Passive Electronically Scanned Antennas - Electronically scanned antenna arrays offer tremendous benefits for enabling radar sensors and broadband communications for a variety of military and commercial applications. The most advanced form of electronically scanned antenna is the phased antenna array. This antenna implementation consists of a large number of individual antenna elements, phased in unison, to create a single antenna beam that is electronically steerable. This beam is steered by adjusting the amplitude and phase of the RF signal at each of the individual antenna elements. Phased array antennas have many advantages over the traditional antenna concepts, including fast, reliable electronic beam steering, a compact volume profile, and graceful degradation with device failures. A variety of military and commercial applications are enabled by phased array antennas. Military applications of electronically scanned antennas include terminal guidance seekers for anti-missile missiles, as well as satellite communications antennas for mobile military communications. Similarly, commercial applications include automotive radars for adaptive cruise control and collision avoidance systems, and wireless LAN communications for computer networking.
To date, traditional phased array antennas have been constructed with active electronics behind every radiating element. This electronics typically includes a phase shifter for setting the beam position and amplification to overcome the losses of the phase shifter and establish output power or noise figure of the system. The cost of this microwave electronics circuitry is typically quite expensive, on the order of $1K-$2K for each antenna element, making electronically scanned antennas very expensive to build. In fact, the main cost driver is the active electronics and its associated housing and cooling system. Due to the expensive nature of this type of antenna architecture, it has not been aggressively deployed in military radar and communication systems.
One option for lowing the cost of these antennas is to utilize “passive” array approaches where each radiator is driven by an ultra-low loss phase shifter, and where multiple radiator/phase shifters are fed by a single electronics module [See Bibliography below]. A block diagram for this antenna architecture is shown below. For antenna arrays that have relatively low radiated power (<0.5 watt/radiator), this option is very cost effective as it amortizes the expensive electronics (the module) over 4, 8, or 16 radiators. However this architecture requires phase shifter losses to be considerably lower than are realized with conventional microwave electronics technology. Typical pin-diode or GaAs FET based 4-bit phase shifters typically have 4-5 dB of loss at X-band while at Ka-band they have 8-10 dB. However, the advent of MEMS technology has enabled phase shifters with considerably lower loss, allowing passive, electronically scanned antenna arrays to become a reality. The use of “thinning” to reduce the number of electronics modules greatly reduces the hardware costs of the antenna array. In addition, the use of innovative manufacturing methods allow not only the phase shifters, but whole antenna arrays or subarrays to be integrated onto a single substrate, greatly reducing the packaging and interconnect complexity and costs. Together, these two factors make possible the development of inexpensive antenna arrays for both space-based and ground-based microwave systems.
If you have applications similar to these, please feel free to contact a MEMtronics representative. We are always interested in talking with potential customers and collaborators on how MEMtronics technology may benefit their application.
Bibliography for MEMS in Passive Electronically Scanned Antennas
B.R. Norvell, R. J. Hancock, J. K. Smith, M.L. Pugh, S.W. Theis, and J. Kviatkofsky, “Micro Electro Mechanical Switch (MEMS) Technology Applied to Electronically Scanned Arrays for Space Based Radar,” 1999 IEEE Aerospace Conference Proceedings, vol. 3, pp.239– 247.
J.K. Smith, F.W. Hopwood, and K.A. Leahy, “MEM Switch Technology in Radar,” IEEE 2000 Radar Conference, Nov. 2000.
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