HK1153311B - Electronic devices with parasitic antenna resonating elements that reduce near field radiation - Google Patents

Description

Electronic device with parasitic antenna resonating element that reduces near-field radiation

Priority of the present application claims U.S. provisional patent application No.61/226,684 filed on 7/17/2009 and U.S. patent application No.12/632,697 filed on 7/12/2009, which are hereby incorporated by reference in their entireties.

Technical Field

The present invention relates to antennas, and more particularly, to antennas for electronic devices.

Background

Electronic devices such as portable computers and handheld electronic devices are becoming increasingly popular. Devices such as these typically have wireless communication capabilities. For example, some electronic devices may use long-range wireless communication circuitry, such as cellular telephone circuitry, to communicate using 850MHz, 900MHz, 1800MHz, and 1900MHz cellular telephone bands (e.g., the bands of the predominant global system for mobile communications or GSM cellular telephones). The 2100MHZ band and other bands may also be handled using long-range wireless communications circuitry. The electronic device may use the short-range wireless communication link to handle communications with nearby devices.For example, the electronic device may use Wi-plus at 2.4GHz and 5GHz(IEEE 802.11) frequency band (sometimes called LAN band) and 2.4GHzThe (bluetooth) band communicates.

Successful incorporation of antennas into electronic devices can be difficult. Some electronic devices are manufactured with small form factors and thus space for the antenna is limited. In many electronic devices, electronic components present near the antenna become a possible source of electromagnetic interference. The operation of the antenna may also be blocked by the conductive structure. This makes it difficult to implement antennas in electronic devices that contain conductive housing walls or other conductive structures that may block radio frequency signals.

There is therefore a need to provide improved antennas for wireless electronic devices.

Disclosure of Invention

Radio frequency signals may be transmitted and received using antenna structures in electronic devices. For example, single and multi-band antennas can be made. Each antenna may have an antenna resonating element. The antenna resonating element may be based on an inverted-F design, slot configuration, or other antenna resonating element arrangement. Each antenna also has a parasitic antenna resonating element formed from one or more conductive members.

The electronic device may have a conductive housing. A portion of the conductive housing in each device may be used as an antenna ground. The antenna may be fed using a positive antenna feed terminal coupled to the antenna resonating element and a ground antenna feed terminal coupled to the conductive housing.

The antenna resonating element may be mounted adjacent to an antenna window within the conductive housing. During operation, the antenna may induce localized currents within the conductive housing. These currents may exhibit thermal zones (hotspots) associated with a relatively concentrated amount of possible electromagnetic radiation in the surrounding environment.

To reduce the strength of radio frequency signals transmitted in the vicinity of the electronic device, the electronic device may have a proximity sensor. The proximity sensor may detect when a human body part or other external object is present within a given distance of the electronic device and the antenna. When the presence of an external object in the vicinity of the antenna is detected, the transmission power of the device may be reduced, thereby ensuring that the radiation transmission level is low enough to meet the limits imposed on near-field radiation power. When no external object is present anymore, the transmission power may be increased.

Other features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.

Drawings

FIG. 1 is a front perspective view of an illustrative electronic device having an antenna including a parasitic antenna resonating element in accordance with an embodiment of the present invention;

FIG. 2 is a rear perspective view of an illustrative electronic device having an antenna including a parasitic antenna resonating element in accordance with an embodiment of the present invention;

FIG. 3 is a schematic diagram of an illustrative electronic device having an antenna structure in accordance with an embodiment of the invention;

FIG. 4 is a cross-sectional side view of an illustrative electronic device with an antenna in accordance with an embodiment of the present invention;

FIG. 5 is a schematic diagram of an illustrative electronic device having an antenna and wireless circuitry that may reduce the amount of power transmitted through the antenna when a proximity sensor detects a foreign object within a given range of the antenna and electronic device in accordance with an embodiment of the present invention;

FIG. 6 is a perspective view of an illustrative antenna having an antenna resonating element overlapping a dielectric antenna window and a parasitic antenna resonating element in accordance with an embodiment of the present invention;

FIG. 7 illustrates how the presence of a parasitic antenna resonating element in an electronic device according to an embodiment of the present invention helps reduce radio frequency signal hotspots and thereby near field radiated hotspots generated by the antenna;

FIG. 8 is a top view of a parasitic antenna resonating element that has been coupled through a capacitor to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention;

FIG. 9 is a top view of a notched parasitic antenna resonating element that has been coupled through a capacitor to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention;

FIG. 10 is a top view of another notched parasitic antenna resonating element that has been coupled through a capacitor to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention;

FIG. 11 is a top view of a parasitic antenna resonating element structure having a rectangular conductor and an elongated curved conductor that have been coupled through a capacitor to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention;

FIG. 12 is a top view of a parasitic antenna resonating element that includes a rectangular conductor and an elongated curved conductor that have been coupled through parasitic capacitances to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention; and

fig. 13 is a top view of an illustrative antenna resonating element formed from an elongated housing structure overlapping or protruding into a dielectric antenna window according to an embodiment of the present invention.

