The first receivers had no tuned circuit, the detector was connected directly between the antenna and ground. Due to the lack of any frequency selective components besides the antenna, the bandwidth of the receiver was equal to the broad bandwidth of the antenna. Due to the impulsive nature of the spark, the energy of the radio waves was spread over a very wide band of frequencies. When more than one spark transmitter was radiating in a given area, their frequencies overlapped, so their signals interfered with each other, resulting in garbled reception.
Different transmitters could then be "tuned" to transmit on different frequencies so they didn't interfere. This is the system used in all modern radio. Tuning was used in Hertz's original experiments  and practical application of tuning showed up in the early to mid s in wireless systems not specifically designed for radio communication. Nikola Tesla 's March lecture demonstrating the wireless transmission of power for lighting mainly by what he thought was ground conduction  included elements of tuning.
The wireless lighting system consisted of a spark-excited grounded resonant transformer with a wire antenna which transmitted power across the room to another resonant transformer tuned to the frequency of the transmitter, which lighted a Geissler tube. By the advantages of tuned systems had become clear, and Marconi and the other wireless researchers had incorporated tuned circuits , consisting of capacitors and inductors connected together, into their transmitters and receivers.
It had a high impedance at its resonant frequency , but a low impedance at all other frequencies. Connected between the antenna and the detector it served as a bandpass filter , passing the signal of the desired station to the detector, but routing all other signals to ground.
In order to reject radio noise and interference from other transmitters near in frequency to the desired station, the bandpass filter tuned circuit in the receiver has to have a narrow bandwidth , allowing only a narrow band of frequencies through. Both primary and secondary were tuned circuits;  the primary coil resonated with the capacitance of the antenna, while the secondary coil resonated with the capacitor across it.
Both were adjusted to the same resonant frequency. This circuit had two advantages. Impedance matching was important to achieve maximum receiving range in the unamplified receivers of this era. The second advantage was that due to "loose coupling" it had a much narrower bandwidth than a simple tuned circuit , and the bandwidth could be adjusted.
This gave the coupled tuned circuits much "sharper" tuning, a narrower bandwidth than a single tuned circuit. In the "Navy type" loose coupler see picture , widely used with crystal receivers , the smaller secondary coil was mounted on a rack which could be slid in or out of the primary coil, to vary the mutual inductance between the coils.
A disadvantage was that all three adjustments in the loose coupler - primary tuning, secondary tuning, and coupling - were interactive; changing one changed the others. So tuning in a new station was a process of successive adjustments. Selectivity became more important as spark transmitters were replaced by continuous wave transmitters which transmitted on a narrow band of frequencies, and broadcasting led to a proliferation of closely spaced radio stations crowding the radio spectrum.
Until recently the bandpass filters in the superheterodyne circuit used in all modern receivers were made with resonant transformers, called IF transformers. Marconi's initial radio system had relatively poor tuning limiting its range and adding to interference.
The Court rejected the Marconi Companies suit saying they could not sue for patent infringement when their own patents did not seem to have priority over the patents of Lodge, Stone, and Tesla. Although it was invented in in the wireless telegraphy era, the crystal radio receiver could also rectify AM transmissions and served as a bridge to the broadcast era. In addition to being the main type used in commercial stations during the wireless telegraphy era, it was the first receiver to be used widely by the public. The millions of people who purchased or homemade these inexpensive reliable receivers created the mass listening audience for the first radio broadcasts , which began around However it continued to be used by youth and the poor until World War 2.
The crystal radio used a cat's whisker detector , invented by Harrison H. Dunwoody and Greenleaf Whittier Pickard in , to extract the audio from the radio frequency signal. Only particular sites on the crystal surface worked as detector junctions, and the junction could be disrupted by the slightest vibration. So a usable site was found by trial and error before each use; the operator would drag the cat's whisker across the crystal until the radio began functioning. Frederick Seitz, a later semiconductor researcher, wrote:.
