Many clear-air VHF wind profiles use coaxial collinear (COCO) arrays for their antenna. A COCO array is composed of long lines of half-wave dipoles spaced one-half wavelength apart. An inexpensive method of checking a COCO array is described and its performance is optimized by measuring and then correcting the relative rf phase among its lines at their feed point. This method also gives an estimate of the rf current amplitude among the lines. The strength and location of the sidelobes in the H-plane of the array can be estimated

Green, J. L.

Warnock, J. M.

English

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6.4A TESTIKG AND OPTIMIZING 1-ST COAXIAL COLLINEAR ARRAYS 
J. M. Walrnock and J. L. Green 
Aeronomy Laboratory 
National Oceanic and Atmospheric Administrat ion 
Boulder, Colorado 80303 
INTRODUCTION 
Many c l ea r - a i r  VHF r a d a r  wind prof i l e r s  use coaxia l  c o l l i n e a r  (COCO) a r r a y s  
f o r  t h e i r  antenna. A COCO a r r a y  i s  composed of long l i n e s  of half-wave d ipoles  
spaced one-half wavelength apa r t .  I n  t h i s  paper we desc r ibe  an inexpensive 
method of checking a COCO a r r a y  and optimizing i t s  performance by measuring and 
then co r rec t ing  the r e l a t i v e  r f  phase among i t s  l i n e s  a t  t h e i r  feed po in t .  This 
method a l s o  g ives  an es t imate  of the r f  cu r ren t  amplitude among the  l i n e s .  
Therefore, t he  s t r eng th  and loca t ion  of the  sidelobes i n  the H plane of the  
a r r a y  can be estimated. 
The only nonstandard equipment needed f o r  these measurements i s  a  probe t o  
de t ec t  the  r f  s igna l  near a r a d i a t i n g  e lanent .  We use a shor t  d ipole  40 cm 
long tuned t o  the opera t ing  frequency by a v a r i a b l e  inductor.  Although the  
measurenents described here  were a l l  made a t  the  Sunset r ada r  s i t e ,  s imi l a r  
t e s t s  have been made a t  the P l a t t e v i l I e ,  Craig, and Ponape r ada r  s i t e s ,  and . 
could be made e a s i l y  on any COCO a r r ay .  
SUNSET RADAR ANTFNNA 
Figure 1 shows the d i s t r i b u t i o n  of r f  power from the transmission feed- 
- l ine t o  each antenna elanent.  The transmission f eed l ine  i s  a  low-loss f ive-  
inch  a i r  d i e l e c t r i c ;  it e n t e r s  a small  well-screened bui ld ing  located  i n  the 
c e n t e r  of the  antenna where i t  feeds a harness. This  harness  d iv ides  the r f  
power i n t o  16 equal p a r t s ,  which a r e  fed  i n t o  16 phase s h i f t e r  boxes. The 
phase s h i f t e r s  a r e  con t ro l l ed  remotely by an on-line computer. For a given 
t i l t  angle  and d i r ec t ion ,  the  computer s e l e c t s  e i t h e r  of two a r r ays  and con- 
putes the  phase s h i f t  requi red  f o r  each of the  16 phase s h i f t e r s  t o  produce the  
des i r ed  phase s h i f t  across  the a r r ay  (GREEN e t  a l . ,  1984). Since a l i n e  of 
- 
an a r r ay  i s  conposed of two s t r i n g s  of d ipoles  each with i t s  own feed,  the  rf 
power output from each phase s h i f t e r  i s  d iv ided i n t o  h a l f ,  and f ed  i n t o  a pa tch  
- - -- 
panel. This patch panel  i s  ac tua l ly  one wa l l  of the building.  The antenna 
.- _ ___- f eed l ines  a r e  a t tached t o  the  panel on the  ou t s ide  of the  building.  
The antenna a t  the Sunset radar  s i t e  i s  cu r ren t ly  two colocated square ar -  
r a y s ;  one s t ee rab le  i n  the east-west v e r t i c a l  plane (denoted E-W a r r a y ) ,  and the  
o the r  s t e e r a b l e  iri the  north-south v e r t i c a l  plane (denoted I?-S a r r ay ) .  Figure 
2 i s  a  plane view of t he  antenna. Each a r r a y  i s  a coaxia l  c o l l i n e a r  a r r ay  com- 
posed of 16 l i n e s  of half-wave dipoles.  These l i n e s  a r e  spaced one-half wave- 
length a p a r t ,  and a r e  one-quarter wavelength above a ground plane. Physica l ly ,  
each l i n e  of the a r r a y  cons i s t s  of two s t r i n g s  of dipoles cons t ruc ted  from RG-8 
coaxia l  cable  by interchanging the  inner-conductor with the b ra id  a t  ha l f  wave- 
