Understanding Radar Measurements and Duty Cycle for Optimal Performance
Radar systems rely on various measurements and metrics to operate effectively. One of the critical parameters is the radar duty cycle, which affects the radar’s average power and overall detection capability. This tutorial provides overview of radar transmitter and receiver measurements. The common tools used for radar maintenance and measurements are multimeter, spectrum analyzer, oscilloscope, power meter, frequency counter, signal generator, crystal detector, attenuator etc.
Radar Transmitter Measurements
The radar transmitter measurements include transmitted Power and Stability, PW, PRF, Duty Cycle/ Factor, Klystron Pulse, Klystron Current, Klystron RF Input Level, Transmitted frequency, Occupied BW
and VSWR. Let us examine these radar transmitter measurement parameters one by one.
Transmitted Power :
The transmitted power is measured with the help of calibrated power meter.
The value is calculated taking into consideration loss of cable as well as duty cycle factor.
➨Peak Power (dBm) = Average power (dBm) - Duty Factor(dB) + Loss(dB)
Where, Duty Factor = 10 log(Pulse Width(sec) * PRF(Hz))
Loss will be path loss between output flange of klystron and rf transmitter monitor connector.
Power Stability :
With Pulse Width of 1 µsec and PRF of 250Hz.
Acceptable level for power stability is about +/-0.5 dB.
For example, if power output varies from -14.95dBm to -15.05dBm in a half an hour period.
Difference in variation of power here is 14.95 - (-15.05) = 0.1 dB.
This is less than acceptable level.

PW, PRF, Duty cycle or duty factor :
This measurement is carried out using oscilloscope. If oscilloscope is not capable of measuring high frequency
than arrangement as shown in the figure is done.
step attenuator and crystal detector is used for this purpose.
To measure PW we need 3dB attenuation, as it is the width at half power points. similarly PRF and duty factor is measured using oscilloscope.
As mentioned, radar measurements include factors like pulse width, pulse repetition frequency (PRF) and range.
These parameters play a role in determining the radar's range resolution, maximum detectable range,
and target identification accuracy. Understanding these metrics is essential for configuring radar systems to meet specific operational requirements.
• Pulse Width: The duration of the radar pulse, influencing range resolution.
• Pulse Repetition Frequency (PRF): The number of pulses transmitted per second, affecting maximum range and detection.
• Radar Duty Cycle: Defined as the ratio of the pulse width to the pulse repetition period, it
measures the proportion of time the radar is transmitting. A high duty cycle indicates a radar with high
average power, useful for detecting distant or low-reflective targets.
Klystron Pulse, Klystron current :
Klystron pulse waveform is measured at the output of transmitter front panel using oscilloscope.
Klystron current is calculated by multiplying oscilloscope value with 10.
For example, oscilloscope reading for max. peak is 1.2V than current is 12Amp.
Klystron RF input level :
In this test, rf drive power level and rf frequency is measured to check whether they are within
normal range or not.
Frequency should be about 5625MHz. The same is measured using either spectrum analyzer or frequency counter.
Occupied Badwidth :
Occupied BW is the width of band over which emitted mean power is about 99% of the total mean power.
Difference between lower and upper frequency points is referred as occupied BW.
VSWR measurement :
It is the measure of how much power is transmitted and how much is reflected.
Return loss in general= Forward power - Reflected power,
Refer RL vs VSWR for more.
Radar receiver measurements
Radar receiver is very critical part in radar system as it has to detect and amplify the received weak signal from antenna. The radar receiver measurements include STALO level measurement, COHO level measurement, receiver Gain, Minimum Detectable Signal(MDS), Dynamic range, intensity check, velocity check etc.
STALO Level Measurement :
Radar usually will have different STALO frequencies and power levels.
The main aim is to determine weak signal receiver power. The digital power meter is used for this
purpose.
COHO Level Measurement :
COHO stands for COHerent Oscillator. It has frequency of about 30MHz.
Receiver Gain :
Radar transmitter is kept off and signal generator frequency is set equal to
radar receiver for this test.
Gain(dB) = output power (dB) - input power(dB).
Similarly dynamic range is calculated by finding MDS and saturated input points.
Refer MDS vs SFDR for more.
Tx IF Out and Exciter RF :
Transmitter IF OUT is pulse modulated COHO output which is up converted to RF level.
Exciter RF signal is passed to the klystron. The spectrum analyzer is used for this purpose.
Intensity Check measurement :
It is done to see how well the system performs the processing of the
reflected signal after coming into LNA through Signal Processor.
Velocity Accuracy :
Velocity accuracy check measurement is done to see how well the system calculates the
velocity of an echo.
Conclusion
Comprehending radar measurements and duty cycle helps in designing radars with the desired power, range, and resolution for varied applications, from navigation to target tracking.
RADAR RELATED LINKS
Doppler Radar
FMCW RADAR
RADAR BANDs
RADAR SCOPE
Weather Radar
Ground Penetrating Radar System
RADAR RANGE and RESOLUTION
Radar calculators
Radar Range calculator
Radar PRF vs Range
Radar Range Resolution