Radar system is widely used, different types of radar application scenarios are also different, it needs to consider a series of factors such as performance, size, cost and so on. For example, police radar often uses continuous wave radar to simply measure the speed of moving vehicles without paying attention to the distance information. Therefore, low cost and small size are more important than advanced performance and characteristics.
In another extreme case, a complex phased array radar may have thousands of transceiver components working at the same time. In addition, they may rely on complex technologies to improve performance, such as sidelobe zeroing, stagger PRI, frequency agility, real-time waveform optimization, etc.
Today, let’s take a look at the measurement of radar parameters and power / spectrum.
Generally, radar transmitter is the most expensive component in the system, which has the highest power consumption, the most stringent cooling requirements and the greatest impact on the system performance. Many different terms are used when talking about power, as shown in the figure below.
Average power is the power integrated on the complete time waveform of radar. If the pulse width and PRF are not constant, the integration time must be long enough to cover all possible changes in pulse parameters. Most typical RF and microwave power meters are average power meters, which are related to the energy of the signal.
The peak power is the maximum instantaneous power. Pulse power is the integral or average power of a complete pulse. Other parameters, including duty cycle, pulse width, PRF, and rise and fall time, are very useful for characterizing the power of radar signal.
From the perspective of radar equation, the power term corresponds to the power of transmitted pulse. If the integral term is excluded, the equation is applicable to a single pulse. Therefore, it is useful to measure the peak value and pulse power on the basis of single pulse. For modern radar system, this technology becomes more and more important, because radar will adjust pulse width and PRF dynamically to improve system performance.
The use of modern test equipment makes measurement easier.
If some characteristics of the pulse are known, such as the duty cycle of the radar signal, the pulse power can be derived or estimated based on the average power. The result is almost equal to the peak amplitude of the pulse, and in the case of square wave pulse, it will be equal to the real peak power or pulse power.
In addition to power measurement, spectrum shape is also very important to verify whether the radar system works effectively.
For example, asymmetric or incorrect spectrum shape indicates that the performance of radar is not optimal. In this case, the radar may transmit power on unnecessary frequency, resulting in power waste and out of band interference. For some radar systems, pulse shaping is used to reduce the level of spectrum sidelobe, improve the efficiency and life of radar components, and reduce the bandwidth.
There are many options for measuring radar power, pulse characteristics and spectrum, including power meter, signal / spectrum analyzer or vector signal analyzer. Because each instrument has its advantages and limitations, the best choice depends on the measurement target and the limitations of radar and test instruments.
Editor in charge: GT