Radar measurement types | Radar measurement basics
This page covers types and basics of radar measurement. It covers block diagram of radar measurement setup. The radar measurements include PRI (Pulse Repetition Interval) or pulse period, PRF (Pulse Repetition Frequency), duty cycle, pulse width, radar range etc.
As we know radar is the system which transmits train of pulses towards target and receives the pulse train back after some time period (Δt). Based on this round trip time (Δt) taken, radar determines range of the target.
There are different types of measurements performed during radar testing. The figure-1 depicts typical pulse waveform from radar transmitter along with various useful parameters.
Following are the types of radar measurement usually carried out.
Radar range: It is the distance between radar antenna and target. It is expressed as R = c*Δt/2. Here R is in meters, ΔT is in seconds and c is 3x108 . The parameters PRI, PRF, Duty cycle and pulse width are measured from the pulse train generated by the radar system.
PRI: It is the abbreviation of Pulse repetition interval. It is also known as Inter Pulse Period (IPP) . It is the time between two consecutive pulses in the pulse train generated by the radar.
PRF: It is the abbreviation of Pulse Repetition Frequency. It is inverse of PRI mentioned above. PRF = 1/PRI
Duty Cycle: It is the ratio of τ/T. Where T = PRI or IPP.
Pulse Width (τ) : It is the width of the radar pulse as shown in the figure-1. Pulse width is usually measured in µsec. The other parameters are rise time and fall time of the radar pulse.
Peak Power : It is the peak transmitter power of the radar. It is usually around 1MWatt.
Antenna Gain: The gain of the antenna measured in dBi. It is typically around 30 dBi.
Peak EIRP: It is the product of radar transmitter power and antenna gain. It is usually around 1 Gwatt.
Frequency Range: It is the radar frequency of operation. The common bands used for radar are HF, VHF, UHF, L, S, C, X, Ku, K, Ka and MMW. It is part of spectrum emission used in radar measurement. Spectrum measurements include out of band emissions, spurious emissions and emissions in the necessary bandwidth of interest etc.
Antenna pattern measurement: This is the radiation pattern measurement of the radar antenna.
Block Diagram of Radar Measurement Setup
The figure-2 depicts block diagram of typical radar measurement setup. As shown it consists of directional coupler used to couple the power from the path between radar transmitter and radar antenna. One can use signal generator with radar application software which can generate radar pulse as per compliance requirement. This ideal pulse shape is used as benchmarking for the measured radar pulse. The radar pulse can be measured using oscilloscope and vector signal analyzer (VSA). The variable attenuator is connected before any measuring equipments which can vary attenuation from 0 dB to 70 dB. Oscilloscope can be used for any time domain radar measurement. VSA can be used for any frequency domain measurement.
One can also perform emission measurement from the radar antenna by connecting appropriate antenna along with VSA. This radiation radar measurement need band pass filter (BPF), LNA and wideband detector as front end components during testing before oscilloscope/VSA.
Links to useful Measurements
Following are the links to other useful measurements available on Test and Measurement World website.
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Current measurement vs Voltage measurement
Inductance measurement vs Capacitance measurement
Difference between Power and Energy measurements
EMC measurement vs EMI measurement
Electric and Magnetic Field Measurements
What is difference between or comparison between
Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer