WO1999013530A1

WO1999013530A1 - Dual band, panel mount antenna

Info

Publication number: WO1999013530A1
Application number: PCT/US1998/018035
Authority: WO
Inventors: Peng Gong; Kevin M. Campbell; Alvaro Mejia
Original assignee: Andrew Corporation
Priority date: 1997-09-08
Filing date: 1998-08-31
Publication date: 1999-03-18
Also published as: AU9471998A

Abstract

A dual band frequency antenna (10) adapted for panel mounting includes an inner conductive element (68), in the form of an elongated rod and an outer conductive element (70), in the form of a conductive sleeve. In one embodiment, the antenna may be tuned by adjusting the extend to which the inner element (68) projects past the sleeve.

Description

DUAL BAND. PANEL MOUNT ANTENNA

Background of the Invention

The present invention relates generally to antenna systems for use in wireless communication systems. More particularly, the present invention relates to dual and multi- band antennas and antenna systems for use in wireless communication systems.

The expansion of mobile and personal cellular telephone systems has been rapid and widespread during the last few years. Originally, cellular telephone systems were designed to provide communications services primarily to vehicles and thus replace mobile radio telecommunication systems. Advancements in technology and production have sufficiently decreased the costs of cellular service to the point at which cellular telephone service has now become affordable to a majority of the general population. Therefore, a "cellular telephone system" no longer strictly refers exclusively to cellular telephones, which originally were physically attached to and made a part of a vehicle. Cellular telephone now include portable, personal telephones which may be carried in a pocket or purse and which may be easily used inside or outside a vehicle or building.

Traditionally, wireless communication systems have included antenna systems which transmit and receive radiofrequency ("RF") signals within the AMPS frequency bandwidth in the United States (about 824 to about 894 MHz) or the GSM frequency bandwidth in Europe (about 890 to about 960 MHz) . Wireless communication systems which operate in the AMPS or GSM frequency band generally operate in a low frequency band. The wireless communications industry has recently broadened the scope of communications services by providing small, inexpensive, hand-held transceivers that transmit and receive voice and/or data communications, notwithstanding the geographic location of the user. This newer communication system operates at a higher frequency band than the AMPS and GSM frequency bands and has been envisioned to eliminate the need for separate telephone numbers for the home, office, pager, facsimile or car. This system is referred to as a personal communication network/personal communication system ("PCN/PCS") .

With the increased use of wireless communication devices, there has grown a need to extend the capacity and to improve the communication quality and security of the applicable wireless communication system. As such, several countries and communication providers have agreed upon international communication standards and set aside a portion of the ultra-high frequency microwave radio spectrum as frequency bands which are dedicated exclusively for PCN/PCS communication systems. On a worldwide basis, the PCN/PCS frequency band is expected to extend from about 1.5 GHz (1500MHz) to about 2.4 GHz (2400 MHz) . Within that band, individual countries have set aside particular portions of it for their respective PCN/PCS wireless communication systems. For example, Japan has set aside from about 1.49 GHz (1490 MHz) to about 1.521 GHz (1521 MHz), Europe has set aside from about 1.710 GHz (1710 MHz) to about 1.880 GHz (1880 MHz) and the United States has set aside from about 1.850 GHz (1850 MHz) to about 1.990 GHz (1990 MHz) for their PCN/PCS systems.

The bandwidths of these different frequency bands represent approximately 11%, or only about 200 MHz, of the total possible bandwidth set aside for PCN/PCS-type wireless communication systems. The lowest frequency included within this bandwidth is almost two times higher than the standard frequency at which cellular telephone communication systems operate within the United States, namely 800 MHz (i.e., the AMPS frequency band) . Wireless communication systems operating in the PCN or PCS frequency bands typically employ principles of digital communication that have improved their communication quality and strengthened their security over those systems which utilize the lower frequency bands.

