Patent Description:
The present invention generally relates to radio communications and, more particularly, to a calibration device, a base station antenna and a communication assembly.

Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as "cells" which are served by respective base stations. Each base station may include one or more base station antennas that are configured to provide two-way radio frequency ("RF") communications with mobile subscribers that are within the cell served by the base station.

In many cases, each base station is divided into "sectors". In perhaps the most common configuration, a hexagonally shaped cell is divided into three <NUM>° sectors, and each sector is served by one or more base station antennas that have an azimuth Half Power Beam width (HPBW) of approximately <NUM>°. Typically, the base station antennas are mounted on a tower structure, with the radiation patterns (also referred to herein as "antenna beams") that are generated by the base station antennas directed outwardly. Base station antennas are often implemented as linear or planar phased arrays of radiating elements.

Due to the growing demand for wireless communications, multi-band technology, Multiple-Input Multiple-Output (MIMO) technology, and beamforming technology have been rapidly developed to support different services and high throughput data transmission. However, with the integration of more and more frequency bands and/or RF ports in one base station antenna, the antenna system such as the feed network and the calibration network become more complicated and more sensitive to interference. Therefore, how to achieve high anti-interference performance of the antenna system at reasonable cost has been a technical problem urgently to be solved by those skilled in the art.

Cited art given in <CIT> discloses a calibration network of an antenna array. The calibration network comprises a first dielectric substrate layer and a second dielectric substrate layer that are laminated; band type line circuits are arranged between the first dielectric substrate layer and the second dielectric substrate layer; microstrip line circuits are arranged at the surface of one side, far away from of the second dielectric substrate layer, of the first dielectric substrate layer; and more than one band type line circuit and more than one microstrip line circuit are arranged, wherein the number of the band type line circuits is identical with that of the microstrip line circuits. One band type line circuit and one microstrip line circuit are connected to form one calibration circuit. In each calibration circuit, the band type line circuit consists of one power combiner and more than two directional couplers; the microstrip line circuit includes more than two amplitude modulators, wherein the number of the amplitude modulators is identical with that of the directional couplers; and each amplitude regulator is connected between a coupling terminal of one directional coupler and an input terminal of the power combiner.

<CIT> discloses a time division-synchronization code division multiple access (TD-SCDMA) and time division-long term evolution (TD-LTE) intelligent antenna multi-channel broadband calibration network. The multi-channel broadband calibration network is characterized in that: a micro-strip coplanar waveguide structure is adopted; the two ends of a coupling line of a coupler are loaded with crossed coupling lines; and a metal shield box is eliminated. An entire structure comprises a plurality of power dividers, a plurality of directional couplers and an installation plate, wherein each power divider and each directional coupler adopt micro-strip coplanar waveguide structures; crossed coupling lines are loaded between coupling lines of each directional coupler; a radiofrequency cable core is welded with each directional coupler through a through hole on the installation plate and a metallized via hole on the directional coupler; the sheath of a cable is welded with a back face grounding layer; one side, in the same direction as an antenna, of the installation plate is provided with a metal flange; and the installation plate is arranged on an antenna bottom plate. The network has the advantages of high electric index, simple structure and contribution to mass production.

According to a first aspect of the present invention, there is a calibration device for an antenna provided according to claim <NUM>. The calibration device comprises a dielectric substrate and a metal pattern printed on the dielectric substrate, wherein the metal pattern includes at least a portion of a calibration circuit, wherein a first portion of the calibration circuit is provided on a first major surface of the dielectric substrate, a second portion of the calibration circuit is provided on a second major surface of the dielectric substrate opposite the first major surface, and the first portion and/or the second portion of the calibration circuit are/is constructed as coplanar waveguide transmission lines. Therefore, a high anti-interference performance of the antenna system can be achieved at reasonable cost.

The first portion of the calibration circuit at least includes a radio frequency (RF) port and/or a coupler.

