US2441086A - Radio antenna - Google Patents

Description

L. W. STIN SON RADIO ANTENNA May 4, 1948.

Filed March 4, 1944 Uv, MA

@(Wmiww Patented May 4,v 1948 RADIO ANTENNA ALawrence W. Stinson, Tulsa,.0kla., assignor to .Raymond Mfwilmotte, Washington, D. C.

Application March 4, 1944,"Serial No. 525,079 l This .invention vrelates to a system or method of supplying auxiliary circuits and services to insulated-base radiating structures, and .for electrical protection of such structures.

It applies particularly tov Aradio towers, insulated from the ground, whose primary function is to lcarry and/or radiate energy vat radio frequency, and which areof'sufcient height from the ground level tothe Vtopof the tower to require or to be used for functions auxiliary toits primary function, such as other .mechanical or electrical services. y

In antenna towers insulated vat the base, such as are commonly used Ain broadcasting, there has often been need to provide auxiliary `services at power frequencies, Vsuch as 60 cycles. It .has been customary to bring these'auxiliary' services into the tower structure through blocking chokes or transformers which provided no .direct conductive path to ground, because of the need to avoid short-circuiting the insulator at the tower base. This invention provides such adirect and straight conductive path to ground without short-circuit ing the tower base insulator.

It is one object of this invention to install low frequency alternating current or direct current circuits, Very high or ultra-high frequency electric-transmission lines, and/cr other auxiliary services 'on antenna towers,'with'out substantially impairng the radiating .eiciency ofthe vantenna at its operating frequency.

It is another object of this inventionto 'pro--y vide, sin'iultaneously and coincidentally,. a low.

impedance path to the :ground for escape of unwanted, wave-distorting, even-numbered har-- monics of the operating frequency, andpossible non-.harmonic oscillationsof frequencies close to such even-numbered harmonic' frequencies.

It is yet another object of this invention .to provide, simultaneously vand coincidentally, `a low impedance path to the'ground for continuous dispersion of katmospheric static electric. charges and to preclude or minimize the danger of equipment damage and/.or service stoppage due to lightning discharges through the tower.

5.Claims. -(Cl. Z50-33.53)

The following description, referring to the accompanying drawings, shows the method .of installation and the relation of componentpa'rts upon which this `invention-.is based:

Figures 1 and 2 'show the invention applied :tol

. 2 the conductive tower .structure which serves. as the antenna, such as may be used for amplitude modulation 'broadcasting service. This antenna structure is vsupported on base insulator 2 and concrete lcaser 3 andlmaintained in position by guy wires 4, which areiinsulated from theground and the antennazfby strain insulators 5, or :the position ofthe leg vhase :may be maintained by anchoringit to an anchored baseinsulator 2 in the case of :a .multiple-:leg fabricated .tower structure as 'showninFigure la. Numeral "6 :indicates the electrical coupling -circuit toa radio broadcasting transmitter, which supplies energy to the antenna at amplitude modulation frequency. Nu-

metal .1 shows-fa conductivexshielding conduit,

containing tower lighting `circuit 8, direct current or power frequency alternating current, which supplies 'electric code beacons 9l and/or electric tower lights lll, and a very high frequency trans mission line Il, `as might be required for radiating from frequency modulated antenna l2 at the top of the tower. I have found that this very high frequency is sufficiently high Iso that it does not .affect transmission 4at amplitude modulation frequencies. The conductive shielding conduit 1 is supported on standoff insulators Il and is .connected to lower 'junction box I3, which is'con-y Anected to earth adjacent to or Abeneath' the tower by an electricjconductor of practically vzero impedancaand is also connected .to'upper junction box I4, which is connected to the conductive tower structure by an electric conductor of practically zero impedance. The conduit 1 may be located inside the tower. This vupper junction box ld is locatedat approximately a quarter wavelength of the antenna broadcasting frequency vabove the ground level. may; comprise 'several conduits in parallel, con-l nected electrically .at frequent. intervals betweenl ythe lower junction box I3. and the'upper junction box I4.

