US3624662A

US3624662A - Mobile deflectable antenna with impedance matching

Info

Publication number: US3624662A
Application number: US637A
Authority: US
Inventors: Alvin Feder
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1970-01-05
Filing date: 1970-01-05
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30

Abstract

A tiltable monopole antenna of the type to be mounted on an automobile rooftop or the like as a transmitting-receiving antenna for mobile radio communication equipment. A novel antenna-to-mounting base structural connection greatly simplifies the antenna and mounting base assembly as these parts provide a rigid pivotal connection and are held together by a transversely extending pin. Impedance matching means is provided within the mounting base of the antenna to match the antenna with the given transmission line connected thereto over a given frequency range.

Description

United States Patent 2,397,151 3/1946 Mitchell 343/888 2,706,608 4/1955 Joseph... 343/882 3,264,647 8/1966 Nuttle 343/900 3,427,769 2/1969 Star 343/900 3,453,618 7/1969 Ukmar et al. 343/715 FOREIGN PATENTS 74,937 1/1961 France 343/882 Primary Examiner- Eli Lieberman Attorney-Mueller and Aichele ABSTRACT: A tiltable monopole antenna of the type to be mounted on an automobile rooftop or the like as a transmitting-receiving antenna for mobile radio communication equipment. A novel antenna-to-mounting base structural connection greatly simplifies the antenna and mounting base assembly as these parts provide a rigid pivotal connection and are held together by a transversely extending pin. Impedance matching means is provided within the mounting base of the antenna to match the antenna with the given transmission line connected thereto over a given frequency range.

PATENTEUNUV 30 197i SHEET 10F 2 m Ill mv /llll/l INVENTOR.

ALVIN F DER W ATTORNEYS.

PATENTEUunv 30 l97l 8, 624,662

SHEET 2 OF 2 INVENTOR ALVIN EDER B Mm.

MOBILE DEFLECTABLE ANTENNA WITH IMPEDANCE MATCHING BACKGROUND OF THE INVENTION This invention relates generally to monopole antenna structures, and more particularly to structural arrangement whereby such antennas are readily tiltable from their. normal position.

Heretofore, several structural arrangements have been proposed when forming mobile antenna structures wherein the antenna can tilt to a substantially horizontal position from its normal upright or vertical position. One such arrangement is where the antenna is held against the antenna mounting base by a flexible cable placed under tension by means of a compression spring. In this arrangement, tilting of the antenna causes the compression spring to exert substantial force which increases the tension on the flexible cable and, ultimately, may cause stretching of the cable. Thus to compensate for the longer length of the cable means must be provided to adjust the tension on the cable from time to time. The flexible cable may also have a tendency to fray when rubbing against other components of the antenna mounting structure, and the requirement of fastening the ends of the flexible cable into threaded sleeves by, for example, brazing or the like is timeconsuming and expensive.

Still another type of antenna structure is one where the mounting base has extended therefrom a relatively heavy coil spring and the tubular antenna portion is fastened to the other end of the spring. However, due to vibration and/or thermal expansion and contraction occurring during various weather conditions, this structural arrangement may tend to part more readily, thus making the antenna inoperative.

A rather common structure for tiltable antennas is one where the bottom end of the tubular antenna portion has formed thereon a ball-like member to fit within the capped-ofi' socket. However, this allows the antenna only to tilt within a limited range of angles from its vertical position, and, in addition, this mounting structure is rather complex and expensive.

SUMMARY OF THE INVENTION It is an object of this invention to provide an antenna structure which overcomes the problems of the prior art and which is simple in design, inexpensive to manufacture and efficient in operation.

Another object of this invention is to provide an improved and simplified tiltable antenna construction.

Yet another object of this invention is to provide a simplified antenna structure with improved impedance matching with transmission lines connected thereto.

