03 Basic Radar Theory

Question 1

Types of Radar used by ATS units?

Answer 1

• Primary Surveillance Radar (PSR) — bearing and distance to ‘target’. PSR systems are based on a pulse and echo technique.
• Secondary Surveillance Radar (SSR) — as for PSR plus identification and altitude.
• Aerodrome Movement Surface Radar (ASMR) — ground movement on aerodromes. SHF 60rpm

Question 2

Radar Frequncies used?

Answer 2

SHF and UHF Bands

Question 3

Ranges measured?

Answer 3

Slant range and ground range.

Question 4

PSR

Magnetron?

Answer 4

EM transmitter device

Question 5

PSR

Duplex switch?

Answer 5

Pulse radars do not send and recieve at the same time.
Allows the Tx only to operate when the Rx is switched off.

Question 6

PSR

Klystron?

Answer 6

An amplifier for the returning signal

Question 7

Types of Remote sensing radar systems?

Answer 7

• Ground based weather radar systems.
• Satellite based radar.

Question 8

Maximum achievable radar range depends on:

Answer 8

• The frequency used. (Absorption, attentuation)
• The height of the antenna. (Earth curvature LoS)
• The height of the aircraft. (Earth curvature LoS)
• The pulse repetition frequency (PRF).
• The pulse length. (Longer pulse more radiated power)
• The power of the pulse. (radiated power radiated)

Question 9

Minimum radar range is dependant on?

Answer 9

Pulse length

Question 10

Pulse width

Answer 10

The duration of the trasnmitted pulse, microseconds.

Question 11

Waiting Period?

Answer 11

Must be equal to 2x the Max design range, to allow for EM

Question 12

PRF or PRR?

Answer 12

Pulse recurrence frequency, or rate, the number of pulses emitted by the Tx per second?

Question 13

PRI or PRP?

Answer 13

Pulse Repetition Interval.
PRF = 1 / PRI

Question 14

MUR?

Answer 14

Maximum Unambiguous Range - Ambiguirty arises when the time taken to reciicve the return is greater than the time between 2 radar pulses.

Question 15

MUR Equation?

Answer 15

MUR = C / (2 x PRF)

Question 16

PSR

Factors effecting the strength of the return signal?

Answer 16

Shape, Surface, Material, Aspect and Manouvre.

Question 17

What is PSR used for?

Answer 17

PSR is used to detect targets that are not equipped with a transponder for SSR.

Question 18

Beamwidth?

Answer 18

Small beam means better focussed power. 3 degree beamwidth is desired.

The bigger the aperature, the narrower the beam.

Question 19

Side lobes?

Answer 19

Unwanted, but inevitable by product of focussing the beam.

Question 20

What radar frequencies are normally used in aviation?

Answer 20

2GHz - 40Ghz
Normally X-Band: 8-12GHz

Question 21

Use of GEO satellites?

Answer 21

Used to report on weather.
35,880km
UHF frequency

Question 22

Relationship between range and power?

Answer 22

A doubling of range, means a 16 fold increase in power
Range [NM] =4√power [W]

Question 23

PAR

Answer 23

Precicion approach radar. Classed as 3D approach.