Patent Application
20080136710
This invention relates generally to apparatus that use current-carrying elements such as antennas and transmission lines and, more specifically, relates to techniques for suppressing mutual coupling between the current-carrying elements.
The wire medium as an artificial electromagnetic material has been known for a long time. For instance, see J. Brown, Progress in Dielectrics 2, 195 (1960). A wire medium is formed, e.g., by a lattice of conducting parallel thin wires, where the wires are separated by a lattice period. Typically, the wires (also called “pins”) are placed into some type of insulating slab, such a dielectric or polystyrene foam. At low frequencies, the wire medium can be described in terms of effective medium parameters, and the permittivity of the wire medium is negative below the plasma frequency. The plasma frequency is determined by the ratio of the wire radius to the lattice period. Hence waves, having an electric field component parallel to the wires, attenuate in the wire medium slab. However, a wire medium slab over a metal ground plane can support propagation of surface waves with the other polarization (e.g., an electric field component perpendicular to the wires), as an impedance surface. See, e.g., R. J. King, The Synthesis of Surface Reactance Using an Artificial Dielectric, IEEE Trans. on Antennas and Propagation, vol. AP-31, No. 3, 471-476 (May 1983).
An antenna that has been known for a while is called a patch antenna. In a patch antenna, there is some flat, conductive shape (called a patch) above an insulating substrate, which is itself above a ground plane. See, e.g., C. Balanis, Antenna Theory: Analysis and Design, 3rd Edition, N.Y., John Wiley, 2005. Generally, the patch is rectangular, but other shapes may be used.
Since patch antennas are often used in arrays, their performance can be improved by suppression of mutual coupling by using wire media. Further, performance of any apparatus using current-carrying elements having mutual coupling may also be improved by using wire media.
In an exemplary embodiment of the invention, an apparatus includes a number of electrically conductive spaced apart elements, and a ground plane situated at least partially in a space between at least two of the electrically conductive spaced apart elements. The apparatus further includes one or more wire media situated over at least a portion of the ground plane and coupled to the ground plane, the one or more wire media situated at least partially in the space between the at least two electrically conductive spaced apart elements.
In another exemplary embodiment, an apparatus includes an antenna and a transceiver. The antenna includes a ground plane and a number of spaced apart radiating elements, where each of the radiating elements has a portion that is approximately parallel to and situated above the ground plane. The antenna also includes one or more connectors having a ground portion coupled to the ground plane and a signal portion coupled to the radiating elements. The antenna further includes one or more wire media situated over and coupled to the ground plane, the one or more wire media situated at least partially in a space between at least two of the radiating elements. The transceiver is coupled to the one or more connectors and is configured to transmit or receive using the antenna.
In another exemplary embodiment, an antenna includes a ground plane and a first patch element having an edge and including a portion that is approximately parallel to the ground plane. The antenna also includes a first insulating substrate positioned between the portion of the first radiating element and the ground plane and a second patch element having an edge and including a portion that is approximately parallel to the ground plane. The first and second patch elements are separated by an area and the area is partially bounded by the edges of the first and second patch elements. The antenna further includes a second insulating substrate positioned between the portion of the second radiating element and the ground plane and one or more connectors having a ground portion coupled to the ground plane and a signal portion coupled to the first and second radiating elements. The antenna additionally includes a wire medium coupled to the ground plane and formed in a third insulating substrate, the third insulating substrate and wire medium situated at least partially in the area between the edges of the first and second patch elements. The antenna also includes a conductive mesh coupled to at least a portion of the wire medium and situated at least partially in the area between the edges of the first and second patch elements.
In yet another exemplary embodiment, a method includes spacing apart a plurality of elements, each of the elements configured to carry current, and situating a ground plane at least partially in a space between at least two of the spaced apart elements. The method further includes situating at least one wire medium over at least a portion of the ground plane, the at least one wire medium situated at least partially in the space between the at least two spaced apart elements, and coupling the at least one wire medium to the ground plane.
