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

is the low pass equivalent of this selectivity characteristic,
then ff is the Fourier transform of IF(_o)t 2 . Let us
assume the receiver has an ideal bandpass characteristic
B Hz wide. Then
sin rrBAr
if(At) - -- (M26)
rtBAT
Since (M25) and (M26) are even function,:, their product
is also even and:
sin 7rBAr
(1 -_.A_) d(Ar)
nBAr
On the other hand, if we use delay phasing on the
pilots only, the loss will be much less since shorter
delays are needed to get the required phase shift at the
pilot frequency.
Pure delay phasing is thus a distinct possibility for
Cyclops when observing wideband signals, and deserves
further study.
CASE IIl - ARRAY PHASED FOR ANGLE 0, DELAYS
ADJUSTED TO PRODUCE OFF AXIS BEAM
Assume the local oscillators are phased for a signal
arriving at an angle 0 from the zenith, and the signal
from antenna A is delayed an amount r a = r + Ar to
produce an off-axis beam making an angle 0 + 6 with the
zenith. The delay at receiver B for a signal from this
direction is
- -- tSi(_rBYi) + -- (cosrrBff i - 1)l
rrB
rrB
Thus the loss due to the delay
distributed from- l/2fi to 1/2fi is
L = 10log2
errors
SiuU cos u - 1/
B
(M27)
uniformly
(M28)
Figure M-3 is a plot of L as a function of Bffi. We see
that for a 100 MHz band centered at 125 MHz (B/f i = 0.8)
the loss is about 0.73 dB. This is the loss we would
incur in observing wideband incoherent signals if we
adjusted the delays of the entire IF signal (both bands
plus the pilot signal) to get the proper phasing, and then
used the pilot to modulate both IF bands down to the
range
0
75 to 175 MHz.
and for 6