WO1999003169A1

WO1999003169A1 - A retractable antenna

Info

Publication number: WO1999003169A1
Application number: PCT/US1997/012537
Authority: WO
Inventors: Kenneth D. Simmons
Original assignee: Centurion International, Inc.
Priority date: 1997-07-09
Filing date: 1997-07-09
Publication date: 1999-01-21
Also published as: AU3670497A

Abstract

A retractable antenna (10) for use with a communications device such as a cellular telephone is described and which may be moved from a fully extended position to a fully retracted position with respect to the telephone housing. The telephone circuitry utilizes a matching circuit (12) to match a high impedance when the antenna (10) is in the extended position. When the antenna is in the retracted position, it changes from a series resonance circuit to a parallel resonance circuit so that it may match the low impedance.

Description

TITLE: A RETRACTABLE ANTENNA

Background of the Invention

1. Field of the Invention The present invention relates to portable communication equipment that utilize retractable antennas. More particularly, the present invention relates to antennas for portable communication equipment that provide performance for the selected mode, retracted or extended.

2. Description of the Related Art There are at least six related designs commonly used in the field of retractable antennas. Perhaps the simplest design is the fixed length linear whip radiator that has an electrical contact on the one end, which makes contact with an electrical connector when the radiator is pulled out of the electronic device. In such a design, retraction of the radiator is accomplished by pushing the whip radiator downwardly from its connection with the connector and into the electronic device.

A further design in the prior art is the telescopic whip that is used for portable consumer products. The telescopic whip generally consists of progressively smaller diameter tubes that fit within the next tube. Such a technique permits the antenna to be collapsed or retracted to a length only slightly longer than the largest diameter tube.

U.S. Patent No. 4,868,576 discloses a third type of design that consists of a linear whip radiator that is air-coupled to a monofilar helical matching device in the extended position. In the retracted mode, the monofilar matching helical device is used as the electromagnetic radiator.

U.S. Patent No. 5,204,687 discloses yet another type of retractable antenna. U.S. Patent No. 5,204,687 describes the retractable antenna as being a 1/4 wavelength retractable antenna that consists of a thin linear radiator having an isolated, short monofilar helical radiator on the end. In the extended mode of operation, the thin linear radiator functions as a whip radiator having approximately a 1/4 wavelength electrical length. The heHcal radiator section is positioned on the upper end of the linear radiator and is isolated therefrom by a short section of dielectric preventing the helical radiator from being in the electrical circuit when the antenna is extended. When the antenna is in the retracted mode, the heHcal radiator is in the electrical circuit due to the retraction of the Hnear radiator into the electronic device with the heHcal radiator's electrical connection being made by a short metal tube below the heHcal radiator.

Yet another type of retractable antenna is that manufactured by Centurion International, Inc. of Lincoln, Nebraska, that consists of a 1/2 wavelength thin Hnear radiator with a short monofilar heHcal radiator connected to the end. In either mode of operation, retracted and extended, the entire antenna package is in the electrical circuit.

Summary of the Invention

A retractable antenna for a portable communication device such as a ceUular telephone, two-way radio, etc., is provided which offers maximum performance in the selected mode of operation, retracted or extended. The maximum performance is accompHshed by an integrated matching circuit within the communication device which has two contact positions. One contact position is for series matching of a high impedance load, i.e., the whip in the extended mode. In the retracted mode, both contacts serve to modify the circuit so that it is a paraUel resonance circuit to match a lower impedance than the extended antenna. This provides proper impedance match in both positions, thereby minimizing mismatch losses in either case.

It is therefore a principal object of the invention to provide an improved antenna.

Another object of the invention is to provide a retractable antenna which offers maximum performance in the selected mode of operation, retracted or extended. Yet another object of the invention is to provide a retractable antenna which offers maximum performance in the selected mode of operation, retracted or extended, which is accompHshed by an integrated matching circuit within the communication device providing two contact positions. Yet another object of the invention is to provide a matching circuit described above wherein in the retracted mode, both contacts serve to modify the circuit so that it is a paraUel resonance circuit to match a lower impedance than the extended antenna.

Yet another object of the invention is to provide a retractable antenna which has a proper impedance match in either the extended or retracted positions.

These and other objects wiH be apparent to those skilled in the art.

Brief Description of the Drawings

Figure 1 is a perspective view of the antenna of this invention; Figure 2 is a longitudinal cross-sectional view of the antenna of Figure 1;

Figure 3 is an exploded perspective view of the antenna of Figure 1;

Figure 4 is a longitudinal sectional view of the antenna illustrating both of the contacts of the matching circuit of the telephone circuitry being in RF engagement with the connector at the lower end of the antenna; and Figure 5 is a view similar to Figure 4 except the antenna has been moved to its fuUy retracted position.

Description of the Preferred Embodiment

The antenna of this invention is referred to generaUy by the reference numeral 10 and is designed to be used with portable communication equipment utilizing retractable antennas. More particularly, the antenna 10 is designed to be used with a ceUular telephone which would include the conventional internal telephone circuitry. The only modification to the conventional telephone circuitry is the utiHzation of a matching circuit referred to generaUy by the reference numeral 12 and which includes a pair of spring contacts 14 and 16 as wiU be described in more detail hereinafter.