An ever increasing number of regions within the United States and Europe now utilize the PCS (United States) or PCN (Europe) frequency bands for wireless communications. In most of those regions, wireless telephone units must be able to operate in both the higher and lower frequency bands, i.e., in both the AMPS and PCS frequency bands in the United States, and in both the GSM and PCN frequency bands in Europe so that a user of such units may selectively choose the frequency band of operation for the unit. Additionally, the units themselves may selectively choose their operating frequency band so that the chosen band matches the frequency of the electromagnetic signals received from a wireless telephone unit placing an incoming call to that particular unit. Under these circumstances, it is desirable to develop antennas that are tuned to resonate within both of the above-identified bands of frequency (i.e., the AMPS and PCS bands for United States-based wireless communication systems and the GSM and PCN bands for European-based wireless communication systems) . One approach would be to use a dual port antenna utilizing two radiators with each radiator being tuned to resonate within a different one of the two respective above-identified frequency bands. Although theoretically feasible, as a practical matter, this type of antenna is undesirable because it would be generally larger than a single radiator system. Furthermore, such an antenna would require two RF signal feed lines resulting in a system more expensive to manufacture, thereby increasing the ultimate cost to the consuming public. In light of these disadvantages, there is a present need for single port, dual band antennas that are tuned to resonate within both frequency bands in the user's particular geographic region: in both of the AMPS and PCS frequency bands in the United States and in both of the GSM and PCN frequency bands in Europe.

There have been some attempts to produce such a dual band antenna in the prior art, but not without certain disadvantages. One type of dual band antenna available in the prior art is one utilizing monopole antennas. Broadband, as opposed to dual band, monopole antennas are widely used in the mobile antenna design industry because of their simple embedding characteristics, their solid mechanical features and their inherent advantages over a ground plane environment.

However, dual band antennas utilizing monopole radiators are unable to maintain the simple structure of a standard broadband monopole antenna and/or obtain the minimum level of efficiency within both of the resonant frequency bands which is necessary for a commercially marketable antenna. As such, the implementation of dual band antenna systems utilizing monopole radiators is commercially impracticable. Significant design modifications are necessary to allow those antenna systems to be marketable and have raised the complexity of the systems as well as their cost. Accordingly, as a practical matter, these antenna systems are not a feasible solution to the above-identified dilemma.

Another prior art dual band antenna is one using microstrip antenna technology. These antennas typically include two microstrip antennas. As such, they typically are not single port dual band antennas, but are rather dual port antennas. This provides a major disadvantage because, as described above, it is necessary to include an additional RF signal feed line for such antennas. A standard microstrip antenna configuration uses two conductive layers of material separated by a passive substrate such as a printed circuit board. One of the conductive layers serves as the radiator portion of the antenna, while the other conductive layer serves as a ground plane.

Further, dual band antennas utilizing microstrip antennas are classified as directional antennas since signals are transmitted from and received by the antenna in a single direction, usually in a direction generally extending from the face of the radiator portion of the antenna and away from its ground plane portion. Wireless communication systems that use an omni-directional antenna rather than a directional antenna are preferred for their inherent advantages. Yet another prior art dual band antenna is one utilizing a monopole-type radiator connected to an external coupling element which is capacitively coupled with an internal coupling element. The internal coupling, element is, in turn, typically connected to the transceiver by an RF signal feed line. These antennas are typically glass mounted and have produced a considerable number of disadvantages.

These glass mount antennas typically utilize two modules which are mounted on the outside and inside surfaces, respectively, of a window glass to transmit signals through the window glass between the opposing modules. In these capacitively coupled antennas, two metal plates are present in the modules and cooperate to act as a capacitor to transmit RF energy through the intervening window glass, which is a dielectric material. The use of these antennas typically requires a ground plane. Since the majority of glass mount surroundings are unable to provide an ideal ground plane for the monopole type radiator section of the antenna, the antenna's performance is degraded. Furthermore, the physical characteristics of the dielectric substrate to which the antenna is mounted (such as an automobile rear window) generally inhibits a sufficient capacitive coupling between the internal and external coupling elements in both frequency bands. As such, loss occurs in the prior art glass mount antennas because they must propagate electromagnetic signals through a dielectric material and match the impedance of the external monopole-type radiator. In light of the aforementioned shortcomings of available dual band antennas, there is clearly a need for a coaxial dual band antenna having a tuning element coaxially disposed within a outer radiating sleeve element. The present invention is therefore directed to a body mount dual band antenna that transmits and receives in both the AMPS/GSM and PCS/PCN communication systems.

