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.

Automotive Radar

Satellite Communications

Missle SeekersWireless Lan

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 (