Multi-beam sector split base station antenna with beamforming network based on improved No matrix

Abstract

A multi-beam base station antenna includes first to M first polarization RF ports, an antenna array including N columns of radiating elements, and a first polarization beamforming network having M rows, N columns of directional couplers, where each row has a different number of directional couplers, where M and N are natural numbers, wherein the last directional coupler in the top row has a port coupled to ground via a mating terminal.

Description

Technical Field

[0001] The present invention generally relates to radio communications, and more particularly, to multi-beam sector split base station antennas used in cellular and other communication systems. Background Art

[0002] Cellular communication systems are well known in the art. In a typical cellular communication system, a geographic area is divided into a series of regions called "cells", each cell being served by a base station. The base station may include baseband equipment, a radio, and a base station antenna configured to provide two-way radio frequency ("RF") communication with users located throughout the cell. In many cases, a cell may be divided into multiple "sectors" in the azimuth plane (the horizontal plane that bisects the antenna, which is parallel to the plane defined by the horizontal line), and separate base station antennas provide coverage for each sector. The base station antenna is typically mounted on a tower or other elevated structure, and the radiation pattern ("antenna beam") generated by the antenna points outward to serve the corresponding sector.

[0003] A common base station configuration is a "three-sector" configuration, in which a cell is divided into three 120° sectors in the azimuth plane, and the base station includes three base station antennas that provide coverage for the three corresponding sectors. Typically, each base station antenna will include one or more vertically extending columns of radiating elements, each vertically extending column being configured to generate a separate antenna beam (or, if dual-polarized radiating elements are used, two antenna beams, as is well understood in the art). Each column of radiating elements is connected to a feed network that subdivides the RF signal and feeds each sub-component of the RF signal to a corresponding subset of one or more radiating elements in the column. Typically, each radiating element is configured to generate a radiation pattern that has a half-power beam width ("HPBW") of approximately 65° in the azimuth plane, which ensures that the antenna beam provides good coverage throughout the 120° sector. The sub-components of the RF signal are phase-aligned such that the radiation patterns generated by each subset of one or more radiating elements constructively combine to produce a composite antenna beam in the elevation (vertical) plane with a narrowed HPBW (e.g., 15° - 30°).

[0004] As the capacity demand grows, cellular network operators now divide some cells into more than three sectors. For example, a cell can now be divided into six, nine, twelve, fifteen, or eighteen sectors in the azimuth plane. Generally, when a cell is divided into more than three sectors, multi-beam "sector splitting" antennas are used. A multi-beam sector splitting antenna refers to a base station antenna that generates multiple antenna beams (for each polarization), where the multiple antenna beams have a narrowed beam width in the azimuth plane (i.e., an azimuth HPBW less than about 65° and typically less than about 35°), and the pointing directions of the multiple antenna beams are designed to split the sector into multiple sub-sectors. This allows a single base station antenna to generate multiple antenna beams (for each polarization) that provide coverage for the corresponding sub-sectors of a 120° sector.

[0005] For example, a six-sector base station will divide each 120° sector into two 60° sub-sectors in the azimuth plane. This six-sector base station is typically served by three base station antennas, each implemented as a "dual-beam" antenna, which is designed to generate a first antenna beam and a second antenna beam (for each polarization) that provide coverage for the corresponding first and second 60° sub-sectors of each 120° sector. Each antenna beam can have an HPBW of about 30 - 35° in the azimuth plane. The first antenna beam can point at an angle of about -27° to -30° from the "boresight" pointing direction of the antenna in the azimuth plane, and the second antenna beam can point at an angle of about 27° to 30° from the "boresight" pointing direction of the antenna in the azimuth plane. The boresight pointing direction of the antenna is the center of the 120° sector served by the antenna in the azimuth plane. In this way, the 120° sector is divided into two 60° sub-sectors covered by the corresponding first and second antenna beams.

[0006] Providing cellular service in large venues such as stadiums, arenas, convention centers, concert halls, etc. can be particularly challenging because a very large number of users may be located in a very small area. In such venues, multi-beam sector splitting base station antennas that generate four, five, six, or more antenna beams for each polarization can be used, where each antenna beam provides coverage for a corresponding 20° - 30° (or smaller) sub-sector in the azimuth plane. When a 120° sector is subdivided into a large number of sub-sectors (e.g., 4 - 6 sub-sectors), the system capacity can increase significantly because the RF energy of each antenna beam is focused into a smaller area, and thus provides a higher antenna gain.

[0007] To generate an antenna beam having a narrowed beam width in the azimuth plane, a multi-beam sector-splitting base station antenna typically includes at least one multi-column antenna array because the effect of transmitting RF signals through multiple columns of radiating elements is to expand the aperture of the antenna in the azimuth plane, which narrows the azimuth beam width of the generated antenna beam. For example, a dual-beam antenna typically uses an array of three or four columns of radiating elements, and a multi-beam antenna that generates three or more antenna beams for each polarization provides more columns. Although separate multi-column arrays of radiating elements can be used to generate each antenna beam, this method is generally commercially unacceptable because the antennas produced in this way are very large and expensive. Therefore, a multi-beam antenna typically includes a beamforming network that allows multiple RF signals to be transmitted through a single multi-column array of radiating elements to generate multiple corresponding antenna beams directed in different directions.

[0008] For example, a multi-beam sector-splitting antenna (for each polarization) including multiple RF ports is known in the art, and the multiple RF ports are coupled to a multi-column array of radiating elements through a beamforming network based on a Butler matrix. The beamforming network generates multiple antenna beams (for each polarization) based on the RF signals input at the multiple RF ports, and the antenna beams are electrically steered so that each antenna beam provides coverage of a different sub-sector of, for example, a 120° sector. Unfortunately, a multi-beam antenna based on a Butler matrix may have many disadvantages. In particular, a beamforming network based on a Butler matrix is expensive, and the azimuth beam width of the generated antenna beams may be greater than desired, which reduces both the antenna gain and increases the interference between sub-sectors. A multi-beam antenna with a beamforming network based on a Butler matrix also suffers from what is referred to as "beam peak walking", which refers to the phenomenon that the azimuth pointing angle of each antenna beam shifts according to the frequency of the input RF signal. Beam peak walking occurs in a beamforming network based on a Butler matrix because the phase difference between the outputs of the Butler matrix is independent of the frequency of the RF signals input to the Butler matrix, while the spacing between the columns of the radiating elements is frequency-dependent. Summary of the Invention

[0009] According to an embodiment of the present invention, there is provided a multi-beam antenna, the multi-beam antenna including: first to M first-polarization RF ports; an antenna array including N columns of radiating elements; and a first-polarization beamforming network having M rows and N columns of directional couplers, where each row has a different number of directional couplers, and M and N are natural numbers.

[0010] In some embodiments, the top row of the M rows of directional couplers has the most directional couplers, and each row below the top row has one less directional coupler than the row above it.

[0011] In some embodiments, the coupling ports of each directional coupler in the top row of the M-row directional couplers are coupled to a corresponding column of radiating elements among the N-column radiating elements.

[0012] In some embodiments, the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first-polarization RF ports in the first-polarization RF ports.

[0013] In some embodiments, the through port of the last directional coupler in the top row of the M-row directional couplers is coupled to ground electrically via a matching terminal.

[0014] In some embodiments, except for the last directional coupler in each row of the M-row directional couplers, the through port of each directional coupler in each row of the M-row directional couplers is coupled to the input port of the corresponding adjacent directional coupler in the row through a corresponding first delay element.

[0015] In some embodiments, except for the top row of the M-row directional couplers, the through port of the last directional coupler in each row of the M-row directional couplers is coupled to the isolation port of the last directional coupler in the row below the row of the M-row directional couplers through a second delay element.

[0016] In some embodiments, the isolation port of each directional coupler in the bottom row of the M-row directional couplers is coupled to ground electrically via a corresponding matching terminal.

[0017] In some embodiments, the isolation port of each directional coupler in the bottom row of the M-row directional couplers is coupled to a synthesizer, and the output of the synthesizer is coupled to ground via a matching terminal.

[0018] In some embodiments, except for the last directional coupler in each row of the M-row directional couplers, the through port of each directional coupler in each row of the M-row directional couplers is coupled to the input port of the corresponding adjacent directional coupler in the row through a corresponding phase shifter.

[0019] In some embodiments, except for the top row of the M-row directional couplers, the through port of the last directional coupler in each row of the M-row directional couplers is coupled to the isolation port of the last directional coupler in the row below the row of the M-row directional couplers through a corresponding phase shifter.

