WO2004066435A2

WO2004066435A2 - Wireless communication device and antenna operable in a plurality of frequency bands

Info

Publication number: WO2004066435A2
Application number: PCT/US2004/000920
Authority: WO
Inventors: Hong-Yong Luo; Guangping Zhou
Original assignee: Motorola, Inc.
Priority date: 2003-01-14
Filing date: 2004-01-14
Publication date: 2004-08-05
Also published as: WO2004066435A3; CN100524945C; CN1518377A

Abstract

A fixed antenna (129) and wireless communication device operable in at least two frequency bands. The fixed antenna (129) has a dual band radiating element (310) with a first radiating element portion (320) and a second radiating element portion (330) having a different length than that of the first radiating element portion (320). There is also a tuning stub (340) having an axial length parallel with a central longitudinal axis (A) of the dual band radiating element (310), this axial length does not exceed one sixth of a total effective length of the dual band radiating element (310). A feed point (350) is electrically coupled to the tuning stub (340) and the dual band radiating element (310). In use, the first radiating element portion (320) provides for tuning into a first frequency and the second radiating element portion (330) provides for tuning into a second frequency.

Description

WIRELESS COMMUNICATION DEVICE AND

ANTENNA OPERABLE IN A PLURALITY OF

FREQUENCY BANDS

FIELD OF THE INVENTION

This invention relates to a wireless corrununication device and an antenna. In particular the invention relates to a wireless communication device and an antenna adapted to operate in more than one frequency band .

BACKGROUND ART

With the increased use of wireless communication devices, spectrum has become scarce. In many cases, network operators providing services on one particular band have had to provide service on a separate band to accommodate its customers. For example, network operators providing service on a GSM system in a 900 MHz frequency band have had to rely on a DCS system at an 1800 MHz frequency band. Accordingly, wireless communication devices, such as cellular radio telephones, must be able to communicate at both frequencies. Further, it is beneficial if the antenna of such cellular radio telephones provides both a sufficiently wide bandwidth and adequate near and far field radiated energy.

In this specification, including the claims, the terms 'comprises',

'comprising' or similar terms are intended to mean a non-exclusive inclusion, such that a method or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed. SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a fixed antenna operable in at least two frequency bands, the antenna comprising: a dual band radiating element with a first radiating element portion and a second radiating element portion having a different length than that of the first radiating element portion, the second radiating element portion being electrically coupled to the first radiating element portion; a tuning stub having a stub axial length parallel with a central longitudinal axis of the dual band radiating element, said stub axial length not exceeding one sixth of an axial length of the dual band radiating element, said axial length of the dual band radiating element being along the central longitudinal axis; and a feed point electrically coupled to said tuning stub and said dual band radiating element, wherein the first radiating element portion provides for tuning into a first frequency and the second radiating element portion provides for tuning into a second frequency.

Suitably, the tuning stub is directly coupled to said feed point.

Preferably, the dual band radiating element is directly coupled to said feed point. In one alternative, the dual band radiating element is coupled to said feed point through said tuning sub.

Suitably, the dual band radiating element is a meander. Preferably, the dual band radiating element is a helical coil.

Suitably, the first radiating element has an average pitch that is smaller than an average pitch of the second radiating element. Preferably, the tuning stub is a straight conductor located along the central longitudinal axis of said dual band radiating element.

Suitably, the tuning stub is a straight conductor located with its length substantially parallel to the central longitudinal axis of the dual band radiating element. The tuning stub may suitably have a straight section substantially parallel to the central longitudinal axis the dual band radiating element. The tuning stub may suitably have a straight section located along the central longitudinal axis of the dual band radiating element.

Preferably, the tuning stub has a total length of at least one twenty fifth of the total effective length of the dual band radiating element.

The antenna may suitably have an associated matching circuit for matching said first antenna element and said second antenna element.

Preferably, the pitch of said first radiating element portion is constant. Suitably, the pitch of said second radiating element portion is constant.

Preferably the tuning stub is a meander. In one suitable specific form, the tuning stub may be a helical coil.

