System Self Calibration

Because calibration data is only valid for specific hardware states, the system can store multiple profiles. Each profile is indexed using the following operational parameters as lookup keys:

• VST Center Frequency
• Input Reference Level
• Coprocessor Data Path (if applicable)
• Coprocessor Minimum Latency (if applicable)

At runtime, the software automatically cross-references the current operational parameters against the saved profiles. If a matching set of keys is found, that calibration data is automatically applied. If any parameter changes and no matching profile exists, the RTG defaults to running uncalibrated. To guarantee peak accuracy across RTG session restarts, always utilize previously saved calibration data.

Each phase of system self-calibration runs back-to-back:

Spectral Optimization—The spectral optimization phase of the system self-calibration consists of two main stages. First, the system analyzes power consumption and stabilizes its temperature. Once the system achieves thermal stability, the VST executes a series of optimizations designed to flatten the spectral response and minimize Local Oscillator (LO) leakage. A standard calibration typically takes 20 minutes to 30 minutes. However, the RTG reduces this calibration to three or four minutes by targeting only the currently configured center frequency.

Delay Calibration —Inherent (non-zero) delays naturally occur during the RTG’s acquisition, DSP processing, and signal generation phases. To ensure that simulated target delays remain highly accurate, this baseline system delay must be precisely measured. Measure this delay by creating a hardware loopback, connecting the RTG’s RF output back to its RF input. You can route this loopback using cables or by toggling a switch if available. Once connected, the RTG generates a test signal and captures the returning data. The RTG then analyzes the acquired signal to calculate minimum target delay.

Minimum Attenuation—Using the same loopback setup as the delay calibration, the minimum attenuation calibration sweeps the VST output power level across its entire usable range. For each power level, the system transmits a signal and measures the resulting losses. Importantly, these measurements are captured not only at the selected center frequency but also at multiple frequencies spread across the instantaneous bandwidth. The system uses this wideband data to build a comprehensive attenuation lookup table, which provides the foundational data necessary to enable frequency correction. Because output power level changes are asynchronous and remain fixed once active target generation begins, this calibration establishes a static baseline. By configuring the Target Common Attenuation setting, you can apply a constant amount of analog attenuation to all targets, effectively compensating for any systemic common losses.

Note You must configure the Target Common Attenuation setting after the calibration is complete, but before initiating target generation.

Offset Frequency—The RTG utilizes the full instantaneous bandwidth (IBW) of the device (2 GHz for the PXIe-5842, and 1 GHz for all other models). For radars operating with a bandwidth smaller than the system's IBW, you have the flexibility to offset the radar's center frequency relative to the RTG's center frequency. For static radars, applying this offset is highly recommended to minimize interference from residual system Local Oscillator (LO) leakage. Alternatively, flexible-frequency radars can leverage the wide IBW to seamlessly support frequency-hopping scenarios.

To accurately apply amplitude and Doppler shifts to the generated targets, the system must account for the difference between the radar frequency and the RTG system frequency. This frequency compensation is managed in one of two modes:

• Static scenarios—The offset frequency is defined manually via the UI or API. This fixed value is then used to apply corrections across all configurations.
• Dynamic scenarios—Compensation is controlled using the Enable Frequency Correction setting. When set to TRUE, the RTG actively measures the incoming radar pulse frequency and applies the appropriate corrections dynamically. When set to FALSE, the system defaults to using the manually entered static offset frequency.

Note In dynamic scenarios, measuring the pulse frequency and calculating the compensation takes a specific amount of processing time. If the requested target delay is shorter than this calculation window, the system will automatically fall back to using the user-entered static offset frequency instead of the measured frequency. For more details on frequency corrections, refer to the Attenuation section.

Agile Attenuator Calibration (if in your system)—The Agile Attenuator module provides a built-in loopback connection required for system self-calibration, which removes the need for additional switching or manual cable changes.

External Attenuation and Delay—The RTG System Self-Calibration procedure is designed to measure the delay and attenuation of the system only. While the calibration loopback captures the defined system signal path, it cannot measure anything outside of that loop.

As a result, any external components used to connect the radar to the RTG—such as external cables, standalone attenuators, mixers, or amplifiers—are excluded from the self-calibration process and will not be automatically compensated for.

Users are responsible for characterizing the cumulative signal loss and delay introduced by these external connections. Once characterized, you must enter these cumulative values into the External Attenuation and External Delay configuration parameters. This informs the RTG of the external path's characteristics, allowing the system to automatically account for these factors and adjust its target generation accordingly.

Note If using the Agile Attenuator module (PXIe-5699), the calibration loopback occurs internally. Physical loopback connection at the test fixture is unnecessary, but the path loss and delay through the test fixture needs to be pre-determined and included in the Output External Delay and Output External Attenuation values.