US2480172A - Radio antenna - Google Patents

Description

A g- 30, 1949. E. o. WILLOUGHBY RADIO ANTENNA 2 Sheets-Sheet 1 Filed Jan. 16, 1945 'INVENTOR. 5% 0550/P/VE Maw/my 2 Sheets-Shet 2 IN VEN TOR.

ATTORNEY Aug- 30, 1 E. o. WILLOUGH'BY RADIO ANTENNA Filed Jan. 16, 1945 rll 1 $5.52!

Patented Aug. 30, 1949 RADIO ANTENNA Eric Osborne Willoughby,

signer, by mesne assignments, St'and'ard'Electr-ic Corporation, a corporation of Delaware London, England, asto International New York, N. Y.,

Application January 16, 1945', Serial No; 573,099 In Great Britain November 5, 1943 Section 1, Public Law 690, August 8, 1946 Patentexpires November 1963 8 Claims. (Cl. 250*33) The present invention relates to radio antenna systems and it has for its chief object to provide an antenna system for use at ultra high frequencies, for example 100-150 megacycles which has a substantially flat amplitude-frequency characte'ri'stic over a wide frequency band of the order or 20% of the mean fre uency on either side of said mean frequency.

According to one aspect of the invention an antenna system having a substantially constant resistance over a broad operating band of ultra high fre'qu'en'c'ies includes an antenna comprising a hollow conducting cylinder erected vertically above the ground but insulated from it and havinga physical length between one quarter and one half the mean operating wave length, and half wave resonant at the mean operating frequency, a central conductor which passes through said hollow cylinder to form therewith a stub and means for tuning the said stub to resonance at the mean operating frequency, a transmission line preferably screened for coupling said antenna to a translation device and a quarter wave line im: pedance transformer at substantially said mean frequency coupling said antenna and said transline.

According to another aspect of the invention a dipole radio antenna system having a substantially constant resistance over a broad operatingband of ultra high frequencies includes a dipoleantenna comprising two hollow conducting cylinders each having aphysical length between one quarter and one half the mean operating wave length, and half wave resonant at the mean operating frequency, central conductors which pass through the respective hollow cylinders forming stubs therewith and means for tuning said stubs to resonance at the mean operating frequency, a transmission line preferably screened for coupling the antenna to a translation device, and a quarter wave line impedance transformer at substantially said mean frequency coupling said antenna and" said transmission line.

The lower end of the vertical antenna is prefer ably conical and tapers towards the ground and the inner ends of the dipole cylindrical members are preferably conical tapering towards each other, and the physical length of the vertical antenna, or each of the dipole members tuned to half waveresonance is between one quarter and one half the mean operating wave length.

An antenna embodying the invention is effectively fed; from the conical end; since the waves pass down the inside of the cylinders from the cylindrical end and along" the outside of the cylinder from the conical end during the radiating' action. In a receiving antenna the reverse action takes lace.

The characteristic impedance of the conical portion of the antenna is preferably of the same order asthe characteristic impedance of the cylindrical portion, the chief purpose of the conical endbeihg to avoid the capacity irregu-= larity present with ends of large cross-sections coming close together at the feed point and to provide a smooth feedinto the e'ifective portion of the antenna system free from excessive shunt capacity e'fs'e'ctsl A An antenna of low characteristic impedance is employed thereby keeping the end radiation resistance' low and a transmission line of relatively high characteristic impedance (particularly if ascre'ene'd" line-is desired) is employed to reduce the impedance transformation ratio in order that a quarter wave line impedance transformer may we used for coupling the antenna and transmission line. The antenna is series tuned throughout the frequency band by using series tuned elements of appropriate value in series with the antenna thus taking advantage of} the fact that the reactance of a half wave antenna varies in the opposite direction with frequency through resonance as does a series tuned circuit consisting of series connected inductance" and capacity.

The series tuning of the antenna throughout the frequency band canbe carried out sufficiently well that the antenna may be considered as a substantially ure resistancevarying with frequencyac'cofding' to a law represented by a smooth curve with-the maximum near the centre of the operating band substantially twice as high as that on the extremes of the operating band, and the problem of coupling tlie'an'tenna to a transmission line then resolves itself into matching the characteristic impedance of the transmission line with that of the said pure resistanc varying in the manner stated.

