Patent Application
20190386383
The present invention generally relates to antennas, and more specifically to the wide-beam antenna with a modular main radiator.
One of the major challenges facing today's wireless carriers is providing coverage and capacity in densely populated environments. One example is urban areas where high-rise buildings provide mounting locations for base station antennas, but they also make it difficult for wireless signals to propagate effectively at the street level. As a result, a rooftop mounting approach may not provide the desired coverage for optimal network performance. One alternative that has received considerable attention lately is the use of small cell antennas where a large number of low-gain antennas are deployed close to street level and distributed throughout the city. Small cell antennas may have unique pattern requirements depending on the mounting location. For example, an antenna may require wide azimuth beamwidth up to 180° to cover an open area along a street or along the side of a building.
Filtering is also desirable for small cell antennas where increased spectrum usage for cellular and other applications creates potential for interference that could degrade system performance. For example, 3.5 GHz and 5 GHz spectrum have recently been approved for mobile wireless services. To limit cost and meet zoning restrictions, wireless carriers generally prefer that multiband antenna be deployed where multiple antennas covering different bands are included in the same package. This could lead to coupling between bands that negatively impacts system performance, and filtering may be required to mitigate the inter-band coupling. There is also unlicensed spectrum in the 3-6 GHz range, and applications using these bands in an urban environment could interfere with a base station system operating from 1.695-2.7 GHz, or harmonics from the base station could create interference for nearby systems using spectrum in the 3-6 GHz range. Filtering is required to mitigate these risks.
Current wide-beam antenna approaches either do not incorporate filtering at the element, or filtering antennas do not exhibit wide enough beamwidth to be useful in the above-mentioned application. There is a need for broadband base station antennas that exhibit wide-beam operation and incorporate filtering for interference management.
The present invention details a broadband, wide-beam antenna configured for linear polarization with a modular center conductor where filtering can be added without significant modification of the antenna. The antenna provides a wide beamwidth for operational environments requiring wide azimuth beamwidth as described in the related art. The radiating element is primarily formed as a sleeve monopole antenna with a grounded reflector and a parasitic director. The sleeve monopole antenna is inherently omnidirectional, but the addition of the reflector provides directionality in the radiation pattern. The parasitic director is found to improve elevation patterns over the operating band.
The antenna also includes filtering for interference mitigation. Additional services offered for advanced 4G and 5G systems increases the amount of spectrum usage at the base station, and interference may occur. Additionally, the mounting locations of small cell and DAS antennas for capacity enhancements in urban environments creates more potential for interference than for traditional tower-mounted macro antennas. The antenna of the present invention incorporates filtering similar to that described in U.S. patent application Ser. No. 15/395,170, Publication No. 2018-0138597 and “Sleeve monopole antenna with integrated filter for base station applications,” 2017 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), San Diego, Calif., 2017, pp. 11-12 for interference mitigation, but the filtering is incorporated as a module along with the main radiator. The main radiator/filtering module can be removed in the field to add filtering capability or remove filtering capability. Additionally, this modular approach could be applied to change the operating band of the antenna or change the filtered frequencies.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description, taken in conjunction with the accompanying drawings.
In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in similar manner to accomplish a similar purpose. Several preferred embodiments of the invention are described for illustrative purposes; it being understood that the invention may be embodied in other forms not specifically shown in the drawings.
With respect to
The RF feed PCB 120 is fabricated as a printed circuit board (PCB) with a bottom that has a copper layer 124 and an etch relief along the outer edge. The RF feed bottom copper layer 124 is soldered to the cable outer conductor 143 for grounding. The outer diameter of the bottom copper disk 124 is 31.75 mm. The top side of the RF feed PCB 120 includes four conductive pads or copper patches 122 arranged in a circular manner about the center of the RF feed PCB 120. These patches are arranged adjacent to the outer diameter of the sleeve 110, and these patches include a plated through hole 125 so that they are directly connected to the ground side of the RF feed bottom copper 124. The sleeve 110 is soldered to four copper patches 122 so that the sleeve 110 is in direct electrical contact with the ground side of the RF feed PCB 120.