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Such variability, bordering on what seemed the mystical, plagued the early history of crystal detectors and caused many of the vacuum tube experts of a later generation to regard the art of crystal rectification as being close to disreputable. The crystal radio was unamplified and ran off the power of the radio waves received from the radio station, so it had to be listened to with earphones ; it could not drive a loudspeaker.
During the wireless era it was used in commercial and military longwave stations with huge antennas to receive long distance radiotelegraphy traffic, even including transatlantic traffic. However it still had poor selectivity compared to modern receivers. Beginning around continuous wave CW transmitters began to replace spark transmitters for radiotelegraphy because they had much greater range. The first continuous wave transmitters were the Poulsen arc invented in and the Alexanderson alternator developed , which were replaced by vacuum tube transmitters beginning around The continuous wave radiotelegraphy signals produced by these transmitters required a different method of reception.
However the new continuous wave radiotelegraph signals simply consisted of pulses of unmodulated carrier sine waves. These were inaudible in the receiver headphones. To receive this new modulation type, the receiver had to produce some kind of tone during the pulses of carrier. The first crude device that did this was the tikker , invented in by Valdemar Poulsen. In Reginald Fessenden had invented a better means of accomplishing this. Thus the "dots" and "dashes" of Morse code were audible as musical "beeps". A major attraction of this method during this pre-amplification period was that the heterodyne receiver actually amplified the signal somewhat, the detector had "mixer gain".
The receiver was ahead of its time, because when it was invented there was no oscillator capable of producing the radio frequency sine wave f O with the required stability. The heterodyne receiver remained a laboratory curiosity until a cheap compact source of continuous waves appeared, the vacuum tube electronic oscillator  invented by Edwin Armstrong and Alexander Meissner in The heterodyne oscillator is the ancestor of the beat frequency oscillator BFO which is used to receive radiotelegraphy in communications receivers today.
The heterodyne oscillator had to be retuned each time the receiver was tuned to a new station, but in modern superheterodyne receivers the BFO signal beats with the fixed intermediate frequency , so the beat frequency oscillator can be a fixed frequency. Armstrong later used Fessenden's heterodyne principle in his superheterodyne receiver below. The Audion triode vacuum tube invented by Lee De Forest in was the first practical amplifying device and revolutionized radio.
The amplifying vacuum tube used energy from a battery or electrical outlet to increase the power of the radio signal, so vacuum tube receivers could be more sensitive and have a greater reception range than the previous unamplified receivers. The increased audio output power also allowed them to drive loudspeakers instead of earphones , permitting more than one person to listen.
The first loudspeakers were produced around These changes caused radio listening to evolve explosively from a solitary hobby to a popular social and family pastime.
The development of amplitude modulation AM and vacuum tube transmitters during World War I, and the availability of cheap receiving tubes after the war, set the stage for the start of AM broadcasting , which sprang up spontaneously around The advent of radio broadcasting increased the market for radio receivers greatly, and transformed them into a consumer product. In the early radios the multiple tuned circuits required multiple knobs to be adjusted to tune in a new station.
One of the most important ease-of-use innovations was "single knob tuning", achieved by linking the tuning capacitors together mechanically. A vacuum tube receiver required several power supplies at different voltages, which in early radios were supplied by separate batteries. By adequate rectifier tubes were developed, and the expensive batteries were replaced by a transformer power supply that worked off the house current. Vacuum tubes were bulky, expensive, had a limited lifetime, consumed a large amount of power and produced a lot of waste heat, so the number of tubes a receiver could economically have was a limiting factor.
Therefore, a goal of tube receiver design was to get the most performance out of a limited number of tubes. The major radio receiver designs, listed below, were invented during the vacuum tube era. A defect in many early vacuum tube receivers was that the amplifying stages could oscillate, act as an oscillator , producing unwanted radio frequency alternating currents. The oscillations were caused by feedback in the amplifiers; one major feedback path was the capacitance between the plate and grid in early triodes.
