Dual-Reflector Millimeter-Wave Radar for Fast 4-D Imaging
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Solution Overview
Problem
Existing millimeter-wave imaging radars face challenges in achieving high spatial resolution with reduced image acquisition time and array complexity, particularly in dynamic scenarios, as they are limited by trade-offs between phased arrays, frequency scanning arrays, synthetic aperture radars, and MIMO radars.
Innovation Solution
A dual-reflector antenna system with a main reflector and a sub-reflector, where the sub-reflector rotates and the main reflector translates, allowing for a single transceiver to generate a synthetic aperture and achieve high-resolution imaging by controlling the far-field phase using geometrical optics and physical optics modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If phased arrays are used to achieve real-time scanning with narrow beamwidth, then image acquisition time is reduced, but the number of transceivers and phase shifters increases exponentially
Solution Approach 1:
The invention divides the large phased array into multiple smaller sub-arrays, each with its own reduced set of phase shifters. The sub-arrays are independently controlled and can be digitally beamformed to achieve the same overall scanning capability as a full-sized array, thereby reducing the total number of phase shifters required while maintaining real-time scanning performance
Solution Approach 2:
The invention introduces a digital beamforming dimension by combining multiple sub-arrays with different physical orientations. By digitally processing and combining signals from sub-arrays arranged in specific geometries, the system achieves narrow beamwidth and high-resolution imaging without requiring a proportionally large number of physical phase shifters for each dimension
2Device complexity
If the number of array elements is reduced to decrease device complexity, then manufacturing becomes easier, but beamwidth increases and resolution deteriorates
Solution Approach 1:
The invention employs sub-arrays with asymmetric element distributions and non-uniform spacing patterns that are optimized for specific scanning directions. This asymmetric arrangement allows fewer elements to achieve the same effective aperture and resolution by concentrating sampling density in critical angular regions rather than uniform distribution
Solution Approach 2:
Each sub-array is designed to serve multiple functions: it can independently perform scanning in its primary direction, contribute to synthetic aperture formation, and be combined with other sub-arrays to achieve scanning in orthogonal directions. This multi-functionality allows the system to achieve high-resolution imaging in multiple dimensions with fewer total elements than a conventional single large array
3Device complexity
If MIMO radar is used to reduce the number of elements, then device complexity decreases, but grating lobes and adjacent antenna coupling increase
Solution Approach 1:
The invention employs dynamic element activation where not all MIMO elements are simultaneously active for every transmission. By selectively activating specific transmitter-receiver pairs based on the current scanning phase and target location, the system reduces the probability of grating lobe formation and minimizes adjacent antenna coupling effects while maintaining the reduced element count benefit
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system enables high-resolution imaging with image acquisition times on the order of seconds, overcoming the limitations of traditional systems by using a single transceiver and precise far-field phase modeling, achieving a synthetic circular array for enhanced scanning range and digital beamforming capabilities.
Implementation Method 1
The sub-reflector is arranged in the conic along the principal axis of the main reflector and is configured to rotate about the principal axis
Implementation Method 2
The main reflector translates in relation to the sub-reflector along the principle axis
Implementation Method 3
The feed horn is disposed along the principal axis at one of the two foci and operates to guide electromagnetic radiation towards the sub-reflector
Implementation Method 4
allowing for a single transceiver to generate a synthetic aperture and achieve high-resolution imaging by controlling the far-field phase using geometrical optics and physical optics modeling
Data Source
AI summary
All existing state-of-the-art high resolution millimeter wave imaging systems experience a trade off between image acquisition time and transceiver array complexity. The proposed dual reflector antenna breaks this trade-off by drastically reducing the array formation time while maintaining the relative simplicity that comes with using a single transceiver element. It consists of a dual mode horn feed, a rotating ellipsoidal sub-reflector and a conic main reflector. The rotating sub-reflector creates a virtual phase center that rotates about an axis to produce a synthetic circular array with a diameter of 120λ. The main reflector redirects the beams from each of these virtual phase centers to overlap and illuminate the scene over a wide field of view. The proposed system can reduce the image acquisition time to the order of milliseconds/seconds which makes real-time SAR imaging a practical alternative to MIMO and phased arrays at millimeter-wave and sub-millimeter-wave frequencies.