US3100893A

US3100893A - Broad band vertical antenna with adjustable impedance matching network

Info

Publication number: US3100893A
Application number: US72816A
Authority: US
Inventors: Helmut Brueckmann
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-11-30
Filing date: 1960-11-30
Publication date: 1963-08-13
Anticipated expiration: 1980-08-13
Also published as: GB934672A

Description

Aug. 13, 1963' H. BRUECKMANN 3 00,8

BROAD BAND VERTICAL ANTENNA WITH ADJUSTABLE IMPEDANCE I MATCHING NETWORK Fi led Nov. 50. 1960 FIG. 2B

FIG.2A I

UTILIZATION DEVICE United States Patent M (Granted under Title 35, US. Code (1952), see. 266) l The invention described herein may be manufactured and used by or for the Government for governmental purposes, without payment of any royalty thereon.

The present invention relates to an improved broadband verticalantenna and more particularly to one for vehicular application constructed in the form of a whip and employing a double feed system, facilitating its use over a broad band of frequencies.

In the prior art, whip antennas for vehicular use required complicated circuitry and were not conveniently adjhstabio for operation over a wide frequency range. The present invention is a vertical Whip antenna (operating, for example, over the frequency range from 20 to 76 me.)

which will permit considerable simplification of the an' tenna circuitry of vehicular radio sets,-especially with respectto simplification of the matching circuitry of the radio sets, and which will also permit an increase, inantenna efliciency.

The present invention is an improvement over my Patent No. 2,913,722, The antenna system described therein comprises an antenna having upper and lower sections, a cable choke connected to the .base'of the lower section, 'reactance'circuits, and switching means for con- I nec'ting the reactance circuits to the upper and lower sec- 5 tions. The invention herein provides improvements over the above-mentioned patent-by having the cable choke wound around a ferrite core to reduce the turns required, and -by havinga tapped shunt coil connected across the cable choke to minimize the ferrite'losses at high frequencies. In addition, the-upper section has now been changed to provide a dual function. While it, still behaves as an upper radiator, it also actsjas an impedance matching stub, being either open-ended or shorted, depending on the load impedance. This, latter structural change results in the voltage standing wave ratio (VSWR) of the antenna being .-reduced. Another means for reducing the VSWR isthe introduction of a taper in the lower section so that a portion thereof will have a relatively high characteristic impedance, the remainder of the lower section having a somewhat lower characteristic impedance. Q 1 I j Principal Advantages 1) The proven mechanical advantages of the whip configurationare not compromised. Theneare no moving parts, telescoping sections, or lumped reactors in'the .whip

A itself. I

(2) v The length of the cable ,choke is kept to a'm-inh mum -by having it wrapped around a ferrite core. I A tapped shunt coil is connected in parallel with thev cable choke todecrease the inductance as the frequency is invariable lumped-reactor comprising the cable choke wound on the ferrite core, the tapped coil shuntingthe choke, the impedance matching networks, and the switch: ing means; By switching to the proper impedance matching network and to the proper tap .on the tappedcoil, by

means of anautomatic" remote control activated the 3 ,190,893 Patented Aug. 13, 1963 2. frequency dial of the utilization device, the frequency range is divided into anumber of fairly wide bands, each band having the proper reactance value. This permits controlling the current distribution along the lower section of the antenna below the feed point within wide limits so that a current node is placed'at or near the lower end of the lower section in all bands. As a result, the distortion of the azimuth pattern and the losscaused by unintentional excitation of the vehicle body are minimized. Most important, the decoupling between antenna and vehicle body actually achieved is sufiicient' to make differences in impedance due to vehicle type, mounting location and ground conditions negligibly small. As a secondary effect, the power gain with respect to the field strength on the ground is improved noticeably at the upper end of the frequency range. In addition, the feed cable from the antenna to the utilization device can be any arbitrary length, no tuning is involved, and the voltage standing wave ratio (VSWR) is kept small over the entire frequency range. I

(4-) To reduce the VSWRin adjoining sections of the antenna, over the entire frequency range, the upper section of the antenna is constructed so that its acts as a radiator and stub simultaneously, and the lower section of the antenna is construoted with a tapered portion. The tapering of the lower section has an additional advantage of equalizing the antenna impedance seen at the lower end of the cable choke and the characteristic impedance of the transmission line connected to the utilization device.

