Patent Application
20100156741
This invention relates to electronic devices and, more particularly, to antennas for electronic devices.
Electronic devices often use wireless communications circuitry. For example, wireless communications circuitry is used in wireless base stations to support communications with computers and other wirelessly networked devices.
Some electronic devices use multiple antennas. For example, a device may use a first antenna to support operations in a first set of communications bands and may use a second antenna to support operation in a second set of communications bands. By using multiple antennas, band coverage may be increased or multiple-input multiple-output (MIMO) antenna schemes may be implemented.
Particularly in electronic devices of relatively small size, it may be necessary to locate different antennas in close proximity. This can cause undesirable coupling effects in which the operation of one antenna interferes with the operation of another antenna. It is therefore challenging to produce successful antenna arrangements in which multiple antennas operate in close proximity to each other without experiencing undesirable interference.
It would therefore be desirable to be able to provide improved antenna structures for wireless electronic devices.
An electronic device is provided that has wireless communications capabilities. The electronic device may have a housing. The housing may contain storage and processing circuitry. A radio-frequency transceiver circuit may be coupled to the storage and processing circuitry. Multiple antennas may be coupled to the radio-frequency transceiver circuitry using respective transmission lines. For example, a first antenna may be coupled to the radio-frequency transceiver using a first coaxial cable and a second antenna may be coupled to the radio-frequency transceiver using a second coaxial cable. The first and second antennas may be single band or multiband antennas. For example, the first antenna may be a single band antenna that operates at 5 GHz, whereas the second antenna may be a dual band antenna that operates at 2.4 GHz and 5 GHz (as an example).
The electronic device may include a conductive structure such as a conductive frame member that serves as a global ground. The first and second antennas may each be electrically and/or electromagnetically coupled to the conductive structure. During operation, signals that are transmitted from one antenna may be received by the other antenna over a free-space path. These signals represent interference. The interference signal can be reduced using a deliberately created cancelling signal. The cancelling signal may be of comparable magnitude and opposite phase to that of the interference signal. The cancelling signal may be routed from one antenna to the other by coupling the antennas through the global ground. The presence of the global ground cancelling path serves to increase isolation between the first and second antennas. Increased isolation may, in turn, improve antenna performance in various modes of operation (e.g., single band and dual band operating modes and operating modes with both antennas transmitting, both antennas receiving, one antenna transmitting and the other antenna receiving, etc.).
To enhance coupling between the antennas and the global ground, one or both antennas may have traces that are configured to form a resonant circuit. For example, an antenna ground element may be formed from a C-shaped trace. The length of the ground element trace gives rise to an inductance for the resonant circuit. A gap in the ground element trace forms a capacitance in series with the inductance.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.
The present invention relates to antennas for electronic devices. The antennas may be used to convey wireless signals for wireless communications links in any suitable communications bands. For example, the antennas may be used to handle communications for local area network links such as an IEEE 802.11 links (sometimes referred to as WiFi® links) or Bluetooth® links. The antennas may also be used to handle other communications frequencies, such as 2G and 3G cellular telephone frequencies. The antennas may be single band antennas or multiband antennas. A given electronic device may have two or more antennas that are isolated from each other to improve antenna performance.
An illustrative configuration in which two antennas are used to handle local area network signals is sometimes described herein as an example. In this type of illustrative configuration, a first antenna of the two antennas may be a single band antenna that handles IEEE 802.11 communications in the 5 GHz band and a second of the two antennas may be a dual band antenna that handles IEEE 802.11 communications in the 2.4 GHz and 5 GHz bands.
Antennas such as these may be used in various electronic devices. For example, the antennas may be used in an electronic device such as a handheld computer, a miniature or wearable device, a portable computer, a desktop computer, a router, an access point, a backup storage device with wireless communications capabilities, a mobile telephone, a music player, a remote control, a global positioning system device, devices that combine the functions of one or more of these devices and other suitable devices, or any other electronic device.
As is sometimes described herein as an example, the electronic device in which the antennas are provided may be a wireless base station such as a router or may be a miniature computer with wireless capabilities. The base station or computer may include local storage such as hard drive storage or solid state drive storage. These are, however, merely illustrative examples. Antennas may, in general, be provided in any suitable electronic device.
