by John Maciel, Ph.D.
Chief Operating Officer, Radant MEMS, Inc.
Rapid beam scanning, beam agility, the performance of diverse functions such as multiple target tracking and fire control, reduced radar cross section (RCS), and reduced physical profile are some of the numerous performance benefits to military systems employing an electronically steerable antenna (ESA) in lieu of more typical, mechanically gimbaled antenna systems. These gains are obtained at the expense of large increases in overall system weight, prime-power consumption, and cost when conventional discrete phase shifter or active transmit/receive (T/R) module control devices are employed. Arrays fabricated with these conventional discrete control devices are excessively heavy, costly, and consume more prime power than available for many applications. Lightweight, low power, and low-cost are mission critical characteristics for elevated sensors such as those proposed for aerostat, airship and space-based antennas. Other defense applications include warfighter protection and situational awareness, national missile defense, theatre missile defense and satellite communications. A lightweight X-Band ESA can be employed in a fire control radar for cruise missile (CM) defense precision track and engagement support, CM horizon surveillance, tactical ballistic missile surveillance and cueing, missile and artillery backtracking, and surface ship surveillance and tracking. The potential applications are diverse and permeate across all services, Air Force, Navy and Army.
Radant has developed a novel approach to one and two-dimensional beam steering that is predicted to meet the lightweight, low-cost, and low prime-power requirements of many antenna platforms. Two novel technologies, lens and MEMS devices, have been allied to construct an electronically steerable antenna that is lighter in weight, lower in cost, more broadband, and consumes less prime power than currently available antennas. This approach avoids using T/R modules behind each radiating element which is the primary component resulting in higher weight, cost, and prime power consumption. The MEMS ESA weighs approximately one-third and is about one-tenth the cost of an equivalent active T/R module based ESA. As an example, a conceptual design for an 8 square meter MEMS ESA has a predicted weight, including all driver and control electronics, illuminator and transmitter, of 1,050 pounds versus the estimated 3000 pound weight of a suitable active ESA!
Typical Radant SPST MEMS switch die (shown in the ear of Roosevelt) is 1.5mm x 1.5mm in area.
Greater than 25,000 X-band MEMS switches like those shown in the figure above were successfully employed to construct a 0.4 square meter proof-of-concept MEMS ESA as shown in the figure below. This MEMS ESA is believed to be the first of its kind. The Radant array architecture employed here has been previously demonstrated with PIN switching diodes. This architecture consists of building loaded-line phase shifters within parallel plate waveguides. Here, the parallel plate waveguides were constructed of plated carbon-fiber composite sheets so as to minimize weight. Employment of MEMS switches in-lieu of PIN switching diodes results in improved antenna performance (lower loss and increased bandwidth) as well as a significant reduction in prime power consumption which is critical for the intended aerostat platform. MEMS switches manufactured by Radant have a volume of only 1.5 cubic millimeters and are produced by wafer capping of a microelectromechanical switch mechanism that travels less than 1 micrometer in 10 microseconds. Extremely high reliability (exceeding 1.5 trillion switch cycles) has been achieved in each of the Tri-Service Department of Defense laboratories (Air Force Research Laboratory, Army Research Laboratory, Naval Research Laboratory) under the auspices of the Defense Advanced Research Projects Agency (DARPA). MEMS switches, in comparison to their semiconductor counterparts, are characterized low insertion loss, high isolation, broad bandwidths, high linearity, near zero power consumption, small size are expected to be an enabling technology for military and commercial systems, like the MEMS ESA.
An X-Band MEMS electronically steerable antenna (ESA) containing 25,000 MEMS switches with a 0.4 square meter aperture area.
The MEMS switches were assembled into a rigid, lightweight structure consisting of the carbon-fiber parallel plate waveguide plates with thin liquid crystal polymer circuit substrate and foam spacers sandwiched between them. Actuating select groups of MEMS switches results in a specified phase shift per column element within the E-plane of the antenna. The column elements are controlled to yield a linear phase gradient that results in electronic beam scanning within the E-plane of the aperture. The antenna scans electronically in azimuth +/- 60 degrees with a 1 GHz bandwidth at X-band with four bits of phase control. Future antennas for this application will incorporate a limited elevation scanning feed, which was not implemented for this proof-of-concept demonstration. Excellent radiation pattern characteristics, like that shown in the figure below, consisting of well formed scanned main beams and low peak and RMS sidelobe levels were obtained for the 0.4 square meter MEMS ESA. The MEMS ESA saves considerable weight, power and cost in comparison to a conventional active ESA as previously noted. The successful ESA demonstration outlined here showed the feasibility of producing much larger antennas exceeding 8 square meters such as those needed by high performance Airborne Moving Target Indicator (AMTI) and Ground Moving Target Indicator (GMTI) X-band radars. Such systems require a large power-aperture product but must be lightweight and have low power consumption for aerostats and airships required for Cruise Missile and low flying aircraft detection. This technology has the ability to enable lightweight and low power platforms with electronic scanning.
Measured radiation pattern of the 0.4 square meter MEMS ESA shown in the figure above as scanned to 60 degrees from broadside. Measurements show good scan performance and minimal impact on Sidelobe Levels.
An initial demonstration of the MEMS Demonstration Radar was performed at Lockheed Martin’s facility in Syracuse, New York where the standard mechanically scanned antenna in one of the company’s commercial AN/APG-67 airborne multimode radars was replaced by a Radant 0.4 square meter MEMS ESA as shown in the figure below.
The 0.4 square meter MEMS ESA is shown integrated with a Lockheed Martin AN/APG-67 airborne multimode radar at Lockheed’s Syracuse, NY facility.
The MEMS ESA was interfaced to the existing transmitter, receiver and display and the MEMS radar beam successfully scanned a 120-degree azimuth sector under control of the AN/APG-67. The beam steering interface electronics were provided by DRS Laurel Technologies of Johnstown, Pennsylvania, a unit of DRS Technologies. Successful AMTI detection was demonstrated with a small Cessna 172 aircraft as well as with commercial aircraft arriving and departing from nearby Hancock International Airport. The Cessna flew 15 nmi sorties inbound and outbound from the Syracuse test site while the APG-67 was operating at reduced transmit power during these initial radar demonstrations. Consistent detection of the small Cessna was observed. GMTI detection was demonstrated with vehicular ground traffic in the vicinity of the test range. This was the first such integration of a large MEMS based ESA with a functioning radar that represented a major milestone for this technology. Radant is actively pursuing military applications of the MEMS ESA technology.
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Dr. John Maciel is the Vice President and Chief Operating Officer of Radant MEMS, Inc. and Manager, Electromagnetics Technology of Radant Technologies, Inc. He has more than 25 years of experience in the RF, Microwave and Microelectronics industries. Dr. Maciel manages the MEMS development effort at Radant MEMS as well as its daily operations. Dr. Maciel received a Ph.D. and a Master of Science, both in Electrical Engineering, from the Polytechnic University of New York in 1990 and 1986, respectively, and a BSEE degree from Northeastern University, Boston, MA in 1983. Dr. Maciel can be reached at [email protected].
Copyright 2010 MEMS Investor Journal
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