Compact wideband dual-polarized radiating elements for base station antenna applications
Radiating elements include a conductive patch having first and second slots that each extend along a first axis and third and fourth slots that each extend along a second axis that is perpendicular to the first axis, a feed network that includes first through fourth feed lines, each feed line crossing a respective one of the first through fourth slots, and a conductive ring that at least partially surrounds the periphery of the conductive patch and that encloses each of the first through fourth slots.
1. A radiating element for a base station antenna, the radiating element comprising:
a printed circuit board that includes a conductive patch having first and second slots that each extend along a first axis and third and fourth slots that each extend along a second axis that is perpendicular to the first axis;
a first coaxial cable and a second coaxial cable that each extend from a reflector of the base station antenna to the printed circuit board; and
a conductive stub that physically and electrically connects an outer conductor of the first coaxial cable to an outer conductor of the second coaxial cable.
2. The radiating element of claim 1 , wherein the printed circuit board is mounted forwardly from the reflector at a distance that is greater than one-quarter of a wavelength corresponding to the center frequency of the operating frequency band of the radiating element.
3. The radiating element of claim 2 , wherein the conductive stub is located at approximately one quarter of the wavelength corresponding to the center frequency of the operating frequency band of the radiating element from the printed circuit board.
4. The radiating element of claim 2 , wherein the conductive stub is located closer to the reflector than it is to the printed circuit board.
5. The radiating element of claim 1 , wherein the outer conductors of the first and second coaxial cables are soldered to the printed circuit board.
6. The radiating element of claim 1 , further comprising first and second conductive tubes that are positioned adjacent the first and second coaxial cables.
7. The radiating element of claim 1 , wherein the printed circuit board further includes a feed network that has a first input that is electrically connected to an inner conductor of the first coaxial cable, a first power divider that is coupled to the first input, first and second transmission lines that extend from the first power divider to cross the respective first and second slots, a second input that is electrically connected to an inner conductor of the second coaxial cable, a second power divider that is coupled to the second input, and third and fourth transmission lines that extend from the second power divider to cross the respective third and fourth slots.
8. The radiating element of claim 7 , wherein the conductive patch is implemented at least partially on a first metal layer of the printed circuit board, wherein the feed network is implemented on a second metal layer of the printed circuit board, wherein the second metal layer further includes a plurality of metal pads that are each electrically connected to the conductive patch, and wherein each of the first through fourth slots extend to a periphery of the conductive patch.
9. The radiating element of claim 7 , wherein at least a portion of the conductive patch is implemented on a first metal layer of the printed circuit board, wherein the first through fourth transmission lines comprise metal traces on a second metal layer of the printed circuit board, and wherein each of the first through fourth slots extend to the periphery of the conductive patch.
10. The radiating element of claim 9 , wherein the conductive patch includes a first portion that is implemented on a first metal layer of a printed circuit board and a second portion that is implemented on the second metal layer of the printed circuit board.
11. The radiating element of claim 1 , wherein the printed circuit board further includes a conductive ring that at least partially surrounds a periphery of the conductive patch and that encloses each of the first through fourth slots.
12. A method of suppressing a common mode resonance in a base station antenna having a reflector, an array of first radiating elements that are configured to operate in a first operating frequency band and an array of second radiating elements that are configured to operate in a second operating frequency band, where each second radiating element includes a radiator unit that is positioned forwardly of the reflector and at least one coaxial feed cable that connects to the radiator unit, the method comprising:
electrically connecting an outer conductor of a first of the coaxial feed cables that feeds a first of the second radiating elements to the reflector at a grounding position that is selected so that the physical distance of the radio frequency (“RF”) transmission path that extends between the grounding position and the radiator unit of the first of the second radiating elements is a distance that is not resonant at any frequency in the first operating frequency band.
13. The method of claim 12 , wherein the grounding position is a position where an outer conductor of the first of the coaxial feed cables is galvanically connected to a rear surface of the reflector.
14. The method of claim 13 , where the first of the coaxial feed cables is galvanically connected to a rear surface of the reflector by exposing a portion of the outer conductor and soldering the exposed portion of the outer conductor to the reflector.
15. The method of claim 12 , wherein the first of the coaxial feed cables extends between the radiator unit and a printed circuit board, and wherein the printed circuit board includes a grounding tab where a ground conductor of the printed circuit board is coupled to the reflector.
16. The method of claim 15 , wherein the physical distance of the RF transmission path that extends between the grounding position and the radiator unit of the first of the second radiating elements is the sum of the length of the first of the coaxial feed cables and a distance between the location where the first of the coaxial feed cables connects to the printed circuit board and the grounding tab.
17. The method of claim 12 , wherein the physical distance of the RF transmission path that extends between the grounding position and the radiator unit of the first of the second radiating elements is not a multiple of a quarter wavelength of any frequency in the first operating frequency band.
18. The method of claim 12 , wherein a second of the coaxial feed cable also feeds the first of the second radiating elements, and wherein a conductive stub physically and electrically connects an outer conductor of the first of the coaxial feed cables to an outer conductor of the second of the coaxial feed cables.
19. The method of claim 18 , wherein the radiator unit of first of the second radiating elements is mounted forwardly from the reflector at a distance that is greater than one-quarter of a wavelength corresponding to the center frequency of the second operating frequency band, and the conductive stub is located at approximately one quarter of the wavelength corresponding to the center frequency of the second operating frequency band of the radiating element from the radiator unit.
20. The method of claim 19 , wherein the conductive stub is located closer to the reflector than it is to the radiator unit.