Detailed Description

The electronic device may have wireless communication circuitry. The wireless communication circuitry may be configured to support wireless communication in one or more wireless communication bands. For example, the wireless communication circuitry may transmit and receive signals in the cellular telephone frequency band.

To meet the user demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of the components used in these devices while providing enhanced functionality. Especially in configurations where electronic devices are used to transmit and receive radio frequency signals in the cellular telephone band and other relatively wide bandwidth communication bands, meeting required antenna performance standards within a compact device is a challenge. To ensure sufficient signal strength during communication, high transmission power and wide antenna bandwidth are required, but these properties may pose challenges for controlling the emitted radiation level.

It is not practical to completely shield the user of the electronic device from the transmitted radio frequency signals. For example, conventional cellular telephone handsets typically transmit signals near the user's head during a telephone call. Government regulations limit the power of radio frequency signals. At the same time, wireless carriers (wireless carriers) require that user equipment used in their networks be capable of generating a certain minimum radio frequency power to ensure that the equipment operates satisfactorily.

In many jurisdictional management (jurisdictions), there is a demand for handset manufacturers to enforce the maximum energy absorption rate (SAR) standard. These standards place limits on the amount of radiation that can be emitted at any particular point within a given distance of the antenna. Special attention is paid to radiation limitations at a distance of about 1-20mm from the device, whereas a body part of the user near the antenna may be in this range.

Satisfactory antenna performance and compliance with regulations may be ensured by using antennas that do not exhibit local "hot spots" where the transmitted power exceeds the required power level. Proximity sensors may also be used to detect the presence of external objects, such as the user's body, in the vicinity of the antenna. When the presence of an external object is detected, the power level of the transmission may be reduced.

The hot spots can be minimized by proper antenna design. If desired, a parasitic antenna resonating element may be placed near the device antenna to help cancel the radiation pattern of the near-field emissions. The electromagnetic shielding structure may also be implemented using ferrite tape or other high permeability material.

Any suitable electronic device may be provided with an antenna using these configurations. By way of example, antennas may be formed within electronic devices such as desktop computers, portable computers such as laptop and tablet computers, hand-held electronic devices such as cellular telephones, and the like. With a suitable arrangement, which is sometimes described as an example in this specification, antennas are formed within fairly compact electronic devices where interior space is at a premium. These compact devices may be portable electronic devices.

Portable electronic devices that may be equipped with antennas include laptop computers and small portable computers such as ultra-portable computers, notebook computers, and tablet computers. The portable electronic device may also be a somewhat smaller device. Examples of smaller portable electronic devices that may be equipped with an antenna include cellular telephones, watch devices, pendant devices, headphone and earphone devices, and other wearable miniature devices.

Space is at a premium in portable electronic devices, and the housings of these devices are sometimes constructed of conductive materials that block antenna signals. An arrangement in which the antenna structure is formed behind the antenna window may help address these challenges. An antenna window may be formed in the conductive housing wall by forming a dielectric antenna window structure from an opening in the conductive housing wall. If desired, a slot-based antenna window may be formed in the conductive housing wall. Within the slot-based antenna window, a window area is defined by the pattern of the window slots. Arrangements in which a dielectric antenna window is used are sometimes described as examples in this specification.

An antenna resonating element may be formed below the antenna window. Portions of the conductive housing or other conductive structure may serve as an antenna ground. The antenna may be fed using a positive antenna feed terminal coupled to the antenna resonating element and using a ground antenna feed terminal coupled to the conductive housing. During operation, radio frequency signals of the antenna may pass through the antenna window. The parasitic antenna resonating element and the ferrite strip may help reduce near-field hot spots. Proximity-based antenna power control circuits may also be used for reducing near-field electromagnetic radiation intensity when the presence of external objects in the vicinity of the antenna is detected. The proximity-based antenna power control circuit may be based on a capacitive proximity sensor. The sensor electrode of the capacitive proximity sensor may be placed in proximity to the antenna. If desired, conductive structures such as sensor electrodes may be used as part of the capacitive sensor and as part of the parasitic antenna resonating element. With this arrangement, the sensor electrodes can simultaneously be used to reduce near-field radiation hot-areas when used as capacitor electrodes of a proximity detector for detecting the presence of external objects in the vicinity.

Antenna structures having configurations such as those described above may be mounted on any suitable exposed portion of a portable electronic device. For example, the antenna may be disposed on a front or top surface of the device. In a tablet computer, cellular telephone, or other device in which the front of the device is fully or nearly fully occupied by a conductive structure, such as a touch screen display, it may be desirable to form at least a portion of the antenna window on the back surface of the device. Other configurations are possible (e.g., mounting the antenna in a more limited location, on a side wall of the device, etc.). Such use of an antenna mounting location is sometimes described in this specification as an example where at least a portion of a dielectric antenna window is formed in the rear surface of a conductive housing, although, in general, any suitable antenna mounting location may be used if desired.

Fig. 1 shows an illustrative portable device that may include an antenna. As shown in fig. 1, device 10 may be a relatively thin device such as a tablet computer. The device 10 may have a display, such as display 50 mounted on its front (top) surface. The housing 12 may have some curved portions that form the edges of the device 10 and relatively flat portions that form the back surface of the device 10 (as an example). An antenna window, such as antenna window 58, may be formed within housing 12. An antenna structure for the device 10 may be formed adjacent the antenna window 58.

