Method and apparatus for a tunable antenna

A method for tuning an antenna comprising determining an operating frequency band of the antenna, and adjusting a capacitance of a tunable load according to the operating frequency band, wherein the tunable load is electromagnetically coupled to the antenna via a parasitic arm, and wherein the operating frequency band depends on the capacitance.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Wireless communication technologies and services continue to proliferate leading to new voice and data services, carrier aggregation, and new demands on roaming to name a few. As technologies advance and user demand for services increases, wireless communication devices need to support an increasing number of operating frequency bands to support the technologies and services. At the same time, wireless communication devices are getting smaller. For example, mobile phones are becoming increasingly thinner, and as a result there may be less volume available for antenna structures and systems, as well as less space for the coexistence of electromechanical components around the antenna.

Smaller devices may result in the need for more compact antennas. However, more compact antennas may not cover enough frequency bands for satisfactory operation. These opposing trends—increasing demands on antennas while shrinking the volume available for antennas—lead to a need for improved antenna designs. Thus, there is a need to provide an antenna compact enough to fit in modern wireless communication devices while covering frequency bands demanded for various services.

SUMMARY

In one embodiment, the disclosure includes a method for tuning an antenna comprising determining an operating frequency band of the antenna and adjusting a capacitance of a tunable load according to the operating frequency band, wherein the tunable load is electromagnetically coupled to the antenna via a parasitic arm, and wherein the operating frequency band depends on the capacitance.

In another embodiment, the disclosure includes an apparatus comprising an antenna, a parasitic arm electromagnetically coupled to the antenna, and a tunable load coupled to the parasitic arm, wherein a capacitance of the tunable load is variable, wherein an operating frequency band of the antenna depends on the capacitance.

In yet another embodiment, the disclosure includes a wireless communication device comprising an antenna, a parasitic arm electromagnetically coupled to the antenna, a tunable load coupled to the parasitic arm, wherein a capacitance of the tunable load is variable, and wherein an operating frequency band of the antenna depends on the capacitance, and a processor coupled to the tunable load and configured to select a first operating frequency band and set the capacitance to a value to achieve the first operating frequency band.

DETAILED DESCRIPTION

It should be understood at the outset that, although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. While certain aspects of conventional technologies have been discussed to facilitate the present disclosure, applicants in no way disclaim these technical aspects, and it is contemplated that the present disclosure may encompass one or more of the conventional technical aspects discussed herein.

Disclosed herein is a tunable antenna. For example, operating frequency bands of the tunable antenna may be adjusted by varying a load of a parasitic arm electromagnetically coupled to an antenna. Also disclosed herein is a method of tuning an antenna. For example, the antenna may be tuned by adjusting a load of a parasitic arm electromagnetically coupled to the antenna. The tunable antenna apparatuses and methods may be suitable for implementation in compact wireless communication devices.

FIG. 1is a schematic diagram of an embodiment of a tunable antenna. The tunable antenna100comprises an antenna102, a feed line110, a parasitic arm104, and a tunable load106configured as shown inFIG. 1. The antenna102may be coupled to a transceiver (not shown) via the antenna feed line110. The parasitic arm104is located in close enough proximity with the antenna102to be coupled to the antenna102electromagnetically. However, as shown there may be no direct connection between the parasitic arm104and the antenna102. Further, the parasitic arm104may be coupled to a tunable load106. The tunable load106may be connected to ground as shown or may be maintained at a substantially constant non-zero voltage level. The tunable load may have a variable or tunable impedance (i.e., combination of resistance, capacitance, and/or inductance). For example, a fixed or non-tunable inductor may be placed in series with a tunable capacitor to provide a variable impedance. The tunable capacitor may be implemented as a radio frequency (RF) switching device, a varactor, a single pole multi throw (“SPxT”) switch, a digital tunable capacitor (“DTC”), or a micro-electromechanical system (“MEMS”) capacitor array. These are illustrative examples as the tunable load106may be implemented by any suitable technology.

The antenna102may be any antenna type that allows for variable and continuous tuning by adjusting the tunable load106. Such antenna types include but are not limited to inverted-F antennas (“IFAs”), loop antennas, slot antennas, or folded inverted conformal antennas (FICAs).