The advantages of lower V SWR are lower line loss, and lower voltage across the transmission line and other components, (less danger of voltage breakdown). Also, lower VSWR permits use of simpler, less lossy matching networks. The' same, advantage accrues from equalizing the impedance seen at the lower end of the cable choke and the characteristics impedance of the transmission line connected to the utilization device, which may be a transmitter or a receiver.

other advantages will bereadily apparent from consideration of the following specification relating to the annexed drawings in which:

and

FIGURES 2A and 2B are enlarged views of alternative connections of the upper radiator (stub) to the lower radiator.

Although the antennamay beused with either receiving or transmitting equipment, it will be referred to, for convenience, as a radiator, asfor a transmitter. Therefore, the termsupper radiator andlower radiator are used throughout the specification andclaims as generic to both transmitting and receiving' antennas. The terms section and radiator applied to the antenna elements, as upper section or upper radiator 12, are equivalent." Also, the term utilization device, asused herein, is to be considered 1 FIGURE 1 is a schematic illustration of the invention;

' generic to t'ransmitter's and receivers.

Referring now to the drawings, wher'einlik-e reference characters designate like or corresponding parts through out the several views, there is shown intFlGU R 'E 1, an

"irnproved double feed whip antennasystem cc'mipri-sing an upper section (upper-radiator), 12"landflower-jsection (lower radiator) 13, the two sections'lz and 13 being I inclosed within an insulating jacket. 14, Q In a preferred emhodimentthe antenna is l22 in ches in length with the upper radiator IZ-beingapproximately 69 inches and gthe lower radiator 13 being approximately 53 inches. Insu lating jacket d4 servesto support; and stiffen the coaxial Spring 45 and base insulator 49, each coaxial with lower section 13 at its bottom end' are positioned outside of and adjacent to insulating jacket 14, as shown, and act as the base support for the antenna. Base insulator 49 is attached to vehiclebcdy member 48 where the lower section 13 passes through that member to connect to cable choke 17.

A shield housing 52 is mounted within vehicle body member 48 about base insulator 49-. Encased within this housing'is ferrite-cored cable cholce 17, tapped shunt coil 60 (shunting the cable choke), impedance matching networks, and ganged switching network 20.

Ganged switching network 20*, remotely controlled firom the radio set or other utilization device 61, and activated automatically from aband selector (not shown), is illustrated as comprising five ganged

switches

23, 24, 25", 26 and 27--each having a switch arm and three switch positions I, II and III. This switch permits changing the impedance of the network (matching

networks

36, 39 and 41, cable choke 17, and tapped shunt coil 60) coupling the antenna to utilization device 61 byinner conductor 43 of coaxial cable 44, as described more 'fully in my Patent No. 2,91 3,7 22.

While'each deck ott ganged switching'network 20 is shown having three positions for covering the entire firequency range, a greater number or such positions and impedance matching networks may be used. Tapped shunt coil 60' will accordingly have an additional number of taps.

The lumped reactor at the base of lower radiator 13 has, an essential component, a section of coaxial cable wound on ferrite core 59 to form cable choke 17, the

(ferrite core being used to keep the number of turns of the cable choke to a minimum.

For the purpose of illustration, cable choke 17 is shown as having one turn in FIGURE 1. Actually, however, it will have a plurality of turns. Because of the ferrite core the preferred embodiment needs only four the ldifiiculty of matching at the lower end of the fre quency range.

Upper section -12 of the antenna comprises a coaxial line having outer conductor 12a and inner conductor 12b. This line acts as aradiator for currents flowing on the outside of outer conductor 12a, and as a stub for currents flowing on the inside of outer conductor 12a and in inner conductor 12b (currents in 12b are always equal in magnitude and opposite in direction to those on the inside of outer conductor 12a). The arrows in FIG- URES 2A and 2B show the current flow for a seriesconnected stub and parallel-connected stud, respectively. The dashed capacitors in these figures depict the capacitance between the cable portions closing the antenna circuit.

