Analytic computer study of antenna noise temperatur

Allen, C. C.

English

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1 
Monthly Progress  Report No. 6 f o r  December 1964 
P ro jec t  T i t l e :  
Contract No. : 
Prepared f o r :  
Antenna Noise Te(n+qaqu$e Study by Computer 
2 E Y -  
NASA-Goddard Space F l i g h t  Center ,  Greenbel t ,  Maryland 
N 6 5 -  1 9 8 7 7  Prepared by : General Electric Company 
I 
Advanced Technology Labora tor ies  ! 
Schenectady, New York 0 p:
General Electric Company 
i c (-$f-gj?&$ Administered by: 2 ", 
(NASA CR O R  TMX OR AD N U M B E R )  
Ordnance Department 
P i t t s f i e l d ,  Massachusetts 
(THRU) 
- 
(CATEGORY 
Schedule: Study - 30 June 1964 t o  2 March 1965 
F ina l  P ro jec t  Report - 30 Apr i l  1965 
Object ive of Contract  and Technical Spec i f i ca t ions  (Abridgedl 
This  i s  t o  b e  an a n a l y t i c a l  computer study of f o c a l  po in t  monopulse t r ack ing  
feeds  f o r  85-foot diameter paraboloidal  r e f l e c t o r s  i n  o rde r  t o  e s t a b l i s h  t h e  
e f f e c t  of t h e  v a r i a t i o n  of design parameters on antenna noise  temperature.  It 
i s  t o  cover t h e  frequency bands 136-137 Mc, 400-401 M c ,  1700-1710 Mc, and 
4080-4170 M c ,  and t o  consider  both i n t e r n a l  and ex te rna l  no ise  sources .  Study 
t a s k s  are: I - Determination of  atmospheric, g a l a c t i c ,  and sun noise;  
I1 - Determination of improvement of noise  temperature wi th  s i d e  lobe  reduct ion ,  
i l l umina t ion  t a p e r ,  f/D r a t i o ,  and feed  support  design;  111 - Considerat ion of 
r e f l e c t o r  edge d i f f r a c t i o n ;  I V  - Analysis of  r e f l e c t o r  sur face  to le rances ;  
V - Experimental scale model antenna; and V I  - P a t t e r n  measurements t o  confirm 
a n a l y t i c a l  r e s u l t s .  
Work Performed During This Period 
Work during December w a s  p r inc ipa l ly  on Task 11. 
and c a l c u l a t i o n  of t h e  i n i t i a l  test case f o r  t h e  secondary p a t t e r n  and ga in  
program, add i t iona l  t r i a l  c a l c u l a t i o n s ,  completion of t he  composite antenna pat-  
t e r n  program and start  of checkout, s e l e c t i o n  of i n i t i a l  parameters,  and completion 
of basic design f o r  experimental s c a l e  model feed and start  of cons t ruc t ion .  
This  cons is ted  of compilation 
The i n i t i a l  tes t  case used t o  check ou t  t h e  secondary p a t t e r n  and ga in  program 
w a s  a t h e o r e t i c a l  primary feed p a t t e r n  having uniform amplitude over t he  r e f l e c t o r  
i l l umina t ion  angle  2 4 1 , ~ ~  and zero amplitude elsewhere. 
frequency of 1 2 2 . 5  M c ,  and p o l a r i z a t i o n  f o r  a horn feed were used so t h a t  t h e  r e s u l t s  
An f /D of 0.424, a 
Microfiche (MF) &, 9 
https://ntrs.nasa.gov/search.jsp?R=19650010276 2020-03-17T00:39:56+00:00Z
. Antenna Noise Temp'erature Study by Computer 
.Monthly Progress  Report No. 6 f o r  December 1964 
Page 2 
could be  compared d i r e c t l y  with the  H-plane p a t t e r n  given by W.V.T. Rusch i n  
Figure 2 of JPL Technical Report No. 32-434. The i n i t i a l  r e s u l t s  ind ica ted  exce l l en t  
agreement wi th  Rusch's p a t t e r n  f o r  t he  main beam and t h e  f i r s t  few s i d e  lobes  out  t o  
about 300, but  considerable  d i f f e rence  occurred f o r  angles  g r e a t e r  than 30° even 
though the  p a t t e r n  remained w e l l  def ined.  The program was rev i sed  t o  ob ta in  g r e a t e r  
accuracy a t  l a r g e r  angles ,  bu t  a departure  from Rusch's p a t t e r n  s t i l l  e x i s t s .  