It is therefore a general object of the present to provide a new and improved dual band antenna.

Another object of the present invention is to provide an externally mounted dual band antenna having a tuning element positioned within a radiating sleeve element.

Still another object of the present invention is to provide a dual band, omni-directional antenna that is inexpensive to manufacture. It is yet still another object of the present invention to provide a dual band antenna having a radiating structure which permits transmission and reception of RF signals in two separate and distinct frequency bands, such as either of both the GSM and PCN frequency bands or both the AMPS and PCS frequency bands.

Yet a still further object of the present invention is to provide a dual band antenna which permits selection of the two resonant frequency bands for the antenna system.

fiιιτnm»τγ of the Invention

In one principal aspect of the present invention and as exemplified by a first embodiment, a dual band antenna is provided having a primary radiator in the form of a conductive sleeve and a secondary radiator in the form of an elongated tuning element that is disposed within the conductive sleeve in a coaxial relationship therewith. The tuning element extends beyond the end of the conductive sleeve and effects a phase shift that results in the dual band operation of the antenna. The extent to which the tuning element exceeds the conductive sleeve determines the frequencies of operation.

In another principal aspect of the present invention and as exemplified by a second embodiment, a half-wavelength dual band antenna includes a conductive sleeve that surrounds a central element in a coaxial relationship. The central element and the sleeve are connected at one common end where they are joined to a phasing coil having its own radiator element. These and other features, objects and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numerals identify like elements throughout.

Brief Description of the Drawings

In the course of the following detailed description, reference will be frequently made to the accompanying drawings in which:

FIG. 1 is a partial perspective view of dual band antenna constructed in accordance with the principles of the present invention mounted on the trunk of a vehicle;

FIG. 2 is a cross-sectional view of the antenna of FIG. 1 taken along line 2-2 thereof;

FIG. 3 is an exploded view of the dual band antenna shown in FIG. 1;

FIG. 4 is a perspective view of an alternate embodiment of a dual band antenna constructed in accordance with the principles of the present invention in place upon the trunk of a vehicle;

FIG. 5 is a cross-sectional view of the antenna of FIG. 4 taken along line 5-5 thereof;

FIG. 6 is an exploded view of the antenna of FIG. 4; and,

FIG. 7 is an enlarged detail view of the inner conductive rod of the antenna of FIG. 6 showing the attachment of the conductive connector thereto.

Detailed Description of the Preferred T^hodiments

FIG. 1 illustrates a dual band antenna system 10 constructed in accordance with the principles of the present invention that permits wireless transmission and reception of RF signals in two distinct bands of frequency. The antenna system 10 incudes an antenna 12 and a mounting assembly 14 for mounting the antenna 12 on a vehicle 11, and particularly on a body panel or similar mounting surface, such as the vehicle trunk 16, as illustrated in FIG. 1. In instances where the mounting surface is metal, it also serves as a groundplane for the antenna 10. Although the antenna 12 is described herein as using a through-mounting assembly 14 that extends through a hole drilled through the trunk panel 16, it will be appreciated that the antenna 12 may be mounted in any manner well known in the art and incorporate a magnetic mount or lip mount.

The antenna system 10 includes an RF signal feed line, such as a coaxial cable 20 having a coaxial connector 22 terminated to one end thereof that enables the antenna 12 to be connected to a transceiver unit (not shown) within the vehicle 11. On its opposite end, the coaxial feedline 20 is electrically connected with the mounting assembly 14 in a manner well known in the art. Specifically, the outer shield- like conductor 21 of the feedline 20 is electrically connected to a grounded, interior housing portion 26 having an integral rim 28, both of which are maintained within the vehicle 11. A neck portion 30 extends upwardly from the rim 28 and includes a threaded section 32 that engages a like threaded section positioned on the inner circumference of an annular ground connector 36. When the retainer 36 is threadedly engaged to the neck portion 30, the retainer 36 is also electrically connected with the outer sheath conductor 21 of the feed cable 20 by way of neck portion 30, among other things.