[0020] According to an embodiment of the present invention, a multi - beam antenna is provided. The multi - beam antenna includes: an antenna array, the antenna array including N columns of radiating elements; and a first - polarization beam - forming network, the first - polarization beam - forming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row, wherein each row of directional couplers below the top row has one less directional coupler than the row above it. The last directional coupler in the top row has a port coupled to ground via a matching terminal.

[0021] In some embodiments, the top row has N directional couplers, and the coupled ports of each directional coupler in the top row are coupled to a corresponding one of the N columns of radiating elements.

[0022] In some embodiments, the multi - beam antenna further includes first to M first - polarization RF ports, wherein the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first - polarization RF ports.

[0023] In some embodiments, for each row of directional couplers, except for the last directional coupler in the row, the through - port of each directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding first delay element.

[0024] In some embodiments, for each row of directional couplers except the top row, the through - port of the last directional coupler in the row is coupled to the isolation port of the last directional coupler in the row of directional couplers below it through a second delay element.

[0025] In some embodiments, the isolation port of each directional coupler in the bottom row is coupled to ground electrically via a corresponding matching terminal.

[0026] In some embodiments, the isolation port of each directional coupler in the bottom row is coupled to a synthesizer, and the output of the synthesizer is coupled to ground via a matching terminal.

[0027] In some embodiments, the through - port of each directional coupler in each row except the last directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding phase shifter.

[0028] In some embodiments, except for the top row, the through - port of the last directional coupler in each row of directional couplers is coupled to the isolation port of the last directional coupler in the row of directional couplers below it through a corresponding phase shifter.

[0029] According to an embodiment of the present invention, a multi-beam antenna is provided. The multi-beam antenna includes: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row. For each row of directional couplers, except for the last directional coupler in the row, the through-port of each directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding first delay element. Additionally, for each row of directional couplers except the top row, the through-port of the last directional coupler in the row is coupled to the isolation port of the last directional coupler in a row of directional couplers below the row through a second delay element.

[0030] In some embodiments, the top row has N directional couplers, and the coupling port of each directional coupler in the top row is coupled to a corresponding one of the N columns of radiating elements.

[0031] In some embodiments, the multi-beam antenna further includes first to M first polarization radio frequency ("RF") ports, where the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first polarization RF ports.

[0032] In some embodiments, the isolation port of each directional coupler in the bottom row is coupled to electrical ground via a matching terminal.

[0033] According to an embodiment of the present invention, a multi-beam antenna is provided. The multi-beam antenna includes: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row, a bottom row, and multiple additional rows between the top row and the bottom row, where the top row and the bottom row each include the same number of directional couplers, and at least one of the additional rows includes fewer directional couplers than the top row.

[0034] In some embodiments, an additional row immediately below the top row in the additional rows includes the same number of directional couplers as an additional row immediately above the bottom row in the additional rows.

[0035] In some embodiments, the through-port of the last directional coupler in the top row is coupled to electrical ground via a matching terminal.

[0036] In some embodiments, the coupling port of each directional coupler in the top row is coupled to a corresponding one of the N columns of radiating elements.

[0037] In some embodiments, the first directional coupler in each row is coupled to a respective one of the first polarized RF ports in the first polarized RF ports. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1A is a schematic block diagram of a multi-beam sector-split base station antenna based on a conventional Butler matrix.

[0039] Figure 1B is a block diagram showing how RF signals are distributed to Figure 1A radiating elements in each column of a multi-column array.

[0040] Figures 2A - 2C is Figures 1A - 1B azimuth patterns of the left three of the six first polarized antenna beams generated by a conventional base station antenna when excited with RF signals at frequencies of 1.7 GHz, 2.2 GHz, and 2.7 GHz, showing how the beam peaks "walk" with frequency in the azimuth plane.

[0041] Figure 3A is a schematic block diagram of a multi-beam sector-split antenna including a beamforming network based on an MxN Blass matrix.

[0042] Figure 3B is a schematic block diagram of a multi-beam sector-split antenna including a beamforming network based on an MxN Nolen matrix.

[0043] Figure 4A is a perspective view of a 2T2R multi-beam sector-split base station antenna including a beamforming network based on a modified Nolen matrix according to an embodiment of the present invention.

[0044] Figure 4B is Figure 4A a schematic front view of a multi-column array included in the base station antenna.

[0045] Figure 4C is Figure 4A a schematic block diagram of a multi-beam sector-split base station antenna.

[0046] Figure 4D is Figure 4C a highly magnified view of the portion labeled "4D" in , which better shows the connections between directional couplers in different rows and columns of the beamforming network based on the modified Nolen matrix.

[0047] Figure 5A is a simulated azimuth pattern of the main lobes of six first polarized antenna beams generated by Figure 4A the multi-beam antenna for five different frequency RF input signals.

[0048] Figure 5B is a graph showing the simulation beam peak walking performance of a multi-beam sector split base station antenna Figure 4A of

[0049] Figure 6 is a combination of a side view and several plan views, showing Figure 4A a printed circuit board implementation of one of the improved Nolen matrix beamforming networks included in a multi-beam base station antenna

[0050] Figure 7A is a perspective view of a scannable multi-beam sector split base station antenna according to other embodiments of the present invention

[0051] Figure 7B is Figure 7A a schematic front view of a multi-column antenna array included in a base station antenna

[0052] Figure 7C is Figure 7A a schematic block diagram of a scannable multi-beam base station antenna

[0053] Figure 7D is a series of graphs showing how the pointing direction of an antenna beam generated by a scannable multi-beam base station antenna can be scanned in the azimuth plane

[0054] Figure 8 is a schematic block diagram of a multi-beam sector split base station antenna according to other embodiments of the present invention

[0055] Figure 9 is a schematic front view of a dual-band base station antenna including a multi-column array in one of several frequency bands according to an embodiment of the present invention

[0056] Figure 10 is a schematic block diagram of a multi-beam sector split base station antenna having a beamforming network that is a hybrid of a Blass matrix and a Nolen matrix according to other embodiments of the present invention Detailed implementation

[0057] Figure 1A and 1B are schematic diagrams together showing the RF signal path of a six-beam (per polarization) sector split antenna 1 based on a conventional Butler matrix. In particular, Figure 1A is a schematic block diagram of base station antenna 1, showing the RF signal paths from the RF ports of the antenna to the columns of a multi-column array of radiating elements, and Figure 1B is a schematic block diagram showing how RF signals are distributed to the radiating elements in each column of a multi-column array of radiating elements

[0058] AsFigure 1A As shown in Figure 1A , the multi-beam sector split base station antenna 1 includes twelve RF connector ports 20-1 to 20-12 (also referred to herein as "RF ports"), and the RF connector ports are used to input RF signals from one or more radio devices such as remote radio heads into the base station antenna 1. Herein, when multiple identical elements are included in the antenna, these elements can be individually referred to by their complete reference numbers (e.g., RF connector port 20-2), and can be collectively referred to by the first part of their reference numbers (e.g., RF connector port 20). The antenna 1 further includes an antenna array 30 having ten columns 32-1 to 32-10 of dual-polarized radiating elements 34, and the ten columns of dual-polarized radiating elements are mounted to extend forward from the reflector 12 (only columns 32-1 and 32-10 are explicitly numbered in Figure 1A to simplify the drawing; it should be understood that the columns 32 are arranged in numerical order). Each dual-polarized radiating element 34 includes a first-polarized radiator 36-1 and a second-polarized radiator 36-2. The base station antenna 1 further includes a pair of beamforming networks ("BFN") 40-1, 40-2 (one for each polarization) and a pair of feed networks 50-1, 50-2 (likewise, one for each polarization). Figure 1A As shown in Figure 1A , only columns 32-1 and 32-10 are explicitly numbered to simplify the drawing; it should be understood that the columns 32 are arranged in numerical order. Each dual-polarized radiating element 34 includes a first-polarized radiator 36-1 and a second-polarized radiator 36-2. The base station antenna 1 further includes a pair of beamforming networks ("BFN") 40-1, 40-2 (one for each polarization) and a pair of feed networks 50-1, 50-2 (likewise, one for each polarization).

