Multiband Circularly Polarized Antenna With Segmented High Impedance Surface
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Solution Overview
Problem
Existing low Size, Weight, and Power (SWaP) circularly polarized antennas face challenges in achieving wide bandwidth and compact design while maintaining electrical isolation, particularly in multi-band applications, as conventional solutions like ground plane reflectors limit bandwidth and HIS topologies provide narrow-band solutions or thick devices.
Innovation Solution
A spiral antenna with a High Impedance Surface (HIS) ground plane split into two distinct regions with different resonant elements allows for operation over two closely spaced frequency ranges, providing electrical isolation and compact design suitable for wearable or surface-mounted applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ground plane reflector is used to achieve electrical isolation, then antenna gain is increased by 3 dB, but bandwidth is limited and device thickness increases
Solution Approach 1:
The ground plane reflector is segmented into two distinct regions with different resonant frequencies. The first region has resonant elements tuned to a higher frequency band, while the second region has resonant elements tuned to a lower frequency band. This segmentation allows each region to independently reflect signals at its respective resonant frequency, enabling the antenna to operate effectively across a wider bandwidth while maintaining the phase reversal property needed for gain enhancement.
Solution Approach 2:
Different regions of the ground plane are given different local properties through the use of resonant elements with different geometries and dimensions. The first region contains resonant elements optimized for higher frequencies, while the second region contains resonant elements optimized for lower frequencies. This local differentiation allows the ground plane to provide frequency-selective reflection, simultaneously supporting multiple frequency bands with the desired phase characteristics.
2Adaptability or versatility
If an absorber is placed on the back side to provide electrical isolation, then wide bandwidth is maintained, but radiated power is lost and device thickness increases
Solution Approach 1:
Instead of using an absorber that dissipates the harmful back lobe radiation as heat, the invention converts this previously harmful radiation into a beneficial component by using a frequency-selective reflector. The reflector reverses the phase of the back lobe by 180 degrees, causing it to constructively interfere with the front lobe and enhance the forward radiation. This transforms the harmful back lobe into a useful signal that increases antenna gain without power loss.
3Length of stationary object
If a High Impedance Surface is used to reduce device thickness, then compact design is achieved, but bandwidth is limited to narrow-band solutions
Solution Approach 1:
The High Impedance Surface is segmented into multiple frequency-selective regions, each containing resonant elements tuned to different frequency bands. This segmentation transforms the traditionally narrow-band HIS into a multi-band structure that can simultaneously support multiple frequency ranges while maintaining the electric wall boundary conditions needed for thin-profile operation.
Solution Approach 2:
The ground plane is designed to perform multiple functions simultaneously: it provides electrical isolation from the mounting surface, reflects back lobe radiation with phase reversal for gain enhancement, and supports operation at multiple frequency bands. The frequency-selective resonant elements enable the same structure to be universally applicable across different frequency ranges without requiring separate designs for each band.
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 the antenna to achieve circularly polarized radiation over two distinct frequency ranges with improved bandwidth and reduced size and weight, suitable for applications like GNSS, with the ability to cover frequency bands spaced as closely as 1:1.2, and can be extended to multiple frequency ranges by adjusting dielectric properties and spiral geometry.
Implementation Method 1
The frequency selective reflector may be configured to reverse the phase of back lobe radiation by 180 degrees, such that the phase reversed back lobe constructively interferes with the forward lobe
Implementation Method 2
The first region has a first resonant frequency at which the electrical phase of a reflected electromagnetic signal is 360 degrees (or a multiple of n x 360 degrees, where n is an integer value) and the second region has a second resonant frequency at which the electrical phase of a reflected electromagnetic signal is 360 degrees
Implementation Method 3
A multiband circularly polarised antenna
Data Source
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AI summary
The present invention provides a circularly polarised, CP, antenna device for multiband GNSS. It comprises a spiral antenna and a high impedance surface, HIS, comprising a conductive layer comprising a first region and a separate second region, and a ground plane. The first region of the conductive layer is provided with at least one resonant element of a first resonant frequency and the second region of the conductive layer is provided with at least one resonant element of a second resonant frequency.