The foregoing and other aspects of embodiments of this invention are made more evident in the following Detailed Description of Exemplary Embodiments, when read in conjunction with the attached Drawing Figures, wherein:
As described above, a wire medium over a metal ground plane can support propagation of surface waves with both TM (transverse magnetic) and TE (transverse electric) polarizations. This is probably the reason why such structures were not proposed for coupling reduction in the past. The inventors have realized that a wire medium and associated insulating substrate can be used for coupling reduction when the wire medium is placed between two radiating elements of an antenna. Additional reduction is also realized when a wire (e.g., conductive) mesh is coupled to the wire medium.
The problem of reduction of mutual coupling between radiating elements in antenna arrays remains very important despite much effort spent in the past for its solution. Conventional solutions to this problem include the use of an electromagnetic band gap (EBG) ground plane (also called photonic band gap (PBG)). Utilization of electromagnetic band gap (EBG) structures is considered now as one of the most promising techniques for decoupling antenna radiating elements. Many different EBG structures were proposed and studied, see, e.g., D. Sievenpiper, “High-impedance electromagnetic surfaces”, Doctoral Thesis, University of California Los Angeles (UCLA), 1999; P. de Maagt, R. Gonzalo, J. Vardaxoglou, J.-M. Baracco, “Review of Electromagnetic Bandgap Technology and Applications”, The URSI Radio Science Bulletin, No. 309, 11-25 (June 2004); D. Sievenpiper, L. Zhang, R. F Jimenez Broaz, N. G. Alexpolous, E. Yablonovich, “High Impedance Electromagnetic Surfaces with a Forbidden Frequency Band”, IEEE Transactions on Microwave Theory and Techniques, Vol. 47, No. 11, 2059-2074 (November 1999); and F. Yang, Y. Rahmat-Samii, “Microstrip Antennas Integrated with Electromagnetic Band-Gap (EBG) Structures: A low Mutual Coupling Design for Array Applications”, IEEE Transactions on Antennas and Propagation, Vol. 51, No. 10, 2936-2946.(October 2003). Typically, these solutions utilize periodically arranged resonant metal elements that form a stop band in a certain frequency range. For example, different modifications of the conventional Jerusalem-cross EBG structure are used. Usually these structures also have complex designs, allow one to suppress only certain kinds of waves capable of propagating between antennas elements, and do not operate in wide frequency ranges due to their resonant nature. Furthermore, the known structures are not compact, since the period of the structure must be comparable to the wavelength.
Wire media, proposed herein as decoupling elements, effectively suppress TM polarization modes, but if no special measures are taken, increase the coupling in the case of the TE polarization, where the coupling is quite small even without an EBG structure. One embodiment of the disclosed invention overcomes the problem of TE surface mode excitation as well as creating a wide frequency band and relatively simple decoupling device. Embodiments of the invention therefore offer new structures for reducing mutual coupling between radiating elements of antenna arrays, for example patch antenna arrays of base stations. Thus, the structures herein reduce mutual coupling for one or both of TM and TE polarizations. The structures can be used in multi-element dual-polarized antennas, for example, in base station antenna arrays. The structures are based on a wire medium placed between radiating elements of an antenna and may further be based on a wire medium and a conductive mesh, connected to tips (tops) of the wires in the wire medium, placed between radiating elements of an antenna.
Reference is made first to
The controller 12G may include one or more semiconductor circuits, which can include application-specific integrated circuits and/or discrete hardware in addition to or in place of the data processor 12A and memory 12B. The programs 10C, 12C, and 14C are assumed to include any program instructions that, when executed by the associated data processor, enable the corresponding electronic device to perform operations.
