Antenna with active elements

A multi-frequency antenna comprising an IMD element, active tuning elements and parasitic elements. The IMD element is used in combination with the active tuning and parasitic elements for enabling a variable frequency at which the antenna operates, wherein, when excited, the parasitic elements may couple with the IMD element to change an operating characteristic of the IMD element.

FIELD OF INVENTION

The present invention relates generally to the field of wireless communication. In particular, the present invention relates to an antenna for use within such wireless communication.

BACKGROUND OF THE INVENTION

As new generations of handsets and other wireless communication devices become smaller and embedded with more and more applications, new antenna designs are required to address inherent limitations of these devices. With classical antenna structures, a certain physical volume is required to produce a resonant antenna structure at a particular radio frequency and with a particular bandwidth. In multi-band applications, more than one such resonant antenna structure may be required. With the advent of a new generation of wireless devices, such classical antenna structure will need to take into account beam switching, beam steering, space or polarization antenna diversity, impedance matching, frequency switching, mode switching, etc., in order to reduce the size of devices and improve their performance.

Wireless devices are also experiencing a convergence with other mobile electronic devices. Due to increases in data transfer rates and processor and memory resources, it has become possible to offer a myriad of products and services on wireless devices that have typically been reserved for more traditional electronic devices. For example, modern day mobile communications devices can be equipped to receive broadcast television signals. These signals tend to be broadcast at very low frequencies (e.g., 200-700 Mhz) compared to more traditional cellular communication frequencies of, for example, 800/900 Mhz and 1800/1900 Mhz.

In addition, the design of low frequency dual band internal antennas for use in modern cell phones poses other challenges. One problem with existing mobile device antenna designs is that they are not easily excited at such low frequencies in order to receive all broadcasted signals. Standard technologies require that antennas be made larger when operated at low frequencies. In particular, with present cell phone, PDA, and similar communication device designs leading to smaller and smaller form factors, it becomes more difficult to design internal antennas for varying frequency applications to accommodate the small form factors. The present invention addresses the deficiencies of current antenna design in order to create more efficient antennas with a higher bandwidth.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a multi-frequency antenna comprises an Isolated Magnetic Dipole™ (IMD) element, one or more parasitic elements and one or more active tuning elements, wherein the active elements are positioned off the IMD element.

In one embodiment of the present invention, the active tuning elements are adapted to vary the frequency response of the antenna.

In one embodiment, the parasitic elements are located below the IMD element. In another embodiment, the parasitic elements are located off the IMD element. In one embodiment, the active tuning elements are positioned on one or more parasitic elements.

In another embodiment, the active tuning elements and parasitic elements may be positioned above the ground plane. In yet another embodiment, the one or more parasitic elements are positioned below the IMD element and a gap between the IMD element and the parasitic element provides a tunable frequency. Further, another embodiment provides that the parasitic element has an active tuning element at the region where one of parasitic element connects to the ground plane.

In another embodiment of the present inventions provides that the multi-frequency antenna contains multiple resonant elements. Further, the resonant elements may each contain active tuning elements.

In another embodiment of the present invention, the antenna has an external matching circuit that contains one or more active elements.

In one embodiment, the active tuning elements utilized in the antenna are at least one of the following: voltage controlled tunable capacitors, voltage controlled tunable phase shifters, FET's, and switches.

Another aspect of the invention relates to a method for forming a multi-frequency antenna that provides an IMD element above a ground plane, one or more parasitic elements, and one or more active tuning elements all situated above the ground plane, and the active tuning element positioned off the IMD element.

Yet another aspect of the present invention provides an antenna arrangement for a wireless device that includes an IMD element, one or more parasitic elements, and one or more active tuning elements, where the IMD element may be located on a substrate, while the active tuning element is located off the IMD element. In a further embodiment, one or more parasitic elements are utilized to alter the field of the IMD element in order to vary the frequency of the antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for purposes of explanation and not limitation, details and descriptions are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions.

Referring toFIG. 1, an antenna10in accordance with an embodiment of the present invention includes an Isolated Magnetic Dipole (IMD) element11and a parasitic element12with an active tuning element14situated on a ground plane13of a substrate. In this embodiment, the active tuning element14is located on the parasitic element12or on a vertical connection thereof. The active tuning element can be any one or more of voltage controlled tunable capacitors, voltage controlled tunable phase shifters, FET's, switches, MEMs device, transistor, or circuit capable of exhibiting ON-OFF and/or actively controllable conductive/inductive characteristics, for example. Further, in this embodiment, the distance between the IMD element11and the ground plane13is greater than the distance between the parasitic element12and the ground plane13. The distance can be varied in order to adjust the frequency due to the coupling between the parasitic element14and the IMD element11. The current is driven mainly through the IMD element11which, in turn, allows for improved power handling and higher efficiency.

The IMD element is used in combination with the active tuning for enabling a variable frequency at which the communications device operates. As well, the active tuning elements are located off of the IMD element in order to control the frequency response of the antenna. In one embodiment, this is accomplished through the tuning of one or more parasitic elements. The parasitic elements, which may be positioned below, above, or off center of the IMD element, couple with the IMD element in order to change one or more operating characteristic of the IMD element. In one embodiment, the parasitic element when excited exhibits a quadrapole-type of radiation pattern. In addition, the IMD element may comprise a stub type antenna.

