Patent Application
20090051615
The present invention relates generally to an antenna construction for a mobile station, or other radio device, operable over multiple frequency bands. More particularly, the present invention relates to antenna apparatus, and an associated methodology for forming a hybrid strip antenna of a multi-mode mobile station, or other radio device, operable, e.g., at the 800/900/1800/1900/2100 MHz frequency bands.
The antenna includes radiation elements comprising a strip including an impedance matching element disposed upon the external surfaces of a three-dimensional rectilinear substrate, such as a parallelepiped, cube, or pyramidal frustum. The length of the strip is chosen to efficiently transduce RF energy in at least one frequency band of as many as four or more frequency bands. Since a relatively long strip antenna is wound around a very compact substrate, the antenna is of compact dimensions and exhibits stable and relatively wide resonant frequency band characteristics and radiation patterns.
In modern society, the ready availability and access to mobile radio communication systems through which to communicate is a practical necessity. Cellular, and cellular-like, communication systems are exemplary radio communication systems whose infrastructures have been widely deployed and regularly utilized by many. Successive generations of cellular communication systems have been developed, and their operating parameters and protocols are set forth in standards promulgated by standard-setting bodies. And, successive generations of network apparatus have been deployed, each operable in conformity with an associated operating standard.
Early-generation cellular communication systems provided voice communication services and limited data communication services. Successor-generation, cellular communication systems provide increasingly data-intensive communication services. Differing operating standards not only provide different communication capabilities, but utilize different communication technologies and differing frequencies of operation in different frequency bands. The installation of different types of cellular communication systems is sometimes geographically dependent. That is to say, in different areas, network infrastructures, operable pursuant to different types of operating standards, are deployed. The network infrastructures deployed in the different areas are not necessarily compatible. A mobile station operable to communicate by way of network infrastructure constructed in conformity with one operating specification is not necessarily operable to communicate by way of network infrastructure operable pursuant to another operating standard.
So-called, multi-mode mobile stations have been developed that provide the mobile station with communication capability in more than one, i.e., multiple, communication systems, which also operate at different frequencies in different frequency bands. Generally, such multi-mode mobile stations automatically select the manner by which the mobile station is to be operable, responsive to the detected network infrastructure in whose coverage area that the mobile station is positioned. If positioned in the coverage area of the network infrastructures of more than one type of communication system with which the mobile station is capable of communicating, selection of a network infrastructure through which to communicate is made pursuant to a preference scheme, or manually. When provided with multi-mode capability, the mobile station contains circuitry and circuit elements permitting its operation to communicate pursuant to each of the communication systems. Most simply, a multi-mode mobile station is formed of separate circuitry, separately operable to communicate pursuant to the different operating standards. Sometimes, to the extent that circuit elements of the different circuit paths can be shared, parts of the separate circuit paths are constructed to be intertwined, or otherwise shared. By sharing circuit elements, the circuitry size and part count is reduced, resulting in cost and size savings.
Sharing of antenna transducer elements between the different circuit paths, however, presents unique challenges. The required size of an antenna transducer element is, in part, dependent upon the frequencies of the signal energy that is to be transduced by the transducer element. And, as mobile station constructions become increasingly miniaturized, housed in housings of increasingly small package sizes, antenna transducer design becomes increasingly difficult, particularly in multi-mode mobile stations when the different modes operate at different frequencies. Significant effort has been exerted to construct an antenna transducer, operable over multiple frequency bands, and also of small dimension to permit its positioning within the housing of a mobile station of compact size.
A PIFA (Planar Inverted-F Antenna) has been used in multi-mode mobile stations because of its relatively compact size, low profile and because it permits dual-band radiation, however, PIFA antennas have narrow bandwidths. In order to enhance the bandwidth of a PIFA, the structure of the PIFA is sometimes combined together with a parasitic element, or a multi-layered, three-dimensional structure. Such additions, however, increase the volumetric dimensions of the antenna, as well as its weight. The additional resonant branches make the antenna difficult to tune and sometimes introduce EMC and EMI, which interferes with transducing of signal energy. A need therefore exists for an improved small-dimension antenna structure which is also capable of use in multiple different frequency bands.
It is in light of this background information related to antenna transducers for radio devices that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides compact, lightweight antenna apparatus, and an associated method, for a mobile station, or other radio device, operable over multiple frequency bands.
