Patent Application
20150022402
This application claims the benefit of U.S. patent application Ser. No. 13/945,083, filed by Joselito Gavilan, et al., on Jun. 18, 2013, entitled “Antenna System and an Electronic Device Including the Same,” commonly assigned with this application and incorporated herein by reference.
This application is directed, in general, to antennas and, more specifically, to antennas for handheld electronic devices.
Handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type, among others.
Due in part to their mobile nature, handheld electronic devices are often provided with wireless communications capabilities. Handheld electronic devices may use long-range wireless communications to communicate with wireless base stations. For example, cellular telephones may communicate using 2G Global System for Mobile Communication (commonly referred to as GSM) frequency bands at about 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, among possible others. Communication is also possible in the 3G Universal Mobile Telecommunication System (commonly referred to as UMTS, and more recently HSPA+) and 4G Long Term Evolution (commonly referred to as LTE) frequency bands which range from 700 MHz to 3800 MHz. Furthermore, communications can operate on channels with variable bandwidths of 1.4 MHz to 20 MHz for LTE, as opposed to the fixed bandwidths of GSM (0.2 MHz) and UMTS (5 MHz). Handheld electronic devices may also use short-range wireless communications links. For example, handheld electronic devices may communicate using the Wi-Fi® (IEEE 802.11) bands at about 2.4 GHz and 5 GHz, and the Bluetooth® band at about 2.4 GHz. Handheld devices with Global Positioning System (GPS) capabilities receive GPS signals at about 1575 MHz.
To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of components that are used in these handheld electronic devices. For example, manufacturers have made attempts to miniaturize the antennas used in handheld electronic devices. Unfortunately, doing so within the confines of the wireless device package is challenging.
Accordingly, what is needed in the art is an antenna, and associated wireless handheld electronic device, that navigate the desires and problems associated with the foregoing.
One aspect provides an antenna. The antenna, in this aspect, includes a feed element electrically connectable to a positive terminal of a transmission line, and a ground element electrically connectable to a negative terminal of the transmission line. Further to this aspect of the antenna, the feed element and ground element capacitively couple to one another without touching to form a capacitively coupled loop antenna.
Another aspect provides an electronic device. The electronic device, in this aspect, includes storage and processing circuitry, input-output devices associated with the storage and processing circuitry, and wireless communications circuitry including an antenna. The antenna, in this aspect, includes: 1) a feed element electrically connected to a positive terminal of a transmission line, and 2) a ground element electrically connected to a negative terminal of the transmission line, wherein the feed element and ground element capacitively couple to one another without touching to form a capacitively coupled loop antenna.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
In modern wireless communication standards such as HSPA+ and LTE, multiple-input-multiple-output (MIMO) technology has become a vital component in the quest for better wireless performance. As shown in
With the current design trends for mobile devices such as mobile phones and tablet devices, the amount of volume available for antenna integration is limited, especially with mobile phones. A typical MIMO implementation in a mobile phone would consist of two antennas, labeled as primary and secondary. For each individual antenna, standard antenna performance metrics would apply, including antenna efficiency, directivity, and radiation pattern.
For a MIMO antenna system, the gain imbalance between the two antennas and the envelope correlation coefficient between the two antennas must be considered, in addition to the individual antenna metrics discussed above. These two relational metrics will have a direct impact on the MIMO antenna system performance. The gain imbalance is the difference of the mean gain between the two antennas in free-space. The envelope correlation coefficient determines the diversity performance and MIMO antenna system quality by taking into account the antenna radiation patterns and the propagation model of the environment. For the correlation coefficient, ρc=0 means the two antennas are completely uncorrelated and ρc=1 means the two antennas patterns are exactly the same and correlated. Recently, U.S. carriers have defined upper limits for the correlation coefficient for mobile devices implementing two antennas, as set forth in Table 1 below.
The present disclosure has recognized that to meet these requirements, various techniques may be used in designing the antenna pair, including spatial diversity, polarization diversity, and pattern diversity. In a handheld electronic device, the spatial and polarization diversity of the antenna designs are limited by the physical dimensions of the device. Depending on the layout of the internal components, it may not be possible to obtain polarization diversity, even by placing the two antennas on opposing edges of the chassis. In a conventional MIMO antenna system, the primary antenna is typically located in the bottom edge of the chassis and the secondary antenna is typically located in the top edge of the chassis—to maximize the spatial diversity.