The top side of the RF feed PCB 120 also includes a feed pad 123 where the cable center pin 141 is soldered to this feed pad 123. Referring to
In addition, the sleeve monopole is modular in that different filter parts can be removed and replaced. For example, the main radiator 100 can be replaced by the radiator 300 of
The reflector 150 in the illustrated, non-limiting embodiment is composed of PCB material where only one side 151 is covered with copper. In one embodiment, the reflector 150 is a flat planar member with two sides 151, 152. The side 152 facing the primary components is non-conductive, and the side 151 opposite the primary components of the antenna is covered with copper. This copper is soldered to the cable outer conductor 143 for grounding, such as at solder point 144. The copper of the reflector 150 is 31.75 mm×127 mm. The sleeve 110 has an outer diameter of 15.875 mm with a wall thickness of 0.74 mm. The height of the sleeve 110 is 31.7 mm, and the distance between the sleeve 110 and the reflector 150 is 40.1 mm. The distance between the sleeve 110 and reflector 150 can be adjusted ±15% to increase or decrease the horizontal beamwidth.
In one embodiment, the main radiator 100 is a tube that is 58.2 mm tall with an outer diameter of 4.7625 mm. The parasitic director 160 is a solid rod with an outer diameter of 3.175 mm and a height of 40 mm. The parasitic director 160 is spaced 8.3 mm from the sleeve 110. The sleeve 110 is a tube with a central opening that receives the main radiator 100 such that the sleeve 110 is concentrically arranged about the main radiator 100. The inner diameter D of the sleeve 110 is substantially larger than the outer diameter d of the main radiator 100, to provide a gap or space between the sleeve 110 and the radiator 100. The ratio
can range from values of 3 to 7 and be optimized to provide impedance matching with negligible impact to radiation patterns.
As shown, the bottommost end of the radiator 100 and the sleeve 110 are substantially flush with one another and attach to the PCB 120. The radiator 100 is substantially longer in length than the sleeve 110, so that only a portion of the radiator 100 is surrounded by the sleeve 110, and the radiator 100 projects outward from the sleeve 110. The sleeve 110 is used to impedance match the radiator 100 over a larger frequency range i.e. >50% impedance bandwidth. The radiator is at least partly exposed to be able to communicate.
The disk load 130 is made of PCB material where the bottom copper has a diameter of 8.5 mm. The feed cable 140 is also fixed at a 55° angle relative to the longitudinal axis of the main radiator 100. This angle is chosen because the feed cable has an impact on the elevation patterns for the antenna. The 55° angle in addition to the parasitic director ensures satisfactory elevation patterns for the preferred embodiment where there is only approximately 6°-7° variation in the 10-dB elevation beamwidth at (p=90°. In the embodiment shown, the disk load 130 has a disk shape that is substantially flat and circular and is located at the topmost end of the radiator 100. The disk size can be used to optimize the impedance bandwidth of the modular radiator.
The antenna of the illustrated embodiment also includes an RF absorber 180 wrapped around the feed cable 140 after it passes the reflector 150. This minimizes pattern impacts from the feed cable 140. The RF absorber 180 can be, for example, ECCOSORB MCS produced by Laird Technologies, Inc. The material properties are simulated as εr=38, tan δ=0.01, μr=5, tan δm=0.6, where μr is the relative permeability and tan δm is the magnetic loss tangent for the material. Note that for simulation of the antennas in this application, the feed cable 140 is modeled to extend approximately 46.75 mm past the back side of the reflector 150. The RF absorber 180 has a 1 mm gap from the back side of the reflector 150 and extends to the end of the feed cable 140. The RF absorber is modeled with a 1 mm thickness.
All PCBs have a dielectric thickness of 0.762 mm with a relative permittivity of εr=3.38 and loss tangent tan δ=0.0035. The metallization on all PCBs can be 0.06 mm thick to account for 0.035 mm of copper and 0.025 mm of finish plating. The material thicknesses and dielectric properties can be chosen differently, but this may require retuning of the antenna.