Through operation of an embodiment of the present invention, a manner is provided by which to form a hybrid strip antenna of a multi-mode mobile station, or other radio device, operable, e.g., at the 800/900/1800/1900 MHz frequency bands.
In one aspect of the present invention, an antenna for a multi-mode mobile station is formed of a cube-shaped dielectric antenna substrate, the surfaces of which carry an end-fed antenna strip, formed of a strip of metal or other conductive material having a length, width and thickness. The length of the strip is much longer than the dimensions of any one face of the antenna substrate, requiring the strip to be folded at least part way over different faces of the antenna substrate. In other words, the length of the antenna strip is multiples of the dimensions of any one face of the cube. The antenna includes a feed point at one end of the strip and a “T”-shaped impedance matching/adjustment element at the end of the strip opposite the feed point.
The cube dimensions and the length and width of the radiation element, which of course also receives signals, are selected so that the radiation element can be “folded” across or “wrapped” around several faces of the cube without the radiation element overlapping itself and without the edges of the radiation element abutting each other. The cube dimensions are also selected so that the cube can fit within the housing of a mobile station.
In the embodiment depicted in the figures, the length of the strip forming the antenna element was approximately one-quarter the wavelength of a signal in the 800 MHz frequency band, and it effectuated resonance in both the 800 and 900 MHz bands. The antenna was also resonant in the 1800, 1900 and 2100 MHz bands.
Since the length of the metal strip forming the radiator is such that the radiator is wrapped around different faces of the cube, the strip forming the radiation element can be thought of, and also described as, several different substantially equal-length conductive segments that are electrically connected to each other in series. Successive segments are joined to each other on the cube face such that each segment's length dimension is orthogonal to the length dimension of adjacent segments. In the embodiments shown, each cube face supports more than one antenna segment. The impedance matching element at the terminus end of the strip is also folded across cube faces.
Due to the compact size, stability of operation, and stable radiation pattern provided by the antenna, the antenna is advantageously utilized in a mobile station, or other radio device, of small volumetric dimensions.
In these and other aspects, therefore, a folded strip antenna, and an associated methodology is provided for a multi-band communication device. The folded strip antenna is embodied by forming a dielectric material into the shape of a cube. A radiation element, such as a thin, flat metal strip, has a length and width such that the strip can be folded to extend at least part way across several of the different faces of the cube.
Turning, therefore, first to
Radio access networks 14, 16, 18, and 22 are representative of four radio networks operable respectively at the 800, 900, 1800, and 1900 MHz frequency bands, respectively. When the mobile station 12 is positioned within the coverage area of any of the radio access networks 14-22, the mobile station is capable of communicating therewith. If the separate networks have overlapping coverage areas, then the selection is made as to which of the networks through which to communicate. The radio access networks 14-22 are coupled, here by way of gateways (GWYs) 26 to a core network 28. A communication endpoint (CE) 32 that is representative of a communication device that communicates with the mobile station.
The mobile station 12 includes a radio transceiver having transceiver circuitry 36 capable of transceiving communication signals with any of the networks 14-22. The transceiver circuitry includes separate or shared transceiver paths constructed to be operable with the operating standards and protocols of the respective networks. The radio station further includes an antenna 50 of an embodiment of the present invention. The antenna is of characteristics to be operable at the different frequency bands at which the transceiver circuitry and the radio access networks are operable. Here, the antenna 50 is operable at the 800, 900, 1800, and 1900 MHz frequency bands. In the exemplary implementation, the antenna 50 is housed together with the transceiver circuitry, in a housing 44 of the mobile station. As the space within the housing that is available to house the antenna is limited, the dimensions of the antenna 50 are correspondingly small while providing for the transducing of signal energy by the antenna over broad frequencies at which the mobile station is operable.
Inasmuch as the antenna substrate 52 is in the shape of a cube, the top face 64 and bottom face 66 are planar or at least substantially planar and lie in corresponding parallel but spaced-apart geometric planes, the separation distance of which defines the height, H, of the cube. The side faces 68, 70, 72 and 74 of the antenna substrate 52 are also planar or substantially planar and orthogonal to the top face 64 and the bottom face 66 with faces adjacent to each other also being orthogonal to each other.