According to another aspect of the invention there is provided a wireless communication device adapted to operate in at least two frequency bands comprising: a transceiver having a housing; a dual band radiating element mounted to said housing, the dual band radiating element having a first radiating element portion for tuning into a first frequency and a second radiating element portion having a different length than that of the first radiating element portion for tuning into a second frequency, the second radiating element portion being electrically coupled to the first radiating element portion; a tuning stub having a stub axial length parallel with a central longitudinal axis of the dual band radiating element, said stub axial length not exceeding one sixth of an axial length of the dual band radiating element, said axial length of the dual band radiating element being along the central longitudinal axis; and A feed point electrically coupled to said tuning stub and said dual band radiating element; and a matching circuit coupled to said feed point for matching said first radiating element portion and said second radiating element portion.

Preferably, the tuning stub is a meander. In one suitable specific form, the tuning stub may be a helical coil.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood and put into practical effect, reference will now be made to preferred embodiments as illustrated with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of a wireless communication device coupled to an antenna in accordance with the invention;

FIG. 2 is a partial cross-sectional view shows an antenna according to the present invention coupled to the wireless communication device of FIG. 1; FIG. 3 is a schematic representation of a first embodiment of an antenna according to the present invention;

FIG. 4 is a schematic representation of a second embodiment of an antenna according to the present invention;

FIG. 5 is a schematic representation of a third embodiment of an antenna according to the present invention;

FIG. 6 is a schematic representation of a fourth embodiment of part of an antenna according to the present invention; and

FIG. 7 is a circuit diagram of a matching circuit of Fig. 1 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF

THE INVENTION

In the drawings, like numerals on different Figs are used to indicate like elements throughout. With reference to Fig. 1 a block diagram of a wireless communication device such as a dual band cellular radiotelephone is shown. In the preferred embodiment, a frame generator ASIC 101, such as a CMOS ASIC available from Motorola,

Inc. and a microprocessor 103, such as a 68HC11 microprocessor also available from Motorola, Inc., combine to generate the necessary communication protocol for operating in a cellular system. Microprocessor 103 uses memory 104 comprising RAM 105, EEPROM 107, and ROM 109, preferably consolidated in one package 111, to execute the steps necessary to generate the protocol and to perform other functions for the communication unit, such as writing to a display 113, accepting information from a keypad 115, controlling a frequency synthesizer 125, or performing steps necessary to amplify a signal according to the method of the present invention. ASIC 101 processes signals from audio circuitry 119, generated from a microphone 117, and also processes signals provided to audio circuitry 119 for broadcasting by a speaker 121.

A transceiver processes the radio frequency signals. In particular, transmitters 123 and 124 transmit through an antenna 129 using carrier frequencies produced by a frequency synthesizer 125. Information received by the communication device's antenna 129 enters receivers 127 and 128 through a matching network and transmit/receive switch 130. A preferred matching network and transmit/receive switch 130 will be shown in more detail in FIG. 7. Receivers 127 and 128 demodulate the symbols comprising the message frame using the carrier frequencies from frequency synthesizer 125. The transmitters and receivers are collectively called a transceiver. The communication device may optionally include a message receiver and storage device 131 including digital signal processing means.

Turning now to FIG. 2, a partial cross-sectional view shows an antenna according to the present invention coupled to a wireless communication device, such as that shown in FIG. 1. Antenna 129 comprises an outer housing or overmold 202 having a dielectric sleeve 204. A monopole 205 comprises a threaded portion 206 which extends to a coupling portion 208. The length of the monopole generally effects vertical polarization, where a longer monopole generally provides greater vertical polarization.

The antenna is coupled to a clip 210 having a contact element 212 at the end of a flexible arm 214 which is coupled to a base portion 216. Base portion 216 is preferably attached to a circuit board having the circuitry of FIG. 1 or some other suitable circuit. Bracket 210 further includes a second contact 218 coupled to flexible arm 220 which also extends to base portion 216. Coupling portion 208 is retained by flexible arms 214 and 220 that also provide an electrical contact. The dimensions of the flexible arms are preferably selected to optimize the efficiency of the antenna. That is, the length and width of the flexible arms are selected to provide the proper inductance or capacitance for the antenna, where a narrower arm provides greater inductance and wider arm provides greater capacitance.

