The total breadboard system includes one pilot transmitter, one pilot receiver, nine phase distribution units, and two power transponders. With this complement of equipment, segments of a typical phase distribution system can be assembled to facilitate the evaluation of significant system parameters. The achievable accuracy of a large phase distribution system, the sensitivity of the system to parameter variations, and the limitations of commercially available components in such applications were determined

Hopkins, P. M.

Rao, V. R.

English

NASA Technical Reports Server

DESIGN AND BREADBOARD EVALUATION OF THE SPS 
REFERENCE PHASE CONTROL SYSTEM CONCEPT 
P. M .  Hopkins and V .  R. Rao 
Lockheed Engineering and Management Services Company, Inc. 
1 .  INTRODUCTION 
Efficient operation of a very large phased array such as the proposed solar 
power s a t e l l i t e  [I], requires precision focusing and pointing of the power 
beam; i .e . ,  t h e  power beam must have a planar wavefront directed precisely 
a t  the  center of the target  antenna (rectenna). To maintain such a power 
beam requires real-time phase compensation a t  each subaperture in order to 
adjust  for  structural  deformations and other t ransi tory factors. In the 
current solar power s a t e l l i t e  (SPS) base1 ine, the spaceborne antenna (Space- 
tenna) i s  an active retrodirective array [2], [3]. A p i lo t  signal trans- 
mitted from the center of the rectenna i s  phase-conjugated a t  each subaper- 
tu re  (power module) of the spacetenna, thereby assuring that  the radiated 
composite wave i s  focused on the target .  This scheme requires a large amount 
of precision electronic c i rcu i t ry  on the spacetenna. Specifically, p i lo t  
receivers must be located a t  each power module and an adaptive distribution 
network i s  required in order to  provide a properly phased reference signal 
a t  each conjugator [4], 153. 
In order t o  verify theoretical and simulation resu l t s ,  a project was in i t i a ted  
by the Tracking and Communication Systems Department of Lockheed Electronics 
Company to  design, develop, and t e s t  a breadboard system comprising a p i lo t  
receiver and transmitter,  phase dis t r ibut ion system, and power transponder. 
This breadboard system i s  t o  be used in the Electronic Systems Test Laboratory 
(ESTL) a t  the Johnson Space Center. The tota l  breadboard system will include 
one p i lo t  transmitter,  one p i lo t  receiver, nine phase distribution units,  and 
https://ntrs.nasa.gov/search.jsp?R=19810008026 2020-03-21T15:13:15+00:00Z
two power transponders. i t  wiii be shown i n  the  foilowing sections of t h i s  
paper t h a t w i t h  t h i s  compiement of equipment, segments of a 'iypicai phase 
distribution system can be assembled t o  f a c i l i t a t e  the evaluation of s ignif-  
icant system parameters. 
The major objectives of the project are  to  determine the achievabie accuracy 
of a i a r se  phase distribution system, the sensi t iv i ty  of the sys.:em to  para- 
meter variations,  and the l imitations of co~ne rc i a l l y  available components 
i n  such applications. 
2.  ACCOKTLISHKENTS 
The desirjn and devei opnent of a breadboard Kaster-Sl ave Returnable Tini ag 
System (MSRTS) w2s the f i r s t  objective of the project. Nine units weye 
planned; three were conpieted and used fo r  proQotype evaluation t e s t s .  Six 
r e ~ a i n i n g  units are in final  assembly. 
2.1 MSRTS BREADBOARD 
The BSRTS breatiboarti system i s  of a mocuiar design with three major e;enenCs. 
These are tfle Phase Tracking Unit ( P T U ) ,  the interface/Return Unit (IRU) 
and the Nain Frame. Koduiar cons5ruction permits the equipment to  be confi- 
giired in various ways as required to model portions of the proposed SPS 
pnase dis t r ibut ion t ree  network. A simplified functional diagram of a single 
MSRTS stage i s  shown in Figure 1.  Figure 2 shows the t ree  distr ibution 
struc.;ure for  wnich the breadboard KSRTS i s  designed. 
The major componenCs of the PTU are  Vo; tage Controi led Oscii l a to r  ( V C O ) ,  
loop f i l t e r ,  c i rcula tor ,  mixers and a phase detector. The phase lock loop 
c i rcu i t ry  i s  used t o  advance the phase of VCO t o  compensate fo r  the e f fec t  
of the delay in-troduced by the path between nodes of a t r e e  structure.  
A t  the IRU, two functions are  performed. F i r s t ,  a portion of the received 
reference signal i s  returned to  the preceding PTU via the single in ter-  
connecting cable. This return signal arr ives  a t  the PTU with a phase delay 
proportional t o  the Sine length. The delay i s  measured in the phase detector 

