Two prototype solid-state phased array systems concepts developed for the solar power satellite (SPS) are described. In both concepts, the beam was centered on the rectenna by means of phase conjugation of a pilot signal emanating from the ground. Also discussed are results of solid state studies

Schroeder, K. G.

English

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9 SOLID-STATE CONFI GURATIONS
___ _ _' K.G. Schroeder
.- K'ocl_vel] international - Anaheim, California
:INTRODUCTION
This paper describes two prototype solid-state phased array systems concepts
developed by Rockwell for the Solar Power Satellite (SPS). In both concepts,
the beam is centered on the rectenna by means of phase conjugation of a pllot
signal emanating from the ground. Also dlscussed are solid-state studies per-
formed at Boeing and Raytheon.
The basic Rockwell concepts are now described in more detail.
OVERVIEW OF SOLID-STATE ARRAY CONCEPTS
Two different solld_state arrays are being developed at this tlme: The End-
Mounted Space System (Figure l) and the Sandwich (Figure 2). Both concepts
use the same element (a dipole) and spacing, but in the end-mounted system
36-watt amplifiers are mounted on the ground-plane, whereas in the sandwich the
amplifiers are elevated to the dipoles, and their waste heat is dissipated by
beryllium oxide discs. The feed lines are underneath the ground-plane, and
a coaxlal transmission line is carried all the way to the amplifier input.
(See sectlon on RF Slgnal Distribution).
REFERENCE PHASE DISTRIBUTION
Phase conjugation at the 5 meter by 5 meter subarray is used to steer the beam.
The reference phase signal is distributed over the apacetenna aperture via a
radlo link. Figure 3 illustrates thls method giving a perspective view of the
top of the aperture. Two important features are: (a) the phase reference
signal originates from a single transmit location at the rear of the aperture;
and (b) phase reference and pilot antennas are orthogonally polarized wlth
respect to the power dipoles to avoid feedback loops. Instead of an endflre
(e.g., "Cigar") array, broadside arrays can be used for reference and pllot
pick-up. Both configurations shall be. considered in more detall in future
studies.
The phase reference signal is distributed as follows:
From the shaped-beam illuminator antenna an RF signal is distributed over a
cone with maximally 90 degrees'beamwldth. All reference pick-up antennas see
approximately the same signal strength. The local oscillator and driver am-
plifer is redundant. Large variations in aperture flatness can be compensated
modulo 2 w since bandwidth is of no concern for the reference phase signal. The
phase at each subarray pick-up point is normalized wlth respect to a perfectly
flat uniform aperture by means of a servo loop shown in Figure 4. For each
subarray center location, a phase delay differential ("reference standard") is
computed which occurs for the two generating frequencies fRl and fR2 If the
receiving antenna Is located on a perfect plane. These del_ys can'_e calculated,
and tuned in the lab to fractions of a degree. The output of the phase bridge
then drives a phase shifter until the path delay differential equals that of
the reference standard.
340
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https://ntrs.nasa.gov/search.jsp?R=19820014865 2020-03-21T16:26:52+00:00Z
Since this circuit is used at every subarray, the subarray center points are
electrically normalized to show _=_S constant across the entire array. This
provides the conjugation circuit with the required reference phase.
RETRODIRECTIVE BEAM CONTROL
A retrodirective control circuit which compensates for pilot-generated beam
shifts (without ionospheric effects) is the Chernoff circuit, with additional
isolation added by (a) separating the pilot and power frequency paths, (b)
using orthogonally polarized radiating elements; and (c) providing the remain-
ing isolation in separate bandpass filters. The total required filter
isolation is 70 dB, according to preliminary pilot system calculations.
This pilot system is predicated on _ 100 dBw pilot power. The proposed
implementation of this pilot system consists of a circular array of low to
medium-gain elements placed at the periphery of the rectenna, on top of
utility poles if necessary to avoid interference from the power collection
and transmission system.
The system provides vastly improved reliability over a single-dlsh, con-
centrated amplifier pilot system, and also provides such a wide power tube
when the near-field beam enters the ionosphere that certain ionospheric effects
will be mitigated. If ionospheric tests show that delay compensation through
the ionosphere is required, a three-tone pilot system will he used.
RF SIGNAL DISTRIBUTION SYSTEM
The current baseline distribution system for the conjugated RF signal is the
same for both solid-state concepts.
Six "levels" of 4-way corporate divisions provide equiphase feeding to the
4,096 elements in each 5m x 5m subarray. The network is contained in one
plane.
The salient features of this distribution network are: weight of 0.67 million
kilograms for the total array using UT-47M; 250°C temperature capability;
approximately 7 dB ohmic loss (in addition to 3_dB splitting loss). All
layers of coax are pressed together behind the ground-plane, and very little
thermal resistance is presented to the heat being radiated rearward from the
ground-plane in the end-mounted concept, and toward the ground-plane (from the
solar cells) in the sandwich concept. The composite heat transfer will be
established by the spacing between the ground plane and the solar cells in
the case of the sandwich.
An alternate approach uses strlpline distribution underneath the groundplane.
The advantage is better manufacturability but the ohmic loss is _ 20 dB
higher, requiring more amplification.
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FIGURE i. KND-MOUNTED SOLID-STATE CONFIGURATION
19200 M
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AVGOlk,]500 N
FIGURE 2. SANDWICH CONFIGURATION
2160 #
2500_1600N
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FIGURE 3.
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PHASE REFERENCE SIGNAL DISTRIBUTION SYSTEM
/k fR! %SELF-CONTAINEDTRANSMITTER / _ •
WITH OMNSOLAR |, |
" fRl. fR2 '__L'R
Af R -- 100 Ntz
ACJ_ 1 DEGREE
(94tT QUAm't_TION)
_180" 0 t'0
NOTE:PICK-UP ANTENNAORTHOGONALLYPOLARIZEDWITH RESI_CT TO PONERBENq
TOTAL ISOLATION IT> 40 ÷ 60 dB >100 dB
-_ ,_ --
CROSSPOt. FRONT-TO-BACKRATIO (CAN BE _ >100 dB)
FIGURE 4. REFERENCE SIGNAL CONTROL LOOP
REF. SIGNALRECEIVE ANTENNA
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(CHARACTERISTIC
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ARRAYUPPERSURFACE
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DIPLEXER
fRl
PHASESHIFTER
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DIRECTIONALCOUPLER
CONTROLPHASESHIFTER
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Solid-state configurations

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