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

ands, each covering a 1.35 to 1 frequency range are
used, giving the following ranges:
Band Range (GHz) Coverage (MHz)
1 0.5 -0.675 175
2 0.675-0.91 235
3 0.91 -1.23 320
4 1.23 -1.66 430
5 1.66 -2.24 580
6 2.24 -3.02 780
The portion of the receiver associated with each band
comprises a circularly symmetric feedhorn coupled to
two up-converters, one for each orthogonal polarization
mode. The up-converters in use are cooled to 20° K and
their outputs are fed to two masers operating at 10 GHz
(or higher) and cooled to 4° K. The maser outputs are
further amplified and then down converted to the IF
frequency. Precision frequencies derived from a hydrogen
maser are used for the up- and down-conversions,
and the array phasing is done in the final down
conversion.
Two IF channels per receiver are proposed, one for
each polarization. As shown in Appendix H, the choice
of orthogonal polarizations is arbitrary. Thus vertical
and horizontal linear, or right and left circular polarization
may be used. From the two polarizations selected
four additional polarizations may be resolved at the central
processing station to give a total of six: V, H, V + H
(or 45°), V - H (or 135°), V + /1t (left circular) and
V-/11 (right circular). If all six are processed the average
loss, for a signal of unknown polarization, is 0.4 dB and
the maximum loss is 1 dB. If only four polarizations are
processed the average loss is 0.7 dB and the maximum
loss is 3 dB. Since 3 dB represents a loss of half the antenna
surface and since processing costs are much less
than antenna costs, it is recommended that all six polarizations
be processed.
A detailed block diagram of the dual polarization
Cyclops receiver is shown in Figure 9-2. Below the
horizontal dashed line in the figure the blocks shown
are used for all bands. Above the dashed line a complete
set of the blocks shown is needed for each of the six proposed
bands. The various blocks and their functions are
described in greater detail in the sections to follow.
ANTENNA OPTICS AND FEED SYSTEM
Because antennas and the associated feed systems
generally obey reciprocity, we may analyze the operation
in either the transmission or the reception mode as best
suits our convenience. Although we are primarily concerned
with reception, we may, for example, choose to
C,CI 0,TR0C0NAL / NHC
-- t rOLAmZAT_ON [ 'l
I c°uPL" / ' '
t O,,Tt
i uF-'-I. F-'-Cff_. I j PNASE - I J uP I
1 CONVERTER _ LOCEED PUMP _'_ I _'"I LOC_D PUNP _-_ CONVERTER I
U ........ L__
EF£F- F?f I SWITCH I
_. i I r 6ROAOEAM_ 1 " : _[ TRAVELING [
I lAVE MASER _ PUMP l I " "[ lAVE MASER I
' I " ' l
SCHOTTI_Y I _ FREOUENCY _" SC_TTI_'
BARRIERFET ' I [ _ SYNTHESIZER '' ["-I IBARRIERIrET
1
ANPLIFIER__JCONPUTER I. Izs.Hz / r---I-_ AII_IFIER
CONTROL I I ÷ , /
SIGNA'SlI I PHASE_ ,(_
L.O. OlSr __._
SYSTEM
STATIOII UNIT /
/5-IT5NHz _ MULTIPLEX IF I"
I
lf tABLE
TS-ITSNHZ
TO NEXT
ANTENNA
Figure 9-2. Dual polarization receiver.
speak of the uniformity with which the feed horn
"illuminates" the antenna surface realizing that this also
describes the uniformity of receiver sensitivity to signals
received from various portions of the antenna surface.
If U(,o,_) is the amplitude of the field over a plane
normal to the axis of the paraboloid and bounded by its
rim, then the far field on-axis radiation intensity at the
distance R is
1
lul 2 = --_2R----7 If UdAI 2 (1)
where dA is an element of the surface and the integral is
over the whole surface. The amplitude U is a complex
vector quantity and lul 2 will be reduced if the phase and
polarization are not constant over the surface. If the
antenna were isotropic the intensity at the same far field
point would be
P
lul= =-- (2)
4rrR 2
88