Antenna 10 includes a lower metaUic connector 17 which provides the electrical path from the communication device into the whip antenna in the extended position as wiU be described in more detail hereinafter. Connector 17 includes a stop 18 and a bore 20 formed therein.

The numeral 22 refers to the metallic whip section or radiator which is RF connected to the metaUic connector 17, as illustrated in Figure 5, in conventional fashion. Radiator 22 is enclosed by a sheath of dielectric material referred to generaUy by the reference numeral 24. MetaUic sleeve 26 is RF connected to the upper end of the radiator 22 and has a head portion 28 provided at the upper end thereof. If desired, head portion 28 may be in the form of a separate bushing which is secured to the upper end of the sleeve 26.

The numeral 30 refers to a monofilar heHcal radiator which is RF connected to the head portion 28, as seen in Figures 4 and 5. HeHcal radiator 30 is enclosed by dielectric overmold or coating 32 in conventional fashion. SHdable connector 34 is provided and has external threads 36 adapted to be threaded into the conventional receptacle at the upper end of the communications device and which is RF connected to the telephone circuitry of the communications device in conventional fashion. When the antenna is in its fuUy extended position, such as iUustrated in Figure 4, only contact 14 is in electrical contact with the connector 17. When the antenna is moved to its fuUy retracted position, such as iUustrated in Figure 5, both of the contacts 14 and 16 engage the sleeve 26.

In some instances, contact 14 could engage connector 34 if desired. In operation, the antenna 10 works in conjunction with the matching circuit 12. In the extended mode, antenna 10 utiHzes a T-type matching circuit to match the feed impedance of the antenna. In the retracted mode, the matching circuit transfers from a series resonance circuit to a paraUel resonance circuit which is still active in the circuit. As stated, there are two contacts in the matching circuit, namely contacts 14 and 16, one on the high impedance side and one on the low impedance side. When the low and high impedance sides are in the retracted mode, both are in contact with the antenna through the sleeve 26. Matching of the lower impedance is not quite 50 ohms. The antenna illustrated in the drawings is utiHzed as a 1/2 wave appHcation, but it may be of any length. As stated, the matching circuit within the communication device wiU match a high impedance when the antenna is in the extended position. When the antenna is in the retracted position, it wiU change from a series resonance circuit to a paraUel resonance circuit so that it may match the low impedance.

The antenna of this invention does not have to be a 1/2 wave or a multiple 1/2 wave antenna. The antenna is driven by a design of the matching circuit and the values incorporated therein. When the antenna is extended, a high impedance point is reached when greater than a 1/4 wave is used at which time the impedance point goes up. When the antenna is in the retracted position, an impedance point along the heHcal and the whip section of the antenna is achieved which is lower than the antenna in the extended position.

By utiHzing the matching circuit in both the extended and retracted modes, it is now possible to obtain the best match obtainable to achieve matching performance of the antenna.

Thus it can be seen that the invention accompHshes at least aU of its stated objectives.

Claims

I claim:

1. A retractable antenna for a ceUular telephone including a housing having a receptacle at the upper end thereof which is RF coupled to the telephone circuitry and which has a bore formed therein, comprising: a first metal connector having upper and lower ends; an elongated cable antenna having upper and lower ends; the lower ends of said cable antenna being RF coupled to said first connector; an elongated metal sleeve having upper and lower ends, said metal sleeve being RF coupled to the upper end of said cable antenna; a heHcal antenna positioned at the upper end of said metal sleeve and being operatively RF coupled thereto; an insulating cap means enclosing said heHcal antenna; an insulating sheath means enclosing said cable antenna between said first connector and said metal sleeve; a second metal connector for RF connection to said receptacle and having a bore extending therethrough, said second connector having lower and upper ends, said lower end of said second connector being received within said bore of said receptacle; said retractable antenna being sHdably received within said bore of said second metal connector whereby said retractable antenna is sHdably movable, with respect to the telephone, from a fuUy retracted position to a fuUy extended position; said heHcal antenna being RF coupled to said receptacle and the telephone circuitry, through said metal sleeve, when said retractable antenna is in its fuUy retracted position; said cable antenna and said heHcal antenna element being RF coupled to said receptacle and the telephone circuitry, through said first connector, when said retractable antenna is in its fuUy extended position; said telephone circuitry including a matching circuit having a first impedance contact and a second impedance contact; said first connector being in RF engagement with said first impedance contact when said retractable antenna is in its said fuUy extended position; said second connector being in operative RF engagement with said first and second impedance contacts when said retractable antenna is in its said fuUy retracted position.

2. The retractable antenna of claim 1 wherein said matching circuit comprises a series matching circuit when said retractable antenna is in its said fuUy extended position and comprises a paraUel resonance circuit when said retractable antenna is in its said fuUy extended position.