Figure 2 shows a broadcasting tower comprising 'several conductive segments la, lb, etc., .separated by insulators 2b,. 2c, retc., and .insulated from the ground by base insulator 2a, the bottom segment la being less than ya quarter wavelength high. .It is evident that lsegment la :alone may constitute the antenna radiator. :In either case the tower structur'eis supported on .base insulator 2a rand concrete base 3 and maintained in position by the means shown in Figure l.. Numeral t shows the electriccoupling circuitv to -a radio broadcasting transmitter; *which supplies energy'.

to the antenna: .at-.amplitude modulation. fre- '.quency. .Numeral 'lalshows va conductive s`hield- -v The conductive shielding conduit f mately a quarter wavelength at the antenna operating frequency, by suitably bending theoonduit. The return conductor of the quarter wavelength line comprises the portionsjof` conductive tower structure adjacent to conductive shielding conduit 1a.

erating frequency, but practically negligible at even-numbered, higher harmonics of operating frequency.l

Where the tower consists of several insulated conductive segments, superpoSed, the auxiliary services may lbe carried from one'segment to another-by installing a second section of conductive shielding conduit, 'Ib from lower junction box I5 to upper junction box I6. The junction boxes I5 and I6 are conductively connected to, or near, the tops of tower legs Ic'. and Ib, respectively. The length of the conductive shielding conduit 'Ib from junction box I5 to junction box I6 is made approximately a quarter wavelength of the antenna operating frequency and thus maintains a very 'high impedance across the gap between its lower end andthe lower end of tower leg Ib at antenna operating frequency, and a very low impedance across that gap at even-numbered higher harmonics of that frequency. The condu-ctive shielding conduit may comprise several sections, in series, providing that each pair of adjacent conduit ends are connected by an electric conductor of negligible impedance, that the :length of the combined sections shall be an odd` multiple, including l, of a' quarter Wavelength of the antenna operating frequency, and that the outer end of the nal section is connected by an electrical conductor oi negligible impedance to a conductive tower structure of length equal to that of the combined sections of conductive shielding conduit.

It has been found that when a pair of parallel conductors, one of which may be the tower itself,

approximating in length .any odd multiple, in-

cluding 1, of a quarter wavelength oi the operating frequency, and shorted at the further end, is energized with alternating current, there is developedV at theopen' end an impedance su ing units i!` and Il),` and very high frequency` through transmission line I'I,'for frequency modulation antennal I2, and .also other possible servloes, not necessarily electrical, are supplied to the 'I'he impedance across theA gap between the lower end of this conductive conduit and the .base of the tower is very high at opergy leakage from the antenna to ground at the antenna operating frequency. The continuous -K low impedance path formed lby the tower struc- 'Ature `from its top through junction box I4,

through conductive shielding conduit 1, through `junction box I3 -to ground, offers easy means for distorting harmonics of the operating frequency, also an easy means for dispersion of atmospheric static charges in the vicinity of the antenna, as well as a favorable path for high frequency lightning discharges to the earth through the tower structure.

Referring to Figure 2, the operation of the combined equipment there shown is as follows: Electrical energy is supplied at amplitude modulation frequency, through electrical coupling circuit 6 from the radio transmitter to the antenna Ia, Ib, etc. Any suitable coupling, not shown, might be used between segments Ia and Ib.' Electrical and/or other auxiliary services are supplied to the antenna Ia, Ib, etc., through the conductive shielding conduits 1a, and/or 1b, etc. The potential at operating frequency, established in the antenna I a, lb, etc., through transmitter coupling .circuit B, is impressed across the gaps at the lower ends of the two quarter wavelengthl pairs-of parallel conductors comprising, rst, conductive shielding conduit 1a, between junction boxes I3 and I4, and conductive tower structure Ia, between base insulator 2a and junction box' I4 and, second, conductive shielding conduit 1b, between junction boxes I5 'and I 6, and conductive tower structure Ib, between base insulator 2b and junction box I6. This creates very high impedances across base insulator 2a and tower insulator 2b. These high impedances serve to block energy leakage from antenna to ground at an-A tenna operating frequency. The continuous low impedance path formed by conductive tower structure Ib, through junction box I 6,1 through conductive shielding conduit 1b, through junction box I5, through conductive tower structure' ticular designs, and it is to be understood that the invention applies also to other arrangements, where the same results are to beV achieved by the same means, without exceeding its scope.v