Regardless of the type of antenna or tunable load used, the parasitic arm104and the antenna102are coupled to each other electromagnetically. The parasitic arm104may be tuned separately from the antenna by varying the tunable load106coupled to the parasitic arm. Varying the tunable load affects the operating frequency band of the antenna102, thus adjusting at least one operating parameter of the antenna102without the need to add capacitance directly to the antenna.

Continuous tuning of the antenna102may be possible if tuning capabilities of the tunable load106are continuous. For example, because both a DTC and a MEMS capacitor array may be continuously tunable, the selection of either of these tunable loads may result in a continuously tunable antenna. Further, the antenna apparatus may be implemented to enable dynamically tunable configurations with suitable feedback mechanism for mitigating different antenna loadings, such as the front proximity sensor for head detection, or other sensors/detectors. For example, the capacitance of the tunable load106may be in the range of 1.8 picofarads (pF) to 5 pF with different loads resulting in different bands for the antenna102as shown in Table 1. The inductance of the tunable load may be relatively constant at about 10 nanohenries (nH). (In Table 1 the “Low Band” may have a return loss less than −4 decibels (dB), and the “High Band” may have a return loss of less than −6 dB). As shown in Table 1, with a loading of the parasitic arm of about 1.8 pF, the low band may be in the range of about 870 megahertz (MHz) to 960 MHz and the high band may be in the range of about 1.42 to 1.59 gigahertz (GHz); with a loading of the parasitic arm of about 2.5 pF, the low band may be in the range of about 810 MHz to 890 MHz and the high band may be in the range of about 1.74 GHz to 2.27 GHz; and with loading of the parasitic arm of about 5 pF, the low band may be in the range of about 690 MHz to 750 MHz, and the high band may be in the range of 1.66 GHz to 2.26 GHz. By adjusting the tunable load106, the antenna performance may be tuned for a predefined frequency band, or a particular operating channel, depending on the requirements of a wireless device employing the tunable antenna100. A tunable antenna with the characteristics of Table 1 may support Long Term Evolution (LTE) bands 11, 12, 13, 17, 18, 19, and 21, as examples, as bands 12, 13, 17, 18, and 19 may be in a range from 690 MHz to 960 MHz and bands 11 and 21 may be in a range from 1.42 GHz to 1.51 GHz. Such a tunable antenna may also support multiple Universal Mobile Telecommunications System (“UMTS”)/Wideband Code Division Multiple Access (W-CDMA)/Global System for Mobile Communications (“GSM”) frequency bands, such as frequency bands located at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz.

Since adjusting the operating frequency band of the antenna is enabled by varying the tuning load on the parasitic arm, the antenna performance enables a wider range of bandwidths without the need for a larger antenna. Thus, as a result of being able to keep the antenna smaller while increasing the performance, the volume of area needed for the antenna apparatus as a whole may be decreased, enabling production of smaller devices.

In designing the antenna apparatus, the amount of electrical energy from surrounding circuitry components, as well as outside environmental influences, may be taken into consideration. For example, antenna performance may be affected by additional electrical energy within the surrounding circuit board as emitted by neighboring circuitry components. For this reason, the antenna(s) may be placed in a region, sometimes referred to as a “keepout” area, that does not include copper (e.g., grounding) or electrical components on the PCB. A keepout area may be intended to keep the antenna(s) away from any nearby conductors or electrical components that could degrade antenna performance. Additionally, the antenna apparatus may be affected by outside environmental issues (e.g., the proximity of a user's head to a mobile device containing the antenna apparatus).

FIGS. 2A and 2Bare cut-away views of an embodiment of a tunable antenna in a wireless communication device200. The tunable antenna comprises an antenna204and a parasitic arm206. BothFIG. 2AandFIG. 2Bshow an x-y plane view of an example wireless communication device200comprising a parasitic arm206; however,FIG. 2Bomits the antenna for a clearer view of the parasitic element coupling. In particular,FIG. 2Ashows an example placement, shape, and size of parasitic arm206in relation to the apparatus as a whole.

