WO2000046873A1

WO2000046873A1 - Wireless phone design for improving radiation performance

Info

Publication number: WO2000046873A1
Application number: PCT/US2000/002791
Authority: WO
Inventors: Guy Klemens; Chung-Yi Lee
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 1999-02-02
Filing date: 2000-02-02
Publication date: 2000-08-10
Anticipated expiration: 2001-08-02
Also published as: AU2979700A

Abstract

An efficient wireless communications device (30). The device includes a housing (34) having an upper earpiece portion (14) and a lower mouthpiece portion (20). A signal processing circuit is disposed within the housing (34) and an antenna (40) is connected to the signal processing circuit. The antenna (40) is mounted on the housing below the mouthpiece portion thereof. In a specific embodiment, the antenna is a dipole antenna and is mounted on a section (32) that is retractable from the phone housing. The dipole antenna is painted on the retractable section (32) via conductive paint or is constructed from flexible conductive patches. The processing circuitry includes a transceiver having a duplexer, and a digital signal processor chip. A balun (52, 60) interfaces the antenna (40) to the duplexer (84) included in the processing circuitry.

Description

WIRELESS PHONE DESIGN FOR IMPROVING RADIATION PERFORMANCE

BACKGROUND OF THE INVENTION

I. Field of Invention:

This invention relates to wireless communications systems. Specifically, the present invention relates to wireless phone designs and associated antenna-positioning schemes for improving phone performance.

II. Description of the Related Art: To achieve optimal performance, cellular telephones require effective antenna radiation patterns, minimal electrical coupling between the antenna and internal telephone circuitry, and minimal radiated energy absorption.

Typically a portion of the electromagnetic energy radiated by a cellular telephone is absorbed by the user's brain tissue. The absorbed electromagnetic energy may reduce phone performance and may pose health risks to the user of the telephone. To reduce potential user health risks, the Federal Communications Commission (FCC) has imposed specific absorption rate (SAR) limits on cellular telephones to control the amount of electromagnetic energy absorbed by the brain tissue of a user. For FCC certification, a cellular telephone must operate in accordance with the SAR limits.

Cellular telephones often employ a metallic whip or helix antenna that extends from the top of the cellular telephone. These antennas typically use the phone housing in addition to the whip or helix to facilitate radiation of electromagnetic energy. Use of the phone housing may increase undesirable electrical coupling between radiated electromagnetic energy and internal phone circuitry such as processing circuits. The electrical coupling results in electromagnetic interference that reduces phone performance. In addition, use of the phone housing may degrade the antenna radiation pattern and thereby further reduce phone performance.

Typically, the whip or helix antennas extend from the top of the phone near the head of the user. The user's head may interfere with and absorb phone radiation and thereby reduce phone performance and increase any associated health risks. To obtain FCC certification, the phones may require specially designed circuitry to minimize energy absorbed by a user's brain tissue, which may increase the cost of the phone. Alternatively, antennas are printed on circuit boards and included within the phone housing. Electromagnetic radiation from these antennas, however, is often partially blocked and absorbed by a user's hand and head.

Hence, a need exists in the art for a wireless phone having a high- performance cost-effective antenna and /or antenna positioning scheme that minimizes the absorption of radiated electromagnetic energy by brain tissue and provides for an effective antenna radiation pattern with minimal coupling between radiated electromagnetic energy and internal phone circuitry.

SUMMARY OF THE INVENTION

The need in the art is addressed by the efficient wireless phone of the present invention. The phone includes a housing having an upper earpiece portion and a lower mouthpiece portion. A signal processing circuit is disposed within the housing and an antenna is connected to the signal processing circuit. The antenna is mounted on the housing below the mouthpiece portion thereof.

In the specific embodiment, the antenna is a dipole antenna and is mounted on a section that is retractable from the phone housing. The dipole antenna is painted on the retractable section via conductive paint or is constructed from flexible conductive patches. The processing circuitry includes a transceiver having a duplexer, and a digital signal processor chip. A balun interfaces the antenna to the duplexer included in the processing circuitry.

