In previous blog posts, we discussed the radar market and active vs passive technologies. Currently, the most widely used technologies are based on active radar. However, more and more research projects are looking at passive technologies. So much so that, according to this report, a compound annual growth rate (CAGR) of 36% is now expected for the passive radar market from 2013 to 2023. Passive radar investments will consist of 41% of all military spending on radar technologies during this period. Why is this so, and why now? The same study claims that deployment flexibility, stealth characteristics, and surveillance capabilities are the driving factors behind this growth. And, under the hood, technological innovations are bringing passive radar back by resolving two major roadblocks that had sidelined the technology for years: algorithmic complexity and processing power requirements.

From static to motion

First, it’s important to remember that passive radar aims at resolving a major disadvantage of active radar: active radar emits electromagnetic signals, which means it can be detected.


Passive radar, by its very nature, does not send out signals. It does, however, require sophisticated algorithms. Common challenges include integrating the signals of multiple receivers and also achieving the high accuracy (dynamic range) required by the digitizer hardware to detect echoes buried in noisy environments. These challenges have already been addressed and resolved for the most part. Fixed passive radar has been around for some time now. The real interest now is in ‘moving’ equipment, suitable for aerospace applications, which puts even more pressure on the algorithms. The good news is that while hardware manufacturers were busy creating more and more powerful devices, research centers kept working and came up with algorithmic solutions that address the challenges of moving passive radar, such as Doppler shift. These solutions are now ready for prototyping and proof of concept.

Just in time for the tip of Moore’s law

The “Moore’s law era”, which saw the number of transistors doubling every two years, is slowly coming to an end. Three years is to become the norm, according to International Technology Roadmap for Semiconductors. It appears, however, that its latest technological babies are ideal for moving passive radar systems.

Developers can now benefit from the incredible innovations of FPGA manufacturers like Xilinx and Altera, as well as, on the CPU side, the highly popular Intel QuadCore i7. New generations of FPGAs with embedded ARM processors also provide great opportunities for cost reduction. As the technology costs decrease, the business case (i.e. return on investment, or ROI) for supporting real-world deployments makes more and more sense. A case in point is Altera’s latest announcement of Generation 10 FPGAs and SoCs. Because power consumption is a key concern for the avionic markets (both military and civilian), the release of Altera’s Arria10 device with its incredible performance/power ratio is likely to open even more doors for airborne passive radar trials.


There are still challenges ahead in the world of passive radars, especially since the avionics market is very stringent in nature when it comes to development and approval cycles. However, we can clearly see why the forecasts are optimistic. With R&D labs sitting on several algorithm approaches that are ready to be tested under real-life conditions, and new breakthroughs in FPGA/CPU technologies, it seems the technological ecosystem is ready to give airborne passive radar a try. As a cutting edge hardware system vendor, we at Nutaq think that being part of this innovative endeavor is a privilege and hope to help as much as we can to make this new idea ‘fly’.