WHAT IS A FOCAL PLANE ARRAY?

A focal plane essentially acts like a camera lens, focusing incoming radio waves. The array is a 2D grid of thousands of tiny detectors covering a rectangular area. The FPA can continuously monitor an area without physically turning, unlike traditional radars that use scanning technology. It can therefore maintain constant illumination of the reflector. The array can capture high-resolution images of an entire picture, receiving energy from all angles at once. By ‘staring’ at the target, the FPA processes multiple channels simultaneously, producing high frame rate video, which is essential for high-resolution imaging, particularly in defense applications. It is capable of capturing 3D imagery and mmWave imaging, which translates into high sensitivity for detecting objects in complex environments.

The use of FPA technology in radar testing is currently emerging and being proven. It has been used for some time in the satcom industry as an alternative to horn reflector antennas, offering benefits such as high spectral resolution, increased capacity for frequency reuse and rapid tracking, which is essential for low Earth orbit constellations.

Using array technology within an RCS measurement system can significantly benefit many RCS test facilities for both defense and commercial test ranges. By introducing technology already available in the commercial telecommunications sector and applying it to the RCS measurement industry, costs can be reduced considerably.

Placing a focal plane array near but offset from the focal point of a CR reflector enables direct control over the aperture distribution of the compact range feed and allows adjustments to the magnitude and phase of each element as a function of operating frequency. To feed a particular CR, the ideal aperture distribution function for that range is numerically estimated and used to set the FPA’s complex weights.

There is a range of additional benefits offered by FPA technology. These include:

  • Electronic Focusing: Element phase and amplitude control enable fine adjustments to pattern shape and FPA phase center to be made electronically
  • Ultra-Wide Bandwidth Single Aperture: Single aperture coverage for 2 to 18 GHz and for 18 to 50 GHz
  • High Power Handling: Typical CR FPA configuration provides > 20 W peak transmit power
  • Low Primary Supply Voltage: All supply and circuitry voltages are ≤ 20 VDC
  • High Power-Added Efficiency: SiGe PAs, LNAs and Phase Shifters achieve 15 to 20 percent power-added efficiency
  • High Reliability: Printed circuit board array meantime between failures (MTBFs) estimated to be greater than 250,000 hours
  • Soft Failure: Element component failures have minimal impact on overall radiated power or radiation pattern quality
  • Built-in Test: Loop backs, monitors and self-test sequences
  • Field Optimization Methods: Technology enables future closed-loop field optimization methods.

Computational electromagnetics are used to evaluate the beam waist function at each array element location. The beam waist function is essential for accurate testing of any radar system in a compact range and refers to the narrowest point of the beam, where the energy density of the radar signal is at its maximum. This means that it is critical for determining the target illumination and the RCS. The beam waist is measured to ensure the radar system performs as specified and that the beam is neither too narrow nor too wide, as either could result in inaccurate detections. The beam waist is often large enough to cover the entire target but small enough to reduce clutter.

WHY DO FPAS MAKE FOR FASTER, MORE COSTEFFECTIVE TESTING?

A test environment utilizing FPAs makes for a much easier setup and comprehensive testing. Conventional CRs rely on a single feed, which must be physically moved to change the wave’s angle. With FPAs, there is no requirement for physical movement and fewer mechanical parts, as there are no scanners involved. This results in significant savings in maintenance costs and less MTBF. FPAs also enable high-throughput testing from multiple angles simultaneously, making them ideal for testing complex radar systems. They provide better illumination due to their uniform power distribution and deliver better overall results.

Microfabrication processes for FPAs at a larger scale means lower production costs while yielding better test performance, and the fact that FPAs are compact and use less power also keeps costs down. FPAs use self-calibration techniques to improve uniformity, thereby reducing maintenance costs.

THE FUTURE OF FPA TECHNOLOGY FOR RADAR TESTING

The future of FPA technology in radar testing will center on the transition from traditional scanning methods to digital, real-time, software-defined systems that provide advanced situational awareness and cutting-edge imagery.

Currently, the testing process is costly and requires significant investment. Lowering the cost of testing can be achieved through automation, since testing is an involved, complex process. Systems in development feature fully automated, end-to-end testing, reducing the time required to complete testing from weeks to days.

FPAs are also beginning to incorporate analog-to-digital conversion directly into each pixel, enabling real-time digital processing and high speed operation, thereby considerably reducing acquisition times.

Using AI techniques, arrays can self-heal by identifying if a single element is about to fail. This improves the overall reliability of the systems and enables them to recover quickly from technical problems.

Software-defined architectures provide high flexibility, enabling radars to take on multiple mission capabilities without swapping out any hardware.

HIGH PRECISION TESTING AT LOWER COST

In a world constantly squeezed by high costs, the introduction of FPA testing for radar systems has the potential to be a significant game-changer for industries that use radar, such as the military and defense sector, as well as other commercial sectors, such as aviation and maritime. By considerably speeding up testing time, heightening efficiency and lowering costs, radars can be deployed where they are most needed, performing the critical role they play in intelligence, surveillance and reconnaissance across a plethora of industries.

For the defense industry in particular, this swiftness in testing is essential, as it influences operational readiness, safety and the ability to stay one step ahead of constantly evolving threats. It is vital that testing technology and capabilities keep pace with the threats themselves to reinforce the reliability and detectability of low-observable targets and to prevent adversaries from jamming them.

Defense programs have notoriously long lead times and often run over budget. However, by using commercial-off-the-shelf technology that has already been proven in other industries, such as satcom, FPAs can help minimize this time and ensure that the radars operate as intended with high reliability and the capability to handle ever more complex threats.

FPAs may be an evolving testing technology for the radar sector, but their use is anticipated to increase significantly as their capabilities are proven, and their overall efficiency holds massive potential for CR testing. As radar capabilities evolve to combine automation and AI with software-defined features, the future of CR testing looks bright and is entering a new era of development.