Project Cyclops, A Design... - Department of Earth and Planetary ...

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APPENDIX
H
POLARIZATION
CONSIDERATIONS
The sensitivity of the Cyclops array depends on the
alignment of the polarization of the transmitter with the
polarization of the receiver. The polarization of the
transmitter is unknown, however, and to avoid loss of
sensitivity, steps must be taken to ensure that the
receiver receives most of the incident polarization. The
discussion is facilitated if the Poincar_ sphere (ref. l)
shown in Figure H-I is used. Any arbitrary polarization
is described by the radius vector from the origin to a
point on the sphere. If the vector representing the
incident polarization makes an angle 0 with the vector
representing the receiver polarization, the received field
strength is:
If horizontally and vertically polarized receivers are
provided, then the angle 0 will be no greater than n/2
from one or the other of the receivers. The maximum
loss would then be 3 dB. An expected value of loss may
also be calculated if the incident polarization is assumed
to be randomly distributed. This number is 1.3 dB.
Suppose now that the horizontal and vertical channels,
designated by H and V, are received, and that after
amplification the processing scheme shown in Figure
H-2a is used. This processing results in an equal spacing
of the receivers around the equator of the Poincard
sphere. Again the maximum loss is 3 dB but the
expected
value of loss is now 0.7 dB.
E
= E0cos-
0
2
Vo
v+___H_
LEFT CIRCULAR
POLARIZATION
I
(0) HO
,°",L.C,vo
H
o V {LHC)
("V')
_V+H
V-H
( "H" )
(RH)
Ho
o H (RHC)
°uA_
v+jH
v-j_____H
.v/r _ 1135"1
qC5
I
RIGHT CIRCULAR
POLARIZATION
Figure H-I. The Poincard sphere.
l
Figure H-2. Polarization conversion.
To carry this operation to its logical conclusion,
receivers would be placed at the cardinal points of the
Poincard sphere. The processing scheme shown in Figure
207