The present disclosure has recognized, however, that at lower frequencies, the quarter-wavelength of the resonant frequency approaches the physical length of the chassis. For purposes of the present disclosure, the term “lower frequencies” means frequencies below about 1000 MHz (i.e., below about 1.0 GHz). Hence, for typical monopole and inverted-F antenna (IFA) antenna types, the chassis will act like a resonator for the antenna at the lower frequencies, and the antenna will be strongly coupled to the chassis resulting in poor isolation with other antennas sharing the chassis. If both antennas use the monopole and/or IFA design, the mutual coupling between the antennas will result in very high correlation coefficient values. With the deployment of HSPA+ and LTE bands (e.g., in the 700-900 MHz frequency range), the correlation coefficient limits set forth in Table 1 above become a significant challenge.
The present disclosure, with the foregoing in mind, recognized that the correlation coefficient issues may be addressed by employing two different antenna type designs for the antenna system. For example, if the primary antenna is of a monopole or IFA design, and thus is strongly coupled to the electronic device chassis (particularly as the frequency approaches 700 MHz), the secondary antenna could be of a different design (e.g., an antenna type design that is not strongly coupled to the chassis). In one embodiment, a loop antenna could be used for the secondary antenna in the MIMO antenna system, as loop antennas do not strongly couple to the chassis. In this embodiment, a loop mode resonance of the loop antenna generally contains the electric and magnetic fields within the antenna volume and concentrates the surface currents on the antenna elements, which typically decouples the loop antenna from the chassis. Accordingly, using a loop antenna design for the secondary antenna can improve the mutual coupling with the primary antenna, which as discussed above may be of a monopole or IFA design, among others.
Turning to
In accordance with one embodiment of the disclosure, the first antenna 310a comprises an antenna type that would use the chassis 395 (whether intentionally or otherwise) as a resonator, particularly at lower frequencies. Accordingly, in this embodiment, the first antenna 310a would be strongly coupled to the chassis 395, typically resulting in poor isolation with other antennas sharing the chassis.
In one embodiment of the disclosure, the first antenna 310a comprises a monopole or IFA antenna type design, both of which typically use the conductive chassis 395 as a resonator. Nevertheless, other antenna types that use the conductive chassis 395 as a resonator are within the scope of the disclosure. Accordingly, the present disclosure should not be limited to any specific first antenna 310a design.
Nevertheless, the first antenna 310a illustrated in
Connected to the feed portion 320 in the embodiment of
The first antenna 310a illustrated in
The second resonant portion 360, in the illustrative embodiment, includes a second different length defined by an inner perimeter of the conductive segment 330. The second different length, in the embodiment of
In accordance with the embodiment of
The first antenna 310a illustrated in the embodiment of
In accordance with one embodiment of the disclosure, the second antenna 310b comprises an antenna type that uses the conductive chassis 395 as a resonator much less than the first antenna 310b would use the conductive chassis 395 as a resonator. Accordingly, the second antenna 310b would not strongly couple to the chassis 395 (whether intentionally or otherwise), particularly at lower frequencies. Accordingly, in accordance with the disclosure, a correlation coefficient of the first and second antennas 310a, 310b is less than about 0.5 for a given communication frequency below about 1000 MHz. In accordance with another embodiment of the disclosure, the correlation coefficient of the first and second antennas 310a, 310b is less than about 0.5 for communication frequencies ranging from about 730 MHz to about 750 MHz and about 870 MHz to about 890 MHz. This is particularly the case when a largest physical dimension of the conductive chassis 395 is about ¼ or less a wavelength of the frequencies below about 1000 MHz, including the communication frequencies ranging from about 730 MHz to about 750 MHz and about 870 MHz to about 890 MHz.
In the illustrated embodiment of
In the embodiment of
In one embodiment, the ground portion 390 might connect to a negative terminal of the transmission line (not shown), such as a coaxial cable, microstrip, etc. The ground portion 390, in accordance with one embodiment of the disclosure, may connect to or form a portion of the ground portion 370. While not shown, the ground portion 390 may also connect to or form a portion of the conductive chassis 395.
