Compact SAR Radar Antenna Design for UAV Platforms
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Solution Overview
Problem
Existing SAR radar systems are too large for small manned vehicles and UAVs, compromising image quality due to the requirement for large antennas with high radiation efficiency across specific frequency bands.
Innovation Solution
A radar system with two antennas and signal processing means, operating in a frequency band with a centre frequency and wide bandwidth of at least one octave, utilizing signal equalization and pulse compression to achieve flat transfer function and one-sided beam forming, with antennas having lengths less than half the wavelength, and a phase difference of 2α degrees between transmit signals, where 2α is approximately 90 degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large antennas are used to achieve high radiation efficiency and maintain image quality in conventional SAR systems, then the antenna gain and resolution are improved, but the platform size requirement increases, making the system infeasible for small manned vehicles and UAVs
Solution Approach 1:
The patent divides the antenna system into multiple small antenna elements (at least two antenna elements) arranged in a specific configuration. Instead of using a single large antenna, the system segments the antenna function across multiple smaller elements that can be accommodated on small platforms, while collectively providing the necessary radiation efficiency and image quality through coordinated operation.
Solution Approach 2:
The patent introduces spatial arrangement of multiple antenna elements in three-dimensional space, utilizing vertical and horizontal positioning to create a synthetic aperture. This dimensional arrangement allows the system to achieve high resolution and radiation efficiency without requiring a single large physical antenna, thereby enabling deployment on small manned vehicles and UAVs.
2Volume of moving object
If the antenna length is reduced to less than half the wavelength, then the antenna size is reduced for small platforms, but the radiation efficiency and antenna gain deteriorate
Solution Approach 1:
The patent combines multiple small antenna elements into a unified antenna system where the collective radiation pattern and gain are achieved through constructive interference. By merging the output of at least two antenna elements with appropriate phase and amplitude control, the system achieves radiation efficiency comparable to or exceeding that of a single large antenna, while maintaining compact size suitable for small platforms.
Solution Approach 2:
The patent employs signal processing means as an intermediary to control and optimize the radiation characteristics. Through digital signal processing, the system compensates for the reduced size of individual antenna elements by dynamically adjusting phase and amplitude, thereby maintaining high radiation efficiency and gain despite the compact dimensions of each individual antenna element.
3Measurement precision
If a wide bandwidth of at least one octave is used, then the SAR image resolution and frequency coverage are improved, but the system complexity and signal processing requirements increase
Solution Approach 1:
The patent implements feedback mechanisms in the signal processing chain, where the received signals from multiple antenna elements are processed through correlation and autocorrelation functions. This feedback processing allows the system to automatically optimize the wideband signal characteristics, maintain coherent integration across the octave bandwidth, and achieve high image resolution without requiring overly complex manual configuration or processing.
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 solution enables smaller SAR antennas for small platforms without compromising image quality, reducing VSWR, and achieving sufficient antenna gain and noise reduction, thus requiring only a moderate increase in transmit power to match conventional systems.
Implementation Method 1
a radar system for a Synthetic Aperture Radar, SAR, comprising an arrangement of at least one transmitter, two receivers comprising a first receiver and a second receiver, two antennas comprising a first antenna and a second antenna
Implementation Method 2
arranging a radar system transfer function Ff to be flat over the frequency band B by arranging for signal equalization and pulse compression of the received signals
Implementation Method 3
one-sided beam forming with wideband antenna gain, by utilizing a first receiver cannel of the first receiver and a second receiver channel of the second receiver where the first receiver channel receives a signal from the first antenna and the second receiver channel receives a signal from the second antenna and further by arranging for matching antenna separation d, with a phase difference of 2α degrees between the transmit signals fed into each antenna
Data Source
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Figure 4
AI summary
The invention provides a radar system for a Synthetic Aperture Radar, SAR, comprising an arrangement of at least one transmitter, two receivers, two antennas and signal processing means located on a platform. The platform is arranged to move over ground and arranged to transmit a known signal shape and receive signals reflected from the ground. The received signals are used to produce a SAR image of the ground. The SAR image comprises a number of resolution cells. The radar system is further arranged to operate in a frequency band with a centre frequency f c and with a wide bandwidth B of at least one octave wherein the radar system comprises a first and a second antenna having a length of less than half the wavelength of the centre frequency f c . The radar system is further arranged for: ° a radar system transfer function F f to be flat over the frequency band B and ° one-sided beam forming with wideband antenna gain. The invention also provides a corresponding method.