Technology Today Volumn 3 Issue 1 - Raytheon

raytheon

Technology Today Volumn 3 Issue 1 - Raytheon

Radars aboard the

F-15, F-14, F/A-18,

AV8B and B2 all provide kill-chain

support in addition to situational awareness.

The classical kill chain is denoted as

find, fix, target, track, engage and assess

(referred to as F2T2EA by the user community).

The modern multi-mode Raytheon

radar finds and fixes targets on the ground

and in the air by using Doppler search

modes for moving targets, and imaging

modes for fixed targets. Once a target is

located, it is targeted and tracked using

additional waveforms. Targets in track can

be engaged, with radar providing targeting

information and weapons support. Finally,

engagement effectiveness can be assessed

through imaging of a fixed site or termination

of the track of a moving target.

A third type of useful information is intelligence,

surveillance and reconnaissance. The

user of this data is as likely to be a ground

commander as it would be a pilot.

Raytheon’s HISAR, ASARS-2A and Global

Hawk radars provide imaging and movingtarget

information of a region of interest

on the ground. Similarly, Raytheon’s APS-

137 radar on the Navy P-3 Orion, as well as

the international maritime radar, SeaVue,

provide location and tracking information

of maritime targets. All of these modern,

multi-mode ISR radars provide location,

tracking and identification of targets to the

battle field commander or the pilot.

Airborne radars are undergoing several

major, capability-enhancing revolutions. A

simple abstraction of a radar system might

be to view it as an RF transmitter and

receiver, a data processing unit and a

directional antenna. Today’s analog transmitters

and receivers are being replaced by

programmable, digital receiver-exciters, similar

to those found on the APG-79. These

receiver-exciters offer the ability to support

a wide variety of radar functions, with the

ability to add growth

functions while under

development. In the same way,

the airborne radar data processor is

undergoing a veritable explosion in capability,

with the commercial field expanding its

capabilities by 100 percent approximately

every 18 months (a phenomenon referred

to as ‘Moore’s law’). This increase in processing

throughput and storage is affording

far more sophisticated radar functionality.

Finally, the radar antenna itself is also

undergoing a major change. Earlier,

mechanically steered arrays are being

replaced by the Active Electronically

Scanned Array (AESA). AESA antennas, as

first deployed on the APG-63(v)2, provided

inertia-less beam pointing, permitting the

radar systems engineer to design functions

that can move the beam more rapidly.

Advantages such as increased sensitivity

and tracking capability result in improved

situational awareness.

Predicting the future of airborne radars is

not difficult. As we extrapolate from the

past, the future will require even better

quality user information. Greater tracking

precision and finer imaging resolutions are

currently under development. Larger quantities

of hard-to-find targets will populate

future battlefields, and Raytheon’s research

is addressing those needs. Fused sensors

(both Radio Frequency and Electro-Optical,)

will allow for enhanced effectiveness as

recently demonstrated by Global Hawk during

Operation Enduring Freedom and

Operation Iraqi Freedom. Additionally, the

lines between RF functions are continually

blurring, with radars providing Electronic

Support Measures and communication

functions. The future holds capabilities not

envisioned by Roddenberry’s Star Trek.

Missile Radar

Missile radar seekers were a natural derivative

of radar technology developed for

fighter aircraft. Once radar was incorporated

into fighters, it became quite apparent

that the aircraft could locate a target, but it

was virtually impossible to destroy the target

at any appreciable standoff range,

using bullets or unguided missiles. In order

to engage the target, some sort of closedloop

control of the missile would be needed.

The first radar-guided, air-to-air missile

developed (in the 1940s and ’50s) was the

Falcon missile. The Falcon was guided to

the target by ‘homing in’ on RF energy

bounced off the target by the fire control

radar. This type of missile-seeker radar is

referred to as a semi-active radar. The semiactive

concept continues to be a valuable

operating mode for a number of presentday

missiles. But as technology continued

to develop, more and more capability was

integrated into missiles. Today’s missile

radars are closely related to fire-control

radars. Modern missile radars adapt the

waveform parameters, receiver configuration

and signal processing for the mode of

operation in use and the missile’s environment

(though it should be noted that no

one missile does everything). Some missile

radars perform air-to-air targeting and others

perform air-to-ground.

Radar-guided missiles use radar sensors for

detecting and tracking both air and surface

targets. These radar sensors provide specific

target information that is used to guide the

missile. The missiles also employ RF communication

links, GPS receivers and RF

proximity fuzes for detonating the warhead

when the missile passes close to the target.

Current missile RF-guidance technology

operates primarily at microwave frequencies

(3-30 GHz). For the guidance function, a

forward-looking sensor, employing either

a reflector antenna or a waveguide array

antenna, is mounted on an electromechanical,

gimbal-controlled platform. An

aerodynamic nose cone or radome,that is

transparent to RF energy protects the

antenna. The RF signals originate either

from a transmitter on the missile (in an

active system), from an illuminating radar

on the launch ship, ground system or aircraft

(in a semi-active system) or, alternatively,

from the target itself (in a passive

system). Signals are reflected from the

target (or originate from the target), and

are received via the missile antenna and

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