[0059] The RF connector ports 20-1 to 20-12 may include, for example, RF connectors and may be connected to the RF ports on one or more radio devices via, for example, coaxial cables. The radio devices are typically external to the antenna 1 and are not shown in Figure 1A . Each beamforming network 40 is implemented as a 6x6 Butler matrix. The six first-polarized RF connector ports 20-1 to 20-6 are connected to the six inputs 42-1 to 42-6 of the Butler matrix 40-1, and the six second-polarized RF connector ports 20-7 to 20-12 are connected to the six inputs 42-7 to 42-12 of the Butler matrix 40-2. The six outputs 44-1 to 44-6 of the Butler matrix 40-1 are connected by the feed network 50-1 to the ten-column antenna array 30, and the six outputs 44-7 to 44-12 of the Butler matrix 40-2 are connected by the feed network 50-2 to the ten-column antenna array 30. In Figure 1A , only inputs 42-1, 42-6, 42-7, and 42-12 and only outputs 44-1, 44-6, 44-7, and 44-12 are explicitly numbered to simplify the drawing; it should be understood that the inputs and outputs of the beamforming network 40 are arranged in numerical order. Figure 1A The RF connector ports 20-1 to 20-12 may include, for example, RF connectors and may be connected to the RF ports on one or more radio devices via, for example, coaxial cables. The radio devices are typically external to the antenna 1 and are not shown in Figure 1A . Each beamforming network 40 is implemented as a 6x6 Butler matrix. The six first-polarized RF connector ports 20-1 to 20-6 are connected to the six inputs 42-1 to 42-6 of the Butler matrix 40-1, and the six second-polarized RF connector ports 20-7 to 20-12 are connected to the six inputs 42-7 to 42-12 of the Butler matrix 40-2. The six outputs 44-1 to 44-6 of the Butler matrix 40-1 are connected by the feed network 50-1 to the ten-column antenna array 30, and the six outputs 44-7 to 44-12 of the Butler matrix 40-2 are connected by the feed network 50-2 to the ten-column antenna array 30. In Figure 1A , only inputs 42-1, 42-6, 42-7, and 42-12 and only outputs 44-1, 44-6, 44-7, and 44-12 are explicitly numbered to simplify the drawing; it should be understood that the inputs and outputs of the beamforming network 40 are arranged in numerical order. Figure 1A In Figure 1A , only inputs 42-1, 42-6, 42-7, and 42-12 and only outputs 44-1, 44-6, 44-7, and 44-12 are explicitly numbered to simplify the drawing; it should be understood that the inputs and outputs of the beamforming network 40 are arranged in numerical order.

[0060] As Figure 1AAlso shown is that the feed network 50-1 includes four power dividers 52-1 to 52-4, each power divider for connecting a selected output among the outputs 44-1 to 44-6 of the Butler matrix 40-1 to a respective pair of columns 32 of the antenna array 30. In particular, the power divider 52-1 connects the output 44-1 of the Butler matrix 40-1 to the third column 32-3 and the ninth column 32-9, the power divider 52-2 connects the output 44-2 of the Butler matrix 40-1 to the fourth column 32-4 and the tenth column 32-10, the power divider 52-3 connects the output 44-5 of the Butler matrix 40-1 to the first column 32-1 and the seventh column 32-7, and the power divider 52-4 connects the output 44-6 of the Butler matrix 40-1 to the second column 32-2 and the eighth column 32-8. The output 44-3 of the Butler matrix 40-1 is connected to the fifth column 32-5, and the output 44-4 of the Butler matrix 40-1 is connected to the sixth column 32-6. Thus, the six outputs 44-1 to 44-6 of the Butler matrix 40-1 feed all ten columns 32 of the antenna array 30. Four additional power dividers 52-5 to 52-8 are provided, which connect selected outputs among the outputs 44-7 to 44-12 of the Butler matrix 40-2 to the respective pairs of columns 32 of the antenna array 30 in a similar manner.

[0061] Figure 1B Shows the connections between the beamforming networks 40-1, 40-2 and the radiating elements 34 of the column 32-5 of the antenna array 30. As Figure 1B shown, the output 44-3 of the Butler matrix 40-1 is coupled to the first phase shifter assembly 56-1. The first phase shifter assembly 56-1 includes a 1x4 power divider that divides the input RF signal into four sub-components, and also includes an adjustable phase shifter configured to apply a progressive phase on the four sub-components so as to electronically change the tilt angle of the antenna beam generated by the radiating elements 34 in the column 32-5. Each output 58 of the first phase shifter assembly 56-1 is coupled to a respective feed plate 60. A pair of radiating elements 34 are mounted on each feed plate 60. A power divider 62 is provided on each feed plate 60, which divides the RF signal input to it from the respective output 58 of the first phase shifter assembly 56-1 into a first sub-component and a second sub-component, and the first sub-component and the second sub-component are transmitted to the respective first and second radiating elements 34 mounted on the feed plate 60. As can be seen, Figure 1BThe portion of the feed network 50-1 depicted feeds the output 44-3 of the Butler matrix 40-1 to the first polarization radiator 36-1 of the radiating element 34 in column 32-5. A second phase shifter assembly 56-2 and four additional feed board power dividers 62 are provided for similarly feeding the RF signals output from the output 44-9 of the Butler matrix 40-2 to the second polarization radiator 36-2 of the radiating element 34 in column 32-5. It should be understood that each of the other nine columns 32 of the antenna array 30 is fed in the same manner as shown in Figure 1B as shown.

[0062] The conventional multi-beam sector split base station antenna 1 has many drawbacks. First, the manufacturing cost of the antenna 1 can be high. Also, the operating bandwidth can be relatively narrow (e.g., less than 25% of the center frequency of the operating frequency band), and the azimuth HPBW (at each polarization) of each of the six antenna beams can be wider than desired and can vary significantly with frequency. Additionally, the generated antenna beams exhibit significant beam peak walking.

[0063] Figures 2A - 2C is a simulation azimuth pattern showing three of the six first polarization antenna beams generated by the multi-beam sector split base station antenna 1 of Figures 1A - 1B . Each graph shows the antenna beams generated by the antenna 1 when excited with RF signals at frequencies of 1.7 GHz, 2.2 GHz, and 2.7 GHz (i.e., the lowest frequency, center frequency, and highest frequency of the 1.7 - 2.7 GHz operating frequency band). Figure 2A shows the leftmost antenna beam of the sector, Figure 2B shows the antenna beam adjacent to the Figure 2A antenna beam, and Figure 2C shows the antenna beam adjacent to the Figure 2B antenna beam. In other words, Figures 2A - 2C shows three antenna beams providing coverage to the left half of the 120° sector. The remaining three antenna beams (at each of the three frequencies) providing coverage to the right half of the 120° sector are the mirror images of the antenna beams shown in Figures 2A - 2C . As shown in Figures 2A - 2C , the beam peak walking (i.e., the shift in the azimuth angle at which the peak gain occurs) increases with the increase in the scan angle and exceeds 20° in the case of the outermost antenna beam (see Figure 2A , showing that the beam peaks at the two ends of the operating frequency band are at 32° and 53°). This beam peak walking results in large variations in the power level of the antenna beams at the outer edge of the sub-sector according to frequency, which is not desirable.

[0064] A multi-beam antenna using a beamforming network based on a Blass matrix or a Nolen matrix is also proposed. The MxN Blass matrix includes M rows and N columns of directional couplers and can be used to feed an antenna array having N columns of radiating elements. Figure 3A Fig. Figure 3A shows a multi-beam sector-split base station antenna 100 implemented using a beamforming network based on a Blass matrix. The sector-split antenna 100 can divide a sector into four sub-sectors, thereby providing a separate antenna beam (for each polarization) for each sub-sector.

[0065] As Figure 3A shown, the multi-beam sector-split base station antenna 100 includes first to fourth first-polarization RF ports 110-1 to 110-4, a multi-column antenna array 120, and a beamforming network 130 based on a Blass matrix. It should be understood that the shown beamforming network 130 is for the first polarization, and if dual-polarization radiating elements are used in the multi-column array 120, a second beamforming network 130 and first to fourth second-polarization RF ports will be provided. The multi-column antenna array 120 includes five columns 122 of radiating elements 124. Each column 122 of radiating elements 124 can extend in the vertical direction, and the columns 122 can be spaced apart from each other in the horizontal direction to form a planar array 120 of radiating elements 124. Each column 122 of radiating elements 124 can also include a power distribution network (not shown, but see Figure 1B a similar power distribution network of Figure 1B , the power distribution network further including phase shifters), which divides the RF signal fed to the column 122 into multiple sub-components, and the multiple sub-components are fed to the respective radiating elements 124.