Edwin Armstrong is one of the most important figures in radio receiver history, and during this period invented technology which continues to dominate radio communication. He invented the feedback oscillator , regenerative receiver , the superregenerative receiver , the superheterodyne receiver , and modern frequency modulation FM.
The first amplifying vacuum tube, the Audion , a crude triode , was invented in by Lee De Forest as a more sensitive detector for radio receivers, by adding a third electrode to the thermionic diode detector, the Fleming valve. To give enough output power to drive a loudspeaker, 2 or 3 additional Audion stages were needed for audio amplification.
In addition to very low gain of about 5 and a short lifetime of about 30 — hours, the primitive Audion had erratic characteristics because it was incompletely evacuated. De Forest believed that ionization of residual air was key to Audion operation. Each Audion stage usually had a rheostat to adjust the filament current, and often a potentiometer or multiposition switch to control the plate voltage. The filament rheostat was also used as a volume control. The many controls made multitube Audion receivers complicated to operate. By , Harold Arnold at Western Electric and Irving Langmuir at GE realized that the residual gas was not necessary; the Audion could operate on electron conduction alone.
These more stable tubes did not require bias adjustments, so radios had fewer controls and were easier to operate. The "soft" incompletely evacuated tubes were used as detectors through the s then became obsolete. The regenerative receiver , invented by Edwin Armstrong  in when he was a year-old college student,  was used very widely until the late s particularly by hobbyists who could only afford a single-tube radio. Today transistor versions of the circuit are still used in a few inexpensive applications like walkie-talkies.
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In the regenerative receiver the gain amplification of a vacuum tube or transistor is increased by using regeneration positive feedback ; some of the energy from the tube's output circuit is fed back into the input circuit with a feedback loop. Regeneration could not only increase the gain of the tube enormously, by a factor of 15, or more, it also increased the Q factor of the tuned circuit, decreasing sharpening the bandwidth of the receiver by the same factor, improving selectivity greatly.
The tube also acted as a grid-leak detector to rectify the AM signal. Another advantage of the circuit was that the tube could be made to oscillate, and thus a single tube could serve as both a beat frequency oscillator and a detector, functioning as a heterodyne receiver to make CW radiotelegraphy transmissions audible.
To receive radiotelegraphy, the feedback was increased until the tube oscillated, then the oscillation frequency was tuned to one side of the transmitted signal. The incoming radio carrier signal and local oscillation signal mixed in the tube and produced an audible heterodyne beat tone at the difference between the frequencies.
A widely used design was the Armstrong circuit , in which a "tickler" coil in the plate circuit was coupled to the tuning coil in the grid circuit, to provide the feedback. Regenerative detectors were sometimes also used in TRF and superheterodyne receivers. One problem with the regenerative circuit was that when used with large amounts of regeneration the selectivity Q of the tuned circuit could be too sharp, attenuating the AM sidebands, thus distorting the audio modulation.
A more serious drawback was that it could act as an inadvertent radio transmitter , producing interference RFI in nearby receivers. In nearby receivers, the regenerative's signal would beat with the signal of the station being received in the detector, creating annoying heterodynes , beats , howls and whistles. One preventative measure was to use a stage of RF amplification before the regenerative detector, to isolate it from the antenna.
This was a receiver invented by Edwin Armstrong in which used regeneration in a more sophisticated way, to give greater gain. In the regenerative receiver the loop gain of the feedback loop was less than one, so the tube or other amplifying device did not oscillate but was close to oscillation, giving large gain. The tuned radio frequency TRF receiver , invented in by Ernst Alexanderson , improved both sensitivity and selectivity by using several stages of amplification before the detector, each with a tuned circuit , all tuned to the frequency of the station. A major problem of early TRF receivers was that they were complicated to tune, because each resonant circuit had to be adjusted to the frequency of the station before the radio would work.
