Electrical antenna assembly and electrical device including same

Abstract: An electrical antenna assembly includes a rod antenna (10), and a coil antenna (20) carried by one end of the rod antenna. The coil antenna has a dielectric core carried by the rod antenna and preformed with a helical recess, an electrically-conductive helical coil seated in the recess, an electrical connector connected to one end of the helical coil by a crimped solderless connection, and a dielectric sleeve enclosing the helical coil.

Description: The present invention relates to an electrical antenna assembly, and also to an electrical device including such an antenna assembly. The invention is particularly useful with respect to the retractable-type antenna assembly described in our US Patent 5,204,687, and is therefore described below with respect to this application. Our prior US Patent 5,204,687 discloses an electrical antenna assembly particularly useful in a CT2 cordless telephone, including a rod antenna and a coil antenna carried by one end of the rod antenna. The whole antenna assembly is movable within a housing to either a retracted position within the housing wherein substantially only the coil antenna is disposed externally of the housing, or to an extended position wherein substantially the complete rod antenna and coil antenna are disposed externally of the housing. Both the rod antenna and coil antenna are pretuned to the same frequency, the arrangement being such that in the retracted position of the antenna assembly the coil antenna is enabled for use in short range operation, and in the extended position of the antenna assembly the rod antenna is enabled for use in long range operation. In the preferred embodiment described in that patent, the coil antenna and the rod antenna are both of quarter wavelength. An object of the present invention is to provide an electrical antenna assembly of the foregoing rod/coil type but having a number of advantages as will be described more particularly below. According to the present invention, there is provided an electrical antenna assembly comprising: a rod antenna, and a coil antenna carried by one end of the rod antenna; characterized in that the coil antenna includes a dielectric core carried by one end of the rod antenna and preformed with a helical recess, an electrically-conductive helical coil seated in the recess, an electrical connector connected to one end of the helical coil by a crimped solderless connection, and a dielectric sleeve enclosing the helical coil. According to further features in the described preferred embodiment, the electrically-conductive conductor includes a metal sleeve at one end formed with a helical recess for receiving the respective end of the helical coil, and a metal stem at the opposite end for electrically connecting the helical coil to an electrical circuit. In addition, the sleeve receiving the helical coil includes a flat end face which abuts against the respective end face of the preformed dielectric core. The foregoing features provide a very sturdy construction enabling the antenna assembly, particularly the coil antenna, to retain its critical electrical radiation characteristics even when subjected to harsh mechanical treatment. According to another embodiment of the invention, the rod antenna and the coil antenna, instead of being one-quarter wavelength as in the preferred embodiment described in US Patent 5,204,687, are both of three-eighths wavelength. This increases the gain of the antenna. In addition, the electrical circuitry includes a common impedance matching circuit comprising an inductance of about 8.2 nH and a capacitance of about 1.4 pF connected to the rod antenna when electrically connected to the circuitry, and connected to the coil antenna when electrically connected to the circuitry. It was unexpectedly found that such an impedance matching circuit could be used for both the rod antenna and the coil antenna, and thereby obviates the need for providing two separate impedance matching circuits. Further features and advantages of the invention will be apparent from the description below. The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: Figs. 1 and 2 illustrate one form of electrical device including an antenna assembly constructed in accordance with the present invention, the antenna assembly being shown in its extended position in Fig. 1 and in its retracted position in Fig. 2; Fig. 3 is an end elevational view more particularly illustrating the antenna assembly of Figs. 1 and 2; Fig. 4 is a view corresponding to that of Fig. 3, but more particularly illustrating various elements of the antenna assembly in longitudinal section; Fig. 5 is an exploded view illustrating the construction of the coil antenna in the antenna assembly of Figs. 1-4; and Figs. 6 and 7 are enlarged fragmentary views, partly in section, more particularly illustrating the construction of the rod antenna in the antenna assembly of Figs. 1-4; and Fig. 8 illustrates the common impedance matching circuit which is used for both the rod antenna and the coil antenna. The electrical device illustrated in Figs. 1 and 2 is an electrical transmitter-receiver unit particularly useful in a wireless radio communication system. The electrical device includes a housing 2 enclosing radio circuitry schematically indicated at 4 of the telephone transmitter-receiver, and a retractible antenna assembly, generally designated 6, which in its extended position (Fig. 1) is adapted for long-range use, and in its retracted position (Fig. 2), is