The adjustment of the active tuning elements as well as the positioning of the parasitic elements allows for increased bandwidth and adjustment of the radiation pattern. The parasitic location, length, and positioning in relation to the IMD element allows for increased or decreased coupling and therefore an increase or decrease in frequency of operation and a modification of radiation pattern characteristics. The active tuning elements being located on the parasitic allows for finer adjustment of the coupling between the IMD and parasitic and, in turn, finer tuning of the frequency response of the total antenna system.

FIG. 2illustrates another embodiment of an antenna20with an IMD element21and one or more parasitic elements24with active tuning elements22. All elements are situated on a ground plane. However, in this embodiment, the multiple parasitic elements24are aligned in an x-y plane being placed one above another for multiple levels of tuning adjustments. The distance between the ground plane and the parasitic elements varies along with the distance between the parasitic and the IMD element. This allows variations in the frequency response and/or radiation patterns from coupling. The parasitic element in this embodiment also has multiple portions varying in length on the y-axis, again in order to further manipulate the radiation pattern created by the IMD element. The current is still driven only through the IMD element, providing increased efficiency of the antenna20.

FIG. 3illustrates yet another embodiment to vary the transmitted signal from the IMD element31. In this embodiment, the antenna30includes an IMD element31and multiple parasitic elements32. Each of the parasitic elements32has active tuning elements34attached to them. The active tuning elements34are situated on a ground plane33of the antenna30. In this embodiment, the parasitic elements32are distributed around the IMD element31. As shown, the parasitic elements34may vary in both length in the x and y plane, and distance to the IMD element31in the z direction. The surface area variation as well as the proximity to the IMD element allow for control of the coupling between the parasitic and IMD element and an increased variance in the radiation pattern of the IMD element31which can then be adjusted to a desired frequency by the active tuning elements33on each respective parasitic element32.

FIG. 4illustrates a side view of an embodiment of an antenna40with a general configuration containing an IMD element41situated slightly above multiple parasitic elements42and multiple active tuning elements44. All elements again are situated on a ground plane43, with connectors extending vertically into the z direction. However, dependent on the configuration of the device in which they are placed, the elements could be located within any plane and should not be limited to those provided in the exemplary embodiments. In this embodiment, multiple active tuning elements44are located on the parasitic element42, varying in stationary height and, in turn, distance to the IMD element41. As well, the active tuning elements44are located between multiple parasitic elements42that extend and vary horizontally in length. In this configuration, each respective active tuning element is able to control the parasitic element located directly above it, further controlling the frequency output of the antenna. Because the distance and surface area of the multiple parasitics42vary in relation to the IMD element41and with each other, more variation is achievable.

In another embodiment,FIG. 5provides a configuration in which a singular parasitic element54may vary in height in the z direction, above the ground plane53. In this regard, the parasitic element54is configured as a plate that is not parallel to the IMD element51. Rather, the parasitic element54is configured such that a free end is positioned closer to the IMD element51than an end connected to a vertical connector. Again, an IMD element51, the parasitic element54and an active tuning element55are all situated on a ground plane, with the active tuning element55being located on the parasitic element54. Because the singular parasitic element54may vary in height above the ground plane, it allows for more control over the coupling between the IMD element51and the parasitic element54. This feature creates a coupling region52between the IMD element51and the parasitic element54. In addition, the active tuning element55may further vary the coupling between the parasitic element54and the IMD element51. The length on the parasitic element54in the x axis may be substantially longer than in other embodiments, providing more surface area to better couple to the IMD element51, and further manipulation of the frequency response and/or the radiation patterns produced. The length of the variable height parasitic may also be much shorter, dependent of the amount of coupling, and, consequently, frequency variance desired.

In a similar embodiment,FIG. 6provides a variation of the concept provided inFIG. 5, with the parasitic element64again varying in height on the z axis. In the embodiment ofFIG. 6, the parasitic element64is configured such that a free end is positioned further from the IMD element61than the end connected to the vertical connector. As discussed inFIG. 5, the length of the parasitic element64may vary and in this embodiment the height of the parasitic element64in relation to the IMD element61may also vary due to the directional change of the ascending height portion of the parasitic. This variance again affects the coupling by the parasitic to the IMD element. Being at a distance more proximate to the IMD element61, the coupling region62is decreased, allowing for slightly less variance in coupling and a more stable control over the frequency output of the antenna. The length of the parasitic element64, similar to that inFIG. 5, is longer than in other embodiments, and may be shorter if less coupling is necessary. The active tuning element65is still located on the parasitic element64allowing for even further control of frequency characteristics of the antenna.

FIG. 7provides an exemplary embodiment similar toFIG. 5, wherein multiple parasitic elements72are varied in height in relation to the IMD element71and the ground plane73. Instead of a continual descent or ascent of the portion of the parasitic element64with one active tuning element65, this embodiment includes a stair step configuration with multiple active tuning elements74to control the frequency to a specific output. One or more portions of the smaller parasitic steps may be individually tuned to achieve the desired frequency output of the antenna.

