Cross-dipole antenna configurations
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.
1. An apparatus comprising:
a cross dipole antenna having a first polarization orientation, the cross dipole antenna comprising:
a coaxial structure having a center conductor and an outer shield;
a plurality of conductive arms comprising at least a first arm, a second arm, a third arm, and a fourth arm, wherein the plurality lie generally in a plane and are spaced apart from each other by about 90 degrees, such that a proximal end of each of the plurality of arms is arranged near a center point and wherein each of the plurality of arms extends generally outward at a distal end, wherein:
the first arm is electrically coupled to the center conductor at a proximal end and has a first predetermined length;
the second arm is electrically coupled to the center conductor at a proximal end and has a second predetermined length different from the first predetermined length;
the third arm is electrically coupled to the outer shield at a proximal end and has a third predetermined length, wherein the third predetermined length is longer than the first predetermined length, the third arm extending opposite the first arm such that the third arm and the first arm form a first dipole; and
the fourth arm is electrically coupled to the outer shield at a proximal end and has a fourth predetermined length, wherein the fourth predetermined length is longer than the second predetermined length, the fourth arm extending opposite the second arm such that the fourth arm and the second arm form a second dipole; and
a second antenna having a second polarization orthogonal to the first polarization.
2. The apparatus of claim 1 , wherein the cross dipole antenna has the horizontally-polarized orientation and the second antenna has the vertically-polarized orientation.
3. The apparatus of claim 1 , wherein the second antenna comprises a monopole antenna.
4. The apparatus of claim 1 , wherein the second antenna comprises a dipole antenna.
5. The apparatus of claim 1 , wherein the cross dipole antenna has the horizontally-polarized orientation, and wherein the second antenna is spaced horizontally apart from the cross dipole antenna, wherein each of the cross dipole antenna and the second antenna are coupled to separate feedlines.
6. The apparatus of claim 1 , further comprising:
one or more additional cross dipole antennas having the same polarization orientation as the cross dipole antenna; and
one or more additional antenna having the same polarization orientation as the second antenna, wherein the apparatus comprises an antenna array.
7. The apparatus of claim 1 , further comprising a second cross dipole antenna as a third antenna, and further comprising a fourth antenna, wherein the second cross dipole antenna has the same polarization orientation as the cross dipole antenna, wherein the fourth antenna has the same polarization orientation as the second antenna, wherein the cross dipole antenna, the second antenna, the second cross dipole antenna, and the fourth antenna are arranged in a 2×2 antenna array such that the second cross dipole antenna is diagonally across from the cross dipole antenna, and the fourth antenna is diagonally across from the second antenna.
8. The apparatus of claim 1 , further comprising a tee joint having a first end, a second end, and a third end, wherein the first end is coupled to a feedline, wherein the cross dipole antenna is disposed at the second end, wherein the second antenna is disposed at the third end, and wherein the second antenna comprises a monopole antenna.
9. An apparatus comprising:
a cross dipole antenna having a first polarization, the cross dipole antenna comprising:
a coaxial structure having a center conductor and an outer shield;
at least a first arm, a second arm, a third arm, and a fourth arm, wherein the arms lie generally in a plane and are spaced apart from each other by about 90 degrees, wherein a proximal end of each arm is arranged near a center point and wherein each arm extends generally outward at a distal end, wherein:
the first arm is electrically coupled to the center conductor at a proximal end;
the second arm is electrically coupled to the center conductor at a proximal end;
the third arm is electrically coupled to the outer shield at a proximal end, the third arm extending opposite the first arm such that the third arm and the first arm form a first dipole; and
the fourth arm is electrically coupled to the outer shield at a proximal end, the fourth arm extending opposite the second arm such that the fourth arm and the second arm form a second dipole;
wherein each of the first arm, the second arm, the third arm, and the 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
a second antenna having a second polarization orthogonal to the first polarization.
10. The apparatus of claim 9 , wherein the cross dipole antenna has the horizontally-polarized orientation and the second antenna has the vertically-polarized orientation.
11. The apparatus of claim 9 , wherein the second antenna comprises a monopole antenna.
12. The apparatus of claim 9 , wherein the second antenna comprises a dipole antenna.
13. The apparatus of claim 9 , wherein the cross dipole antenna has the horizontally-polarized orientation, and wherein the second antenna is spaced horizontally apart from the cross dipole antenna, wherein each of the cross dipole antenna and the second antenna are coupled to separate feedlines.
14. The apparatus of claim 9 , further comprising:
one or more additional cross dipole antennas having the same polarization orientation as the cross dipole antenna; and
one or more additional antenna having the same polarization orientation as the second antenna, wherein the apparatus comprises an antenna array.
15. The apparatus of claim 9 , further comprising a second cross dipole antenna as a third antenna, and further comprising a fourth antenna, wherein the second cross dipole antenna has the same polarization orientation as the cross dipole antenna, wherein the fourth antenna has the same polarization orientation as the second antenna, wherein the cross dipole antenna, the second antenna, the second cross dipole antenna, and the fourth antenna are arranged in a 2×2 antenna array such that the second cross dipole antenna is diagonally across from the cross dipole antenna, and the fourth antenna is diagonally across from the second antenna.
16. The apparatus of claim 9 , further comprising a tee joint having a first end, a second end, and a third end, wherein the first end is coupled to a feedline, wherein the cross dipole antenna is disposed at the second end, wherein the second antenna is disposed at the third end, and wherein the second antenna comprises a monopole antenna.
17. An apparatus comprising:
a cross dipole antenna having a first polarization, the cross dipole antenna comprising:
a coaxial structure having a center conductor and an outer shield;
a first dipole comprising a first pair of arms; and
a second dipole comprising a second pair of arms;
wherein the arms of at least one pair of the first pair or the second pair 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
a second antenna having a second polarization orthogonal to the first polarization.
18. The apparatus of claim 17 , wherein the cross dipole antenna has the horizontally-polarized orientation and the second antenna has the vertically-polarized orientation.
19. The apparatus of claim 17 , wherein the second antenna comprises a monopole antenna.
20. The apparatus of claim 17 , wherein the second antenna comprises a dipole antenna.
21. The apparatus of claim 17 , wherein the cross dipole antenna has the horizontally-polarized orientation, and wherein the second antenna is spaced horizontally apart from the cross dipole antenna, wherein each of the cross dipole antenna and the second antenna are coupled to separate feedlines.
22. The apparatus of claim 17 , further comprising:
one or more additional cross dipole antennas having the same polarization orientation as the cross dipole antenna; and
one or more additional antenna having the same polarization orientation as the second antenna, wherein the apparatus comprises an antenna array.
23. The apparatus of claim 17 , further comprising a second cross dipole antenna as a third antenna, and further comprising a fourth antenna, wherein the second cross dipole antenna has the same polarization orientation as the cross dipole antenna, wherein the fourth antenna has the same polarization orientation as the second antenna, wherein the cross dipole antenna, the second antenna, the second cross dipole antenna, and the fourth antenna are arranged in a 2×2 antenna array such that the second cross dipole antenna is diagonally across from the cross dipole antenna, and the fourth antenna is diagonally across from the second antenna.
24. The apparatus of claim 17 , further comprising a tee joint having a first end, a second end, and a third end, wherein the first end is coupled to a feedline, wherein the cross dipole antenna is disposed at the second end, wherein the second antenna is disposed at the third end, and wherein the second antenna comprises a monopole antenna.