What is Jet engine modulation?

What is Jet engine modulation?

Jet Engine Modulation (JEM) [1], [5] occurs when radar observes a jet airplane at an aspect angle that allows electromagnetic radiation to be backscattered from moving parts of the compressor and blade assembly of the jet engine. JEM increases when radar is orthogonal to the axis of blade rotation.

What is modulation in radar?

Modulation techniques play a key role in in radar technology. The mode of transmission makes a huge difference in the performance of radar and hence the technique will change as per the application. The two most commonly used techniques are Frequency Continuous Modulated wave (FMCW) and the Pulsed Doppler technique.

Are radar signals modulated?

In simple ranging radars, the carrier will be pulse modulated and in continuous wave systems, such as Doppler radar, modulation may not be required. Most systems use pulse modulation, with or without other supplementary modulating signals.

What is meant by radar signature?

radar signature: 1. The detailed waveform of a detected radar echo. Note: Radar signatures may be used to identify or distinguish among objects, i.e., targets, such as aircraft, decoys, missiles with warheads, and chaff.

What is radar cross section area?

The radar cross section (RCS) of a target is the equivalent area seen by a radar. It is the fictitious area intercepting that amount of power which, when scattered equally in all directions, produces an echo at the radar equal to that from the target.

How far can radar travel?

This permits target detection at distances from about 500 to 2,000 nautical miles (900 to 3,700 km). Thus, an HF over-the-horizon (OTH) radar can detect aircraft at distances up to 10 times that of a ground-based microwave air-surveillance radar, whose range is limited by the curvature of the Earth.

What is an advantage of using high PRF Doppler?

By using multiple sample volumes, the pulse repetition frequency is increased (the pulses from different sample volumes are added) and thus the aliasing speed is increased. This is referred to as high PRF Doppler or extended range Doppler. The advantage of high PRF Doppler is that greater velocities can be measured.

What is low PRF?

Low PRF. Systems using PRF below 3 kHz are considered low PRF because direct range can be measured to a distance of at least 50 km. Radar systems using low PRF typically produce unambiguous range. Unambiguous Doppler processing becomes an increasing challenge due to coherency limitations as PRF falls below 3 kHz.

What is jet engine modulation (JEM)?

Much more important for the respective radar signature are special Doppler frequencies through parts moving at or in the target, e.g. rotor blades or compressor blades of the engines, which also gave these modulations their name: Jet Engine Modulation (JEM). These Doppler frequencies depend on the number of parts and their rotational speed.

How does jet engine modulation affect radar cross-section?

Figure 2: Jet engine modulation of a propeller aircraft and of a wind power plant. The Radar Cross-Section is very strongly dependent on the direction from which the reflecting object is illuminated by the radar. Here characteristic changes are significant, which can also contain information about the attitude of the target relative to the radar.

What does Jem stand for in aviation?

Jet Engine Modulation Much more important for the respective radar signature are special Doppler frequencies through parts moving at or in the target, e.g. rotor blades or compressor blades of the engines, which also gave these modulations their name: Jet Engine Modulation (JEM).

How are Doppler filters implemented in radar?

These Doppler filters can be implemented either as hardware by resonance filters, or after the digitization of the received signals as a software routine. For a fully coherent radar with digital receiver and monopulse processing , the MTI system is somewhat more complex than with pseudo-coherent radar devices.