The second portion of the calibration circuit at least includes a calibration port and/or a power combiner.

The first portion of the calibration circuit comprises a plurality of first conductive traces and the second portion of the calibration circuit comprises a plurality of second conductive traces, and the metal pattern further includes a first coplanar ground area printed on both sides of at least some of the first conductive traces and a second coplanar ground area printed on both sides of at least some of the second conductive traces.

In some embodiments, the first coplanar ground area is spaced apart from the first conductive traces by a first slot, in which metallization is removed, and the second coplanar ground area is spaced apart from the second conductive traces by a second slot, in which metallization is removed.

In some embodiments, with reference to a direction perpendicular to the first major surface of the dielectric substrate, the first portion of the calibration circuit is directly above at least a portion of the second coplanar ground area, and/or the second portion of the calibration circuit is directly below at least a portion of the first coplanar ground area.

In some embodiments, the first portion of the calibration circuit and/or the second portion of the calibration circuit are/is at least partially configured as coplanar waveguide transmission lines with back metallization.

In some embodiments, the first slot has a width between <NUM> and <NUM>, and the second slot has a width between <NUM> and <NUM>.

In some embodiments, the first portion of the calibration circuit is electrically connected to the second portion of the calibration circuit by means of a first conductive structure.

In some embodiments, the first conductive structure includes a via or a metal conductor.

In some embodiments, the first coplanar ground area is electrically connected to the second coplanar ground area by means of a second conductive structure.

In some embodiments, the second conductive structure includes a via or a metal conductor.

According to a second aspect of the present invention, there is a base station antenna provided according to claim <NUM>. The base station antenna comprises a reflector, a calibration device according to any of claims <NUM> to <NUM> and a baseplate, wherein an antenna array is provided on the front side of the reflector, the calibration device and the baseplate are provided on the rear side of the reflector, and the calibration device is mounted on the baseplate.

In some embodiments, the baseplate is provided with a groove, in which metal is removed, wherein the first portion of the calibration circuit falls within the range of the groove to avoid direct electrical contact between the first portion of the calibration circuit and the baseplate.

In some embodiments, the calibration device is configured as a single-layer printed circuit board including only one dielectric substrate between the first portion and the second portion of the calibration circuit.

The present invention will be described below with reference to the drawings, in which several embodiments of the present invention are shown. The invention is specifically defined by the attached claims. It should be understood, however, that the present invention may be implemented in many different ways, and is not limited to the example embodiments described below. In fact, the embodiments described hereinafter are intended to make a more complete disclosure of the present invention and to adequately explain the scope of the present invention to a person skilled in the art. The embodiments disclosed herein can be combined in various ways to provide many additional embodiments.

The wording in the specification is only used for describing particular embodiments and is not intended to limit the present invention. All the terms used in the specification (including technical and scientific terms) have the meanings as normally understood by a person skilled in the art, unless otherwise defined. For the sake of conciseness and/or clarity, well-known functions or constructions may not be described in detail.

In the specification, when an element is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element, there are no intervening elements present. In the specification, references to a feature that is disposed "adjacent" another feature may have portions that overlap, overlie or underlie the adjacent feature.

In the specification, words describing spatial relationships such as "up", "down", "left", "right", "forth", "back", "high", "low" and the like may describe a relation of one feature to another feature in the drawings. It should be understood that these terms also encompass different orientations of the apparatus in use or operation, in addition to encompassing the orientations shown in the drawings. For example, when the apparatus in the drawings is turned over, the features previously described as being "below" other features may be described to be "above" other features at this time. The apparatus may also be otherwise oriented (rotated <NUM> degrees or at other orientations) and the relative spatial relationships will be correspondingly altered.

The term "A or B" used through the specification refers to "A and B" and "A or B" rather than meaning that A and B are exclusive, unless otherwise specified.

The term "schematically" or "exemplary", as used herein, means "serving as an example, instance, or illustration", rather than as a "model" that would be exactly duplicated. Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations.