In general, the various embodiments of the user equipment 10 can include, but are not limited to, handsets, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image..capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
In terms of
To suppress mutual coupling, a finite-thickness wire medium and associated insulating substrate is placed between radiating elements (or any current-carrying elements, as noted above). Referring now to
Each of the patch elements 220, 230 is a radiating element and has a corresponding connection (e.g., “L”) portion 221, 231, respectively. The connection portion 221, 231 is connected to the signal connectors 241, 251 using conductive couplings 242, 252, respectively. Each of the patch elements 220, 230 is separated from the top surface 206 of the ground plane 205 by a respective one of the insulating substrates 225, 235. The top surfaces 227, 237 of the insulating substrates 225, 235 (respectively) are connected to the bottom surfaces 222, 232 of the patch elements 220, 230 (respectively), typically using glue or other connection methods. The bottom surfaces 226, 236 of the insulating substrates 225, 235 (respectively) are connected to the top surface 206 of the ground plane 205, typically using glue or other connection methods.
Each pin 206 has a top (e.g., “tip”) 217 and a bottom 218. The top 217 is not connected to anything in
Certain parameters of the antenna 200 (and 700, described below) are the following. Copper wire was used as the pins 216. The copper wire had a diameter 290 of 0.8 mm (millimeter), the spaces 291, 292 between the pins was 5 mm, the distance 294, 295 between an edge 298, 297 of the wire medium 215 and an edge 234, 224 of the patch element 230, 220 is 2.5 mm, the length 299 of pins 216 is the same as the distance d between the patch elements 220, 230 and the top surface 206 of the ground plane 205 (d=20 mm). It is noted that these measurements and materials are merely exemplary, and the cross section of wires can be arbitrary, e.g., they can be made of metal strips. It is noted that the antenna 200 is symmetric around axis 281 and around line 3-3′ (which may also be considered an axis).
The antenna 200 (arid the antenna 700 shown in
For decoupling of TM-polarized waves, it would be enough to place the wire medium 215 and associated insulating substrate 210 between the patch elements 220, 230. However, simulations and experiments have shown that such a solution increases coupling for TE-polarized waves, which have a non-zero electric vector component parallel to the ground plane, as shown in
To suppress TE polarization, it is proposed that the tops (tips) 217 of pins 206 are connected with a conductive mesh 710.
This combination of the conductive mesh 710 and the wire medium 215 improves the characteristics of the decoupling device, as shown in
It is noted that the conductive mesh 710 in
One aspect of an exemplary embodiment is that the tops 217 of the pins 216 are connected with a conductive mesh 710 in order to lessen (e.g., forbid) propagation of the surface wave having electric field perpendicular to the pins 216. The new structure of conductive mesh 710 and wire medium 215 offers a solution with extremely attractive characteristics. Exemplary advantages include, but are not limited to, one or more of the following: The antenna 200/700 has a wide stop band due to a non-resonant origin of the effect; and the antenna 200/700 is simplistic compared with other EBG structures; and the antenna 700 provides decoupling of radiating elements for any polarizations in a very wide frequency range, while the antenna 200 provides reduction in TM polarization but may not provide suitable reduction in TE polarization, depending on application.
Referring now to
Method 1000 begins in block 1005 when the conductive mesh 710 is formed. The conductive mesh can be formed in any number of ways. For instance, conductive wires (e.g., typically copper) could be formed into a grid and soldered together in block 1005 to form the conductive mesh 710. Printed circuit board techniques could be used to form the conductive mesh. In block 1010, the wire medium 215 is formed. In block 1015, the conductive mesh 710 is coupled to the pins of the wire medium 210. In block 1020, the insulating substrate 210 is formed, and in block 1025, the pins 216 of the wire medium 215 are coupled to the ground plane 205.
