Developing an X-Band Hybrid Beamformer Digital Twin

Breaking the Limits of Hardware Prototyping

Analog Devices, Inc., based in Wilmington, Massachusetts, is a long-time industry leader in analog signal-processing semiconductor technology. X-band (8 to 12 GHz) radar uses techniques like phased antenna arrays for hybrid beamforming, and aerospace, defense, and weather radar design teams turn to Analog Devices (ADI) for critical RF components in the signal chain. ADI offers customers a hardware enablement platform for X-band hybrid beamforming based on its ADAR1000 beamformer and AD9081 MxFE® chipsets.

In a two-year project, three to five ADI engineers, plus added experience and assistance from Keysight Field Solutions Engineering Fellow Murthy Upmaka, set out to create a digital twin of this X-band hybrid beamformer system. This digital twin uses Keysight PathWave System Design to quickly adapt to various phased array configurations and newer ADI components as they become available.

Challenge: From components to system-level models

Hardware provides a level of comfort for RF engineers. Teams can take measurements in a lab, in an anechoic chamber, or in the field with a hardware prototype. But RF hardware also provides a fixed set of boundaries, some based on the architecture of the implementation and some based on the physical realization of the elements involved.

Figure 1 shows a photo of the ADI hardware enablement platform for an X-band phased array hybrid beamformer depicted in the block diagram from the introduction. “These platforms scale to some degree, and there is interchangeability in the signal chain by upgrading boards to newer versions if available,” says Sam Ringwood, Systems Platforms Application Engineer at ADI. Still, the Stingray board (far left) implements one configuration: four subarrays of eight elements each. “X-band phased array radar designs now run into hundreds and even thousands of elements,” continues Ringwood. Physical interconnects between the hardware are crucial in a beamforming application. What might appear to be simple coaxial cabling is a phase-matched set of cables between each board or module; if one breaks, the repair or replacement must maintain phase stability or performance changes.

ADI application teams wanted a platform that could quickly scale to many more array configurations while still providing flexibility to interchange any parts in the signal chain. “Moving to a digital twin provides a reference design that would work for more customers, including those designing with legacy ADI parts, new ADI parts before an evaluation board is available, or other commercially available components to fit a particular aspect of a beamforming application,” observes Ringwood. “We’d then be able to validate our digital twin performance against a basic configuration, then scale it to a larger array configuration.”

The first step ADI took in moving to its digital twin was getting comfortable with the PathWave System Design environment and discovering how to leverage its capabilities. “We’d used RF Link for simple signal chain cascade analysis, and stepping up to PathWave System Design for a more comprehensive cross-domain simulation environment with data flow analysis was a bit of a learning curve,” shares Ringwood. ADI also has some homegrown spreadsheets, again for simple cascade analysis. A realization emerged: they needed better model fidelity for the more powerful solvers in PathWave System Design if its simulations were to provide results close to the hardware.

Pieces of modeling existed, but significant gaps remained. Many ADI RF components have Sys-parameters, measurement-based characterizations of mixers and power amplifiers describing linear and

non-linear behavior such as P1dB, IP3, gain, noise figure, return loss, and more. Where Sys-parameter models didn’t exist, S-parameter models would work, especially since wideband analysis wouldn’t be required in an X-band system. Teams also had some groundwork in MATLAB models for ADI data converters, mixed-signal components with analog and digital properties. All three model types integrate with PathWave System Design. “Things got much easier once we figured out how to drop MATLAB blocks within the system model as code,” Ringwood offers with perceptible relief.

Ultimately, the challenge ADI faced was architecting a virtual system model representing the performance of its existing hardware enablement platform in the 4x8 array configuration. At first, the team thought they would need an exact 1:1 match for the hardware. “Our definition is based on perspective,” says Ringwood. “You can avoid overcomplicating the model while still achieving accuracy representative of the system.” Abstracting the model allowed the team to break the relationship between the features of a specific chip and the capability needed in the beamforming system.

Solution: A simpler, scalable digital twin

A digital twin is a detailed virtual representation of a system made from measurement-based or predictive behavioral models, incorporating real-world effects and delivering fast, accurate simulation results close to system hardware measurements. It can become an instance of the physical system it represents with feedback on actual measurements made under operating conditions and any maintenance performed.

In a more straightforward prototyping context, ADI’s digital twin seeks to provide a faster path to a proof-of-concept for an X-band hybrid phased array beamformer, delivering equivalent performance to the 4x8 hardware enablement platform and, by extension, different and larger configurations. Figure 2 shows the block diagram for the X-Band hybrid beamforming enablement platform (pictured in Figure 1) used initially to guide the digital twin system design and gauge its performance.