adapted for short-range use. Antenna assembly 6 is connected to the radio circuitry 4 by means of an impedance matching circuit 8 and a feed line 9. Antenna assembly 6 comprises a straight rod antenna 10 and a coil antenna 20 carried at the upper end of the rod antenna. The antenna assembly is slidable within an electrical connector 30 fixed to housing 2 and electrically connected via matching circuit 8 and feed line 9 to the radio circuitry 4, such that when the antenna assembly is in its extended position (Fig. 1) electrical connection is made from the radio circuitry 4 to the rod antenna 10, and when the antenna is in its retracted position (Fig. 2), electrical connection is made from the radio circuitry to the coil antenna 20. Figs. 3-7 more particularly illustrate the construction of the rod antenna 10 and the coil antenna 20 in antenna assembly 6. Thus, the rod antenna 10 includes a central metal rod 11 and an outer dielectric sleeve 12. The lower end of the rod antenna 10 includes a metal sleeve 13 electrically connected to the central metal rod 11 and externally exposed to provide an electrical connection to the central metal rod 11. The upper end of rod antenna 10 includes a dielectric sleeve 14 covering the upper end of the metal rod 11 and its dielectric sleeve 12 to support the coil antenna 20 while at the same time interrupting electrical continuity thereto. For this purpose, the upper end of dielectric sleeve 14 is formed with an externally-threaded dielectric stem 15 (Figs. 6, 7) for receiving the coil antenna 20. The structure of the coil antenna 20 is more particularly seen in Figs. 4 and 5. It includes a dielectric core 21 preformed with an electrical recess 22 extending for its complete length except for an end section 23 of reduced diameter at one end, and an enlarged head 24 at the opposite end. The enlarged head 24 is formed with an annular shoulder 24a at the juncture with the helically-recessed section 21, and with a semi-spherical outer face 24b. Coil antenna 20 further includes a helical coil 25 of electrically-conductive (metal) wire received within helical recess 22 of the dielectric core 21. One end 25a of coil 25 bears against the annular shoulder 24a of the core enlarged head 24. The opposite end 25b of coil 25 is received within a helical recess 26a formed in a metal connector 26. One end of metal connector 26 includes a flat end face 26b which abuts against the end section 23 of core 21 in the assembled condition of the coil antenna 20, the end face 23a of the end section 23 being flattened for this purpose. The opposite end of connector 26 includes a metal stem 27 formed with an internally-threaded bore 27a for receiving the externally-threaded dielectric stem 15 (Figs. 6, 7) of the rod antenna 10. A dielectric sleeve 28 encloses the core 21, the wire coil 25, and electrical connector 26, leaving the metal stem 27 exposed. Electrical connector 30 is formed with a threaded body 31 for threadedly applying the connector into an opening formed in housing 2. Electrical connector 30 is engageable with metal sleeve 13 formed at the end of the rod antenna 10 in the extended position (Fig. 1) of the antenna, and with the metal stem 27 in the retracted position (Fig. 2) of the antenna. Thus, when the antenna assembly is in its extended position (Fig. 1), the electrical connection between connector 30 and metal sleeve 13 electrically connects the rod antenna 10 to the radio circuitry 4; and when the antenna assembly is in its retracted position (Fig. 2), metal sleeve 30 engaging sleeve 27 electrically connects the coil antenna 20 to the radio circuitry 4. Following is one manner of constructing the antenna 6 illustrated in the drawings: A dielectric sleeve 14 is applied, as by injection molding, to one end of the central metal rod 11 of the rod antenna 10 to cover the upper end of the metal rod 11 and also to define an externally-threaded stem 15 (Figs. 6, 7). In order to more firmly fix the central rod 11 within the dielectric sleeve 14, the upper end of the metal rod is preferably flattened, as shown at 11a in Fig. 6. The lower end of the dielectric sleeve 14 is formed with an annular gap, as shown at 14a, for receiving the upper end of the preformed dielectric sleeve 12. The latter sleeve is of a length to completely cover the central metal rod 11. Metal sleeve 13 is then applied over the lower end of the central metal rod 11 and the outer dielectric sleeve 12. To establish good electrical contact between metal sleeve 13 and the central rod 11, the metal sleeve is preferably forced inwardly of the outer end of the metal rod 11 and the dielectric sleeve 12; the outer tip of the metal rod is then flattened; and the metal sleeve 13 is then forced outwardly of the metal rod and dielectric sleeve so that the flattened end of the metal rod wedges firmly against the inner surface of the metal sleeve. The coil antenna 20 is then assembled by applying the helical wire 25 in the helical recess 22 of the preformed core 21 until end 25a of the wire abuts against shoulder 24a of the thickened end 24 of the core. The opposite end 25b of the helical wire 25 is threaded into helical recess 26b of metal connector 26 until the flat face 26b of the metal connector abuts against the flat face 23a of the core. End 25b of helical wire 25 is then crimped onto the metal connector 26 to provide a good electrical contact. This electrical contact is preferably solderless because solder tends to wick and thereby to change the electrical characteristics of the coil 25. Dielectric sleeve 28 is then applied