If Z9 is the characteristic impedance of the reed line, a quarter wave impedance matching transformer whose impedance is /R,Zo where R istlie mean resistance of the antenna over the frequency band, gives an impedance mismatch between the antenna and line of the order 5:4, i.- e. o'fthe order of 0.2 db. Such a coupling unit is compact and'by slight over-compensation of the antenna as seen at its reaetance of the half-wave base, the s'm'all' reactance-introduced by deviation of thematcfiing transformer from quarter wavelength-in the tuning band'lcan be largely compensated'; By overcompensation is meant introducing a greater series reactance than is required for neutralisation of the antenna reactance 1n the operating frequency band. Such a quarter wave line coupling impedance transformer is thus suitable for coupling the antenna and a screened transmission line. With a coupling unit of this type the losses at the extremes of the frequency band are smaller the lower the impedance transformation ratio.

Such a coupling unit has also mechanical advantages since it is extremely compact, rigid, and simple, and can be carried with the antenna at the end of a long length of transmission line, whereas a more theoretically perfect coupling unit involves a plurality of condensers and inductances and is complicated and voluminous, and its superiority in performance over the simple quarter wave transmission line is small.

trical contact therewith and through the bushing 6 so that it can be manipulated to adjust the q capacity and at the same time connect the condenser across the tube.

The condenser at the same time series tunes the lower open end of the stub to the mean operating frequency and thus makes the impedance across the open or lower end of the stub or antenna zero at the mean operating frequency.

-The location of this condenser may be used 7 to make the reactance characteristic across the open end of the stub vary unsymmetrically with The accompanying drawings show by Way of example some practical embodiments of the invention.

In the drawings, Figure 1 shows an antenna system according to the invention utilising an unbalanced antenna with respect to earth potential.

' Figure '2 shows an antenna system according to the invention utilising a dipole or balanced antenna and transversely arranged transmission line.

Figure 3shows a supporting arrangement for the antenna system shown in Figure 2.

Figures 4, 5 and 6 show a dipole antenna system according to the invention with the-transmission line coaxial with the dipole antenna. Figures 5 and 6' are partial views showing modified connections for use with a concentric and twowire transmission line respectively.

Figures '7 and 8 show supporting arrangements for the antennasystems of the type shown in Figures 4, 5 and 6.

In all the figures like reference characters.

Referring to Figure 1,- the reference numeral I indicates the hollow conducting cylinder which is closed at its upper end 2 and has a conical lower end 3 tapering towards the ground or earth plane indicated at 4. The antenna is enclosed in an insulating tubular casing 5 and held in position therein by means of asupporting bushing 6, for example, of polystyrene located substantially at the voltage node on the cylinder I and this tubular'casing is supported directly on the earth plate 4 but holds the antenna I insulated from the ground. The central conductor is shown at 1 its upper end to the closed end 2 of the hollow conducting'eylinder I, and passes through the lower conical end at which, if necessary, a low capacity centring insulator may be used; 8 indicates the transmission line for connection to a translating device. The quarterwave line impedance transformer is. indicated at H) connecting the transmission line 8 to the antenna I.

The cylindrical hollow conductor I has a physical length of less than half the mean operating wavelength. The central conductor 1 together with the hollow conductor I closed at its upper end forms a short circuited stub having an electrical length between one-quarter and one-half the mean operating wavelength. This stub is tuned to resonance at substantially the mean frequency of the operating band by parallel tuning the upper closed end of the stub by means of an adjustable condenser I I accommodated within the. hollow cylindricalmember I and connected parts are given the same frequency about the mean operating frequency to an extent that matches the unsymmetrical reactance characteristic of the antenna with respect to the mean operating frequency.

The characteristic impedance of the stub is chosen for example, by suitable diameter of the central conductor so that the reactance seen across its open end is equal and opposite to the reactance at the base of the antenna, that is, of the hollow cylindrical member alone, at frequencies near the outer limits of the operating frequency band.

Actually a single open wire line a quarter of the mean operating wave length long or an open stub and tuned to quarter wave series resonance at the mean operating frequency in the cylinder will couple the antenna to the transmission line and give a good degree of reactance compensation, but the reactance changes obtainable by this means are not so great as in the preferred form shown in Fig. 2. 7 Also the circuit constants are inconvenient in value and the system is not so satisfactory mechanically as the preferred form.