In one example, the wire medium 215 is formed (block 1010) by connecting each pin 216 to the conductive mesh 710, e.g., by soldering or using conductive epoxy. The insulating substrate 210 is formed (block 1020) in the appropriate size, e.g., from polystyrene or other dielectrics such as polytetrafluoroethylene (PTFE) in combination with woven glass, random microfiber glass, and ceramics, and thermoset plastic/ceramic/woven glass. Any insulating substrate may be used. The pins 216 are pushed through the polystyrene and are coupled (block 1025) to the ground plane, e.g., using galvanic action or capacitive coupling. To realize capacitive coupling, the bottom ends of the wires should end with a large enough metal element, positioned near the ground plane, e.g. a metal plate parallel to the ground plane. The ends of the wires would therefore be large enough to create a certain amount of capacitance between the wires and the ground plane. See, for instance,
The conductive mesh 710 (if used) is situated (e.g., placed) over the pins 216 and is coupled to the pins 216 using, e.g., conductive adhesives or soldering. As yet another example, the wire medium 215 is formed by attaching the pins 216 in a lattice to the ground plane using such-techniques as soldering, galvanic action, conductive adhesive, etc. The formed insulating substrate 210 is pushed onto the wire medium 215. As an other example, the conductive mesh 1005 could be formed as conductive traces on a printed circuit board. The printed circuit board could have through-holes that mate with pins 216, and the pins 216 would therefore be soldered to the through-holes. As can be seen, there are a number of possible techniques for performing blocks 1005-1025, and not all techniques have been described.
In block 1030, the radiating elements are formed (e.g., patch elements 220, 230). It is noted that the patches 220, 230 are merely exemplary, and many different shapes may be used. The insulating substrates 225, 235 for the radiating elements are formed in block 1035. In block 1040, the radiating elements are situated (e.g., placed) in position over insulating substrates 225, 235 and also in relationship to each other and to the conductive mesh 210. The conductive mesh 710 (and/or the wire medium 215) is positioned between the radiating elements. It is noted that the conductive mesh 710 (and/or wire medium 215) could be formed prior to or after the placement of the radiating elements.
In block 1045, the ground plane 205 is coupled to the ground portion of the connector(s). In the example of
It is noted that any block of “forming” an element could include situating the element. Illustratively, forming a radiating element (block 1030) could include situating (e.g., placing) the radiating element wherever the element is to be situated. Similarly, blocks 1005, 1010, 1020, and 1035 may also include situating provided parts.
In an exemplary embodiment, the antenna 200/700 might be implemented on a semiconductor, e.g., as antenna 10E of user equipment 10. For instance, the ground plane 205 could be formed on the backside of a semiconductor or as a layer on the semiconductor. The insulating substrates 210, 225, and 235 could be formed using, e.g., deposition and etching. The pins 216 could be formed using techniques used for forming conductive vias. The patch elements 220, 230 could be formed using deposition or other techniques. Exemplary embodiments of the disclosed invention may be implemented on a semiconductor as an element to reduce coupling between any current-carrying elements (e.g., transmission lines), not necessarily between patch elements of antennas. Typically, the sizes of patch antennas are larger than the size of a semiconductor, and therefore semiconductor techniques are generally not used for patch antennas. Nonetheless, scaling of the antennas 200/700 may be performed to enable use of antennas 200/700 on a semiconductor. Further, as described above, certain embodiments of the disclosed invention may be used to reduce coupling between any current-carrying elements formed on or not formed on semiconductors. For instance, certain user equipment 10 might have multiple antennas, possibly formed on a semiconductor or not formed thereon, and the use of a wire medium (e.g., in conjunction with the wire mesh) may be used to reduce coupling between the antennas. Consequently, a user equipment 10 formed, e.g., using a handset, could contain and use one or more wire media (and, if desired, corresponding wire mesh) in order to reduce coupling between or in antennas and other current carrying elements.
An example is shown in
The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best techniques presently contemplated by the inventors for carrying out embodiments of the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. All such and similar modifications of the teachings of this invention will still fall within the scope of this invention.
For instance, although only two current-carrying (e.g., radiating elements or transmission lines) were shown above, the disclosed invention is applicable to multiple such elements. For instance, shown in
Furthermore, some of the features of exemplary embodiments of this invention could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of embodiments of the present invention, and not in limitation thereof.
