Target Tracking - MATLAB Simulations for Radar Systems Design - page 404

A B A B A A

B B

D C D C D C D C

(b) (d)

(a)

(c)

Figure 9.8. Illustration of monopulse concept. (a) Target is on the
tracking axis. (b) - (d) Target is off the tracking axis.

(A+C)-(B+D)

∆ el

A

(A+B)-(D+C)

elevation error

(A+D)

∆ az

(A+D)-(B+C)

azimuth error

D
B

Σ

(A+D)+(B+C)

sum channel

(B+C)

C

Figure 9.9. Monopulse comparator.

To generate the elevation difference beam, one can use the beam difference
(A - D) or (B - C). However, by first forming the sum patterns (A+B) and (D+C)
and then computing the difference (A+B) - (D+C), we achieve a stronger eleva-
tion difference signal, . Similarly, by first forming the sum patterns (A+D)
and (B+C) and then computing the difference (A+D) - (B+C), a stronger azi-
muth difference signal,

∆ el

∆ az , is produced.

A simplified monopulse radar block diagram is shown in Fig. 9.10 . The sum
channel is used for both transmit and receive. In the receive mode the sum
channel provides the phase reference for the other two difference channels.
Range measurements can also be obtained from the sum channel. In order to
illustrate how the sum and difference antenna patterns are formed, we will
assume a sin ϕ ⁄ ϕ single element antenna pattern and squint angle ϕ 0 . The

sum signal in one coordinate (azimuth or elevation) is then given by

sin
ϕϕ 0

( ϕϕ 0 – ) sin

ϕϕ 0

( ϕϕ 0 + )

Σ() = ---------------------------- + ---------------------------- (9.7)

( – ) ( + )