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Publication Number
US-8441406-B2
Publication Date
2013-05-14
Expiration Date
Abstract
An apparatus has an improved antenna pattern for a cross dipole antenna. Such antennas desirably have an omnidirectional antenna pattern. Conventional cross dipole antennas exhibit nulls in their antenna patterns, which can cause antennas to deviate from a standard or specification. Applicant recognized and confirmed that the connection of a coaxial cable to the antenna arms is a cause of the nulls in the antenna pattern, and has devised techniques disclosed herein to compensate or cancel the effects of the connection. In one embodiment, the arms of the cross dipole antenna that are coupled to a center conductor of the coaxial cable remain of conventional length, but the arms of the cross dipole antenna that are coupled to a shield of the coaxial cable are lengthened by a fraction of the radius of the outer diameter of the coaxial cable.
Core Innovation
The invention provides a cross dipole antenna with a coaxial structure having a center conductor and an outer shield, and a plurality of conductive arms lying generally in a plane and spaced apart by about 90 degrees. The arms extend outward at a distal end and are arranged near a center point at a proximal end, with a first arm electrically coupled to the center conductor and a second arm electrically coupled to the center conductor, the second arm having a different predetermined length from the first predetermined length.
The cross dipole antenna further includes a third arm electrically coupled to the outer shield and having a third predetermined length longer than the first predetermined length, with the third arm extending opposite the first arm so that the third arm and the first arm form a first dipole. A fourth arm is electrically coupled to the outer shield and has a fourth predetermined length longer than the second predetermined length, with the fourth arm extending opposite the second arm so that the fourth arm and the second arm form a second dipole, and a second antenna has a second polarization orthogonal to the first polarization.
The invention addresses antenna pattern nulls and distortion induced by the coaxial structure and by coaxial cable connection effects. It compensates for distortion of the antenna pattern induced by the coaxial structure by using different predetermined arm lengths, including lengthening outer-shield-coupled arms relative to center-conductor-coupled arms by an amount proportional to an outer-shield radius R, and is also described for polarization diversity systems, arrays, reflector-backed configurations, and miniaturization using loading while maintaining effective electrical lengths.
Claims Coverage
The independent claims are clm-00001, clm-00009, and clm-00017. Across these claims, the coverage includes a cross dipole antenna with orthogonal polarization generated by center-conductor-coupled arms and outer-shield-coupled arms, and compensation via predetermined arm length relationships, together with a second antenna having orthogonal polarization.
Orthogonal polarization cross dipole from coaxial center conductor and outer shield
A cross dipole antenna comprising a coaxial structure having a center conductor and an outer shield, and a plurality of conductive arms in a plane spaced apart by about 90 degrees, where a first dipole is formed by a third arm and a first arm electrically coupled to the outer shield and center conductor, respectively, and a second dipole is formed by a fourth arm and a second arm electrically coupled to the outer shield and center conductor, respectively, and the apparatus further includes a second antenna having a second polarization orthogonal to the first polarization.
Arm length compensation for pattern distortion induced by coaxial structure
An apparatus in which each of a first arm, a second arm, a third arm, and a fourth arm have different predetermined lengths, as measured from a center of the coaxial structure, to compensate for distortion of the antenna pattern induced by the coaxial structure, and the apparatus further includes a second antenna having a second polarization orthogonal to the first polarization.
Fixed asymmetric arm lengths with outer-shield arm longer than center-conductor arm
An apparatus where, in a first dipole comprising a first pair of arms and a second dipole comprising a second pair of arms, at least one pair of arms have fixed asymmetric lengths such that an arm coupled to the outer shield is longer than an arm coupled to the center conductor, as measured from a center of the coaxial structure, and the apparatus further includes a second antenna having a second polarization orthogonal to the first polarization.
The claims consistently require a cross dipole antenna built from a coaxial structure with center-conductor-coupled and outer-shield-coupled arms arranged about 90 degrees apart, producing orthogonal polarization components, and a second antenna with orthogonal polarization. The independent claims differ in how compensation is expressed: through different predetermined arm lengths to compensate for pattern distortion, or through fixed asymmetric lengths specifically requiring the outer-shield-coupled arm to be longer than the center-conductor-coupled arm.
Stated Advantages
Provides compensation for distortion of the antenna pattern induced by the coaxial structure.
Enables near-omnidirectional antenna pattern behavior within a stated tolerance (within about 1 dB) in example implementations.
Supports polarization diversity by combining the cross dipole with a second antenna having orthogonal polarization.
Documented Applications
Used in omnidirectional antenna pattern designs where nulls and distortion arise from coaxial structure and coaxial cable connection effects.
Polarization diversity systems combining the cross dipole antenna with orthogonally polarized monopole or dipole antennas, including tee feed concepts.
Antenna arrays, including extension to array configurations described for multiple similarly polarized elements.
Reflector-backed or cavity-backed configurations for circular polarization referenced in the document summary.
Antenna miniaturization via loading while maintaining effective electrical lengths, as described at the conceptual level.
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