Herein, the term "substantially", is intended to encompass any slight variations due to design or manufacturing imperfections, device or component tolerances, environmental effects and/or other factors.

In this context, the term "at least a portion" may be a portion of any proportion, for example, may be greater than <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or even <NUM>%.

In addition, certain terminology, such as the terms "first", "second" and the like, may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, the terms "first", "second" and other such numerical terms referring to structures or elements do not imply a sequence or order unless clearly indicated by the context.

Further, it should be noted that, the terms "comprise/include", as used herein, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings.

<FIG> is a schematic top view of a communication assembly according to some embodiments of the present invention. As shown in <FIG>, the communication assembly includes a base station antenna and an integrated RRU. The base station antenna <NUM> may be mounted on a raised structure, such as an antenna tower or the like, with its longitudinal axis extending substantially perpendicular to the ground for convenient operation. The base station antenna <NUM> includes a radome <NUM> that provides environmental protection and a reflector <NUM>. The reflector <NUM> may include a metal surface that provides a ground plane and reflects electromagnetic waves reaching it, for example, the metal surface redirects the electromagnetic waves for forward propagation. The base station antenna <NUM> further includes a feed board <NUM> disposed on a front side of the reflector <NUM>. An antenna array <NUM> and its feeding circuits may be integrated on the feed board <NUM> in some embodiments. In other embodiments, a plurality of feed boards <NUM> may be provided and subsets of radiating elements of the antenna array <NUM> are mounted on the respective feed boards <NUM>. The base station antenna <NUM> further includes mechanical and electronic components, such as a connector, a cable, a phase shifter, a remote electronic tilt (RET) unit, a duplexer, a calibration device <NUM>, a filter <NUM> and the like, which may be disposed on a rear side of the reflector <NUM>. In addition, a remote radio unit (RRU) <NUM> may be integrated outside the base station antenna <NUM>, for example, installed on the rear side of the base station antenna <NUM>.

In some types of the base station antennas <NUM>, such as beamforming antennas, due to uncontrollable errors in the design, manufacture or use of RF control systems (such as the RRU <NUM>) or the antenna feed networks, a calibration device <NUM> is typically required to compensate for the phase offsets and/or amplitude offsets of the RF signals that are input at different RF ports. This process is often referred to as "calibration.

The calibration device <NUM> may be configured as a printed circuit board that may be separate from the feed board <NUM>. Typically, with the structural strength taken into account, the calibration device <NUM> needs to be mounted on a baseplate <NUM>, which may be a plate in any suitable form, such as a metal plate. For the purpose of calibration, the calibration device <NUM> and the RRU <NUM> may bi-directionally transmit RF signals by, for example, a known coaxial connection device <NUM>, which may be a coaxial connector or a coaxial cable.

A calibration device may include a dielectric substrate, a microstrip calibration circuit disposed on a first major surface of the dielectric substrate, and a ground metal layer disposed on a second major surface of the dielectric substrate. However, as more and more frequency bands and/or RF ports are integrated in the base station antenna, for example, from 8x8 MIMO (8R8T) to 64x64 MIMO (64R64T), the calibration device <NUM> becomes more sensitive to external interference signals, which may be noise signals coming from surrounding environments, and may also be RF signals reflected back from metal components near or within the base station antenna <NUM>. As the calibration device <NUM> is disposed adjacent the RRU <NUM> which has a metal housing <NUM>, the RF signal emitted from the calibration device <NUM> tend to be reflected by the metal housing <NUM> back to the calibration device <NUM>. Such reflected signals can interfere with a calibration circuit <NUM> in the calibration device <NUM>.

