Emerging genetic algorithms, HEMTs, SAWs, superconductors, MEMS, photonics, and “chaos” are improving the capabilities of components for lower-cost wireless communications and for radar.
Research advances in genetic algorithms, HEMTs,
SAWs, MEMS, superconductors, photonics, and “chaos” are improving the capabilities
of components for lower-cost wireless communications and radar.
A genetic algorithm has been used to design an inexpensive GPS/IRIDIUM antenna. The “crooked wire” genetic antenna consists of 7 wires connected in series, whose unorthodox shape would be impossible to optimize using conventional inductive techniques. The response varies less than 4 dB for angles above 5 degrees over the horizon. The genetic algorithm is a very powerful and robust optimization technique, which emulates the biology of reproduction, mutation, and natural selection.
High Electron Mobility Transistors (HEMT) provide high gain and low noise at millimeter-wave frequencies. These frequencies are of interest for satellite cross-links in communications satellite constellations. A pseudomorphic, 50-nm self-aligned-gate (SAG), HEMT (AlInAs/GaInAs/InP) has been used in a monolithic oscillator at 213 GHz, a world-record.
Surface Acoustic Wave (SAW) and superconducting filters have much lower insertion loss and volume than conventional filters. SAWTEK, Inc. has recently gone public to raise capital to establish a new production line to meet the worldwide demand for SAW filters, with insertion loss as low as 1.5 dB for wireless applications. CONDUCTUS Inc. has developed a receiver with a superconducting filter and low-noise amplifier. When cooled from room temperature (273 K) to 60K, the noise figure drops from 0.5 dB to 0.1 dB. When CELLCOM, Inc.(De Pere, WI) used this superconducting receiver in their base-station, they observed a 20-percent reduction in dropped phone calls.
Microelectromechanical systems (MEMS) technology can produce switches with very low insertion loss and high power handling. Texas Instruments has recently produced a 4-bit switched-line phase shifter, with membrane MEMS switches, having a maximum insertion loss of only 1.5 dB from 8 to 12 GHz .
Photonically excited semiconducting antennas radiate pulses whose width is comparable to the 80 psec laser pulse. Wide band microwave radiation is emitted by photoconducting electrons accelerated by a dc electric field on the semi-insulating GaAs or InP antenna element. An 80 psec pulse has a spatial length of only 2.4 cm, which is useful for short-range and high-resolution radars for covert object and unexploded ordnance detection.
The discovery that chaotic oscillators can be synchronized opens the possibility for secure communications. Baseband communications links have been demonstrated, based on various forms of synchronization and modulation. The Aerospace Corporation is currently extending these concepts to microwave frequencies.
Paul H. Carr, Ph.D. (Physics, Brandeis U.)
led the Component Technology Branch,
AF Rome Laboratory, Hanscom AFB, MA 01731-3010, from 1967 to 1995. He is presently a consultant. His 77 research papers and 8 patents include contributions to microwave ultrasonics, surface acoustic waves (SAW), superconductivity, and photonics. He has won numerous awards including Rome Laboratory’s “Engineer of the Year” in 1991.
Dr. Carr has been active in the IEEE, serving as chairman of the Boston Section Chapter on Microwave Theory and Techniques (1989-90, 1994-95). He served on the Technical Program Committee of the 1971-1989 Ultrasonics Symposia, of which he was chairman in 1976. He served on the Technical Program Committee for the Microwave and Millimeterwave Monolithic Circuits Symposia (1986-1988). He was elected fellow of the IEEE in 1979.