Briefly, the tiltable antenna as disclosed in the illustrated embodiment has a tubular antenna portion extending from a mounting base and a dielectric sleeve fastened to the other end of the tubular member with a phasing coil positioned within the dielectric sleeve. Extending from the dielectric sleeve, at the end opposite the tubular antenna portion, is a rod antenna fastened thereto and forming the remainder of the extended antenna structure.

In accordance with an aspect of this invention the tubular antenna portion is tiltably but securely held to a mounting, base which is formed of dielectric material, merely by the use of a transversely extending pin passing through a raised island portion of the mounting base and a pin receiving sluglike member associating with a coupling device extending from the tubular antenna portion. Most advantageously, an elongated rod extends into the tubular antenna portion and a compression spring is positioned about the rod and held in place within the tubular antenna portion by suitable restraining means. The end of the elongated rod extending from the tubular antenna portion has a hook formed thereat to engage an eye portion formed on one end of the pin receiving sluglike member. The hook and eye of the rod and slug, respectively, are located very near, but spaced from the mounting base to insure the freely tiltable action of the antenna. Preferably, a collar is formed about the base of the tubular antenna portion to engage an angular surface of the mounting base and to provide a multitude of circumferential pivot points about which the antenna will rotate toward a collapsed or substantially horizontal position relative to the mounting base.

In accordance with another aspect of the illustrated embodiment of the invention the antenna is made freely rotatable about its longitudinal axis relative to the mounting base without causing twisting of any of the components within the antenna or any of the components within the mounting base. This is accomplished by providing a thrust bearing at one end of the compression spring which is positioned about the elongated rod within the tubular antenna portion, preferably it being the end furthest from the mounting base, to allow relative rotation between the elongated rod and the compression spring mounted thereon.

Yet another aspect of the invention resides in the novel combination of the antenna structure of the illustrated em bodiment with that of a small, substantially disc-shaped impedance-matching device positioned within the mounting base which matches the impedance of a transmission line connected thereto, such as a coaxial cable or the like, with the impedance of the antenna over a limited range of frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary perspective, exploded view of an antenna constructed in accordance with this invention;

FIG. 2 is a fragmentary sectional view showing details of connecting the tubular antenna portion to a mounting base in accordance with this invention;

FIG. 3 is an enlarged sectional view of a portion of the mounting base of Fig. 2 showing details of an impedancematching device coupled between the antenna and a transmission line connected thereto;

FIG. 4 is a fragmentary sectional view showing the tilting feature of the antenna of this invention; and

FIG. 5 is a plan view of an impedance-matching device used in this invention as illustrated in Fig. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2, there is seen an antenna structure designated generally by reference numeral 10. The antenna structure 10 includes a mounting base 12 preferable of molded dielectric material and a tubular antenna portion 14 tiltably but firmly held to the mounting base 12. Preferably, the mounting base 12 includes a raised island portion 16 substantially defined by a metallic shield which serves to increase the electrical connection of the tubular antenna portion 14 with that of a signal-translating connector 18 imbedded within the mounting base 12, and additionally this shield 16a serves to provide a hard surface for receiving a cuplike collar 20. The raised island 16 and the signal-translating connector 18 with its recess 18a form an assembly pin receiving means which, together with the transverse pin 50, holds the antenna structure 14 to the base 12, as seen in Fig. 2. The collar 20 is fastened to the tubular antenna portion 14 by any suitable means such as a brazing fillet 22 or the like. Preferably, the bottom portion of the collar 20 is rounded as viewed in the cross section and is designated in reference numeral 20a. This rounded portion 200 provides a pivot point about any and all circumferential locations of the collar 20 so that the antenna will readily tilt from its normal position to a collapsed position, as, for example, from its normal vertical position to a horizontal or substantially horizontal position.

