Compact PIFA antenna

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/272,265, filed May 7, 2014; U.S. patent application Ser. No. 13/891,430, filed May 10, 2013, which claims priority to U.S. Patent Application Ser. No. 61/720,798, filed Oct. 31, 2012, U.S. Patent Application Ser. No. 61/677,706, filed Jul. 31, 2012, and U.S. Patent Application Ser. No. 61/668,799, filed Jul. 6, 2012; U.S. patent application Ser. No. 13/891,399, filed May 10, 2013, which claims priority to U.S. Patent Application Ser. No. 61/720,798, filed Oct. 31, 2012, U.S. Patent Application Ser. No. 61/677,706, filed Jul. 31, 2012, and U.S. Patent Application Ser. No. 61/668,799, filed Jul. 6, 2012; and U.S. patent application Ser. No. 13/891,445, filed May 10, 2013, which claims priority to U.S. Patent Application Ser. No. 61/720,798, filed Oct. 31, 2012, U.S. Patent Application Ser. No. 61/677,706, filed Jul. 31, 2012, and U.S. Patent Application Ser. No. 61/668,799, filed Jul. 6, 2012; each of which is fully incorporated herein by reference in their entirety.

This application relates to U.S. Non-Provisional patent application Ser. No. 14/583,625, filed Dec. 27, 2014, entitled “Receivers for Wireless Power Transmission,” U.S. Non-Provisional patent application Ser. No. 14/583,630, filed Dec. 27, 2014, entitled “Methodology for Pocket-Forming,” U.S. Non-Provisional patent application Ser. No. 14/583,634, filed Dec. 27, 2014, entitled “Transmitters for Wireless Power Transmission,” U.S. Non-Provisional patent application Ser. No. 14/583,640, filed Dec. 27, 2014, entitled “Methodology for Multiple Pocket-Forming,” U.S. Non-Provisional patent application Ser. No. 14/583,641, filed Dec. 27, 2014, entitled “Wireless Power Transmission with Selective Range,” U.S. Non-Provisional patent application Ser. No. 14/583,643, filed Dec. 27, 2014, entitled “Method for 3 Dimensional Pocket-Forming,” all of which are incorporated herein by reference in their entirety.

BACKGROUND

Field of the Disclosure

The present disclosure relates in general to antennas, and more specifically, to compact planar inverted-F antennas (PIFAs) that can be integrated into receivers for wireless power transmission.

Background Information

Wireless power transmission may include a transmitter for forming and directing RF waves towards a receiver which may convert RF waves or pockets of energy into usable power for charging or powering an electronic device. The receiver may be integrated into the electronic device (i.e. a smartphone, a tablet) or may be in the form of a case that can be operatively coupled with the electronic device for suitable charging or powering. The receiver may include an antenna array with a plurality of antenna elements configured as will be described.

One important factor considered in wireless power transmission is the continuous improvement of the antenna elements used in the receiver. This is becoming more relevant as the trend of smaller hand held electronic devices with an increasing number of wireless functions may significantly complicate the antenna selection and integration process. As such, it may be desirable to decrease the size of antenna elements so that these antenna elements can be easily incorporated into the receiver or electronic device, while sustaining or improving their performance. It may be also desirable to have antenna elements with robust mechanical properties for long lasting integration and operation.

SUMMARY

Various embodiments of PIFAs described herein may include an antenna element with two or more slots formed over the top layer of a printed circuit board (PCB), where these antenna slots may be designed for reducing the area of the antenna while keeping a suitable impedance bandwidth. These PIFA configurations may also include a ground element formed on the bottom layer of the PCB and operatively coupled with the antenna element through ground and signal vias. The ground element may also include one or more slots designed for reducing the area of the ground while increasing the radiation efficiency of the PIFA system. The ground element may also have a large part of its central area missing, provided its perimeter is electrically connected. This may further increase radiation efficiency, and may also allow for other systems to be inserted within that region. The missing central ground area may not significantly affect the antenna operation, except possibly in de-tuning the impedance bandwidth, which can be adjusted by the antenna element itself.

In one embodiment, a PIFA configuration may include a folded ground formed over the empty space of a PCB top layer, without interfering with the operation of an antenna element which may be also formed over the PCB top layer. This folded ground may be operatively connected with a ground element on the PCB bottom layer through folded ground vias. An object of this folded ground may be to allow the reduction in the system area while maintaining an omnidirectional radiation pattern and a suitable performance in terms of impedance bandwidth and radiation efficiency.

