| ABSTRACT: A
motion sensing, micro-power impulse radar MIR impresses on the transmitted
signal, or the received pulse timing signal, one or more frequencies lower
than the pulse repetition frequency, that become intermediate frequencies
in a "IF homodyne" receiver. Thus, many advantages of classical RF receivers
can be thereby be realized with ultra-wide band radar. The sensor includes
a transmitter which transmits a sequence of electromagnetic pulses in response
to a transmit timing signal at a nominal pulse repetition frequency. A
receiver samples echoes of the sequence of electromagnetic pulses from
objects within the field with controlled timing, in response to a receive
timing signal, and generates a sample signal in response to the samples.
A timing circuit supplies the transmit timing signal to the transmitter
and supplies the receive timing signal to the receiver. The relative timing
of the transmit timing signal and the receive timing signal is modulated
between a first relative delay and a second relative delay at an intermediate
frequency, causing the receiver to sample the echoes such that the time
between transmissions of pulses in the sequence and samples by the receiver
is modulated at the intermediate frequency. Modulation may be executed
by modulating the pulse repetition frequency which drives the transmitter,
by modulating the delay circuitry which controls the relative timing of
the sample strobe, or by modulating amplitude of the transmitted pulses.
The electromagnetic pulses will have a nominal center frequency related
to pulse width, and the first relative delay and the second relative delay
between which the timing signals are modulated, differ by less than the
nominal pulse width, and preferably by about one-quarter
wavelength at the nominal center frequency of the transmitted pulses. |