Method of eliminating resonances in multiband radiating arrays

Abstract

A multiband radiating array according to the present invention includes a vertical column of lower band dipole elements and a vertical column of higher band dipole elements. The lower band dipole elements operate at a lower operational frequency band, and the lower band dipole elements have dipole arms that combine to be about one half of a wavelength of the lower operational frequency band midpoint frequency. The higher band dipole elements operate at a higher frequency band, and the higher band dipole elements have dipole arms that combine to be about three quarters of a wavelength of the higher operational frequency band midpoint frequency. The higher band radiating elements are supported above a reflector by higher band feed boards. A combination of the higher band feed boards and higher band dipole arms do not resonate in the lower operational frequency band.

Claims

1. A multiband antenna, comprising: a low band radiating element having a first operational frequency band, the low band radiating element including a low band dipole that includes first and second low band dipole arms and a low band feed board; a high band radiating element having a second operational frequency band that is higher than the first operational frequency band, the high band radiating element including a high band dipole that includes first and second high band dipole arms and a high band feed board, wherein the high band dipole has an impedance of about 40052-60052 when operating in the second operational frequency band.

2. The multiband antenna of claim 1, wherein a combination of the high band feed board and the first high band dipole arm do not resonate in the first operational frequency band.

3. The multiband antenna of claim 2, wherein the second operational frequency band includes the 1710-2170 MHz frequency band.

4. The multiband antenna of claim 3, wherein the first and second high band dipole arms each capacitively couple to respective first and second feed lines on the high band feed board, wherein the high band feed board includes first and second capacitive sections that capacitively couple with the respective first and second high band dipole arms, and wherein first and second inductors are coupled between the first and second feed lines and the respective first and second capacitive sections.

5. The multiband antenna of claim 2, wherein the first and second high band dipole arms are configured to resonate at a second resonant frequency that is within the second operational frequency band.

6. The multiband antenna of claim 2, wherein an aggregate length of the first and second high band dipole arms is approximately three-quarters of a wavelength of the center frequency of the second operational frequency band, and a height of the high band feed board is approximately one-quarter of a wavelength of the center frequency of the second operational frequency band.

7. The multiband antenna of claim 2, wherein a combined length of the high band feed board and the first high band dipole arm exceeds one-quarter of a wavelength at the frequencies of the first operational frequency band.

8. The multiband antenna of claim 2, wherein a combined length of the high band feed board and the first high band dipole arm is selected to tune a frequency of a common mode resonance of the high band radiating element to be below the first operational frequency band.

9. The multiband antenna of claim 2, wherein a combined length of the high band feed board and the first high band dipole arm is selected to tune a frequency of a common mode resonance of the high band radiating element to be above the first operational frequency band.

10. The multiband antenna of claim 1, wherein the first and second high band dipole arms have an aggregate length that is between 0.6 wavelengths to 0.9 wavelengths of a frequency in the second operational frequency band.

11. The multiband antenna of claim 1, wherein the first and second high band dipole arms each capacitively couple to respective first and second feed lines on the high band feed board.

12. The multiband antenna of claim 11, wherein the high band feed board includes first and second capacitive sections that capacitively couple with the respective first and second high band dipole arms.

13. The multiband antenna of claim 12, wherein a first inductor is coupled between the first feed line and the first capacitive section and a second inductor is coupled between the second feed line and the second capacitive section.

14. The multiband antenna of claim 13, wherein the first and second inductors are each implemented as trace sections on the high band feed board that are narrower than the first and second feed lines.

15. The multiband antenna of claim 1, wherein the first and second high band dipole arms are configured to resonate at a second resonant frequency that is within the second operational frequency band.

16. The multiband antenna of claim 1, wherein an aggregate length of the first and second high band dipole arms is approximately three-quarters of a wavelength of a center frequency of the second operational frequency band.

17. The multiband antenna of claim 1, wherein a height of the high band feed board is approximately one-quarter of a wavelength of a center frequency of the second operational frequency band.

18. The multiband antenna of claim 1, wherein a combined length of the high band feed board and the first high band dipole arm exceeds one-quarter of a wavelength at frequencies of the first operational frequency band.

19. The multiband antenna of claim 1, wherein a combined length of the high band feed board and the first high band dipole arm is selected to tune a frequency of a common mode resonance of the high band radiating element to be below the first operational frequency band.

20. The multiband antenna of claim 1, wherein a combined length of the high band feed board and the first high band dipole arm is selected to tune a frequency of a common mode resonance of the high band radiating element to be above the first operational frequency band.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically diagrams a conventional dual band antenna 10.

(2) FIG. 2a schematically diagrams a first example of a dual band antenna according to one aspect of the present invention.

(3) FIG. 2b schematically illustrates a second example of a dual band antenna according to one aspect of the present invention.

(4) FIG. 3 is a graph of Common Mode and Differential Mode responses of the prior art dual band antenna of FIG. 1.