to abut the flat annular wall 24a of the thickened head 24 and to cover the complete metal coil 25 and electrical connector 26 at the opposite end of the coil, but to leave exposed substantially the full length of the metal stem 27. If desired, a glue may be applied over the outer surface of core 21 and its coil 25 to produce a strong mechanical bond between the dielectric sleeve 28, core 21, metal coil 25 and electrical connector 26. When the antenna has thus been assembled, it may then be inserted through connector 30 fixed by its threaded body 31 to housing 2. Thus, antenna assembly 6 may then be moved to its extended position (Fig. 1), whereupon connector 30 engages metal sleeve 13 to electrically connect the rod antenna 10 to the radio circuitry 4. When the antenna assembly is moved to its retracted position (Fig. 2), electrical connector 30 engages metal stem 27 to thereby connect the coil antenna 12 to the electrical circuitry. The extended position of the antenna assembly (Fig. 1) thus enables the rod antenna 10 for long range operation; whereas the retracted position (Fig. 2) of the antenna assembly enables the coil antenna 20 for short range operation. It has been found that if the rod antenna 10 and coil antenna 20 are each of three-eighths wavelength, rather than one-quarter wavelength, the antenna gain is increased. However, this has been found to require an impedance matching circuit as shown at 8 in Figs. 1 and 2. Fig. 8 illustrates one impedance matching circuit which has been unexpectedly found to be usable for both the rod antenna 10 and the coil antenna 20 thereby obviating the need for a separate matching circuit for each of the two antennas when enabled. As shown in Fig. 8, the impedance matching circuit 8 includes an inductance coil L of a value of 8.2 nH, connected between the feed line 9 and the enabled rod antenna 10 or coil antenna 20, and a capacitance C of 1.4 pF, between ground and the juncture of the inductance coil L and the antenna.

Claims: An electrical antenna assembly (6), comprising: a rod antenna (10), and a coil antenna (20) carried by one end of the rod antenna; characterized in that said coil antenna includes a dielectric core (21) carried by said one end of the rod antenna and preformed with a helical recess (22), an electrically-conductive helical coil (25) seated in said recess, an electrical connector (26) connected to one end of said helical coil by a crimped solderless connection, and a dielectric sleeve (28) enclosing said helical coil. The antenna assembly according to Claim 1, wherein said electrical connector is formed at one end formed with a helical recess (26a) for receiving the respective end of the helical coil, and includes a metal stem (27) at the opposite end for electrically connecting the helical coil to an electrical circuit. The antenna assembly according to Claim 2, wherein said electrical connector receiving an end of the helical coil includes a flat end face (26b) which abuts against the respective end face (23a) of the preformed dielectric core. The antenna assembly according to Claim 2, wherein said dielectric core is preformed with an enlarged head (24) at its free end, said helical recess (22) in the core terminating at said enlarged head with the free end (25a) of the helical coil abutting said enlarged head. The antenna assembly according to Claim 2, wherein said metal stem (27) is formed with an internally-threaded bore (27a) and receives an externally-threaded pin (15) of dielectric material carried at the respective end of the rod antenna for fixing the coil antenna to the rod antenna. The antenna assembly according to Claim 5, wherein the end of the rod antenna opposite that of said externally-threaded pin of dielectric material includes an electrical connector, such that either the rod antenna maybe electrically connected to an electrical circuit via said latter electrical connector, or the coil antenna may be electrically connected to an electrical circuit via said metal stem. An electrical device, comprising: a housing assembly enclosing electrical circuitry; an antenna assembly according to Claim 6 movable to a retracted position within the housing where substantially only the coil antenna is exposed externally of the housing, or to an extended position wherein substantially the complete rod antenna and coil antenna are exposed externally of the housing; and an electrical connector carried by the housing and effective to electrically connect said metal stem of the coil antenna to the electrical circuitry in the retracted position of the antenna assembly, or to electrically connect said electrical connector of the rod antenna to the electrical circuitry in the extended position of the antenna assembly. The electrical device according to Claim 7, wherein both the rod antenna and the coil antenna are pretuned to the same frequency for short range operation and long range operation, respectively. The electrical device according to Claim 8, wherein the rod antenna and the coil antenna are both of three-eighths wavelength, said electrical circuitry including a common impedance matching circuit comprising an inductance of about 8.2 nH and a capacitance of about 1.4 pF connected to the rod antenna when electrically connected to said circuitry, and connected to the coil antenna when electrically connected to said circuitry.

Inventors: ELLIOTT MICHAEL, MARTISKAINEN MATTI, ELLIOTT, MICHAEL, MARTISKAINEN, MATTI
Applicants: GALTRONICS LTD, GALTRONICS LTD.
Application year: 1995
Main classification: H01Q1
IPC codes: H01Q9, H01Q1