An examination w a s  made of t he  phase funct ion used i n  the  present  computer program, 
and it appears that the  number of i n t eg ra t ion  po in t s  used are adequate t o  ob ta in  t h e  
requi red  accuracy. A plot of t h e  phase pa th  length  across the r e f l e c t o r  diameter i n  
60°, and 90° i s  given i n  Figure 1 for p a t t e r n  ang le s  8 = 30' 
A correaponding p l o t  o f  t he  phase pa th  length  around 
is given in  Figure 2.  In  t h e  present program, i n t e g r a t i o n  
Oo. 
r e spec t  to r from 0 to  42.5 f e e t  f o r  s e l e c t e d  values of 5 
reatest phase s e f o r  the r inte 
spuds t o  an equiv 
en from Figure 1 
of 26.9 (when 
tas a requi red  
t o  occur w = 90°. A t  136.5 unts to a phas 
42.5 feet is normalized t o  -1 to +1) 
number of points for  Gaussian quadrature  i n t e g r a t i o n  equal t o  about 14 per  radial .*  
t h e  a c t u a l  ca l cu la t ions ,  16 po in t s  i n  r were used i n i t i a l l y  (two sub- in te rva ls  of 8 
po in t s  each). 
In 
I f  t he  i n t e g r a t i o n  with respec t  t o  5 were performed f i r s t ,  t h e  phase func t ion  would 
have i t s  g r e a t e s t  s lope when r - 42.5 f e e t ,  5 = + d 2 ,  and 8 = 90°, as given i n  
Figure 2 .  
which corresponds t o  a n  equivalent  umax of 28.3 (when the  i n t e r v a l  from 5 = Oo t o  90° 
i s  normalized t o  -1 t o  +1) and ind ica t e s  a requi red  number of Gaussian-quadrature- 
i n t e g r a t i o n  po in t s  equal t o  about 14 per  quadrant. Since t h e  r i n t e g r a t i o n s  are per- 
formed f i r s t  i n  t h e  present  program and the  phase of each of t h e  r e s u l t i n g  i n t e g r a l s  
w i l l  be t h a t  of a point  a t  somewhat less than  r = 21.25 f e e t  on each r a d i a l  (due t o  
amplitude weighting favoring t h e  smaller r a d i i ) ,  t he  a c t u a l  phase func t ion  f o r  the  5 
i n t e g r a t i o n  w i l l  have less than  ha l f  the  value given i n  Figure 2 and thus  should r e q u i r e  
only about 7 Gaussian-quadrature-integration po in t s  per  quadrant.  
cu l a t ions ,  8 po in t s  i n  5 per  quadrant were used i n i t i a l l y ,  making a t o t a l  of 512 (r,5) 
po in t s  (16 x 8 x 4). 
Mc, even fewer in t eg ra t ion  po in t s  should b e  required.  
A t  136.5 Mc, t h i s  amounts t o  a phase s l o p e  of 0.628 r ad ian  per  degree i n  5 ,  
I n  the  ac tua l  cal- 
Since t h e  test case uses  a frequency of 122.5 Mc i n s t ead  of 136.5 
Fur ther  computer ca l cu la t ions  were made using a l a r g e r  number of ( r , S )  po in t s  with some 
improvement i n  accuracy a t  angles  near  8 = 90°, but a departure  from Rusch's p a t t e r n  
s t i l l  occurred. 
s i d e  lobe l e v e l s  a t  angles  from 8 = 45O t o  120' were somewhat d i f f e r e n t  and t h e  p a t t e r n  
minima were displaced.  
The general  c h a r a c t e r i s t i c s  of t he  p a t t e r n  were the  same, but  t he  
It was concluded t h a t  something more b a s i c  than accuracy of 
* See: C. C. Allen,  "Numerical In t eg ra t ion  Methods f o r  Antenna P a t t e r n  Calculations,".  
I R E  Transact ions on Antennas and Propagation, vo l .  A€'-7, Special  Supplement, 
p. S396; December 1959. 
. 
. Antenna Noise Temperature Study by Computer 
.Monthly Progress  Report No. 6 f o r  December 1964 
Page 3 
9 
i n t e g r a t i o n  was involved, and an examination of t h e  bas i c  formulat ions was made. 
