INTRODUCTION In the present

INTRODUCTION

In the present, where technology is advanced, radars are used to detect objects near their surroundings. “A radar is a system for detecting the presence, distance, direction and speed of aircraft, ships, and other objects, by sending out pulses of radio waves which are reflected off the object back to the source.” There are many different kinds of radars being used in both the civilian and military market. One of the radars that the military uses is the Low Probability of Intercept (LPI) Radar. LPI radar is special as compared to other radars as it acquires a few capable characteristics that make them not be detected by intercept receivers.

What exactly is an LPI radar? The LPI radar has the design characteristic of “to see and not be seen”. This design characteristic is achieved as LPI radar uses a special emitted waveform, the waveform is used to prevent a non-cooperative receiver from intercepting and detecting its emission. Therefore, if the intercept receivers are not able to detect the LPI radar, it achieved its purpose.

Electronic Warfare (EW) intercept receivers are designed to intercept radars that transmit short duration pulses with relatively high peak power. It is probable to design an LPI radar that can stop EW intercept receivers from intercepting. There are a few techniques that the LPI radar uses and is effective against the intercept receivers.
In the source above, it shows how interception and detection works in a fighter aircraft. The Electronic Support (ES) system and Electronic Intelligence (ELINT) system was used to intercept and detect the target using the concept of LPI.

In this essay, the techniques that the LPI radars uses to make it undetectable by intercept radars, the pros and cons of LPI radar and the future trend of LPI radar on the military systems will be discussed.

Techniques used by LPI Radars

To prevent LPI Radars to be detected by intercept receivers. LPI Radar make changes to make other intercept receivers not being able to detect by Electronic Intelligence (ELINT) systems or Electronic Support (ES) systems . The LPI radar has many characteristics that distinguish them from other ordinary radars. Below are the features:
? Low Sidelobe Antennas
? Transmitter Considerations
? Large Time-Bandwidth

1. Low Sidelobe Antennas
The antennas for the LPI radar need to have a radiation pattern with low sidelobes. The low sidelobes antennas transmitting pattern lower the chance of an intercept receiver to sense Radio Frequency (RF) emissions. The low sidelobe level are as low as -45 dB.

Apart from the sidelobe, there is the mainlobe. The mainlobe is very different from the sidelobe, the radiated energy will spread across a wide area therefore the beam that is transmitting need to be broad. This design makes it difficult to intercept the radar and locate the direction of the signal.
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2. Transmitter Considerations
LPI radar are mostly using Continuous Wave (CW) signals. By using CW signals, it is linked to the low peak power. It has a low continuous power compared to pulse train radar, even though it has a lower peak power, both gives equivalent performance. LPI radar

3. Large Time-Bandwidth
“Large time-bandwidth radar signals are used in a number of radar applications such as search-surveillance, tracking, ground mapping, radar imaging. A large time-bandwidth signal is usually generated either by frequency or phase modulation to widen the signal bandwidth.”
A large time-bandwidth greatly affect the degree of noise that will be input to the intercept receiver. For LPI radar, large time-bandwidths will be effective, by this the peak power will be lowered. A large bandwidth signal of 10 MHz will be required for high range resolution, a bandwidth of 1000 is possible to achieve in the present.

Pros of LPI Radars

a) Reduced receiver noise temperature
It increases the difficulty to detect the LPI radar due to the reduced receiver noise temperature. The receiver noise level affects the signal level that the intercept receiver can detect. This noise level can be lowered by reducing the operating temperature of the receiver, this can be done by constant cooling . The lower the noise temperature, the LPI radar will be undetectable to intercept receiver.

b) Low Peak Power
It was found out that having low peak power is effective to prevent Electronic Warfare (EW) receivers to detect the radar. The low peak power is achieved in relevant to the size of the bandwidth signals. The greater the bandwidth the lower the peak power will be. The large time-bandwidth of 1000, the peak power of the LPI radar will be reduced by a factor of 1000 or 30dB. Having low peak power is an advantage of LPI radar as only the minimum power is required.

c) Stealth Technology
How stealth technology works is by eliminating radar reflections. For naval ships, the stealth technology blends the naval ships together with other merchant ships and boats as it looks smaller on radar. This means that a large warship can appear like a tiny boat on the radar. The stealth technology on the LPI radar increases the ability to be not detected by intercept receivers.

Cons of LPI Radars

a) Cost
b) Weight
c) Complexity

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Future trend

In the present, technology is very advanced making LPI radar more and more available.

Conclusion