Microwave motion detector with target angle detection
View Patent ↗The present invention is an alarm system that includes a dual technology motion sensor. The dual technology sensor includes a PIR sensor with a PIR detection pattern and a Doppler microwave frequency motion detector with a detection pattern wider than that of the PIR sensor. The microwave detector's processing circuitry distinguishes motion beyond the PIR detection pattern, and limits the microwave detector's field of view to match the PIR detector's detection pattern. The microwave detector has a transmitting antenna, two receiving antennas, and processing circuitry for processing received signals. The microwave detector's processing circuitry uses phase information from the two receiving antennas to distinguish motion beyond the PIR detection pattern.
1. A method of limiting the field of view of a microwave motion detector comprising a transmitting antenna and two receiving antennas, comprising the steps of:
transmitting a microwave frequency signal with the transmitting antenna,
receiving microwave frequency signals reflected from a target with the two receiving antennas, each receiving antenna providing a received signal in each of two separate channels,
determining a target ratio from a phase difference between each received signal in the separate channels, and
disregarding motion from the target when the target ratio is less than a predetermined amount.
2. The method of claim 1 wherein the step of determining a target ratio comprises the steps of:
summing and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a sum pattern signal;
subtracting and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a difference pattern signal; and
determining the target ratio from the ratio of the sum pattern signal and the difference pattern signal.
3. The method of claim 1 further comprising the step of generating an alarm condition when the target ratio is more than a predetermined amount.
4. The method of claim 1 further comprising the steps of adapting the target angle limit to meet installation requirements.
5. The method of claim 1 further comprising the step of generating a warning signal when the target ratio is less than a predetermined amount and when the target ratio has increased above a previous target ratio.
6. A microwave motion detector comprising:
a transmitting antenna for transmitting microwave signals,
two receiving antennas for receiving from each antenna reflected transmitted microwave signals from a target in two separate channels, and
processing circuitry adapted to:
determine a target ratio from a phase difference between each signal in the separate channels, and
disregard motion from the target when the target ratio is less than a predetermined amount.
7. The microwave motion detector of claim 6 wherein the processing circuitry is adapted to determine the target ratio by:
summing and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a sum pattern signal;
subtracting and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a difference pattern signal; and
determining the target ratio from the ratio of the sum pattern signal and the difference pattern signal.
8. The microwave motion detector of claim 6 wherein the processing circuitry is further adapted to generate an alarm condition when the target ratio is more than a predetermined amount.
9. The microwave motion detector of claim 6 wherein the processing circuitry is further adapted to generate a warning signal when the target ratio is less than a predetermined amount and when the target ratio has increased above a previous target ratio.
10. An alarm system comprising:
a PIR sensor with a PIR detection pattern,
a microwave motion detector with a microwave detection pattern that is wider than and overlaps the PIR detection pattern, wherein the microwave motion detector comprises a transmitting antenna for transmitting microwave signals and two receiving antennas for receiving reflected transmitted microwave signals from a target in two separate channels, and
processing circuitry adapted to:
determine a target ratio from a phase difference between each signal in the separate channels, and
disregard motion from the target when the target ratio is less than a predetermined amount.
11. The alarm system of claim 10 wherein the processing circuitry is adapted to determine the target ratio by:
summing and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a sum pattern signal;
subtracting and mixing, with a portion of the transmitted microwave frequency signal, the two channels of received reflected signals to generate a difference pattern signal; and
determining the target ratio from the ratio of the sum pattern signal and the difference pattern signal.
12. The alarm system of claim 10 wherein the processing circuitry is further adapted to generate an alarm condition when the target ratio is more than a predetermined amount.
13. The alarm system of claim 10 wherein the processing circuitry is further adapted to transmit an alarm signal when the target ratio is more than the predetermined amount and the PIR sensor also detects the target.
14. The alarm system of claim 10 wherein the processing circuitry is further adapted to:
automatically select a target angle limit from a number of stored target angle limits based on a predefined condition occurring, and
select from a memory look up table the predetermined amount that corresponds to the selected target angle limit.
15. The alarm system of claim 10 wherein the processing circuitry is further adapted to generate a warning signal when the target ratio is less than a predetermined amount and when the target ratio has increased above the previous determined target ratio.
16. The alarm system of claim 13 wherein the predetermined amount corresponds to a target angle that is equal to the PIR detection pattern.
17. The alarm system of claim 13 wherein the predetermined amount corresponds to a target angle that is less than the PIR detection pattern.