The antenna is supported by non-metallic supports 171a, 171b to position the RF feed PCB 120 relative to the reflector 150. The supports 171 are L-shaped having a shorter leg 171a that attaches to the reflector 150 and a longer leg 171b that extends outward substantially orthogonal to the planar surface of the reflector 150 to form a shelf for the PCB 120. The PCB 120 is connected at the distal end of the longer leg 171b, to position the PCB 120 (as well as the radiator 100, sleeve 110 and director 160) at a desired distance from the reflector 150. The distance between the sleeve 110 and reflector 150 can be adjusted ±15% to increase or decrease the horizontal beamwidth.
A non-metallic director support 170 is included to position the director 160 relative to the sleeve 110. The director support 170 also includes mounting holes to ensure proper alignment of the director 160. The fasteners 172, 173 are non-metallic and are used to secure the antenna supports 170, 171a, 171b, 174 to the proper parts of the antenna. The director support 170 is formed by a support bracket having a first or proximal end with a ring and a second or distal end with an opening. The ring is substantially larger than the opening. The ring has a central opening that receives the sleeve 110 and supports the sleeve 110 on the PCB 120. The sleeve 110 can be connected to the ring in any suitable manner, such as by a friction fit, mechanical device or adhesive. The ring is positioned part-way up on the sleeve to provide better support to the sleeve 110 and the director 160.
A mounting bracket extends downward from the ring and forms a tab on the top surface of the PCB 120. A fastener 172 (such as a screw or bolt or the like) extends through an opening in the mounting tab, an opening in the PCB (
The feed cable 140 extends from the bottom of the PCB 120 to reflector 150. The fastener 173 attaches one end of the cable 140 to the bottom of the PCB 120. A non-metallic cable support 174 is used to support the feed cable 140 and maintain the appropriate angle. The cable 140 can extend through a slot at the bottom edge of the reflector 150 to the opposite side of the reflector 150.
The material for the support structures is selected to account for the dielectric properties of the support structures, which can impact the impedance match and the pattern performance of the antenna. In one embodiment, the support structures 170, 171a, 171b are 3D printed ABS (acrylonitrile butadiene styrene) where the desired fill factor is set to 5% to ensure minimal material is used while providing enough mechanical stability to properly secure all parts. This maintains a low dielectric constant to reduce material loading effects on the antenna. However, note that the particular geometry of the part and the 3D printer used to print the parts can impact the fill in certain regions and, as a result, material properties of the part. These effects are considered in the design where the wall thickness can be 0.5 mm, and the 3D printed ABS can have εr=2.5 and tan δ=0.007. The cable support 174 can be 100% filled and does not have a significant impact on impedance matching or pattern performance for the antenna.
As the diameter of the monopole radiator 100 increases, it lowers the effective Q resulting in a smaller impedance variation over frequency than a smaller diameter. Loading at the top of the main radiator 100 with the disk load 130 increases the effective height of the radiator. The first resonance of the sleeve monopole occurs when the effective length of the radiator is one-quarter wavelength. This resonance is located at the lower end of the operating frequency band. Increasing the diameter of the disk load 130 can reduce the height of the main radiator to 70% of the required height of a monopole without disk loading. The main function of the sleeve 100 dimensions are to act as an impedance transformer to match the system to Z0. The bottom portion of the sleeve 100 is soldered to the ground pads 122, which are connected to the ground plane 124 with plated-thru-hole vias creating a RF and DC short. The main function of the reflector 150 and director 160 is to focus the radiation from the radiator 100 generally in a line from the radiator 100 towards the director 160. Spacing between these components can be adjusted to produce different degrees of pattern focus but range from 0.1<λ<0.5.
In an alternative embodiment shown in
The filter elements used in the present embodiment are shown in
On the rear surface of the dielectric 210 are formed back vertical copper traces 203a, 203b. The vertical traces 203a, 203b are formed along the two peripheral sides of the length of the dielectric, shown on the left and right in the embodiment of
In addition, plated through-holes 202 are provided along the front and back vertical traces 200, 203. The through-holes 202 extend through the dielectric 210 from the front surface where it connects with the front traces 200, to the rear surface where it connects with the rear traces 203. The through-holes 202 are plated to be conductive and provide a direct electrical connection between the front and back copper traces 200, 203. The plated through-holes reduce surface currents that reduce the filter performance.
