An antenna assembly having an operating frequency and a vertical radiation pattern with a main lobe axis defining a downtilt angle with respect to the earth's surface. The antenna assembly comprises a plurality of antennas in first, second, and third antenna groups physically disposed along a backplane, the backplane having a longitudinal axis along which the antennas are disposed, and a phase adjustment mechanism disposed electrically connected between the second first and third antenna groups, such that adjustment of the phase adjustment mechanism results in variation of the vertical radiation pattern downtilt angle.
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24. An A base station array antenna assembly having an operating frequency and a vertical radiation pattern with a main lobe axis defining a downtilt angle with respect to the earth's surface, the antenna assembly comprising:
a plurality of antennas in first, second, and third antenna groups physically disposed along a backplane, the backplane having a longitudinal axis along which the antennas are disposed;
a phase adjustment mechanism disposed electrically connected between the second first and third antenna groups, the phase adjustment mechanism including:
an input coupling element;
a movable coupling section having a pivotally mounted first end electromagnetically coupled to the input coupling element; and
a semicircular, air-substrated transmission line section electromagnetically coupled to a second end of the movable coupling section;
such that pivotal position adjustment of the phase adjustment mechanism results in variation of the vertical radiation pattern downtilt angle between a first fixed position and a second fixed position.
1. An A base station array antenna assembly having an operating frequency and a vertical radiation pattern with a main lobe axis defining a downtilt angle with respect to the earth's surface, the antenna assembly comprising:
a plurality of antenna means in first, second, and third antenna groups physically disposed along a backplane, the backplane having a longitudinal axis along which the antenna means are disposed;
differential phase adjustment means disposed electrically connected on a path of transmission line means between the second first and third antenna groups configured to simultaneously advance a phase angle of a signal to one of said second first and third antenna groups and delay the phase angle of said signal to the other of said second first and third antenna groups;
such that adjustment of the phase adjustment means results in variation of the vertical radiation pattern downtilt angle between a first fixed position and a second fixed position;
said differential phase adjustment means including coupling means arcuately moveable along an arcuate section of said transmission line means to cause said simultaneous advance of a phase angle of a signal to one of said first and third antenna groups and a delay of the phase angle of said signal to the other of said first and third antenna groups.
32. An A base station array antenna assembly having an operating frequency and a vertical radiation pattern with a main lobe axis defining a downtilt angle with respect to the earth's surface, the antenna assembly comprising:
a plurality of antennas in first, second, and third antenna groups physically disposed along a backplane, the backplane having a longitudinal axis along which the antennas are disposed;
a phase adjustment mechanism disposed electrically connected between the second first and third antenna groups, the phase adjustment mechanism including:
an input coupling element;
a movable coupling section having a pivotally mounted first end electromagnetically coupled to the input coupling element; and
a semicircular, air-substrated transmission line section electromagnetically coupled to a second end of the movable coupling section;
the phase adjustment mechanism having a range of adjustment including a minimum downtilt position, a mid-point, and a maximum downtilt position;
a drive mechanism coupled to the movable coupling section;
electrical path lengths at the operating frequency, from the input coupling element to each of the antennas, are selected to define a progressive phase shift between each of the antennas such that, with the phase adjustment mechanism set at its mid-point, the vertical radiation pattern downtilt angle is approximately 7 degrees;
such that adjustment of the phase adjustment mechanism results in variation of the vertical radiation pattern downtilt angle.
2. The antenna assembly of
4. The antenna assembly of
5. The antenna assembly of
6. The antenna assembly of
8. The antenna assembly of
9. The antenna assembly of
input coupling means;
movable coupling means having a pivotally mounted first end electromagnetically coupled to the input coupling means; and
transmission line means electromagnetically coupled to a second end of the movable coupling means.
10. The antenna assembly of
13. The antenna assembly of
14. The antenna assembly of
15. The antenna assembly of
16. The antenna assembly of
17. The antenna assembly of
18. The antenna assembly of
19. The antenna assembly of
the phase adjustment means has a range of adjustment including a minimum downtilt position, a mid-point, and a maximum downtilt position; and
electrical path lengths at the operating frequency, from the input coupling means to each of the antenna means, are selected to define a progressive phase shift between each of the antenna means such that, with the phase adjustment means set at its mid-point, the vertical radiation pattern downtilt angle is approximately 7 degrees.