Positioned within the tubular antenna portion 14 is an elongated rod 24 which has a stop sleeve 26 mounted at one end thereof. The stop sleeve may be fastened to the rod 24 by any suitable means but, preferably, as here illustrated it is restrained by means of a bend 28 formed near the end of the rod 24. A pair of

washers

30 and 32 are positioned about the rod 24 to confine a thrust bearing 34 therebetween which allows the antenna portion freely to rotate relative to the mounting base 12. A compression spring 36 has one end thereof abutted against the washer 32 with the other end thereof abutted against a washer 38. The washer 38 is substantially the same size as the inner diameter of the tubular antenna portion 14 and is held in place by an annular restriction 40 which may be formed by any suitable means such as rolling or crimping techniques.

A hook 42 is formed at the other end of the rod 24 to engage an eye portion 44 which extends from a slug member 46. Preferably, the hook-and-

eye connection

42 and 44, respectively, are maintainedrelatively close to the raised island portion 16 so that pivoting of these components is readily obtained. The slug 46 is provided with an aperture 46a which is positioned in alignment with a pair of spaced-apart aligned

apertures

16b and 16c extending through the raised island portion 16.

Most advantageously, the mechanical coupling between the mounting base l2 and the tubular antenna portion 14 is accomplished readily by means of a pin 50 extending through the

aligned apertures

16b, 16c and 460. As best seen in FIG. 4 the assembled structure of Fig. 2 is readily tiltable at the point of connection of the mounting base 12 and the antenna portion 14 without causing interference, jamming or chafing of any of the interconnected components. Furthermore, it should be noticed that the rounded portion 20a of the collar 20 provides a pivot point uniformly about the collar 20.

An additional novel feature of the antenna structure disclosed by the illustrated embodiment is that the antenna portion 14, extending from the mounting base 12, is fully rotatable 360 and more about its longitudinal axis relative to the mounting base 12. As mentioned hereinabove this is accomplished by the provision of the thrust bearing 34 which allows rotation of the compression spring 26 relative to the rod 24.

The other components of the antenna structure include a dielectric sleeve 52 which is inserted into the open end of the tubular antenna portion 14 and abuts against a metal disc or washer 54 which by means of a restricted diameter portion 56 forms a transverse restraining wall within the antenna portion 14. The dielectric sleeve 52 is securely held in a permanent position within the tubular antenna portion 14 by means of an annular detent 58 formed, for example, by a rolling technique. A coil spring 60 is positioned within the dielectric sleeve 52 and compressed somewhat therein by means of a threaded bushing 62 which is threadedly engaged at the upper end of the dielectric sleeve 52 and has a depending portion 620 tapered at its end to engage the coil spring 60 and compress the same. A split lockwasher 63 may be positioned between the dielectric sleeve 52 and the bushing 62. The bushing 62 has formed therein an aperture 62b for receiving the reduced diameter portion 640 of a rod antenna 64 which is to extend therefrom The rod antenna 64 is secured within the bushing 62 by means ofa setscrew 66, or the like.

The coil spring 60 acts as a phasing coil for the antenna and is used to control the current distribution of the antenna. The

phasing coil acts as a delay line so that the current distribution of the upper and lower radiation sections, (e.g. the antenna rod 64 and the tubular antenna portion 14, respectively,) provide the optimum radiation pattern. This type of phasing is common to antenna structures of the disclosed type and the length of the phasing coil varies according to the type or length of antenna elements used.

Refer now to FIGS. 1 and 3. In accordance with another aspect of this invention an impedance-matching device 70 is used'in combination with the disclosed antenna structure greatly to improve the impedance match between the signaltranslating connector 18 and a transmission line connector 71. The impedance-matching device 70 most advantageously is fashioned to fit within a cavity 72 formed within the mounting base 12 through a cavity opening 72a. A dislike flat spring74 is provided adjacent the impedance-matching device 7 and positioned to have the inner substantially flat portion 74a thereof in contact with the impedance-matching device 70 and the arcuately severed longitudinally displaced springlike portions 74b extending toward and in contact with a contact disc 76. A terminating contact 78, connected to the end of the center conductor 79 of a transmission line 80, engages the contact disc 76 thus electrically coupling the transmission line 80 to the antenna 10. A retaining ring 82, preferably of a dielectric material, is inserted into the cavity 72 to hold the components therein.