[0066] The beamforming network 130 is implemented using a 4x5 Blass matrix 132. As shown, the Blass matrix 132 includes twenty directional couplers 140 arranged in four rows 134 and five columns 136. "Horizontal" delay lines 150 are provided between adjacent directional couplers 140 in each row 134, such that a total of sixteen horizontal delay lines 150 are provided. The horizontal delay lines 150 may include, for example, meandered transmission line segments that add the required amount of phase delay. Each directional coupler 140 has an input port 142 (upper left port), a through port 144 (lower left port), an isolation port 146 (upper right port), and a coupled port 148 (lower right port). Four RF ports 110-1 to 110-4 are coupled to the respective input ports 142 of the first (leftmost) directional coupler 140 in each row 134. The coupled port 148 of each directional coupler 140 in the first (topmost) row 134-1 of the Blass matrix 132 is coupled to a respective one of the radiating elements in each column 122 of radiating elements 124. The isolation port 146 of each directional coupler 140 in the last (bottommost) row 134-4 of the Blass matrix 132 is coupled to a respective load 160 (e.g., a respective 50 ohm resistor). The through port 144 of each directional coupler 140 in the last (rightmost) column 136-5 of the Blass matrix 132 is coupled to a respective load 160 (e.g., a respective 50 ohm resistor) through a respective one of the horizontal delay lines 150. As Figure 3A shown, the remaining ports of the directional couplers 140 are interconnected. In particular, the through port 144 of each of the remaining directional couplers 140 is coupled through a respective one of the horizontal delay lines 150 to the input port 142 of the next directional coupler 140 in the same row 134. Also, the isolation port 146 of each directional coupler 140 in row 134 is coupled to the coupled port 148 of the directional coupler 140 in the row below 134 (except for the isolation port 146 of the directional coupler 140 in the last row 134, as discussed above).

[0067] As described above, the multi-beam sector-splitting base station antenna 100 can generate M (here M equals 4) antenna beams (for each polarization) pointing in different directions. However, the Blass matrix 132 is a lossy matrix both in transmission and reception, which reduces the gain of the antenna 100. Additionally, the Blass matrix 132 requires a large number of directional couplers 140, which can result in a physically large and expensive beamforming network 130.

[0068] The Nolen matrix is another beamforming network implementation for a multi-beam sector-splitting antenna base station antenna. The MxN Nolen matrix includes M rows and N columns of directional couplers, where each row has a different number of directional couplers. Figure 3BShows a multi-beam sector-split base station antenna 200 implemented using an MxN Nolen matrix beamforming network. The multi-beam sector-split base station antenna 200 can divide a sector into four sub-sectors, thereby providing a separate antenna beam (for each polarization) for each sub-sector.

[0069] As Figure 3B shown, the sector-split antenna 200 includes first to fourth first-polarization RF ports 210-1 to 210-4, a multi-column antenna array 120, and a first-polarization beamforming network 230 (if the multi-column antenna array 220 includes dual-polarization radiating elements, additional RF ports 210 and a second beamforming network 230 are provided). The multi-column antenna array 220 can be the same as the multi-column array 120 included in the Figure 3A sector-split antenna 100, so further description thereof will be omitted.

[0070] The beamforming network 230 is implemented using a 4x5 Nolen matrix 232. As shown, the Nolen matrix 232 includes ten directional couplers 140 arranged in four rows 234 and four columns 236. The top row 234-1 includes four directional couplers 140, and each of the remaining rows 234-2 to 234-4 has one less directional coupler 140 than the row 234 above it. Compared with a 4x5 Blass matrix, this design halves the number of directional couplers 140 required. The directional couplers 140 can be the same as the directional couplers 140 included in the Figure 3A sector-split antenna 100, so further description thereof will be omitted. "Vertical" delay lines 152 are provided between adjacent directional couplers 140 in each row 234, such that a total of twelve vertical delay lines 152 are provided. In this context, a "horizontal" delay line refers to a delay line extending between directional couplers in the same row, while a "vertical" delay line refers to a delay line extending between directional couplers in different rows or between a directional coupler and the antenna array 120. The vertical delay lines 152 can be the same as those described above with respect to Figure 3AThe horizontal delay line 150, discussed for the sector-split antenna 100 (e.g., as a meandered transmission line segment), is implemented in the same manner and thus further description thereof will also be omitted. Four RF ports 210-1 to 210-4 are coupled to the respective input ports 142 of the first (leftmost) directional coupler 140 in each row 234. The coupled ports 148 of each directional coupler 140 in the first (topmost) row 234-1 of the Nolen matrix 232 are coupled to a respective column of radiating elements 124 in the columns 122. The through port 144 of the last directional coupler 140 in the first (topmost) row 234-1 of the Nolen matrix 232 is coupled to the last column 122-5 of the radiating elements 124 via a vertical delay line 152. The isolated port 146 of the last directional coupler 140 in the fourth (bottommost) row 234-4 of the Nolen matrix 232 is coupled to a load 160 (e.g., a 50 ohm resistor).

[0071] As Figure 3B shown, the remaining ports of the directional couplers 140 are interconnected. In particular, except for the last directional coupler 140 in each row 234, the isolated port 146 of the directional coupler 140 is coupled to the coupled port 148 of the directional coupler 140 in the row 234 below it. Regarding the last (rightmost) directional coupler 140 in each row 234, for all rows except the bottom row, the isolated port 146 of each directional coupler 140 is coupled to the through port 144 of the last directional coupler 140 in the previous row 234 via a respective vertical delay line 152, and the isolated port 146 of the last (rightmost) directional coupler 140 in the bottom row 234-4 is coupled to the load 160, as described above. Similarly, the through port 144 of each directional coupler 140 in each row 234 is coupled to the input port 142 of the next directional coupler 140 in that row (except for the through port 144 of the last directional coupler 140 in each row 234, as discussed above).

[0072] The 4x5 Nolen matrix 232 can be used to generate four antenna beams that point in different directions and can be electronically scanned over a wide scan range. Additionally, the Nolen matrix 232 includes only a single matching load 160 and will thus exhibit lower losses than the Blass matrix 132. However, the performance of the Nolen matrix 232 may not be as good as that of the corresponding Blass matrix because the Nolen matrix has fewer parameters that can be adjusted to optimize performance.

[0073] According to embodiments of the present invention, there is provided a multi-beam sectorized split base station antenna, which includes a beamforming network based on a modified version of the Nolen matrix. In particular, the multi-beam sectorized split base station antennas according to embodiments of the present invention may each include a modified Nolen matrix that includes additional directional couplers in each row of the matrix, which can improve performance. The modified Nolen matrix disclosed herein may also include a "vertical delay" (i.e., a delay inserted between connections spanning different rows of the modified Nolen matrix), which can at least partially compensate for the fact that each row in the modified Nolen matrix has fewer directional couplers than the row above it. The modified Nolen matrix disclosed herein is not completely lossless during transmission (as is the case with a conventional Nolen matrix), but the losses during transmission may be very low, and the losses (during both transmission and reception) may be much lower than those of a comparable Blass matrix-based multi-beam sectorized split base station antenna.

[0074] Compared to a conventional multi-beam antenna having a Butler matrix-based beamforming network, the modified Nolen matrix can generate antenna beams with a narrower azimuth HPBW, and the variation of the azimuth HPBW with frequency is reduced. The antennas according to embodiments of the present invention can also generate antenna beams with a low side lobe level and low interference between adjacent antenna beams. Additionally, the multi-beam antennas according to embodiments of the present invention exhibit almost no beam peak walking even over a wide frequency range, and may have less loss compared to a conventional multi-beam antenna having a Blass matrix beamforming network. Furthermore, the beamforming network based on the modified Nolen matrix included in the multi-beam base station antennas according to embodiments of the present invention can include fewer directional couplers than a comparable Blass matrix-based beamforming network, which reduces the size and cost of the antenna.

[0075] According to some embodiments of the present invention, there is provided a multi-beam base station antenna, the multi-beam base station antenna including first to M first polarization RF ports, an antenna array including N columns of radiating elements, and a first polarization beamforming network having M rows and N columns of directional couplers, wherein each row has a different number of directional couplers. In these antennas, the top row of the M rows of directional couplers may have the most directional couplers, and each row below the top row may have one fewer directional coupler than the row above it. The coupling ports of each directional coupler in the top row are coupled to a corresponding one of the columns of radiating elements in each column of radiating elements, and the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first polarization RF ports in the first polarization RF ports.

[0076] The through-port of the last directional coupler in the top row of directional couplers can be coupled to ground via a matching terminal. Additionally, the through-ports of all directional couplers in each row except the last directional coupler can be coupled to the input port of the next directional coupler in that row via corresponding first delay elements.

[0077] According to other embodiments of the present invention, there is provided a multi-beam base station antenna, the multi-beam base station antenna comprising: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row, wherein each row of directional couplers below the top row has one less directional coupler than the row above it. The last directional coupler in the top row has a port coupled to ground via a matching terminal.

[0078] According to further embodiments of the present invention, there is provided a multi-beam base station antenna, the multi-beam base station antenna comprising: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row. For each row of directional couplers, the through-port of each directional coupler in that row except the last directional coupler is coupled to the input port of an adjacent directional coupler in that row via a corresponding first delay element. For each row of directional couplers except the top row, the through-port of the last directional coupler in that row is coupled to the isolation port of the last directional coupler in the row of directional couplers below that row via a second delay element.

