Introduction to Radar Basics - MATLAB Simulations for Radar Systems Design - page 5

Clearly, range ambiguity is associated with echo 2. Therefore, once a pulse is
transmitted the radar must wait a sufficient length of time so that returns from
targets at maximum range are back before the next pulse is emitted. It follows
that the maximum unambiguous range must correspond to half of the PRI,

c T

c
2 f r

R u ==

---

-------

(1.5)

t = 0

t = 1 ⁄ f r

PRI

τ

pulse 1 pulse 2 time or range

transmitted puls es

∆ t

echo1 echo 2 time or range

received pulses

c ∆ t
2

R 1 = --------

∆ t

R u

R 2

Figure 1.3. Illustrating range ambiguity.

1.3. Range Resolution
Range resolution, denoted as , is a radar metric that describes its ability
to detect targets in close proximity to each other as distinct objects. Radar sys-
tems are normally designed to operate between a minimum range

∆ R

, and

R min

maximum range . The distance between and is divided into R max R min R max M

range bins (gates), each of width , ∆ R

M = ( – R min ) ∆ R ⁄

(1.6)

max

Targets separated by at least will be completely resolved in range. Targets
within the same range bin can be resolved in cross range (azimuth) utilizing
signal processing techniques. Consider two targets located at ranges

∆ R

and

R 1

, corresponding to time delays and , respectively. Denote the difference

R 2 t 1 t 2

between those two ranges as : ∆ R

( t 2 – t 1 )

c δ t ∆ R = – R 1 = c ------------------- =

----

(1.7)

2

2

Now, try to answer the following question: What is the minimum such
that target 1 at and target 2 at will appear completely resolved in range
(different range bins)? In other words, what is the minimum

δ t

R 1 R 2

? ∆ R