The design of the disclosed apparatus is facilitated by the fact that the antenna is positioned near the bottom of the wireless phone and away from the head of the user. This positioning reduces interference and absorption of wireless electromagnetic signals by the user's head. In addition, the use of a dipole antenna, which is a balanced antenna, provides for an efficient radiation pattern that results in minimal coupling and interference between internal phone circuitry and transmitted electromagnetic energy. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram of a conventional cellular telephone having a whip antenna positioned near the top of the cellular telephone. Fig. 2 is a diagram of a cellular telephone constructed in accordance with the teachings of the present invention and showing a retractable section extendable from the housing of the cellular telephone.

Fig. 3 is a diagram showing a side view of the cellular telephone of Fig. 2. Fig. 4 is a diagram of the cellular telephone of Fig. 2 showing a first embodiment of a dipole antenna of the present invention positioned on the retractable section.

Fig. 5 is a diagram of the cellular telephone of Fig. 3 showing a second embodiment of a dipole antenna of the present invention. Fig. 6 is a circuit diagram of a discreet element balun circuit adapted for use with the dipole antenna of Fig. 5.

Fig. 7 is a diagram of a barrel skirt balun adapted for use with the dipole antenna of Fig. 5.

Fig. 8 is a more detailed diagram of cellular telephone of Fig. 5 showing internal circuitry.

Fig. 9 is a diagram of an alternative embodiment of the dipole antenna of the present invention having an electromagnetic coupling device.

DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.

The following review of a conventional cellular telephone design is intended to facilitate an understanding of the present invention. Fig. 1 is a diagram of a conventional cellular telephone 10 having a whip antenna 12 positioned near the top of the cellular telephone 10 and connected to a circuit board 11. The cellular telephone 10 also includes a speaker 14 positioned near the top of the cellular telephone 10, a display screen 16 positioned below the speaker 14, a keypad 18 positioned below the display screen 16, and a microphone 20 positioned near the bottom of the cellular telephone 10 and directly below the keypad 18.

In operation, a user of the cellular telephone 10 places a call and subsequently positions the cellular telephone 10 so that microphone 20 is near the mouth and the speaker 14 is near the ear. In this position, the antenna 12 is in close proximity to the head of the user and runs parallel to the side of the user's head. This positioning results in excess absorption of electromagnetic energy by the head of the user, which may interfere with signal transmission, may pose user health risks, and may increase the expense of the cellular telephone 10 due to circuit design modifications required to have the cellular telephone 10 meet specific absorption rate (SAR) requirements. In addition, the use of the whip antenna 12 may increase electrical interference due to coupling between transmitted electromagnetic energy and internal cellular telephone circuitry (not shown) on the circuit board 11. The circuit board 11 coupled to the whip antenna 12 forms a dipole antenna with the whip antenna 12 forming a top half of the dipole antenna and the circuit board 11 forming the bottom half of the dipole antenna. As a result, the circuit board 11 is rife with radio frequency currents from the whip antenna 12. The additional radio frequency currents often cause leakage of transmitted signals back into electronics on the circuit board 11. In addition, the large rectangular shape of the circuit board 11 results in an inferior radiation pattern compared to the radiation pattern of the dipole antenna of the present invention as is discussed more fully below.

Fig. 2 is a diagram of a cellular telephone 30 constructed in accordance with the teachings of the present invention. The phone 30 has a retractable section 32 extendable from a housing 34 of the telephone 30 near the bottom thereof. In this context, the 'bottom' is defined as the mouthpiece end of the phone 30. The 'top' is defined as the earpiece end of the phone 30. The speaker 14 is positioned in an earpiece portion of the phone 30 comprising approximately the lower third of the phone 30 while the microphone 20 is positioned in a mouthpiece portion of the phone 30 comprising approximately the upper third of the phone 30. The retractable section 32 provides a surface 36 upon which to dispose an antenna as is discussed more fully below.

The retractable section has a main section 38 with a cross-sectional shape similar to the shape of the phone housing 34 with the exception that the main section 38 is smaller to easily slide out of the bottom the cellular telephone housing 34. A bottom section 40 of the retractable section 32 is attached to the main section 38. Outside edges of the bottom section 40 align with the phone housing 34 when the retractable section 34 is inserted into the phone housing 34. When the cellular telephone 30 is in use, the retractable section 32 is extended to expose an antenna positioned thereon or therein. Note that the retractable section 32 ensures that the antenna is positioned away from the head and near a jaw of a user. Those skilled in the art will appreciate that a slight increase in distance between the antenna and a user's head may greatly reduce electromagnetic energy absorbed by the user's head.