[0079] According to still other embodiments of the present invention, there is provided a multi-beam sector-split base station antenna, the multi-beam sector-split base station antenna comprising: first to M first polarization RF ports; an antenna array including N columns of radiating elements; a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row, wherein each row has a different number of directional couplers; and a first power divider coupled between the first polarization beamforming network and the first and second columns of radiating elements among the N columns of radiating elements. The first power divider can be used to couple a column of directional couplers in the first polarization beamforming network to multiple columns of radiating elements, which can allow for the use of a smaller beamforming network.

[0080] According to other embodiments of the present invention, a multi-beam antenna is provided. The multi-beam antenna includes: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers. The multiple rows of directional couplers include a top row and a bottom row and multiple additional rows between the top row and the bottom row. The top row and the bottom row each include the same number of directional couplers, and at least one of the additional rows includes fewer directional couplers than the top row.

[0081] Reference will now be made to Figures 4A - 9 a multi-beam sector-splitting base station antenna according to an exemplary embodiment of the present invention will be described in more detail.

[0082] Figure 4A is a perspective view of a 2T2R multi-beam sector-splitting base station antenna 300 according to an embodiment of the present invention. Figure 4B is Figure 4A a schematic front view of a multi-column antenna array 320 included in the base station antenna 300. Figure 4C is Figure 4A a schematic block diagram of the multi-beam sector-splitting base station antenna 300. Figure 4D is Figure 4C a highly magnified view of the portion labeled "4D" in

[0083] First, referring to Figure 4A , the multi-beam sector-splitting base station antenna 300 includes a housing 302. At least the front surface of the housing 302 may include a radome 304 that is substantially transparent to RF energy in the operating frequency band of the base station antenna 300. First RF ports 310-1 to twelfth RF ports 310-12 extend through the housing 302. In the depicted embodiment, each RF port 310 is implemented as an RF connector port. The first RF ports 310-1 to 310-6 may be first polarization RF ports (meaning they are connected to the first polarization radiators of the radiating elements 324 included in the antenna array 320), and the seventh RF ports 310-7 to twelfth RF ports 310-12 may be second polarization RF ports (meaning they are connected to the second polarization radiators of the radiating elements 324 included in the antenna array 320). Corresponding radio ports (which may all be on the same radio device or on multiple different radio devices, not shown) may be connected to the RF ports 310-1 to 310-12 via, for example, corresponding coaxial cables.

[0084] Figure 4Bis a schematic front view of a multi-column antenna array 320 that can be mounted directly behind the radome 304. The multi-column antenna array 320 (in this embodiment) includes twelve columns 322 of dual-polarization radiating elements 324. Each column 322 of radiating elements 324 can extend in the vertical direction, and the columns 322 can be spaced apart from each other in the horizontal direction to form a planar array 320 of radiating elements 324. Although Figure 4B not shown, each column 322 of radiating elements 324 may also include a power distribution network (for each polarization) that divides the RF signal fed to the column 322 into multiple sub-components, and the multiple sub-components are fed to the respective radiating elements 324. The power distribution network may optionally include a phase shifter that can be used to apply a phase progression to the sub-components of the RF signal that are fed to the radiating elements in each column 322 of radiating elements 324. The power distributor / phase shifter network discussed above with respect to Figure 1B can be used to implement the power distributor / phase shifter network for each column 322, except that Figure 1B each phase shifter assembly shown in has five outputs to feed five radiating elements 324 in the column 322.

[0085] Each radiating element 324 can be implemented as an inclined -45° / +45 ° crossed dipole radiating element, which includes a first dipole radiator 326-1 configured to transmit and receive RF energy with an inclined -45° linear polarization and a second dipole radiator 326-2 configured to transmit and receive RF energy with an inclined +45° linear polarization. However, it should be understood that other types of radiating elements can be used, such as dual-polarization patch radiating elements. Each column 322 includes a total of five radiating elements 324, but it should be understood that a different number of radiating elements 324 can be used. The number of radiating elements 324 in each column 322 can be selected, for example, based on the desired HPBW of the antenna beam generated by the multi-column antenna array 320 in the elevation plane. In the depicted embodiment, the adjacent columns 322 are staggered with respect to each other in the elevation (vertical) plane to increase the amount of isolation between the radiating elements 324 in the adjacent columns 322. The radiating elements 324 can each extend forward from the reflector 306 toward the front surface of the radome 304. The reflector 306 may include a metal sheet that acts as a ground plane for the radiating elements 324 and also redirects most of the backward-directed radiation emitted by the radiating elements 324 forward.

[0086] Figure 4C is a schematic block diagram of a beamforming network 330 included in the base station antenna 300. Figure 4D is Figure 4CA greatly magnified view of the portion labeled "4D" in [the figure] better shows the connections between the directional couplers 340 in different rows and columns of the beamforming network 330 based on the improved Nolen matrix included in the multi-beam base station antenna 300. The beamforming network 330 is only for the first polarization, meaning that the beamforming network 330 couples the first polarization RF ports 310-1 to 310-6 of the radiating elements 324 in the multi-column antenna array 320 to the first polarization radiator 326-1. Since the radiating element 324 is a dual-polarization radiating element, it should be understood that the antenna 300 will include a second beamforming network 330 that couples the second polarization RF inputs 310-7 to 310-12 of the radiating elements 324 in the multi-column antenna array 320 to the second polarization radiator 326-2. The second beamforming network may be the same as the beamforming network 330, and thus further description thereof will be omitted.

[0087] As Figures 4C - 4D shown, the beamforming network 330 is implemented using an improved 6x12 Nolen matrix 332. As shown, the improved Nolen matrix 332 includes fifty-seven directional couplers 340 arranged in six rows 334 and twelve columns 336. The first (top) row 334-1 includes twelve directional couplers 340, the second row 334-2 includes eleven directional couplers 340, the third row 334-3 includes ten directional couplers 340, the fourth row 334-4 includes nine directional couplers 340, the fifth row 334-5 includes eight directional couplers 340, and the sixth (bottom) row 334-6 includes seven directional couplers 340. Thus, each row 334 has one more directional coupler 340 than the row 334 below it and one less directional coupler 340 than the row 334 above it.

[0088] If equal amounts of RF power are to be fed to each column of the antenna array, the first directional coupler 340 in the first row 334-1 can be designed to transfer 11 / 12 of the RF power input at the input port 342 to the through port 344 and the remaining 1 / 12 of the input RF power to the coupled port 348. The second directional coupler 340 in the first row 334-1 can be designed to transfer 10 / 11 of the RF power input to it at the input port 342 to its through port 344 and the remaining 1 / 11 of the input RF power to the coupled port 348. The third to eleventh directional couplers 340 in the first row 334-1 transfer 9 / 10, 8 / 9, 7 / 8, 6 / 7, 5 / 6, 4 / 5, 3 / 4, 2 / 3, and 1 / 2 of the power input at their respective input ports 342 to their respective through ports 344. The last directional coupler 340 in the first row 334-1 can be designed to transfer a small portion of the power input to it to the load 360 (here a 50-ohm resistor) and couple most of the power to the column 322-12 of the radiating element 324. The directional couplers 340 in the remaining rows 334 can be designed similarly, where the amount of coupling is changed to reflect the smaller number of directional couplers 340 in each row 334. It should also be understood that in many cases, the middle columns of a multi-column array are fed a higher percentage of RF power than the outer columns, and thus, some further adjustment of the coupling ratios of the directional couplers 340 can be made to feed a larger percentage of power to the middle columns 322 of the array 320.

[0089] "Horizontal" delay lines 350 are provided between adjacent directional couplers 340 in each row 334 such that a total of fifty-one horizontal delay lines 350 are provided. In particular, the first (top) row 334-1 includes eleven horizontal delay lines 350, the second row 334-2 includes ten horizontal delay lines 350, the third row 334-3 includes nine horizontal delay lines 350, the fourth row 334-4 includes eight horizontal delay lines 350, the fifth row 334-5 includes seven horizontal delay lines 350, and the sixth (bottom) row 334-6 includes six horizontal delay lines 350. "Vertical" delay lines 352 are also provided that extend between the last (rightmost) directional coupler 340 in each row 334 and the last (rightmost) directional coupler in the row 334 below it such that a total of five vertical delay lines 352 are provided.

[0090] As Figure 4D shown, each directional coupler 340 has an input port 342 (upper left port), a through port 344 (lower left port), an isolation port 346 (upper right port), and a coupled port 348 (lower right port). Figures 4C - 4D All the directional couplers 340 in Figure 4DThe port labels for the two directional couplers 340 shown in apply to Figures 4C - 4D all of the directional couplers 340 in. Each directional coupler 340 can be designed to couple a predetermined amount of RF energy input at the input port 342 to the through port 344 and the coupled port 348. Ideally, no RF energy is transferred from the input port 342 to the isolation port 346, but in practice, a small amount of RF energy will be coupled to the isolation port 346. The directional coupler 340 can also impose a -90° phase shift between the RF energy transferred from the input port 342 to the through port 344 compared to the RF energy transferred from the input port 342 to the cross-coupled port 348.

