Compound radio interferometer with independent heterodynes to investigate radio emission source

Alekseyev, V. A.

English

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https://ntrs.nasa.gov/search.jsp?R=19690022783 2020-03-12T05:08:08+00:00Z
sNational Aeronautics and Space Administration
GUddard Space Flight Center
Contract No.NAS-5-12487
ST— RA— INS —10851
COMPOUND RADIOINTERFEROMFTER
WITH INDEPENDENT HETERODYNES FOR THE INVESTIGATION
OF EMISSION SOURCES' RADIOIMAGES
by
V. A. Alekseyev
(USSR)
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ST — RA — INS — 10851
COMPOUND RADIOINTERFEROMETER
WITH INDEPENDENT HETERODYNES FOR THE INVESTIGATION
OF EMISSION SOURCES' RADIOIMAGES
Radiotekhnika i Elektronika	 by V. A. Alekseyev
Tom 14, No.6, 1091 - 1093,
Izdatel'stvo "NAUKA", 1969
SUMMARY
The present work develops further the methods,
earlier proposed by R. C. Jennison and MacPhil [2, 31
for the creation of a compound radiointerferometer
with independent heterodynes, valid for the study of
the angular structure of emission sources. The latter
is indeed one of the fundamental problems of astrophy-
sics.
One of the basic problems of astrophysics is the investigation of
the angular structure of the emission sources. For the study of sources
with small angular dimensions in the radioband, the application of radio-
interferometers with independent heterodynes of high sensitivity to measure-
ments and with practically unlimited angular resolution, is most promising,
(see ref. [1]). However, because of the uncertainty of initial phases of
heterodyne signals and their instability in time, a two-antenna interfero-
meter with independent heterodynes allows us to measure only the amplitude
spectrum of spatial frequencies of brightness distribut on over the source,
which is found to be insufficient in a series of cases.
Jennison proposed in 1958 a circuit of three-antenna radiointerfero-
meter, allowing to determine the relative phase of two spectral components
and thereby obtain a complex spectrum of spatial frequencies [2]. Subse-
quently, the three-antenna system was utilized in a compound-interferometer
of intensities [3].
i
2The block-diagram of the compound radiointerferometer with independent
heterodynes is shown in Figure 1. The interferometer antennas Al. A2 , A 3 are
disposed along the base line at distances A I A2 = S o , A2 A 3 = nSo (n = 1, 2, 3..).
Antenna A 3 is movable. The receivers
IT, and 11 1 are connected by a single
heterodyne F,, while heterodyne r2 is at	 A? A3
used in the receiver H 3 •	 The absence
of high-frequency connection with re-
^pE'^
ceiver H 3 allows us the increase prac-
tically unlimitedly the distance AlA2.
The intermediate frequency signal trans- Ha^
mission from the receivers' output to
the analyzer may be materialized by com-
munication lines, as well as by way of
signal registration by memory devices K?1
with subsequent reading information
for simultaneous processing. In the
Fig.1
Block-diagram of a compound radio-
interferometer:
A l , A2 , A 3 , are the antennas; 77. IIt• II,
are the receivers; r.. r, are heterodyr.z:;;
K 1 , K2 are the correlators; j Ai . RA,
cy separation. Magnetophones with cor- 	 are the amplitude measurers.a ,;t is the
responding compensation for the insta-
bility of the registration and reproauction.
Assume that the source is at an angle 0 with respect to the base line of
the interferometer with angular extension W, within the bounds of which -,he
brightness radiodistribution is given by the funct 4 on T(0). Making use of the
well known theory of the two-element interferometer (see, for example ,4),
let us write tae expression for the antenna temperature of a two-antenna inter-
ferometer A A 3 with independent ;ieterodynes F  and i'_ at reception of the
emission in the frequency band .'',w in the form
last case signals from receivers 11  and
fl  outputs are registered by a single
memory device with utilization either
of two-channel registration, or frequen-
3I V/2
	 ! Vr2
(
T„ rt
 (3)	 T (^l') (10' + T,, (Tn)	 T (H') jos 12.Z	 j^ ..._	 rD ( t )] X
r: cos 2z - 4 	 s:n	 a	 },	 m(t)^ :^n^z ...- ^^ d6'
nS°9J
_. T o J
- `^'n (Tn) V _n COS ;'.:L — 	— .1_ (D (t) -- an
.
, ,	 (1)
where
1V-2
in (Afor, 12)	 nspg°
	