The device 10 may have user input and output means such as buttons 59. The display 50 may be a touch screen display that is used to collect touch input by a user. A dielectric member, such as a flat cover glass member, may be used to cover the surface of the display 50. The central portion of the display 50 (represented in fig. 1 as region 56) may be an active region (activeregion) that is sensitive to touch input. A peripheral region of the display 50, such as region 54, may be an inactive region without touch sensor electrodes. A layer of material, such as an opaque ink, may be disposed within the perimeter area 54 on the underside of the display 50 (e.g., on the underside of the cover glass). This layer may be transparent to radio frequency signals. Conductive touch sensor electrodes in area 56 tend to block radio frequency signals. However, the radio frequency signal may pass through opaque ink (as an example) covering the glass and inactive display area 54. The radio frequency signals may also pass through an antenna window 58.

The housing 12 may be formed of one or more structures. For example, the housing 12 may include an internal frame and a flat housing wall mounted on the frame. The housing 12 may also be formed from a single block of material, such as a cast or machined block of aluminum. Devices utilizing both methods may also be used if desired.

The housing 12 may be formed of any suitable material, including plastic, wood, glass, ceramic, metal, or other suitable material, or a combination of materials. In some cases, portions of the housing 12 may be formed of a dielectric or other material of low conductivity so as not to interfere with the operation of the conductive antenna element located near the housing 12. In other cases, the housing 12 may be formed from a metal element. An advantage of forming housing 12 from metal or other structurally robust conductive material is that it can improve the aesthetics of the device and help improve durability and portability.

With one suitable arrangement, the housing 12 may be formed from a metal, such as aluminum. Portions of the housing 12 near the antenna window 58 may be used as antenna ground. The antenna window 58 may be formed from a dielectric material such as Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), a PC/ABS blend, or other plastics (as examples). The window 58 may be attached to the housing 12 using an adhesive, fasteners, or other suitable attachment mechanism. To ensure that the device 10 has a good appearance, the window 58 needs to be formed such that the outer surface of the window 58 conforms to the edge contour presented by the housing 12 in the remainder of the device 10. For example, if housing 12 has straight edges 12A and a flat bottom surface, window 58 may be formed with a right angle bend and vertical sidewalls. If the housing 12 has a curved edge 12A, the window 58 may have a surface that is also curved.

Fig. 2 is a rear perspective view of the device 10 of fig. 1, showing how the device 10 has a relatively flat rear surface 12B, and showing how the antenna window 58 may be rectangular, having a curved portion shape that matches the shape of the curved housing edge 12A.

Fig. 3 shows a schematic diagram of the device 10, showing how the device 10 may include one or more antennas 26 and transceiver circuitry in communication with the antennas 26. The electronic device 10 of fig. 3 may be a portable computer such as a laptop computer, a portable tablet computer, a mobile phone with multimedia player functionality, a handheld computer, a remote control, a game console, a Global Positioning System (GPS) device, a desktop computer, a combination of these devices, or any other suitable electronic device.

As shown in fig. 3, the electronic device 10 may include storage and processing circuitry 16. The storage and processing circuitry 16 may include one or more different types of storage devices, such as hard disk drive storage devicesNon-volatile memory (e.g., flash memory or other electrically programmable read only memory), volatile memory (e.g., static or dynamic random access memory), and so forth. Processing circuitry in storage and processing circuitry 16 may be used to control the operation of device 10. The processing circuitry 16 may be based on a processor such as a microprocessor and other suitable integrated circuits. With one suitable arrangement, the storage and processing circuitry 16 may be used to run software on the device 10, such as Internet browsing applications, voice over Internet protocol (VoIP) phone call applications, email applications, media playback applications, operating system functions, control functions for controlling radio frequency power amplifiers and other radio frequency transceiver circuitry, and so forth. The storage and processing circuitry 16 may be used to implement a suitable communication protocol. Communication protocols that may be implemented using the storage and processing circuitry 16 include Internet protocols, cellular telephone protocols, wireless local area network protocols (e.g., IEEE802.11 protocols-sometimes referred to as Wi-) Protocols for other short-range wireless communication links such asProtocols, and the like.

Input-output circuitry 14 may be used to allow data to be provided to device 10 and to allow data to be provided from device 10 to external devices. Input-output devices 18 such as touch screens and other user input interfaces are examples of input-output circuitry 14. The input-output devices 18 may also include user input-output devices such as buttons, joysticks, click wheels, scroll wheels, touch pads, keypads, keyboards, microphones, cameras, and the like. A user may provide commands through these user input devices to control the operation of device 10. Display and audio devices 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 may be included in device 18. The display and audio components in the input-output device 18 may also include audio devices such as speakers and other devices for creating sound. If desired, the input-output devices 18 may include audio-visual interface devices, such as jacks and other connectors for external headphones and monitors.

Wireless communications circuitry 20 may include Radio Frequency (RF) transceiver circuitry 23 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 processing RF wireless signals. Wireless signals may also be transmitted using light (e.g., using infrared communication).