[0091] As Figure 4C can be seen, the connections between the directional couplers 340 vary based on the position of the directional couplers 340 within the matrix. In particular, the directional couplers 340 in the center of the modified Nolen matrix 332 (i.e., not along any outer edge) are interconnected such that the input port 342 is horizontally delayed through a respective one of the horizontal delays 350 to the through port 344 of the previous directional coupler 340 in row 334, the through port 344 is coupled through a respective one of the horizontal delay lines in the horizontal delays 350 to the input port of the next directional coupler 340 in row 334, the isolation port 346 is connected to the coupled port 348 of the directional coupler 340 in the same column 336 in the next row 334 below, and the coupled port 348 is connected to the isolation port 346 of the directional coupler 340 in the same column 336 in the next row 334 above.

[0092] The directional coupler 340 outside the improved Nolen matrix 332 has a slightly different connection scheme. In particular, the input port 342 of the first (leftmost) directional coupler 340 in each row 334 is coupled to a corresponding one of the first polarization RF ports 310-1 to 310-6, rather than to the through port of an adjacent directional coupler 340. The coupled port 348 of each directional coupler 340 in the topmost row 334-1 is coupled to a corresponding column of radiating elements 324 in each column 322, rather than to the isolation port 346 of a directional coupler 340 in a different row 334. The isolation port 346 of each directional coupler 340 in the bottommost row 334-6 is coupled to a corresponding load 360 (e.g., a corresponding 50-ohm resistor), rather than to the coupled port 348 of a directional coupler 340 in a different row 334. The through port 344 of the last directional coupler 340 in each row 334 is coupled to the isolation port 346 of the last directional coupler 340 in the row above it through a corresponding one of the vertical delays 352, except for the through port 344 of the last directional coupler 340 in the topmost row 334-1, which is coupled to the load 360.

[0093] Figure 5A is a schematic azimuthal diagram showing the six first polarization antenna beams generated by Figure 4A a multi-beam antenna, where different curves represent different frequencies distributed across the 1695 - 2690 MHz band. As Figure 5A shown, the six antenna beams provide coverage over a 90° quadrant in the azimuth plane (i.e., the -10 dB points on the left of the leftmost antenna beam and on the right of the rightmost antenna beam are separated by approximately 90°). Thus, the six antenna beams divide the 90° sector in the azimuth plane into six 15° sub-sectors. The average cross of the antenna beams is at -7 dB, which means that each antenna beam provides good coverage within its sub-sector and has a relatively low interference level to adjacent sub-sectors. The side lobe level is below -12 dB within the coverage area and is thus not visible in Figure 5A In addition, these high performance levels are maintained across the 1695 - 2690 MHz band, indicating that the multi-beam sector-splitting base station antenna 300 exhibits broadband performance. Thus, Figure 5A shows that the multi-beam sector-splitting base station antenna 300 generates antenna beams with good shape and size to divide the 90° sector in the azimuth plane into six sub-sectors.

[0094] Figure 5B is a diagram showing Figure 4AGraph of the beam peak walking performance of the multi-beam sector-split base station antenna 300. As discussed above, traditional Butler matrix-based multi-beam sector-split base station antennas tend to exhibit a high level of beam peak walking, which refers to the phenomenon that the pointing direction of the antenna beam in the azimuth plane (i.e., the angular direction at which the antenna beam exhibits peak gain) varies with frequency. This phenomenon is also referred to as "beam squint". As mentioned above, using a base station antenna based on a conventional six-beam Butler matrix, the beam peak walking can exceed 20°. Therefore, the operating bandwidth of such antennas is typically limited to a sub-band (e.g., the 1710 - 2180 MHz sub-band of the 1695 - 2690 MHz band when the antenna array includes mid-band radiation elements).

[0095] As Figure 5B shown in, the multi-beam antenna 300 exhibits a very low level of beam peak walking over the entire 1695 - 2690 MHz band. Figure 5B The six curves in the graph of represent the beam peak walking performance of the six first-polarization antenna beams generated by the multi-beam antenna 300. Although there is a slight difference in the beam peak walking performance between the antenna beams, generally speaking, the beam peak only moves approximately 1° on average with frequency in the azimuth plane over the entire 1695 - 2690 MHz band. Therefore, Figure 5B shows that the multi-beam antenna 300 exhibits excellent beam peak walking performance.

[0096] Figure 4A The multi-beam sector-split base station antenna 300 of uses a 6x12 modified Nolen matrix to feed a twelve-column antenna array. According to another embodiment of the present invention, a multi-beam antenna is provided that includes a simpler modified Nolen matrix. The simpler modified Nolen matrix provides slightly less control over the shape and size of the antenna beam, but can also reduce the cost of the beamforming network included in these antennas.

[0097] Figure 6 is a combination of a side view (on the right side of the figure) and several plan views (on the left side of the figure), which shows Figure 4A the printed circuit board implementation of one of the modified Nolen matrix beamforming networks 332 included in the multi-beam base station antenna 300 of.

[0098] As Figure 6As shown in the side view, a multi-layer printed circuit board 500 can be used to implement the improved Nolen matrix 332, which includes a first dielectric substrate 502 and a second dielectric substrate 504. A first (top) metallization layer 510 is disposed on the top side of the first dielectric substrate 502, a second (bottom) metallization layer 512 is disposed on the bottom side of the second dielectric substrate 504, and a third metallization layer is disposed between the two dielectric substrates 502, 504.

[0099] Figure 6 The front view of the first metallization layer, the second metallization layer, and the third metallization layers 510, 520, 530 is depicted on the left side. The directional coupler 340 and the delays 350, 352 are formed in these metallization layers 510, 520, 530. The third metallization layer 530 may include a substantially solid metal layer having a plurality of slots 532 formed therein. Figure 6 The components of one of the directional couplers 340 are enclosed by the dashed box in. The directional coupler 340 is formed as a slot-type directional coupler, where a first widened trace 512 is formed in the first metallization layer 510, a second widened trace 522 is formed in the second metallization layer 520, and one of the slots 532 is interposed therebetween. RF energy is coupled between the first widened trace 512 and the second widened trace 522 through the slot 532. The amount of coupling between the first widened trace 512 and the second widened trace 522 varies with the length of the slot 532, the width of the slot 532, the thickness and dielectric constant of the first dielectric substrate and the second dielectric substrate 502, 504, and the width of the first widened trace and the second widened trace 512, 522. In the depicted embodiment, each slot 532 has the same length (i.e., the same length in the x direction), and the thickness and dielectric constant of the first dielectric substrate and the second dielectric substrate 502, 504 are constant. Therefore, the amount of coupling between the first widened trace and the second widened trace 512, 522 can be set by appropriately adjusting the width of the slot 532 and the width of the first widened trace 512 and the second widened trace 522. In the depicted embodiment, the first widened trace and the second widened trace 512, 522 have the same width for each directional coupler 340, but the width is different for different directional couplers 340. The widths of the first widened trace and the second widened trace 512, 522 and the slot 532 can be selected to achieve the desired coupling amount while also maintaining the desired impedance to minimize the return loss.

[0100] The input port 342 and the through port 344 of each directional coupler 340 are formed in the first metallization layer 510, and the isolation port 346 and the coupling port 348 of each directional coupler 340 are formed in the second metallization layer 520.

[0101] As Figure 6It can also be seen that the horizontal delay 350 can be implemented as a meandering microstrip trace 550 in the first metallization layer 510. It can be seen that the amount of each horizontal delay 350 can be constant within a row of the directional coupler 340 and can be incrementally increased such that the minimum horizontal delay 350 is in the top row of the directional coupler 340 and the maximum horizontal delay 350 is in the bottom row of the directional coupler 340. Similarly, the vertical delay 352 can be implemented as a meandering microstrip trace in the second metallization layer 520. It can be seen that the amount of each vertical delay 352 can be incrementally increased such that the minimum vertical delay 352 is in the top row of the directional coupler 340 and the maximum vertical delay 352 is in the bottom row of the directional coupler 340.

[0102] Also as Figure 6 shown in, a first plurality of plated vias 540 are formed through the printed circuit board 500, which electrically connect each vertical delay 352 to the isolation port of the directional coupler 340 in the row above the row including the vertical delay 352. Circular regions 541 are provided on the third metallization layer 530 where the metal is omitted such that the plated vias 540 do not short circuit to the metallization of the third metallization layer 530. It should be noted that the matching terminals 360 are Figure 6 not shown in and can be implemented, for example, as surface mount resistors mounted on the printed circuit board 500.

