Patent ID: 12261373

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG.2A, there is shown one preferred embodiment comprising a bidirectional 2×3 BFN at20configured to form 2 beams with 3 columns of radiators, where the two beams are formed at signal ports24. A 90° hybrid coupler22is provided, and may or may not be a 3 dB coupler. Advantageously, by variation of the splitting coefficient of the 90° hybrid coupler22, different amplitude distributions of the beams can be obtained for radiator coupling ports26: from uniform (1-1-1) to heavy tapered (0.4-1-0.4). With equal splitting (3 dB coupler) 0.7-1-0.7 amplitudes are provided. So, the 2×3 BFN20offers a degree of design flexibility, allowing the creation of different beam shapes and sidelobe levels. The 90° hybrid coupler22may be a branch line coupler, Lange coupler, or coupled line coupler. The wide band solution for a 180° equal splitter28can be a Wilkinson divider with a 180° Shiffman phase shifter. However, other dividers can be used if desired, such as a rat-race 180° coupler or 90° hybrids with additional phase shift. InFIG.2A, the amplitude and phase distribution on radiator coupling ports26for both beams Beam1and Beam2are shown to the right. Each of the 3 radiator coupling ports26can be connected to one radiator or to a column of radiators, as dipoles, slots, patches etc. Radiators in column can be a vertical line or slightly offset (staggered column).

FIG.2Bis a schematic diagram of a bidirectional 2×4 BFN30according to another preferred embodiment of the present invention, which is configured to form 2 beams with 4 columns of radiators and using a standard Butler matrix38as one of the components. The 180° equal splitter34is the same as the splitter28described above. The phase and amplitudes for both beams Beam1and Beam2are shown in the right hand portion of the figure. Each of 4 radiator coupling ports40can be connected to one radiator or to column of radiators, as dipoles, slots, patches etc. Radiators in column can stay in vertical line or to be slightly offset (staggered column).

FIG.2Cis a schematic diagram of another embodiment comprising a bidirectional 2×4 BFN at50, which is configured to form 2 beams with 4 columns of radiators. BFN50is a modified version of the 2×4 BFN30shown inFIG.2B, and includes two phase shifters56feeding a standard 4×4 Butler Matrix58. By changing the phase of the phase shifters56, a slightly different AzBW between beams can be selected (together with adjustable beam position) for cell sector optimization. One or both phase shifters56may be utilized as desired.

The improved BFNs20,30,50can be used separately (BFN20for a 3 column 2-beam antenna and BFN30,50for 4 column 2-beam antennas). But the most beneficial way to employ them is the modular approach, i.e. combinations of the BFN modules with different number of columns/different BFNs in the same antenna array, as will be described below.

FIG.3shows a dual-polarized 2 column antenna module with 2×2 BFN's generally shown at70. 2×2 BFN10is the same as shown inFIG.1A. This 2×2 antenna module70includes a first 2×2 BFN10forming beams with −45° polarization, and a second 2×2 BFN10forming beams with +45° polarization, as shown. Each column of radiators76has at least one dual polarized radiator, for example, a crossed dipole.

FIG.4shows a dual-polarized 3 column antenna module with 2×3 BFN's generally shown at80. 2×3 BFN20is the same as shown inFIG.2A. This 2×3 antenna module80includes a first 2×3 BFN20forming beams with −45° polarization, and a second 2×3 BFN20forming beams with +45° polarization, as shown. Each column of radiators76has at least one dual polarized radiator, for example, a crossed dipole.

FIG.5shows a dual-polarized 4 column antenna module with 2×4 BFN's generally shown at90. 2×4 BFN50is the same as shown inFIG.2C. This 2×4 antenna module80includes a first 2×4 BFN50forming beams with −45° polarization, and a second 2×4 BFN50forming beams with +45° polarization, as shown. Each column of radiators76has at least one dual polarized radiator, for example, a crossed dipole.

Below, inFIGS.6-10, the new modular method of dual-beam forming will be illustrated for antennas with 45 and 33 deg., as the most desirable for 5-sector and 6-sector applications.

