Introduction to Radar Basics - MATLAB Simulations for Radar Systems Design - page 6

First, assume that the two targets are separated by , where is the
pulsewidth. In this case, when the pulse trailing edge strikes target 2 the lead-
ing edge would have traveled backwards a distance , and the returned pulse
would be composed of returns from both targets (i.e., unresolved return), as
shown in Fig. 1.4a. However, if the two targets are at least apart, then as
the pulse trailing edge strikes the first target the leading edge will start to return
from target 2, and two distinct returned pulses will be produced, as illustrated
by Fig. 1.4b . Thus,

c τ 4 ⁄ τ

c τ

c τ 2 ⁄

should be greater or equal to . And since the radar ∆ R c τ 2 ⁄

bandwidth is equal to , then

B 1 τ ⁄

c τ
2

c
2 B

∆ R == ----- -------

(1.8)

In general, radar users and designers alike seek to minimize in order to
enhance the radar performance. As suggested by Eq. (1.8), in order to achieve
fine range resolution one must minimize the pulsewidth. However, this will
reduce the average transmitted power and increase the operating bandwidth.
Achieving fine range resolution while maintaining adequate average transmit-
ted power can be accomplished by using pulse compression techniques.

∆ R

R 1 R 2

incident pulse

c τ

c τ
4

-----

return
tgt1

return
tgt2

reflected pu lse

tgt1 tgt2

3
--- c τ

shaded area has returns from both targets

(a)

R 2

R 1

c τ
2

-----

return
tgt1

return
tgt2

reflected pulses

c τ

c τ

tgt1 tgt2

(b)

Figure 1.4. (a) Two unresolved targets. (b) Two resolved targets.