Fig. 3 is a diagram showing a side view of the cellular telephone 30 of Fig. 2. In the illustrative embodiment, the retractable section 32 extends from the phone housing 34 approximately 1/2 of an inch. However those skilled in the art will appreciate that the section 32 may be different lengths without departing from the scope of the present invention. In addition, the retractable section 32 may be different shapes or sizes without departing from the scope of the present invention.

The retractable section 32 is made of a non-conductive material such as plastic and supports an antenna made from a conductive material as discussed more fully below.

Fig. 4 is a diagram of the cellular telephone 30 of Fig. 2 showing a first embodiment of a dipole antenna 50 (shown in phantom) of the present invention positioned on the retractable section 32. The dipole antenna 50 is disposed on the convenient surface 36 or within the bottom section 40 of the retractable section 32. The dipole antenna 50 is connected to a balun 52 (shown in phantom) positioned within the phone housing 34 or within the retractable section 32.

The dipole antenna 50 is constructed in accordance with design methods known in the art and may be implemented in a variety of shapes and sizes. In addition, the dipole antenna 50 may be positioned in different locations on the retractable section 32 such as on a side of the retractable section 32 rather than on the bottom section 40.

The balun 52 may be a lumped-element balun, a discrete-element balun, a sleeve balun, or another type of balun. The dipole antenna 50 may be constructed with wire, flexible conductive patches, or a conductive paint on an interior of the bottom section 40. Those skilled in the art will appreciate that another type of antenna such as a patch antenna may be used in place of the dipole antenna 50 without departing from the scope of the present invention. In addition, the type of the balun 52 is application specific and different baluns may be used for different types of antennas and for different applications.

The balun 52 facilitates the transfer of electrical energy between the antenna 50 and internal phone circuitry as is discussed more fully below. The balun 52 impedance matches the antenna 50 to the internal phone circuitry, however, those skilled in the art will appreciate that the balun 52 may be omitted without departing from the scope of the present invention.

When the dipole antenna 50 is retracted from the circuit board 11 via the retractable section 32, any undesirable coupling between the circuit board 11 and accompanying circuitry is reduced. This allows the antenna 50 to operate more efficiently and minimizes induced RF currents on the circuit board 11.

Fig. 5 is a diagram of the cellular telephone 30 of Fig. 3 showing a second embodiment of a dipole antenna 54 of the present invention. The dipole antenna 54 includes a first element 56 and a second element 58 that wrap around the sides of the retractable section 32. These elements are illustrated more clearly in Fig. 7 below.

Fig. 6 is a circuit diagram of a discreet element balun circuit 60 adapted for use with the dipole antenna 54 of Fig. 5. The balun circuit 60 replaces the balun 52 of Fig. 5 and includes a power splitter 63 connected to internal phone circuitry such as a duplexer on the circuit board 11 (as discussed more fully below) at a first node 62. Power splitter 63 is also connected to a second node 64 and to a third node 66. The second node 64 is connected, in parallel, to one end of a first inductor LI and to one end of a first capacitor Cl. The opposite end of the first inductor LI is connected to ground, and the opposite end of the first capacitor Cl is connected the first antenna element 56. The third node 66 is connected, in parallel, to one end of a second inductor L2 and to one end of a second capacitor C2. The opposite end of the second capacitor C2 is connected to ground, and the opposite end of the second inductor L2 is connected to the second antenna element 58.

The power splitter 62 directs power to and from the first node 62 included in the circuit board 11 and the first and second antenna elements, 56 and 58, respectively. A signal entering the balun 60 at the first node 62 is split by the power splitter 63 and is phase-shifted by the capacitors Cl and C2 and the inductors LI and L2. The values for the capacitors Cl and C2 and for the inductors LI and L2 are application specific and those skilled in the art may easily determine appropriate values for a particular application.