By d e f i n i t i o n ,  t h e  test case set up t o  be c a l c u l a t e d  by t h e  present program was 
intended t o  be t h e  same as t h a t  ca l cu la t ed  by Rusch, even though t h e  s p e c i f i c  
mathematical formulations d i f f e r  (Rusch assumes c i r c u l a r  symmetry and reduces t h e  
double i n t e g r a l  t o  a s i n g l e  i n t e g r a l  involving Bessel func t ions) .  
however, i t  appears t h a t  t he  two problems d i f f e r  i n  the  func t ions  used f o r  t he  feed 
p o l a r i z a t i o n  vec to r ,  e,-even though both are intended f o r  a horn feed. 
do t  products  of 
Actually,  
- 
Since the 
and ifi are taken wi th  E x & x e, t h e  r e s u l t i n g  p a t t e r n  i n t e g r a l s  
observed. Since t h e  feed  p o l a r i z a t i o n  vec to r  
w i l l  d i f f e r  as a f unction of (e,@), t hus  a f f e c t i n g  both t h e  magnitude of t h e  s i d e  
rogram has  been v e r i f i e d  experimental ly  by 
t is assumed t o  be c o r r e c t .  
i t e  antenna p a t t e r n  (Step 111) was completed 
dary p a t t e r n ,  r a t h e r  t han  w r i t i n g  a sepa ra t e  
as an input  t o  b e  fed back i n t o  t h e  can- 
incorpora t ing  t h e  ope ra t ions  t o  be performed 
pu te r .  
otherwise have t o  be saved from t h e  secondary p a t t e r n  program f o r  use as input  t o  t h e  
composite antenna p a t t e r n  program. This composite antenna p a t t e r n  program inc ludes  
t h e  s h i f t  i n  phase re ference  descr ibed i n  Report No.  4,  t h e  coord ina te  t ransformation 
descr ibed i n  Report N o .  5, and provis ion  f o r  adding t h e  primary feed p a t t e r n  a t  a l l  
( G , 0 )  angles  t o  the  transformed secondary pa t t e rn .  
s i g n  should be added on page 3 of Report No. 5 as follows: 
Th i s  w a s  deemed advisable  i n  view of t h e  l a r g e  amounts of d a t a  which would 
As a minor co r rec t ion ,  a minus 
The r e s u l t i n g  composite antenna p a t t e r n  is: 
Dipole Feed - 
+ i  n [ p t +  n j q t ]  n 
Horn Feed - 
where t h e  f i r s t  bracketed term i n  t h e  p r i n c i p a l l y  po la r i zed  p a t t e r n  i n  each case, and 
t h e  second bracketed term is t h e  cross polar ized  pa t t e rn .  
c 
. Antenna Noise Temperature Study by Computer 
Page 4 
,Monthly Progress  Report No. 6 f o r  December 1964 
Following some add i t iona l  test  runs of the comb-aed secondary p a t t e r n  and composite 
antenna p a t t e r n  program, composite antenna p a t t e r n  ca l cu la t ions  w i l l  be made i n  
January f o r  the  i n i t i a l  parameters and feed p a t t e r n s .  Values of f/D se l ec t ed  f o r  
the  i n i t i a l  ca l cu la t ions  are 0.375, 0.400, 0 .423,  and 0.450, which thus  include t h e  
Rosman I va lue  (0.423) and give near ly  equal spacing. Larger o r  smaller values  can 
be added based on eva lua t ion  of the  i n i t i a l  r e s u l t s .  I l lumina t ion  t ape r s  used i n  
t h e  i n i t i a l  c a l c u l a t i o n s  w i l l  be those produced by t h e  var ious primary feed p a t t e r n s  
without p a t t e r n  sca l ing .  
illumination taper. 
t h e  Roman I p a t t e r n s  (p r inc ipa l  planes only), t h e  four-horn monopulse sum p a t t e r n s ,  
and the tri-made 
Primary p a t t e r n  angles  can later be scaled t o  vary the  
Primary feed  pa t t e rns  ava i l ab le  f o r  i n i t i a l  c a l c u l a t i o n s  are 
d f o r  scale model tests was completed and 
nal discrepancy between t h e  d e t a i l e d  p iece  
assembled view. The scale model dimensions 
tograph and t o  the  dipale spacings and ground 
cons t ruc t io  i c u l t y  was experienced i n  s c a l i n g  from the 
p lane  dimensions furnished by Rantec i n  response t o  an inqui ry  made t o  resolve t h e  
discrepancy. 
diameter scale model r e f l e c t o r  was ordered. 
primary p a t t e r n  measurements w i l l  be  made f o r  use as inpu t s  t o  t h e  composite antenna 
p a t t e r n  c a l c u l a t i o n  program. 
