The simulation and testing of frequency-stepped radar systems is actually that complicated

SFR can synthesize frequency-stepped pulse echoes in the frequency domain to obtain a wider signal bandwidth; frequency hopping is used to achieve high resolution and high signal-to-noise ratio. With the advantages of high resolution and low cost, frequency-stepped radar is now widely used in commercial and aerospace/defense (A/D) fields. However, it is difficult to accurately analyze the performance of SRF receivers due to the background clutter reflected by objects such as the ground, buildings, and plants. Therefore, simulation becomes particularly important. It helps designers accurately design, verify, and test SFR systems in real environments, so it is an indispensable tool for designers.

Understanding SFR

To better understand why SFR provides such advanced capabilities, let’s first take the pulse radar waveform shown in Figure 1 (left-most image) as an example.

Figure 1: The left side shows a pulse radar waveform, and the right side shows an SFR waveform.

Assuming the pulse width is τ and the signal bandwidth is f0 = 1/τ, the distance resolution Rs can be calculated according to the following formula:

Here, c is equal to the speed of light.

Assuming pulse width τ = 0.25us, pulse repetition interval T = 10us, then the distance resolution Rs = 37.5m. To achieve a resolution less than 1m, according to equation (1), the pulse width must be reduced, such as T = 3.9ns. The resulting distance resolution will be 0.58m. Without changing the 4MHz signal bandwidth, the new system bandwidth will be 250ns/3.9ns = 64 times wider than the original system bandwidth.

In order to achieve a high resolution of 0.58m without shortening the pulse duration, SFR can be used. As shown in Figure 1, the frequency-stepped radar transmits a sequence of N pulses at a fixed pulse repetition frequency (rather than a fixed radar frequency). Unlike pulse signals, all pulses in a frequency-stepped waveform sequence have the same pulse width and duration, but different carrier frequencies. This frequency can be calculated by f_i=f_0+N×dF, where dF refers to the frequency increase, indicating that frequency hopping and time division are used.

Assuming that the frequency is stepped N times, the pulse width and pulse repetition are still τ=0.25us and T=10us, with N=64, as in the previous example, dF=4MHz, then the distance resolution bandwidth result will be:

It is clear from the results that SFR has a higher range resolution (less than 1m). In addition, it does not require resolution reduction, making it suitable for pulse radar in this scenario.

SFR Design and Test Platform

In an SFR radar, clutter will interfere with target detection, making it more difficult to find a realistic number of targets, or even preventing the radar from detecting smaller targets. Closed-loop analytical solutions that can analyze target detection in clutter conditions are extremely rare. Because the analysis of these types of scenarios is extremely important, simulation is key, as is the use of platform solutions to simulate SFR systems in real environments. The platform can also be used to validate and test SFR systems. A simulation platform with a test environment must include the return signal radar cross section (RCS) and background clutter,

To better understand how to use this platform to design, verify, and test SFR systems, an SFR design template is provided below. Engineers can customize the SFR design template for their own system and then run simulations in the platform to test the performance of the design. When design simulations are used in conjunction with test equipment, the simulation platform can also serve as a test platform to test SFR component hardware. For example, when designing an SFR system to detect two target echoes against a background of ground clutter, the platform can be used for simulation and hardware testing. Simulating SFR Systems

Take the basic SFR design shown in Figure 2 as an example. In the signal generator, the SFR signal source is followed by an RF modulator, so two target models and one clutter model are used. At the SFR receiver input, the received signal includes the target echo and clutter.

Figure 2: This SFR simulation example was performed using the Agilent SystemVue electronic system-level design platform.

The received signal is measured at the SFR input as shown in Figure 3. Note that the frequency vs. time plot of Figure 3C is consistent with the expected SFR signal (using the carrier frequency calculation method described above). The unwrapped phase is also as expected. Additionally, the simulation shows that the SFR receiver is operating well.

Figure 3: Spectrum of the received frequency-stepped radar signal measured at the receiver input (A), waveform amplitude reflecting the random nature of the target echo and clutter characteristics (B), frequency hopping of the received signal (C), and spread phase (D).

Figure 4 shows that using this high-resolution stepped frequency radar design, we can easily detect two targets in close proximity. To detect the same two targets using pulsed radar, the pulse width must be increased by at least 8 times, significantly increasing the system cost.

Figure 4: Detecting two adjacent targets using a high-resolution stepped frequency radar design. SFR system testing

Once a simulation model that replicates an actual SFR system is built, it can be used for testing under realistic conditions (including RCS and background clutter). In addition to designing high-resolution SFR systems, the simulation platform can also be used to perform hardware receiver testing. An SFR signal generator is required to perform this testing. The received signal contains the target echo as well as environmental signals such as background clutter and noise.

First, a test signal containing two adjacent target echoes and clutter is generated using the design in Figure 2. The signal is then downloaded into a vector signal generator and up-converted to RF frequency. Next, a signal analyzer is used to measure the SFR receiver input, and based on the measured data, the test signal is verified using signal analysis software.

SFR transmitter testing requires an SFR receiver. The SFR receiver can be created by the simulation platform. Use a vector signal analyzer running vector signal analysis software to measure the signal. Then download the received signal from the signal analyzer to the EDA software for demodulation and detection to restore it to the original target signal. Use the created SFR software receiver and the test setup in Figure 5 to test the actual received SFR signal.

Figure 5: Test setup for SFR transmitter and receiver hardware testing.

in conclusion

The platform solution can simulate the system in the actual environment and is the best tool for engineers to design, verify and test modern radar systems. It is especially important when using high-resolution frequency stepped radar systems to detect targets in cluttered environments (closed solutions are difficult to obtain satisfactory analysis results at this time). The simulation platform is suitable for the design and testing of SFR systems. In SFR system testing, a simulated software receiver can be used for transmitter component testing, and a simulated software transmitter can be used for receiver component testing.