The filter dielectric 210 has a thickness of 0.762 mm and the same dielectric properties as all other PCBs described previously. The copper traces 200a, 200b, 201, 203a, 203b can be 0.06 mm thick. The front vertical copper traces 200a, 203b and the back vertical copper traces 203a, 203b can have a height of 14.5 mm and a width of 0.75 mm. The horizontal copper trace can have a width of 0.25 mm and an overall length of approximately 5.36 mm. The overall height and width of the filter dielectric is 15.5 mm and 5.36 mm, respectively.
The full assembled antenna with filtering is shown in
To modify the original antenna (
The bottom portion has a smaller outer diameter to accommodate the filter elements as well as provide impedance matching with the filter elements in place. The filter elements are based on metamaterial structures, and they generate an effective dielectric constant in the sleeve as described in U.S. patent application Ser. No. 15/981,556 (Publ. No. 2018/0261923), the entire contents of which are hereby incorporated by reference. The thinner main radiator section helps to accommodate this effective dielectric constant. The filter support 320 is used to support the placement of the filter elements, and the top portion of the filter support is used to help impedance match the antenna in an approach similar to that described in US Publ. No. 2018/0261923. The top portion of the filter support 320 has a height of 12.64 mm and an outer diameter of 9.1625 mm.
The filter support 320 is best shown in
The filter support 320 has a thickness of 0.8 mm on either side of the filter slots 321, and the filter support 320 is designed to position the filter dielectric 210 at a height of 0.8 mm from the RF feed dielectric 121. The filtered antenna of the embodiment shown includes 3 filter elements (such as the filter element of
The simulated return loss for the antennas described herein are plotted in
The simulated radiation patterns for the antennas described herein are plotted in
The elevation (El) patterns for the antenna without filtering are shown in
The Az patterns for the antenna with filtering are shown in
The elevation (El) patterns for the antenna with filtering are shown in
In another non-limiting example embodiment of the present invention, the antenna performance can be tuned by changing out the main radiator 100 (e.g., removing the radiator 100 and replacing it with another radiator 100). With respect to
The reduced height of the first tuned main radiator 700 shifts the antenna response to higher frequency compared to the original antenna of
Turning to
It is further noted that the electrical characteristics of the sleeve monopole can be adjusted by a number of features including but not limited to controlling the gap between the radiator 100 and the sleeve 110, the size and shape of the disk load 130, the size and shape of the sleeve 110, the distance between the main radiator 100 and the reflector 150, the size and shape of the director 160, the distance between the director 160 and the main radiator 100 and the sleeve 110, and the angle of the feed cable.
It is further noted that the description and claims use several geometric or relational terms, such as circular, parallel, orthogonal, concentric, planar, and flat. In addition, the description and claims use several directional or positioning terms and the like, such as top, bottom, left, right, up, down, inner, outer, distal, and proximal. Those terms are merely for convenience to facilitate the description based on the embodiments shown in the figures. Those terms are not intended to limit the invention. Thus, it should be recognized that the invention can be described in other ways without those geometric, relational, directional or positioning terms. In addition, the geometric or relational terms may not be exact. For instance, walls may not be exactly perpendicular or parallel to one another but still be considered to be substantially perpendicular or parallel because of, for example, roughness of surfaces, tolerances allowed in manufacturing, etc. And, other suitable geometries and relationships can be provided without departing from the spirit and scope of the invention.
Within this specification, the various sizes, shapes and dimensions are approximate and exemplary to illustrate the scope of the invention and are not limiting. The sizes and the terms “substantially” and “about” mean plus or minus 15-20%, or in other embodiments plus or minus 10%, and in other embodiments plus or minus 5%, and plus or minus 1-2%. In addition, while specific dimensions, sizes and shapes may be provided in certain embodiments of the invention, those are simply to illustrate the scope of the invention and are not limiting. Thus, other dimensions, sizes and/or shapes can be utilized without departing from the spirit and scope of the invention.
The foregoing description and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not intended to be limited by the preferred embodiment. Numerous applications of the invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 62/684,838, filed Jun. 14, 2018, and U.S. Provisional Application No. 62/696,538, filed Jul. 11, 2018. The entire contents of those applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62684838 | Jun 2018 | US | |
| 62696538 | Jul 2018 | US |