FIG. 2 also shows a housing 230 of the wireless communication device of FIG. 1. The housing includes a receiving sleeve 232, shown in partial cross-section, which retains a threaded nut 234 for receiving a threaded portion 205 of the antenna. Although a feed point of the antenna is preferably made at contact elements 212 and 218 near the base of coupling portion 208, the feed point could be made at or adjacent the threaded nut 234 according to the present invention.

In FIG. 3 there is illustrated a schematic representation of a first embodiment of the antenna 129, detached from the wireless communication device, the overmold 202 and dielectric sleeve 20 being removed for illustration purposes. The antenna 129 is a fixed antenna operable in at least two frequency bands and comprises a dual band radiating element 310 with a first radiating element portion 320 and a second radiating element portion 330 having a different length than that of the first radiating element portion. The second radiating element portion 330 preferably provides for tuning to a DCS system at an 1800 MHz frequency band (a second frequency) and it is electrically coupled to the first radiating element portion 320 that preferably provides for tuning to a GSM system in a 900 MHz frequency band (a first frequency). The antenna 129 also has a tuning stub 340, proximal to the dual band radiating element 310, and the tuning stub 340 has an stub axial length AXL1 parallel with a central longitudinal axis A of the dual band radiating element 310. The stub axial length AXL1 does not exceed one sixth of an axial length AL1 of the dual band radiating element 310, the axial length AL1 of the dual band radiating element 310 being along the central longitudinal axis A. Further, a feed point 350 is electrically coupled to the tuning stub 340 and the dual band radiating element 310.

As will be apparent to a person skilled in the art, the dual band radiating element 310 is a helical coil with a total effective length determined when it is unwound or uncoiled into a straightened length. Also, the first radiating element 320 has an average pitch that is smaller than an average pitch of the second radiating element 330 and preferably both pitches are constant. The tuning stub 340 is directly coupled to the feed point 350. In this embodiment, the tuning stub is a straight conductor located along the central longitudinal axis A of dual band radiating element 310 and the dual band radiating element 310 is coupled to feed point 350 through the tuning sub 330. Furthermore, the tuning sub 330 and dual band radiating element 310 are a continuous length of conductive wire and the tuning stub 340 has a total length of at least one twenty fifth of the total effective length of the dual band radiating element.

In FIG. 4 there is illustrated a schematic representation of a second embodiment of the antenna 129, detached from the wireless communication device, the overmold 202 and dielectric sleeve 204 being removed for illustration purposes. The antenna 129 is a fixed antenna operable in at least two frequency bands and comprises a dual band radiating element 410 with a first radiating element portion 420 and a second radiating element portion 430 having a different length than that of the first radiating element portion. The second radiating element portion 430 preferably provides for tuning to a DCS system at an 1800 MHz frequency band (a second frequency) and it is electrically coupled to the first radiating element portion 420 that preferably provides for tuning to a GSM system in a 900 MHz frequency band (a first frequency). The antenna 129 also has a tuning stub 440, proximal to the dual band radiating element 310, and the tuning stub 440 has a stub axial length AXL2 parallel with a central longitudinal axis B of the dual band radiating element 410.

As shown, the dual band radiating element 410 is a helical coil. Also, the tuning stub 440 in this embodiment is a helical coil that is coaxial with the central longitudinal axis B. The stub axial length AXL2 does not exceed one sixth of an axial length AL2 of the dual band radiating element 410, the axial length AL2 of the dual band radiating element 410 being along the central longitudinal axis B. Further, a feed point 450 is electrically coupled to the tuning stub 440 and the dual band radiating element 410. The first radiating element 420 has an average pitch that is smaller than an average pitch of the second radiating element 430 and preferably both pitches are constant.

The tuning stub 440 and dual band radiating element 410 are directly coupled to the feed point 450. In this embodiment, the tuning stub is proximal to the dual band radiating element 410 that is in the form of a helical coil. Further, the tuning stub 440 has a total length of at least one twenty fifth of a total effective length of the dual band radiating element. Again, the total effective length of the dual band radiating element 410 is determined when it is unwound or uncoiled into a straightened length. Similarly, the total length of the tuning stub 440 is determined when it is unwound or uncoiled into a straightened length

In FIG. 5 there is illustrated a schematic representation of a third embodiment of the antenna 129, detached from the wireless communication device, the overmold 202 and dielectric sleeve 20 being removed for illustration purposes. The antenna 129 is a fixed antenna operable in at least two frequency bands and comprises a dual band radiating element 510 with a first radiating element portion 520 and a second radiating element portion 530 having a different length than that of the first radiating element portion. The second radiating element portion 530 preferably provides for tuning to a DCS system at an 1800 MHz frequency band (a second frequency) and it is electrically coupled to the first radiating element portion 520 that preferably provides for tuning to a GSM system in a 900 MHz frequency band (a first frequency).