The insulating casing 5 provides a weather screened space around the antenna and weather conditions have a reduced and more uniform effect on the performance of the antenna over the operating frequency band than one which is not screened.

,It should be noted that the single matching transformer I0 may be replaced by two matching transformers in series of characteristic impedances ZI and Z2 respectively such that R, Zl, /ZIZ2, Z2, and Z0 are in geometrical progression, where R is the mean resistance of the antenna, and Z0 is the characteristic impedance of the transmission line. This arrangement would provide a slight improvement in performance over the single transformer.

Referring now to Figure 2 a dipole antenna comprises two members as described in connection with Figure I placed with their conical ends 3-, S'adjacent each other and the transmission line comprises two coaxial transmission lines, but may be a two wire screened transmission line, brought horizontally to the two conical ends of the hollow conducting cylinders and. each is coupled to its respective central conductor 1, 1' of the two members through a quarter wave line impedance transformer I0; I 0' of suitable characteristic impedance as described in connection with Figure 1. (It should be understood that screened lines are here recommended'for ease of mounting in such cases as ship installations but an unscreened balanced transmission line may be used.)

The two dielectric cylinders 5, 5

m e sea isogwa cured together; and: the antenna suspended: th'ere-.

byfrom aguy wire. I23. asshowir-in Figure 31 or maybesecuredt'o the topofi awoodenm'ast.

A smallilen'gth I141of'conductor may be allowed" between thecoupling transformer- L: and the central conductor 1: (Fig. l=) or conductors T, i. (Fig. 2) as it will compensate for some displacement of the mean tuning condenser from the optimum position which displacement itself: effects compensation for the unsymmetrical antenna. reactancecharacteristic;

The balanced: or twovwire-screened transmisquired on the outer screen of the transmission line. This latter feature is of great value when the: antenna: is to operate over a wide frequency band and renders the dipole antenna describedthe simplest and'best balanced antenna in, regard to performance throughout the operating' nequency-band.

It ispossible to feed the dipole antenna by means of a single, unbalanced. transmission line, but due to a larger impedance transformation ratio, an; increase of; approximately 0.1 db. in. the

mismatch at the extremes of thefrequency band will occur anditisunecessary to use a standing wave suppressor on the outside of the transmission: line.

When thedipole antennaiis-ifedzby a transmissien line in; alignmentwithzthe antenna as shown in Figures4, 5..and.6.(rather than'transverse-to the, dipole as. shown in. Figure 2E)- the coupling impedance transformer liiis accommodated withinlthe cylindrical.memberintoiwhich the line is taken, that: is.the lower. one as shown in Figures 4, 5- and 6; so that. the formerly closed lower end is now open and=it is, necessary to put a short circuit between the outer conductor of the quarter wave: line impedance-transformer and the hollow cylindrical-member at-suc-h a distance from the open conical end of the cylindrical member to form a quarter wave closed stub at the mean operating frequency in order to suppress standing waves on the said outer conductor of the impedance transformer and transmission line. This short circuit is shown as a conducting disc l5 having a central aperture for the passage of the central conductor.

The central conductors of the quarter wave line transformer where a concentric line is used (Figs. 4 and 6) or one of the conductors of a two wire line (Fig. 5) is connected to the central conductor I of the upper cylindrical member. In the case of the two wire line (Fig. 5) the other wire is connected to the outside of the lower cylindrical member I as shown at 16 and in the case of the coaxial line (Figs. 4 and 6) the outer conductor of the quarter wave line transformer is connected to the apex of the conical end of the lower cylindrical member I as shown at I1 (Figs. 4 and 6).

In regard to suppressing the standing Waves on the outer conductor or screen of the transmission line a low characteristic impedance antenna is an advantage as it allows a relatively high impedance suppressing stub to be constructed. As a refinement it may be beneficial to 6. conneotxsuppresson" stubs tunedztoa and inequen'ciesof; the frequency bandiatpositions along the fee'ddinedetermined:experimentally, but simplicity would probably dictate-a compromise such.