A threaded locking nut 84 preferably having threads at both the inside and outside diameters, is imbedded into the mounting base 12 which is dielectric material to provide sound mechanical connection with the connector 71 for mounting to an antenna-receiving surface 86 through an aperture 86a formed therethrough. If the antenna-receiving surface 86 is, for example, the rooftop of an automobile, it is desired to remove a portion of paint about the aperture 86 as indicated by the area 86b. This assures a firm grounding connection of the antenna system. An O-ring 88 may be provided within an annular recess 89 formed in the locking nut 84. The O-ring provides a watertight seal about the aperture 86a through the antenna -receiving surface 86.

Now referring to FIG. 5 there is seen a plane view showing the details of the impedance-matching device 70. The impedance-matching device 70 includes a pair of spaced-apart

members

90 and 92 of conductive material, such as steel or the like, spaced apart by a dielectric member 94. The conductive member 90 includes an annular inner portion 90a which also has formed thereat a domelike portion 90b. The annular inner portion 900 extends to a portion 90c which, in turn, is integrally formed with an annular outer portion 90d having a gap 90 e formed therein at the region at the extended portion 900. A plurality of equally spaced-apart screw-receiving holes 95 are formed in the top metal member 90, one of which receives an assembly screw 96 which threads into the bottom metal member 92 at 97, HO. 3. The four spaced-apart apertures 95 provide means for adjusting the impedance of the impedance-matching device 70 within relatively narrow, but contiguous, frequency ranges over the entire frequency range in which it is capable of being used. For example, if the anten- .na structure l0is to be used within a frequency range 450-455 MHz. the first hole, as viewed at the bottom of FIG. 5 however, is used to receive the assembly screw 96. On the other hand, if the frequency range is to be between 455-460 MHz. the second hole will receive the assembly screw 96. But as seen in FIG. 5, the assembly screw 96 passes through the third hole to provide an impedance match with a frequency range of 460-465 MHz. Also, ifa frequency range of 465-470 MHz. is used, the fourth hole, the top hole as viewed in FIG. 5, is used to receive the assembly screw 96. As all of the screwreceiving holes 95 are located along a common radius of the metal member 90, alignment of the

metal members

90 and 92 and the dielectric member 94 is maintained in all four positions, and adjustment to any of the four positions is a relatively simple matter. The bottom member 92 is substantially of the same configuration as the member 90 except for the four screw-receiving holes 95.

Accordingly, the disclosed embodiment of this invention provides means for quickly, inexpensively and efficiently fastening a tubular antenna portion to a mounting base so as to be readily tiltable relative to the mounting base, yet being firmly held in a neutral position extending therefrom under normal use. Additionally, an impedance-matching device of small size is used in combination with the mounting base of the antenna to increase efficiency of the antenna. Therefore, it will be understood that variations and modifications of this invention may be made without departing from the spirit and scope of the specification and claims.

I claim:

1. A tiltable antenna comprising:

a mounting base to be securely fastened to an antenna receiving surface, assembly pin receiving means formed at the end of said mounting base to be spaced from said antenna-receiving surface, said assembly pin receiving means including a recessed portion extending into said mounting base, and transversely extending aligned apertures through a portion of the mounting base at opposite sides of said recessed portion;

a tubular antenna portion extending from said end of said mounting base;

coupling means having a sluglike member extending into said recessed portion, and having a transversely extending aperture in alignment with said apertures through said mounting base for receiving pin means, the other end of said coupling means extending into said tubular antenna portion and longitudinally resiliently fastened therein, said coupling means having a pivotal portion intermediate said sluglike member and said other end; and

pin means passing through said assembly pin receiving means and said sluglike member thereby maintaining said coupling means in a state of longitudinal force firmly to hold said antenna portion in an outwardly extended position relative to said mounting base, said antenna portion being pivotal to an angularly displaced position relative to said mounting base by means of said pivotal portion of said coupling means and urged back to its normal position by said coupling means.

