Compact antenna system having folded dipole and/or monopole
View Patent ↗An antenna and multi-antenna system are provided. Each antenna of the system is a mirror image and comprises first and second conductive elements each having a first end and a second end portion, the second end portions being capacitively coupled to each other. Each antenna can be operated as a lower-frequency folded dipole having a series capacitive gap which facilitates electrical lengthening of the antenna, or as a higher-frequency monopole antenna having a parasitic element which facilitates improved bandwidth. The antennas' feedpoints may be placed at opposite corners of a ground plane, and separated by a distance which is less than one quarter of an operating wavelength of the dipole but greater than one quarter of an operating wavelength of the monopole. Locating the feedpoints at the ground plane corners facilitates orthogonal polarization of the two antennas at least in dipole mode. The antennas thus provided exhibit good isolation.
1. An antenna operable in a monopole mode and a dipole mode comprising:
first and second conductive elements, each of the conductive elements haying first and second end portions;
an antenna feedpoint operatively coupled to the first end portion of the first conductive element; and
a ground operatively coupled to the first end portion of the second conductive element;
wherein the first end portions of the first and second conductive elements are substantially proximate to one another for a first length in which the first end portion of the first conductive element electromagnetically couples with the first end portion of the second conductive element, and wherein the first and second conductive elements diverge from each other following the first length, and wherein the first and second conductive elements converge toward the second end portions to form a capacitive gap, wherein the second end portions are proximate to one another for a second length less than the first length, and
wherein, when the antenna is operated at a first, relatively low operating frequency, the antenna is operable in a monopole mode in which the second conductive element operates as a counterpoise for the first conductive element, and, when the antenna is operated at a second, relatively high operating frequency, the antenna is operable in a dipole mode in which the first conductive element couples the antenna feedpoint to the second conductive element.
2. The antenna according to claim 1 , wherein the first conductive element further comprises a branched section providing a third end of the first conductive element.
3. The antenna according to claim 1 , wherein the antenna is operable in a monopole mode and a folded dipole mode, wherein, in the monopole mode, at least a portion of the first element operates as an active monopole element and the second element operates as a passive monopole element, and wherein, in the folded dipole mode, at least a portion of the first element operates as a first active dipole element and the second element operates as a second active dipole element.
4. The antenna according to claim 1 , wherein the antenna is provided within a region having a maximum dimension less than or equal to one quarter of an operating wavelength.
5. The antenna according to claim 1 , wherein the antenna is operatively coupled to a ground plane, and wherein the feedpoint is located proximate to a corner of the ground plane.
6. The antenna according to claim 5 , wherein the ground plane has a maximum dimension less than or equal to one quarter of an operating wavelength.
7. The antenna according to claim 6 , wherein the maximum dimension is substantially less than one quarter of the operating wavelength.
8. A multi-antenna system comprising a pair of the antennas according to claim 1 , the pair oriented as mirror images of each other with respect to a predetermined axis of symmetry.
9. The multi-antenna system according to claim 8 , wherein the mirror images are non-identical mirror images.
10. The multi-antenna system according to claim 8 , wherein each of the pair of antennas comprise a polarization substantially at 45 degrees relative to the axis of symmetry, the polarizations of the pair of antennas further being substantially orthogonal to each other.
11. The multi-antenna system according to claim 8 , wherein each of the pair of antennas are operatively coupled to a common ground plane, and wherein the feedpoints of each of the pair of antennas are located proximate to opposite corners of the ground plane.
12. The multi-antenna system according to claim 11 , wherein the opposite corners of the ground plane are separated by a distance less than or equal to one quarter of an operating wavelength.
13. The multi-antenna system according to claim 11 , wherein each of the pair of antennas is operable in a monopole mode and a dipole mode, wherein the pair of antennas have polarizations substantially orthogonal to each other when operated in the dipole mode, thereby facilitating an envelope correlation coefficient of about 0.1 in a predetermined band about an operating frequency of the pair of antennas.
14. The multi-antenna system according to claim 13 , wherein the pair of antennas are substantially isolated from each other when operating in either the monopole mode or the dipole mode.
15. A method of providing one or more antennas operable in a monopole mode and a dipole mode, the method comprising:
providing each of the one or more antennas as a printed circuit on a flexible substrate, each of the one or more antennas comprising:
(a) first and second conductive elements, each of the conductive elements having first and second end portions;
(b) an antenna feedpoint operatively coupled to the first end portion of the first conductive element: end
(c) a ground operatively coupled to the first end portion of the second conductive element,
wherein the first end portions of the first and second conductive elements are substantially proximate to one another for a first length in which the first end portion of the first conductive element electromagnetically couples with the first end portion of the second conductive element, and wherein the first and second conductive elements diverge from each other following the first length, and wherein the first and second conductive elements converge toward the second end portions to form a capacitive gap, wherein the second end portions are proximate to one another for a second length less than the first length, and
wherein, when the antenna is operated at a first, relatively low operating frequency, the antenna is operable in a monopole mode in which the second conductive element operates as a counterpoise for the first conductive element, and, when the antenna is operated at second, relatively high operating frequency, the antenna is operable in a dipole mode in which the first conductive element couples the antenna feedpoint to the second conductive element; and
mounting each of the one or more antennas onto a curved surface.