Millimeter wave imaging system
A millimeter wave imaging system that includes at least one millimeter wave frequency scanning antenna for collecting frequency dependent beams of millimeter wave radiation from a narrow one-dimensional field of view. The collected radiation is amplified at the collected frequencies and the amplified signals are separated into frequency dependent bins with a tapped-delay beam-former. These bins are then sampled to produce a one-dimensional image of the antenna field of view. A two dimensional image of a target may be obtained by moving the target across the field of view of the scanning antenna. In a preferred embodiment the antenna is only 4.5 inches in length and constructed from WR-10 waveguide with inclined slots cut in one of the narrow walls at 79 mil spacings. This geometry creates a frequency-scanned antenna spanning a 20 degree vertical field of view over a 75.5–93.5 GHz operational band of the sensor, starting at approximately 1 degree below horizontal at 93.5 GHz and ranging to approximately 21 degrees below horizontal at 75.5 GHz. In this embodiment 64 of these antenna elements are arranged in four stacks of 16 antennas focused at about 18 inches to construct a portal contraband screener. In another preferred embodiment called the single stick imager, the antenna is 24 inches long with 300 inclined slots serving as receive apertures.
1. A single stick millimeter wave imaging system comprising:
A) a single millimeter wave frequency scanning antenna for collecting frequency dependent beams of millimeter wave radiation from a narrow one-dimensional field of view;
B) a millimeter wave amplifier for amplifying at the collected frequencies said millimeter wave radiation;
C) a beam-former for separating said amplified collected radiation to produce frequency dependent signals corresponding to said frequency dependent beams, said beam-former comprising:
1) a plurality of delay lines,
2) a millimeter wave lens, and
3) a plurality of millimeter wave power detectors; and
D) a sampling circuit for reading out frequency dependent signals to produce a one-dimensional image of the antenna field of view.
2. An imaging system as in claim 1 wherein said single millimeter wave frequency scanning antenna is at least 20 inches long.
3. An imaging system as in claim 1 wherein said single millimeter wave frequency scanning antenna is about 26 inches long and comprises about 300 inclined slots functioning as receiving apertures.
4. An imaging system as in claim 1 and also comprising a focusing means for focusing said frequency-scanning antenna.
5. An imaging system as in claim 1 wherein said focusing means comprises a cylindrical reflector and a cylindrical lens.
6. An imaging system as in claim 1 wherein said millimeter wave amplifier comprises three MMIC amplifiers fabricated on an indium phosphate substrate and a band pass filter.
7. An imaging system as in claim 1 wherein said amplifier comprises a co-planar waveguide design.
8. An imaging system as in claim 1 wherein said amplifier provides gains of at least 50 dB.
9. An imaging system as in claim 1 wherein said delay lines are comprised of etched copper to create circuit patterns of varying lengths.
10. An imaging system as in claim 1 wherein said delay lines define copper surfaces having surface roughness less than 300 nanometers.