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4. Consideration
4.1 Consideration on comparison between circular and horizontal polarization
 
The reason why the SART signal of circular polarization is superior to that of horizontal polarization should be considered as follows:
 
.1 According to the equation of transmission of radar beam, received wave is the mixture of direct transmission and reflected transmission at sea surface, in both ways from radar antenna to a object (irradiation) and from objects to radar antenna (reflection). The phase of the wave changes by pi radian (180 degrees) at the sea surface reflection. The difference of distance of wave passes between the direct transmission and the transmission reflected at sea surface causes the divergence of the phase at the mixture of both wave at receiving point (radar antenna and at objects). This divergence results in weakening the power of the mixture which decreases along the distance between the radar and the object in showing the maximum and the minimum. The phenomenon has been known well.
 
.2 It is also known well that the degree of the phase change at sea surface reflection depends on the polarization of wave which goes into the reflection point. The wave from radar, which polarization is horizontal, changes its phase at sea surface reflection by pi radian. Then its return signal from the object shows clear maximum and minimum of power at the receiver of the radar.
 
.3 The SART signal of circular polarization changes continuously the polarization plane in 360 degrees. Therefore, the phase change at the sea surface is not constant. This results in the fact that the compensation happened at mixture of direct wave and reflected wave is not constant and the radar can receive the maximum power of the mixture. Then, this fact leads the extension of the maximum visible distance of SART of circular polarization.
 
.4 The SART antenna is always rolling at sea. This movement affects the polarization plane of the SART signal. The SART signal of circular polarization would have much probability to be caught by radar antenna which polarization of horizontal than SART signal of horizontal polarization would have.
 
All the reasons mentioned above show the superiority of circular polarization for SART signal, and these have been proved by the sea trials.
 
3.2 Consideration of possible amendment to the SART standard
In order to allow the sue of circular polarization antenna for SART, the following amendment to the third sentence of paragraph 2.5 of ANNEX to the Assembly resolution A.802(19) has been derived. This amendment has no effect of existing standards of radar.
 
Proposed amendment:
Insert "and/or any polarization which is received effectively by search radards" after "Horizontal polarization" in the third sentence of paragraph 2.5 of ANNEX to the Assembly resolution A.802(19).
 
So, the whole sentence should read:
"Horizontal polarizatrion and/or any polarization which is received effectively by search radards should be used for transmission and reception."
 
3.3 Merit of SART of circular polarization
This amendment will allow the use of circular polarization which shall contribute the enhance of maritime safety by the following merits:
 
.1 It will allow a development of a new type of SART which needs smaller power in keeping its capability of radio-communication at sea.
 
.2 The signal from such SART can be observed stably by 9GHz radar in further distance than existing SART can be.
 
.3 It will allow more flexible design of SART by not limiting the polarization in horizontal. Such SART may be of lighter weight and smaller and easy to install into liferafts and lifeboats. It will be also possible to develop a smaller SART which can be fitted in lifejackets and float-free VDR
 
.4 There is no need to change the existing radars and the existing standards for radars.







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