T (9') Ci8 ; T,(rn)	
^tJfn' ;	 Trt
-- v12
	
t^..,n
	
yaT2..}- G u-.	 bn la,,;
ti',-2	 ^y .^
	
raSo	 1	 nS°8''
nn = =	 T (0') Cos +i °a -a-- 6' J rl(j';	 bn — S T (0') sin (2-t ti —^ W.
--►V/2
Correspbndingly, for a two-antenna interferometer A I A3 we shall obtain
T,, (Ili 1)(0) — V_ + %F(I,. t) 00+0 "-(,1+1) Cos J 2,T (n + 1) So eo + !D (t) — a(n+tj	 (2)
where
Y(„+ r) - (n f t) So©o%; V '
_(n, t) — 1""' a2 , 	,- 1,2 i) ' t' g a(n+t) — b(nr t) ^a(n+t);
tV'2
T (01 Cos l 2 t (n ^^t) So 0') de';
- w/2
W/2
	
b(n+t) -	 T(0')cos ( ^_T ^n 1^)S0 0')
 
W.
- 12
In the expressions (1) and (2)
	
(D (4) --- for, (t) — wr,(t) + toll V --- wr l V + q r,( t — At) — (or,( t),	 (3)
where wo is the mean frequency of the received radiation; wr, and wr.. are
respectively the signal frequencies of heterodynes I' 1 and I' 2 ; VIM and T,.(t)
are their random phases; At is the relative lag of intermediate frequency
signals from different receivers, either on account of interferometer shoulder
assymetry, or because of imprecise reading coincidence. At is, in its turn,
a function of time determinable by fluctuations of electric lengths of trans-
:,)ission lines from the receiver to the analyzer, or by fluctuations of signal
registration and reproduction by the memory devices. From expressions (1) and
(2) it is not difficult to notice that the amplitudes V_ n and V-(n + 1) and
4phases an and a (n + 1) of " interference components" are amplitudes and phases
of Fourier - transformation of brightness distribution T(0) for spatial frequen-
cies nS o /a and (n + 1)S o /a respectively. For measurements of V_. and
amplitudes, one must necessarily have
Y(0) — 1,
which is attained by introducing intermediate frequency lags by the times Tn
and T(n + 1) into the corresponding shoulders of the interferometer. In this
case the interference components of signals ( 1) and ( 2) will have the form
(^	 n.So
	
C,-)3 Pa - - Oo+(D• t( r) .._(fn1.
	(4)
(n	 1 )So	 1
where
'n- ( r ) -- d'(., 1 t ) M = : ( < 'o - - air) ( r„ -- r;,:: 0 :-: co,:, , At.
	
The determination of Ir..,,1 and	 is conducted by the standard methods
of determination of quasi -sinusoidal signals. Measurement of phases an and
Nn + 1) does not appear to be possible; however, comparison of signals by
phases allows us to determine the difference phase of spectral components of
spatial frequencies nS p /a and (n + 1)SO/a:
^n _y 
2:c SUE). _
U •r U(„41) r m(a+1) (r) — Q^u (1^.
The quantity Q p,,,. 1 40 --- N„(r).- 
	 can be determined with a sufficiently high
precision by the calculation method, or directly measured by way of correspond-
ing calibration of lags introduced into the shoulders of the interferometer.
We may write
So8o }
	
2;, ;.
	 . u(n+1)— a n __ An .	 (6)
The quantity An
 determines the phase shift between the two above-indicated
spectral components of bri ghtness distribution over the source, shifted by an
angle	 from the normal to interferometer's base line. Changing the length
of the base A,A „ we may determine the amplitude and the relative phase of
spectral components of spatial fre uencies corresponding to various values of n,
and ther-2by obtain the complex spectrum of radiobrightness distribution over
the source. At the same time, in view of the total autonomy of the third re-
ceiving complex, a high resolution of the radiointerferometer can be achieved,
5which would allow us to investigate the fine angular structure of the source
of radioemission.
*** T H E E N D ***
DCL CDCAT'1V0
1. L. I. MATVEYENKO, N. S. KARDASHEV, G. B. SHOLOMITSKIY. Izv.vuzovMVSSO USSR
(Radiofizika), 8, 4, 651,
1965.
2. R. C. jENNISON. Monthly Notices Roy. Astronom. Soc. 118, 276, 1958.
3. MAC PHIL, IEEE Trans. Antennas and Propagat., 14, 3, 1966.
Manuscript received on 21.5.1968.
CONTRACT No.NAS-5-12487
	
Translated by ANDRE L. BRICHANT
VOLT INFORMATION SCIENCES, INC.
1145 - 19th St.NW	 on 1 July 1969
WASHINGTON D.C. 20036.
Telephone: (202)- 223-6700 (X-36),


Compound radiointerferometer with independent heterodynes for the investigation of emission sources radioimages

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