ABSTRACT
Emerging genetic algorithms, HEMTs, SAWs, superconductors, MEMS, photonics, and “chaos” are improving the capabilities of components for lower-cost wireless communications and for radar.
SUMMARY
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.