Radar Waveforms - MATLAB Simulations for Radar Systems Design - page 152

and in most radar applications this is done by setting . Therefore, B = 1 τ ⁄

range resolution is given by

∆ Rc ()2 = ⁄ = c ⁄ 2()

(3.47)

Radar users and designers alike seek to accomplish High Range Resolution
(HRR) by minimizing . However, as suggested by Eq. (3.47) in order to
achieve HRR one must use very short pulses and consequently reduce the aver-
age transmitted power and impose severe operating bandwidth requirements.
Achieving fine range resolution while maintaining adequate average transmit-
ted power can be accomplished by using pulse compression techniques, which
will be discussed in Chapter 5. By means of frequency or phase modulation,
pulse compression allows us to achieve the average transmitted power of a rel-
atively long pulse, while obtaining the range resolution corresponding to a very
short pulse. As an example, consider an LFM waveform whose bandwidth is

∆ R

B

and un-compressed pulsewidth (transmitted) is . After pulse compression the τ

compressed pulsewidth is denoted by , where , and the HRR is τ′ τ′ τ «

c τ′
2

c τ
2

∆ R = ------- « ----- (3.48)

Linear frequency modulation and Frequency-Modulated (FM) CW wave-
forms are commonly used to achieve HRR. High range resolution can also be
synthesized using a class of waveforms known as the ÐStepped Frequency
WaveformsÑ (SFW). Stepped frequency waveforms require more complex
hardware implementation as compared to LFM or FM-CW; however, the radar
operating bandwidth requirements are less restrictive. This is true because the
receiver instantaneous bandwidth is matched to the SFW sub-pulse bandwidth
which is much smaller than the LFM or FM-CW bandwidth. A brief discussion
of SFW waveforms is presented in the following section.

3.6. Stepped Frequency Waveforms
Stepped Frequency Waveforms (SFW) produce Synthetic HRR target pro-
files because the target range profile is computed by means of Inverse Discrete
Fourier Transformation (IDFT) of frequency domain samples of the actual tar-
get range profile. The process of generating a synthetic HRR profile is
described in Wehner. 1 It is summarized as follows:

A series of narrow-band pulses are transmitted. The frequency from
pulse to pulse is stepped by a fixed frequency step

n 1.

. Each group of

∆ f n

pulses is referred to as a burst.

1. Wehner, D. R., High Resolution Radar, second edition, Artech House, 1993.