Beam squint is eliminated by using received phase at each array element to control transmitted phase at another element. Correction method may extend to multi-element array by using ring structure

Baritt, P.

Satre, W.

Sielman, P.

English

NASA Technical Reports Server

Figure 1. Squint Correction 
December 1971 Brief 71-10444 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Beam Squint Correction for a Diplex, Retrodirective Phased Array 
Beam squint—the aiming error produced by a 
retrodirective phased array when the received signal 
phase is directly impressed upon a different-fre-
quency transmitted signal—can be eliminated by 
using the received phase at each array element to 
control the transmitted phase at another element. 
The relative spacing of the two elements is deter-
mined by the ratio of transmitted to received wave-
length. 
In a simplex retrodirective system, the conjugate 
phase of the signal received at each element is ap-
plied to the transmitted signal of the same element. 
This generates a transmitted phase front identical 
to that received and focuses the transmitted beam 
back along the path of the received beam.
Such a system will perform well as long as the 
transmit and receive frequencies remain identical. 
However, it is frequently necessary to use a diplex 
system, in which the transmit and receive frequen-
cies are different. Under these conditions, the trans-
mined beam will focus along a path different from 
that of the received beam; this abberation is called 
beam squint. For large-aperture, narrow-beam 
arrays, beam squint can greatly reduce system gain. 
The simplest technique for eliminating beani 
squint (see Fig. I) involves positioning the receiving 
(A) and transmitting (B) elements as shown, accord-
ing to the ratio:
K = "r/"t (1) 
where ''r and A t are the received and transmitted 
wavelengths, respectively. For a single phase front 
received at an angle (I, the phase angle /, of the 
signal received at element A is: 
27rKL . 
sin	 (2) 
In order to establish the same phase front by trans-
mission from element B, the necessary phase angle 
"B is:
(•) 2r L (3) sill 
By substituting equation (I) into equation (2), it 
can be seen that A = 
This method of squint correction can be extended 
to a multi-element array by using a ring structure 
such as that shown in Figure 2. In this design, the 
elements are radially positioned on a set of concen-
tric circles. The radius of each successive circle is 
determined by equation (I) (i.e., R = KR). To 
produce a squint-free, retrodirective array, the 
received-signal phases from elements at radius R 
are fed through conjugate phase networks to control 
This documefct was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000441 2020-03-17T02:30:45+00:00Z
z (Boresight Ax
ments at radius R. 
the transmitted-signal phases of corresponding ele- 
Note: 
Requests for further information may be directed 
to:
. 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B71-10444 
Patent status: 
No patent action is contemplated by NASA. 
Source: P. Baritt

NASA Headquarters, and

W. Satre and P. Sielniin of

Cutler-Hammer, Inc.

under contract to

Goddard Space Flight Center

(GSC- l 1023) 
0 1 0 f 0 
0 0 0 I
On 
/ o 0 0
0 a I 0
e/o	 o 0/	 0
0
o8 0 o e0 00 e 0	 0	 0 0 0 0 0 0 0 0 ,Ii 0a0 °6 N-2	 0 0 0 o5 N-i 0
/jo0
0 
N dl 0 , 4 
/2
/
Figure 2. Ring Array
. 
. 
Brief 71-10444	
Category 02 


Beam squint correction for a diplex, retrodirective phased array

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