The antenna 129 also has a turiing stub 540, proximal to the dual band radiating element 510, and the tuning stub 540 has a stub axial length AXL3 parallel with a central longitudinal axis C of the dual band radiating element 510. The stub axial length AXL3 does not exceed one sixth of an axial length AL3 of the dual band radiating element 510, the axial length AL3 of the dual band radiating element 510 being along the central longitudinal axis C. Further, a feed point 550 is electrically coupled to the tuning stub 540 and the dual band radiating element The dual band radiating element 510 is in the form of a helical coil and the first radiating element 520 has an average pitch that is smaller than an average pitch of the second radiating element 530. Preferably, both pitches are constant. The tuning stub 540 and dual band radiating element 510 are directly coupled to the feed point 550.

In this embodiment, the tuning stub is bent conductor with at a straight section 460 located proximal to and along a central longitudinal axis C of dual band radiating element 510. Further, the tuning stub 540 has a total length of at least one twenty fifth of the total effective length of the^' dual band radiating element. As will be apparent to a person skilled in the art, the total length of the tuning stub 540 is the sum of the lengths of sections 541, 542 and 543 that form the stub 540.

In FIG. 6 there is illustrated a schematic representation of a fourth embodiment of part of an antenna detached from the wireless communication device. The antenna is a fixed antenna operable in at least two frequency bands and comprises a dual band radiating element 610 in the form a meander and comprises a first radiating element portion 620 and a second radiating element portion 630 having a different length than that of the first radiating element portion. The second radiating element portion 630 preferably provides for tuning to a DCS system at an 1800 MHz frequency band (a second frequency) and it is electrically coupled to the first radiating element portion 620 that preferably provides for tuning to a GSM system in a 900 MHz frequency band (a first frequency).

The antenna also has a tuning stub 640, proximal to the dual band radiating element 610, and the tuning stub 640 has an axial length

AXL4 parallel with a central longitudinal axis D of the dual band radiating element 610. The stub axial length AXL4 does not exceed one sixth of an axial length AL4 of the dual band radiating element 610, the axial length AL4 of the dual band radiating element 610 being along the central longitudinal axis D. Also, a feed point 650 is electrically coupled to the tuning stub 640 and the dual band radiating element 610. The first radiating element 620 has an average pitch that is smaller than an average pitch of the second radiating element 630 and preferably both pitches are constant. The tuning stub 640 and dual band radiating element 610 are directly coupled to the feed point 650.

In this embodiment, the tuning stub 640 is meander located with its axis X substantially parallel to a central longitudinal axis D of dual band radiating element 610. The tuning stub 640 is proximal to the dual band radiating element 610 and need not necessarily be a meander and it may be of a shape such as the stub shape in the embodiment of FIG. 5 with only part of its length (a straight section) being substantially parallel to a central longitudinal axis D. Furthermore, the dual band radiating element 610 and tuning stub 640 are each formed on a foldable substrate 660, and the tuning stub 640 is has a total length of at least one twenty fifth of the total effective length of the dual band radiating element 610. As will be apparent to a person skilled in the art, the total effective length of the dual band radiating element 610 is determined by the sum of the combined lengths of each part (each straight section in this embodiment) of the dual band radiating element 610. Similarly, the total effective length of the tuning stub 640 is determined by the sum of its combined lengths of each part (each straight section in this embodiment).

Further to the above, the tuning stub 640 and feed point 650 are also formed on the foldable substrate 660. The foldable substrate 660 is bent to form a tube surrounding the dielectric sleeve 204 and forms the antenna 129 when when mounted to the threaded portion 206 and covered by the overmold 202.

