Millimeter wave imaging system with frequency scanning antenna
A millimeter wave imaging system. The system includes one or more millimeter wave frequency scanning antenna for collecting frequency dependent beams of millimeter wave radiation from a narrow one-dimensional field of view and millimeter wave amplifier components for amplifying the millimeter wave radiation collected by each antenna. The system includes a beam-former that separates the amplified radiation to produce frequency dependent signals corresponding to the frequency dependent beams. The beam-former includes delay lines, a millimeter wave lens, and an array of millimeter wave power detectors for detecting the power in each frequency dependent beam. A sampling circuit reads out the frequency dependent signals 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 (or having the target move) across the field of view of the scanning antenna or by moving the antenna in order to scan its line of focus over the target. In preferred embodiments a 2×2 Dicke switch is provided to permit sampling a reference thermal source for gain control while continuing to collect image information. This 2×2 Dicke switch provides a square root of 2 improvement in temperature sensitivity over a single receiver version. Preferred embodiments also include features for focusing the antenna within a range of about 5 feet to infinity.
1. A millimeter wave imaging system comprising:
1) at least one millimeter wave frequency scanning antenna for collecting millimeter wave radiation emanating from a one-dimensional field of view;
2) millimeter wave amplifier components for amplifying at millimeter wave radiation collected by said frequency scanning antenna to produce amplified signals,
3) a beam-former for separating said amplified signals into frequency dependent signals corresponding to frequency dependent millimeter wave beams from said narrow one-dimensional field of view, said beam-former comprising:
1) a plurality of delay lines,
2) a millimeter wave lens, and
3) a plurality of millimeter wave power detectors;
4) a sampling circuit for reading out frequency dependent signals to produce a one-dimensional image of the antenna field of view, and
5) an adjustable focusing means for focusing said frequency-scanning antenna to restrict said one-dimensional field of view to a narrow one-dimensional field of view at a target distance.
2. The system as in claim 1 wherein said focusing means comprises a cylindrical reflector and a cylindrical lens.
3. The system as in claim 1 wherein said millimeter wave amplifier components comprise a Dicke switch.
4. The system as in claim 3 wherein said Dicke switch is a 2×2 Dicke switch.
5. The system as in claim 3 wherein said Dicke switch comprises GaAs PIN diodes fabricated on or in a semi-insulating GaAs substrate.
6. The system as in claim 1 wherein said millimeter wave amplifier components comprises three MMIC amplifiers fabricated on an indium phosphate substrate and a band pass filter.
7. The system as in claim 6 wherein said amplifier comprises a co-planar waveguide design.
8. The system as in claim 6 wherein said amplifier provides gains of at least 50 dB.
9. The system as in claim 1 wherein said delay lines are comprised of etched copper to create circuit patterns of varying lengths.
10. The system as in claim 9 wherein said delay lines define copper surfaces having surface roughness less than 300 nanometers.
11. The system as in claim 1 wherein said at least one frequency scanning antenna is one frequency scanning antenna.
12. The system as in claim 1 wherein said one frequency scanning antenna is at least 20 inches long.
13. The system as in claim 1 wherein said one frequency scanning antenna is about 26 inches long and comprises about 300 inclined slots functioning as receiving apertures.