Fig. 7 is a diagram of a barrel skirt balun 70 adapted for use with the dipole antenna 54 of Fig. 5. A tube 72 is a standard metal tube that is hollow or is filled with a non-magnetic dielectric. The tube 72 is placed around a coaxial feed line 74 near the dipole antenna 54. The coaxial feed line 74 is open at an antenna end 76 and closed, i.e., shorted to tube 72 at the other end 78. The first dipole element 56 is connected to a centerline 80 of the coaxial line 74. The second dipole element 58 is connected to a cylindrical outer conductor 80 of the coaxial line 74. The shapes, sizes, resistivities, and other applicable properties of the tube 72, dipole elements 56 and 58 and coaxial line 74 are application specific and may be determined by those skilled in the art. Fig. 8 is a more detailed diagram of cellular telephone 30 of Fig. 5 showing internal circuitry. The cellular telephone 30 includes the dipole antenna 54 and the balun 60 of Fig. 6. The balun 60 is connected to a duplexer 84 and the dipole antenna 54. The duplexer 84 is connected to transceiver circuitry 86 and the transceiver circuitry 86 is connected to a computer 88 that includes a digital signal processor and accompanying chip and memory (not shown). The computer 88 is connected to voice encoding and decoding circuitry 92, a keypad 18, and a screen 16. The voice encoding and decoding circuitry 92 is connected to a microphone 20 and a speaker 14.

The connection of the antenna 54 to the circuit board 11 having the balun 60 and other circuits may be made via a flexible cable (not shown) from the duplexer 84 and/or balun 60 to the antenna 54 that folds slightly when the retractable section 32 is retracted. Alternatively, those skilled in the art can easily employ a sliding contact, or electromagnetic coupling to effect the necessary connection between the circuit board 11 and the antenna 54 on the retractable section 32.

In the present specific embodiment, the retractable section is implemented via similar methods as those employed for folding telescopes. Those having ordinary skill in the art can easily implement the retractable section 32 by employing such methods. In operation, the dipole antenna 54 transmits signals input via the duplexer 84 and the balun 60 and receives signals that are subsequently input to the duplexer 84 via the balun 60. The duplexer 84 facilitates sharing of resources of the dipole antenna 54 and balun 60 between transmit and receive functions. The transceiver circuitry 86 includes transmit circuitry for transmitting signals such as encoded voice signals or service negotiation signals via the dipole antenna 54 and balun 60 and duplexer 84. The transceiver circuitry 86 also includes receive circuitry for receiving signals such as service negotiation messages or encoded voice signals via another phone, base station, or mobile switching center. The transceiver circuitry 86 also includes any necessary downconversion circuitry required to convert receive signals to digital baseband signals in preparation for processing via the computer 88. In addition, the transceiver circuitry 86 includes any necessary upconversion circuitry required to convert transmit signals from digital baseband signals to radio frequency signals in preparation for transmission via the dipole antenna 54 and balun 60.

A user may initiate a call by dialing a number via the keypad 18. Software or hardware algorithms running on the computer 88 negotiate a service connection with an available wireless service provider via the transceiver circuitry 86, the duplexer 84, and the dipole antenna 54 and balun 60. Once service is established, the user's voice is input to the microphone 20, encoded by the voice encoding and decoding circuitry 92 and transmitted via the computer 88, transceiver circuitry 86, duplexer 84, and then dipole antenna 54 and balun 60. Similarly, received voice messages are decoded by the voice encoding and decoding circuitry 92 and as voice via the speaker 14.

Positioning the dipole antenna 54 near the bottom of the cellular telephone 30 reduces the absorption of transmitted electromagnetic energy by a user's brain tissue and associated signal interference. The dipole dipole antenna 54 is a balanced antenna and does not require use of the phone housing to facilitate radiation. As a result, undesirable coupling between the dipole antenna 54 and internal phone circuitry such as the computer 88 is reduced. The retractable and extendable nature of the retractable section 32 allows the dipole antenna 54 to be further separated from internal phone circuitry, thereby reducing any undesirable coupling between radiated electromagnetic energy and internal phone circuitry.

The retractable section 32 and the interfacing of the retractable section 32 with internal phone circuitry such as the duplexer 84 or balun 60 are easily constructed by those ordinarily skilled in the art. For example, flex circuits may be employed to connect the dipole antenna 54 and balun 60 to the duplexer 84.

For clarity, additional circuitry such as clocking circuitry and power supplies are not shown in the cellular telephone 30, but those ordinarily skilled in the art will know where and how to include the requisite additional circuitry.