20. The antenna assembly of
21. The antenna assembly of
22. The antenna assembly of
23. The antenna assembly of
25. The antenna assembly of
27. The antenna assembly of
28. The antenna assembly of
29. The antenna assembly of
the phase adjustment mechanism has a range of adjustment including a minimum downtilt position, a mid-point, and a maximum downtilt position; and
electrical path lengths at the operating frequency, from the input coupling element to each of the antennas, are selected to define a progressive phase shift between each of the antennas such that, with the phase adjustment mechanism set at its mid-point, the vertical radiation pattern downtilt angle is approximately 7 degrees.
30. The antenna assembly of
31. The antenna assembly of
33. The antenna assembly of
0. 34. The antenna assembly of claim 1 wherein the coupling means is capacitively coupled to the transmission line means.
0. 35. The antenna assembly of claim 1 wherein the coupling means includes a pivotally mounted, electrically conductive section.
0. 36. The antenna assembly of claim 1 further comprising drive means coupled to the coupling means.
0. 37. The antenna assembly of claim 36 wherein the drive means comprises an electric motor.
0. 38. The antenna assembly of claim 36 wherein the drive means receives control inputs from a remote location.
0. 39. The antenna assembly of claim 38 wherein the drive means further includes means configured to transmit position information relating to the phase adjustment means to the remote location.
0. 40. The antenna assembly of claim 39 wherein said means configured to transmit position information includes a position detector.
0. 41. The antenna assembly of claim 40 wherein said position detector comprises a Hall effect sensor, an optical encoder, a synchro servo system or other position detection device.
0. 42. The antenna assembly of claim 36 wherein said drive mechanism is a resolver, or servomotor, or stepping motor or other electric motor, or other positioning device.
0. 43. The antenna assembly of claim 1 wherein at least one of said antenna groups includes in a feed comprising a dielectric-substrated microstrip transformer.
0. 44. The antenna assembly of claim 1 wherein said arcuate section of said transmission line means comprises an air-substrated metal conductor.
0. 45. The antenna assembly of claim 24 wherein the second end of the movable coupling section is capacitively coupled to the transmission line section.
0. 46. The antenna assembly of claim 24 wherein at least one of said antenna groups includes in a feed comprising a dielectric-substrated microstrip transformer.
0. 47. The antenna assembly of claim 25 wherein said drive mechanism comprises a resolver, or servomotor or stepping motor or other electric motor, or other positioning device.
0. 48. The antenna assembly of claim 28 wherein the drive mechanism includes a position detector.
0. 49. The antenna assembly of claim 48 wherein said position detector comprises a Hall effect sensor, an optical encoder, a synchro servo system or other position detection device.
0. 50. A plurality of antenna assemblies each as defined in claim 1, supported by a tower or other common support structure.
0. 51. The assemblies of claim 50 designed such that each assembly covers a sector of a cell.
0. 52. The assemblies of claim 51 comprising three in number, wherein each of the assemblies covers a 120 degree sector of a cell.
0. 53. The assemblies of claim 50, wherein each assembly is coupled to a drive mechanism receiving control inputs provided from a remote location.
0. 54. The assemblies of claim 53, wherein each assembly provides beam position information to the remote location.
0. 55. The assemblies of claim 54, wherein the position information is provided in each assembly by a position detector.
0. 56. The assemblies of claim 55 wherein the position detector comprises a Hall effect sensor, a synchro/servo system, or optical encoder.
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This invention relates generally to antennas and in particular to antennas having variable radiation patterns, and is more particularly directed toward an antenna in which the vertical radiation pattern downtilt angle is electrically variable.
RF (radio frequency) communication systems that act to maximize spectrum efficiency through frequency reuse include cellular radiotelephone systems, some types of trunked communication systems, among others. A common feature that these systems generally share is the division of a service area into smaller areas known as “cells.”
Within each cell, a group of relatively low power base stations provides RF communication services to subscribers within that cell over a group of RF channels. Because of the low power, the same group of RF channels may be reused only a short distance away to provide communication services to subscribers in another (although not generally adjacent) cell.
Although offering distinct advantages in terms of spectrum efficiency, a system of the type just described demands considerable investment in infrastructure. Because of the relatively small cell size, a large number of cells may be required to provide adequate service over a large coverage area, and each cell requires a number of base stations, a controller, and an antenna system.