length i n t e r v a l s  (BALSLEY and ECKLUND, 1972). Each s t r i n g  conta ins  12 hal f -  
wave d ipoles ,  s i x  on each s ide  of i t s  f eed l ine ,  g iv ing 24 d ipoles  i n  each l i n e  
of an a r r ay .  
MEASUREMENT PROCEDURE 
It i s  important t o  make the measuranents under condit ions as  c lose  t o  the 
a c t u a l  r ada r  opera t ing  env i romen t  a s  poss ib le ;  t he re fo re  a l l  p a r t s  of the  
power d i s t r i b u t i o n  systen and antenna elements a r e  exci ted  during the  measure- 
ments. A s igna l  generator feeds three  wa t t s  of r f  power a t  the opera t ing  f r e -  
https://ntrs.nasa.gov/search.jsp?R=19850024205 2020-03-20T18:06:26+00:00Z
Anlenno 
Build~nq '1 Transmitter Feed Line 
Phase 
Shiften 
Y Patch Panel . 
Antenna Feed L i e s  
IIIIIIIIIIIIII~IIIIIIIIIIIIII~III 
Figure 1. Schematic diagram of rf  power 
d i s t r i b u t i o n  fo r  the Smse t radar.  
Figure 2. Plan view of Sunset radar  antenna. 
quency (40.475 tlHz) i n t o  the f r o n t  end of the  transmission feedl ine .  We place  
the  shor t  d ipo le  probe a few inches from the  f i r s t  s t r i n g  of dipoles a t  i t s  
feedpoint .  One end of a long RG-8 f eed l ine  i s  attached t o  the  probe; the  o the r  
end i s  connected t o  a vector  voltmeter i n  the antenna building.  T?e compare the  
rf s ignal  from the  probe wi th  a convenient reference from the patch panel. 
Af ter  the amplitude and phase a re  measured with the vector voltmeter and re-  
corded, t h e  probe i s  moved ca re fu l ly  t o  the next s t r i n g ,  and the  measuranents 
continued u n t i l  a l l  32 s t r i n g s  of an a r ray  have been measured. Pe r iod ica l ly ,  
we re tu rn  the  probe t o  the f i r s t  s t r i n g  t o  confirm the r ep roduc ib i l i t y  of the  
measurements. Next we co r rec t  the r e l a t i v e  phases among the  s t r i n g s  by adding 
a co r rec t ion  cable  t o  each f eed l ine  a t  the patch panel. F ina l ly ,  we remeasure 
t h e  e n t i r e  correc ted  antenna. 
RESULTS 
The f i r s t ,  and perhaps the  most use fu l ,  r e s u l t  i s  t h a t  these measurements 
provide a cont inui ty  t e s t  of the e n t i r e  'system from the  transmission f eed l ine  
t o  the s t r i n g s  of dipoles. A t  S m s e t  there  a r e  nore than 1500 connections i n  
t h i s  system; de fec t ive  or missing components or interchanged connections a r e  
found eas i ly .  Furthermore, periodic t e s t i n g  allows the performance of the 
system t o  be monitored. 
Next, we compare the uncorrected and corrected antennas. Figure 3 shows 
th ree  broadside antenna pa t t e rns  i n  the H plane of the E-W array.  The f i r s t  
pa t t e rn  (Figure 3a) i s  coniputed from the measurements made before the correc- 
t i o n  cables were added. It has l a rge  broad sidelobes;  the l a rges t  sidelobe i s  
only 10 bd below the main bem. The second pa t t e rn  ( ~ i g u r e  3b) i s  the correct -  
ed pa t t e rn ;  i t s  sidelobes a r e  small and narrow s imilar  t o  the idea l  pat tern  
shown i n  Figure 3c. These sidelobes reduce considerably the radar  horizon f o r  
c l u t t e r ,  a i rp lanes ,  meteors, and o the r  competing targets .  
REFERa CES 
Balsley,  B. B. and W. L. Ecklund (1972), A por table  coaxial  c o l l i n e a r  an- 
tenna, IEEE Trans. Antennas Propanat., AP-20, 513-516. 
Green, J. L., J. H. Warnock, W. L. Clark, F. J. Eggert and K. J. Euth (1984), 
Modification t o  the  Sunset Radar t o  provide antenna bean s teer ing,  p r e p t i n t  
20th Conference on Radar I.leteorology, 1981, Boston, MA. 
0 
WEST EAST 
Figure 3. Broadside antenna pa t t e rns  i n  
H plane. The t i c k  marks on the r a d i a l  
a x i s  a r e  separate& by 3 dB f o r  one-way 
propagation and 6 dB f o r  two-way propa- 
gation.  a )  Pa t t en i  ca lcula ted from 
phase and r e l a t i v e  power measured before 
phase correct ion cables a re  added. 
b) Pat tern  calcula ted from phase and 
r e l a t i v e  power measured a f t e r  phase 
correct ion cables were added. 
c )  Idea l  pattern.  


Testing and optimizing MST coaxial collinear arrays, part 6.4A

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