In
In one embodiment, a three-dimensional rectilinear antenna substrate 52 depicted is fabricated as a solid piece of molded dielectric material, in which case, the substrate will of course have multiple sides. A cube-shaped substrate 52 will have six sides. In embodiments where the antenna substrate 52 is solid, the bottom face 66 of the substrate 52 will abut a surface of the supporting substrate 76 when the antenna substrate 52 is mounted atop a supporting substrate 76. Since a solid substrate 52 will add weight and cost, in at least one other embodiment, the three-dimensional rectilinear antenna substrate 52 is not solid but is instead constructed from one or more separate panels of dielectric material that is folded into a desired shape for the antenna substrate 52. In yet another embodiment, the parallelepiped is constructed from several separate discrete panels affixed to each other. Various well-known methods of attachment can be used including, but not limited to, adhesives, heat, ultrasonic welding or mechanical fasteners.
In embodiments where the antenna substrate 52 is not solid but is instead composed of multiple panels and therefore hollow, a cube-shaped antenna substrate 52 can have either five or six sides, the construction of which is referred to herein as being a panelized substrate. In embodiments wherein a panelized antenna substrate 52, such as a cube-shaped substrate is constructed to have only five sides and which is then mounted to a separate supporting substrate 76, the portion of the supporting substrate 76 that is directly below the hollow antenna substrate 52 is then considered to be a de facto “side” of the antenna substrate 52. The portion of the supporting substrate 76 directly below the antenna substrate 52 is considered herein to be the “bottom” face 66 of the parallelepiped antenna substrate 52.
As can be seen in
The radiation element 80 has length, width and thickness, the length of which is chosen to be approximately one-quarter the wavelength of a signal in the antenna's fundamental band, e.g., the 800 Mhz band. As will be appreciated from the figures and description below, the length and width will determine the resonant frequencies and characteristic impedances of the antenna 50, however, the width of the strip is also chosen to allow the radiation element 80 to be folded over the faces of the parallelepiped-shaped substrate without having the segments overlap or abut each other.
Note that a “T”-shaped impedance matching element 88 is located at the terminus end 90 of the strip. The input impedance of the antenna 50 at the feed point 82 can thereby be adjusted by varying the length as well as the width of the impedance matching element 88. As with the metal strip that forms the radiation element 80, the metal strip or strips forming the impedance matching element 88 are also disposed on one or more faces of the antenna substrate 52. In the embodiment shown, the impedance matching element 88 wraps over the top face 64 and two side faces 70 and 74.
Segments forming the radiation element 80 and segments forming the impedance matching element 88 can be over coated with a thin layer of insulative material (not shown). A non-conductive, i.e., insulative material deposited over the segments can reduce or prevent oxidation of the segments, prevent the segments from being separated from surfaces of the antenna substrate 52 but also prevent the segments from being short circuited during or after installation of the antenna 50 into a mobile device 12.
An even better understanding of the construction and operation of the antenna 50 can be had from
Because of the symmetry of the layout of the segments on the antenna substrate 52, a zero current point occurs at the geometric center point P of the antenna 50. The geometric center point for the high frequency bands i.e., the 1800, 1900 and 2100 MHz bands will shift however along the EF at various different frequencies of operation. The shifting zero current point P makes the current flow along the strips in the Y direction, i.e., strips IH and BC, and current flowing along the strips in the Z direction, i.e., strips DE and GF, HG and CD, JI and AB, KJ and SA, to be in-phase with respect to each other, resulting in high gain, uniform radiation patterns for the cube-shaped antenna 50, as depicted in
Note that for every two segments that are electrically connected to each other, such as the segments AB and BC, or BC and CD, or DE and EF, one of them extends at least part way across two adjacent faces of the substrate so that one of the segments folds over an edge of the cube to allow the metal strip forming the radiation element to change direction and extend onto an adjacent face. Stated another way, segments of the radiation element 80 that are electrically and physically adjacent to each other in the concatenation of elements SA, AB, BC, CD, DE, EF, FG, GH, HI, IJ, JK, KL and LO, are also orthogonal to each other at their points of connection.