Specific antenna type designs have been disclosed for each of the first and second antennas 310a, 310b. It should be noted that even though these specific designs have been disclosed with regard to
Loop antenna designs, particularly at lower frequencies, tend to be quite large. Accordingly, for certain antenna applications, including antenna applications for small electronic devices (e.g., tablet computers, handheld computers, game consoles, mobile phones, etc.) operating at the lower frequencies, traditional loop antennas will not fit within the form factor (e.g., conductive chassis 395) of the handheld electronic device. The present disclosure, however, recognized for the first time that capacitively coupled loop antennas could be used in place of traditional loop antennas and more easily fit within the form factor (e.g., conductive chassis 395) of the handheld electronic device. In one aspect of the disclosure, a largest physical dimension of the conductive chassis 395 is about ¼ or less a wavelength of a given frequency below about 1000 MHz. In another aspect, the largest physical dimension of the conductive chassis 395 is about ¼ or less a wavelength of communication frequencies ranging from about 730 MHz to about 750 MHz and about 870 MHz to about 890 MHz.
Turning to
In one embodiment, the antenna 400 includes a feed element 410 and a ground element 450. For example, the feed element 410 might directly connect to a positive terminal of a transmission line (not shown), such as a coaxial cable, microstrip, etc., to receive radio frequency signals from associated transceivers. The feed element 410 may additionally receive radio frequency signals from other antennas, and thus provide them to the associated transceivers. In contrast, the ground element 450 might directly connect to a negative terminal of the transmission line (not shown). The ground element 450, in accordance with one embodiment of the disclosure, may connect to or form a portion of the conductive chassis 495.
In accordance with the disclosure, the feed element 410 and ground element 450 capacitively couple to one another (e.g., in one embodiment by at least partially overlapping) to form a capacitively coupled loop antenna. A capacitively coupled loop antenna behaves like a loop antenna but without a continuous electrical conductor. It achieves this by orienting the feed and ground elements closely spaced together and effectively closing the loop by the capacitive coupling of the arms. By utilizing capacitive coupling, the effective length of the antenna increases and the resonant frequency decreases. The amount of coupling and its impact to the effective length of the antenna can be controlled by the spacing between the arms and amount of overlap of the arms. Compared to a conventional loop antenna with similar physical dimensions, a capacitively coupled loop antenna has a lower resonant frequency.
In the embodiment of
In the embodiment of
The embodiment of
As indicated above, the various configurations and dimensions of the feed element 410 and ground element 450 may be adjusted to tailor the resonant frequencies of the antenna 400, including the both the lower and higher band frequencies. Take for example the antenna 400 of
In contrast, by decreasing the length (L2), and thus decreasing the distance (D1), the lower band resonant frequency would increase and the lower band impedance loop would remain the same size but rotate counter clockwise, and the higher band resonant frequency and impedance loop (e.g., both in size and rotation) would remain about the same. The increase in the length (L2) would typically have just the opposite effect on both the lower and higher band frequencies and impedance loops. Interestingly, decreasing the length (L2) does not have the exact same effect on the antenna 400 as decreasing the length (L1).
In yet further contrast, by increasing the minimum spacing (S1), the lower band resonant frequency would increase and the lower band impedance loop would reduce in size and rotate counter clockwise, and the higher band resonant frequency and impedance loop (e.g., both in size and rotation) would remain about the same. Additionally, the increase in the minimum spacing (S1) would typically have just the opposite effect on both the lower and higher band frequencies and impedance loops.
Notwithstanding the foregoing, the distance (D1) that the feed element 410 and ground element 450 overlap may be an important feature of the antenna 400 design. For example, in one embodiment, the distance (D1) may be at least about ⅙ the length (L2) of the second ground element section 465. In yet another embodiment, the distance (D1) may be at least about ¼ the length (L2) of the second ground element section 465. In yet another embodiment, the distance (D1) may be at least about ⅓ the length (L2) of the second ground element section 465. The greater overlap, at least as it relates to length (L2) of the second ground element section 465, is particularly important in smaller electronic devices (e.g., tablet devices, mobile phones, etc.) wherein the volume to implement the antenna is greatly reduced.
