Electronic systems must peer into ever-greater swathes of the electromagnetic spectrum to ensure a battlefield edge.
Michael HoffSuch electronic systems are used in ground, air, and sea vehicles and even in space.
The designs combine sensors and electronic circuitry for tasks such as radar, electronic warfare, communications and targeting.
Existing systems are custom designs undertaking particular tasks. The challenge facing military equipment makers is that enhancing such systems is becoming prohibitively expensive.
One proposed cost-saving approach is to develop generic radio frequency (RF) and sensor technology that can address multiple tasks.
“Now, each sensor will have to satisfy the requirements for all of the backend processing,” says Michael Hoff, senior research engineer at Lockheed Martin Advanced Technology Laboratories.
Such hardware will be more complex but upgrading systems will become simpler and cheaper. The generic sensors can also be assigned on-the-fly to tackle priority tasks as they arise.
"This is a foundational architectural shift that we see having relevance for many applications," says Hoff.
Generic sensing
The proposed shift in architectural design was discussed in a paper presented at the IEEE International Symposium on Phased Array Systems and Technology event held in October.
Co-authored by Lockheed Martin and Ayar Labs, the paper focuses on generic sensing and the vast amount of data it generates.
Indeed, the data rates are such that optical interconnect is needed. This is where Ayar Labs comes in with its single-die electro-optical I/O chiplet.
Lockheed Martin splits sensing into two categories: RF sensing and electro-optic/ infrared (or EO/IR). Electro-optic sensors are used for such applications as high-definition imaging.
"When we talk about platform concepts, we typically lump EO/IR into one category," says Hoff. The EO/IR could be implemented using one broadband sensor or with several sensors, each covering specific wavelengths.
Source: Lockheed Martin
A representation of current systems is shown above. Here, custom designs comprising sensors, analogue circuitry, and processing pass data to mission-processing units. The mission equipment includes data fusion systems and displays.
Lockheed Martin proposed architecture uses two generic sensor types - RF and EO/IR - which can be pooled as required (see diagram below).
For example, greater resources may need to be diverted urgently to the radar processing at the expense of communications that can be delayed.
“It's a more costly individual development, but because it can be shared across different applications and in different teams, cost savings come out ahead,” says Hoff.
An extra networking layer is added to enable the reconfigurability between the sensors and the mission functions and processing systems that use, process, and digest the data.
Source: Lockheed Martin
Optical interconnect
Data traffic generated by modern military platforms continues to rise. One reason is that the frequencies sensed are approaching millimetre-wave. Another is that phased-array systems are using more elements so that more data streams must be be digitised and assessed.
Lockheed Martin cites as an example a military platform comprising 16 phased-array antennas, each with 64 elements.
Each element is sampled with a 14-bit, 100 gigasample-per-second analogue-to-digital converter. The data rate is further doubled since in-phase and quadrature channels are sampled. Each phased array thus generates 179.2 terabits-per-second (Tbps) while the total system data is 2.87 petabits-per-second.
Algorithms at the sensor source can trim the raw data by up to 256x, reducing each antenna’s data stream to 700Gbps, or 11.2Tbps overall.
Optical communications is the only way to transport such vast data flows to the mission processors, says Lockheed Martin.
Multi-chip modules
Any interconnect scheme must not only transfer terabits of data but also be low power and compact.
“The size, weight and power constraints, whether an optical transceiver or processing hardware, get more constrained as you move towards the sensor location,” says Hoff.
The likelihood is that integrated photonics is going to be required as bandwidth demand increases and as the interconnect gets closer to the sensor, he says.
Lockheed Martin proposes using a multi-chip module design that includes the optics, in this case, Ayar Labs’s TeraPhy chiplet.
The TeraPhy combines electrical and silicon photonics circuitry on a single die. Overall, the die has eight transceiver circuits, each supporting eight wavelengths. In turn, each wavelength carries 32 gigabit-per-second (Gbps) of data such that the 54mm2 die transmits 2Tbps in total.
Lockheed Martin has compared its proposed multi-chip module design that includes integrated optics with a discrete solution based on mid-board optics.
The company says integrated optics reduced the power consumed by 5x, from 224W to 45W, while the overall area is reduced a dozen fold, from 3,527 mm2 to 295mm2.
“You're going to need optical interconnects at many different points,” says Hoff; the exact locations of these multi-chip modules being design-dependent.
Charles Wuischpard, CEO of Ayar Labs, points out that the TeraPhy is built using macro blocks to deliver 2Tbps.
“There are customer opportunities that require far less bandwidth, but what they want is a very tiny chip with very low energy consumption on the input-output [I/O] transport,” says Wuischpard. “There are different areas where the size, weight and power benefits come into play, and it may not all be with our single chiplet solution that we offer.”
Investor
Lockheed Martin became a strategic investor in Ayar Labs in 2019.
"We see this [Ayar Labs’ optical I/O technology] as a foundational technology that we want to be out in front of and want to be first adopters of,” says Hoff.