Radar Flashcards
What are the four factors affecting an aircrafts detection on radar?
Material
Shape
Size
Distance
What does Radar mean?
Radio detection and ranging
What is the usual length of an aerial in relation to wavelength?
The aerial length is 1/2 the wavelength
What general frequencies do radars operate on?
UHF, SHF, EHF
1-300 GHz
Would a high frequencies have a shorter or longer aerial?
Shorter aerial due to shorter wavelength
When a radar is metric, it……
Operates on a wavelength of one metre or More
What is a centimetric radar?
Operates on a wavelength of 1 centimetre or more
A radar operating on a wavelength of 1 millimetre or more is….
Millimetric
What three ways can radar systems be described as? (Wavelength they operate on)
Metric - 1m or more
Centimetric - 1cm or more
Millimetric - 1mm or more
What is the speed of EM waves?
3 x 10^8 metres per second
How many milliseconds is 1 mile?
10.75
Or
1.075 x 10^-5 seconds
How does frequency affect wavelength and aerial length?
High frequency = shorter wavelength = shorter aerial
Low frequency = longer wavelength = longer aerial
Describe primary radar
A radar that transmits energy, and receives that same energy back (known as echos or returns) after being reflected by a target.
It is used to track both hostile and friendly targets.
Primary radar acts independently from an aircraft.
Describe secondary radar
A radar system transmits energy to an aircraft, known as interrogation.
This energy triggers a transponder in the aircraft being interrogated,which sends a coded reply to the interrogator.
This acts with an aircraft or target and has a greater range than most primary radars.
Usually SSRs are used with primary radars
What band would 3 GHz, 10cm wavelength belong to?
E or F band
What band would a 3cm wavelength, 10GHz belong to ?
I to J band
What effect does frequency have on range and antenna size?
High freq = lower range due to greater attenuation
= small antenna
Low freq = higher range = large antenna
What is PRF and what is it’s main element?
Pulse repetition frequency, how many pulses in a second.
Higher prf = more pulses = larger data rate
What is the importance of pulse width?
Large pulse width = more power = further
But
Large pulse width = less accurate/defined
What is ARP?
Aerial rotation period
What is SSR and IFF?
Secondary surveillance radar - civil
Identification friend or foe - mil
What frequencies do secondary radars interrogate and reply on?
1030 MHz - interrogate
1090 MHz - replies
What are the four main parts of secondary radars?
Transponder
Controller
Aerials
Interrogator (ground)
What are the common civilian modes on aircraft (SSR)?
Mode A
Mode B
Mode C
Mode S
What is mode 5?
Encrypted data link
Includes mode 1,2 and 3 information as well.
What is mode 3/A?
This is mode emits an identification code
Mode 3 is the military equivalent.
What does mode C do?
It gives altitude information, helpful for controllers.
What is mode S ?
A selective interrogation from controllers.
Is used in T-CAS
What does squawk ident mean?
Ident is a button that can be pressed in the aircraft, that will allow identification of your position.
It will cause a flashing image on the Controllers screen.
What is T-CAS?
Traffic collision and avoidance system
Uses mode C and S to build a 3D picture of surrounding traffic
It is autonomous.
What two types of settings are on T-CAS systems?
Traffic advisory (3.3nm - 850ft) - provides traffic advise on surrounding traffic
Resolution advisory (2.1nm - 600ft) - mandatory, you must listen to the instructions given
What are the VHF frequency ranges?
118 - 137 MHz
8.33 KHz spacings
What is the useable UHF range?
25.0 to 399.95 MHz
25KHz spacings
What are the main types of primary radars?
Continuous wave
Moving target indicator (MTI)
Synthetic aperture
What are the three types of continuous wave radars, and describe how they work
Pure CW - uses Doppler shift to determine the relative velocity of a target.
Frequency modulated continuous wave radar-
Used to measure target range, and can be used to measure down to zero range
What are some issues with cw radar
Problems with CW:
2 aerials needed
Difficult to isolate the receiver from direct transmission from the receiver
What is MTI radar?
Moving target indicator
This uses Doppler shift to remove clutter.
It then determines a speed threshold for low and high moving targets
What are the two types of radar display?
Type A (horizontal display with vertical displacement) - displays range
PPI (plan position indicator) - displays a range and a bearing. A circular display where target bright up.
Also displays clutter.
How can range be measured with radars?
Using a rotating radar aerial with a fan shaped beam in azimuth.
This movement is then synchronised with PPI display allowing bearing and range.
How can height and elevation be measured using radars?
Nodding a radar aerial beam in elevation.
Vertically, thin
Horizontally, wide
What is SAR?
Synthetic aperture radars
A fixed antenna on an aircraft, scanning is achieved through movement of the aircraft
What is strip/swath SAR?
Using synthetic aperture radars to send multiple pulses and processing the returns
The returning signal is similar to that of radars with aerials 100s of feet long.
What is spot SAR?
Through movement of the aircraft, a beam can be focused to a point of interest, allowing a high definition picture.
What is inverse synthetic aperture radar? (ISAR)
Target movement and Doppler is used.
Returns from moving targets allow an image of the target.
What are the types of radars and their designations?
Circular = A
Sectoring = B
Complex = J
What is PRF?
Pulse repetition frequency
Number of pulses per second
What is PRI?
Pulse repetition interval/period
Time from start of one pulse to the start of the next
What is ARP?
Aerial rotation period
Time taken to complete one rotation
