  This work presents techniques which can allow low-cost phased-array receivers
to be reconfigured as interferometric imagers and thereby reducing cost. Since
traditional phased arrays power combine incoming signals prior to digitization,
orthogonal code-modulation is applied to each incoming signal using phase
shifters within each front-end. These code-modulated signals can then be
combined and processed coherently through a shared hardware path. Visibility
functions can be recovered through squaring and code-demultiplexing operations.
The proposed system modulates incoming signals but demodulates desired
correlations. Firstly, we present the operation of the system, a validation of
its operation using behavioral models of a traditional phased array and a
benchmarking of the code-modulated interferometer against traditional
interferometer using simulation results and sensitivity analysis. Secondly, we
present a simple CMI system operating in the license-free 60-GHz band using a
four-element phased-array receiver. The four-element phased array is thinned to
obtain a 13-pixel image and the system is demonstrated through a point-source
detected at different locations. Finally, the operation and capabilities of
code-modulated interferometry (CMI) are demonstrated at 10-GHz using
commercially-available phased arrays. A 33-pixel, eight-element prototype is
created using two commercially-available ADAR1000 phased-array receivers from
Analog Devices Inc. The chips are connected at board level to a patch antenna
array. The 33-pixel camera is demonstrated in hardware for point-source
detection. Further to demonstrate the scalability of the concept, a 16-element,
169-pixels CMI imaging system is presented at 10-GHz using the four of the same
commercially-available phased arrays from ADI. Two active point sources are
imaged simultaneously to present the resolution of the system.

Signal Processing