The type of antenna system selected for use within a cell is important both for maximizing system efficiency and for effectively tailoring system operation for particular categories of users. In many systems, each cell is further divided into sectors, multiplying at least the receive antenna requirement for the cell by the number of sectors selected. In a commonly used configuration, each cell is divided into six equal sectors, with each sector having its own directional receive antenna with a radiation pattern closely approximating the sector shape. A single transmit antenna having an omnidirectional radiation pattern is used for transmission into all sectors of the cell.
In other cell configurations, the cell may be divided into sectors for transmitting, as well. This type of system is useful for dealing with cells having irregular boundaries caused, for example, by natural or man-made obstructions. Omnidirectional transmit patterns, in contrast, are most often employed where the desired coverage pattern is approximately circular in shape.
Naturally, antenna systems used in sectored cells are directional antennas. Although the radiation patterns of these antennas are selected to approximate the sector shape, the patterns are not generally easy to alter after installation. A need to alter the radiation pattern may arise based upon studies of system performance, newly constructed obstacles to RF propagation, altering of the shapes of adjacent cells, or for a variety of other reasons.
It may even be required that cell boundaries be altered as a function of time. During periods of relatively low usage, in the evenings and on weekends and holidays, for example, overlapping coverage areas can be created by extending the radiation patterns of the antennas slightly into adjacent cells. This increases the number of channels available to users in the overlap areas, and minimizes the need for hand-offs, but it also increases the likelihood that co-channel interference may occur. During peak periods, when many channels are in use providing service to a relatively large number of users, the radiation patterns should be restored to a state that minimizes adjacent cell overlap.
Of course, extension of radiation patterns can be done with power control, but increasing the power of the RF signals transmitted by the antenna directly impacts the likelihood of undesired interference. Another way of altering antenna radiation patterns is to physically move the antennas themselves, but this is difficult to do after initial installation. It is possible, of course, to provide a mechanism to alter an antenna's azimuth and elevation, much the same way a radar antenna is moved, but such mechanisms are expensive, and the mechanical linkages required to support such movement would degrade the structural integrity of the antenna mounting system.
Accordingly, a need arises for an antenna system that provides an economical and easily manipulated adjustment to its radiation pattern without compromising the integrity of its mechanical mounting structure.
These needs and others are satisfied by the antenna assembly of the present invention, having an operating frequency and a vertical radiation pattern with a main lobe axis defining a downtilt angle with respect to the earth's surface. The antenna assembly comprises a plurality of antenna means in first, second, and third antenna groups disposed along a backplane, the backplane having a longitudinal axis along which the antenna means are disposed, and a phase adjustment means second first and third antenna groups 116 115, 117. Operation and effect of the phase adjustment mechanism 108 will be discussed in detail subsequently.
As can be appreciated more readily from an examination of the side view of
The backplane 111 also provides a mounting surface for an RF connector 109, the phase adjustment mechanism 108, and a plurality of dielectric-substrated microstrip transformers 112-114 used as power dividers, and the transmission lines that interconnect the antenna assembly components (1105-1110 in
The antenna assembly 100 includes five individual, log-periodic dipole array (LPDA) antennas 101-105, the design of which is generally well-known in the art. The particular configuration used in the preferred embodiment of the invention is illustrated in
As can be appreciated from an examination of
The phase adjustment mechanism 108, illustrated in
The input coupling element 301 is electromagnetically coupled to movable coupling means, such as a movable coupling section 302, which is fixed near a first end to a pivot point 303. The movable coupling section 302 is also preferably formed from a sheet of 0.062 inch half-hard brass. The second end of the movable coupling section 302 terminates in a conductive plate 304 that is electromagnetically coupled to transmission line means, such as a semicircular, air-substrated transmission line section 305. Preferably, the conductive plate 304 is an integrally formed part of the movable coupling section 302.
The semicircular transmission line section 305, which is also preferably formed from 0.062 inch half-hard brass sheet stock, has first and second opposed end portions 306, 307 from which antenna feeder cables (1109, 1110 in
Ground connection brackets 308, 309 are provided near the respective opposed end portions 306, 307 for attachment of the shield portions of the antenna feeder cables. A similar ground bracket 310 is provided near the input coupling element 301 for attachment of the shield of an antenna assembly cable (1102 in
From one of the opposing ends 307 of the semicircular transmission line section 305, a first antenna feeder cable (1109 in
Power divider 112, illustrated in
The vertical radiation pattern 1000, illustrated in
The radiation pattern 1000 can be tilted down with respect to the earth's surface (the 0 degree reference line) by feeding the individual antennas 101-105 slightly out of phase with one another. In order to avoid significant side lobe (1001, 1002, for example) distortion in the radiation pattern 1000, the phase shift is ordinarily made progressive. In other words, one of the antennas or antenna groups in the antenna assembly 100 (the first antenna group 115, in the preferred embodiment) is chosen as the reference group for phase purposes.
