International audienceWe present a 3D computational imaging system based on a mode-mixing cavity at microwavefrequencies. The core component of this system is an electrically large rectangular cavity with onecorner re-shaped to catalyze mode mixing, often called a Sinai Billiard. The front side of the cavityis perforated with a grid of periodic apertures that sample the cavity modes and project them intothe imaging scene. The radiated fields are scattered by the scene and are measured by low gainprobe antennas. The complex radiation patterns generated by the cavity thus encode the scene informationonto a set of frequency modes. Assuming the first Born approximation for scatteringdynamics, the received signal is processed using computational methods to reconstruct a 3D imageof the scene with resolution determined by the diffraction limit. The proposed mode-mixing cavityis simple to fabricate, exhibits low losses, and can generate highly diverse measurement modes.The imaging system demonstrated in this letter can find application in security screening and medicaldiagnostic imaging

Abstract:We propose a polarimetric microwave imaging technique that exploits recent advances in computational imaging. We utilize a frequency-diverse cavity-backed metasurface, allowing us to demonstrate high-resolution polarimetric imaging using a single transceiver and frequency sweep over the operational microwave bandwidth. The frequency-diverse metasurface imager greatly simplifies the system architecture compared with active arrays and other conventional microwave imaging approaches. We further develop the theoretical framework for computational polarimetric imaging and validate the approach experimentally using a multi-modal leaky cavity. The scalar approximation for the interaction between the radiated waves and the targetoften applied in microwave computational imaging schemes-is thus extended to retrieve the susceptibility tensors, and hence providing additional information about the targets. Computational polarimetry has relevance for existing systems in the field that extract polarimetric imagery, and particular for ground observation. A growing number of short-range microwave imaging applications can also notably benefit from computational polarimetry, particularly for imaging objects that are difficult to reconstruct when assuming scalar estimations.

We present a reconfigurable, dynamic beam steering holographic metasurface aperture to synthesize a microwave camera at K-band frequencies. The aperture consists of a 1D printed microstrip transmission line with the front surface patterned into an array of slot-shaped subwavelength metamaterial elements (or meta-elements) dynamically tuned between "ON" and "OFF" states using PIN diodes. The proposed aperture synthesizes a desired radiation pattern by converting the waveguide-mode to a free space radiation by means of a binary modulation scheme. This is achieved in a holographic manner; by interacting the waveguide-mode (reference-wave) with the metasurface layer (hologram layer). It is shown by means of full-wave simulations that using the developed metasurface aperture, the radiated wavefronts can be engineered in an all-electronic manner without the need for complex phase-shifting circuits or mechanical scanning apparatus. Using the dynamic beam steering capability of the developed antenna, we synthesize a Mills-Cross composite aperture, forming a single-frequency all-electronic microwave camera.

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