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A Self-Calibrating SDR for High Fidelity Beam- and Null-forming Arrays

Yongjun Kim, Aditya Dhananjay, Sundeep Rangan, Sachin Shetty, C. Nicolas Barati, Michael Zappe, Kimberly Gold, Junil Choi

Abstract

Null forming is increasingly essential in modern wireless systems for spectrum-sharing, anti-jamming, and covert communications in contested and congested environments. Achieving deep nulls, however, is far more demanding than conventional beam steering: nulls are intrinsically narrow, and even small phase, timing, or gain mismatches across RF chains can significantly degrade suppression. This work develops and validates a self-calibrating SDR architecture tailored for high-fidelity null forming using a compact reference transmitter directionally coupled to the antenna feeds. We demonstrate the effectiveness of the approach through simulation and experimental measurements on an SDR platform operating from 3.0 to 3.5GHz, a band of growing importance for Department of Defense spectrum-sharing initiatives.

A Self-Calibrating SDR for High Fidelity Beam- and Null-forming Arrays

Abstract

Null forming is increasingly essential in modern wireless systems for spectrum-sharing, anti-jamming, and covert communications in contested and congested environments. Achieving deep nulls, however, is far more demanding than conventional beam steering: nulls are intrinsically narrow, and even small phase, timing, or gain mismatches across RF chains can significantly degrade suppression. This work develops and validates a self-calibrating SDR architecture tailored for high-fidelity null forming using a compact reference transmitter directionally coupled to the antenna feeds. We demonstrate the effectiveness of the approach through simulation and experimental measurements on an SDR platform operating from 3.0 to 3.5GHz, a band of growing importance for Department of Defense spectrum-sharing initiatives.

Paper Structure

This paper contains 11 sections, 9 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Calibration Problem
  3. Calibration Procedure
  4. Calibration Filter Design
  5. Timing and Phase Offset Estimation
  6. Hardware description
  7. Self-calibration validation
  8. Error Analysis with null forming
  9. Simulation Result
  10. Experimental result
  11. Conclusion

Figures (6)

  • Figure 1: Receive array self-calibration
  • Figure 2: Overall SDR for self-calibration where an RFSoC (bottom) is connected to a front-end MIMO transceiver board (middle), and then on to the antenna board (top).
  • Figure 3: (a) Self-observation antenna board used for self-calibration in the 3.0 to 3.5 GHz bands. The transmission lines for the reference transmitter and receiver are on the bottom side of the PCB through a length-matched Wilkinson divider that is directionally coupled to the antenna feeds on the top side. (b) The SDR mates to the antenna board through a front-end MIMO transceiver board with standard SMA connectors.
  • Figure 4: Comparison of simulated beampattern pre/post calibration.
  • Figure 5: Simulated average nulling ratio and standard deviation across different frequency bins w.r.t. noise power.
  • ...and 1 more figures