In another embodiment, a PIFA configuration may include a folded ground extended or moved closer to an antenna element formed over the top layer of a PCB. By moving the folded ground closer to the antenna element and slightly increasing the PCB thickness, the PIFA system may achieve significant reductions in the system area, while maintaining an omnidirectional radiation pattern and improving performance in terms of impedance bandwidth and radiation efficiency.

In yet another embodiment, a PIFA configuration may include a folded ground formed over the top layer of a PCB, where this folded ground may be at its maximum allowable distance from an antenna element. This maximum folding may allow the system area to be greatly reduced, while maintaining a suitable performance in terms of impedance bandwidth, radiation pattern, and efficiency.

The PIFA configurations described herein may be implemented in a monolithic form factor for complete integration into a single, double layer, printed circuit board (PCB) of compact dimensions. These PIFA configurations may also be embedded into larger PCBs, for example a receiver PCB or an electronic device PCB. The omnidirectional radiation pattern of the disclosed PIFA configurations may allow ad-hoc placement into a receiver or electronic device. Moreover, the disclosed PIFA configurations may achieve compact dimensions while maintaining suitable performance for wireless power transmission.

Additional features and advantages may become apparent in view of the detailed descriptions which follow, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. In the figures, reference numerals designate corresponding parts throughout the different views.

FIG. 1 illustrates a three-dimensional (3-D) view of a planar inverted-F antenna integrated in a printed circuit board (PCB).

FIG. 2A shows an omnidirectional 3-D radiation pattern of the PIFA of FIG. 1 oriented as shown in FIG. 1.

FIG. 2B depicts the return loss of the PIFA shown in FIG. 1 when fed by a 50-Ohm port.

FIG. 3 depicts a 3-D view of a PIFA with a folded ground.

FIG. 4A shows an omnidirectional 3-D radiation pattern of the PIFA of FIG. 3 as oriented in FIG. 3.

FIG. 4B illustrates the return loss of the PIFA shown in FIG. 3 when fed by a 50-Ohm port.

FIG. 5 shows a 3-D view of a PIFA with a folded ground moved closer to an antenna element.

FIG. 6 depicts the return loss of the PIFA shown in FIG. 5 when fed by a 50-Ohm port.

FIG. 7 shows a 3-D view of a PIFA with folded ground moved at a maximum allowable distance from an antenna element.

FIG. 8 illustrates the return loss of the PIFA shown in FIG. 7 when fed by a 50-Ohm port.

DETAILED DESCRIPTION

The present disclosure is here described in detail with reference to embodiments illustrated in the drawings, which form a part here. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the present disclosure. The illustrative embodiments described in the detailed description are not meant to be limiting of the subject matter presented here.

Definitions

As used here, the following terms may have the following definitions:

“Wireless Power Transmission” may refer to the action of a transmitter capable of pocket forming for generating pockets of energy that may be utilized by a receiver for charging or powering an electronic device.

“Pocket-forming” may refer to generating two or more RF waves which converge in 3-d space, forming controlled constructive and destructive interference patterns.

“Pockets of energy” may refer to areas or regions of space where energy or power may accumulate in the form of constructive interference patterns of RF waves.

“Null-space” may refer to areas or regions of space where pockets of energy do not form because of destructive interference patterns of RF waves.

“Transmitter” may refer to a device, including a chip which may generate two or more RF signals, at least one RF signal being phase shifted and gain adjusted with respect to other RF signals, substantially all of which pass through one or more RF antennas such that focused RF signals are directed to a target.

“Receiver” may refer to a device including at least one antenna element, at least one rectifying circuit, and at least one power converter, which may utilize pockets of energy for powering or charging an electronic device.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a three-dimensional (3-D) view of a planar inverted-F antenna (PIFA) 100 integrated in a printed circuit board (PCB) 102. This PIFA 100 may be designed to be as small as possible while maintaining a suitable performance for wireless power transmission, and it may be integrated in a double layer PCB for achieving a monolithic form. In one embodiment, PIFA 100 may be formed on the PCB of an electronic device such as a smartphone, tablet, a laptop computer, a PDA, and the like. In another embodiment, PIFA 100 may be formed on the PCB of a receiver that may be used for wireless power transmission. Yet in another embodiment, PIFA 100 may be formed on its own PCB which may be connected to the PCB of an electronic device or a receiver.