(5) FIG. 4 is a graph of Common Mode and Differential Mode responses of dual band antenna according to one aspect of the present invention as illustrated in FIG. 2b.

(6) FIG. 5 is a graph of Common Mode and Differential Mode responses of cross dipole dual band antenna according to one aspect of the present invention as illustrated in FIG. 2b.

(7) FIG. 6 is a high impedance dipole with capacitively coupled dipole arms according to another aspect of the present invention.

(8) FIG. 7 is a schematic diagram of the high impedance dipole radiating element with a capacitively coupled matching circuit according to another aspect of the present invention.

(9) FIGS. 8a-8c illustrate radiating element feed boards according to another aspect of the present invention.

(10) FIGS. 9a-9c illustrate radiating element feed boards according to another aspect of the present invention.

(11) FIG. 10 illustrates the feed boards for the high impedance radiating elements arranged in an array.

(12) FIG. 11 illustrates a plan view of a first configuration of a dual band antenna according to the present invention.

(13) FIG. 12 illustrates a plan view of a second configuration of a dual band antenna according to the present invention.

(14) FIG. 13 illustrates a plan view of a third configuration of a dual band antenna according to the present invention.

(15) FIG. 14 illustrates a plan view of a fourth configuration of a dual band antenna according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(16) FIG. 1 schematically diagrams a conventional dual band antenna 10. The dual band antenna 10 includes a reflector 12, a conventional high band radiating element 14 and a conventional low band radiating element 16. Multiband radiating arrays of this type commonly include vertical columns of high band and low band elements spaced at about one-half wavelength to one wavelength intervals. The high band radiating element 14 comprises a half-wave dipole, and includes first and second dipole arms 18 and a feed board 20. Each dipole arm 18 is approximately one-quarter wavelength long at the midpoint of the high band operating frequency. Additionally, the feed board 20 is approximately one-quarter wavelength long at the high band operating frequency.

(17) The low band radiating element 16 also comprises a half-wave dipole, and includes first and second dipole arms 22 and a feed board 24. Each dipole arm 22 is approximately one-quarter wavelength long at the low band operating frequency. Additionally, the feed board 24 is approximately one-quarter wavelength long at the low band operating frequency.

(18) In this example, the combined structure of the feed board 20 (one-quarter wavelength) and dipole arm 18 (one-quarter wavelength) is approximately one-half wavelength at the high band frequency. Since the high band frequency is approximately twice the low band frequency, and wavelength is inversely proportional to frequency, this means that the combined structure also is approximately one-quarter wavelength at the low band operating frequency. As illustrated in FIG. 3, with such a conventional half-wave dipoles, CM resonance (ml) occurs in the critical 700-1000 MHz region, which is where the GSM900 band and Digital Dividend band are located.

(19) FIG. 2a schematically diagrams a dual band antenna 110 according to one aspect of the present invention. The dual band antenna 110a includes a reflector 12, a high band radiating element 114a and a conventional low band radiating element 16. The low band element 16 is the same as in FIG. 1, the description of which is incorporated by reference.

(20) The high band radiating element 114a comprises a high impedance dipole, and includes first and second dipole arms 118 and a feed board 20a. In a preferred embodiment, the dipole arms 118 of the high band radiating element 114a are dimensioned such that the aggregate length of the dipoles arms 118 is approximately three-fourths wavelength of the center frequency of the high band. In wide-band operation, the length of the dipoles may range from 0.6 wavelength to 0.9 wavelength of any given signal in the higher band. Additionally, the feed board 20a is approximately one-quarter wavelength long at the high band operating frequency, keeping the radiating element 114a at the desired height from the reflector 12. In an additional embodiment, a full wavelength, anti-resonant dipole may be employed as the high-impedance radiating element 114a.

(21) In the embodiments of the present invention disclosed above, the combination of the feed board 20a and high impedance dipole arm 118 exceeds one-quarter of a wavelength at low band frequencies. Lengthening the combination of the feed board and dipole arm lengthens the monopole, and tunes CM frequency down and out of the lower band.

(22) In another example, tuning the CM frequency up and out of the lower band may be desired. This example preferably includes capacitively-coupled dipole arms on the high band, high impedance dipole arms 118. FIG. 6 illustrates an example of a high impedance dipole 114b where the dipole arms 118 are capacitively coupled to the feed lines 124 on the feed boards 120. The feed boards 120 include a hook balun 122 to transform an input RF signal from single-ended to balanced. Feed lines 124 propagate the balanced signals up to the radiators. Capacitive areas 130 on a PCB couple to the dipoles 118. Inductive traces 132 couple the feed lines 124 to the capacitive areas 130. See, e.g., U.S. application Ser. No. 13/827,190, which is incorporated by reference. The capacitive areas 130 act as an open circuit at lower band frequencies. Accordingly, as illustrated in FIG. 2b, the dipole arm 118 and feedboard 20b no longer operate as a monopole at low band frequencies of interest. Each structure is independently smaller than ¼ wavelength at low band frequencies. Thus, CM resonance is moved up and out of the lower band.