The outer circumference of the retainer 36 is threaded at 38. A washer 39 is provided at the bottom of the retainer 36 to secure the mounting assembly 14 with a ground plane 42 (e.g., the trunk panel 16 of FIG. 1) by tightening the retainer 36 against the rim 28. In this assembled arrangement as shown in FIG. 2, the ground plane 42 (trunk panel 16) is electrically connected to the rim portion 28, neck portion 30, retainer 36 and the outer shield conductor 21 of the feed cable 20.

A hollow exterior housing 44 encloses the retainer 36 to seal it from the environment, and it includes a lower rim 46 and a tapered portion 48 which extends upwardly at a reduced diameter. The lower rim 46 has internal threads 52 that engages the threaded exterior 38 of the retainer 36.

The inner conductor 23 of feedline 20 is electrically connected to a transceiver unit (not shown) within the vehicle at its one end 22 and terminates in a conductive pin 54 at its other end. The conductive pin 54 extends out of the cable 20 to a point where it may be inserted within the female connection slot 56 of a conductive receptacle 58.

The conductive pin 54 extends coaxially within the neck portion 30 of the mounting assembly 14 and is electrically isolated from it by an electrical isolator such as a cylindrical dielectric spacer 60. The housing 44 includes a threaded aperture 50 that is sized to accommodate the pin receptacle 58 and a threaded neck portion 62 thereof. The antenna 12 further includes an electrically conductive tuning element 64 that engages the pin insert 58. The tuning element 64 includes a conductive whip holder 66, preferably brass or brass-filled, having an axial threaded passage 67 that engages the external threads of the pin receptacle 58. The tuning element 64 further includes a metal rod 68 that extends from the whip holder 66. Inasmuch as all of the components of the tuning element 64 are conductive (typically metal) , the entire tuning element 64 is in electrical communication with the inner conductor of coaxial cable 20 when the whip holder 66 is threaded onto the pin insert 58.

An electrically conductive metal sleeve 70 is positioned over tuning element 64 so that the tuning element rod 68 extends through the sleeve 70 in a coaxial relationship therewith. The conductive sleeve 70 and the tuning element 64 are electrically connected to each other because the inner wall 72 of the conductive sleeve 70 contacts the outer surface of whip holder 66, preferably in a press-fit fashion. In this embodiment, the conductive sleeve 70 and tuning element 64 have different lengths so that, when assembled, a portion 69 of rod 68 extends above the upper edge 74 of the conductive sleeve 70. The radiating structure 12 of antenna system 10 is therefore able to operate as a dual band radiator because the RF signals radiating from the inner rod 68 and the conductive sleeve 70 have their own phase, so that the sleeve 70 will add a phase component to the signals to and from the rod 68. Consequently, when the two respective signals are combined, their resonant frequency response falls within two separate frequency bands. Although both radiate radiofrequency ("RF") energy, the conductive sleeve 70 serves as the primary radiator for the antenna and the tuning element 64 permits the radiating structure to effect dual band operation. The antenna 12 as shown is a quarter-wavelength antenna which has a zero decibel (0 db) gain in both its lower and higher frequency bands. Those skilled in the art will recognize that the two resonant frequency bands are determined by, among other things, the effective electrical length of the antenna radiating structure 12 , including the length of its respective elements.

A plastic cap 76 is included to protect antenna system 10 from the environment and is placed over the tuning element rod 68 until a flange 78 of the cap 76 abuttingly engages the upper rim 74 of sleeve 70.

FIG. 4 illustrates a second embodiment of a dual band antenna 100 and antenna system 110 constructed in accordance with the principles of the present invention. This antenna 100 differs from the first embodiment in that the antenna 100 has a zero decibel gain (0 db) in its lower frequency band and a three decibel gain (3 db) in its higher frequency band. The antenna 100 also includes a half- wavelength radiating structure. The second antenna system 110 has a radiating assembly 112 and a mounting assembly 114 that permits mounting of the antenna 100 to a ground plane panel of a vehicle 118, such as a trunk panel 116. The antenna system 110 includes an RF signal feed line such as a coaxial cable 120 that terminates in a coaxial connector (not shown) at its far end that permits the connection thereof to a transceiver unit (not shown) . On its opposite end, the feed cable 120 is electrically connected to the mounting assembly 114 by connecting the outer sheath conductor of the cable 120 to interior housing 126.

