Some military phased-array radars have been designed to perform multiple functions. For example, the AN/APG-81 and MP-RTIP airborne radars and the AN/SPY-1 and SPY-3 shipboard radars routinely perform multiple functions, typically including a mix of surveillance and tracking activities and in some cases other functions as well. These functions are usually carried out sequentially using a prioritized control scheme, but the SPY-1 has even demonstrated concurrent weather and aircraft surveillance capabilities. One face of a SPY-1 system is used in the National Weather Radar Testbed (NWRT) facility in Oklahoma.
There has been previous interest in the MPAR concept for aircraft and weather surveillance. A Federal Aviation Administration (FAA)-sponsored study (ITT 1997) determined that phased-array radar could meet most of the requirements for both aircraft and weather surveillance in an airport terminal area. However, the anticipated cost of such a system (in the mid-1990s time frame) was too high to warrant implementation of the concept at that time. Cost remains a major consideration in the feasibility of implementing the MPAR approach.
The potential introduction of MPAR presents an opportunity to combine the diverse radar missions of weather surveillance, civil aircraft tracking and possibly homeland defense against airborne threats on a single1 standardized advanced technology platform. Implementation of an MPAR system to provide multiple functions could obviate, or at least diminish, the need for separate radar systems to support the individual functions. This could permit reduction in the total number of different radar types and radar units required to meet the nation’s coverage goals for weather and aircraft surveillance. Weber et al. (2007) provide a hypothetical example of this, wherein some 334 MPAR radars of one basic type (two distinct configurations) might replace 510 existing radars of seven unique types, while providing essentially the same coverage of weather and aircraft targets at 5,000 ft or more above ground level. If one assumed that the ongoing support costs per unit remained the same as the average for the systems the MPARs replaced, this would substantially reduce the annual system support costs. With the absence, in a full Active Electronically Steered Arrays (AESA) system, of a single high-power transmitter and a rotating antenna (both sources of major maintenance costs with many present-day radar systems), there is expectation that the ongoing support costs per MPAR unit should even be smaller. Furthermore, the support functions would be required to deal only with the one (or two) MPAR system types, in contrast to the seven or eight different systems providing those coverages today. That suggests important potential savings in engineering, logistics, and training areas.
Developing time budgets for sequential allocation of scan capabilities to achieve the needed combinations of aircraft and weather data outputs could prove a difficult challenge. Consequently, two or more essentially separate radar systems, perhaps operating at different but nearby frequencies and using the same antenna, may be required to accomplish the desired concurrent missions (Weber et al., 2007).
Operation in the S-band frequency range (2.7-2.9 GHz) of the current NEXRAD and FAA terminal area aircraft surveillance radars would provide desired characteristics
The JAG/PARP report (Chapter 6) and more recent supporting literature advocates the development of two separate but related radar designs, the MPAR and the Terminal-MPAR or T-MPAR. This distinction is discussed further below.