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TWR4.....GROUND [**OR HOME/APT WALL**] PENETRATING RADAR

THIS IS TEXT EXCERPTED FROM GROUND-PENETRATING RADAR MANUFACTURER
PATRIOT SCIENTIFIC CORPORATION.  THE PURPOSE OF INCORPORATING THIS
TEXT IS THAT GROUND-PENETRATING RADAR SYSTEMS OVERCOME THE PARTLY-
CONDUCTIVE-WALL BARRIER TO PASSIVE MILLIMETER WAVE THRU-WALL RADAR.

The original link for this text (as of March 22, 2000) is:
http://www.ptsc.com/radar/index.html

Patriot Scientific Corporation

Patriot Scientific Corporation has developed radar
technologies with a wide range of possible applications.

This description below will highlight possibilities for use in:

- Ground Penetrating Radar (GPR)
- Communications
- Surveillance
- Ordnance Detection
- Stealth Radar

The Demonstration System:







...is a diagram of the demonstration system. A pulse generator
is used to drive the transmit antenna. The pulse is a positive
spike going up to 100V then falling back to ground in one and
a half nanoseconds corresponding to a pulse transmit frequency
of 750 MHz.

The return signal is read by the receive antenna.  At this
point some simple analog processing is done and the signal is
digitized at a resolution of 6 GHz, and sent to a PC.

The PC correlates the data into a conventional waveform, does
some processing, then transmits the data over an ethernet
cable to a Pentium workstation (not shown).

The Pentium workstation is used to apply different digital
filters, combine waveforms, and display the results.  This
system can be used to demonstrate detection of small targets
buried in sand, people behind walls, and other targets.







Patriot has used its antenna system to demonstrate detection
of objects as small as a coke can buried in sand, through a
wall. Even small targets disturb the wavefront of the pulse,
producing reflections and modifing the field in measurable
ways.

Patriot will be testing this technology for suitability for
mine detection. We will be acquiring sample casings and
running further tests.

Advantages of Patriot's Impulse Radar System







The key to Patriot's Radar system is its ability to transmit
and receive pulses barely longer then single cycles at the
transmit frequency. The first waveform shown here is a pulse
generated by an earlier Patriot Design, based on "off the
shelf" antenna technology. The waveform on the bottom was
produced and received by Patriot's current Design.

The current Patriot antenna system produces a pulse at the
desired frequency with little leading or trailing noise. The
Patriot antenna system provides many advantages over
pulse-based systems.

Patriot originally developed the impulse radar system to allow
time domain processing in Patriot's GPR systems.  Because the
impulse is extremely short (3 nanoseconds), the time to return
can be used to gauge the distance traveled by the pulse.

Furthermore, the transmit and receive antenna's are very
directional, eliminating much of the multipath components of
the return signal.

The short pulse combined with the directional transmit and
receive to provide us with a number of important advantages:

- Very low average power during transmission
- Low interference from other transmitters
- Transmission invisible to conventional receivers
- High bandwidth digital data transmission possible
- Difficult detection by other impulse receivers







Interference with other sources and receivers is further
reduced by using directional antennas. The antenna design
shown is highly directional.

When penetrating the ground, we wish to eliminate as much of
the multipath signal as possible. The directional antennas
reduce the multipath signals detected to those that are
relatively inline with the wave path, and eliminate much of
the multipath signal that returns at odd angles.

Impulse radar uses low power inherently because the
transmissions occur in pulses separated by periods of no
transmission. The power of the pulses is offset by the dead
time between the pulses. The average output of the current
system is about 300 MICROwatts. THE LOW AVERAGE POWER OF AN
IMPULSE SYSTEM EFFECTIVELY HIDES THE TRANSMISSIONS FROM
CONVENTIONAL RECEIVERS.

Interference can be further reduced in an impulse system by
using random interval spacing. As long as the transmit and
receive antennas are in sync, the period between pulses can be
varied to prevent aliasing with other continuous- or
pulse-transmission systems that might be operating in the same
locale. Furthermore, if an impulse system is being used to
transmit data, varying the intervals between pulses prevents
other impulse systems from locking onto the signal. Patriot
Scientific's current GPR system does not use random interval
spacing.