summery: CH2 P1,2,3,4

Question 1

Define transmitter:

Answer 1

The source of the electromagnetic radiation emitted by a radar. It generate the high frequency signals which leaves the radar’s antenna and goes out into the atmosphere

Determine the wavelength of the antenna. (antenna must match the transmitter’s wavelength)

Question 2

Kinds of transmitters:

Answer 2

• Magnetron
• Klystron
• Solid state transmitter

Question 3

Transmitters are designed to:

Answer 3

Optimize particular characteristics

Question 4

Compare the three transmitters:

Answer 4

Solid state:

• By combining multiple transmitters into an array and controlling the timing of each element it is possible to achieve useful power outputs
• Used in phased array antenas to improve time taken to collect radar data

Question 5

Define modulator:

Answer 5

• an electromagnetic device that control the transmitter

Question 6

Purpose of modulator:

Answer 6

• switch transmitter on and off
• correct the wave form of transmitted pulse
• tell the transmitter when to transmit and for what duration
• stores energy between transmitter pulses so later it will have stored energy available to use

Question 7

How to operate weather radar

Answer 7

Using an interface between the operator and the radar to translate our wishes into radar commands

Question 8

What is the control panel of radar:

Answer 8

Provide a number of choices and a way to select them to communicate with the radar.

Question 9

Define circuits:

Answer 9

Used to convert selections to control signals

Question 10

What do operators usually select?

Answer 10

• Range of display
• Elevation angle of antenna
• Azimuth to scan
• Number of pulses in each second
• How long are the pulses

Question 11

Master clock:

Answer 11

(old radars) generate the appropriate signals and send them to the components

Question 12

Ubiquitous computers:

Answer 12

• (modern radars) control operation of radars
• (signal processors): control the processing of received data

Question 13

Signal processors can:

Answer 13

Question 14

Main function of the mater clock/computer:

Answer 14

Control how often and how long the transmitter transmits

Question 15

PRF:

Answer 15

The rate at which the radar transmits. Short for pulse repetition rate or pulse repetition frequency. (200-3000Hz)

Question 16

PRF is usually measured in:

Answer 16

Pulses of cycles per second or HZ (1 HZ=1 cycle/second)

Question 17

PRF values for different radars:

Answer 17

Non Doppler ground based weather radars

150 – 300 HZ

Doppler weather radar

Capable of detecting the speed of targets moving toward or away from the radar

700 – 3000 HZ

Weather radars used onboard aircraft

500 – 1500 HZ

Question 18

Pulse duration (t):

Answer 18

Measured in units of time (0.1-10цs)

Question 19

Pulse length (h):

Answer 19

Units of distance

Question 20

How to convert (t) to (h) or the opposite:

Answer 20

Distance = rate x time or (h=c x t) where c is the speed of light

Question 21

Wave guide:

Answer 21

The conductor connecting the transmitter and the antenna

Question 22

Regular wires pros and cons:

Answer 22

• Pros: conducting electricity and low frequency signals
• Cons: very lossy “energy is lost”

Question 23

Coaxial cables:

Answer 23

• Special conductors that carry radio frequency signals (works well at many radio frequencies)
• Contain a center conductor surrounded by insulation and then by a layer of shielding conductor and another layer of insulation
• Very loosy

Question 24

Waveguide shape:

Answer 24

• Usually hollow
• Rectangular (sometimes round) metal conductor
• Interior dimensions depend on the wavelength of the signals being carried
• Cross section is usually rectangular

Question 25

Waveguide connections:

Answer 25

• Long pieces connected together by joints
  
  • to connect the transmitter/receiver and antenna
  • Has to conduct signals around corners

Question 26

Reason for waveguide connection:

Answer 26

Allow transmitter and receiver to be located at one place while the antenna is mounted else where (up on a tower is the conventional location of a ground based weather radar)

Question 27

Signals conducted inside waveguide consist of both:

Answer 27

• Electric component
  
  • (E-plane bend): Direction of electric field: Shorter dimension
• magnetic components
  
  • (H-plane bend): direction of magnetic field: longer direction

Question 28

Which plane band is better? Why?

Answer 28

E-plane bends, because it has less looses

Question 29

Flexible waveguide

Answer 29

• Special form of waveguide The metal part of the wave guide can bend to accommodate:
  
  • Slight misalignment in wave guide or
  • Allow for slight movement between adjacent components

Question 30

Flexible waveguide shape:

Answer 30

Outside is usually rubber coated to make it air and water tight

Question 31

Rotary joint:

Answer 31

• Special form of waveguide used to allow antennas to rotate to be able to:
  
  • Scan horizontally (azimuthally)
  • In elevation
• Used between waveguide fixed to the radar tower and waveguide fixed to the antenna
• Second rotary joint is used so the antenna can scan up and down

Question 32

Shape of wave guide in rotary joint:

Answer 32

Circular in cross section