2. The tiltable antenna of claim 1 wherein the said mounting base includes a raised island portion at said end and a recessed portion substantially centrally of said island portion and extending into said mounting base, a sluglike member formed at said one end portion of said coupling means and extending into the recessed portion of said mounting base, aligned apertures extending transversely of said island portion and through said sluglike member whereby said pin means passes through the aligned apertures to fasten together said antenna portion and said mounting base.

3. The tiltable antenna of claim 2 further including a collar formed at the mounting base engaging end of said tubular antenna portion and extending radially outwardly and downwardly to circumscribe said raised island portion completely to conceal said island portion.

4. The tiltable antenna of claim 3 wherein said collar has a curved bottom portion as viewed in the cross section to engage said end of said mounting base substantially uniformly radially outwardly said island portion so that angular displacement of said antenna portion relative to said mounting base will occur at any point around said collar, the engaging parts of said collar and said mounting base at the point of angular displacement acting as a pivot.

5. A tiltable antenna comprising:

a mounting base to be securely fastened to an antenna receiving surface, assembly means formed at the end of said mounting base to be spaced from said antennareceiving surface;

a tubular antenna portion extending from said end of said mounting base, said tubular antenna portion having a annular detent formed within the outer wall thereof and displaced from the end adjacent to the mounting base, said annular detent forming a restriction within said tubular antenna portion;

coupling means including one end portion extending from said tubular antenna portion and fashioned to mate with said assembly means, and a second end portion extending into said tubular antenna portion and longitudinally resiliently fastened therein, said coupling means including rigid pivotal means intermediate said end portions, an elongated rod extending from said pivotal means through said tubular antenna portion, restraining means secured to the end of said elongated rod which is within the tubular antenna portion, a compression spring mounted on said elongated rod and having one end thereof abutting said restraining means, and an annular disc positioned about said elongated rod at the other end of said compression spring to engage with the restriction formed by said annular detent, said coupling means thereby being longitudinally resiliently mounted within said antenna portion b restrainingsaid annular disc to place said spring un er compression; said assembly means holding said one end portion to maintain said coupling means in a state of longitudinal force firmly to hold said antenna portion in an outwardly extended position relative to said mounting base, said antenna portion being pivotal to an angularly displaced position relative to said mounting base by means of said rigid pivotal portion and urged back to its normal position by means of said compression spring.

6. The tiltable antenna of claim 5 wherein the said rigid pivotal portion of said coupling means is formed by a hookand-eye connection near said one end portion of said coupling means extending from said antenna portion.

7. The tiltable antenna of claim 5 wherein said mounting base has formed therein signal-translating connection means coupled to said antenna portion and extending into said mounting base, a cavity formed in said mounting base with a cavity opening arranged'to be facing said antenna receiving surface, said cavity exposing at least a portion of said signaltranslating connection means, a conductive cover plate positioned within said cavity and spaced from the exposed portion of said signal-translating connection means, and a substantially disc-shaped impedance-matching device positioned in said cavity to be intermediate to the exposed portion of said signal-translating connection means and said conductive cover plate for pressure connection therewith, the axis passing through the plane of said impedance-matching device extending substantially parallel through the longitudinal axis of said antenna portion, said impedance-matching device serving to match the impedance of the antenna with that of transmission line means to be connected at said cavity opening of the mounting base over a given limited frequency range.

8. The tiltable antenna of claim 7 further including a discshaped spring contact interposed between said impedancematching device and said conductive cover plate, said discshaped spring contact having segmented portions severed from the main body of the spring contact and displaced from the plane thereof to form springlike portions which extend toward said conductive cover plate with the flat center portion of the spring contact engaging said impedance-matching device.

9. The tiltable antenna of claim 5 wherein the coupling means include an elongated rod extending through said antenna portion, a compression spring positioned about said rod and having one end thereof abutted against stop means formed at the end of the rod within said antenna portion and the other end thereof abutting stop means held in place within said antenna portion, said stop means formed at the end of said elongated rod including a pair of spaced-apart disc members and a thrust bearing interposed between said disc members, thereby allowing the antenna to rotate freely about the longitudinal axis.