PIFA 100 may include an antenna element 104 formed over the top layer of PCB 102, and a ground element 106 formed over the bottom layer of PCB 102. Both PCB layers may be made of suitable metals such as copper of small metal thickness relative to the total PCB 102 thickness. PCB 102 may include a dielectric base with a suitable dielectric constant. In one embodiment, an Isola FR408HRIS may be used for PCB 102 materials.

Antenna element 104 may include two slots 108 designed for reducing the area of antenna element 104 while maintaining a suitable bandwidth operation. For example, PIFA 100 may achieve a bandwidth of about 160 MHz. Without the two slots 108, PIFA 100 may still be able to achieve a similar bandwidth, but the area of antenna element 104 may have to be increased about 34%. More slots may be introduced on antenna element 104 for even further area reduction if necessary, according to application.

Similarly to antenna element 104, ground element 106 may include a slot 110 the main purpose of which may be to reduce the area of the ground element 106 while reducing losses and increasing radiation efficiency. For example, by including slot 110, PIFA 100 may achieve a radiation efficiency of about 69%. In one embodiment, slot 110 in ground element 106 may increase the radiation efficiency of PIFA 100 by about 22% and about 32% for PCB 102 substrates having a thickness of about 1.4 mm and about 0.8 mm, respectively. In another embodiment, the combination of ground slot 110 and ground element 106 missing central area may increase the radiation efficiency by about 32% and about 54% for 1.4 mm-thick and 0.8 mm-thick PCB 102 substrates, respectively, relative to designs with solid ground.

PIFA 100 may also include a signal via 112, a ground via 114, and a RF port 116 for electrical connection purposes. In one embodiment, a semi-rigid 50 Ohm coax cable can be connected to RF port 116 for prototype measurements. For integration purposes, PIFA 100 may be fed through RF port 116 by a transmission line integrated in a larger PCB.

In an embodiment, dimensions of PIFA 100 may be about 12 mm, 3.5 mm, and 1.4 mm in the x-axis, y-axis, and z-axis respectively, for an estimated system area of about 42 mm² and a system volume of about 58.8 mm³.

FIGS. 2A and 2B show the performance 200 of PIFA 100 according to embodiments described herein.

FIG. 2A shows an omnidirectional 3-D radiation pattern of PIFA 100 oriented as shown in FIG. 1. This omnidirectional radiation pattern in FIG. 2A may be similar to radiation patterns exhibited in dipole antennas, thereby allowing flexible placement or integration of PIFA 100 into larger form factors, for example, a receiver PCB or an electronic device PCB. In one embodiment, PIFA 100 may exhibit a maximum gain of about −0.0099 dBi at 5.8 GHz.

FIG. 2B illustrates the return loss of PIFA 100 when fed by a 50-Ohm port. As seen from probes m1 and m2, PIFA 100 may exhibit an impedance bandwidth of about 160 MHz at −10 dB, where this bandwidth may provide sufficient margins for possible detuning upon integration of PIFA 100 into an electronic device or a larger PCB. Radiation efficiency of PIFA 100 may be around 69% at 5.8 GHz.

Although PIFA 100 may exhibit suitable characteristics for wireless power transmission, it may be an object of the following embodiments to provide PIFAs with a similar monolithic PCB form factor, but with a reduced size and a similar or improved performance in terms of impedance bandwidth, radiation pattern, and maximum radiation efficiency.

FIG. 3 is a 3-D view of a PIFA 300 with a folded ground 302, according to embodiments. This PIFA 300 may be designed to be as small as possible while maintaining a suitable performance for wireless power transmission, and it may be integrated in a double layer PCB for achieving a monolithic form. In one embodiment, PIFA 300 may be formed on the PCB of an electronic device such as a smartphone, tablet, a laptop computer, a PDA, and the like. In another embodiment, PIFA 300 may be formed on the PCB of a receiver that may be used for wireless power transmission. Yet in another embodiment, PIFA 300 may be formed on its own PCB which may be connected to the PCB of an electronic device or a receiver.

Similarly to PIFA 100, PIFA 300 in FIG. 3 may include PCB 102, antenna element 104, ground element 106, antenna slots 108, ground slot 110, signal via 112 and ground via 114. However, unlike PIFA 100, PIFA 300 may include folded ground 302 which can be formed over an empty region of the top layer of PCB 102 without interfering with the performance of antenna element 104. Folded ground 302 can be raised over the top layer of PCB 102 and can be connected to ground element 106 through folded ground vias 304 which may not significantly affect the performance of PIFA 300. Folded ground 302 may act as an extension of ground element 106.