The RF signal applied to the next antenna 102 is then phase shifted by some amount X with respect to the reference antenna 101. The RF signal applied to the third antenna 103 is phase shifted by X degrees with respect to the second antenna 102 (2X degrees with respect to the first antenna 101). This progressive phase shift is continued for all of the antennas 101-105 in the antenna assembly 100.
For the antenna assembly 100 of the present invention, with the phase adjustment mechanism 108 positioned at its mid-point, the progressive phase shift is approximately equal to one inch (each of the transmission paths to the individual antennas differs in electrical length, at the design operating frequency, by one inch, resulting in a phase shift of about 30 degrees at the operating frequency) and the vertical pattern tilts down five degrees.
The overall electrical path length, measured from the output of power divider 113, where the input signal splits, to the point where the antenna cable 1109 couples to the first antenna 101, is approximately 20 inches, with the phase adjustment mechanism 305 at its mid-point 1101. This means, of course, that approximately one-half of the semicircular, air-substrated transmission line section 305 is included in the electrical path length for antennas of the first antenna group 115 and antennas of the third antenna group 117.
Similarly, the overall electrical path length from the divider 113 output point to the second antenna 102 is 21 inches, to the third antenna 103 is 22 inches, to the fourth antenna 104 is 23 inches, and to the fifth antenna 105 is 24 inches, all with the phase adjustment mechanism 108 set at its mid-point 1101.
Thus, with the phase adjustment mechanism 108 set at its mid-point 1101, a true progressive phase shift of approximately 30 degrees has been established between the antennas 101-105 of the antenna assembly. With the phase adjustment mechanism 108 set at this mid-point 1101 position, the radiation pattern of the antenna exhibits a 5 degree downtilt as illustrated in
Moving the phase adjustment mechanism to its maximum downtilt position 1112 shortens the effective electrical path lengths from the phase adjustment mechanism input point 1103 to the first antenna group 115, while lengthening the paths to the antennas 104-105 of the third antenna group 117. Of course, since the second antenna group is not fed through the phase adjustment mechanism, the path length to the second antenna group does not change.
In the preferred embodiment, the effective electrical path length to the first antenna group 101 is now about 18 inches, to the fourth antenna 104 about 25 inches, and to the fifth antenna 105 about 26 inches.
The relative phase relationships induced as a result of these electrical path lengths causes a vertical radiation pattern downtilt of about 14 degrees, as shown in
With the phase adjustment mechanism set at its minimum downtilt position 1113, at least some of the phase relationships among the antennas of the first and second antenna groups 106, 107 are effectively reversed. The electrical path length to the first antenna 101 is now lengthened to 22 inches. The electrical path length to the fourth antenna is about 21 inches, and the path to the fifth antenna is about 22 inches.
The effect on the vertical radiation pattern of the antenna assembly 100 with the phase adjustment mechanism 108 set at this minimum downtilt position 1113 is to restore the downtilt angle to zero degrees, as illustrated in
Of course, adjusting the phase adjustment mechanism directly, by climbing an associated antenna support structure, would be nearly as inconvenient as adjusting the antenna mounting assembly to tilt the antenna.
With the antenna assembly 100 mounted in its normal operation position on a support structure, drive means, such as a drive mechanism 1401 is provided, mechanically connected to the movable coupling element of the phase adjustment mechanism 108. The drive mechanism may be an electric motor, a resolver or servomotor, a stepping motor, or any of a number of known positioning devices. Control inputs 1403 for the drive mechanism 1401 may be provided from a remote location, such as a maintenance facility of the local service provider.
Position information 1404 is provided to the remote location by a position detector 1402. The position detector may be implemented by Hall effect sensors, optical encoders, a synchro/servo system, or any of a number of other known position detection devices.
There has been described herein an electrically variable beam tilt antenna that is relatively free from the shortcomings of prior art antenna systems. It will be apparent to those skilled in the art that modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except as may be necessary in view of the appended claims.
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