RADAR ENGINEERING AND NAVIGATIONAL AIDS

Outline
Unit - IV
 Radar receivers:
Super regenerative, crystal video, TRF, Superheterodyne
 Mixers:
Crystal, balanced, double balanced, product return, image
enhanced, image recovery mixers.
 Radar displays:
(I) Raw video :: (1)deflection mounted displays: A, A scope, J,
M, O, N, K, R (2) Intensity modulated : B, C, D, E, H, RHI
(II) Synthetic Video :: ADT : Digital computers,
microprocessor, micro computers, mini computers, ARM
processors
 Receiver protectors:
Passive TR limiter, solid state limiter, ferrite limiters, circulator
Function of the radar receiver

 To detect desired echo signals in the

presence of noise, interference, or clutter.
 Receiver must separate wanted from
unwanted signals, to a level where target
information can be displayed to an operator,
or used in an automatic data processor.
 The design of a radar receiver will depends
on
type of waveform to be detected, nature of
the noise interference and clutter echoes.
 Good radar receiver design is based on
maximizing the output SNR,
to maximize SNR, the receiver must be
designed as a matched filter
 Receiver design must be consider
sufficient gain, phase, amplitude stability,
dynamic range, tuning ruggedness, and
simplicity
 Protection must be provided against over
load or saturation and burnout from near by
interfering transmitter.
 Timing and reference signals are needed to
properly extract target information
eg: MTI radar, tracking radar.
 Super regenerative, crystal video, and TRF
receiver .
 Which type of receiver is mostly preferred?

 The superhetrodyne receiver preferred for

most of the application the reason is as
they have good sensitivity, high gain,
selectivity and reliability.
 No other receiver type has been competitive
to the superhetrodyne receivers.
 Mixers
Mixers ::
a) Broad Band Mixers :
Crystal Mixer
b) Narrow Band Mixers :
Balanced Mixer : Hybrid junctions, Magic
Tee or an equivalent
Mixers :: a) Silicon point contact
b) Schottley barrior diodes : Si / GaAs
(Broad band)
 Mixers

 Many super heterodyne type Radar receiver do not

use a low-noise RF Amplifier. LNRFA
 The first stage is simply the mixer instead LNRFA

The Function of the mixer is to convert RF Energy

to IF Energy with minimum loss and without spurious
responses.
 Mixers
 Silicon point-contact and Schottky-barrier diodes
Mixers, Semiconductor contacts have been used
as mixing element.

 Schottky-barrier diodes are made of either silicon

or GaAs, with GaAs preferred for the higher MW
frequencies

 Schottky-barrier have lower noise figure and lower

flicker noise, than conventional point-contact diodes.
1. Conversion Loss
2. Noise Temperature Ratio.
Conversion Loss
 Conversion loss of the Mixer is defined as

Lc = Available RF Power/Available IF Power.

 It is a measure of the efficiency of the mixer in converting

RF signal into IF.
Lc (Conversion Loss) varies from 5 to 6.5dB.
Theoretical can never be < 3dB.
 A crystal mixer is called " broad band“ when the signal and
image frequencies are both terminated in matched loads.
 Conversion Loss cont…
 The image frequency is defined as that

Frequency which is displaced from the local oscillator frequency

fLO by the IF Frequency, and which appear on the opposite of the
L.O frequency as the signal frequency fRF.

 Short -circuiting or open- circuiting the image frequency

termination result in a narrowband mixer.

 The Conversion loss, Lc is less in the narrowband than is the

broad band mixer about 2 db Lower

 broad band mixer has been simpler to achieve and less critical
than a narrowband mixer.
2. NOISE-TEMPERATURE RATIO.

NOISE TEMPERATURE RATIO of a crystal mixer is

defined as Tr = Actual available IF Noise power/ Available
noise power from an equivalent resistance

Fc= Crystal mixer noise figure ;

Lc= 1/Gc = Conversion loss.

 BALANCED MIXER (Narrow Band Mixers )

Introduction
 Because of the non-linear action the mixer the LO signal can
appear at the IF Frequency
 The LO Noise must be removed if receiver sensitivity is to
maximized
 One method for eliminating LO noise that interferes with the
desired signal is to insert a narrow-band pass RF Filter
Between LO and the Mixer
Balanced mixer

 The Center Frequency of the filter is that of the LO, and its
BW must be narrow so that LO noise at the signal and the
image frequencies do not appear at the mixer

 A method of eliminating LO Noise with out the

disadvantages of a narrow bandwidth filter is the balanced
mixer
 A balanced mixer uses a hybrid junction, a magic T or an
Equivalent.
There are four port junctions. Fig1 : illustrates magic T , in which the LO
and RF signals are applied to two ports. Diode mixer are in each of the
remaining two arms of the magic T.
At one end of diodes the sum of of RF and LO signals appears , at the
other diode difference of the two obtained.
LO would be applied to H plane arm, and RF would be applied to E plane arm
 Receiver protectors
1. Passive TR limiter is widely used as a receiver protector