Fig. 9 is a diagram of an alternative embodiment 100 of the dipole antenna of the present invention having an electromagnetic coupling device comprising a first coupler 102 and a second coupler 104. The first and second couplers, 102 and 104, respectively are conductive coils that electromagnetically couple elements of the antenna 50. The coil turns, density of turns, and the shape of the turns in the first coupler 102 and the second coupler 104 are designed to cause the couplers 102 and 104 to act as a balun in addition to a coupling device for coupling the antenna 50 to internal phone circuitry. The couplers 102 and 104 couple electromagnetic energy between the antenna 50 and the power splitter 63, which splits power between the duplexer 84 and the couplers 102 and 104. The couplers 102 and 104 also impedance match the antenna 50 to the internal phone circuitry that includes the power splitter 63, the duplexer 84.

The couplers 102 and 104 allow for easy accommodation of the retractable section 32. By employing electromagnetic coupling, the need for additional flex circuits to connect the antenna 50 to internal phone circuitry is eliminated. Those skilled in the art will appreciate that an electromagnetic coupler such as the coupler 102 may be employed with an antenna having a single conductive path rather than two elements as in the dipole antenna 50 without departing from the scope of the present invention.

Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof.

It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.

WHAT IS CLAIMED IS:

Claims

1. An efficient wireless phone comprising: a housing having an upper earpiece portion and a lower mouthpiece portion; a signal processing circuit disposed within said housing; and an antenna connected to said signal processing circuit and being mounted on said housing below said mouthpiece portion thereof.

2. The phone of Claim 1 wherein said antenna is mounted on a section which is retractable from said phone housing.

3. The phone of Claim 2 wherein said antenna is a dipole antenna.

4. The phone of Claim 3 wherein said dipole antenna is painted on said section via conductive paint.

5. The phone of Claim 3 wherein said antenna includes flexible conductive patches.

6. The phone of Claim 2 further including a balun for interfacing said antenna to said processing circuitry.

7. The phone of Claim 6 wherein said processing circuitry includes a transceiver having a duplexer, and a digital signal processor chip, said balun interfacing said antenna to said duplexer.

8. The phone of Claim 2 further including an electromagnetic coupling device for interfacing said antenna to said signal processing circuit.

9. A wireless phone having an efficient antenna positioning scheme comprising: a wireless phone section including a housing having a signal processing circuit, a speaker, and a microphone; a retractable section positioned adjacent to said speaker, said retractable section retractable from said housing; and a dipole or patch antenna disposed on said retractable section, said dipole or patch antenna in electrical communication with said signal processing circuitry.

10. An efficient wireless phone design comprising: a wireless phone housing, including a transceiver circuit for providing a first signal and receiving a second signal to and from a processing circuit, respectively, an input device for providing input to said processing circuit, an output device for providing output from said processing circuit, said output based on said first signal; a retractable section included on said phone housing and positioned near a bottom portion of said phone housing near said input device; and an antenna disposed on said retractable section, said antenna in electrical communication with said processing circuit via said transceiver circuit.

11. The phone of Claim 10 wherein said antenna is a dipole antenna or a patch antenna.

12. A high performance wireless phone comprising: a receiver for receiving receive signals; a transmitter for transmitting transmit signals; a microphone for outputting electronic speech signals to said processing circuit in response to acoustic input signals provided by a user of said wireless phone; a speaker for converting said received electronic speech signals to acoustic output signals and providing said transmit signals to said transmitter in response thereto; a duplexer connected in parallel to said receiver and said transmitter for facilitating the dual use of said antenna by said receiver and said transmitter; an antenna connected to said duplexer for facilitating the transmission and reception of said receive signals and said transmit signals via said receiver, said transmitter, and said duplexer, said antenna mounted adjacent to said speaker; and a processing circuit for processing said receive signals and said transmit signals in preparation for output by said transmitter and /or said speaker, respectively.

13. An efficient wireless communications device comprising: first means for processing received electromagnetic signals; second means for outputting acoustic signals in response said received electromagnetic signals; third means for receiving acoustic input signals and providing encoded electromagnetic signals in response thereto; and fourth means positioned adjacent to said third means and opposite to said second means for transmitting said encoded electromagnetic signals and for receiving said received electromagnetic signals.

14. The device of Claim 13 wherein said fourth means is a dipole antenna or a patch antenna disposed on a retractable section of said efficient communications device.