A second problem was that the multiple radio frequency stages, all tuned to the same frequency, were prone to oscillate,   and the parasitic oscillations mixed with the radio station's carrier in the detector, producing audible heterodynes beat notes , whistles and moans, in the speaker. From the standpoint of modern receivers the disadvantage of the TRF is that the gain and bandwidth of the tuned RF stages are not constant but vary as the receiver is tuned to different frequencies.
The Neutrodyne receiver, invented in by Louis Hazeltine ,   was a TRF receiver with a "neutralizing" circuit added to each radio amplification stage to cancel the feedback to prevent the oscillations which caused the annoying whistles in the TRF. The reflex receiver , invented in by Wilhelm Schloemilch and Otto von Bronk,  and rediscovered and extended to multiple tubes in by Marius Latour   and William H.
Priess, was a design used in some inexpensive radios of the s  which enjoyed a resurgence in small portable tube radios of the s  and again in a few of the first transistor radios in the s. In the reflex receiver the RF signal from the tuned circuit is passed through one or more amplifying tubes or transistors, demodulated in a detector , then the resulting audio signal is passed again though the same amplifier stages for audio amplification. In addition to single tube reflex receivers, some TRF and superheterodyne receivers had several stages "reflexed".
The superheterodyne , invented in during World War I by Edwin Armstrong  when he was in the Signal Corps , is the design used in almost all modern receivers, except a few specialized applications. In the superheterodyne, the " heterodyne " technique invented by Reginald Fessenden is used to shift the frequency of the radio signal down to a lower " intermediate frequency " IF , before it is processed. This design was used for virtually all commercial radio receivers until the transistor replaced the vacuum tube in the s. The invention of the transistor in revolutionized radio technology, making truly portable receivers possible, beginning with transistor radios in the late s.
Although portable vacuum tube radios were made, tubes were bulky and inefficient, consuming large amounts of power and requiring several large batteries to produce the filament and plate voltage. Transistors did not require a heated filament, reducing power consumption, and were smaller and much less fragile than vacuum tubes. The development of integrated circuits ICs in the s created another revolution, allowing an entire radio receiver to be put on a chip.
ICs reversed the economics of radio design used with vacuum tube receivers. Since the marginal cost of adding additional amplifying devices transistors to the chip was essentially zero, the size and cost of the receiver was dependent not on how many active components were used, but on the passive components; inductors and capacitors, which could not be integrated easily on the chip. As a result, the current trend in receivers is to use digital circuitry on the chip to do functions that were formerly done by analog circuits which require passive components.
In a digital receiver the IF signal is sampled and digitized, and the bandpass filtering and detection functions are performed by digital signal processing DSP on the chip. Another benefit of DSP is that the properties of the receiver; channel frequency, bandwidth, gain, etc.
Many of the functions performed by analog electronics can be performed by software instead. The benefit is that software is not affected by temperature, physical variables, electronic noise and manufacturing defects. Digital signal processing permits signal processing techniques that would be cumbersome, costly, or otherwise infeasible with analog methods. A digital signal is essentially a stream or sequence of numbers that relay a message through some sort of medium such as a wire.
DSP hardware can tailor the bandwidth of the receiver to current reception conditions and to the type of signal. A typical analog only receiver may have a limited number of fixed bandwidths, or only one, but a DSP receiver may have 40 or more individually selectable filters. DSP is used in cell phone systems to reduce the data rate required to transmit voice. A "PC radio" may not have a front-panel at all, and may be designed exclusively for computer control, which reduces cost.
Some PC radios have the great advantage of being field upgradable by the owner. New versions of the DSP firmware can be downloaded from the manufacturer's web site and uploaded into the flash memory of the radio. The manufacturer can then in effect add new features to the radio over time, such as adding new filters, DSP noise reduction, or simply to correct bugs. A full-featured radio control program allows for scanning and a host of other functions and, in particular, integration of databases in real-time, like a "TV-Guide" type capability.
This is particularly helpful in locating all transmissions on all frequencies of a particular broadcaster, at any given time. Some control software designers have even integrated Google Earth to the shortwave databases, so it is possible to "fly" to a given transmitter site location with a click of a mouse.
