Compact Microstrip Antenna with Wilkinson Coupler for GNSS
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Solution Overview
Problem
One-point-feed microstrip antennas face challenges in achieving a required axial ratio within the GNSS frequency band while maintaining a compact size, as they tend to increase in size when trying to cover a wider frequency band, and struggle to maintain an axial ratio of 4 dB or lower.
Innovation Solution
A microstrip antenna with two feed points, utilizing a feeder circuit comprising a Wilkinson coupler unit and a phase-shift unit formed as lumped constant circuits, where the distance between feed points and the antenna's center is set to be larger than the impedance-matched distance, allowing for a compact design while achieving an excellent axial ratio within the GNSS frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the size of the microstrip antenna is increased to widen the operable frequency band, then the frequency band coverage is improved, but the axial ratio deteriorates and the antenna becomes less compact
Solution Approach 1:
The patent divides the single feed point into two separate feed points, allowing independent control of feeding signals. This segmentation enables the use of a Wilkinson coupler to provide equal-magnitude signals with 90-degree phase difference to each feed point, thereby achieving circular polarization with axial ratio of 4 dB or less across the GNSS frequency band while maintaining a compact antenna size of 50 mm x 50 mm or less.
2Manufacturing precision
If the size of the microstrip antenna is increased to improve axial ratio, then the axial ratio is improved, but the antenna becomes less compact and the operable frequency band may not be sufficiently widened
Solution Approach 1:
The patent changes the feeding parameters by introducing a 90-degree phase difference between the two feed points through a Wilkinson coupler. This parameter change enables the antenna to achieve an axial ratio of 4 dB or less without increasing the antenna size, as the circular polarization is achieved through the phase relationship rather than physical dimensions.
3Device complexity
If a one-point-feed configuration is used to simplify the structure, then the device complexity is reduced, but the axial ratio cannot be maintained at 4 dB or lower within the GNSS frequency band
Solution Approach 1:
The patent introduces a Wilkinson coupler as an intermediary device between the signal source and the two feed points. This coupler generates two signals with equal magnitude and 90-degree phase difference, which are then fed to the respective feed points. This intermediary component enables precise control of the feeding signals to achieve the required axial ratio while maintaining a relatively simple overall structure.
4Adaptability or versatility
If two feed points are provided with 90-degree phase difference to widen frequency band, then the frequency band coverage is improved, but the device complexity increases due to the required feeder circuit
Solution Approach 1:
The Wilkinson coupler serves multiple functions simultaneously: it divides the input signal into two equal-magnitude signals, provides the required 90-degree phase difference between the two output signals, and ensures proper impedance matching. This multi-functionality reduces the overall feeder circuit complexity while achieving the desired frequency band coverage and polarization characteristics.
Data Source
AI summary
A microstrip antenna has two feed points. The microstrip antenna includes a feeder circuit which is configured to feed, to the two feed points, electric signals whose phases are different by 90° from each other. The feeder circuit includes a Wilkinson coupler unit and a phase-shift unit each of which is formed as a lumped constant circuit.