2. Solid state limiters

3. Ferrite limiters

4. Circulator and receiver protector

5. Duplexer protector :On transmission it protects a receiver
from the damage (branch type and balanced duplexers)

6. PIN diode protectors may also be used to achieve

additional sensitivity time control(STC)
 Receiver protectors
 A receiver protector is a necessary in addition to
the duplexer to limit the receiver input with in a
nanosec, and fast acting PIN diodes are useful for
purpose

 The TR is not usually energized when the radar is

turned off,

 more power is needed to break down the TR than

when it is energized
 Radiation from near by transmitters may therefore
damage the receiver with out firing the TR

 To protect the receiver under these conditions

 A mechanical shutter can be used to short circuit

the input to the receiver whenever the radar is not
operating.

must be designed to attenuate a signal by 25 to

50dB
 TR is not perfect switch ; some transmitter
power always leaks through the receiver

 The envelop of RF leakage might be shown

in fig.
 The short duration, large amplitude “spike” at the
leading edge of the leakage pulse is the result of
the finite time required for the TR to ionize or
breakdown order of 10 nsec

 After the gas in the TR tube is ionized , the power

leakage through the tube is considerably reduced
from peak value of the spike.

 This portion of the leakage pulse is termed the flat

 Damage to the receiver front end may result
when either the energy contained with in the
spike or the power in the flat portion of the
pulse is too large

 Spike leakage of one erg or less

 RADAR DISPLAYS
(I) Raw video : when displays connected directly to the
video output of the receiver, the information displayed is
called raw video

(II) Synthetic Video: when the receiver video output is first

processed by an automatic detector or automatic detection
and tracking processor(ADT), the output displayed is called
synthetic video

1. CRT display : has been almost universally used as radar display

1. Deflection modulated CRT

2. Intensity modulated CRT
 RADAR DISPLAYS

The original radar display, the A-scope or A-display, shows only the range , not the
direction, to targets. Some people referred to these displays also as R-scope for range
scope. A-scopes were used on the earliest radar systems during World War II,
This image shows several target "blips" at ranges between 15 and 30 miles from the station.
The large blip on the far left is the leftover signal from the radar's own transmitter, targets in
this area could not be seen. The signal is inverted to make measurement simpler.
The L-scope was basically two A-scopes placed side-by-side and rotated
vertically. By comparing the signal strength from two antennas, the rough direction
of the blip could be determined. In this case there are two blips, a large one
roughly centred, and a smaller one far to the right.
A C-scope displays a "bullseye" view of azimuth vs.
elevation. The "blip" was displayed indicating the direction
of the target off the centreline axis of the radar, or more
commonly, the aircraft or gun it was attached to. They were
also known as "moving spot indicators", the moving spot
being the target blip.
Almost identical to the C-scope is the G-scope, which
overlays a graphical representation of the range to the
target.[1] This is typically represented by a horizontal line
that "grows" out from the target indicator "blip" to form a
wing-like diagram
The PPI display provides a 2-D "all round" display of the airspace around a radar
site. The distance out from the center of the display indicates range, and the angle
around the display is the azimuth to the target. The current position of the radar
antenna is typically indicated by a line extending from the center to the outside of the
display, which rotates along with the antenna in realtime.[1]
 Radar displays:
Raw video ::
(I) (1)deflection mounted displays: A scope, J, M, O,
N, K, R scopes
(II) (2) Intensity modulated : B, C, D, E, H,
RHI (Range Height Indicator) scopes
PPI (Plane Position Indicator also called P-scope)

Synthetic Video :: ADT : Digital computers,

microprocessor, micro computers, mini
computers, ARM processors
1. Synthetic video display:
Automatic detection and tracking(ADT)
Digital computers used as an ADT: to extract
target information results in synthetic display
Air traffic control display
Ex: Air traffic control display in which such information as
target identity and altitude is desired to be
displayed
 The use of computer
to generate the graphics and control the CRT
display offers flexibility in the choice of such things
as range scale
physical map outlines
grid displays
airport runways
raw video display of several successive radar
scans
 In long range air traffic control radar located in
busy area these might be more than a hundred
target for display extracted
The data on the synthetic display must be
refreshed
at a sufficiently high rate to obtain a high
brightness and to avoid flicker

When the no. of displays are used with the

of singe radar,
a dedicated mini computer can be used at
display position for the refresh of data
 Principle of direction finders
When the ship reached to the port
 Loop antenna used as a directional finder

 Radio direction finder are still widely employed in radio

navigation in variety of forms.

 Direction of radio transmission from a port to aid the

ship to reach port using directional antenna

 An aircraft approaching an airport needs greater

precision in direction finding, for which specialized
antenna is employed in the aircraft or at the airport
 Principle of direction finders

 These directional finders are specially called homing

systems or radio ranges

 All the directional finders, the determination of

direction is made by utilizing the directional property of
a loop antenna or modified form
Aircraft Homing and Instrument Landing System

Homing

Instrument landing system

Instrument landing aids

VHF Omnirange (VOR)

 Instrument Landing System
1. Homing
The guidance of an aircraft towards an airport is called
homing.
In busy airports, large number of aircrafts are scheduled to
arrive simultaneously,
the pilot of each aircraft must know its own bearing in
flying, with precision
other wise such a simultaneous approach to an airport by
no. of aircrafts may lead to collision between adjacent
aircrafts
 Instrument Landing System
 Instrument Landing System (ILS)
When the aircraft approaching closely to the
airport the landing of an aircraft is often
aided by radio aids called ILS.