In many cases the user is able to see the transmitting antennas where the signal is originating from. Since the Graphical User Interface to the radio has considerable flexibility, new features can be added by the software designer. Features that can be found in advanced control software programs today include a band table, GUI controls corresponding to traditional radio controls, local time clock and a UTC clock, signal strength meter, a database for shortwave listening with lookup capability, scanning capability, or text-to-speech interface.
The next level in integration is " software-defined radio ", where all filtering, modulation and signal manipulation is done in software. There will be a RF front-end to supply an intermediate frequency to the software defined radio. These systems can provide additional capability over "hardware" receivers.
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For example, they can record large swaths of the radio spectrum to a hard drive for "playback" at a later date. All-digital radio transmitters and receivers present the possibility of advancing the capabilities of radio. Companies first began manufacturing radios advertised as portables shortly after the start of commercial broadcasting in the early s. The vast majority of tube radios of the era used batteries and could be set up and operated anywhere, but most did not have features designed for portability such as handles and built in speakers.
Crystal sets such as the Westinghouse Aeriola Jr. Thanks to miniaturized vacuum tubes first developed in , smaller portable radios appeared on the market from manufacturers such as Zenith and General Electric. The bezel may include at least one gap. The gap may be filled with a solid dielectric such as plastic. The antenna may be formed from the portion of the bezel that includes the gap and a portion of a ground plane.
To avoid excessive sensitivity to touch events, the antenna may be fed using a feed arrangement that reduces electric field concentration in the vicinity of the gap. An inductive element may be formed in parallel with the antenna feed terminals, whereas a capacitive element may be formed in series with one of the antenna feed terminals.
The inductive element may be formed from a transmission line inductive structure that bridges the antenna feed terminals. The capacitive element may be formed from a capacitor that is interposed in the positive feed path for the antenna. The capacitor may, for example, be connected between the positive ground conductor of the transmission line and the positive antenna feed terminal.
A switchable inductor circuit may be coupled in parallel with the inductive element. A tunable matching circuit may also be interposed in the positive feed path for the antenna e. A variable capacitor circuit may bridge the gap. The switching inductor circuit, the tunable matching circuit, and the variable capacitor serve as antenna tuning circuitry that can be used to allow the antenna to resonate at different frequency bands. A wireless device formed using this arrangement may be operable in first and second modes.
In the first mode, the switchable inductor circuit may be turned to enable the antenna of the wireless device to operable in a first low-band region and a high-band region. In the second mode, the switchable inductor circuit may be turned off to enable the antenna of the wireless device to operate in a second low-band region and the high-band region. The first and second low-band regions may or may not overlap in frequency.
The tunable matching circuit may be configured to provide desired sub-band coverage within a selected band region. The variable capacitor circuit may be adjusted to fine tune the frequency characteristic of the loop antenna. 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.
Electronic devices may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include one or more antennas. The antennas can include loop antennas. Conductive structures for a loop antenna may, if desired, be formed from conductive electronic device structures.
The conductive electronic device structures may include conductive housing structures. The housing structures may include a conductive bezel. Gap structures may be formed in the conductive bezel. The antenna may be parallel-fed using a configuration that helps to minimize sensitivity of the antenna to contact with a user's hand or other external object. Any suitable electronic devices may be provided with wireless circuitry that includes loop antenna structures.
As an example, loop antenna structures may be used in electronic devices such as desktop computers, game consoles, routers, laptop computers, etc. With one suitable configuration, loop antenna structures are provided in relatively compact electronic devices in which interior space is relatively valuable such as portable electronic devices. An illustrative portable electronic device in accordance with an embodiment of the present invention is shown in FIG. Portable electronic devices such as illustrative portable electronic device 10 may be laptop computers or small portable computers such as ultraportable computers, netbook computers, and tablet computers.
Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the portable electronic devices are handheld electronic devices such as cellular telephones. Space is at a premium in portable electronic devices. Conductive structures are also typically present, which can make efficient antenna operation challenging.