Claims

1. A tiltable antenna comprising: a mounting base to be securely fastened to an antenna receiving surface, assembly pin receiving means formed at the end of said mounting base to be spaced from said antenna-receiving surface, said assembly pin receiving means including a recessed portion extending into said mounting base, and transversely extending aligned apertures through a portion of the mounting base at opposite sides of said recessed portion; a tubular antenna portion extending from said end of said mounting base; coupling means having a sluglike member extending into said recessed portion, and having a transversely extending aperture in alignment with said apertures through said mounting base for receiving pin means, the other end of said coupling means extending into said tubular antenna portion and longitudinally resiliently fastened therein, said coupling means having a pivotal portion intermediate said sluglike member and said other end; and pin means passing through said assembly pin receiving means and said sluglike member thereby maintaining said coupling means in a state of longitudinal force firmly to hold said antenna portion in an outwardly extended position relative to said mounting base, said antenna portion being pivotal to an angularly displaced position relative to said mounting base by means of said pivotal portion of said coupling means and urged back to its normal position by said coupling means.

5. A tiltable antenna comprising: a mounting base to be securely fastened to an antenna receiving surface, assembly means formed at the end of said mounting base to be spaced from said antenna-receiving surface; a tubular antenna portion extending from said end of said mounting base, said tubular antenna portion having an annular detent formed within the outer wall thereof and displaced from the end adjacent to the mounting base, said annular detent forming a restriction within said tubular antenna portion; coupling means including one end portion extending from said tubular antenna portion and fashioned to mate with said assembly means, and a second end portion extending into said tubular antenna portion and longitudinally resiliently fastened therein, said coupling means including rigid pivotal means intermediate said end portions, an elongated rod extending from said pivotal means through said tubular antenna portion, restraining means secured to the end of said elongated rod which is within the tubular antenna portion, a compression spring mounted on said elongated rod and having one end thereof abutting said restraining means, and an annular disc positioned about said elongated rod at the other end of said compression spring to engage with the restriction formed by said annular detent, said coupling means thereby being longitudinally resiliently mounted within said antenna portion by restraining said annular disc to place said spring under compression; said assembly means holding said one end portion to maintain said coupling means in a state of longitudinal force firmly to hold said antenna portion in an outwardly extended position relative to said mounting base, said antenna portion being pivotal to an angularly displaced position relative to said mounting base by means of said rigid pivotal portion and urged back to its normal position by means of said compression spring.

6. The tiltable antenna of claim 5 wherein the said rigid pivotal portion of said coupling means is formed by a hook-and-eye connection near said one end portion of said coupling means extending from said antenna portion.

7. The tiltable antenna of claim 5 wherein said mounting base has formed therein signal-translating connection means coupled to said antenna portion and extending into said mounting base, a cavity formed in said mounting base with a cavity opening arranged to be facing said antenna receiving surface, said cavity exposing at least a portion of said signal-translating connection means, a conductive cover plate positioned within said cavity and spaced from the exposed portion of said signal-translating connection means, and a substantially disc-shaped impedance-matching device positioned in said cavity to be intermediate to the exposed portion of said signal-translating connection means and said conductive cover plate for pressure connection therewith, the axis passing through the plane of said impedance-matching device extending substantially parallel through the longitudinal axis of said antenna portion, said impedance-matching device serving to match the impedance of the antenna with that of transmission line means to be connected at said cavity opening of the mounting base over a given limited frequency range.

8. The tiltable antenna of claim 7 further including a disc-shaped spring contact interposed between said impedance-matching device and said conductive cover plate, said disc-shaped spring contact having segmented portions severed from the main body of the spring contact and displaced from the plane thereof to form springlike portions which extend toward said conductive cover plate with the flat center portion of the spring contact engaging said impedance-matching device.