Base Station Antenna Feed Board Reducing Passive Intermodulation
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Solution Overview
Problem
Conventional base station antennas suffer from high levels of passive intermodulation (PIM) distortion due to nonlinearities in mechanical components, which are exacerbated by material junctions, corrosion, and environmental factors, leading to interference and degraded signal quality.
Innovation Solution
The design incorporates a substrate with specific through-holes and solder pads on a printed circuit board, where the inner conductor of a coaxial cable passes through an unplated through-hole and is electrically connected to a metal trace via plated through-holes, minimizing direct contact and reducing PIM distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional mechanical components and material junctions are used in the antenna feed board, then the structural integrity and electrical connection are maintained, but passive intermodulation distortion increases due to nonlinearities at junctions and interfaces
Solution Approach 1:
The invention extracts and eliminates the problematic plated through-holes from the signal path. Instead of having the RF signal pass through multiple plated interfaces that generate PIM, the signal travels through a single unplated through-hole that maintains structural integrity while minimizing nonlinear interactions at junctions.
Solution Approach 2:
The invention introduces an intermediary unplated through-hole that serves as a low-PIM connection path between the front and back surfaces of the feed board. This intermediary structure provides electrical connection while avoiding the nonlinearities associated with plated interfaces, effectively mediating between the need for structural integrity and the need to minimize PIM.
2Reliability
If plated through-holes are used to provide electrical connection between front and back surfaces, then electrical connectivity is achieved, but the number of material junctions increases leading to higher PIM distortion
Solution Approach 1:
The invention removes the plated through-holes from the RF signal path entirely, extracting the source of PIM distortion. The RF signal instead passes through unplated through-holes that provide necessary electrical connectivity without creating the nonlinear material junctions that generate intermodulation products.
Solution Approach 2:
The invention segments the electrical connection path into distinct functional zones: unplated through-holes for RF signal passage (minimizing PIM) and plated through-holes reserved exclusively for ground connections (providing structural integrity and grounding without interfering with the RF signal path).
3Strength
If multiple material junctions and interfaces are present in the feed board, then structural strength and electrical connection are maintained, but nonlinearities at these junctions generate interfering signals
Solution Approach 1:
The invention segments the feed board into distinct functional layers and connection types: RF signal paths use unplated through-holes to minimize PIM, while ground paths use plated through-holes for structural integrity and grounding. This segmentation allows each path to be optimized for its specific function without compromising the other.
Solution Approach 2:
The invention extracts the ground connections from the RF signal path by providing separate dedicated ground paths. This removal of overlapping functions eliminates the nonlinear interactions between RF signals and ground paths, reducing PIM distortion while maintaining necessary structural strength through the plated ground connections.
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 significantly reduces passive intermodulation distortion, enhancing the quality of radio frequency signals by minimizing nonlinear interactions and maintaining signal integrity across mechanical components.
Implementation Method 1
A metal trace (e.g., 50-ohm trace) is provided on the front surface of the substrate. The metal trace is electrically connected to the solder pad by electrically conductive plating in a second of the plurality of through-holes
Implementation Method 2
An electrically conductive pad and an electrically conductive feed conductor are provided on the back surface of the printed circuit board. The feed conductor extends at least partially through a first of the plurality of through-holes and is electrically connected to the electrically conductive pad
Data Source
AI summary
An antenna assembly includes a substrate having front and back surfaces thereon and a plurality of through-holes therein, along with a solder pad on the back surface of the substrate. An input cable is also provided, which is attached to the back surface of the substrate. The input cable includes an outer conductor, which contacts the back surface of the substrate, and an inner conductor, which extends at least partially through a first of the plurality of through-holes and is electrically connected to the solder pad. A metal trace (e.g., 50-ohm trace) is provided on the front surface of the substrate. The metal trace is electrically connected to the solder pad by electrically conductive plating in a second of the plurality of through-holes.