are available for US territories only, with subsampled SRTM-3 (3 arc second) data provided for the rest of the world. The USGS is responsible for archiving the data, with 3 arc second data being made freely available on a continent-by-continent basis. All data processing was completed in July 2004. Comparison of SRTM DEM data with older GTOPO and altimetric DEMs shows a significant improvement in horizontal and/or vertical resolution, similar to that achieved by ASTER. The SRTM DEM data provide a useful new resource, especially in areas where limited topographic data are available.

Design of a Vlasov antenna with reflector

The Vlasov antenna, composed of a slant-cut radiator and a parabolic cylinder reflector, is designed by using vector diffraction theory. The experiential formulae on the antenna design are given. A C-band Vlasov antenna, composed of a cylindrical waveguide of 4.5 cm radius with 35° as the bevel-cut angle, and a reflector, was designed. The calculations and measurement results show that the antenna can work over a wide bandwidth (from 3.6 GHz to 5.6 GHz). The gain is about 21 dBi at 4 GHz and over 23 dBi at 5.6 GHz. The energy emission efficiency exceeds 90% at 4 GHz and the overall efficiency exceeds 88% in the range from 3.6 GHz to 5.6 GHz.

Study on the wide-band and high-gain microstrip antenna element

A novel three layers microstrip antenna element that has the advantages of wideband and high-gain is proposed. The eigenvalue equation and the frequency characteristic formulas of the input Voltage Stand Wave Ratio (VSWR) are obtained by using the spectral domain method and equivalent circuit method, respectively. With the aid of the numerical results, a C-band microstrip antenna element with bandwidth of 16% (VSWR<1.5) or 25% (VSWR<2) and gain of 10.2–11.3 dB is developed, which are much larger than the bandwidth of 5–6% and the gain of 6–7 dB of the common microstrip antenna element.

Investigation of Telstar 4 spacecraft Ku-band and C-band antenna components for multipactor breakdown

Multipactor is an electron resonance phenomenon which occurs at radio frequencies in components and transmission lines operating in vacuum. Multipactor represents a possible payload failure mechanism for communications satellites since it can destroy RF components or transmission lines, or it can significantly raise noise levels. The Telstar 4 series of spacecraft presently being built for AT&T by Martin Marietta will carry 24 high-power transponders for Ku-band (/spl sim/60 W/transponder) and 24 medium-power transponders for C-band (/spl sim/25 W/transponder). The outputs of a number of transponders are frequency multiplexed prior to being input to the Ku-band or C-band antenna feed networks (AFN). Computation shows that instantaneous peak powers due to the combined signals can reach 4500 W at Ku-band and 3900 W at C-band. For the purpose of ensuring that the AFN would not suffer multipactor breakdown in orbit, each of the individual components in the C-band and Ku-band AFN were subjected to instantaneous peak powers well in excess of that which will be experienced in space. The high instantaneous peak powers required for this pre-flight testing were realized by phasor addition of the high-VSWR standing waves of two diplexed carriers of slightly different frequencies. This technique effectively provided an instantaneous peak power 32 times the average power output of each of the two input carriers. Test sets to accomplish this were constructed at both C-band and Ku-band. The ability to detect multipactor (by two independent means) was assured by measuring test cells which were specifically designed to break down for the test levels previously mentioned. Investigations of the separate AFN components for the Telstar 4 spacecraft showed that all components passed with substantial margin.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anik-E2 recovery mission

Anik-E2 was launched from Kourou on an Ariane 44P on 4 April 1991. Upon a successful completion of a series of apogee burns, the satellite reached the predicted drift orbit. Subsequently, two anomalies on deployment occurred. The first anomaly was the delay in deploying the Ku-band reflector. The full deployment did not occur until 2 days after the tie-down pyro firing. The second anomaly was noticed in connection with the deployment of the C-band reflector which did not deploy. An intensive investigation was immediately organized by Telesat and supported by Spar Aerospace and GE Astro to identify the possible cause(s) of the C-band antenna deployment failure. The investigations were focused on possible causes of failure which included the wiring of the pyro harness, freezing of the hinge damper, structural failure of the struts supporting the reflectors, alignment of the reflector tie-downs and interference of the thermal blankets surrounding the tie-down mechanisms. Due to some outstanding logistic planning effort and execution of a number of Anik-E2 flight manoeuvres and Anik-E1 ground testing, it was soon concluded that the most likely cause for the C-band reflector deployment failure was an interference resulting from the loosening of the thermal blankets surrounding the tie-down mechanisms. Based on the results of ground testing on Anik-E1, the required breakaway force for the snag was determined. This force requirement created a reflector deployment environment which was much more severe than the nominal design environment. In order to safely deploy the C-band reflector, another series of non-stop activities were performed by Telesat and its contractors to define a more dynamic satellite maneuver, e.g. high degree of nutation, coupled with a cold soak for the hinge dampers in order to provide a high breakaway force and efficient energy absorption during deployment to reduce the force at impact. A series of complex maneuvers with gradually increasing nutation was performed and the C-band reflector was eventually safely deployed on 3 July 1991 which was 3 months after the launch. Due to the constraints of the omni antenna coverage and the battery capacity, Telesat had conducted a large number of maneuvers which were never envisaged and rarely if ever carried out before. This paper will detail all the fault investigation events and mission maneuvers which led to the final recovery of the Anik-E2 satellite, and briefly describe the modification implemented on Anik-E1 which was subsequently launched and on which all deployments were executed flawlessly.

The TOPSAR interferometric radar topographic mapping instrument

The authors have augmented the NASA DC-8 AIRSAR instrument with a pair of C-band antennas displaced across track to form an interferometer sensitive to topographic variations of the Earth's surface. During the 1991 DC-8 flight campaign, data were acquired over several sites in the US and Europe, and topographic maps were produced from several of these flight lines. Analysis of the results indicate that statistical errors are in the 2-4-m range, while systematic effects due to aircraft motion are in the 10-20-m range. The initial results from development of a second-generation processor show that aircraft motion compensation algorithms reduce the systematic variations to 2 m, while the statistical errors are reduced to 2-3 m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cross-dipole fed square horn

A circularly polarized cross-dipole fed square horn feed for C-band antenna system is designed to have a minimum axial ratio when radiating into free space. This type of feed can be used for dual band antennas in space. An analysis of multipactor break-down in the feed is also given.

Determination of KU-band earth station antenna G/T using the moon as RF source

The Moon has been successfully used as a calibrated source of RF emissions in determining the gain-to-noise-temperature ratios (G/Ts) of medium size C-band antennas. This method to determining G/T has recently been applied to Ku-band antennas as well, and the results have agreed well with independent measurements of gain and temperature. However, because of the fact at the Moon's angular diameter may extend beyond the main lobe of lobe antenna, a gain correction factor has to be applied. This factor requires accurate knowledge of the gain pattern for its determination, but once such knowledge has been obtained by pattern measurement, the G/T can be calculated with reasonable accuracy.