A modular, building-block approach brings greater design flexibility to Active Electronically Scanned Array (AESA) radar technology, simplifying system integration, and permitting rapid first-line repair with no downtime using standard off-the-shelf components.

Until recently, AESA radar was utilized almost exclusively by prime aerospace contractors within their own proprietary systems. These customized solutions were relatively costly and time-consuming to manufacture, and not reconfigurable to alternative uses.

Figure 1. The “roadmap” to an Active Array Antenna Unit (AAAU).
Meanwhile, growing requirements such as border security have punctuated the need for a modular, building-block approach that expands the use of AESA radar technology to a wide array of applications including naval, airborne, vehicle-mounted, and ground-based systems; coastal and harbor security; air traffic control; foreign object detection (FOD) for airport runways; satellites; and data links.

AESA radar systems contain multiple transmit/receive modules (TRMs) that transmit and receive high-power radio waves of varying frequencies, scanning rates, and radiation patterns on demand to provide highly agile beam steering. By generating unpredictable scan patterns, AESA radar systems can track multiple targets simultaneously. These scan patterns are also difficult to detect by radar warning receivers (RWRs) – particularly older systems – thus providing high jamming resistance. These systems can also operate in a receiver-only mode to track the source of jamming signals, or to act as a radar warning receiver. AESA radar can also serve as a high-speed data link able to support peer-to-peer networking by combining data from multiple platforms while also delivering expanded radar coverage and enhanced resolution.

AESA radar does have its limitations; the highest field of view (FOV) achievable for a flat phased array antenna is generally between 90 to 120 degrees. Wider coverage can be obtained through multiple antenna faces or two rotating antenna faces. Similarly, an X-band array mounted onto the nose of an aircraft can expand its FOV through the use of a mechanical gimbal.

Thermal management is also required to dissipate heat generated by the power amplifiers (PAs) that are distributed across the antenna face. The cooling system must fit within the limited space envelope between the elements.

A Modular, Stackable Approach

Figure 2. An X-band sub-array face.
A recently introduced Active Antenna Array Unit (AAAU) consists of modular Quad Transmit Receive Module (QTRM) sub-arrays (Figure 1), which are also available as a standalone product or as scalable planks. The typical plank is constructed from four QTRMs, along with an integrated, linear, 16-element antenna array; liquid cooling with quick-release, non-drip connections; and distribution networks to provide RF and DC control signals to each QTRM. The Planks are designed to plug into slots in the main array structure to create a 2D array solution.

Each QTRM module (Figure 2) consists of four T/R channels, each containing a power amplifier (PA), a low-noise amplifier with receiver protection, along with digitally controlled phase and gain control elements to reduce undesirable sidelobes. QTRM modules also feature local DC power supply conditioning, a built-in logic interface for serial control and BITE power supply monitoring, and a protective thermal shutdown facility.

The QTRMs are supplied factory-calibrated and individually addressed for plug-and-play installation and rapid integration. The system integrator simply programs in adjustments for external system loss, antenna offsets, and phase offsets. A key performance attribute is graceful degradation, as each T/R channel is individually controlled, so the failure of any individual T/R channel will not impact the rest of the module. By contrast, legacy radar systems can become inoperable due to a single Point of Failure (PoF), such as the loss of the travelling wave tube (TWT) power amplifier.

Modular, stackable QTRMs use standard commercial off-the-shelf (COTS) components, and are designed as Line Replaceable Units (LRUs) to reduce first-line repair costs. Individual QTRMs have unique address codes so individual modules can be swapped out anywhere within the overall array without incurring any system downtime. By contrast, with older, non-modular AESA systems, the entire platform needs to be taken off-line in order to perform routine repairs, maintenance, and upgrades.

Choosing the Right Frequency Range

Modular, stackable QTRMs are available at X-band and C-band, along with a Dual Transmit Receive Module (DTRM) at Sband (Figure 3). Dual-module S-band systems are ideal for long-range applications such as seaborne surveillance and tracking, where higher output power per element and lower atmospheric attenuation must be achieved. S-band systems utilize Silicon LDMOS or GaN discrete transistors for the output stage of the PA.