The wireless communication circuitry 20 may include radio-frequency transceiver circuitry for handling multiple radio-frequency communication bands. For example, circuitry 20 may include transceiver circuitry 22 that handles 2.4GHz and 5GHz frequency bands for WiFi (IEEE 802.11) communications, as well as 2.4GHz Bluetooth communication bands. The circuitry 20 may also include cellular telephone transceiver circuitry 24 for handling wireless communications in cellular telephone frequency bands, such as the 850MHz, 900MHz, 1800MHz, and 1900MHz GSM bands and the 2100MHz data band (as an example). The wireless communication circuitry 20 may include circuitry for other short-range and long-range wireless links, if desired. For example, the wireless communication circuitry 20 may include Global Positioning System (GPS) receiver equipment, radio circuitry for receiving radio frequency and television signals, call circuitry, and the like. In WiFi as well as bluetooth links and other short range wireless links, data is typically communicated over tens or hundreds of feet using wireless signals. In cellular telephone links or other long distance links, data is typically transmitted over thousands of feet or miles using wireless signals.

The wireless communication circuit 20 may include an antenna 26, such as an antenna located near the antenna window 58 of fig. 1 and 2. The antennas 26 may be single-band antennas, each covering a particular desired communication band, or the antennas 26 may be multi-band antennas. Multi-band antennas may be used, for example, to cover multiple cellular telephone communication bands. If desired, a dual-band antenna may be used to cover two WiFi bands (e.g., 2.4GHz and 5 GHz). Different types of antennas may be used for different frequency bands or combinations of frequency bands. For example, it may be desirable to form a dual-band antenna for forming a local wireless link antenna, a multi-band antenna for handling cellular telephone communication bands, and a single-band antenna for forming a global positioning system antenna (as examples).

Radio frequency signals may be transmitted between the transceivers 22, 24 and the antenna 26 using the transmission line path 44. Radio frequency transceivers such as radio frequency transceivers 22 and 24 may be implemented using one or more integrated circuits and associated components (e.g., switching circuitry, matching network elements such as discrete inductors, capacitors, and resistors, and integrated circuit filter networks, etc.). These devices are mounted on any suitable mounting structure. With one suitable arrangement, the transceiver integrated circuit may be mounted on a printed circuit board. Path 44 may be used to interconnect transceiver integrated circuits and other components on a printed circuit board with an antenna structure in device 10. Path 44 may include any suitable conductive path, including transmission lines via structures such as coaxial cables, microstrip transmission lines, etc., through which radio frequency signals may be transmitted.

The antenna 26 may generally be formed by using any suitable antenna type. Examples of suitable antenna types for antenna 26 include antennas having resonant elements formed from patch antenna structures, inverted-F antenna structures, closed and open slot antenna structures, loop antenna structures, monopoles, dipoles, planar inverted-F antenna structures, hybrids of these designs, and the like. In one suitable arrangement, sometimes described as an example in this description, portions of housing 12 (e.g., portions of housing 12 near antenna window 58) may form a ground structure for the antenna associated with window 58.

Fig. 4 shows a cross-sectional view of the device 10 near the antenna window 58. As shown in fig. 4, antenna 26 may have an antenna resonating element 68 (e.g., a patch antenna resonating element, a single-arm inverted-F antenna structure, a two-arm inverted-F antenna structure, or other suitable multiple-or single-arm inverted-F antenna structure, a closed or open slot antenna structure, a loop antenna structure, a monopole, a dipole, a planar inverted-F antenna structure, a hybrid of these designs, etc.). The housing 12 may serve as an antenna ground for the antenna 26.

Antenna 26 may also have a parasitic antenna resonating element formed from one or more conductive structures, such as structure 66. If desired, a layer of ferrite material, such as ferrite tape 74, may be placed between the antenna resonating element 68 and the window 58 to help reduce the near-field signal strength without unduly attenuating the near-field signal. In the example of fig. 4, ferrite strip 74 has been placed below parasitic antenna resonating element 66.

As shown in fig. 4, antenna 26 may be fed using a positive antenna feed terminal, such as positive antenna feed terminal 76, coupled to antenna resonating element 68, and a ground antenna feed terminal, such as ground antenna feed terminal 78, coupled to housing 12.

As shown in fig. 4, antenna resonating element 68 may be positioned near dielectric antenna window 58 so that radio frequency signals may be transmitted through window 58 (e.g., along directions 72 and 71). Radio frequency signals may also be transmitted through a transparent display cover member, such as cover glass 60. The display 50 may have an active area, such as area 56, in which the cover glass 60 has an underlying conductive structure, such as a display panel module 64. Structures in display panel 64, such as touch sensor electrodes and active display pixel circuitry, may be conductive and, therefore, may attenuate radio frequency signals. However, in region 54, display 50 may be inactive (i.e., may not have plate 64). An opaque ink, such as ink 62, may be formed on the underside of transparent cover glass 60 in region 54 to block antenna resonating element 68 from view. The ink 62 in the area 54 and the dielectric material of the cover 60 are sufficiently transparent to radio frequency signals so that radio frequency signals can be transmitted through these structures in the direction 70.

