Design Considerations for Digital Transmit Phased Arrays: Data converter performance asymmetries remedy and calibration

This module provides a comprehensive overview of digital phased array architecture for aperture-level simultaneous transmit and receive applications, addressing practical implementation challenges at compensating data converter and RF front-end asymmetries. Fundamental Concepts: The workshop begins with a brief discussion of digital and hybrid phased-array architectures and the trade-offs among performance metrics: power consumption, multiple-beam configurations, and dynamic range. The roles of ADCs and DACs in the signal chain will be discussed, including gain, phase, and bandwidth mismatches that degrade beam accuracy and nulling depth. For instance, the selection of the main path decimation factor and channelization decimation factor must be considered for the usage case. Ideally, all rates will match across all paths, allowing data to be transferred over a single JESD link. In reality, they may not match. Some paths may require wider bandwidth than others for application purposes. Accommodating these baseband rate differences requires either (1) more JESD links or (2) rate adjustment between the path output and the JESD link via the upsampler. Further design strategies to mitigate asymmetries will be discussed in this section. Calibration Techniques: The topic will describe the algorithms developed for cabled (using a calibration board) and over-the-air calibration to compensate for system-level asymmetries. Algorithms such as the Rotating Electric Field Vector Method (REV) rely on power-only measurements to obtain phase and amplitude information. Improved Rotating Electric Vector Methods reduce the sensitivity of phase shifter error. Orthogonal Code Methods uses a set of orthogonal antenna channel weightings so that the resulting beam from all orthogonal weightings produces a set of linearly independent equations to solve for the channel imbalances. The presenters will discuss methods and implementation troubleshooting in the topic presentation. Case study: A case study will present the design of an FR3 16x3 elements hybrid array, developed at UC Boulder MW Lab for spectrum sharing and aperture-level in-band full-duplex applications. The system operates from 7-8.4 GHz, with an instantaneous bandwidth of 160 MHz, 16-channel transmit, and 16-channel receive. Beamforming operations and calibration are performed in baseband at 3.5 GHz using an ADI QUAD-MxFE Platform board, cascaded with a frequency conversion to 7-8.4 GHz, and an RF amplification stage to achieve the required output power to the 16 X 3 element array. The system radiates a minimum of 44 dBm of EIRP over a ±40 ° FoV. Keywords: Digital phased arrays, beam steering, data converter, multi-channel frequency converter, antenna array, phased array calibrations.