When inner conductor 12b is shorted to outer conductor 12a (FIGURE 23), the line acts asa shorted stub. With this type of termination, the center conductor 12b is usually connected in parallel with the feedpoint impedance of the antenna (see FIGURE 2B) although in narrow-band applications the series connection might be employed to advantage.

Upper radiator '12 may alsobe open-ended, as in FIG- URE 2A, wherein the length of the inner conductor is the; length of the stub and the length of the outer conductor is equalto or greater than the stub length. In this arrangement upper radiator 12 is connected usually in series will lower radiator 13.

The embodiments shown in FIGURES 2A and 2B are not equivalent, but are complementary. The series conmotion of the stub (usually resonant in the middle ofthe frequency range) is most effective with respect to broadband compensation when the load impedance (in this case the steed point impedance) is high. On the other hand, the parallel connection is useful when the load impedance is low.

Lower section 13" is formed oftwo transmission lines 1 63 and 640i different diameter and characteristic. im-

and' one-hali turns or cable (twenty-three inches of cabie I length) to [obtain an inductance ost 2' wh. The ferrite core'in this embodiment is a cylinder 1.0 inch in diameter and 2.0 inches long. p

Connector 62 couples one end of cable choke 17 to the base ocflower radiator 13. If desired, the cable choke can be formed. integral with the lower radiator. At the other end of the cable choke the inner conductor is connected toswitching network 20, and the outer-conductor is grounded to housing 52 which shields network 20' I Tapped shunt coil 60, a cylindrical air-core coil, with relatively loose coupling between turns, is connected in parallel with cable choke. -17. The taps are each connected to a switch terminal of switch. deck 24 to permit adjustment of the coil, acconding to the switch position, to tune the selfcapacitance of the cable choke and the capacity of the base insulator-and other associated hardware to enhance the broad-band properties of the antenna. Adjustment ofthe inductance value of this coil, by the use of the taps,'is preferable to an adjustment of the cable cholce, particularly in the; higher frequency range to minimize the ferrite-losses or core 59. As the frequency is increased the inductance of the shunt coil is lowered pedance. The lower end of 63 is tapered to match the smaller diameter of 64, as shown in :FIG. 1.

The tapering of the line made up of 63 and 64 has the effect of equalizing the antenna impedance seen at 35 to that of the characteristic impedance of coaxial cable 44. Any tapering, [gradual or instep's, can be done. to the inner conductor alone, to the router conductor alone, or to both. v

The stub 12 and the tapered section made up of 63 and 64 can be used either together or' independently of each other to reduce the VSWR'oye-r the entire frequency range. The advantages of lower VSWR are lower line-loss and lower uoltage (less dan'ger of voltage breakdown). Also, low VSWR permits the use. of simple,

It should be understood, of course, that the foregoing disclosure relates to only a'preferred'embodiment of the I invention and that numerous: modifications or alterations may be made therein without departing from the spirit and scope of the invention as set torth the appended due to the capacity of the base assembly flowsthrouigh I it rather than through. the cable choke. As, a result thelosses in thebase reactor assembly, using a ferrite core 7 such as that, commonly known. as Q.-2,' do not exceed 5% of the antenna inputpower.

The. criterion used in, adjusting the taps \ot the shunt A p coil is primarily' the position of the node of the current "distribution along the antenna. Specifically, positioning thenode at the base minimizes its coupling to the vehicle body, whereas positioning. the (virtuallcurrent node below thebase of the antenna, corresponding to a capacitivesusceptanc'e o f'the. base reactor, greatly alleviates claims.

What is claimed is:

1. An improved broad-band whip antenna for vehic'u- V 7 laruse comprising: an antenna having an uppersection and a lower section electrically coupled tosaidupper section; a' fer-rite core; a cable choke wound around said ferrite-core; means for connectingsaid lower section to said cable choke; a tapped shunt coil connected in parallel with said cable choke and having a plurality of taps; a plurality of impedance matching networks; and switching means for connecting any one of said impedance matching networks to said antenna and for changing the inductance of said shunt coil by the tap setting according to the frequency band at which the antenna is to operate.