An illustrative electronic device 10 such as a wireless base station or computer in which the antennas may be provided is shown in
Device 10 may have antennas such as antennas 14 and 16. Radio-frequency transceiver circuitry 18 may include a radio-frequency receiver and a radio-frequency transmitter. Transmission line paths such as transmission lines 22 and 24 may be used to couple transceiver circuitry 18 to antennas 14 and 16. In the
Transceiver circuitry 18 may be coupled to circuitry such as storage and processing circuitry 20 using paths such as path 26. During data transmission operations, data from storage and processing circuitry 20 may be routed to transceiver 18 over path 26 and may be wirelessly transmitted to external equipment using transceiver 18 and antennas 14 and 16. During data reception operations, incoming radio-frequency signals may be received using antennas 14 and 16, paths 24 and 22, and transceiver circuitry 18. Transceiver circuitry 18 may provide received signals to storage and processing circuitry 20 over path 26.
For optimum wireless performance, it is desirable for antennas such as antennas 14 and 16 to interfere with each other as little as possible. Antenna interference can lead to degraded signal-to-noise ratios and reduced data communications throughput. Undesirable levels of interference can arise when antennas such as antennas 14 and 16 are placed in close proximity to each other. Due to the relatively small size of electronic devices such as device 10, it may be difficult or impossible to separate antennas 14 and 16 by extremely large distances. Nevertheless, satisfactory isolation between antennas 14 and 16 may be achieved by configuring the structures that make up antennas 14 and 16 so as to reduce interference.
With one suitable arrangement, antenna-to-antenna isolation levels of 30 dB or greater may be achieved (as an example). Isolation performance of this level may be achieved when operating antennas 14 and 16 in the same communications band (e.g., both in a first communications band) and may be achieved when operating antenna 14 in a first communications band and operating antenna 16 in a second communications band that is different than the first communications band. The first antenna, such as antenna 14 may, as an example, operate at a communications band of 5 GHz (e.g., for IEEE 802.11 communications), whereas the second antenna such as antenna 16 may operate at communications bands such as 2.4 GHz and 5 GHz bands (e.g., for IEEE 802.11 communications). While operating in this configuration, the first and second antennas may exhibit antenna isolations of more than 30 dB for both bands (2.4 GHz and 5 GHz) that are handled by the second antenna.
A schematic circuit diagram of an illustrative electronic device such as device 10 of
Storage and processing circuitry 20 may include processing circuitry that is used to control the operation of device 10. The processing circuitry may be based on one or more circuits such as a microprocessor, a microcontroller, a digital signal processor, an application-specific integrated circuit, and other suitable integrated circuits. Storage and processing circuitry 20 may be used to run software on device 10 such as operating system software, code for implementing the functions of a server with an array of one or more hard disk drives, solid state drives, or other server storage, software for implementing the functions of router or other communications hub, or other suitable software. To support wireless operations, storage and processing circuitry 20 may include software for implementing wireless communications protocols such as wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), 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, WiMAX® communications protocols, communications protocols for other bands, etc.
Input-output devices 28 may be used to allow data to be supplied to device 10 and to allow data to be provided from device 10 to external devices such as electronic equipment 34. Input-output devices 28 may include user input-output devices such as buttons, display screens, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, cameras, etc. A user can control the operation of device 10 by supplying commands through the user input devices. This may allow the user to adjust settings such as security settings, etc. Input-output devices 28 may also include data ports, circuitry for interfacing with audio and video signal connectors, and other input-output circuitry.
As shown in
Device 10 may use wired data paths such as path 36 and wireless data paths such as path 38 to communicate with external equipment 34. External equipment 34 may include any suitable electronic equipment such as desktop computers, handheld computers and other portable computers, cellular telephones (e.g., multifunction cellular telephones with IEEE 802.11 capabilities), music players, remote controllers, peer devices (i.e., other equipment such as device 10), network equipment (e.g., in a local area network or in a cellular telephone network), etc. Wired paths such path 36 may be formed using wired data cables. Wireless paths such as path 38 may be formed by transmitting and receiving radio-frequency signals using antennas 30.
Any suitable technique may be used in device 10 to isolate antennas 14 and 16. For example, antennas 14 and 16 may be isolated using blocking techniques in which conductive structures are interposed between antennas 14 and 16 to mitigate interference. Isolation may also be improved by reducing antenna scattering through proper antenna placement, by using orthogonal antenna polarizations, by reducing common mode resonances, etc.