According to some aspects of this embodiment, folded ground 302 may allow the dimensions of PIFA 300 to be reduced compared to the dimensions of PIFA 100, while improving or at least maintaining similar performance characteristics. For example, PIFA 300 dimensions in the x-axis, y-axis, and z-axis may be about 10 mm, 3.3 mm, and 1.4 mm respectively, for a system area of about 33 mm² and a system volume of about 46.2 mm³. This can be translated to a 21% reduction in system area and volume as compared to PIFA 100.

FIGS. 4A and 4B show the performance 400 of PIFA 300 according to embodiments described herein. Performance 400 of PIFA 300 may be fairly similar to performance 200 of PIFA 100, but significant reductions in size may be achieved as previously stated.

FIG. 4A shows an omnidirectional 3-D radiation pattern of PIFA 300 oriented as shown in FIG. 3. As seen in FIG. 4A, PIFA 300 may still exhibit a suitable omnidirectional radiation pattern which may allow a flexible placement or integration of PIFA 300 into larger form factors, for example, a receiver PCB or an electronic device PCB. In one embodiment, PIFA 300 may exhibit a maximum gain of about −0.078 dBi at 5.8 GHz.

FIG. 4B illustrates the return loss of PIFA 300 when fed by a 50-Ohm port. As seen from probes m1 and m2, PIFA 300 may exhibit an impedance bandwidth of about 140 MHz at about −10 dB which may be slightly lower than the impedance bandwidth of PIFA 100, but it may still be able to provide sufficient margins for possible detuning upon integration of PIFA 300 into an electronic device or a larger PCB form. PIFA 300 may exhibit a radiation efficiency of about 62% which may be slightly lower than the radiation efficiency exhibited by PIFA 100, but it may be still suitable for effective wireless power transmission.

FIG. 5 illustrates a 3-D view of a PIFA 500 with folded ground 302 extended closer to antenna element 104, according to embodiments of the present invention. This PIFA 500 may be designed to be as small as possible while improving or at least maintaining a suitable performance for wireless power transmission. PIFA 500 may be integrated in a double layer PCB for achieving a monolithic form. In one embodiment, PIFA 500 may be formed on the PCB of an electronic device such as a smartphone, tablet, a laptop computer, a PDA, and the like. In another embodiment, PIFA 500 may be formed on the PCB of a receiver that may be used for wireless power transmission. In yet another embodiment, PIFA 500 may be formed on its own PCB which may be connected to the PCB of an electronic device or a receiver.

Similarly to PIFA 300, PIFA 500 may include PCB 102, antenna element 104, ground element 106, antenna slots 108, ground slot 110, signal via 112, ground via 114, folded ground 302, and folded ground vias 304. However, compared to PIFA 300, folded ground 302 in PIFA 500 may be moved closer to antenna element 104 as seen in FIG. 5. In addition, the thickness of PIFA 500 may be increased from about 1.4 mm to about 2.4 mm. PIFA 500 dimensions in the x-axis, y-axis, and z-axis may be about 10 mm, 2.4 mm, and 2.4 mm respectively, for a system area of about 24 mm² and a system volume of about 57.6 mm³.

According to some aspects of this embodiment, by extending folded ground 302 towards antenna element 104, the system area of PIFA 500 can be reduced about 27% and 43% compared to PIFA 300 and PIFA 100 respectively. Moreover, by combining this extended folded ground 302 with a slightly thicker PCB, the overall performance of PIFA 500 may be significantly improved. For example, PIFA 500 may achieve a radiation efficiency of about 82% at 5.8 GHz compared to about 69% in PIFA 100 and 62% in PIFA 300.

FIG. 6 shows the performance 600 of PIFA 500 according to embodiments described herein. Compared to PIFA 100 and PIFA 300, the performance of PIFA 500 may be significantly improved, while also achieving significant reductions in system area as previously stated.

In addition to a higher radiation efficiency, the return loss of PIFA 500 when fed by a 50-Ohm port, as shown in FIG. 6, may exhibit a higher impedance bandwidth of about 180 MHz at −10 dB, compared to 160 MHz and 140 MHz for PIFA 100 and PIFA 300 respectively. This bandwidth may provide sufficient margins for possible detuning upon integration of PIFA 500 into an electronic device or a larger PCB form factor.