(23) Another aspect of the present invention is to provide an improved feed board matching circuit to reject common mode resonances. For the reasons set forth above, capacitive coupling is desirable, but an inductive section must be included to re-tune the feedboard once the capacitance is added. However, when the inductor sections 132 are connected to the feed lines 124, the inductor sections 132 coupled with feed lines 124 tend to extend the overall length of the monopole that this high band radiator forms. This may produce an undesirable common mode resonance in the low band.

(24) Additional examples illustrated in FIGS. 7, 8a-8c and 9a-9c improve the LC matching circuit by adding an extra capacitor section in the matching section (using a CLC matching section instead of an LC matching section). Referring to FIGS. 8a-8c, three metallization layers of a feed board 120a are illustrated. A first outer layer is illustrated in FIG. 8a, an inner layer is illustrated in FIG. 8b, and a second outer layer is illustrated in FIG. 8c. The first and second outer layers (FIGS. 8a, 8c) implement the feed lines 124. The inner layer (FIG. 8b) implements hook balun 122, first capacitor sections 134, inductive elements 132, and second capacitor sections 130. The first capacitor sections 134 couple to the feed lines 124 capacitively rather than directly connecting the inductive elements 132 to the feed lines 124. The second capacitor sections 130 are similar to the capacitor from the LC matching circuit illustrated in FIG. 6.

(25) The first capacitor section 134 is introduced to couple capacitively from the feed lines 124 to the inductive sections 132 at high band frequencies where the dipole is desired to operate and acts to help block some of the low band currents from getting to the inductor sections 132. This helps reduce the effective length of the monopole that the high band radiator forms in the lower frequency band and therefore pushes the Common Mode Resonance Frequency higher so that it is up out of the desired low band frequency range. For example, FIG. 4 illustrates that the CM resonance (ml) is moved significantly higher by replacing the standard one-half wavelength radiating element 14 with a high-impedance radiating element 114. In addition to single-polarized dipole radiating elements, the present invention may be practiced with cross dipole radiating elements. FIG. 5 illustrates that the CM resonance is moved out of the low band frequency range when a high-impedance cross dipole is employed.

(26) Referring to FIGS. 9a-9c, another example of a feed board 120b implementing a CLC matching circuit is illustrated. In this example, the first capacitors 134, inductive sections 132, and second capacitors 130 are implemented on the first and second outer layers (FIG. 9a, FIG. 9c, respectively). Hook balun 122 is implemented on the first outer layer (FIG. 9a). Feed sections 124 are implemented on an inner layer (FIG. 9c).

(27) While FIGS. 8a-8c and 9a-9c illustrate multiple layers of metallization for maximum symmetry of the CLC matching circuit, it is contemplated that the feed boards may be implemented on non-laminated PCBs having only two layers of metallization, For example, a PCB with metallization layers as illustrated in FIG. 9a on one side and 9b on the other side.

(28) FIG. 10 is an illustration of two cross dipole radiator feed boards 140a, 140b mounted on a backplane 142 including a feed network 144. The feed board PCBs 140a, 140b are configured to be assembled together via slots in the feed boards as one means of forming the supports for the radiators. There are other means of arranging the feed boards 140a, 140b as well to feed a crossed dipole. The feed boards 140a, 140b are further arranged such that radiator arms (not shown) would be a +/−45 to a longitudinal axis of the backplane.

(29) The antenna array 110 according to one aspect of the present invention is illustrated in plan view in FIG. 11. Low band radiating elements 16 comprise conventional cross dipole elements arranged in a vertical column on reflector 12. High band elements 114 comprise high impedance cross dipole elements and are arranged in a second and third vertical column. Preferably, the high band elements have CLC coupled dipoles, as illustrated in FIG. 7.

(30) The antenna array 210 of FIG. 12 is similar to antenna array 110 of FIG. 11, however, it has only one column of high band radiating elements 114. There are twice as many high band elements 114 as there are low band elements 16. The antenna 310 of FIG. 13 is similar to the antenna 210, but the high band elements are spaced more closely together, and there are more than twice as many high band elements 114 as low band elements 16. FIG. 14 illustrates another configuration of radiating elements in antenna 410. In this configuration, an array of high band elements is disposed in line with, and interspersed with, an array of low band elements 16.

(31) The base station antenna systems described herein and/or shown in the drawings are presented by way of example only and are not limiting as to the scope of the invention. Unless otherwise specifically stated, individual aspects and components of the antennas and feed network may be modified, or may have been substituted therefore known equivalents, or as yet unknown substitutes such as may be developed in the future or such as may be found to be acceptable substitutes in the future, without departing from the spirit of the invention.