Radar systems have represented a vital core market area for the RF/microwave industry since before there even was an industrybeginning around 1939 with the invention of the cavity magnetron. Once suitable signal power levels were available from that and succeeding device technologies, the simple idea of transmitting a high-frequency signal and measuring reflected return signals gave birth to what would become present-day radar technologies. Today, these are used for everything from automotive collision-avoidance systems to weather and weapons detection. And as practical uses for radar technologies continue to expand, the effects are felt throughout the industry.
For example, avionics and satellite-communications (satcom) systems typically demand lighter-weight components than those used for terrestrial applications, but without sacrifices in performance. Packaging must be hermetic to withstand harsh environments. In fact, in recent years, most designers of radar and avionics systems and their components and assemblies will agree that they have been asked to make everything smaller, lighter, and at lower cost. These three customer demands drive the technologies for radar and avionics applications from the systems level to the device, component, and even substrate materials levels. And as a kind of "design glue" that helps efficiently brings all the parts together, computer-aided-engineering (CAE) simulation software continues to meet the needs of system designers.
Modern radar benefits from a number microwave-based advances, including improvements in active antenna arrays and the use of agile beam steering. Also of note is progress in digital devices, including digital signal processors (DSPs) and field-programmable gate arrays (FPGAs). Larger portions of newer radar systems are devoted to digital processing and circuitry, with the goals of the antennas and front-end circuitry to render received signals into the digital realm as quickly as possible. In addition to performance improvements, these enhancements in electronic components, such as active antenna arrays, can lead to increased reliability due to less reliance on moving parts.
The used of phased-array antennas and electronic beam-steering techniques has translated into powerful performance improvements for some major tactical radar systems. Raytheon Co., for example, has built its next-generation radar systems around active electronically scanned array (AESA) technology. The firm's APG-82(V)1 radar system for the US Air Force's F-15E fighters (and also employed on the F-15C, F/A-18E/F and EA-18G aircraft) is an extended-range platform with multiple-target tracking capabilities. More than 300 AESA-based radar systems are now in use.
That AESA technology is a staple of Northrop Grumman's newest radar systems, along with the beam-steering technology and multifunction sensors used on the Scalable Agile Beam Radar (SABR) developed for the F-16 fighter. The SABR is an airborne AESA-based fire-control radar system that is designed to operate in dense electronic threat signal environments. The AESA technology is also employed in the firm's Highly Adaptable Multimission Radar (HAMMR) system. A lightweight ground radar system with AESA antenna technology, it provides 360-deg. coverage while mounted on a vehicle (Fig. 1).
The HAMMR's AESA system consists of more than 1000 programmable transmit/receive (T/R) modules that combine for a wide range of antenna patterns under software programmable control. Because system performance can be quickly redefined, the HAMMR system can readily adapt to new threats without additional hardware. Also, groups of modules can be dedicated to different targets, allowing them to be tracked simultaneously.
The Active Phased Array multifunction Radar (APAR) system developed by Thales also employs phased-array antenna technology and T/R modules in its design. The APAR antenna features four arrays, each with more than 3000 T/R elements. The four arrays together enable full 360-deg. coverage. Having control over so many T/R modules provides for excellent antenna beam control. Conversely, the large number of modules can drive the cost of these phased-array-based radar systems, and requires carefully manufacturing control.
Reliability improvements are critical, as radar systems are being used for a growing number of applications and on nontraditional platforms. Last year, Raytheon announced that it delivered the first of three SeaVue airborne surveillance radar systems with expanded mission capability (SeaVue XMC)not to the Navy for installation on a fighter, but to the US Customs and Border Protection to fly on the organization's second Guardian unmanned aerial vehicle (UAV). The Guardian (Fig. 2) is a maritime version of the Predator B UAV used for surveillance in Iraq and Afghanistan. Raytheon will deliver an additional pair of the SeaVue radar systems for installation on traditional P-3 anti-submarine/surveillance aircraft.
Lockheed Martin has also participated in the evolution of radar technology, notably through its 360-deg. scanning technology on the EQ-36 radar. The enhanced AN/TPQ-36 (EQ-36) counterfire target acquisition radar (Fig. 3) is now in production as the AN/TPQ-53 (Q-53) Counterfire Target Acquisition radar system. It can operate in 90- and 360-deg. modes, detecting, identifying, tracking, and locating the source of indirect enemy fire.