Referring again toFIG. 2A, the parasitic arm206, which may be made of a conductive material (e.g. copper), is traced onto a printed circuit board (PCB) and is electromagnetically coupled to antenna204. In many cases, the PCB may be FR4, which may be a glass-reinforced epoxy laminate. Both the parasitic arm206and the antenna204are supported and encapsulated within the keepout area202of the PCB. Because the parasitic arm206is electromagnetically coupled to the antenna204, and does not require physical coupling to the antenna204, the parasitic arm206may be placed at a plurality of locations in proximity to the antenna204. For example, there may be a four millimeter space between the parasitic arm and the antenna.

In order to more clearly understand the placement and coupling of the parasitic arm,FIG. 2Bshows the antenna apparatus with the antenna removed. In particular, parasitic arm206is located within the nonconductive keepout area202and coupled to a tunable load208. Both the parasitic arm206and the tunable load208are electromagnetically coupled but not physically coupled to the antenna. The parasitic arm206has a fixed inductance, and the tunable load208comprises a tunable capacitor. The tunable load208may further comprise a fixed inductor in parallel with the tunable capacitor. The combination of the parasitic arm206and the tunable load208may be viewed as a variable impedance. The tunable load208may be connected to a ground plane216. As understood by one of skill in the art, a ground plane216may be a substantially flat conducting surface. Further, although not shown in the figure there may be other electrical components occupying some of the area shown as being occupied by the ground plane216.

FIG. 3Ashows a perspective cut-away view of the wireless communication device200in order to further illustrate the relationship of the parasitic arm206with respect to the antenna204. As shown inFIG. 3A, the parasitic arm206may be located above the antenna element204, and between to the two ends of the antenna element204. Further,FIG. 3Aillustrates an antenna feed line210, as well as the antenna ground line212, to which the antenna204is coupled. The feed line210couples the antenna204to a transceiver and the antenna ground line212couples the antenna204to ground.

Antenna204may reside on an antenna carrier, or plastic housing (not shown), which resides four millimeters above the PCB. The parasitic arm206may be printed on the PCB and thus may reside four millimeters below the antenna204.

FIG. 3Bshows the same perspective cut-away view of the wireless communication device200ofFIG. 3A, but with the housing214shown. Note that a view of the parasitic arm206, the antenna feed line210, and antenna ground line212is obstructed by the housing214. The housing214provides a surface separated from the PCB on which all or part of the antenna204may reside. For example, the antenna204may be deposited or traced onto the housing214.

The tunable antenna configuration illustrated inFIGS. 2A, 2B, 3A, and 3Bmay be used to achieve the results presented in Table 1. The relationship shown inFIGS. 2A, 2B, 3A, and 3Bis one example of many possible relationships between an antenna, such as antenna204, and a parasitic arm, such as parasitic arm206, that result in electromagnetic coupling. The tunable load used for the results in Table 1 (and the results ofFIGS. 18 and 19below) is a DTC in parallel with a fixed inductor.

FIG. 4is a block diagram of a general tunable load300that may be used in a wireless device. The tunable load300comprises parasitic arm310and a variable impedance320. The tunable load may optionally include a fixed impedance330and a fixed impedance340connected to ground (or a ground plane) as shown. Each of the fixed impedances330and340may be an inductor, a capacitor, or a resistor. The variable impedance320may be a tunable capacitor. Thus, the fixed impedance330may be in parallel with the variable impedance320, and the combination may be in series with a fixed impedance340. The tunable load300may be electromagnetically coupled to an antenna via the parasitic arm310.

The size of the parasitic arm may vary depending on the needs of the device utilizing the antenna apparatus. For example, in one embodiment, the parasitic arm may be of a larger size to enable a wider range of accessible bandwidths. In another embodiment, however, the parasitic arm may be of a smaller size on order to provide tuning of the antenna in a smaller device, such as a small and/or thin handheld mobile device.