[0103] Figure 7A is a perspective view of a scannable multi-beam sector split base station antenna 600 according to further embodiments of the present invention. Figure 7B is Figure 7A a schematic front view of a multi-column antenna array included in the base station antenna of. Referring to Figure 7A and 7B it can be seen that externally, the scannable multi-beam sector split base station antenna 600 can be the same as the multi-beam sector split base station antenna 300 discussed above, having a housing 302 that includes a radome 304, a reflector 306, and first RF ports 310-1 to twelfth RF ports 310-12. The scannable multi-beam sector split base station antenna 600 can also include a multi-column antenna array 320, which can be the same as the antenna array 320 of the multi-beam sector split base station antenna 300. Therefore, further description of these aspects of the base station antenna 600 will be omitted.

[0104] Figure 7C is Figure 7A a schematic block diagram of the scannable multi-beam base station antenna 600 of. As by comparing Figure 4C and Figure 7CIt can be seen that the beamforming network 630 based on the improved Nolen matrix included in the scannable multi-beam base station antenna 600 can be almost the same as the beamforming network 330 based on the improved Nolen matrix included in the base station antenna 300. The only difference is that the horizontal delay and vertical delay 350, 352 included in the beamforming network 330 are replaced by an adjustable phase shifter 650 in the beamforming network 630. The phase shifter 650 may include, for example, an electromechanical phase shifter, such as a brushless phase shifter or an electronic phase shifter.

[0105] By replacing the horizontal delay and vertical delay 350, 352 with the phase shifter 650, the phase delay between the respective directional couplers 340 can be adjusted. This allows the cellular operator to (1) shift the pointing directions of the six antenna beams in the azimuth plane (while keeping the shape and size of the antenna beams substantially the same) and / or (2) adjust the size of the main lobe of each antenna beam and / or the distance between adjacent main lobes.

[0106] Figure 7D is a series of graphs showing how the pointing directions of the antenna beams generated by the scannable multi-beam base station antenna can be scanned in the azimuth plane. For simplicity, Figure 7D shows the simulation results of a three-beam base station antenna. As Figure 7D shown, by changing the settings of the phase shifter, the scannable multi-beam base station antenna can scan the pointing directions of the three antenna beams in the azimuth plane. It can be seen that the size and shape of the main lobes of the three antenna beams do not change much as the pointing angles of these antenna beams are scanned, but there are changes in the side lobes. The ability to change the pointing directions of the antenna beams may be useful in cases where different coverage areas are desired at different times.

[0107] Figure 8 is a schematic block diagram of a multi-beam base station antenna 700 according to some other embodiments of the present invention. The multi-beam base station antenna 700 is very similar to Figures 4A - 4D the multi-beam base station antenna, so the following description will focus on the differences between these two antennas. As can be seen by comparing Figure 4C and Figure 8It can be seen that, apart from the design of their beamforming networks 330, 730, the base station antennas 300 and 700 can be the same. The beamforming network 730 differs from the beamforming network 330 in that additional directional couplers 340 are added in its rows 734-4 to 734-6, resulting in an improved Nolen matrix 732 that is generally symmetric about a horizontal axis extending between its third row 734-3 and fourth row 734-4. Thus, in the improved Nolen matrix 732, the fourth row 734-4 includes ten directional couplers 340, the fifth row 734-5 includes eleven directional couplers 340, and the sixth row 734-6 includes twelve directional couplers 340. The additional directional couplers 340 included in the improved Nolen matrix 732 result in some additional losses as more resistive loads 360 are required, but can produce an improved pattern shape (especially in terms of sidelobe levels in the azimuth plane).

[0108] As Figure 8 can be seen, the multi-beam sector-split base station antenna 700 includes: an antenna array 320 having N columns 322 of radiating elements 324; and a first polarization beamforming network 730 having multiple rows 334 of directional couplers 340, the multiple rows of directional couplers including a top row 334-1, a bottom row 334-6, and multiple additional rows 334-2 to 334-5 between the top row 334-1 and the bottom row 334-6. The top row 334-1 and the bottom row 334-6 each include the same number (here 12) of directional couplers 340, and at least one of the additional rows (e.g., row 334-2) includes fewer directional couplers 340 than the top row 334-1. It can also be seen that the second row 334-2 includes the same number of directional couplers 340 as the fifth row 334-5, and the third row 334-3 includes the same number of directional couplers 340 as the fourth row 334-4.

[0109] Figure 9 is a schematic front view of a dual-band base station antenna 800 including a multi-column array in one of a number of frequency bands according to an embodiment of the present invention. The base station antenna 800 can be similar to Figures 4A - 4DBase station antenna 300. Except that compared with base station antenna 300, in base station antenna 800, each column 322 of the multi-column antenna array 320 includes more radiation elements 324. In an exemplary embodiment, the radiation elements 324 in the multi-column antenna array 320 can be mid-band radiation elements configured to operate in the 1427 - 2690 MHz frequency band or a part thereof. Additionally, the base station antenna further includes four linear arrays 820-1 to 820-4 of low-band radiation elements 824 that operate in all or part of the 617 - 960 MHz frequency band. The low-band radiation elements 824 are positioned between the mid-band radiation elements 324.

[0110] The four linear arrays 820-1 to 820-4 of the low-band radiation elements 824 can be operated in any suitable manner. For example, in some embodiments, the four linear arrays 820-1 to 820-4 of the low-band radiation elements 824 can be used to implement sector split dual-beam (for each polarization) antennas in the low band. In other embodiments, the four linear arrays 820-1 to 820-4 of the low-band radiation elements 824 can be used to support 4xMIMO communication in two sub-bands of the low-band operating frequency range or support 8xMIMO in one sub-band.

[0111] Figure 9 An example of a dual-band base station antenna is shown, which includes at least four-beam (for each polarization) sector split capability in a first operating band and an array of radiation elements operating in different bands. It should be understood that linear arrays of low-band radiation elements can be added to any of the base station antennas disclosed herein. For example, two columns of low-band radiation elements can be added to Figures 3A - 3B base station antennas 100 and 200. The low-band radiation elements can be positioned between the mid-band radiation elements in these antennas in the same manner as shown in Figure 9 . Figures 7A - 7D Base station antenna 600 and / or Figure 8 base station antenna 700 can be modified in the same manner as shown in Figure 9 to include four (or two or three) linear arrays of low-band radiation elements.

[0112] According to another embodiment of the present invention, a multi-beam sector split antenna is provided, which includes a beamforming network that is a hybrid of a Blass matrix and a Nolen matrix. Figure 10 is a schematic block diagram of such a "hybrid" multi-beam sector split base station antenna 900 according to an embodiment of the present invention. As Figure 10As shown, the base station antenna has a beamforming network that is a hybrid of a Blass matrix and a Nolen matrix. In this particular embodiment, the first three beams each have twelve couplers 340 per row, while the remaining three beams have eleven, ten, and nine couplers 340 per row. It should be understood that Figure 10 the embodiment depicted in may be varied in other embodiments of the "hybrid" Blass / Nolen matrix beamforming network to have two, three, four, or five beams, each having twelve couplers 340 per row.

[0113] Although the multi-beam antennas discussed above are 2T2R antennas (i.e., they support 2xMIMO operation), it should be understood that two multi-beam antennas according to embodiments of the present invention can be stacked in the same housing to provide a multi-beam antenna with 4T4R capabilities.

[0114] Although the above examples of the present invention mainly have a six-beam sector-split base station antenna, it should be understood that embodiments of the present invention are not limited thereto. In other embodiments, the base station antenna can generate fewer than six antenna beams (e.g., two, three, four, or five antenna beams) per polarization, or can generate more than six antenna beams (e.g., seven, eight, nine, or more). Generally, as the number of antenna beams increases, the number of columns of radiating elements tends to increase. For example, a multi-beam base station antenna configured to generate four antenna beams per polarization according to an embodiment of the present invention can have an eight-column antenna array. The number of rows in the beamforming network based on the modified Nolen matrix included in the base station antenna according to an embodiment of the present invention can be equal to the number of antenna beams generated by the antenna per polarization. Thus, a four-beam (per polarization) multi-beam antenna according to an embodiment of the present invention can include, for example, a beamforming network based on a modified Nolen matrix having four rows and eight columns of directional couplers. The number of antenna columns included in the multi-beam base station antenna according to an embodiment of the present invention can be set based on the required side lobe suppression and interference amount between adjacent antenna beams. The azimuth beam width of each antenna beam can be selected based on the spacing between adjacent column radiating elements and the azimuth beam width of each radiating element.

