Cloaked Low-Band Dipole Elements for Multiband Array Pattern Stability
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Solution Overview
Problem
Undesirable interactions occur between radiating elements of different frequency bands in multiband antennas, causing scattering of high band signals, perturbations in radiation patterns, variation in azimuth beam width, and beam squint due to resonance of low band elements in the high band frequency range.
Innovation Solution
The use of low band radiating elements with conductive segments shorter than one-half wavelength at high band frequencies, coupled by inductive elements to attenuate high band currents and minimize interaction, and optionally using parasitic elements with similar configurations to shape beam patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If low band radiating elements are used in multiband antennas, then low band coverage is provided, but high band signals are scattered due to resonance of low band elements at high band frequencies
Solution Approach 1:
The low band radiating element is divided into multiple conductive segments (first, second, third, and fourth dipole arms) that are spatially separated and oriented at different angles. This segmentation prevents the element from forming a continuous resonant structure at high band frequencies, thereby reducing signal scattering while maintaining low band functionality.
Solution Approach 2:
Each dipole arm is designed with specific length characteristics - the first and third arms have lengths less than one-half wavelength at high band frequencies, while the second and fourth arms have lengths between one-quarter and one-half wavelength. This local variation in electrical length creates non-uniform current distribution that suppresses resonance at high frequencies while preserving low band radiation characteristics.
2Reliability
If low band dipole arms are made longer to improve low band radiation, then low band performance is enhanced, but resonance at high band frequencies increases causing beam squint and pattern perturbations
Solution Approach 1:
The four dipole arms are configured with asymmetric length relationships - specifically, the first and third arms have different lengths from the second and fourth arms. This asymmetric configuration disrupts the symmetry required for resonant modes at high band frequencies, preventing beam squint and radiation pattern perturbations while maintaining effective low band radiation.
Solution Approach 2:
The dipole arm lengths are carefully controlled within specific ranges: first and third arms are less than one-half wavelength at high band frequencies, while second and fourth arms are between one-quarter and one-half wavelength. This parameter optimization ensures that the element radiates effectively at low band frequencies while avoiding resonant conditions at high band frequencies, thus maintaining stable radiation patterns.
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
Minimizes the scattering of high band signals and controls beam patterns by reducing high band current flow, effectively cloaking the low band elements at high frequencies, thereby improving radiation performance.
Implementation Method 1
The inductive elements are selected to appear as high impedance elements at the high band operational frequency and as lower impedance elements at the low band operational frequency
Data Source
AI summary
A multiband antenna, having a reflector, and a first array of first radiating elements having a first operational frequency band, the first radiating elements being a plurality of dipole arms, each dipole arm including a plurality of conductive segments coupled in series by a plurality of inductive elements; and a second array of second radiating elements having a second operational frequency band, wherein the plurality of conductive segments each have a length less than one-half wavelength at the second operational frequency band.