Next, referring to the embodiment provided inFIG. 8, an IMD element81and parasitic element82with active tuning element85are all situated on a ground plane83. In this embodiment, an active element is included in a matching circuit84external to the antenna structure. The matching circuit84controls the current flow into the IMD element81in order to match the impedance between the source and the load created by the active antenna and, in turn, minimize reflections and maximize power transfer for larger bandwidths. Again, the addition of the matching circuit84, allows for a more controlled frequency response through the IMD element81. The active matching circuit can be adjusted independently or in conjunction with the active components positioned on the parasitic elements to better control the frequency response and/or radiation pattern characteristics of the antenna.

In another embodiment,FIG. 9illustrates another configuration where IMD element91with an active tuning element92are incorporated on the IMD element91structure and situated on the ground plane94. Similar to previous embodiments, the parasitic element93also has an active tuning element92in order to adjust the coupling of the parasitic93to the IMD element91. In this embodiment, the addition of the active tuning element92on the IMD element91comprises a device that may exhibit ON-OFF and/or controllable capacitive or inductive characteristics. In one embodiment, active tuning element92may comprise a transistor device, a FET device, a MEMs device, or other suitable control element or circuit. In an embodiment, where the active tuning element exhibits OFF characteristics, it has been identified that the LC characteristics of the IMD element91may be changed such that IMD element91operates at a frequency one or more octaves higher or lower than the frequency at which the antenna operates with a active tuning element that exhibits ON characteristics. In another embodiment, where the inductance of the active tuning element92is controlled, it has been identified that the resonant frequency of the IMD element91may be varied quickly over a narrow bandwidth.

FIG. 10illustrates another embodiment of an antenna wherein the IMD element101contains multiple resonant elements105, with each resonant element105containing an active element104. As well, a parasitic element102has an active tuning element104. The parasitic and IMD elements are both situated on the ground plane103. The addition of the resonant elements105to the IMD element101, permits for multiple resonant frequency outputs through resonant interactions and modified current distributions.

FIG. 11illustrates an embodiment of an antenna with various implementations of active tuning elements115utilized in combination with the main IMD element111and parasitic element113, which are both situated on the ground plane114of the antenna. In this embodiment, the IMD element111has multiple resonant elements117, each having an active element115for tuning. The parasitic element113has an active element115on the structure of the parasitic113as well as an active element115at the region where the parasitic113connects to the ground plane114. As well, there is an external matching circuit116connected to the IMD element111and an external matching circuit116connected to the parasitic element113. Active tuning elements115are also included in matching circuits116external to the IMD element111and the parasitic element113. The addition of the elements allows for finer tuning of the precise frequency response of the antenna. Each tuning element and its location, both on the resonant elements and parasitic elements can better control the exact frequency response for the transmitted or received signal.

FIG. 12aandFIG. 12bprovide exemplary frequency response achieved when an active tuning element positioned off the IMD element is used to vary the frequency response of the antenna.FIG. 12aprovides a graph of the return loss121(y axis) versus the frequency122(x axis) of the antenna. The return loss displayed along the y axis ofFIG. 12arepresents a measure of impedance match between the antenna and transceiver.FIG. 12bprovides a graph of the efficiency123versus the frequency122of the antenna. In each graph, F1represents the frequency response of the IMD element prior to activating the tuning element, e.g. the base frequency of the antenna. F2represents the frequency response of the antenna when the active tuning element is used to shift the frequency response lower in frequency. F3represents the frequency response of the antenna when the active tuning element is used to shift the frequency response higher in frequency.

FIG. 13aandFIG. 13bprovide graphs displaying exemplary embodiments where the active tuning elements are adjusted, which alters the transmitted or received signal, i.e. frequency response, of the antenna. The figures show that wide band frequency coverage can be achieved through the adjustments of the active tuning elements. A return loss requirement and efficiency variation over a wide frequency range can be also achieved by generating multiple tuning “states”. This allows for the antenna to maintain both efficiency and return loss requirements even when the output frequency is manipulated.

As previously discussed, the surface area exposed to the IMD element, distance to the IMD element, and shape of the parasitic may affect the coupling and, in turn, variable frequency response and/or radiation patterns produced by the IMD element.FIGS. 14A-Dprovide some embodiments of the possible shapes for the parasitic element141,142,143,144. For example, in one simplistic embodiment, the parasitic element141provides a minimal surface area and simplistic straight shape that may be exposed to the IMD element, and tuned by the active element145. The smaller and less exposure the parasitic provides to the IMD element means less frequency variation is achievable. For parasitic elements like the embodiments provided in143and144a larger bandwidth achievable and still actively tunable145in the antenna's frequency response. The shape of the parasitic element is not constrained to the types shown and can be altered to achieve the desired frequency of the antenna as needed for use within many different types of communication devices.

While particular embodiments of the present invention have been disclosed, it is to be understood that various different modifications and combinations are possible and are contemplated within the true spirit and scope of the appended claims. There is no intention, therefore, of limitations to the exact abstract and disclosure herein presented.