The inner housing 126 has an elongated neck portion 130 that extends upwardly from a rim 128 and includes a threaded section 132 that is sized and adapted to atingly engage with an interior threaded section 134 of a circular retainer 136. When the retainer 136 engages the neck portion 130, the retainer is electrically connected to the outer sheath conductor of coaxial cable 120 by way of the neck portion 130. These elements contact the body panel 116 of the vehicle 118 and thus are grounded.

The retainer 136 also includes an outer threaded section 138 that engages an exterior housing 144. A washer 139 provided on the bottom surface of the retainer 136 to firmly secure contact between the housings 126 and 146 with a ground plane e.g., trunk panel 116 (FIG. 4), by tightening the retainer 136 on to the inner housing rim 128. When so assembled, the ground plane body panel 116 is electrically connected to the rim 128, the threaded neck portion 130, the retainer 136 and the outer sheath conductor of coaxial cable 120.

The exterior mounting housing 144 is hollow and has a rim portion 146 and an upper tapered portion 148 that reduces the diameter of the exterior housing 144. The rim portion 146 is internally threaded at 152 and is sized to threadedly engage the outer threaded section 138 of the retainer 136 during assembly. As for the radiating structure 112 of the antenna

100, the inner conductor of coaxial cable 120 has a central conductor that is electrically connected to a transceiver unit (not shown) in the vehicle and to a conductive pin 154 at its other end. The conductive pin 154 extends from the feed cable 120 to a point where it can be inserted within a receptacle

156 of a pin insert 158. The conductive pin 154 is coaxially positioned within the inner housing neck portion 130 and is isolated from it by an electrical isolator such as a dielectric spacer 160. The exterior housing 144 has an opening 150 sized to receive the threaded neck 162 of the pin insert 158.

An electrically conductive first radiating element, generally 164 threadedly engages the pin insert 158 and includes a conductive whip holder 166, preferably brass or bras-filled. The whip holder 166 has an internal threaded opening that engages the external threads of the pin insert 158. The first radiating element 164 also includes a metal rod 168 that extends up from the top of whip holder 166 to an electrically conductive coil holder 169. In this second embodiment, the rod 168 serves primarily as a radiating element of the antenna 100 rather than a tuning element and the top thereof preferably lies flush with the top 170 of the conductive coil holder 169. This structural feature may be accomplished through the process described in FIG. 7.

One preferred way of attaching the interior rod 168 to the coil holder 169 in a manner that assures that it will be flush with the top of the coil holder 169 is to subject the end 167 of the rod 168 to a swaging process in order to enlarge the end 167 of the rod 168 to an extent that it has a diameter slightly larger than that of the rod 168. The coil holder 169 may then be slid up the rod 168 under pressure into firm engagement wit the enlarged end portion 167 to effect a flush mounting.

When the whip holder 166 is screwed onto the exterior housing 144, the first, or inner, radiating element 164 is in electrical communication with the inner, conductor of coaxial cable 120. The second radiating element in the form of a conductive sleeve 171 is coaxially disposed around a portion of rod 168. The conductive sleeve 171 preferably has a uniform diameter throughout its length and is press-fit or otherwise connected to coil holder 169 so that it is in electrical communication with the interior rod 168 through the coil holder and so that a portion of the rod extends below the lower rim 172 of the sleeve. In this half-wavelength radiating structure 112 depicted, the conductive sleeve 171 is spaced above the whip holder 166. The inner rod 168 is coaxially spaced away from sleeve 171 by an electrical isolator, such as a flexible boot 175. In addition to serving as a spacer, the flexible boot 175 also provides environmental protection.

A third conductive radiating element 176 is present and is supported by the top coil holder 169 and contacts this third radiating element 176 has a coil 178 that rests upon the coil holder 169 and is covered by a flexible boot 180. The third radiating element 176 includes a metal rod portion 182 which extends from the coil 178 and may have its end covered by a cap 184 for protection.

During operation of antenna 100, the coil portion 178 of the third radiating element 176 introduces a phase shift to the radiating RF signal which, along with the other elements of radiating structure 112, causes antenna system 110 to operate in two separate frequency bands and achieve the aforementioned 3 db gain in its higher frequency band.

