Coaxial Multiband Antenna Feed With Offset Choke for Cross-Pol Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Multiband antennas operating in close frequency bands, such as Ka and Ku, face issues with unwanted cross-polarization radiation due to larger inner diameters of the outer low-band coaxial waveguide, leading to greater electric field bending and radiation pattern distortions.
Innovation Solution
A coaxial feed design featuring a tubular high-band waveguide with an axially offset annular choke, dielectric loading, and a radial groove in the low-band waveguide to optimize impedance matching and phase tuning, reducing cross-polarization radiation by minimizing energy leakage and improving radiation patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the outer low-band coaxial waveguide has a larger inner diameter to accommodate close frequency bands (Ka and Ku), then the waveguide can support multiple bands, but unwanted cross-polarization radiation increases due to greater electric field bending at the aperture
Solution Approach 1:
An axial choke is introduced as an intermediary structure between the inner and outer waveguides. This choke acts as a mediator that suppresses unwanted cross-polarization radiation while allowing the outer waveguide to maintain its larger inner diameter for multiband operation. The choke creates a current discontinuity that prevents the harmful radiation without compromising the waveguide's ability to support multiple frequency bands.
Solution Approach 2:
The axial choke is positioned at a specific location (axially offset from the aperture) where it locally modifies the electromagnetic field distribution. By concentrating the impedance discontinuity at a particular axial position rather than uniformly throughout the waveguide, the solution selectively suppresses cross-polarization radiation while maintaining optimal performance for the desired polarization and frequency bands.
2Object-generated harmful factors
If the axial choke is positioned close to the aperture to suppress cross-polarization, then cross-pol radiation is reduced, but impedance matching to free space deteriorates
Solution Approach 1:
The choke is positioned in the axial dimension rather than at the aperture plane itself. By moving the choke structure along the axial direction and offsetting it from the aperture, the solution separates the functions of cross-polarization suppression and impedance matching. This dimensional adjustment allows the choke to suppress cross-pol radiation effectively while the offset position maintains proper impedance matching to free space.
3Reliability
If the axial choke is positioned far from the aperture to maintain impedance matching, then impedance matching is improved, but cross-polarization radiation increases
Solution Approach 1:
The axial offset distance of the choke from the aperture is optimized to specific values (e.g., 0.1λ to 0.25λ where λ is the wavelength) to simultaneously achieve both impedance matching and cross-polarization suppression. By carefully selecting this dimensional parameter, the solution balances the competing requirements of maintaining good impedance matching while effectively suppressing cross-pol radiation through the choke's electromagnetic shielding effect.
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 effectively reduces cross-polarization radiation and enhances radiation efficiency by ensuring the majority of wave energy is constructively combined, improving antenna performance across multiple frequency bands.
Implementation Method 1
the HB waveguide may be dielectrically loaded with a dielectric member. The dielectric member may have a relative permittivity equal to or greater than 2.
Implementation Method 2
an annular high-band (HB) choke located in the outer conducting surface of the HB waveguide, the HB choke being axially offset from the HB aperture. The offset of the HB choke may be configured to provide impedance matching to free space for LB frequencies of the LB waveguide.
Implementation Method 3
a tubular high-band (HB) waveguide, the HB waveguide including an outer conducting surface, an inner HB conducting surface, and a HB aperture defined by the inner HB conducting surface
Data Source
AI summary
A coaxial feed for multiband antenna for a multiband antenna includes: a tubular high-band (HB) waveguide, the HB waveguide including an outer conducting surface, an inner HB conducting surface, and a HB aperture defined by the inner HB conducting surface; a tubular low-band (LB) waveguide disposed coaxially around the HB waveguide, the LB waveguide including an outer feed surface, an inner LB conducting surface, and an annular LB aperture defined by the inner LB conducing surface and the outer conducting surface of the HB waveguide; and an annular high-band (HB) choke located in the outer conducting surface of the HB waveguide, the HB choke being axially offset from the HB aperture.