The parasitic arm is not restrained to only one shape as the shape of the parasitic arm may vary depending on the needs of the device utilizing the antenna apparatus. For example, in one embodiment, the device may be a rectangular shaped smart phone comprising a rectangular shaped printed circuit board (PCB). Thus, in one embodiment, the shape of the parasitic arm may be “L” shaped in order to enable optimal coupling for a rectangular PCB. However, in another embodiment, in order to enable performance of the antenna tuning, the parasitic arm may be of another shape, such as a straight line or an “S” shape.

In one example embodiment, the device containing the antenna apparatus may be a handheld wireless device such as a mobile phone. In this embodiment, the mobile phone may be four inches across, with a keepout area measuring 9 millimeters (mm) thick. The load of the parasitic arm206may have a capacitor tuning range of about 1.8 pF to 5 pF, yielding a ratio between smallest and largest capacitance of approximately 1 to 2.7.

A tunable antenna according to this disclosure is not limited to the particular embodiments inFIGS. 2A, 2B, 3A, and 3B, as those figures illustrate an example exemplary embodiment. Tunable antennas according to this disclosure may have a variety of embodiments.FIGS. 4-12illustrate example embodiments of parasitic arms with tunable loads.FIGS. 4-12illustrate a variety of shapes of parasitic arms covered by this disclosure. The operating frequency band of a tunable antenna may depend not only on impedance of a tunable load, but also depend on the shape the parasitic arm.

FIG. 5is a cut-away view of an embodiment of a parasitic arm402and tunable load404in a wireless communication device400. Likewise,FIGS. 6-10are cut-away views of embodiments of parasitic arms502,602,702,802, and902, respectively. The parasitic arms inFIGS. 6-10are coupled to tunable loads504,604,704,804, and904, respectively, with the tunable loads connected to a ground plane.FIGS. 11 and 12are cut-away views of embodiments of parasitic arms1002and1102. Each of parasitic arms1002and1102may be coupled to tunable loads1004and1104, respectively, at one end of the parasitic arms. Further each of parasitic arms1002and1102may be coupled to a ground plane at another end as shown. The parasitic arms inFIGS. 5-12may be electromagnetically coupled to an antenna, such as antenna204inFIGS. 3A and 3B.FIGS. 5-12represent portions of wireless communication devices400-1100, respectively.

FIG. 13is a cut-away view of an embodiment of two parasitic arms1202and1206, which may be electromagnetically coupled to an antenna. The parasitic arms1202and1206may be coupled to tunable loads1204and1208, respectively. Thus, the operating frequency band of a tunable antenna may also depend on the number of parasitic arms and tunable loads.

FIG. 14is a side view of another embodiment of a tunable antenna1300. The tunable antenna comprises an antenna1310and a parasitic arm1308. The antenna1310may reside on a first housing1304, and the parasitic arm1308may reside on a second housing1308. The tunable antenna further comprises a tunable load (not shown).

FIG. 15is a side view of another embodiment of a tunable antenna1400. The tunable antenna comprises an antenna1410and a parasitic arm1408. The antenna1410may reside on a first housing1406, and the parasitic arm1408may reside on a second housing1404. The tunable antenna further comprises a tunable load (not shown).

FIG. 16Ais a cut-away side view of another embodiment of a tunable antenna in a wireless communication device1500. The tunable antenna comprises an antenna1508situated on a housing1504as shown inFIG. 16A.FIG. 16Bshows a top view of the tunable antenna. The top view illustrates a parasitic arm1506as part of the tunable antenna1500.FIG. 16Cis also a side view of the tunable antenna but with the connections1510and1512to ground plane shown (the connections are not shown inFIG. 16A). The connection1510connects the parasitic arm1506to a ground plane, and the connection1512connects the antenna1508to the ground plane. The tunable antenna may further comprise a tunable load that may be placed between the parasitic arm1506and the ground plane.

