14.02.2013 Views

Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Chapter 3 / Sensors / Radar<br />

_ _<br />

3.8.6 Radar Equation and Signal-to-Noise Ratios<br />

The SNR is derived from the Radar Equation that appears in many radar<br />

texts, Barton [B.10] . The prefix identifying the parameters as those from the<br />

radar “RD” is ignored in the derivation of the SNR with respect to the<br />

target. The signal strength for an isotropic reflector and a perfect receiving<br />

antenna (S) is the product of the reflected power density at the receiver (IR)<br />

and its effective receiver aperture (AE).<br />

I : S ⋅ =<br />

3.8-8<br />

R E A<br />

Equation 3.8-22<br />

The receiver aperture depends on the receiver gain (GR), the average gain<br />

over the angle illuminated by the target’s motion during the observation<br />

time, and (λt) the transmission wavelength. Assuming reciprocity,<br />

A<br />

E<br />

: =<br />

GR<br />

⋅ λ<br />

4 ⋅ π<br />

2<br />

T<br />

Equation 3.8-23<br />

If (PT) represents the maximum power in a single pulse from the<br />

transmitting antenna, (GT) its average gain, the power density at the target,<br />

I<br />

S<br />

: =<br />

P<br />

T<br />

⋅ G<br />

4 ⋅ π ⋅ P<br />

T<br />

2<br />

o,<br />

t<br />

Equation 3.8-24<br />

The effective radiating area of the target is often referred to as its Radar<br />

Cross Section (RCS) (σRCS). Typical values of RCS are subjective<br />

depending not only on physical size, but shape and materials for stealth - the<br />

following list is merely a guide:<br />

• Missile 10 -2 to 10 1<br />

• Fighter aircraft 10 -1 to 10 2<br />

• Bombers and transports 10 0 to 10 3<br />

• Armoured vehicles 10 1 to 10 2<br />

• Small ships 10 2 to 10 4<br />

• Large ships 10 2 to 10 6<br />

A default RCS of 1 has been selected. Combining terms, the signal power<br />

collected by the receiving antenna from an isotropic reflector using the same<br />

antenna for transmission and reception with a common gain (G),

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!