In order to improve the anti-interference performance of the calibration device, the calibration circuit of a conventional calibration device may be designed as a stripline network. For this purpose, the conventional calibration device may be implemented as a multilayer printed circuit board including at least two dielectric substrates, wherein a first ground metal layer may be disposed on an upper surface of the upper dielectric substrate, a second ground metal layer may be disposed on a lower surface of the lower dielectric substrate, and the calibration circuit is provided in a metal layer between the two dielectric substrates. As a result, the calibration circuit is surrounded by the first and second ground metal layers, and may thus constitute a stripline network. The stripline network may be advantageous in that it can reduce losses of radiation signals and shield RF transmission lines from external radiation. However, the stripline network also has some disadvantages: First, it is complex to manufacture a stripline based calibration circuit. Second the cost is high. Third, it is difficult to tune the RF performance of the calibration circuit. Therefore, how to achieve high anti-interference performance of the antenna system at reasonable cost has been a technical problem urgently to be solved by those skilled in the art.

Next, the calibration device <NUM> according to some embodiments of the present invention will be described in more detail with reference to <FIG>, where <FIG> is a schematic partial sectional view of the calibration device <NUM> according to some embodiments of the present invention, <FIG> is a simplified schematic view showing a first portion <NUM>-<NUM> of the calibration circuit <NUM> on the calibration device <NUM>, <FIG> is a simplified schematic view showing a second portion <NUM>-<NUM> of the calibration circuit <NUM> on the calibration device <NUM>, <FIG> is an enlarged partial schematic view showing the first portion <NUM>-<NUM> of the calibration circuit <NUM>, and <FIG> is a partial schematic view showing the second portion <NUM>-<NUM> of the calibration circuit <NUM>.

Referring to <FIG>, the calibration device <NUM> according to some embodiments of the present invention may be configured as one printed circuit board, such as a single-layer printed circuit board. In order to provide structural support, the calibration device <NUM> may be mounted on a baseplate <NUM> or a support plate (see <FIG>). In the embodiment of <FIG>, the baseplate <NUM> is advantageously disposed on the front side of the calibration device <NUM>, so a majority of the pressing force caused by the RRU <NUM> may not be borne by the calibration device <NUM>, but by the baseplate <NUM>, whereby the structural safety of the calibration device <NUM> is guaranteed.

The calibration device <NUM> may include a dielectric substrate <NUM>, and a metal pattern printed on the dielectric substrate <NUM>. The metal pattern may include at least a portion of the calibration circuit <NUM>. In some embodiments, the calibration device <NUM> may be configured as a single printed circuit board, and the printed circuit board may include an entirety of the calibration circuit <NUM>. In other embodiments, the calibration device <NUM> may include two or more printed circuit boards, each of which may include a portion of the calibration circuit <NUM>, and the individual portions of the calibration circuit may be in RF signal connection to each other using conductive connection devices, such as coaxial cables, coaxial connectors or electrical conductors.

The calibration circuit <NUM> may include a calibration port <NUM>, transmission lines <NUM>, power combiners <NUM> and couplers <NUM>. The power combiners <NUM> may be configured as Wilkinson power combiners, and the couplers <NUM> may be configured as directional couplers. The calibration circuit <NUM> may be used to identify any unintended variations in the amplitude and/or phase of the RF signals that are input to the different RF ports <NUM> of the antenna <NUM>.

Pursuant to some embodiments of the present invention, the calibration circuit <NUM> may be divided into at least two portions, wherein the first portion <NUM>-<NUM> of the calibration circuit <NUM> may be on the first major surface <NUM> of the dielectric substrate <NUM>, and the second portion <NUM>-<NUM> of the calibration circuit <NUM> may be on the second major surface <NUM> of the dielectric substrate <NUM> opposite the first major surface <NUM>. The first major surface <NUM> of the dielectric substrate <NUM> may face away from the RRU <NUM>, whereas the second major surface <NUM> of the dielectric substrate <NUM> may face the RRU <NUM>. In this way, the first portion <NUM>-<NUM> of the calibration circuit <NUM> can be at least further away from the RRU <NUM>, thereby reducing the interference of the RRU <NUM> to at least a portion of the calibration circuit <NUM>. In addition, dividing the calibration circuit <NUM> into at least two portions can reduce the size of the calibration device <NUM> to thereby maintain the compact structure of the base station antenna <NUM>.