It is useful during poor visibility conditions

and during night.
 Instrument Landing Aids (ILAs)
 Radio aids for landing of an aircraft to the airport
are called Instrument Landing Aids.
 The Radio aids may be incorporated with in the
aircraft operated and controlled by the pilot.
These are called Instrument Landing Systems.
 GCA (Ground Control Approach) : Alternatively, it
may be systems controlled from the ground when
the pilot is to landing following instructions from
the ground control operator obtained from the
Ground Control Approach systems
 I.L. Systems enables blind landing of an
aircraft under poor visibility conditions.
 The I.L. Systems guides the air craft both in
elevation and azimuth supported by an aid
called Radio Altimeter.
 Elevation guidance using radiation pattern
 Elevation guidance using lobe switching
 I. L. Systems is also called as the guide
slope system in airports (UHF 339.3 - 335
MHz)
 Radio Altimeter

 A Radio altimeter is designed to the altitude

indication of an aircraft while it is landing
phase is based on a FM-CW radar
 Due to the modulation the transmitted
frequency will fallow the modulation
 Fig c The transmitted frequency at the
instant 0,when the modulation wave from
passes through a zero, with the carrier
frequency fc
 Radio Altimeter
 This transmission will be received back the
reflection at the ground after delay

2h
Δt  c
 During the delta t the transmitted frequency
is changed to a new value fc differing from
fc by '
f f f
b c c
 LOCALIZER
 Localizers operate in the VHF range and provide horizontal
course guidance to runway centerline.
 Transmitters are located on the centerline at the opposite
end of the runway from the approach threshold.
 The signal transmitted consists of two fan shaped patterns
that overlap at the centre. The overlap area provides the
on-track signal.
 The angular width of the beam is between 3°and 6°.
Normally width is 5°, resulting in full scale deflection at
2.5°.
 The width of the beam is adjusted to be 700 feet wide at
runway threshold.
 beginning with X, aligned localizer identifiers begin with I.
 The localizer may be offset from runway centerline by up to
3°. Localizers offset more than 3° will have an identifier
 A cautionary note will be published in the CAP whenever
localizer is offset more than 3°.
 Normal reliable coverage of localizers is 18nm within 10° of
either side of course centerline and 10nm within 35°.
 Localizer installations provide back course information, and
non-precision localizer back course approaches may be
published.
 Caution: a localizer signal is transmitted differently than a
VOR radial. Aircraft receivers are not supplied with azimuth
information relative to magnetic or true north. It is simply a
beam aligned with the runway centerline.
 Glide Path
 Glide path information is paired with the
associated localizer frequency.
 The glide path is normally adjusted to an angle of
3° (may be adjusted 2° to 4.5°) and a beam width
of 1.4°(0.7° for full scale deflection).
 The antenna array is located approx. 1000ft from
the approach end of the runway and offset approx.
400ft. (if glide path is followed to the pavement
touchdown point will be at the 1000ft markers)
 In installations with an ILS serving both ends of a
runway the systems are interlocked so only one
can operate at a time.
 Note: on a standard 3° glide path 320ft/1nm can
be used to verify.
RUNWAY LIGHTING AND TRANSMISSOMETERS
 The following must be fully serviceable to meet CAT II/III
standards:
 Airport lighting:
– approach lights
– runway threshold lights
– touchdown zone lights
– centerline lights
– runway edge lights
– runway end lights
– all stop bars and lead-on lights
– essential taxiway lights
 ILS components:
– localizer
– glide path
 RVR equipment:
– CAT II- two transmissometers- approach end, mid-field
– CAT III- three transmissometers- approach end, mid-
field, departure end
 Power source:
– Airport emergency power as primary power source for
all essential system elements.
– Commercial power available within one second as a
backup.
 Hyperbolic Navigational systems
 LORAN-A
 LORAN- C
 OMEGA
DECCA navigator company :
 DELRAC
 Inland Shipping aids

 VOR (VHF Omni range )

 LORAN-A and LORAN-C
 LORAN : Long rang aid to navigation
 Principle
 Operating frequency
 Range
 Transmitted power
 OMEGA
 OMEGA was the first truly global navigation
system for aircraft. it enabled ships and aircraft to
determine their position by receiving VLF radio
signal transmitted by a network of fixed terrestrial
radio beacons, using a receiver unit.
 Principle: Omega is a phase difference system
similar to DECCA
 but operating at lower frequency in the VLF band
around 10 kHz at which the reliable ground wave
courage may be increased to a few thousand
kilometers with,
 base line lengths of several thousand kilometers