By way of example, segment SA is connected to segment AB on the top surface 64. As can be seen in
Referring now to
The antenna 50 depicted in
First, and as indicated by the block 102, a three-dimensional rectilinear substrate is formed, such as the cube depicted in the figures described above. As indicated in block 104, a first radiation element is formed and deposited onto the surface of the substrate.
The radiation element is formed in the shape of an elongated, thin strip of metal or other conductive material. The strip has a predetermined length, which is substantially equal to one-quarter the wavelength of the lowest frequency band at which the antenna will operate. It is important that the antenna strip be provided with a feed point, such as the one described above, whereat signal energy can be introduced to and obtained from the antenna.
The radiation element can be formed upon the faces of the antenna substrate by different methods. Such methods include but are not limited to, electro-plating, chemical vapor deposition or CVD or by adhesives. In one embodiment, the segments forming the radiation element and the surfaces of the antenna substrate are overcoated with a thin layer of dielectric material as indicated by step 106, which will protect the segments from oxidation as well as inadvertent short circuiting.
As shown in block 108, radio frequency signal energy is then transduced within first, second, third or fourth sets of frequency bands at which the radiation element is resonant.
The antenna 50 described above defines a strip antenna of small dimensions and which is easily positioned within the housing of a compact mobile station. The antenna enables a mobile station to operate on multiple frequency bands, including the quad-bands of a quad-mode mobile station operable at the 800/900/1800/1900 MHz frequency bands, however, the foregoing description should not be construed as limiting because the inventive concept extends to antenna substrates that are not necessarily cube-shaped.
While the embodiment depicted in the figures and described above used an antenna substrate in the shape of a cube having the radiation element 80 around its faces, a more general description of the antenna 50 is that the antenna is formed from a substrate 52 in the shape of any three-dimensional rectilinear dielectric body. A radiation element 80 is disposed on, i.e., wrapped around, multiple sides of the body, with the possible exception of one face on which the substrate is attached to a supporting substrate or mobile unit. The antenna substrate 52 and the radiation element 80 are sized together so that it can fit within the small and confined spaces of a multi-band mobile unit 12 yet transduce radio frequency energy in multiple different frequency bands.
Three-dimensional rectilinear bodies that are usable to form an antenna include but are not limited to, truncated prisms and truncated pyramids, and parallelepipeds generally, e.g., cubes and cuboids, whether such bodies are solid or hollow. As used herein, a truncated prism is considered to be any polyhedron with two polygonal faces lying in parallel planes and with the other faces that connect the two polygonal faces being parallelograms. The polygonal faces can include regular polygons such as triangles, squares, rectangles, pentagons, octagons as well as irregular polygons. The parallelogram sides can include rectangles and squares. In such a body, the two polygonal faces may or may not correspond to the top face 64 and the bottom face 66 of the cube described above.
A pyramid is of course a polyhedron having for its base a polygon and faces that are triangles with a common vertex. A truncated pyramid is therefore a pyramid with a top portion that is removed to provide a flat top in the shape of a regular polygon. The sides of a truncated pyramid are trapezoidal. In a truncated pyramid, the shape of the bottom face and the shape of the top face will be the same but with the bottom face being larger than the top. The slope or inclination of the sides is a design choice and can vary from just over 90 degrees to virtually any angle.
It will be recognized by those of ordinary skill in the art that as the shape of the antenna substrate 52 varies from a cube, the spatial relationships between antenna segments on differently arranged faces will also vary. As the spatial relationship between the segment vary, the pattern of RF signal energy is radiated from them will also vary. It is therefore expected that an emitted radiation pattern for an antenna formed from a substrate other than the cube depicted in
By using three-dimensional wrapping, the antenna disclosed herein significantly reduces the physical size or extension of a multi-band antenna while also increasing the bandwidth of the antenna. Increasing bandwidth is equivalent to reducing the energy stored around the antenna.
The compact size of the three-dimensional wrapped antenna also lends itself to use in multiple antenna systems, including multiple input and multiple output (MIMO) antenna systems. Because of their size, prior art antennas cannot be used to implement a MIMO antenna system in a portable communications device.
Presently preferred embodiments of the invention and many of its improvements and advantages have been described with a degree of particularity. The description is of preferred examples of implementing the invention, and the description of preferred examples is not necessarily intended to limit the scope of the invention. The scope of the invention is defined by the following claims.
