NIMBUS II VHF MULTIPATH INVESTIGATIONS.
NATIONAL AVIATION FACILITIES EXPERIMENTAL CENTER ATLANTIC CITY N J
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An over ocean and limited over land flight test program was conducted to obtain data on performance degradation of VHF radio frequency satellite-to-aircraft communication links resulting primarily from multipath propagation fade effects. The Nimbus II satellite was used to provide a signal source for the measurements which were made in an instrumented aircraft equipped with a conventional VHF blade antenna and a special design circularly polarized satellite communications antenna. In addition to the acquisition of multipath data, the aircraft received a real time printout of Nimbus Automatic Picture Transmission System weather pictures. Data were obtained for varying satellite azimuth angles with the elevation angles ranging from near grazing to 90 degrees. The special airborne satcom antenna was used in both the low and high elevation angle operation modes with results indicating only minor fades of 1 dB or less in the high angle mode. For the low angle mode, below 40 degrees, the measurements showed that multipath propagation can be a significant source of satellite-to-aircraft link performance degradation. Results of the tests indicated that for 98 percent of the data samples fade degradation was less than 8 dB. The average fade depth measured was 4 dB and the maximum was 10 dB. Author
- Radiofrequency Wave Propagation
- Radio Communications