Any suitable conductive material may be used to form the antenna structure of antenna 26. There is a suitable arrangement in which the conductive structures for antenna resonating element 68 and parasitic antenna resonating element 66 may each be formed from conductive traces on a dielectric support. The conductive traces may be formed of copper or other metals (as an example) to help ensure low loss and good performance at radio frequencies. The dielectric support for these structures may be a printed circuit board or a plastic component. Plastic support structures may also be used to support the printed circuit board. Generally, printed circuit boards may be rigid or flexible. Rigid printed circuit boards may be formed from epoxy (e.g., FR4) or other dielectric substrates. Flexible printed circuit boards (flex circuits) may be formed from flexible polymer sheets such as polyimide sheets or other flexible dielectric materials. When the antenna structure is formed from a flexible circuit substrate sheet, the flexible circuit can be bent to form a curved surface (e.g., to accommodate a curved plastic support structure), if desired. With respect to rigid substrate structures, printed circuit boards are generally flat.

These antenna structures, such as conductive structure 66, serve multiple functions. For example, because structure 66 is located near antenna resonating element 68, structure 66 affects the electromagnetic behavior of antenna 26 and, therefore, may act as a parasitic antenna resonating element. At the same time, the conductive structure 66 can be used as a sensor electrode of a proximity sensor, if desired.

Transceiver circuitry 23 may be mounted to printed circuit board 79 and connected to the wires in transmission line 44 by connector 81 and traces within circuit board 79. Transmission line 44 may have a positive conductor and a ground conductor and may carry radio frequency antenna signals between feed terminals 76, 78 of transceiver 23 and antenna 26.

The device 10 and antenna window 58 may have any suitable dimensions. For example, the device 10 may have a lateral dimension of about 10-50 cm. The thickness of the device 10 may be greater than 2cm, less than 1.5cm, or less than 0.5 cm.

In a thin device configuration, the elimination of the conductive housing portion immediately adjacent antenna resonating element 68 helps to ensure that antenna 26 has satisfactory efficiency and bandwidth (e.g., for supporting long-range communications over a wide bandwidth, such as the cellular telephone communications band).

Fig. 5 is a circuit diagram showing how the proximity sensor signal is used to control the amount of power transmitted by the antenna 26. As shown in fig. 5, the device 10 may include storage and processing circuitry 16 (see, e.g., fig. 3). Device 10 may also include a proximity sensor such as proximity sensor 80. The proximity sensor 80 may be implemented using any suitable type of proximity sensor technology (e.g., capacitive, optical, etc.). An advantage of capacitive proximity sensing techniques is that they are relatively sensitive to changes in the reflectivity of external objects 87.

As shown in the example of fig. 5, the proximity sensor 80 may contain capacitor electrodes formed from conductive members, such as conductive member 66 (fig. 4). Conductive member 66 may act as a parasitic antenna resonating element for antenna 26, if desired.

The proximity sensor 80 may be mounted within the housing 12 near the antenna 26 (as shown in fig. 4) to ensure that the signal from the proximity sensor 80 indicates the presence of an external object 87 near the antenna 26 (e.g., within a distance D from the antenna 26 and/or the device 10).

The output signal of the proximity sensor 80 is communicated to the storage and processing circuitry 16 by way of a path 86. The signal from the proximity sensor 80 may be an analog signal or a digital signal that provides proximity data to the storage and processing circuitry 16. The proximity data may be boolean data representing whether the object 87 is located within a given predetermined distance of the antenna 26 or the proximity data may be continuous data representing the current estimated distance value of D.

Storage and processing circuitry 16 may be coupled to transceiver circuitry 23 and power amplifier circuitry 82. Dashed line 83 represents how the received radio frequency signal is transmitted from antenna 26 to transceiver circuitry 23. During data transfer operations, control signals may be transmitted from the storage and processing circuitry 16 to the transceiver circuitry 23 and the power amplifier circuitry 82 using the control lines 84 to adjust the output power in real time. For example, when data is being transmitted, transceiver 23 and its associated output amplifier 82 are commanded to increase or decrease the power level of the radio frequency signal being provided to antenna 26 via transmission line 44 to ensure that the prescribed limits of electromagnetic radiation emission are met. For example, if the proximity sensor 80 does not detect the presence of the external object 87, power is provided at a relatively high (unrestricted) value. However, if the proximity sensor 80 determines that the user's leg or other body part or other external object 87 is in close proximity (e.g., at or below 20mm, at or below 15mm, at or below 10mm, etc.) to the antenna 26, the storage and processing circuitry responds accordingly by commanding the transceiver circuitry 23 and/or the power amplifier 82 to transmit a radio frequency signal at a reduced power through the antenna 26.

Fig. 6 shows a perspective view of an illustrative antenna 26. As shown in fig. 6, antenna resonating element 68 may contain one or more conductive traces, such as conductive trace 96. In the example of fig. 6, antenna resonating element 68 has an inverted-F configuration. In this configuration, antenna resonating element 68 may have a dielectric substrate, such as a rigid or flexible printed circuit substrate 90, on which a conductive pattern, such as conductive traces 94, have been formed. Conductive trace 94 may have a main resonant element arm 92, a shorting branch such as branch 96 that shorts arm 92 to ground (e.g., a path coupled to antenna feed terminal 78 of fig. 4), and a branch 98 to which a positive antenna feed terminal is coupled. If desired, the arm 92 may have a different shape (e.g., multiple branches) to support operation within a desired communication band having a desired bandwidth. The trace pattern of antenna resonating element 68 shown in fig. 6 is illustrative only. Generally speaking, antenna resonating element 68 may use any suitable type of antenna resonating element pattern, if desired.