In order to prevent the first portion <NUM>-<NUM> of the calibration circuit <NUM> from short-circuiting to the baseplate <NUM>, a groove (not shown) may be provided in an area of the baseplate <NUM> corresponding to the first portion <NUM>-<NUM> of the calibration circuit <NUM>, wherein the metal in the groove is removed to avoid direct electrical contact between the first portion <NUM>-<NUM> of the calibration circuit <NUM> and the baseplate <NUM>. As there is only the need to provide a groove for a portion (i.e., the first portion <NUM>-<NUM>) of the calibration circuit <NUM>, the grooved area of the baseplate <NUM> is relatively limited, thereby ensuring high structural strength of the baseplate <NUM>.

Referring to <FIG> and <FIG>, in some embodiments, the first portion <NUM>-<NUM> of the calibration circuit <NUM> may include the RF port <NUM> and the couplers <NUM>. The second portion <NUM>-<NUM> of the calibration circuit <NUM> may include the calibration port <NUM> and the power combiner <NUM>. An output end <NUM> of each coupler <NUM> may be electrically connected with an input end <NUM> of a power combiner <NUM> by means of a first conductive structure (not shown), such as vias or metal conductors. The design of the calibration circuit <NUM> according to <FIG> and <FIG> is advantageous in that: Firstly, the RF ports <NUM> and the couplers <NUM> can be disposed away from the RRU <NUM>: as the couplers <NUM> are relatively sensitive to radiant energy and near-field coupling, arranging of the RF ports <NUM> and the couplers <NUM> on a side facing away from the RRU <NUM> can reduce interference of the RRU <NUM> to the calibration circuit <NUM>. Secondly, the first portion <NUM>-<NUM> of the calibration circuit <NUM> occupies only a part of the entire calibration circuit <NUM>, so the grooved area on the baseplate <NUM> is relatively limited.

Pursuant to some embodiments of the present invention, in order to further reduce the interference of external interference signals to the calibration circuit <NUM>, the calibration circuit <NUM> may be configured as a coplanar waveguide transmission line. Referring to <FIG>, <FIG> and <FIG>, coplanar ground areas (hereinafter referred to as first coplanar ground areas <NUM>) are printed on both sides of signal transmission lines of the first portion <NUM>-<NUM> of the calibration circuit <NUM>, and coplanar ground areas (hereinafter referred to as second coplanar ground areas <NUM>) are printed on both sides of signal transmission lines of the second portion <NUM>-<NUM> of the calibration circuit <NUM>. The first coplanar ground areas <NUM> may be spaced apart from the first portion <NUM>-<NUM> of the calibration circuit <NUM> by a first slot <NUM>, in which metalization is removed, and the first slot <NUM> may have a width W of any suitable size, for example, from <NUM> to <NUM> or from <NUM> to <NUM>. The second coplanar ground areas <NUM> may be spaced apart from the second portion <NUM>-<NUM> of the calibration circuit <NUM> by a second slot <NUM>, in which metallization is removed, and the second slot <NUM> may have a width the same as or similar to that of the first slot <NUM>. That is to say, the metal patterns on dielectric substrate may comprise coplanar ground areas surrounding the first portion <NUM>-<NUM> of the calibration circuit <NUM> and the second portion <NUM>-<NUM> of the calibration circuit <NUM> respectively.

