Abstract of the Investigation on Performance of Circular Polarization SART from Research and Study on Performance Improvement about SART
This study was conducted by Japan Ship-Machinery Quality Control Association in co-operation with Japan Coast Guard and other related organizations.
Only horizontal polarization is currently allowed and being used as method of polarization of SART. However, from the recent examinations, Japan thought that the circular polarization would be able to use to SART. Then the SART using signal of circular polarization with a helical antenna is made for trial purposes, and the water tank experiment and sea trial have been conducted. The results showed the superiority of circular polarization used in SART and it was prospected that it will enable to miniaturize the size of SART. As the necessity of the data in rough weather condition was pointed out, the outline of observation results both in calm and rough weather condition are briefly described in this annex.
1 Observation results in calm weather condition
The experiments in calm wave condition are described in COMSAR 7/11, annex. The point is described here.
1.1 Observation results on visibility of SART signal at tank tests
Measurement of received power of SART signal and observation of visibility of the signal on radar PPI were carried out in Tokyo University of Marine Science and Technology. The results showed that the circular polarization was superior to the horizontal polarization for SART.
1.2 Observation results on visibility of SART signal at on-sea trial in calm weather condition
This experiment was conducted on 2000 in co-operation of ships and aircrafts of Maritime Authorities of Japan in Sagami Bay to observe visibility of the SART signal on the radars on board the ships and the aircrafts. In the meantime, the received power of the SART signal was measured by a land-based radar. The following results have been obtained.
.1 by aircraft radar, the maximum visible distance of SART signal of circular polarization was 37 NM, while that of horizontal polarization was 30 NM. This confirms the superiority of circular polarization.
.2 by marine radar, the maximum visible distance of SART signal of circular polarization was 14 NM, while that of horizontal polarization was 11.5 NM. These results confirm the superiority of circular polarization.
.3 by land-based marine radar, the result shown in Figure-1 was obtained. The SART of circular polarization was moved on sea by an escorting small vessel. The distance between the radar and the SART was changed. The received power of the SART was measured by the land-based marine radar. In Figure-1, black dots means data that actually measured SART signal of circular polarization, and dotted line means theoretical value of SART signal of horizontal polarization. The measured data always appear above the theoretical value curve for "SART to radar". Appearance of SART signal of circular polarization on the radar PPI was stronger and clearer than that of horizontal polarization. These results confirm the superiority of circular polarization.
||Observed data of SART signal of circular polarization and theoretical value of horizontal polarization
2 Observation and measurement by land-based radar in rough weather condition
A 9GHz radar of research purpose owned by Tokyo University of Marine Science and Technology installed on a vehicle was used to observe and measure the SART signal of circular polarization and horizontal polarization. Both SARTs were installed on a buoy for this experiment and their antenna height kept 1 m from the sea level. Both SARTs used the transmission module of the same specification. The difference was only antenna. The buoy with SARTs was anchor in offing. The radar observed both SARTs while changing the observation points. The conditions of two observations are as follows.
.1 At Niigata prefecture in October 2003.
The distance of the radar and SARTs: 1.52 NM - 12.9 NM.
Weather: fine Wave height: 0.8 - 1.0 m Wind velocity: 2 - 3 m
.2 At Kanagawa prefecture in March 2004.
The distance of the radar and SARTs: 1.3 NM - 15.6 NM.
Weather: fine Wave height: 2 - 3 m Wind velocity: 5 - 8 m
The following results have been obtained.
2.1 Observation results by land-based radar in rough weather condition
The observation results were shown in Figure-2 and Figure-3.
||Signal strength that radar received from SART in wave height 0.8 - 1.0 m
||Signal strength that radar received from SART in wave height 2 - 3 m
The maximum value of the SART signal of circular polarization and that of horizontal polarization in each observation point were compared. The difference is -0.8 to +5.6 dB. The plus means the signal of circular polarization is strong. Therefore, the signal of circular polarization is stronger than that of horizontal polarization or almost same.
It was confirmed that SART of circular polarization was not inferior compared with that of horizontal polarization.
The detailed consideration and the merits of circular polarization are referred in paragraphs 7 - 9 of the main text of this document.