Retractable antenna system

• US 5,374,937 A
• Filed: 01/28/1994
• Issued: 12/20/1994
• Est. Priority Date: 07/08/1991
• Status: Expired due to Term

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Ando, Atsuya, Tsunekawa, Koichi
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): LE, HOANGANH T
• Application Number:
  US08/188,104
• Time in Patent Office: 326 Days
• Field of Search: 343/702, 343/895, 343/901, 343/906, 343/724, 343/725, 343/900, 343/752, 343/749, 343/850, 343/852, 343/853, 343/858, 343/860
• US Class Current: 343/702
• CPC Class Codes: H01Q 1/244 extendable from a housing along a given path

Abstract

An antenna element (1) has a linear antenna rod (1b) of predetermined length and a top load (1a) at the end of the rod (1b). The antenna element (1) takes a first position in which the rod is extended out of a housing (8), and a second position in which the rod is retracted within the housing. There are provided two feed terminals (5, 6) along the rod (1b). The first feed terminal (5) is essentially matching the impedance of a node point in a current distribution in the resonant antenna element, and feeds the antenna element at the end of the rod in the first position. The second feed terminal (5) is matching the impedance of an anti-node point in a current distribution in the resonant antenna element, and feeds the antenna element at approximate center of the rod in the second position. A first feed terminal (5) might contact the rod in a second position, but it does not feed the same because of mismatching. Thus, the antenna system is always fed with matched condition whether it is extended or retracted, through the automatic switching of feed terminals.

Claims

1. A retractable antenna system for a portable transceiver having a housing for holding an inner circuit and an antenna system connected with said inner circuit, comprising:

an essentially linear antenna element having an electrical length essentially the same as an integer multiple of a half wavelength of an operating frequency of the transceiver, said antenna element having a first position extended from the housing through an outlet thereof and a second position in which most of a length of the antenna element is restricted in the housing;

a feed line connected with an output of the inner circuit;

two feed terminals set in the housing along said antenna element so that a first feed terminal is located closer to the outlet of the housing than a second feed terminal; and

at least one matching circuit mounted in the housing and operatively located between said feed line and one of said feed terminals so as to provide impedance matching between said feed line and a corresponding feed terminal contacted to said antenna element, wherein

said matching circuit has a predetermined matching impedance that comprises a first impedance which is almost the same as an impedance of a current node point on said resonant antenna element when said first feed terminal is connected with said matching circuit, and comprises a second impedance which is almost the same as an impedance of a current anti-node point on said resonant antenna element when the second feed terminal is connected with said matching circuit,

in the first position of the antenna element, said first feed terminal matching with the node point in a current distribution of said resonant antenna element,

in the second position of the antenna element, said second feed terminal matching with the anti-node point in a current distribution of said resonant antenna element.

2. An antenna system according to claim 1, wherein said antenna element has an elongated antenna rod, and a conductive top load at an outer extreme end of the antenna rod, and the top load is located outside of the housing in the second position of said antenna element.

3. An antenna system according to claim 2, wherein the top load is a coil with an axis essentially coinciding with a longitudinal direction of the antenna rod.

4. An antenna system according to claim 2, wherein the top load is a flat conductive plate mounted at an extreme end of the antenna rod.

5. An antenna system according to claim 2, wherein the top load has first and second coils connected in series with each other so that a junction of the first and second coils is connected to the outer extreme end of the antenna rod, and a winding direction of the first coil is opposite a winding direction of the second coil.

6. An antenna system according to claim 1, further comprising:

a conductive linear means extending from a minus terminal of said second feed terminal along the antenna rod, the antenna rod and said conductive linear means making a balanced pair cable with an electrical length approximately a quarter wavelength of the operating frequency on the transceiver; and

a third feed terminal which is connected to said conductive linear means and grounded, said third feed terminal being operatively positioned so as to contact an inner extreme end of the antenna rod when in the second position.

7. An antenna system according to claim 6, wherein said conductive linear means is a hollow cylindrical tube, and the antenna rod and said hollow tube operate as a coaxial cable.

8. An antenna system according to claim 1, wherein said antenna rod has a chip for engaging with at least one of said first and second feed terminals, the chip and each of said feed terminals having defined thereon a concave surface and a convex surface, respectively, for engagement with each other so as to have a snap connection of the antenna rod.

9. A retractable antenna system for a portable transceiver, comprising:

a housing for holding an inner circuit;

a linear antenna element having an electrical length substantially equal to an integer multiple of a half wavelength of an operating frequency of the transceiver, said antenna element having a first extended position from said housing through an outlet thereof and a second retracted position in which most of a length of said antenna element is retracted into said housing;

a feed line connected with an output of the inner circuit;

first and second feed terminals positioned in said housing along said antenna element so that the first feed terminal is located closer to the outlet of said housing than the second feed terminal; and

first and second matching circuits mounted in said housing and operatively located between said feed line and said first and second feed terminals, respectively, so as to provide impedance matching between said feed line and a corresponding feed terminal in contact with said antenna element, wherein

said first matching circuit includes a first predetermined matching impedance that comprises a first impedance substantially equal to an impedance of a current node point on said antenna element when resonant in the first extended position of the antenna element when said first feed terminal is connected with said first matching circuit, and

said second matching circuit includes a second predetermined matching impedance that comprises a second impedance substantially equal to an impedance of a current anti-node point on said antenna element when resonant in the second retracted position of the antenna element when said second feed terminal is connected with said second matching circuit.

10. An antenna system according to claim 9, wherein said antenna element includes an elongated antenna rod, and a conductive top load at an outer end of the antenna rod, the top load being located outside of said housing in the second position of said antenna element.

11. An antenna system according to claim 10, wherein the top load is formed as a coil with an axis concentric with a longitudinal direction of the antenna rod.

12. An antenna system according to claim 10, wherein the top load is formed as a flat conductive plate mounted at the outer end of the antenna rod.

13. An antenna system according to claim 10, wherein the top load has first and second coils connected in series with each other so that a junction of the first and second coils is connected to the outer end of the antenna rod, and a winding direction of the first coil is opposite a winding direction of the second coil, and further an axis of the first and second coils is concentric with the longitudinal direction of the antenna rod.

14. An antenna system according to claim 9, further comprising:

a conductive linear means extending from a minus terminal of said second feed terminal along the antenna rod, the antenna rod and said conductive linear means forming a balanced pair cable with an electrical length approximately a quarter wavelength of the operating frequency on the transceiver; and

a third feed terminal which is connected to said conductive linear means and to ground, said third feed terminal being operatively positioned so as to contact an inner end of the antenna rod when in the second position.

15. An antenna system according to claim 14, wherein said conductive linear means is a hollow cylindrical tube, and the antenna rod and said hollow tube operate as a coaxial cable.

16. An antenna system according to claim 9, wherein said antenna rod has a chip for engaging with at least one of said first and second feed terminals, the chip and each of said feed terminals having defined thereon a concave surface and a convex surface, respectively, for engagement with each other so as to have a snap connection of the antenna rod.