. 2. The improved broad-band'vvhip antenna of claim 1 wherein said lower section is formed of two coaxial lines, one line having a lower characteristic impedance lower section, respectively.

4. The improved broad-band whip antenna of claim 3 wherein said upper section is formed of a coaxial line having the upper extremity of the inner conductor insulated from the outer conductor and the lower extremity of the inner conductor connected to said inner conductor of said lower section.

5. The improved broad-band whip antenna of claim 3 'wherein said upper section is formed of a coaxial line withthe inner conductor connected to-the outer conductor of said lower section and the outer conductor connected to the inner conductor of said lower section.

6. An antenna system for vehicular use comprising: an antenna insulated from and projecting outwardly from the structure of the vehicle so as to be electrically exposed to space, said antenna having upper and lower sections; an insulating jacket encasing said antenna; a ferrite core; a cable choke wound around said ferrite core and connected to the lower extremity of said lower section; a tapped shunt coil having a plurality of taps and its extremities connected in parallel with said cable choke; a plurality of impedance matching networks; a switching means for interconnecting said impedance matching networks to said antenna and for changing the tap connections on said tapped shunt coil.

7. An improved broad-band whip antenna system for vehicular use comprising: an nppersection formed of a coaxial line; a lower section having an upper and lower portion, each portion being formed of a coaxial line, the lower end of said upper portion being tapered and buttconnected to the upper end of said lower portion; section' connection means for connecting said lower section to said upper section; an insulating jacket encasing said upper and lower sections; a ferrite core; a cable choke of coaxial cable wound around said ferrite core; means for connecting said cable choke to said lower section; a tapped V shunting coil having a plurality of taps, said shunting coil connected in parallel with said cable choke across the outer conductor of said coaxial cable forming said cable choke; a plurality of impedance matching networks; a'

ductance of said shunt coil by the tap setting according to the frequency band at which the antenna is to operate.-

8. An improved broad-band whip antenna system for vehicular use comprising: an upper radiating section formed of a coaxial line; a lower radiating section having an upper and a lower portion, each portion being formedlof a coaxial line, said upper portion having a higher characteristic impedance than said lower portion, said upper portion having its lowest extremity tapered, said lower portion having its upper extremity connected to said tapered extremity of said portion; section connection means for connecting said upper section to said lower section; an insulating jacketencasing and supporting said upper and lower sections; a ferrite core; a cable choke of a coaxial cable wound around said ferrite core; a switching means; means for connecting the inner and outer conductors of one end of said cable choke to the inner and outer conductor,respectively, of said lower portion of said lower section, the inner and outer conductors of the other end of said cable choke being connected to said switching means and ground, respectively, said outer conductor of said one end of said cable choke being connected to said switching means; a tapped shunt coil having a plurality of taps and connected to the outer conductor of said.

cable choke in parallel therewith, said taps being connected to said switching means; a utilization device; and means for connecting said utilization device to said switching means; whereby said switching means connects one of said plurality of impedance matching networks between.

said antenna and said utilization device and changes the inductance of said shunt coil by the tap setting according to the frequency band at which the antenna will operate.

9. The improved broad-band whip antenna "system of claim 8 wherein the inner conductor of said upper section is connected to the outer conductor of said lower section and said outer conductor of said upper section is connected to said inner conductor of said lower section to form said section connection means, so that said upper section acts as a radiator and parallel connected stub simultaneously.

10. The improved broad-band whip antenna system of claim 8 wherein the lower extremity of the inner conductor of'said upper section is connected directly to the inner conductor of said lower section to form said section connection means, so that said upper section acts asa radiator and a series-connected stub simultaneously.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,145 Dorne et al Nov. 3, 1953 2,748,386 Polydoroif May 29, 1956 2,913,722 Bruechmann Nov. 17, 1959 2,991,355 Spindler July 4, 1961