[0115] In the above discussion, the "rows" and "columns" of the modified Nolen matrix beamforming network according to embodiments of the present invention are mentioned. It should be understood that "rows" and "columns" are defined functionally, and the directional couplers do not need to be physically aligned in actual rows and columns during implementation. For example, referring to Figure 4C, the directional couplers forming row 334-1 are such that the through-port 344 of one directional coupler 340 is connected to the input port 342 of the next directional coupler 340 in row 334-1. Thus, row 334-1 includes a total of twelve directional couplers 340. However, these directional couplers 340 do not need to be aligned in a horizontal row as shown in Figure 4C . Instead, some of the directional couplers 340 in row 334-1 may be offset from other directional couplers in the vertical direction and may even be aligned with the directional couplers 340 of other rows 334 in the horizontal direction. Similarly, the directional couplers 340 forming column 336-1 are such that the coupled port 348 of one directional coupler 340 is connected to the isolated port 346 of the next directional coupler 340 in column 336-1. Thus, column 336-1 includes a total of six directional couplers 340. However, these directional couplers 340 do not need to be aligned in a vertical column as shown in Figure 4C . Instead, some of the directional couplers 340 in column 336-1 may be offset from other directional couplers 340 in the horizontal direction and may even be aligned with the directional couplers 340 of other columns 336 in the vertical direction.

[0116] It will be appreciated that this specification only describes several exemplary embodiments of the present invention, and the techniques described herein have applicability beyond the above-described exemplary embodiments.

[0117] The above description has mainly described the transmission paths of the base station antenna described herein. It will be appreciated that the base station antenna includes bi-directional RF signal paths and that the base station antenna will also be used for receiving RF signals. In the receive path, RF signals will typically be combined, while in the transmit path, RF signals are separated. Thus, it will be apparent to those skilled in the art that the base station antenna described herein can be used for receiving RF signals.

[0118] Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the present invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the text, like reference numerals denote like elements.

[0119] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the present invention, a first element may be termed a second element, and similarly, a second element may be termed a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0120] It will be understood that when an element is described as being "on" another element, the element can be directly on the other element or there can also be intervening elements. In contrast, when an element is described as being "directly on" another element, there are no intervening elements. It will also be understood that when an element is described as being "connected" or "coupled" to another element, the element can be directly connected or coupled to the other element, or there can be intervening elements. In contrast, when an element is described as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other words used to describe the relationship between elements should be interpreted in a similar manner (i.e., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.).

[0121] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that the terms "comprises", "comprising" and / or "having", when used herein, specify the presence of the stated features, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, operations, elements, components and / or their groups.

[0122] Aspects and elements of all the embodiments disclosed above can be combined in any way and / or combined with aspects or elements of other embodiments to provide a plurality of additional embodiments.

Claims

1. A multi-beam antenna, comprising: First to M first-polarization radio frequency ("RF") ports; An antenna array, the antenna array comprising N columns of radiating elements; A first-polarization beamforming network, the first-polarization beamforming network having M rows and N columns of directional couplers, where each row has a different number of directional couplers, and where M and N are natural numbers.

2. The multi-beam antenna according to claim 1, wherein the top row of the M rows of directional couplers has the most directional couplers, and each row below the top row has one less directional coupler than the row above it.

3. The multi-beam antenna according to claim 2, wherein the coupling port of each directional coupler in the top row of the M rows of directional couplers is coupled to a corresponding one of the N columns of radiating elements.

4. The multi-beam antenna according to claim 2, wherein the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first-polarization RF ports.

5. The multi-beam antenna according to claim 4, wherein the through port of the last directional coupler in the top row of the M rows of directional couplers is coupled to electrical ground via a matching terminal.

6. The multi-beam antenna according to claim 2, wherein, except for the last directional coupler in each row of the M rows of directional couplers, the through port of each directional coupler in each row of the M rows of directional couplers is coupled to the input port of a corresponding adjacent directional coupler in the row via a corresponding first delay element.

7. The multi-beam antenna according to claim 6, wherein, except for the top row of the M rows of directional couplers, the through port of the last directional coupler in each row of the M rows of directional couplers is coupled to the isolation port of the last directional coupler in the row below the row of the M rows of directional couplers via a second delay element.

8. The multi-beam antenna according to claim 2, wherein the isolation port of each directional coupler in the bottom row of the M rows of directional couplers is coupled to electrical ground via a corresponding matching terminal.

9. The multi-beam antenna according to any one of claims 2-8, wherein the isolation port of each directional coupler in the bottom row of the M rows of directional couplers is coupled to a synthesizer, and the output of the synthesizer is coupled to ground via a matching terminal.

10. The multi-beam antenna according to any one of claims 1-9, wherein, except for the last directional coupler in each row of the M rows of directional couplers, the through port of each directional coupler in each row of the M rows of directional couplers is coupled to the input port of a corresponding adjacent directional coupler in the row via a corresponding phase shifter.

11. The multi-beam antenna according to any one of claims 1-10, wherein, except for the top row of the M rows of directional couplers, the through port of the last directional coupler in each row of the M rows of directional couplers is coupled to the isolation port of the last directional coupler in the row below the row of the M rows of directional couplers via a corresponding phase shifter.

12. A multi-beam antenna, comprising: An antenna array, the antenna array including N columns of radiating elements; and A first polarization beamforming network, the first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row, where each row of directional couplers below the top row has one less directional coupler than the row above it, where the last directional coupler in the top row has a port coupled to ground via a matching terminal.

13. The multi-beam antenna according to claim 12, wherein the top row has N directional couplers, and wherein the coupled ports of each directional coupler in the top row are coupled to a corresponding one of the N columns of radiating elements.

14. The multi-beam antenna according to claim 13, further comprising first to M first polarization radio frequency ("RF") ports, wherein the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first polarization RF ports.

15. The multi-beam antenna according to claim 14, wherein for each row of directional couplers, except for the last directional coupler in the row, the through port of each directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding first delay element.

16. The multi-beam antenna according to claim 15, wherein for each row of directional couplers except the top row, the through port of the last directional coupler in the row is coupled to the isolation port of the last directional coupler in the row of directional couplers below it through a second delay element.

17. The multi-beam antenna according to claim 16, wherein the isolation port of each directional coupler in the bottom row is coupled to ground electrically via a corresponding matching terminal.

18. The multi-beam antenna according to claim 16, wherein the isolation port of each directional coupler in the bottom row is coupled to a synthesizer, and the output of the synthesizer is coupled to ground via a matching terminal.

19. The multi-beam antenna according to any one of claims 12-18, wherein the through port of each directional coupler in each row except the last directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding phase shifter.

20. The multi-beam antenna according to any one of claims 12-18, wherein for each row of directional couplers except the top row, the through port of the last directional coupler in the row is coupled to the isolation port of the last directional coupler in the row of directional couplers below it through a corresponding phase shifter.

21. A multi-beam antenna, comprising: An antenna array, the antenna array including N columns of radiating elements; and A first polarization beamforming network, the first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row, where for each row of directional couplers, except for the last directional coupler in the row, the through port of each directional coupler in the row is coupled to the input port of an adjacent directional coupler in the row through a corresponding first delay element, and For each row of directional couplers except the top row, the through port of the last directional coupler in the row is coupled to the isolation port of the last directional coupler in a row of directional couplers below the row through a second delay element.

22. The multi-beam antenna according to claim 21, wherein the top row has N directional couplers, and the coupling port of each directional coupler in the top row is coupled to a corresponding one of the N columns of radiating elements.

23. The multi-beam antenna according to claim 22, further comprising first to M first polarization radio frequency ("RF") ports, wherein the first directional coupler in each row of directional couplers is coupled to a corresponding one of the first polarization RF ports.

24. The multi-beam antenna according to claim 23, wherein the isolation port of each directional coupler in the bottom row is coupled to electrical ground via a matching terminal.

25. A multi-beam antenna, comprising: an antenna array including N columns of radiating elements; and a first polarization beamforming network having multiple rows of directional couplers, the multiple rows of directional couplers including a top row and a bottom row and a plurality of additional rows between the top row and the bottom row, wherein the top row and the bottom row each include the same number of directional couplers, and at least one of the additional rows includes fewer directional couplers than the top row.

26. The multi-beam antenna according to claim 25, wherein one of the additional rows immediately below the top row includes the same number of directional couplers as one of the additional rows immediately above the bottom row.

27. The multi-beam antenna according to claim 25 or 26, wherein the through port of the last directional coupler in the top row is coupled to electrical ground via a matching terminal.

28. The multi-beam antenna according to claim 27, wherein the coupling port of each directional coupler in the top row is coupled to a corresponding one of the N columns of radiating elements.

29. The multi-beam antenna according to claim 28, wherein the first directional coupler in each row is coupled to a corresponding one of the first polarization RF ports.

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