FIG. 17Ais a cut-away side view of another embodiment of a tunable antenna in a wireless communication device1600. The tunable antenna comprises an antenna1608situated on a PCB as shown inFIG. 17A.FIG. 17Bshows a top view of the tunable antenna. The top view illustrates a parasitic arm1606as part of the tunable antenna.FIG. 17Cis also a side view of the tunable antenna but with the connection1610to ground plane shown (the connection is not shown inFIG. 17A). The connection1610connects the parasitic arm1606to a ground plane using a via. The tunable antenna may further comprise a tunable load that may be placed between the parasitic arm1606and the ground plane. The tunable antenna may be on one side of the PCB, and the ground plane may be on an opposing side of the PCB.FIGS. 17A-17Cdemonstrate that a tunable antenna may reside only on a PCB (i.e., may use no housing).

FIG. 18is a flowchart1700of an embodiment of a method for tuning an antenna. In step1702an operating frequency band of an antenna is selected or determined. For example, the antenna may be employed in a wireless communication device that needs to use a low band in the range of 0.69 GHz to 0.75 GHz. In step1703, a capacitance of a tunable load that corresponds to the selected frequency band of step1702is determined. The capacitance may be determined by accessing a lookup table, such as Table 1, containing operating frequencies corresponding to capacitance values. In step1704a capacitance of a tunable load may be adjusted according to the frequency band. The steps in the flowchart1700may be repeated periodically or at predetermined time intervals or any time a wireless communication device employing the method needs to change operating frequency bands.

In the method for tuning an antenna described inFIG. 18, the tunable load may be electromagnetically coupled to the antenna via a parasitic arm, and wherein the operating frequency band depends on the capacitance. In one embodiment, a processor coupled to the communication device may access a table of related capacitance values and operating frequency bands stored in memory. The table may be generated from laboratory experimentation or simulation models to determine that tuning the capacitance to a certain value results in a specific range of operating frequency bands. When a communication device requests a specific operating frequency band, the processor may look up in the table the capacitance value associated with the requested operating frequency band. The processor may then tune the load on the parasitic arm to the retrieved capacitance value, resulting in the correct tuning of the antenna.

FIG. 19is a line graph depicting the return loss for three loads of the tunable antenna illustrated inFIGS. 2A, 2B, 3A, and 3B. The tunable load used for these results is a DTC. State A, represented by a solid line as shown inFIG. 19, represents return loss when the tunable load has a capacitance of about 5 pF. State B, represented by a dashed line as shown inFIG. 19, represents return loss when the tunable load has a capacitance of about 2.5 pF. In particular,FIG. 19shows that for State B the tunable antenna has a return loss of approximately −21 dB at a frequency of 1 GHz, has a return loss of approximately −13 dB at a frequency of 1.75 GHz, and a return loss of 0 dB at a frequency of 2.4 GHz. State C, represented by a dotted line as shown inFIG. 19, represents return loss when the tunable load has a capacitance of about 1.8 pF. For example, FIG.19shows that for State C the tunable antenna has a return loss of approximately 0 dB at a frequency of 1.45 GHz, has a return loss of approximately −24 dB at a frequency of 1.5 GHz, and a return loss of −5 dB at a frequency of 2 GHz. As shown inFIG. 19, the results indicate that the tunable antenna in State A may exhibit satisfactory performance for LTE band 17; the tunable antenna in State B may exhibit satisfactory performance at an operating low band frequency of 850 MHz; and the tunable antenna in State C may exhibit satisfactory performance at an operating low band frequency of 900 MHz.

FIG. 20shows a line graph depiction the system efficiency for three loads of the tunable antenna illustrated inFIGS. 2A, 2B, 3A, and 3B. As understood by one of skill in the art, system efficiency is a measure of how efficiently the power delivered to the antenna can be radiated into free space. State A, represented by a solid line as shown inFIG. 20, represents system efficiency when the tunable load has a capacitance of about 5 pF. In particular,FIG. 20shows that State A has a system efficiency of 55% at a frequency of approximately 0.7 GHZ, having a peak efficiency of approximately 92% at frequency of 1.78 GHz, and 5% system efficiency at a frequency of 2.5 GHz. State B, represented by a dashed line as shown inFIG. 20, represents return loss when the tunable load has a capacitance of about 2.5 pF. In particular,FIG. 20shows that State B has a system efficiency of 45% at a frequency of approximately 1.5 GHZ, having a peak efficiency of approximately 85% at frequency of 0.8 GHz, and 5% system efficiency at a frequency of 2.5 GHz. State C, represented by a dotted line as shown inFIG. 20, represents return loss when the tunable load has a capacitance of about 1.8 pF. For example,FIG. 20shows that in State C the tunable antenna has a system efficiency of 55% at a frequency of approximately 1.0 GHZ, a peak efficiency of approximately 75% at frequency of 0.95 GHz, and a system efficiency of 5% at a frequency of 2.5 GHz.