The coplanar waveguide transmission lines include coplanar waveguide transmission lines without back metallization, and coplanar waveguide transmission lines with back metallization. In the embodiment of <FIG>, the calibration circuit <NUM> may be at least partially configured as a coplanar waveguide transmission line with back metallization. Referring to <FIG>, in a direction perpendicular to the first major surface <NUM> of the dielectric substrate <NUM> (indicated by arrow R), the first portion <NUM>-<NUM> of the calibration circuit <NUM> and at least a portion of the first coplanar ground area <NUM> may be directly above at least a portion of the second coplanar ground area <NUM>, and the second portion <NUM>-<NUM> of the calibration circuit <NUM> and at least a portion of the second coplanar ground area <NUM> may be directly below at least a portion of the first coplanar ground area <NUM>. The first coplanar ground area <NUM> may be electrically connected to the second coplanar ground area <NUM> by means of a second conductive structure <NUM>, such as a via or a metal conductor. Such coplanar waveguide transmission lines with back metallization are beneficial to further shield the calibration circuit <NUM> from external signals to improve the robustness and reliability of the calibration circuit <NUM>.

In some embodiments, the RRU <NUM> may first input RF signals into the respective RF ports <NUM>. Then, the calibration circuit <NUM> may extract, by means of the couplers <NUM>, a small amount of each of the RF signals from the respective RF ports <NUM>, and then combine these extracted signals to a calibration signal by means of the power combiners <NUM> and pass the calibration signal back to the RRU. The RRU <NUM> may adjust the amplitude and/or phase of the RF signals to be input to the RF ports <NUM> according to the calibration signal so as to provide an optimized antenna <NUM> beam.

It should be understood that the calibration device <NUM> and the calibration circuit <NUM> may include other suitable structural forms and/or operating modes, and are not limited to the embodiments described above.

In other embodiments, the first portion <NUM>-<NUM> of the calibration circuit <NUM> may further include, in addition to the RF port <NUM> and the coupler <NUM>, other RF elements such as a matching impedance, a power combiner <NUM>, or the like. The second portion <NUM>-<NUM> of the calibration circuit <NUM> may further include, in addition to the calibration port <NUM> and the power combiner <NUM>, a matching impedance or the like.

In other embodiments, the calibration process may be performed in a reversed manner, and the power combiner <NUM> functions as a power divider at this time. In this case, the RRU <NUM> may first input a calibration signal to the calibration port <NUM>. Then, the calibration signal is passed from the calibration port <NUM> via the respective transmission lines <NUM> to the power dividers which divide the calibration signal into a plurality of sub-components. The sub-components of the calibration signal are passed by the respective couplers <NUM> to the respective feed branches. The RF ports <NUM> may each extract a small portion of the calibration signal by means of the couplers <NUM>. The RRU <NUM> may read the amplitude and/or phase of the RF signals that are electrically coupled from the calibration circuit <NUM> via the couplers <NUM> to the RF ports <NUM>. Thus, the RRU may accordingly adjust the amplitude and/or phase of the RF signal to be input to the RF port <NUM> so as to provide an optimized antenna <NUM> beam.

Claim 1:
A calibration device (<NUM>) for an antenna (<NUM>), comprising:
a dielectric substrate (<NUM>); and
a metal pattern printed on the dielectric substrate,
wherein the metal pattern includes at least a portion of a calibration circuit (<NUM>),
wherein a first portion of the calibration circuit (<NUM>-<NUM>) is on a first major surface (<NUM>) of the dielectric substrate, a second portion of the calibration circuit (<NUM>-<NUM>) is on a second major surface (<NUM>) of the dielectric substrate that is opposite the first major surface, and the first portion and the second portion of the calibration circuit is constructed as a coplanar waveguide transmission line,
wherein the first portion of the calibration circuit comprises a plurality of first conductive traces and the second portion of the calibration circuit comprises a plurality of second conductive traces, and the metal pattern further includes a first coplanar ground area (<NUM>) printed on both sides of at least some of the first conductive traces and a second coplanar ground area (<NUM>) printed on both sides of at least some of the second conductive traces,
wherein the first portion of the calibration circuit includes at least one radio frequency, RF, port (<NUM>) and at least one coupler (<NUM>), and
wherein the second portion of the calibration circuit includes at least one calibration port (<NUM>) and at least one power combiner (<NUM>).