Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/146848
Techniques Reducing Size And Power In Phased-Array Radar Systems The combination of technology, system, and circuit analysis is driving the development of new MMIC technologies to address the SWaP-C concerns of phased-array systems. By Charles Trantanella P hased-array radar systems are important instruments in national electronic defense strategies. From the large, ship-based systems that scan for distantly launched missiles, to the more compact arrays installed on fighter aircraft and unmanned aerial vehicles (UAVs), electronic phasedarray radars come in many sizes and forms, providing reliable signal detection and identification. These modern systems offer many advantages over earlier radar systems that relied on the physical movement of an antenna to steer a radar beam in search of a target. While the physical movement method is certainly proven and reliable, having been used in military platforms and commercial aviation for more than 70 years, it is limited in scan rate by the mechanical motion of the antenna. By contrast, a phased-array radar system uses a large number of equally spaced antenna elements with phase shifters, with each element contributing a small amount of electromagnetic (EM) radiation Figure 1: The PAVE PAWS system at Eldorado Air Force Station is typical of a large phased-array radar to form a much larger beam. As system with many separate antenna elements. the phase of each antenna element is shifted and aligned, the direction of the radar beam changes and, as the amplitude of each element is varied, the pattern of the far-field response is shaped into the desired response. Thus, the overall radar antenna beam can be steered without need for a mechanically rotated antenna. Beamforming, which can be now performed by means of analog or digital control, can take place at extremely high speeds, limited only by the switching speed of electronic components. Historically, phased-array radar systems have been large in both cost and weight. With the explosive growth of UAVs and unmanned ground vehicles (UGVs) as key elements of the defense arsenal, the need for lighter phased-array radar systems in these weight-sensitive 36 Electronic Military & Defense ■ www.vertmarkets.com/electronics systems will continue to grow. In addition, the increased use of such radars for nonmilitary applications, such as tornado detection by the U.S. National Weather Service, Springfield, MO, is helping drive the demand for lowercost systems. These growing demands placed on phasedarray radar systems can be met with the help of modern RF/microwave integrated circuit (IC) and monolithic microwave integrated circuit (MMIC) technologies. Phased Array Benefits And Drawbacks The benefits of phased-array radar systems far outweigh their limitations, thus accounting for their growing use in many military electronic systems and platforms. Since beam steering in phased arrays can be performed at millisecond and faster speeds, the signal can jump from one target to the next very quickly, while frequency agility can be used to search quickly across a sector for targets. The coverage of a phased-array antenna beam is typically limited to a 120˚ sector in azimuth and elevation. While this response is a known limitation of phased arrays, mechanically scanned radar systems also have limitations in the physical area available for the motion of the antenna. Important factors hindering the adoption of phased-array radar systems in many applications continue to be size, weight, power, and cost (SWaP-C). Efforts aimed at minimizing these four attributes represent a significant technological challenge that until recently has seemed a rather formidable hurdle. Phased-array radars are, after all, quite complex and even growing in this regard as target identification becomes more difficult. How can SWaP-C reduction be accomplished? A New Path Forward A phased-array radar system (Figure 1) is constructed from large numbers (often thousands) of transmit/receive (T/R) modules that enable the array to function as both a transmitter and a receiver. Initially designed with discrete hybrid components such as amplifiers, filters, mixers, phase shifters, and switches, these modules are now more commonly fabricated with high-frequency IC or MMIC technology. This switchover to IC technology has provided tremendous benefits in terms of SWaP-C reduction, but simply replacing components can only get a designer so far. Gaining additional SWaP-C benefits in any phased-array radar system also requires knowledge of how to best apply available IC and