FIG. 21is a schematic diagram of an embodiment of a wireless communication device2000. The communication device2000comprises a transceiver2004, a processor2006, a memory2012, and a tunable antenna2014as shown inFIG. 21. The tunable antenna2014comprises an antenna2002, a parasitic arm2008, and a tunable load2010as shown inFIG. 21. The tunable antenna2014is configured such that the parasitic arm2008and the antenna2002are electromagnetically coupled. For example, the tunable antenna may be configured similarly to the tunable antenna shown inFIGS. 2A, 2B, 3A, and 3B. The tunable load2010may be any type of tunable load discussed herein, such as a varactor or a MEMS capacitor array. The processor2006may be implemented as one or more central processing unit or CPU chips, cores (e.g., a multi-core processor), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and/or digital signal processors (DSPs). The tunable load2010may be controlled by the processor2006. The processor2006may be implemented using hardware, software, or both. The memory2012may be used to store volatile or non-volatile data including instructions for the processor2006. The memory2012may comprise read-only memory (ROM), a random access memory (RAM), and/or secondary storage devices such as tape drives or disk drives. The wireless communication device2000may be a cellular phone, smart phone, tablet computer, laptop computer or any other type of wireless communication device that needs to employ a plurality of operating bands.

The wireless communication device2000may optionally include a proximity sensor2016as shown inFIG. 21. A proximity sensor may detect the proximity of a human head or other objects. An object in close proximity to the wireless communication device2000may affect the return loss of the antenna2002. A proximity sensor, for example, may comprise a capacitive sensor comprising one or more capacitors to assist in detecting a presence and a proximity of a human body relative to a wireless device. A person of skill in the art will recognize that there are many types of available proximity sensors. Therefore, the processor2006may take into account feedback from the proximity sensor in selecting a capacitance of tunable load2010.

There may be a control interface between the processor2006and the tunable load2010to allow the processor2006to control the tunable load2010. The control interface may be Serial Peripheral Interface Bus (SPI), a Mobile Industry Processor Interface (MIPI), or any other suitable interface. The processor2006may be configured to send a control signal to the tunable load2010and the tunable load2006may be configured to receive the control signal and adjust the capacitance accordingly.

The memory2012may store a table, such as Table 1, of operating frequency bands for the communication device2000and associated capacitance values of tunable load2010that achieve those frequency bands. The processor2006may load or access the table from memory2012. If the communication device2000desires to use a frequency band, the processor2006may look up the associated capacitance value of the tunable load2010in the table and send a control signal to the tunable load to set the capacitance of the tunable load2010. For example, a communication device (e.g., a mobile phone) may request an operating frequency band of about 870 MHz to 960 MHz. Using Table 1 as an example, the processor2006may access the table stored in the memory2012to see that the associated capacitance value to achieve an operating frequency band of about 870 MHz to 960 MHz is 1.8 pF. The processor2006may then adjust the capacitance of the tunable load2010to 1.8 pF in order to achieve the requested operating frequency band. Further, the table stored in memory may take into account readings from the proximity sensor in the lookup of tunable load. For example, operating frequency band may be a function of a proximity measurement and a tunable load.

References to “one embodiment,” “an embodiment,” “some embodiment,” “various embodiments,” or the like, indicate that a particular element or characteristic is included in at least one embodiment of the invention. Although the phrases may appear in various places, the phrases do not necessarily refer to the same embodiment.

The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, while the various embodiments have been described in terms of a variable tunable antenna coupled to a parasitic arm, this context shall not be read as a limitation as to the scope of one or more of the embodiments described—the same techniques may be used for other embodiments. It is intended that the following claims be interpreted to embrace all such various and modifications.