As in PIFA 100 and PIFA 300, PIFA 500 may still exhibit an omnidirectional radiation pattern (not shown in FIG. 6) for allowing flexible placement or integration of PIFA 500 into larger form factors, for example, a receiver PCB or an electronic device PCB. In one embodiment, PIFA 500 may exhibit a gain of about +0.55 dBi at 5.8 GHz.

FIG. 7 shows a 3-D view of a PIFA 700 where folded ground 302 can be extended even closer to antenna element 104, according to embodiments of the present invention. This PIFA 700 may be designed to be as small as possible while improving or at least maintaining a suitable performance for wireless power transmission. PIFA 700 may be integrated in a double layer PCB for achieving a monolithic form. In one embodiment, PIFA 700 may be formed on the PCB of an electronic device such as a smartphone, tablet, a laptop computer, a PDA, and the like. In another embodiment, PIFA 700 may be formed on the PCB of a receiver that may be used for wireless power transmission. Yet in another embodiment, PIFA 700 may be formed on its own PCB which may be connected to the PCB of an electronic device or a receiver.

Similarly as in PIFA 300 and PIFA 500, PIFA 700 may include PCB 102, antenna element 104, ground element 106, antenna slots 108, ground slot 110, signal via 112, ground via 114, folded ground 302, and folded ground vias 304. However, as seen in FIG. 7, folded ground 302 can be moved even closer to antenna element 104 as compared to PIFA 500 and PIFA 300. In an embodiment, the thickness of PIFA 700 may be about 2.4 mm. Overall PIFA 700 dimensions in the x-axis, y-axis, and z-axis may be about 9 mm, 2.4 mm, and 2.4 mm respectively, for a system area of about 21.6 mm² and a system volume of about 51.8 mm³.

According to some aspects of this embodiment, by extending folded ground 302 even closer to antenna element 104 as compared to PIFA 500, the system area and volume area of PIFA 700 may be reduced about 10% more, while maintaining a similar performance. For example, PIFA 700 may exhibit a radiation efficiency of about 76%, at 5.8 GHz, just slightly lower than radiation efficiency in PIFA 500, but higher compared to PIFA 300 and PIFA 100. In one embodiment, folded ground 302 in PIFA 700 may be at a maximum allowable distance from antenna element 104 for maintaining a suitable performance for wireless power transmission.

Compared to PIFA 300 and PIFA 100, the system area reductions achieved in PIFA 700 may be significantly higher, about 35% and 49% respectively. Similarly, PIFA 700 may exhibit an enhanced performance in terms of higher impedance bandwidth and radiation efficiency as compared with PIFA 300 and PIFA 100.

FIG. 8 shows the performance 800 of PIFA 700 according to embodiments described herein. Compared to PIFA 100, PIFA 300, and PIFA 500, performance of PIFA 700 may be maintained fairly similar and in some cases, it may be enhanced; all of this while achieving significant reductions in system area.

The return loss of PIFA 700 when fed by a 50-Ohm port, as shown in FIG. 8, may exhibit an impedance bandwidth of about 180 MHz at −10 dB, which is about the same bandwidth exhibited by PIFA 500, but higher compared to 160 MHz and 140 MHz for PIFA 100 and PIFA 300 respectively. This bandwidth may provide sufficient margins for possible detuning upon integration of PIFA 700 into an electronic device or a larger PCB form factor.

PIFA 700 may still exhibit an omnidirectional radiation pattern (not shown in FIG. 8) for allowing flexible placement or integration of PIFA 700 into larger form factors, for example, a receiver PCB or a electronic device PCB. In one embodiment, PIFA 700 may exhibit a maximum gain of about +0.019 dBi at 5.8 GHz.

In general, folded ground 302 in PIFA 300, PIFA 500, and PIFA 700 may allow significant reductions in the system area compared to the prior art. And by combining folded ground 302 with a slightly thicker PCB, the performance in PIFA 500 and PIFA 700 may be improved even more.

It may be apparent to someone skilled in art that the selection of the optimal PIFA configuration may depend on the characteristics and form factor of a particular receiver or electronic device. For example, optimal configurations may be selected based on criteria of having a PIFA with the smallest system area; the higher impedance bandwidth; the higher radiation efficiency; the smallest system volume; or a combination of criteria as required by the application.

The preceding description of the disclosed embodiments is provided to enable persons skilled in the art to make or use the present invention. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.