The design and development team for the EQ-36 radar system included SRC, Inc., which last year received a contract from the US Army's Intelligence and Information Warfare Directorate to develop an omnidirectional weapon location (OWL) radar system, with a technology demonstrator prototype for evaluation in 2013. The OWL system, which provides surveillance over a hemispherical coverage area, will be able to track and locate weapons sources over a wide range of threat trajectories.
Of course, the OWL and other electronically steered radar systems count on the availability of such components as T/R modules, beam-steering networks, and even high-performance circuit materials to form reliable circuits at radar frequencies and power levels. Traditionally, solid-state radar T/R modules have been fabricated by means of gallium arsenide (GaAs) monolithic-microwave-integrated-circuit (MMIC) technology. But with the emergence of alternative semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN), opportunities exist for creating T/R radar modules with higher transmit levels.
Last year, for example, Fujitsu Laboratories Ltd. unveiled details on a T/R module based on high-electron-mobility-transistor (HEMT) GaN technology. The module combined a power amplifier capable of 10 W transmit power from 6 to 18 GHz with a low-noise amplifier (LNA), and could support applications in phased-array radars, as well as in communications systems. The LNA chip, which measures just 2.7 x 1.2 mm, provides 16-dB gain from 3 to 20 GHz with noise figure of 2.7 dB or less.
Teledyne Microwave is another supplier of T/R modules for radar applications, applying GaAs, GaN, and even indium-phosphide (InP) device technologies where appropriate (including for use in millimeter-wave commercial automotive radar systems). The firm's British Teledyne Defence Ltd. has developed a complete radar-warning receiver (RWR) in a component-type housing measuring just 114.5 x 62.85 x 14.05 mm and weighing only 200 g. The model RR009 RWR contains two amplitude measurement channels to allow direction finding (DF) by amplitude comparison between adjacent antennas. It covers 8 to 18 GHz with 6-b frequency measurement resolution (156 MHz) and detects signals at levels from -63 to 0 dBm and minimum pulse widths of 100 ns. The small size and light weight make it ideal for use on UAVs.
In support of a variety of phased-array systems, model BFN 44122 from TRM Microwave is a beamforming network (Fig. 4) that has been used on Raytheon's ALR-67(V)3 digital radar warning receiver (RWR). This receiver is integrated on such vehicles as the F/A-18 A/B/C/D Hornets and the F/A-18E/F Super Hornets. The RWR features a channelized digital receiver architecture with dual processors. In a housing measuring just 2.0 x 3.5 x 0.7 in., the passive assembly integrates ferrite, coaxial, and microstrip technologies, with eight 0-deg. power dividers, four 0-deg. power combiners, four 180-deg. power combiners, and 50-O coaxial delay lines.
The greatest number of RF/microwave hardware suppliers for military and commercial radar systems are still at the component level, so that system-level contractors such as Raytheon often buy the functions they need at the component level and perform in-house module design and fabrication. A large number of RF/microwave companies currently provide component-level functions suitable for use in radar T/R modules.
Several years ago, TriQuint Semiconductor supported several EASA-based systems with GaAs-based amplifiers and bulk-acoustic-wave (BAW) filters for use in T/R modules for phased-array radars. In recent years, the firm appears more focused on higher frequencies, developing transceiver ICs for 77-GHz automotive distance-sensing and collision-avoidance radar systems.
M/A-COM Technology Solutions recently introduced its model MASW-011021 monolithic SPDT switch for high-power X-band radar circuits from 6 to 14 GHz. The surface-mount chip-scale device measures about 2.7 x 4.9 mm but can handle 10 W CW power. It exhibits typical insertion loss of 0.70 dB at 8 GHz and 0.65 dB at 12 GHz, with typical input-to-output isolation of 30 dB at all frequencies. It has typical switching speed of 130 ns.
Finally, Mini-Circuits also supplies the miniature, rugged components needed for reliable radar T/R modules. Among these are the wideband model ZX60-183+ amplifier, with 24-dB typical gain from 6 to 18 GHz, accompanied by typical gain flatness of 1 dB. The two-stage amplifier, which runs on a single +5-VDC supply, is housed in a package measuring 0.75 x 0.74 in.
Editor's Note: For a more in-depth review of current-generation radar systems, don't miss the the October/November issue of Defense Electronics, a supplement to Microwaves & RF.