JET PROPULSION LABORATORY INTEROFFICE MEMORANDUM 315-RSA-91-08 25 November, 1991 TO: Distribution FROM: R. S. Austin l SUBJECT: Magellan Telecom Antenna Patterns for Radioscience Occultation Data Reduction LABEL ID = ANTL.88258;1 PURPOSE This IOM contains the Magellan S and X-band telecom high-gain- antenna (HGA) gain profiles necessary for reduction of the radioscience occultation data collected on 5 and 6 October, 1991. This data product, along with the received S and X-band doppler data recorded at DSS 43 (Label ID=RSODR.43), appropriate navigation files (Label ID=EPHEMDR.3212-3214;1), and the reconstructed spacecraft limb-track-maneuver and AGC profiles (LABEL IDs LTMAGCDR.3212-3214;1) form the Radioscience Occultation Experiment "raw data set". These antenna gain profiles are required to determine the effective gain of the antenna along the spacecraft to earth ray path vector. This information is necessary to de-couple changes in the received signal level that result from atmospheric attenuation from those due to changes in the effective antenna gain. ANTENNA DOWNLINK HGA GAIN PATTERNS For both the X and S-band patterns, data are given over two ranges. The first spans an angle of +/- 6 degrees from antenna boresight. The second set covers only the 3 dB beamwidth allowing more accurate gain estimates to be made in this region. Patterns for two principal orthogonal plane cuts (phi = 0 degrees and phi =90 degrees) are provided. Since the X-band antenna feed is circularly polarized, both RHCP and LHCP patterns are included. The S-band feed is linearly polarized so the Co-pol and Cross-pol data are provided. Note that the 3 dB only beamwidth patterns are not available for the S-band Cross-pol data. ANTENNA UPLINK GAIN PATTERNS Since the Magellan onboard reference oscillator does not possess the required stability for a radioscience occultation experiment, the uplink S-band signal from the DSS 43 station (80 kw transmit power) was used as the reference time base. An automatic gain control (AGC) loop in the Magellan receiver provides the necessary attenuation to maintain the uplink reference signal at the proper level. This commanded AGC (in dB) was recorded and is provided along with spacecraft attitude data in the spacecraft limb-track- maneuver and A&C profile data product. Since this data might prove useful as an independent check on atmospheric attenuation, the S-band uplink antenna pattern data are also provided. ANTENNA PATTERN FIGURE LISTING Downlink Figure # Frequency Plane Cut Range Polarization 102 X-band phi=0 deg +/-6 deg RHCP 103 X-band phi=90 deg +/-6 deg RHCP 104 X-band phi=0 deg +/-6 deg LHCP 105 X-band phi=90 deg +/-6 deg LHCP 107 X-band phi=0 deg & 3 dB RHCP 90 deg 108 X-band phi=0 deg & 3 dB LHCP 90 deg 52 S-band phi=0 deg +/-6 deg Co-pol 53 S-band phi=90 deg +/-6 deg Co-pol 54 S-band phi=0 deg +/-6 deg Cross-pol 55 S-band phi=90 deg +/-6 deg Cross-pol 58 S-band phi=0 deg 3 dB Co-pol 59 S-band phi=90 deg 3 dB Co-pol Uplink 48 S-band phi=0 deg +/-6 deg Co-pol 49 S-band phi=90 deg +/-6 deg Co-pol 50 S-band phi=0 deg +/-6 deg Cross-pol 51 S-band phi=90 deg +/-6 deg Cross-pol 56 S-band phi=0 deg 3 dB Co-pol 57 S-band phi=90 deg 3 dB Co-pol ANTENNA PATTERN GAIN MEASUREMENTS (APPENDIX A) The data in this IOM were obtained from measurements of the Magellan high-gain antenna made at the Near-Field Test Laboratory of the Martin Marietta Astronautics Group. The results were published in a final report prepared by Neil Kefauver (September 20, 1988). An excerpt from this report which briefly describes how the data were measured, including estimates of the measured gain accuracies, is included in this IOM as appendix A.