Antenna Ground Conductor Extension for Wearable SAR Reduction
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Solution Overview
Problem
In wearable devices, the performance of multiband antennas deteriorates due to their small size, and existing solutions do not adequately consider Specific Absorption Rate (SAR) values, leading to higher electric current distribution density and SAR values.
Innovation Solution
The antenna device incorporates a ground conductor and a ground conductor extension with lengths proportional to ¼ of a wavelength in the middle frequency range between the first and second frequency bands, ensuring an unbalanced feed system while minimizing SAR values by optimizing the design of the ground conductor and extension unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the antenna size is reduced for wearable devices, then the device portability is improved, but the antenna performance deteriorates
Solution Approach 1:
The ground conductor is extended in a direction substantially perpendicular to the antenna element, utilizing the vertical dimension to increase the effective ground area without increasing the planar footprint. This dimensional transition allows the antenna to achieve better performance in a compact form factor suitable for wearable devices.
2Reliability
If an unbalanced-type feed system is used to achieve wider bandwidth and higher gain, then the antenna performance is improved, but the electric current distribution density in GND increases leading to higher SAR values
Solution Approach 1:
The ground system is segmented into two parts: the ground conductor on the circuit board and the ground conductor extension. This segmentation allows the current distribution to be spread across both components, reducing the current density in the circuit board GND and thereby lowering SAR values while maintaining the benefits of the unbalanced feed system.
Solution Approach 2:
The ground conductor extension acts as an intermediary component that connects to the ground conductor and provides an additional current path. This intermediary structure reduces the current concentration in the circuit board GND, effectively lowering SAR values while preserving antenna performance.
3Reliability
If the ground conductor and ground conductor extension have length proportional to 1/4 wavelength in middle frequency range, then the working volume of antenna appears larger improving bandwidth and gain, but the electric current distribution density in GND increases
Solution Approach 1:
The lengths of the ground conductor and ground conductor extension are specifically designed to be proportional to 1/4 of the wavelength of frequencies in the middle range between the first and second frequency bands, and not a natural number multiple of 1/4 of the wavelength of the first frequency band. This parameter optimization achieves wider bandwidth and higher gain while controlling SAR values.
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
This configuration maintains antenna performance while reducing SAR values, achieving a well-balanced SAR characteristic across multiple frequency bands, even in small wearable devices.
Implementation Method 1
an antenna device including: a ground conductor; a ground conductor extension that is connected to the ground conductor; and an antenna element that is connected to the ground conductor and that operates in both a first frequency band and a second frequency band
Implementation Method 2
the ground conductor and the ground conductor extension having a length that is 1⁄4 of a wavelength of a frequency included in a middle range between the first frequency band and the second frequency band
Data Source
AI summary
An antenna device includes a ground conductor; a ground conductor extension that is connected to the ground conductor; and an antenna element that is connected to the ground conductor and that operates in both a first frequency band and a second frequency band higher than the first frequency band, the ground conductor and the ground conductor extension having a length that is ¼ of a wavelength of a frequency included in a middle range between the first frequency band and the second frequency band and that is not a natural number multiple of ¼ of a wavelength of the first frequency band.