lclaim: 1

1. In combination, a" conductive antenna'struc-LA ture, less thanv a quarter wavelength in height, insulated from the ground, used at a predetermined radio frequency, a conductiveshielding conduit carrying an auxiliary service to Vthe antenna structure, a IoWimpedance'bond between the upper. 'end offsaid conduit andan-adjacent point on the said conductive antenna structure, and a low impedance connection to earth at the lower end of said conduit, said conduit being suitably bent so that the distance between said low impedance bond and said low impedance connection to earth, measured along said conduit, is approximately a quarter wave-length for the said predetermined radio frequency.

2. In combination, a conductive antenna structure, comprising several superposed conductive segments, insulated from the ground and insulated between the top of each conductive segment and the base of the superposed conductive segment, used at a predetermined radio frequency, a first conductive shielding conduit carrying an auxiliary service to the bottom conductive segment, a low impedance first bond between the upper end of .said rst conduit and an adjacent point on the said bottom conductive segment, a low impedance connection to earth at the lower end of said first conduit, the distance between said rst low impedance bond and said low impedance connection to earth, measured along said first conduit being approximately a quarter wavelength for the said predetermined radio frequency, a second conductive shielding conduit carrying said auxiliary service to a second said conductive segment of the antenna structure, a second low impedance bond between the upper end of said second conduit and an adjacent point on the said second conductive antenna segment, a second low impedance connection for the lower end of said second conduit to an adjacent point on the bottom conductive antenna segment, the distance between said second low impedance bond and said second low impedance connection being approximately a quarter wavelength for the said predetermined radio frequency.

3. In combination, a conductive antenna structure, insulated from ground, and used at a predetermined radio frequency, an auxiliary antenna supported by the antenna structure, means including an outer conductor for energizing the auxiliary antenna at a frequency higher than the said predetermined frequency, said outer conductor having a connection to the antenna structure and a connection to earth, the distance between the said connections measured along the outer conductor being approximately a quarter wavelength for the predetermined frequency, said conductor being adjacent and external to the antenna structure from its first mentioned to its second mentioned connection the cross-section of said conductor being small compared to the cross-section of said antenna structure, whereby an external path to ground is provided for lightning without substantially decreasing the radiation resistance of the said conductive antenna structure.

4. In combination, a conductive antenna tower, means for insulating the antenna tower from the ground, means for impressing radio frequency voltages between the antenna tower and ground, means for supplying an auxiliary service to said antenna tower including a conductor connected to the antenna tower and ground at points substantially an odd number of quarter wave-lengths apart measured along said conductor, said conductor being external and closely adjacent to said tower between said points the cross-section of said conductor being small compared to the cross-section of said tower, whereby an external path to ground is provided for lightning without substantially decreasing the radiation resistance of said tower.

5. In combination, an antenna tower having corner legs, an insulator between said antenna tower and ground, means for supplying energy at a radio frequency to the antenna tower, means for supplying electric power at another frequency to said antenna tower including a conductor external to the antenna tower having connections to the antenna tower and to ground, said connections having a low impedance at the said radio frequency and being spaced from each other substantially an odd number of quarter wavelengths, said conductor and one of said corner legs forming a pair of substantially .parallel conductors in close electrostatic relation throughout the distance between said connections.

LAWRENCE W. STINSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNTTED STATES PATENTS Number Name Date 2,140,174 Smith Dec. 13, 1938 2,147,165 Koch Feb. 14, 1939 2,158,875 Leeds May 16, 1939 2,393,218 Caraway Jan. 15, 1946 FOREIGN PATENTS Number Country Date- 457,468 Great Britain Nov. 30, 1936

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