Antenna resonating element 68 may be mounted so as to overlap antenna window 58 and be below inactive region 54 of display 50 (fig. 4). Conductive structure 66 may be interposed between antenna resonating element 68 and window 58.

During operation of antenna 26, the electromagnetic field generated by antenna resonating element 68 may induce a current in conductive housing 12, such as current 95 near window 58. The relative shapes and sizes of the components of the antenna 26 may cause detrimental current concentrations if left unattended. When the induced current re-radiates electromagnetic energy through the antenna window 58, the current concentration, in turn, causes undesirable hot spots in the near-field radiation pattern of the antenna 26.

Fig. 7 illustrates how the antenna signal causes unwanted hot spots. In fig. 7, the power associated with a near-field transmitted radio frequency signal (e.g., a signal of antenna 26 that has been transmitted through antenna window 58 in directions 72 or 71) is shown as a function of position (e.g., position along the inner edge of antenna window 58). The solid line 120 corresponds to a possible near-field radiation pattern without a suitable antenna structure to reduce hot spots in the current 95 and associated hot spots in the transmitted rf signal power. The dashed line 122 represents how hot spots are minimized or eliminated by including suitable hot spot reduction structures. Since the dashed line 122 is smoother and has a lower peak power than the line 120, the dashed line 122 reflects a reduced spatial concentration of the rf signal power. The smooth radiation characteristic helps the antenna 26 to transmit the desired amount of signal power when communicating with a remote base station without exceeding the prescribed limits of the radiated radiation level.

The near field radiation pattern smoothing structure may include structures such as parasitic antenna resonating element 66. The ferrite strip 74 may also help reduce hot-zone and/or near-field signal strength while allowing the required far-field antenna efficiency criteria to be met. Proximity sensor based conditioning may be used in conjunction with these techniques if desired.

Parasitic antenna resonating element 66 may be formed from one or more conductive structures. An illustrative configuration of the conductive structure of parasitic antenna resonating element 66 is shown in top views of the interior of device 10 shown in fig. 8-13.

Fig. 8 is a top view of parasitic antenna resonating element 66, which is formed from a substantially rectangular conductive member (e.g., a rectangular patch). The patch may have a transverse dimension LP, WP. Any suitable dimensions can be used as dimensions LP, WP if desired. As an example, LP may be about 40mm (e.g., 10-70mm) and WP may be about 15mm (e.g., about 5-25 mm). The outline of the antenna window 58 may also be rectangular and may have any suitable dimensions. For example, the profile of the antenna window 58 may have a lateral dimension L, W. As one suitable arrangement, L may be about 80mm (e.g., 50-110mm) and W may be about 15mm (e.g., about 5-25 mm).

Capacitor 124 may be coupled between housing 12 (e.g., antenna ground) and parasitic antenna resonating element 66 using capacitor terminals 126, 128. The capacitance of capacitor 124 may be selected to provide sufficient coupling between terminal 126 and terminal 128, and thus between housing 12 and element 66, at the operating frequency of antenna 26 (e.g., 850-. For example, a capacitor such as capacitor 124 may have a capacitance of approximately 1-5pF (i.e., less than 100 pF).

The location of the terminals 126, 128 and the coupling provided by the capacitor 124 creates an impedance discontinuity along the induced current path in the housing 12 (i.e., current 95, which flows in the housing 12 along the edge of the housing 12 adjacent the antenna window 58, as shown in fig. 6). The location and size of the capacitor 124 and the size and shape of the conductive structure of the parasitic antenna resonating element structure 66 may be adjusted to ensure that these impedance discontinuities cause the antenna 26 to exhibit less pronounced hot spots and thus improved compliance with regulatory limits on emitted radiation.

In the example of fig. 9, parasitic antenna resonating element 66 has a notch 130. Adjustments to features of the parasitic antenna resonating element 66, such as the location and shape, bends, openings, or other features of the notch 130, may be used to tune the performance of the parasitic antenna resonating element at the operating frequency of interest.

Fig. 10 shows an illustrative configuration in which parasitic antenna resonating element 66 has a notch 130 at its narrower one end. The example of fig. 10 also shows how the recess 130 has an elongated interior, such as portion 132.

In the illustrative arrangement of fig. 11, the parasitic antenna resonating element 66 has a first conductive member (a rectangular conductive member 66A) and a second conductive member (a curved elongated conductive member 66B). Capacitor 124 may be coupled to conductive member 66A or 66B, or two capacitors may be used, a first of which is connected between housing 12 and conductive member 66A and a second of which is connected between housing 12 and conductive member 66B (as an example).