Turning now to FIG. 7, a matching network or circuit and transmit/ receive switch 130 is shown in more detail. In particular, a matching network 1002 comprising a capacitor 1004 and an inductor 1006. In order to function as a matching network for the GSM and DCS bands, capacitor 1004 could be approximately 4.7 pf while inductor 1006 is approximately 8.2 nH, for example. The a matching circuit , in use, is coupled to the feed point of the antenna for matching the first radiating element portion and the second radiating element portion. Another benefit of the matching network is that the inductor provides a DC path for providing static protection. Finally, any conventional transmit/receive switch 1008 could be used according to the present invention.

Advantageously, the dimensions, configuration and location of the tuning stub, relative to the dual band radiating element, provides for both a sufficiently wide bandwidth and adequate near and far field radiated energy. The detailed description provides a preferred exemplary embodiment only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the detailed description of the preferred exemplary embodiment provides those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

WE CLAIM:

1. A fixed antenna operable in at least two frequency bands, the antenna comprising: a dual band radiating element with a first radiating element portion and a second radiating element portion having a different length than that of the first radiating element portion, the second radiating element portion being electrically coupled to the first radiating element portion; a tuning stub having a stub axial length parallel with a central longitudinal axis of the dual band radiating element, said stub axial length not exceeding one sixth of an axial length of the dual band radiating element, said axial length of the dual band radiating element being along the central longitudinal axis; and a feed point electrically coupled to said tuning stub and said dual band radiating element, wherein the first radiating element portion provides for tuning into a first frequency and the second radiating element portion provides for tuning into a second frequency.

2. The fixed antenna of claim 1 wherein tuning stub is directly coupled to said feed point.

3. The fixed antenna of claim 1 wherein said dual band radiating element is directly coupled to said feed point.

4. The fixed antenna of claim 1 wherein said dual band radiating element is coupled to said feed point through said tuning sub.

5. The fixed antenna of claim 1 wherein said dual band radiating element is a meander.

6. The fixed antenna of claim 1 wherein said dual band radiating element is a helical coil.

7. The fixed antenna of claim 5 wherein the first radiating element has an average pitch that is smaller than an average pitch of the second radiating element.

8. The fixed antenna of clai 6 wherein the first radiating element has an average pitch that is smaller than an average pitch of the second radiating element.

9. The fixed antenna of claim 1 wherein said tuning stub is a straight conductor located along the central longitudinal axis of said dual band radiating element.

10. The fixed antenna of claim 1 wherein the tuning stub is a straight conductor located with its length substantially parallel to the central longitudinal axis of the dual band radiating element.

11. The fixed antenna of claim 1 wherein the tuning stub has a straight section substantially parallel to the central longitudinal axis the dual band radiating element.

12. The fixed antenna of claim 1 wherein the tuning stub has a straight section located along the central longitudinal axis of the dual band radiating element.

13. The fixed antenna of claim 1 wherein the tuning stub has a total length of at least one twenty fifth of the total effective length of the dual band radiating element.

14. The fixed antenna of claim 8 wherein the pitch of said first radiating element portion is constant.

15. The fixed antenna of claim 8 wherein the pitch of said second radiating element portion is constant.

16. The fixed antenna of claim 13 wherein the tuning stub is a meander.

17. The fixed antenna of claim 13 wherein the hining stub is a helical coil.

18. A wireless communication device adapted to operate in at least two frequency bands comprising: a transceiver having a housing; a dual band radiating element mounted to said housing, the dual band radiating element having a first radiating element portion for tuning into a first frequency and a second radiating element portion having a different length than that of the first radiating element portion for tuning into a second frequency, the second radiating element portion being electrically coupled to the first radiating element portion; a tuning stub having a stub axial length parallel with a central longitudinal axis of the dual band radiating element, said stub axial length not exceeding one sixth of an axial length of the dual band radiating element, said axial length of the dual band radiating element being along the central longitudinal axis; and A feed point electrically coupled to said tuning stub and said dual band radiating element; and a matching circuit coupled to said feed point for matching said first radiating element portion and said second radiating element portion.

19. A wireless communication device of claim 18, wherein the tuning stub has a total length of at least one twenty fifth of the total effective length of the dual band radiating element.

20. A wireless communication device of claim 19 wherein the tuning stub is a meander.

21. A wireless communication device of claim 19 wherein the tuning stub is a helical coil.