MIR Technology Overview

   The Micropower Impulse Radar (MIR) is a fundamentally different type
   of radar that was invented and patented by Lawrence Livermore National
   Laboratory (LLNL). It is a pulsed radar like other ultra-wideband
   radars, but it emits much shorter pulses than most and, because it is
   built out of a small number of common electronic components, it is
   compact and inexpensive.

   The genesis of these radars starts with LLNL's 100-trillion-watt Nova
   laser, the world's highest power laser system, which was developed for
   nuclear fusion research. The pulsed laser generates high-speed
   (sub-nanosecond) events that must be recorded. In answer to this need,
   special fast electronic circuitry was developed for driving a 33
   gigasample-per-second transient digitizer that records such events.
   Thomas McEwan, the LLNL engineer who designed this high-speed data
   acquisition system, then had an important insight: these new circuit
   concepts could be augmented by additional electronics into extremely
   small, low-power radar systems.

   Soon after McEwan's breakthrough in 1993, it became evident that such
   radars had the possibility of impacting an extremely wide range of
   applications. Since then, nearly 30 patents have been filed, hundreds
   of commercial applications have been identified, and MIR technology
   has become LLNL's biggest technology transfer activity.

   Licenses with industry have been signed in the areas of automobile
   back-up systems and in hand-held tools for finding studs and other
   objects behind walls. Many other diverse applications are under
   investigation, including fluid level sensing (electronic dipsticks),
   heart monitoring for medical applications, security systems, detection
   of breathing through walls or rubble (e.g., finding survivors of
   earthquakes), monitoring of infants for the possible prevention of
   Sudden Infant Death Syndrome (SIDS), underground and through-wall
   imaging, and many others.

   McEwan and his team continue to innovate and develop new ideas for the
   MIR technology including new electronics, antennas, signal processing,
   and imaging concepts. LLNL is following the dual paths of licensing
   the technology to qualified manufacturers and developing programs that
   use the technology in support of the laboratory mission.

   One unique feature of the MIR is the pulse generation circuitry,
   which, while small and inexpensive, had never before been considered
   in radar applications. Each pulse is less than a billionth of a second
   and each MIR emits about two million of these pulses per second.
   Actual pulse repetition rates are coded with random noise to reduce
   the possibility of interference from other radars, while each is
   "tuned" to itself. The same pulse is used for transmitting to send via
   the transmit as for sampling the received signal. Three direct
   advantages of the short pulse-width are:

    1. With pulses so short, the MIR operates across a wider band of
       frequencies than a conventional radar, giving high resolution and
       accuracy, but also making it less susceptible to interference from
       other radars.
    2. Since current is only drawn during this short pulse time and the
       pulses are infrequent, there are extremely low power requirements.
       One type of MIR unit can operate for years on a single AA battery.
    3. The microwaves emitted by the pulse are at exceedingly low, and
       therefore medically safe, levels (microwatts). Indeed, the MIR
       emits less than one-millionth the energy of a cellular telephone!

   Probably the main unique feature of this radar is the cost. The
   current version uses off-the-shelf electronic components so that a
   standard MIR board can be assembled with less than $20 of parts.
   Future development plans include reducing the MIR components to
   multi-chip modules or ASIC's as the demand increases and it becomes
   economically feasible.

   As with conventional radars, the antenna configuration on the MIR
   determines much of its operating characteristics. Several antenna
   systems have been designed to match the ultra-wide frequency
   characteristics of the MIR sensor. For the standard MIR motion sensor
   with a center frequency of about 2 GHz, we use a small 1.5-inch
   antenna. However, the MIR is also flexible enough that it can operate
   at a relatively lower center frequency, using larger antenna systems,
   giving it longer range and better capability for penetrating water,
   ice, and mud.

   What makes the MIR so useful for security applications is its range
   gating capability. Imagine that each radio pulse is a large wave
   traveling across a lake. The wave bounces off an island and comes back
   to you. The amount of time it takes the wave to return depends on the
   distance to the island. By setting the radar's "gate," or echo
   acceptance range, to open only at the right time to receive echoes
   from a certain distance, it can ignore all other echoes. Range gating
   can therefore be used to set up an invisible security bubble around
   the radar. In a burglar alarm, for instance, the range might be set at
   20 feet. The radar then detects only objects that modulate the
   reflected signal at this distance. It detects motion by repeatedly
   checking the echo pattern to see whether it changes over time; a
   change means the bubble has been penetrated by a moving object. This
   eliminates triggering on stationary background objects or "clutter."

   The current MIR motion sensor can be fully concealed behind walls or
   inside drawers while detecting intruders at ranges up to 20 feet. Its
   sharply-bounded detection range is easily adjusted for any situation.
   In addition, the MIR can project a set or sweep of range shells to
   generate a filled volume of sensitivity. It does not respond to
   objects outside the current range gate, and it attempts to avoid false
   triggering on near objects such as insects. However, the range-gating
   mechanism may be susceptible to triggering on large-object movement in
   the near-field (inside the range bubble) because radar phenomena like
   multiple scattering will modulate the range-gate return.

   Averaging of many thousands of pulses is done on the MIR to reduce the
   effects of noise and to increase sensitivity. A single received pulse
   in the nanosecond time scale may be contaminated with various forms of
   outside interference, but if the returns of many pulses at the same
   range gate are combined, the result is much more representative of the
   actual return. The number of averages per range gate is adjustable
   (nominally it is about 10,000 samples) and is one of the tradeoffs in
   the MIR design.

   The exact pulse emission and detection times are randomized for three
   reasons.

    1. Continuous wave (CW) interference, such as from radio and TV
       station harmonics, may cause beat frequencies with the received
       echoes that can trigger false alarms. When the 10,000 samples of
       MIR return echoes are averaged at randomly-dithered times, random
       samples of CW interference are effectively averaged to zero.
    2. Random operation also means that multiple MIR units can be
       collocated without interfering with each other. Channel
       allocations are not needed and a nearly unlimited number of
       sensors can be in the same vicinity even though they occupy the
       same wideband spectrum.
    3. Randomizing also spreads the sensor's emission spectrum to the
       point that it resembles random thermal noise, making it difficult
       to distinguish from background noise. That is, this randomizing
       makes the MIR very stealthy.

   UCRL-ID-109089-94