In general, there may be any suitable number of conductive members (e.g., one conductive member, two conductive members, more than two conductive members, etc.) in parasitic antenna resonating element 66. Fig. 11 illustratively shows a parasitic antenna resonating element 66 that uses two conductive members.

Fig. 12 illustrates how parasitic antenna resonating element 66 may have one or more conductive components that are coupled to housing 12 with parasitic capacitance rather than discrete capacitors. With the arrangement of fig. 12, there is a first parasitic capacitance between conductive member 66A and housing 12 that results from the gap between opposing conductive edges 134, 136. Similarly, there is a second parasitic capacitance between conductive member 66B and housing 12 resulting from the gap between opposing conductive edges 138, 140.

Parasitic antenna resonating element 66 may be formed from a portion of housing 12, if desired. An arrangement of this type is shown in figure 13. As shown in fig. 13, the antenna window 58 may have a rectangular profile (when viewed in the top view of fig. 13). The dashed line 146 may separate the longest side of the antenna window 58 from the conductive material of the housing 12. Parasitic antenna resonating element 66 may be formed from an elongated portion of housing 12 that is integrally connected to housing 12 and projects rightward of line 146 in direction 144 into antenna window 58. Other arrangements may be used. For example, there may be two or more protruding housing portions that make up parasitic antenna resonating element 66. These housing portions need not be elongated or curved as shown in fig. 13. For example, the housing portions may be straight, serpentine, curved, rectangular, etc. These housing portions may protrude into the antenna window 58 from the shorter (upper and lower) sides of the antenna window 58, if desired. A hybrid of these approaches (e.g., having one or more different types of housing bumps in combination with one or more parasitic antenna resonating element structures of fig. 8-11) may also be used.

Parasitic antenna resonating elements of the type shown in fig. 8-13 may be constructed from: conductive traces on a flexible circuit or rigid printed circuit board substrate, metal or other conductors formed directly on a plastic support structure, patterned metal foil, or using other suitable antenna structures. One or more conductive components in a given parasitic antenna resonating element 66 may act as both a proximity sensor electrode and a parasitic antenna resonating element.

According to one embodiment, there is provided an electronic device having a front surface and a back surface, the device comprising: a conductive housing; a dielectric antenna window in the conductive housing; an antenna resonating element mounted in the conductive housing such that radio frequency signals are transmitted through the dielectric antenna window; and a parasitic antenna resonating element located between the antenna resonating element and the dielectric antenna window.

In accordance with another embodiment, the electronic device further includes a display on a front surface of the electronic device, and the display has an inactive region through which radio frequency signals are transmitted from the antenna resonating element.

According to another embodiment, the electronic device further comprises a display having a panel circuit, the panel circuit is covered by a transparent dielectric cover member, and the antenna resonating element emits radio frequency signals that pass through the transparent dielectric cover member but not through the panel circuit.

According to another embodiment, the dielectric antenna window comprises a plastic component mounted in the conductive housing, and the parasitic antenna resonating element comprises a capacitive proximity sensor electrode.

In accordance with another embodiment, the electronic device further comprises a proximity sensor that detects the antenna resonating element and an external object near the dielectric antenna window, and the parasitic antenna resonating element comprises a capacitor electrode for the proximity sensor.

In accordance with another embodiment, the antenna resonating element includes an inverted-F antenna resonating element formed on a flexible circuit.

According to another embodiment, the parasitic antenna resonating element comprises a rectangular conductive member.

In accordance with another embodiment, the electronic device further includes a capacitor having a first end connected to the conductive housing and a second end connected to the parasitic antenna resonating element.

According to one embodiment, there is provided a tablet computer comprising: a conductive housing; a dielectric antenna window in the conductive housing; radio frequency transceiver circuitry; an antenna with which the radio-frequency transceiver circuitry transmits radio-frequency signals in at least one cellular telephone frequency band, and comprising: an antenna ground formed by at least a portion of the conductive housing; an antenna resonating element mounted adjacent to the dielectric antenna window; and a parasitic antenna resonating element formed from a planar metal component interposed between the antenna resonating element and the dielectric antenna window.

In accordance with another embodiment, the tablet computer further comprises a capacitor connected between the conductive housing and the parasitic antenna resonating element.

According to another embodiment, the tablet computer further comprises a capacitive proximity sensor that detects when an external object is in proximity to the antenna, and the parasitic antenna resonating element comprises a capacitor electrode in the capacitive proximity sensor.

According to another embodiment, the tablet computer further comprises a display mounted to the conductive housing, the conductive housing forming a planar back surface of the tablet computer, and the display having a cover glass having an inactive area through which radio frequency signals are transmitted.

In accordance with another embodiment, the tablet computer further comprises a ferrite layer interposed between the parasitic antenna resonating element and the dielectric antenna window.

According to another embodiment, the parasitic antenna resonating element comprises at least two separate metal structures.

According to one embodiment, there is provided a portable computer including: at least one conductive housing structure to which a ground antenna feed terminal is connected; an antenna window in the conductive housing structure; an antenna resonating element formed on a flexible circuit from conductive traces, a positive antenna feed terminal connected to the antenna resonating element; a radio frequency transceiver circuit coupled to the positive antenna feed terminal and the ground antenna feed terminal and transmitting radio frequency signals through the antenna window using the antenna resonating element; and a parasitic antenna resonating element interposed between the antenna resonating element and the antenna window.