For example, conductive housing structures may be present around some or all of the periphery of a portable electronic device housing. In portable electronic device housing arrangements such as these, it may be particularly advantageous to use loop-type antenna designs that cover communications bands of interest. The use of portable devices such as handheld devices is therefore sometimes described herein as an example, although any suitable electronic device may be provided with loop antenna structures, if desired.
Handheld devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers also sometimes called personal digital assistants , remote controllers, global positioning system GPS devices, and handheld gaming devices. Handheld devices and other portable devices may, if desired, include the functionality of multiple conventional devices.
Examples of multi-functional devices include cellular telephones that include media player functionality, gaming devices that include wireless communications capabilities, cellular telephones that include game and email functions, and handheld devices that receive email, support mobile telephone calls, and support web browsing. These are merely illustrative examples. Device 10 of FIG. Device 10 includes housing 12 and includes at least one antenna for handling wireless communications.
Housing 12 , which is sometimes referred to as a case, may be formed of any suitable materials including, plastic, glass, ceramics, composites, metal, or other suitable materials, or a combination of these materials. In some situations, parts of housing 12 may be formed from dielectric or other low-conductivity material, so that the operation of conductive antenna elements that are located within housing 12 is not disrupted.
In other situations, housing 12 may be formed from metal elements. Device 10 may, if desired, have a display such as display Display 14 may, for example, be a touch screen that incorporates capacitive touch electrodes. A cover glass member may cover the surface of display Buttons such as button 19 may pass through openings in the cover glass. Housing 12 may include sidewall structures such as sidewall structures Structures 16 may be implemented using conductive materials.
For example, structures 16 may be implemented using a conductive ring member that substantially surrounds the rectangular periphery of display Structures 16 may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming structures Structures 16 may serve as a bezel that holds display 14 to the front top face of device Structures 16 are therefore sometimes referred to herein as bezel structures 16 or bezel Bezel 16 runs around the rectangular periphery of device 10 and display Bezel 16 may have a thickness dimension TT of about 0.
The sidewall portions of bezel 16 may be substantially vertical parallel to vertical axis V.
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Parallel to axis V, bezel 16 may have a dimension TZ of about 1 mm to 2 cm as an example. The aspect ratio R of bezel 16 i. It is not necessary for bezel 16 to have a uniform cross-section. For example, the top portion of bezel 16 may, if desired, have an inwardly protruding lip that helps hold display 14 in place.
If desired, the bottom portion of bezel 16 may also have an enlarged lip e. In the example of FIG. This is merely illustrative. The sidewalls of bezel 16 may be curved or may have any other suitable shape. Display 14 includes conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. These conductive structures tend to block radio-frequency signals. It may therefore be desirable to form some or all of the rear planar surface of device from a dielectric material such as plastic.
Portions of bezel 16 may be provided with gap structures. For example, bezel 16 may be provided with one or more gaps such as gap 18 , as shown in FIG. Gap 18 lies along the periphery of the housing of device 10 and display 12 and is therefore sometimes referred to as a peripheral gap.
Gap 18 divides bezel 16 i. As shown in FIG. For example, gap 18 may be filled with air. To help provide device 10 with a smooth uninterrupted appearance and to ensure that bezel 16 is aesthetically appealing, gap 18 may be filled with a solid non-air dielectric such as plastic. Bezel 16 and gaps such as gap and its associated plastic filler structure may form part of one or more antennas in device For example, portions of bezel 16 and gaps such as gap 18 may, in conjunction with internal conductive structures, form one or more loop antennas.
The internal conductive structures may include printed circuit board structures, frame members or other support structures, or other suitable conductive structures. In a typical scenario, device 10 may have upper and lower antennas as an example. An upper antenna may, for example, be formed at the upper end of device 10 in region A lower antenna may, for example, be formed at the lower end of device 10 in region The lower antenna may, for example, be formed partly from the portions of bezel 16 in the vicinity of gap Antennas in device 10 may be used to support any communications bands of interest.
