Multifunction Phase Array Radar (MPAR) is a multi-US Agency initiative by the Federal Aviation Administration, the National Atmospheric and Oceanic Administration, the Dept. of Defense, and the Dept. of Homeland Security to investigate the feasibility of deploying a common phased array radar platform for the multi-use purposes of air traffic control, air surveillance, and weather tracking.

MPAR aims to address life cycle replacements of the US national radar infrastructure with a network of advanced phased array systems that will have capabilities well beyond what is achievable with today's legacy rotating radar systems.

Such legacy systems include the national network of NEXRAD weather radars as well as the Air Route Surveillance Radars (ARSR - which track flights between airports), Air Surveillance Radars (ASR - which track aircraft in the immediate region of an airport), and Terminal Doppler Weather Radars (TDWR - which sense extreme weather conditions at or near airports).

The MPAR effort is well described in the article "Multifunction Phased Array Radar for Aircraft and Surveillance" by Judson Stailey and Kurt Hondl, contained in the March 2016 issue of the Proceedings of the IEEE Special Issue on Phased Array Technologies (Vol. 104, No. 3).

Much of the motivation for MPAR grew out of US Government studies that pointed to limitations of rotating radar platforms for weather tracking, especially in tornado-prone regions where the 5-min tracking of current NEXRAD systems do not provide sufficient time and volumetric resolution to accurately detect precursors of tornados and other extreme weather.

Phased array radar has been proven useful for tacking such weather, as proven by research efforts conducted by NOAA's National Severe Storms Laboratory (NSSL) in Norman OK, which has re-purposed a US Navy SPY/1 warship radar for the study of weather.

Phased arrays have the important ability to point radar beams of various sizes and geometries towards targeted areas and volumes to attain unprecedented accuracy in target resolution with updates in just a couple of seconds. This contrasts with the several minutes conventional spinning radars require for updates. Unlike the latter, phased arrays are generally stationary with their radar beam scans achieved through "electronic steering".

Such steering is accomplished by a radar architecture in which hundreds or thousands of small radiating and receiving elements send and detect radar pulses, respectively, such that the phase of the signals is slightly different at each element. This phase difference effectively accomplishes the radar beam steering over the ensemble of the elements making up the physical radar face.

Because of the fast scanning times of phased arrays and the ability to focus beams on specific areas or volumes, having a common phased array platform for both weather and aircraft surveillance comes as a logical path towards upgrading the US weather and air traffic surveillance infrastructure for the decades to come.

To put it simply, the operation of a phased array enables a configuration for very wide and far reaching beams to support wide weather scans (as in the current operation of NEXRAD weather radars). Meanwhile, the same array can be configured to simultaneously produce narrower beams for the tracking of aircraft and suspicious aerial objects (e.g., drones, which could be deemed to impose a potential threat).

MPAR array designs under consideration take on many sizes and geometries, ranging in sizes of a few thousand to as many as 80,000 elements, with geometries covering flat faces (three to six sides for 360 degree coverage), cylindrical forms, pyramid forms, and other designs.

Because of the commonality of operation across weather and air surveillance uses, many of the hundreds of radar systems currently deployed could be eliminated while the remainder are replaced with a common phased array design of just a few sizes to meet regional needs.

The arrays would be produced at reduced costs through mass production of the underlying array electronics, radar face tiles, and systematic testing procedures. Thanks to new advancements in high speed microwave and digital processing electronics, new phased array designs are now capable of producing dozens of simultaneous beams with sub-second sweep rates and sufficient bandwidths for unprecedented object resolution.

These new technologies, coupled with dual-polarization capability, will provide for ever more accurate and timely weather forecasting while keeping our skies safer.