According to another embodiment, the parasitic antenna resonating element comprises a capacitor electrode in a capacitive proximity sensor.

According to another embodiment, the portable computer further comprises a layer of ferrite tape between the parasitic antenna resonating element and the antenna window.

According to another embodiment, the portable computer further comprises a capacitor connected between the conductive housing structure and the parasitic antenna resonating element.

According to another embodiment, the electronic device includes a display and at least some of the radio frequency signals are transmitted through an inactive portion of the display.

In accordance with another embodiment, the parasitic antenna resonating element includes a portion of the conductive housing structure that overlaps the dielectric antenna window.

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. The foregoing embodiments may be implemented individually or in any combination.

Claims (19)

1. An electronic device having a front surface and a back surface, comprising:

a conductive housing;

a dielectric antenna window in the conductive housing;

an antenna resonating element mounted in the conductive housing such that radio frequency signals are transmitted through the dielectric antenna window;

a parasitic antenna resonating element located between the antenna resonating element and the dielectric antenna window; and

a display on a front surface of the electronic device, wherein the display has an inactive region through which radio frequency signals are transmitted from the antenna resonating element.

2. The electronic device defined in claim 1 further comprising a display having panel circuitry that is covered by a transparent dielectric cover component, wherein the antenna resonating element emits radio frequency signals that pass through the transparent dielectric cover component but not through the panel circuitry.

3. The electronic device defined in claim 1 wherein the dielectric antenna window comprises a plastic component mounted in the conductive housing and wherein the parasitic antenna resonating element comprises a capacitive proximity sensor electrode.

4. An electronic device having a front surface and a back surface, comprising:

a conductive housing;

a dielectric antenna window in the conductive housing;

an antenna resonating element mounted in the conductive housing such that radio frequency signals are transmitted through the dielectric antenna window;

a parasitic antenna resonating element located between the antenna resonating element and the dielectric antenna window; and

a proximity sensor that detects the antenna resonating element and an external object near the dielectric antenna window, wherein the parasitic antenna resonating element includes a capacitor electrode for the proximity sensor.

5. The electronic device defined in claim 4 wherein the antenna resonating element comprises an inverted-F antenna resonating element formed on a flexible circuit.

6. The electronic device defined in claim 5 wherein the parasitic antenna resonating element comprises a rectangular conductive member.

7. The electronic device defined in claim 6 further comprising a capacitor having a first end connected to the conductive housing and a second end connected to a parasitic antenna resonating element.

8. A tablet computer, comprising:

a conductive housing;

a dielectric antenna window in the conductive housing;

radio frequency transceiver circuitry;

an antenna with which the radio-frequency transceiver circuitry transmits radio-frequency signals in at least one cellular telephone frequency band, wherein the antenna comprises:

an antenna ground formed by at least a portion of the conductive housing;

an antenna resonating element mounted adjacent to the dielectric antenna window; and

a parasitic antenna resonating element formed from a planar metal component interposed between the antenna resonating element and the dielectric antenna window.

9. The tablet computer of claim 8 further comprising a capacitor connected between the conductive housing and the parasitic antenna resonating element.

10. The tablet computer of claim 8 further comprising a capacitive proximity sensor that detects when an external object is in proximity to the antenna, wherein the parasitic antenna resonating element comprises a capacitor electrode in the capacitive proximity sensor.

11. The tablet computer of claim 10 further comprising a display mounted to the conductive housing, wherein the conductive housing forms a planar back surface of the tablet computer, and wherein the display has a cover glass having an inactive area through which radio frequency signals are transmitted.

12. The tablet computer of claim 11 further comprising a capacitor connected between the conductive housing and the parasitic antenna resonating element.

13. The tablet computer of claim 12 further comprising a ferrite layer between the parasitic antenna resonating element and the dielectric antenna window.

14. A portable electronic device, comprising:

at least one conductive housing structure to which a ground antenna feed terminal is connected;

an antenna window in the conductive housing structure;

an antenna resonating element formed on a flexible circuit from conductive traces, a positive antenna feed terminal connected to the antenna resonating element;

a radio frequency transceiver circuit coupled to the positive antenna feed terminal and the ground antenna feed terminal and transmitting radio frequency signals through the antenna window using the antenna resonating element; and

a parasitic antenna resonating element interposed between the antenna resonating element and the antenna window.

15. The portable electronic device defined in claim 14 wherein the parasitic antenna resonating element comprises a capacitor electrode in a capacitive proximity sensor.

16. The portable electronic device defined in claim 15 further comprising a layer of ferrite tape between the parasitic antenna resonating element and the antenna window.

17. The portable electronic device defined in claim 16 further comprising a capacitor connected between the conductive housing structure and the parasitic antenna resonating element.

18. A portable electronic device as claimed in claim 17, wherein the electronic device comprises a display and wherein at least some of the radio frequency signals are transmitted through an inactive portion of the display.

19. The portable electronic device defined in claim 14 wherein the parasitic antenna resonating element comprises a portion of the conductive housing structure that overlaps the dielectric antenna window.