Professor Umran Inan

Winter 2000-2001

Date: Wednesday, January 31, 2001
Time: 4:15-5:30 PM; Refreshments at 4:00 PM
Location:Bldg. 200, Rm 34

A New Phased Array Radar for Ionospheric Studies

Dr. Craig Heinselman & Dr. John Kelly
SRI International


Various radio techniques have been employed to study the ionosphere since its discovery in the early 1900's. The more familiar radar approaches use HF frequencies to reflect off of ionospheric plasmas in regions where the local plasma frequency equals the radar frequency. Another class of instruments uses more powerful radio waves at (typically) UHF frequencies and detects the very weak Thomson scattering from the free electrons themselves. These instruments, called incoherent scatter radars (ISRs), typically transmit multiple megawatts with antennas measuring at least 10's of meters in diameter and employ extremely sensitive receivers. Because of a well developed theory, ISRs are capable of characterizing the plasma state in great detail.

Several ISR facilities are presently operating from equatorial to auroral (cusp) latitudes. The US-owned ISRs were all built in the 1960's and 1970's and, though they have seen upgrades over the years, they all still fundamentally rely on technology from that era. In particular, with one exception they utilize very large reflector-type antennas for which steering requires physical movement of tons of steel and aluminum. We are presently in the prototyping stage of a thrust to develop a totally new ISR system utilizing state-of-the-art technologies. The system will use a phased array approach to the antenna design, thus allowing inertia-less steering of the beam on a pulse by pulse basis. The amplifier will consist of several thousand solid-state modules distributed over the antenna (present ISRs all use central, tube-based amplifiers). Each antenna element will, likewise, have a sensitive receiver, phase control electronics, and control and monitoring circuitry.

In this talk we will discuss the status of the design effort as well as a number of issues that have not yet been fully resolved.