Radar Signal Processing.
The term radar is an acronym for the phrase Radio Detection And Ranging. Radar is a remote sensing technique: Capable of gathering information about objects located at remote distances from the sensing device. It is used to describe systems that use electromagnetic energy to detect distant objects and possibly determine other characteristics such as direction and range This is accomplished by illuminating a volume of space with electromagnetic energy and sensing the energy reflected by objects in that space.
Operating Principles of Radar Signals:
The simplest radar operation can be divided into 4 steps:
- The radar is transmitting an EM pulse:
2. The radar switches to listening mode:
3. The pulse is reflected by a target:
4. The radar receives the echoes from the transmitted pulse.
Using various properties of the received echo, the radar can extract parameters such as the range and velocity of the target.
Block Diagram of Radar Signal Processor:
The signal processor is that part of the system which separates targets from clutter on the basis of Doppler content and amplitude characteristics. In modern radar sets the conversion of radar signals to digital form is typically accomplished after IF amplification and phase sensitive detection. At this stage they are referred to as video signals, and have a typical bandwidth in the range 250 KHz to 5 MHz The Sampling Theorem therefore indicates sampling rates between about 500 KHz and 10 MHz Such rates are well within the capabilities of modern analog-to-digital converters (ADCs).The signal processor includes the following components:
The plot extraction and plot processing elements are the final stage in the primary radar sensor chain. The essential process is that of generating and processing plots as distinct from processing waveforms. The main components are:
- the plot extractor or hit processor (translates hits from the signal processor to plots),
- the plot processor (combines primary radar plots and minimizes false plots) and
- the plot combiner (combines primary and secondary plots, uses complementary features to minimize false alarms).
The radar data chain can include the following devices:
- a sensor tracker (it combines some plots of a target to a track), and
- the Multiple Sensor tracker (it combines plots or tracks of other radar sensors).
(The distinction between a correlator and a tracker being, that in the case of a correlator the plot positions are not changed by the process.)
Principles of measurement of Radar Signal Processor:
- Radar Equation:
The radar equation is referring to the power of the echo returning to the radar;
𝑃𝑡 : Transmit power;
𝐺 : Antenna gain;
𝜆 : Radar operating wavelength;
𝜎 : Target radar cross section (RCS);
𝑅 : Range from the radar to the target;
𝐿 : Other losses (system, propagation).
Low frequencies are preferable for long-range radar; Low RCS targets are harder to detect.
2. Distance Determination:
To determine the distance between the radar and a target, the delay of the echoed pulse id utilized; — Given that EM waves travel at 𝒄 = 3 × 108m/s — If the echo delay is 𝝉, the range of the target is: 𝑹 = 𝜏𝑐 2
3. Range Resolution:
The resolution of radar is its ability to distinguish between targets that are in very close proximity.
The range resolution 𝝆 of a radar is: 𝜌 ≥ 𝑐𝑇 2 ≈ 𝑐 2𝐵 𝑻: Duration of pulse 𝑩: Bandwidth of signal
Sorter pulses will have higher bandwidth, leading to better resolution
4. Direction Determination:
The target’s direction is determined by the directivity of the antenna, which represents the ability of the antenna to transmit the energy in a particular direction. Both the target’s azimuth and elevation angles can be determined by measuring the direction in which the antenna is pointing when the echo signal is received.
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