An illustrative isolation scheme for antennas 14 and 16 is shown in the schematic diagram of
With the configuration shown in
Antenna 14 may be coupled to global ground 42 by near-field electromagnetic coupling (illustrated by radio-frequency signal path 48 in
Isolation may be improved by coupling antenna 14 to antenna 16 through global ground 42 such that the antenna signals from antenna 14 that reach antenna 16 through ground 42 cancel the signals from antenna 14 that reach antenna 16 through free-space path 40 (and vice versa). With this type of arrangement, signals that travel from antenna 14 along path 44 and/or path 48, path 42, and path 46 and/or path 50 have equal magnitude and are 180° out of phase with the signals that travel from antenna 14 to antenna 16 over free-space path 40.
The magnitude of the signal that reaches antenna 16 through path 42 can be increased by increasing the coupling between antenna 14 and ground 42 and by increasing the coupling between antenna 16 and ground 42. The phase of the cancelling signal traveling through ground 42 can be adjusted using matching components (e.g., resistors, inductors, capacitors, antenna elements with resistive, inductive, and capacitive properties, etc.), by making adjustments to the lengths of structures such as global ground 42 and paths 48, 44, 50, and 46, etc. Magnitude and phase adjustments such as these may be used to ensure that the cancelling signal between antennas 14 and 16 that passes through global ground 42 cancels other signals such as the signals conveyed over free-space path 40. Antenna 14 can be isolated from antenna 16 and antenna 16 can be isolated from antenna 14 in this way.
If desired, the antenna resonating element and local ground of antenna 14 and/or antenna 16 can be adjusted to create a resonating circuit (e.g., by adjusting inductive, capacitive, and resistive antenna components to form a circuit that resonates at frequencies associated with the operation of antennas 14 and/or 16). Resonant circuit behavior that is created in this way can enhance the coupling efficiency associated with antenna 14 and global ground 42 and the coupling efficiency associated with antenna 16 and global ground 42 to increase the magnitude of the cancelling signal. Resonant circuit effects can be used in combination with other antenna structure adjustments to adjust the amplitude and phase of the canceling signal provided through global ground path 42 to obtain maximum isolation between antennas 14 and 16.
An illustrative resonant circuit 52 that may be used in an antenna such as antenna 14 or antenna 16 is shown in
The dimensions of elements 14A and 14B can be selected to tune the electrical properties of antenna 14. For example, ground element 14B of
Antenna 14 may be fed using any suitable feed arrangement. For example, a transmission line (transmission line 24 of
A perspective view of an illustrative configuration for antenna 16 is shown in
Antenna 16 may be fed by connecting coaxial cable conductors or other transmission line paths in a path such as path 22 of
Bracket 98 may be formed from a conductive material such as metal and may be used in forming local ground 16B. Bracket 98 may be mounted to conductive structures in device 10 such as conductive structures that form global ground 42 (
As shown in
Antennas 14 and 16 may have substantially planar substrates on which patterned traces are formed. The planes of the substrates may be oriented to be orthogonal to each other as shown in
Transmission line 78 may be a coaxial cable having center conductor 104, a dielectric layer 106, an outer conductor 108, and a plastic jacket 110. Clip 112 may be used in attaching cable 78 to frame 72 (e.g., at portion 82 using a screw). Center conductor 104 may be connected to antenna resonating element 14A at antenna feed terminal 66 (
An illustrative antenna mounting structure to which antenna 14 may be mounted in device 10 is shown in
When antennas 14 and 16 are mounted within device 10 as shown in
Although antennas 14 and 16 are spaced apart to increase isolation, there will still be a free-space signal path such as path 40 of
Consider, as an example, a situation in which one antenna is transmitting. In this scenario, the free-space signal path (path 40) serves to convey a first version of a transmitted signal from a first of the antennas to a second of the antennas, whereas the path through global ground 42 serves to convey a second version of the same transmitted signal between the first and second antennas. The first version of the signal can serve as a source of interference for the second antenna. However, when cancelling path 42 is present, the first and second versions of the signal cancel each other at the second antenna, thereby reducing interference from the first version of the signal. Because the amount of interfering signal that is received at the second antenna from the first antenna is reduced, the isolation between the antennas is improved. This allows antennas 14 and 16 to be placed closer to each other in device 10 than would otherwise be possible and/or improves the wireless performance of device 10. The presence of path 42 can enhance antenna isolation regardless of the mode of operation of antennas 14 and 16 (e.g., transmitting, receiving, simultaneously transmitting and receiving, etc.).
The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.
