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.


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