Figure 2. MSRTS Elements in a Phase Distribution Tree !Jetwork m\ 
of the  PTU, and the VCO phase i s  appropriately adjusted so tha t  the reference 
phase i s  correct  a t  the IRU input. Second, the reference signal a t  the IRU 
i s  doubled in frequency t o  match the reference input to  the PTU. When the 
PTU i s  phase locked, the phase of the IRU output signal i s  the same as  the 
phase of the preceding PTU input signal,  within the accuracy l imitations 
of the  hardware. Each IRU can provide u p  to  four outputs. 
The Main Frame contains supplies and a patch pane7 tha t  f a c i l i t a t e s  the 
interconnection between PTU1s and IRU's mounted in separate mainframes. 
Each mainframe i s  capable of supporting a to ta l  of three PTU1s and/or IRU1s. 
2.2 MSRTS BREADBOARD TEST RESULTS 
Three prototype MSRTS breadboard units were used in a variety of t e s t  con- 
figurations t o  evaluate the accuracy of phase control and the effects  of 
component imperfections. These t e s t  configurations included those shown 
in Figure 3. 
For example, the three-node se r ies  network of Figure 3c was tested with 30 
dif ferent  cabl e combinations, using RG-14 coaxial cabl e in lengths between 
200 and 250 f ee t  (60 - 80 meters); tha t  i s ,  a f t e r  i n i t i a l  adjustment of the 
t e s t  configuration with zero phase e r ro r  on the vector voltmeter, 30 dif ferent  
combinations of cables were substi tuted for  Test Cables A and B. For each 
combination, the result ing phase error  was measured and recorded. The resu l t s  
are presented in the histogram of Figure 4, which indicates a standard 
deviation of error  of 4.2O. This experiment i s  intended to demonstrate the 
accuracy of the breadboard MSRTS w i t h  arbi t rary  cable lengths. I t  i s  impor- 
t an t  t o  note that  the cables were not cut  t o  preGse measurements. 
Another type of phase error measurement was made w i t h  the configuration of 
Figure 3a. Minor variations in e lect r ical  1 ine length were introduced by 
means of a phase sh i f t e r  (PS2). The phase e r ro r  a t  the vector voltmeter 
was i n i t i a l l y  nulled w i t h  PS2 s e t  t o  zero. Then PS2 was varied from 0 to  
180°, equivalent to a half-wave variation in cable length. The result ing 
phase error i s  shown in Figure 5. 
TEST i+*
C A B L E  
VECTOR - 
VOLTMETER - 
a )  TWO-NODE 
?EST 
C A B L E  
A 
7ES T 
CABLE 
B 
980 Nnr  
SOURCE 
- - _ b) THREE-NODE SERIES 
T E s r  . 
980 MHz 
SOU RCE 1 . j f * 2  J c * ~  A 1 f k f l  
f E f l -  
CABLE 
C 
2 
Trsr cneLe B 
4 
C)  FOUR-NODE SERIES 
T E S T  
TFS: 
CABLE 
980 MHz 
S O U R C €  3-x 2 
VECTOR 
VOLT METER 
l V O L t M  ETE L - 3  
Figure 3. MSRTS Breadboard Test Configuration , 
STANDARD DEVIATION OF 30 TRIAL SAMPLE = 4.2 DEGREES 
0 
C) 1 2 3 4 5 6 7 8  
PHASE ERROR I N  DEGREES 
(ABSOLUTE VALUE) 
F igure  4. Histogram o f  Three-Node Test  Resul ts  
PTU1 - IRU2 
8 0  FEET RG-188 
e A LINE LENGTH, DEGREES O 1000 MHz 
F i g u r e  5.  Phase  E r r o r  V e r s u s  M i n o r  L i n e  L e n g t h  V a r i a t i , o n s .  
2.3 INTERPRETATION OF TEST RESULTS 
A detailed report of the MSRTS breadboard test results has been prepared 
6 The conclusions from that report are summarized in the following: 
s Satisfactory performance can be obtained using readily 
available components under closely control led conditions. 
e Commercially available components exhi bit non-ideal behavior 
which is critical to MSRTS performance, e.g. port-to-port 
isolation of mixers and circulators was not sufficient to 
prevent extraneous signal s which can cause phase errors. 
These effects can be minimized with compensating networks. 
3. CONTINUING DEVELOPMENT 
The breadboard MSRTS will be used as part of a larger breadboard system 
which models the total SPS phase control concept. A pilot transmitter 
will generate a pseudonoise (PM) code-modulated spread spectrum pilot 
carrier at 2450 MHz. A central pilot receiver will phaselock to the pilot 
carrier and provide a reference for the MSRTS. At the final level of the 
MSRTS tree, each IRU will provide a reference phase signal for a power 
transponder. Each power transponder will receive the pilot carrier, phase- 
conjugate, and retransmit. The ESTL breadboard system, shown functionally 
in a typical test configuration in Figure 6, will consist of the following 
units. 
One Pilot Transmitter 
@ One Central Pilot Receiver 
e Nine MSRTS Elements 
e Two Power Transponders 
e One Klystron Power Amp1 ifier 
These units can be interconnected in various test configurations. Tests 
will be performed to evaluate the feasibility of the MSRTS phase control 
concept and to determine the sensitivity of the phase control system to 
variations in system parameters. In addition, techniques for suppressing 
the phase noise of the klystron power amplifier will be investigated. 