Similarly, the minimum spacing (S1) is an important feature of the antenna 400. For example, in one embodiment, the minimum spacing (S1) between the second feed element section 425 and second ground element section 465 is less than about two times a minimum thickness (T2) of the second ground element section 465. In yet another embodiment, the minimum spacing (S1) between the second feed element section 425 and second ground element section 465 is less than about the minimum thickness (T2) of the second ground element section 465. Similar to the overlap discussed above, the minimum spacing (S1) is particularly important in smaller electronic devices (e.g., tablet devices, mobile phones, etc.) wherein the volume to implement the antenna is greatly reduced.
Returning to
The length (L3) of the parasitic arm 510 may be modified to help tune the resonant frequency of the antenna 400, particularly the higher band resonant frequency. For example, by increasing the length (L3), the lower band resonant frequency and lower band impedance loop would remain about the same, but the higher band resonant frequency would slightly decrease, while the higher band impedance loop would remain about the same. Those skilled in the art, given the present disclosure, would understand the steps required to employ a parasitic arm, such as the parasitic arm 510.
As shown in
Communications protocols that may be implemented using storage and processing circuitry 610 include, without limitation, internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3G communications services (e.g., using wide band code division multiple access techniques), 2G cellular telephone communications protocols, etc. Storage and processing circuitry 610 may implement protocols to communicate using 2G cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands) and may implement protocols for handling 3G and 4G communications services.
Input-output device circuitry 620 may be used to allow data to be supplied to device 600 and to allow data to be provided from device 600 to external devices. Input-output devices 630 such as touch screens and other user input interfaces are examples of input-output circuitry 620. Input-output devices 630 may also include user input-output devices such as buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. A user can control the operation of device 600 by supplying commands through such user input devices. Display and audio devices may be included in devices 630 such as liquid-crystal display (LCD) screens, light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), and other components that present visual information and status data. Display and audio components in input-output devices 630 may also include audio equipment such as speakers and other devices for creating sound. If desired, input-output devices 630 may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors.
Wireless communications circuitry 640 may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). Wireless communications circuitry 640 may include radio-frequency transceiver circuits for handling multiple radio-frequency communications bands. For example, circuitry 640 may include transceiver circuitry 642 that handles 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and the 2.4 GHz Bluetooth® communications band. Circuitry 640 may also include cellular telephone transceiver circuitry 644 for handling wireless communications in cellular telephone bands such as the GSM bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, as well as the UMTS, HSPA+ and LTE bands (as examples). Wireless communications circuitry 640 can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry 640 may include global positioning system (GPS) receiver equipment, wireless circuitry for receiving radio and television signals, paging circuits, etc. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles.
Wireless communications circuitry 640 may include antennas 646. Device 600 may be provided with any suitable number of antennas. There may be, for example, one antenna, two antennas, three antennas, or more than three antennas, in device 600. For example, in one embodiment, the antennas 646 form at least a portion of a MIMO antenna system. In this embodiment, the MIMO antenna system might include a primary antenna comprising a monopole or IFA type antenna, and a secondary antenna comprising a loop type antenna, such as that discussed above with regard to
Paths 650, such as transmission line paths, may be used to convey radio-frequency signals between transceivers 642 and 644, and antennas 646. Radio-frequency transceivers such as radio-frequency transceivers 642 and 644 may be implemented using one or more integrated circuits and associated components (e.g., power amplifiers, switching circuits, matching network components such as discrete inductors, capacitors, and resistors, and integrated circuit filter networks, etc.). These devices may be mounted on any suitable mounting structures. With one suitable arrangement, transceiver integrated circuits may be mounted on a printed circuit board. Paths 650 may be used to interconnect the transceiver integrated circuits and other components on the printed circuit board with antenna structures in device 600. Paths 650 may include any suitable conductive pathways over which radio-frequency signals may be conveyed including transmission line path structures such as coaxial cables, microstrip transmission lines, etc.
The device 600 of
The chassis 660, in one embodiment, is a metal chassis. For example, the chassis 660 may be made of various different metals, such as aluminum. Chassis 660 may be machined or cast out of a single piece of material, such as aluminum. Other methods, however, may additionally be used to form the chassis 660. In certain embodiments, the chassis 660 will act like a resonator for certain ones of the antennas 646, and will not act as a resonator for other ones of the antennas 646—particularly at lower operating frequencies.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
