In-Depth Analysis of the UWB650 Module (Part 4): Antenna Delay Calibration and Module Deployment Considerations & Best Practices

Sep . 2025

By sdga:

Antenna Delay Calibration

This chapter is the most technically dense part of the report. It will systematically deconstruct the entire process of antenna delay calibration, starting from basic physical principles and delving into implementation analysis at the code level. Mastering this process is key to unlocking the full precision potential of the UWB650 module.

Theoretical Foundation: Why Antenna Delay is a Major Source of Ranging Error

Definition: Antenna Delay is the total propagation time of a signal between the reference point where the timestamp is generated inside the UWB chip and the physical radiation point of the antenna. It includes the delay of the signal's transmission and reception within the chip, on the PCB traces, and through the antenna itself.
Impact on Accuracy: Although this delay is extremely short (on the nanosecond level), it is not part of the signal's time of flight (ToF) through the air, yet it is included in the raw ToF measurement. The accuracy of UWB ranging is built upon the precise measurement of nanosecond-level time intervals. Any uncompensated fixed time deviation will directly translate into a distance error. The official documentation provides a very intuitive metric: a 1 ns error in time measurement will result in a ranging error of approximately 30 cm.
Necessity of Calibration: Due to manufacturing tolerances of components, differences in PCB materials, and the type of antenna used, the antenna delay value of each UWB650 module is unique. The pre-set ANTDELAY value at the factory (defaulting to 16440) is just an empirical value suitable for general situations. For applications requiring high accuracy of less than ±10cm, performing an independent and precise antenna delay calibration for each module is not an option, but a necessary step.

Mathematical Method: Solving for Delay Using Least Squares

The provided calibration method is based on the principle recommended by Qorvo, the core idea of which is to use redundant measurement data between multiple modules to solve for their respective unknown delays.

Problem Modeling: The calibration process requires at least three UWB modules. First, the antenna delay parameters of all modules are set to zero. Then, in a scenario with known physical distances, two-way ranging is performed between each pair of modules, resulting in a measured distance matrix (EDM_Measured) containing 6 measurements (d12, d21, d13, d31, d23, d32). Concurrently, a true distance matrix (EDM_Actual) is obtained from physical measurements.
Optimization Goal: The goal of calibration is to find a set of antenna delay values that minimizes the difference between the compensated measured distances and the true distances. This is mathematically expressed as minimizing the difference between the norms of the two matrices:

Linear Least Squares Solution: Although the problem is described as minimizing the matrix norm, the provided C code reveals its specific implementation method—linear least squares. The problem can be transformed into an overdetermined system of linear equations. For any measurement between a pair of modules i and j, the measurement error is mainly contributed by the sum of their antenna delays. We can establish the following relationship:

where c is the speed of light. After converting distance to time, each measurement can provide a linear equation regarding the unknown delays τ_i and τ_j. When there are enough measurements (e.g., 6 measurements between 3 modules), an overdetermined system of equations Ax=b can be constructed, where x is a vector containing all unknown delays. This system can be solved for the least-squares solution by solving the normal equations (A^TA)x = A^Tb.

Practical Calibration Workflow

The following are the standardized operational steps for engineers to perform precise antenna delay calibration for UWB650 modules in a lab or in the field:

Physical Setup: Choose an open area with no significant reflectors. Securely place at least 3 UWB650 modules and accurately measure the physical distance d_Act between them using high-precision tools like a laser rangefinder. To reduce the interference of multipath effects, the distance between modules should be sufficiently large (e.g., greater than 30 meters), or the transmit power of the modules should be appropriately reduced.
Initial Configuration: Using a serial tool, send the command UWBRFAT+ANTDELAY=0 to all 3 modules to zero out their antenna delay compensation.
Data Collection: Perform two-way ranging between all pairs of modules in sequence. For example, for modules 1 and 2, first have module 1 act as the initiator to range module 2, recording the distance d21; then have module 2 act as the initiator to range module 1, recording the distance d12. Complete the measurements for all 3 pairs of modules (6 measurements in total) and record all 6 ranging values.
Calculate Delay Values: Launch the provided Qt calibration tool, Antdelay_cal.exe. In the interface, enter the 6 measured distance values and the 1 previously measured actual physical distance d_Act, then click the "Calculate" button.
Write Parameters: The tool will output 3 ANTDELAY register values corresponding to each module. Send the UWBRFAT+ANTDELAY=command to each module respectively via the serial port to write the calculated calibration values to the modules.
Save and Verify: Send the UWBRFAT+FLASH command to each module to permanently save the new antenna delay values to the module's flash memory. After saving is complete, perform ranging again. The distance reported by the modules should now be highly consistent with the actual physical distance, with an error typically within ±10cm, indicating a successful calibration.

