ICT 1

RADAR An introduction to basic performance

International workshop: Trends in Radar Ornithology National Environmental Research Institute (NERI), Aarhus Denmark

21st January 2010

Yngve SteinheimSINTEF ICT/NINA

ICT 2

Radar

What is a radar, and what can it do?

Detection and location of objects by radio waves

Emits a particular type wave form, and detects the nature of the

return

How well can it do it?

Detection capability

Accuracy and resolution

Tx

Rx

Duplx

ICT 3

Transmission equation (1)

24 RPS t

t

tt

t GR

PS 24Pt

: Transmitted power

R: Range

Gt

: Tx

antenna gain

St1

St2

St1

> St2

R

ICT 4

Transmission equation (2)Radiated energy is intercepted by an object with a radar cross section σ:

24 RGPSP tt

ti

222 44 RGP

RPS tti

s

Captured energy is scattered isotropically:

σ: Target radar cross section

ICT 5

Transmission equation (3)Reflected energy is received by an antenna with effective area Ar

:

rtt

rsr ARGPASP 224

4

2r

rGA

Ar

: Receiver antenna effective area

Gr

: Receiver antenna gain

λ: Radar wavelength

ICT 6

Free space transmission equation

43

2

4 RGGPP rtt

r

22 44 RA

RGPP r

ttr

Effective radiated power x intercepted by target x captured by Rx antenna

ICT 7

Example

Received power from a (large) bird with RCS 0.01 m2

at 2000 m illuminated by a S-band ship radar:

Pt

=30 kW

R=2000 m

Gt

=Gr

= 26dB (400)

σ=0,01 m2

λ=0,1 m

WWPr 150000000000,0105,12000)4(

01,01,040040030000 1123

2

ICT 8

Multipath

Rht

hr

ICT 9

General transmission equation (4)

Free space antenna pattern

Effect of ”lobing”

Csc2

antenna pattern

LRFGGP

P rttr 43

42

4

ICT 10

Noise in the radar receiver

Tx

Rx

Duplx

Ground noise in lower sidelobe

Solar or galactic noise

Solar or galactic noise

Atmospheric noise

WG and duplexer noise

Receiver noise

ICT 11

Signal to noise ratio

ns BkTN

NLRFGGP

NP

NS rttr

43

42

4/

ICT 12

Radar range equation

ns

rtt

BkTLRFGGP

NS

43

42

min 4)/(

4

min3

42

max )/(4 ns

rtt

BkTLNSFGGP

R

ICT 13

Detection in noise

pdf

Signal amplitudevt

Pd

Pfa

noise

Tgt

and noiseSNR->

ICT 14

Maximum detection range

Pd

range

0.8

1.0

Rm_0.8Rm_0.5

0.5

ICT 15

Resolution and accuracy

Radar operates in a 4-dimensional space:

Time (Range)

Two angles: (Usually) azimuth and elevation

Frequency (doppler)

A target is resolved if it can be separated from other targets in at least one of these coordinates

After having detected and resolved a target, the radar must deliver an estimate of its position

ICT 16

Range (time)

2cR

Resolution (for a rectangular pulse)

RMS Error (for a rectangular pulse)

)/(42 NSBc

R

ICT 17

Angular resolution and accuracy

Resolution: When separated by 1 half-power beam width

angle

amplitude

θ3

θ3

RMS error:

nNS

)/(5.0 3

ICT 18

Doppler

Doppler shift

r

dv

f2

Doppler resolution

DD T

B 1

ICT 19

Doppler resolution, example

ICT 20

Summary

Radar: Detection

and location of

objects

Fundamental performance

Detection

in the

clear. (Pd, Pfa)

Resolution

and accuracy

ICT 21

References

Skolnik

M. I. (1980): Introduction

to radar systems, McGraw-Hill

(2nd

ed).

Barton

David K (1988): Modern

Radar System Analysis, Artech

House

Blake Lamont

V. (1986): Radar Pange-Performance Analysis, Artech

House

http://www.radartutorial.eu/