Although the present invention have been shown and described with reference to two preferred embodiments, those skilled in the art will recognize that changes and modifications may be made therein without departing from its true spirit and scope, which is defined by the appended claims.

Claims

WE CLAIM╧è

1. A dual band mast antenna for transmitting and receiving signals in two separate and distinct frequency bands, comprising: a mounting assembly for mounting the antenna to a mounting surface, an electrically conductive tuning element extending up from the mounting assembly, an electrically conductive sleeve extending up from said mounting assembly, the tuning element including a conductive rod disposed within said conductive sleeve, said conductive sleeve extending upwardly away from said mounting assembly and terminating in a free end and said tuning element conductive rod having a free end that extends past said conductive sleeve free end.

2. The antenna of claim 1, wherein said antenna includes a whip holder that engages said mounting assembly and said tuning element, the whip holder having a passage extending axially therethrough, said tuning element conductive rod being received in said passage.

3. The antenna of claim 2 , wherein said conductive sleeve engages said whip holder by press-fitting.

4. The antenna of claim 1, further including an additional conductive rod disposed exterior of said conductive sleeve, said additional conductive rod including a phasing coil that is electrically connected to both of said conductive sleeve and said tuning element conductive rod.

5. The antenna of claim 4, further including a conductive cylindrical connector that engages said conductive sleeve free end and said tuning element conductive rod free end.

6. The antenna of claim 5, wherein said additional conductive rod includes a phasing coil and said conductive connector includes a support for said phasing coil.

7. The antenna of claim 6, wherein said conductive sleeve is interposed between said mounting assembly and said phasing coil.

8. The antenna of claim 1, further including a dielectric spacer that engages said tuning element conductive rod and maintains said conductive sleeve and tuning element conductive rod in a coaxial relationship.

9. The antenna of claim 1, wherein said mounting assembly includes interior and an exterior housing members that are adapted to engage each other on opposite sides of a vehicle body panel.

10. The antenna of claim 5, wherein said tuning element conductive rod is received within said cylindrical connector but does not project past an end thereof.

11. A dual band antenna for transmitting and receiving signal in two separate and distinct frequency bands, the antenna being adapted for mounting on a body panel of a vehicle, said antenna comprising: a base for mounting to the body panel, the base being electrically connected to said body panel, a radiator in the form of an elongated first conductive rod extending up from said base, said first conductive rod being electrically connected to an inner conductor of a coaxial feedline that engages said base, a hollow conductive metal sleeve having opposing first and second ends, the conductive sleeve being disposed around said first conductive rod, said conductive sleeve having a preselected length whereby a portion of said first conductive rod projects past said conductive sleeve first end, said conductive sleeve and first conductive rod being electrically connected at said second end of said conductive sleeve;

12. The dual band antenna as claimed in claim 11, further including a conductive holder in which said first conductive rod is received, said conductive holder engaging said conductive sleeve second end.

13. The dual band antenna as claimed in claim 12, wherein said conductive holder engages said base.

14. The dual band antenna as claimed in claim 12, wherein said conductive holder is disposed above said base.

15. The dual band antenna as claimed in claim 14, wherein said conductive holder is spaced apart from said base.

16. The dual band antenna as claimed in claim 12, further including a second conductive rod, the second conductive rod including a phasing coil, the phasing coil engaging said conductive holder.

17. The dual band antenna as claimed in claim 16, wherein said first conductive rod extends through said conductive holder without extending past one end thereof.

18. The dual band antenna as claimed in claim 12, further including an insulative spacer member disposed on said first conductive rod and spaced apart from said conductive holder> said spacer member and said conductive holder cooperatively supporting said first conductive rod within said conductive sleeve.

19. The dual band antenna as claimed in claim 18, wherein said spacer member is disposed on said conductive sleeve at said conductive sleeve first end.

20. The dual band antenna as claimed in claim 18, wherein said spacer member and said conductive holder cooperatively support said first conductive rod in a coaxial relationship within said conductive sleeve.

21. The dual band antenna as claimed in claim 12, wherein said antenna is a quarter wavelength antenna.

22. The dual band antenna as claimed in claim 12, wherein said antenna is a half wavelength antenna.