Page 324 - Radar Technology Encyclopedia

pulse, predetected pulse, uncoded [simple] 314

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Table P5
Pulse Shapes and Spectra

Time-
Pulse description Pulse shape Spectrum shape Spectral width bandwidth
product
Gaussian:
2
u(t) = U exp(-a t ),
0
1
-¥ < t <¥
0.26 b 0.426
1
4ln (1 b ¤)
a = ------------------------
1
t
i
Cosine:
u(t) = U cos(pt/t),
0
i
0.73
|t| < t/2, ---------- 0.43
i
t
i
u(t) =0, |t| > t/2
i
Rectangular:
u(t) = U , |t| < t/2,
i
0
0.81
u(t) = 0, |t| > t /2 ---------- 0.73
i
t
i
Triangular:
2U 0 æ t
ut () ---------- ---- –= i t , ö
t è 2 ø
i 0.84 0.46
----------
t
i
|t| < t/2,
i
u(t) = 0, |t| > t /2
i
Exponential:
u(t) = U exp(-ct),
0
|t| < t/2, 0.98c 1.13
i
u(t) = 0, |t| > t /2
i

Predetected pulse is the term sometimes used for video- Typically, this waveform has a rectangular envelope
detected pulses employed to make a decision in target detec- (Fig. P23). The time-bandwidth product for a simple pulse is
tion. SAL equal to unity. Usually, long and short pulses are distin-
guished: the first corresponds to the narrowband waveform
Ref.: Wehner (1987), p. 69.
(approaching CW) and has good resolution in doppler and
pulse repetition frequency (see PULSE REPETITION poor resolution in range; the second is a wideband waveform
FREQUENCY). having good range but poor doppler resolution. Simple pulses
were widely used in old-generation radars as magnetrons pri-
An uncoded [simple] pulse is an amplitude modulated wave-
marily used in those facilities are not easily compatible with
form with carrier frequency f without intrapulse modulation.
0 pulse-compression waveforms. Now it is used primarily in