Referring now toFIG.6, there is generally shown at100a dual polarized antenna array for two beams each with a 45° AzBW. The respective amplitudes and phase for one of the beams is shown near the respective radiators76. The antenna configuration100is seen to have 3 2×3 modules80s and two 2×2 modules70. Modules are connected with four vertical dividers101,102,103,104, having 4 ports which are related to 2 beams with +45° polarization and 2 beams with −45° polarization, as shown inFIG.6. The horizontal spacing between radiators columns76in module80is X3, and the horizontal spacing between radiators in module70is X2. Preferably, dimension X3 is less than dimension X2, X3<X2. However, in some applications, dimension X3 may equal dimension X2, X3=X2, or even X3>X2, depending on the desired radiation pattern. Usually the spacings X2 and X3 are close to half wavelength (λ/2), and adjustment of the spacings provides adjustment of the resulting AzBW. The splitting coefficient of coupler22was selected at 3.5 dB to get low Az sidelobes and high beam cross-over level of 3.5 dB.

Referring toFIG.7A, there is shown at110a simulated azimuth patterns for both of the beams provided by the antenna100shown inFIG.6, with X3=X2 =0.46λ and 2 crossed dipoles in each column76, separated by 0.87λ As shown, each azimuth pattern has an associated sidelobe that is at least −27 dB below the associated main beam with beam cross-over level of −3.5 dB. Advantageously, the present invention is configured to provide a radiation pattern with low sidelobes in both planes. As shown inFIG.7B, the low level of upper sidelobes121is achieved also in the elevation plane (<−17 dB, which exceeds the industry standard of <−15 dB). As it can be seen inFIG.6, the amplitude distribution and the low sidelobes in both planes are achieved with small amplitude taper loss of 0.37 dB. So, by selection of a number of 2×2 and 2×3 modules, distance X2 and X3 together with the splitting coefficient of coupler22, a desirable AzBW together with desirable level of sidelobes is achieved. Vertical dividers101,102,103,104can be combined with phase shifters for elevation beam tilting.

FIG.8Adepicts a practical dual-beam antenna configuration for a 33° C. AzBW, when viewed from the radiation side of the antenna array, which has three (3) 3-column radiator modules80and two (2) 4-column modules90. Each column76has 2 crossed dipoles. Four ports95are associated with 2 beams with +45 degree polarization and 2 beams with −45 degree polarization.

FIG.8Bshows antenna122when viewing the antenna from the back side, where 2×3 BFN133and 2×4 BFN134are located together with associated phase shifters/dividers135. Phase shifters/dividers135, mechanically controlled by rods96, provide antenna130with independently selectable down tilt for both beams.

FIG.9is a graph depicting the azimuth dual-beam patterns for the antenna array122shown inFIG.8A,8B, measured at 1950 MHz and having 33 degree AzBW.

Referring toFIG.10, there is shown at140the dual beam azimuth patterns for the antenna array122ofFIG.8A,8B, measured in the frequency band 1700-2200 MHz. As one can see fromFIGS.9and10, low side lobe level (<20 dB) is achieved in very wide (25%) frequency band. The Elevation pattern has low sidelobes, too (<−18 dB).

As can be appreciated inFIGS.9and10, up to about 95% of the radiated power for each main beam, Beam1and Beam2, is directed in the desired sector, with only about 5% of the radiated energy being lost in the sidelobes and main beam portions outside the sector, which significantly reduces interference when utilized in a sectored wireless cell. Moreover, the overall physical dimensions of the antenna122are significantly reduced from the conventional 6-sector antennas, allowing for a more compact design, and allowing these sector antennas122to be conveniently mounted on antenna towers. Three (3) of the antennas122(instead of six antennas in a conventional design) may be conveniently configured on an antenna tower to serve the complete cell, with very little interference between cells, and with the majority of the radiated power being directed into the intended sectors of the cell.

For instance, the physical dimensions of 2-beam antenna122inFIG.8A,8Bare 1.3×0.3 m, the same as dimensions of conventional single beam antenna with 33 degree AzBW.

In other designs based on the modular approach of the present invention, other dual-beam antennas having a different AzBW may be achieved, such as a 25, 35, 45 or 55 degree AzBW, which can be required for different applications. For example, 55 and 45 degree antennas can be used for 4 and 5 sector cellular systems. In each of these configurations, by the combination of the 2×2, 2×3 and 2×4 modules, and the associated spacing X2, X3 and X4 between the radiator columns (as shown inFIGS.6and8A), the desired AzBW can be achieved with very low sidelobes and also adjustable beam tilt. Also, the splitting coefficient of coupler22provides another degree of freedom for pattern optimization. In the result, the present invention allows to reduce azimuth sidelobes by 10-15 dB in comparison with prior art.

Though the invention has been described with respect to a specific preferred embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present application. For example, the invention can be applicable for radar multi-beam antennas. The intention is therefore that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.