Design of t he  balun and feed network i s  s t i l l  i n  process.  
Upon completion of the  experimental feed,  
The 5-foot 
Resul t s  of t h e  a n a l y s i s  of edge d i f f r a c t i o n  done on Task I11 were w r i t t e n  up f o r  
i n c l u s i o n  i n  Report No. 5. 
and showed t h a t  such regions on t h e  r e f l e c t o r  exac t ly  cancel led d i r e c t  feed r a d i a t i o n  
f o r  d i r e c t i o n s  from t h e  feed to  t h e  shadow region of the  r e f l e c t o r .  The next s t e p  
i s  to  analyze s t a t i o n a r y  phase regions of the  second kind, which m c u r  a t  t h e  edge of 
the  r e f l e c t o r ,  bu t  no f u r t h e r  a n a l y s i s  was done on Task 111 i n  December. 
This t r e a t e d  s t a t iona ry  phase reg ions  of t h e  f i r s t  kind 
Tabulat ion of no ise  sources  on Task I, evaluat ion of s t r u t  e f f e c t s  on Task I I ( d ) ,  
formulat ion of t he  noise  temperature ana lys i s  on Task I1 (Step I V ) ,  and cons idera t ion  
of to l e rance  e f f e c t s  on Task I V  are not y e t  completed. 
Schedule S t a t u s  
It has  become apparent during December t h a t  a l l  of t h e  def ined t a sks  cannot be  com- 
p l e t ed  as thoroughly as had been expected, due i n  p a r t  t o  problems encountered i n  
obta in ing  a good checkout of t h e  computer program wi th  a high l e v e l  of confidence i n  
the  accuracy obtained and a l s o  because of t h e  delay i n  obta in ing  an ex tens ion  t o  the  
con t r ac t  t o  include Phase I1 work. What can be accomplished most e f f e c t i v e l y  wi th in  
the  remaining t i m e  and funds i s  being re-evaluated.  
complete t h e  composite antenna p a t t e r n  ca l cu la t ions  f o r  a l l  parameters even i f  very 
l i t t l e  n o i s e  temperature a n a l y s i s  is done, r a t h e r  than t o  c a l c u l a t e  only a few p a t t e r n s  
and perform a prel iminary noise  temperature a n a l y s i s  on those.  
foundat ion w i l l  have been l a i d  t h a t  can be b u i l t  upon la ter ,  r a t h e r  than  having one o r  
two i s o l a t e d  cases c a r r i e d  through. 
th i s  s tudy  of foca l  po in t  fed  antennas and t o  t h e  planned study of Cassegrain antennas 
(Phase 11), it had been i n i t i a l l y  an t i c ipa t ed  t h a t  t h e  t w o  phases would over lap  i n  
o rde r  t o  t a k e  advantage of such cormnon areas of work. It is bel ieved  t h a t  t h e  present  
work can now be completed most e f f e c t i v e l y  by i n t e g r a t i n g  t h e  two phases of t he  program. 
It i s  p resen t ly  f e l t  b e s t  t o  
I n  t h a t  way, a bas i c  
Because of t h e  areas of work t h a t  are common t o  
* 
, Antenna 
,Monthly 
Page 5 
Noise Temperature Study by Computer 
Progress Report No. 6 for December 1964 
Work Planned for Next Period 
Complete checkout of composite antenna pattern program, and calculate patterns on 
computer for initial parameters and primary feed patterns. 
Complete design and construction of experimental feed for scale model tests. 
Continue formulation of noise temperature analysis on Task 11. 
Prepare tabu 
Evaluate measuremen 
Analyze stat 
on Task 111. 
Continue c0n$ effects on Task I V .  
ise sources and results on Task I. 
de an Task II(d) for analysis of strut effects. 
the second kind with regard to edge diffraction 
Project Engineer: 5.g-  
C. C. Allen 
Date : January 11, 1965 
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Antenna noise temperature study by computer monthly progress report no. 6, dec. 1964

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