The success of the entire calibration process is fundamentally based on the accuracy of the physical distance measurement. The algorithm itself assumes that the input reference value is the absolute truth. Any error introduced during the physical measurement phase will be treated by the algorithm as a systematic bias and "calibrated" into the antenna delay values, leading to a systematic offset in the final results. Therefore, ensuring that the precision of the physical measurements matches the precision sought by the UWB system is a crucial part of the calibration process.

Deployment Considerations and Best Practices

This chapter aims to translate the aforementioned technical details into actionable advice for deploying UWB650 modules in the real world. The content will synthesize troubleshooting and FAQ from the official documentation to provide a practical deployment guide for system integrators.

Mitigating Environmental Factors: Obstruction and Multipath Effects

The performance of a UWB system is closely related to the physical characteristics of the deployment environment.

Line-of-Sight (LoS) is Crucial: Although UWB signals have some penetration capability, they cannot effectively penetrate high-density materials like reinforced concrete walls. When signals encounter such obstacles, they reflect. While a communication link may still be established, the increased path length of the reflected signal leads to larger time-of-flight measurements, introducing severe ranging errors. Metal plates or large metal objects are particularly absorptive of UWB signals and can create signal dead zones.
Impact Analysis of Common Obstructions:

Solid Walls: Signals cannot penetrate. Any ranging result obtained by going around a corner is produced by reflected signals and the data is not reliable.
Glass Walls: Have a significant impact on ranging accuracy.
Poles, Trees, etc.: The degree of impact depends on the distance. When the modules are far apart (e.g., 100 meters), an obstruction in the middle has less impact. However, if the obstruction is less than 1 meter from either antenna, it can cause significant data drift.
Cardboard, Wooden Boards: If not too thick (≤5cm), the impact on ranging accuracy is limited, but they will still cause signal strength attenuation.

Deployment Best Practices: In a positioning system, Anchors should be installed at a high position (recommended above 2 meters from the ground) to maximize the probability of a clear line-of-sight path between Tags and Anchors, avoiding obstruction by people, vehicles, or ground equipment. A successful UWB deployment is not just an electronics engineering problem but also an RF environmental engineering task that requires careful planning.

Troubleshooting Common Ranging and Positioning Accuracy Issues

When system accuracy does not meet expectations, you can troubleshoot using the following steps:

Poor Ranging Accuracy:

Environment Check: Confirm whether there are any unexpected physical obstructions between the modules or strong electromagnetic interference sources nearby.
Interference Check: Check for other UWB devices operating in the same frequency band (CH5) in the vicinity.
Hardware Check: Ensure the antenna is correctly installed and securely connected.
Calibration Check: Confirm that precise antenna delay calibration has been performed on all modules involved in ranging.

Poor Positioning Accuracy:

Coordinate Verification: The most common source of error is inaccurate Anchor coordinate settings. Be sure to repeatedly check that the measured values of the physical deployment locations are completely consistent with the values written to the modules via the UWBRFAT+COORDINATE command, and that the units are correct (centimeters).
Geometric Layout: Check if the deployment of the Anchors follows the recommended geometric configurations (e.g., triangle, rectangle). A poor geometric layout (e.g., all Anchors are approximately in a straight line) can lead to the Geometric Dilution of Precision (GDOP) effect, where small ranging errors are amplified, severely affecting the final positioning accuracy.
Height and Co-planarity: Confirm that all Anchors are deployed at the recommended height. For 2D planar positioning applications, ensure that all Anchors are roughly on the same horizontal plane.
Coverage Area: Confirm that the Tag is within the effective positioning area enclosed by the Anchors. When the Tag moves outside the Anchor coverage area, the positioning accuracy will rapidly degrade.

In-Depth Analysis of the UWB650 Module Series