As an example, the lower antenna in region 20 of device 10 may be used in handling voice and data communications in one or more cellular telephone bands. A schematic diagram of an illustrative electronic device is shown in FIG. Storage and processing circuitry 28 may include storage such as hard disk drive storage, nonvolatile memory e. Processing circuitry in storage and processing circuitry 28 may be used to control the operation of device This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, applications specific integrated circuits, etc.
Storage and processing circuitry 28 may be used to run software on device 10 , such as internet browsing applications, voice-over-internet-protocol VOIP telephone call applications, email applications, media playback applications, operating system functions, etc.
To support interactions with external equipment, storage and processing circuitry 28 may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry 28 include internet protocols, wireless local area network protocols e. Input-output circuitry 30 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. Input-output devices 32 such as touch screens and other user input interface are examples of input-output circuitry Input-output devices 32 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 10 by supplying commands through such user input devices. Display and audio devices such as display 14 FIG. Display and audio components in input-output devices 32 may also include audio equipment such as speakers and other devices for creating sound.
If desired, input-output devices 32 may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors. Wireless communications circuitry 34 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. Wireless communications circuitry 34 may include radio-frequency transceiver circuits for handling multiple radio-frequency communications bands. Other cellular telephone standards may be used if desired. These cellular telephone standards are merely illustrative. Wireless communications circuitry 34 can include circuitry for other short-range and long-range wireless links if desired.
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For example, wireless communications circuitry 34 may include global positioning system GPS receiver equipment, wireless circuitry for receiving radio and television signals, paging circuits, etc. 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 34 may include antennas Antennas 40 may be formed using any suitable antenna types. For example, antennas 40 may include antennas with resonating elements that are formed from loop antenna structure, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link.
With one suitable arrangement, which is sometimes described herein as an example, the lower antenna in device i. When a user holds device 10 , the user's fingers may contact the exterior of device For example, the user may touch device 10 in region To ensure that antenna performance is not overly sensitive to the presence or absence of a user's touch or contact by other external objects, the loop-type antenna may be fed using an arrangement that does not overly concentrate electric fields in the vicinity of gap A cross-sectional side view of device 10 of FIG.
Housing 12 may include sidewalls formed from bezel 16 and one or more rear walls formed from structures such as planar rear housing structure Structure 42 may be formed from a dielectric such as plastic or other suitable materials. Snaps, clips, screws, adhesive, and other structures may be used in attaching bezel 16 to display 14 and rear housing wall structure Device 10 may contain printed circuit boards such as printed circuit board Printed circuit board 46 and the other printed circuit boards in device 10 may be formed from rigid printed circuit board material e.
Printed circuit board 46 may contain interconnects such as interconnects Interconnects 48 may be formed from conductive traces e. Connectors such as connector 50 may be connected to interconnects 48 using solder or conductive adhesive as examples. Integrated circuits, discrete components such as resistors, capacitors, and inductors, and other electronic components may be mounted to printed circuit board Antenna 40 may have antenna feed terminals. For example, antenna 40 may have a positive antenna feed terminal such as positive antenna feed terminal 58 and a ground antenna feed terminal such as ground antenna feed terminal In the illustrative arrangement of FIG.
Components 44 may include one or more integrated circuits that implement the transceiver circuits 36 and 38 of FIG. Connector 50 may be, for example, a coaxial cable connector that is connected to printed circuit board Cable 52 may be a coaxial cable or other transmission line. Microwave Symp. Digest, session WE1C-1, June Pourakbar, L. Linton, M. Tormanen and M. Digest, session WE2B-6, June Morris III and V. Digest, session WE1C-6, June Obiya, T.
Wada, H. Hayafuji, T. Ogami, M. Tani, M. Koshino, M. Kawashima and N. Digest, session WEP, June Tani, K. Ikada, H. Kando, T. Obiya, M.