Phase- and Timing-Accurate Multi-Channel Radar

The Keysight G3 Vector Signal Generator enables the flexible generation of versatile phase- and timing-accurate, multi-channel radar signals. This ability is supported by the G3 Vector Signal Generator’s features and specifications, including:

• Wideband performance to 40 GHz and 500 MSa/s data processing capability supporting 400 MHz signal bandwidth
• 512 MSa internal memory with 32 bits per sample supporting sequential and waveform segment ID selective playbacks
• Fast frequency and amplitude switching ranges from less than a microsecond to a few microseconds depending on the frequency change range
• Phase coherence and phase-coherent switching
• Fast control port (FCP) for rapid modulation parameter setting and digital IQ data streaming up to 250 MSa/s

Now you can get user-friendly and cost-efficient software to support the radar signal generation on multi-channel G3 Vector Signal Generators.

Pulse descriptor word

Engineers testing radar require the ability to generate multi-pulse streams, with each pulse supporting dozens of parameters, such as frequency, amplitude, phase, pulse width, time position, and intrapulse modulation or chirping. Table 1 summarizes the typical parameter set describing a single radar pulse, known as a pulse descriptor word (PDW). A list of PDWs will fully describe a radar pulse stream.

Multi-patch radar antenna arrays require additional parameters for full characterization. For these arrays, inter-channel phase coherence, which addresses relative phase stability, becomes important. Phase-coherent switching, where the relative phase between channels is stored in memory, and inter-channel timing accuracy are also critical parameters.

Table 1: Typical structure of a PDW

Signal generation modes of the Keysight G3 Vector Signal Generator

The G3 Vector Signal Generator accommodates two different modes for generating the PDWs, implemented with circuitry within the vector signal generator. Figure 1 depicts the block diagram for the two PDW-related operation modes.

Figure 1. Operation modes of the PDW list playback

Mode 1: Sequential PDW playback

In this mode, a list of PDWs, precompiled in a data format, can be uploaded into the G3 Vector Signal Generator internal memory through the Ethernet or USB communication port. During playback, each PDW is translated to the corresponding modulation parameters, sequentially and in real time. This generates a stream of modulated radar signals, allowing multi-channel G3 Vector Signal Generators to play back accurately timed PDW sequences.

Mode 2: PDW live-streaming

In this mode, individual PDWs are fed into the G3 Vector Signal Generator internal memory sequentially and in real time through the G3 Vector Signal Generator FCP for immediate playback.

Key features and performance points

There are several features that are important for generating radar pulse sequences that approximate real sequences. Fast switching is a key parameter. The vector signal generator must support a pulse width ranging from less than a microsecond to a few microseconds. The frequency chirp rate is limited by the modulation bandwidth of 400 MHz. At a 1 μs pulse width, a signal generator can produce chirp rates of close to 400 MHz / μs with excellent signal quality.

Phase coherence is another important capability, and the one that allows a multi-channel vector signal generator to implement the correct radar beam angle specification. The phase difference variation of the G3 Vector Signal Generator over hours of operation is 0.3 degrees RMS between two channels generating 5 GHz signals.

Deterministic phase differences between the channels are essential for sustaining the angle information during radar operation. For a given frequency and power setting, the phase difference between channels does not change, even when the supply power switches on and off. This is called phase-coherent switching, illustrated in Figure 2. The red sinusoidal signal is the reference channel. The blue signal switches to a different frequency with a phase offset, but the blue signal maintains the same relative phase to the red signal when both return to the same frequency setting.

Figure 2. Phase-coherent switching illustration

A multi-channel G3 Vector Signal Generator supports fine delays to + / – 1 ps RMS precision over the entire operating frequency range. This allows generations of multiple radar signal streams with accurate timing. This capability is known as timing-accurate multi-channel triggering. A unique delay mechanism enables this fine trigger delay adjustment. The effective resolution is a very small fraction, typically less than 1/2000, of the sample time. This equates to less than 1 ps with a physical sample time of 2 nsec. Figure 3 illustrates the fine delay setting capability.

Figure 3. Setting delays on identical chirping signals

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