Design and development of t h e  ESTL breadboard system wil l  be completed by 
March 1980. The t e s t  and evaluat ion program wi l l  be completed by Ju ly  1980. 
4. ACKNOWLEDGEMENTS 
The work described i n  t h i s  paper was performed under NASA Contract Number 
NAS 9-15800. The design,  development, and i n i t i a l  t e s t i n g  of t he  breadboard 
MSRTS was done by Dr. James C. Vanell i of Lockheed Electronics  Company, Inc. 
5. REFERENCES 
1 .  " I n i t i a l  Technical,  Environmental and Economic Evaluation of Space Solar  
Power Concept." NASA Lyndon B. Johnson Space Center, Houston, Texas, 
JSC-11568, August 31, 1971. 
2. Skolnick, M .  I .  and King, D. D . :  "Self-phasing Array Antennas." IEEE 
Transactions on Antennas and Propagation, Volume AP-12, pp. 142-149, 
March 1964. 
3. Ghose, R .  N . :  "E lec t ronica l ly  Adaptive Antenna Systems." IEEE Trans- 
ac t i ons  on Antennas and Propagation, Volume AP-12, pp. 161 -169, 
March 1964. 
4. Lindsey, W.  C. and Kantak, A.  V .  : "Automatic Phase Control i n  Solar  
Power S a t e l l i t e  Systems." Lincom Technical Report TR-7802-0977, 
February 15,  1978. 
5. Lindsey, W .  C . :  "A Solar  Power S a t e l l i t e  Transmission System Incorpo- 
r a t i ng  Automatic Beamforming, Steering and Phase Control." Lincom 
Technical Report TR-7806-0977, 1 978. 
6. Vanell i ,  J .  C. :  "Design and Test ing of a Master-Slave Returnable Timing 
System f o r  t h e  Solar  Power S a t e l l i t e . "  Lockheed Electronics  Company, 
Houston, Texas, LEC-10474lEE7-79-714, December 1979. 


Design and breadboard evaluation of the SPS reference phase control system concept

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