. as can be obtained with a. quarter wave. suppressing stub. of relatively highimpedance together with some small increase in loss at the extremes of the operating frequenc'y band; Thisstub is formed by the shortcircuit device I5 betweenthe cylinder I? and the quarter wave-fin pedanc'e-trainsformer I 0; thus providi-ng aquar ter wave blocking stub on the outer conductor of a transmission line.

In the case of the unbalanced transn-i-i'ssion' line Figs. 4-and-6 the outer concentric conductorof the line is terminated on the lower half-waveantennamember i; but thecase of atwo: Wire transmission line; a tuning capacity as indicated at lain Figure-Sis necessary topa-rallel' tune the short oi-rcuited stub, formed by" theshort circuit disc t5 the outer screenconductor o'f the quarter wave line impedance transformer and the'inside of the'antenna lower cylindrical memher I. To keep the resistance frequency re-- sponse characteristic as fi'at-aspo'ssible', the short circuiting device the form of adisc annulus, should lee-thin and a relatively low. character istic impedance antenna usedso' that the i-mr pedance of the blocking stub will benign.

shown" in Figure 7- the antenna with the transmission line coaxial therewith may be supported-iroma=guy wii=e=-l3 or as shown in'Fig. 8" may be supportedonthetop of the wooden mast '9;

What is-claimed-is:

l; A radio antenna system hmiing a' substantially constant resistance-over a broad operating band of \ultrahigh frequencies including anan.- tenna comprising a liollow'conducting" cylinder having'a physical length' between one quarter'and one half the mean operating wavelength and half wave resonant at the meanoperating' fre'- quency, a central conductor which extends through the length of said hollow cylinder and is connected-to one end thereof to form therewith a short circuited stub, a reactance element connected'between' said central conductor and said cylinder at a point intermediate the ends thereof for =tuning'said' stub" to resonance at the. mean operating frequency; a transmission line for coupling said antenna to a translation device and an impedance transformer substantially a quarter wave length of said mean frequency coupling the open circuited end of said antenna and said transmission line.

2. A dipole radio antenna system having a substantially constant resistance over a broad operating band of ultra high frequencies including a dipole antenna comprising two hollow con ducting cylinders each having a physical length between one quarter and one half the mean operating wave length and half wave resonant at the mean operating frequency, a central conductor which extends through the length of one of said hollow cylinders and is connected to one end thereof forming a stub therewith, a central conductor which extends through the length of the other of said hollow cylinders and connects with the inner side of said cylinder forming a stub therewith, a reactance element connected between said central conductor and said cylinder at a point intermediate the ends thereof for tuning said stubs to resonance at the mean operating frequency, a transmission line for coupling the antenna to a translation device and an impedance transformer substantially a quarterwave length of said mean frequency coupling the open circuited end of said antenna and said transmission line,

3. A radio antenna system; having a substantially constant resistance over a broad operating band of ultra-high-frequencies including an antenna comprising a hollow conducting cylinder having a physical length between one-quarter andone-half of the mean operating wavelength and half wave resonant at the mean operating frequency, a central conductor extending through said hollow cylinder connected to one end thereof and forming therewith a, stub, the outer end of said vertical cylinder being closed, said cylinder having a reactance element connected between said central conductor and said hollow cylinder at a point intermediate the ends thereof for parallel tuning to resonance at the mean frequency.

of operation a length of the cylinder and central conductor not greater than one-quarter of the mean operating wavelength from the closed end, said reactance element also series tuning the other portion of said cylinder and central conductor to substantially the mean frequency and forming a quarter wave stub of said other portion, thereby making the impedance across the open end of the stub substantially zero at the mean operating frequency; a transmission line for coupling said antenna to a translation device and a quarter wave line impedance transformer at substantially said mean frequency coupling said antenna and said transmission line.

4. A radio antenna system as claimed in claim 3, said reactance element comprising an adjustable capacity connected across the said cylinder and the central conductor. 7

5. A dipole antenna system having a substantially constant resistance over a broad operat ing band of ultra-high frequenciesincluding a dipole antenna comprising two hollow conducting cylinders each having a physical length between one quarter and one half the mean operatin g wave length and half wave resonant at the mean operating frequency, two central conductors, one extending through the length of each of said hollow cylinders and connected to the ends thereof to form a short circuited stub therewith and two reactance elements; one being connected between each of said central conductors and said cylinders at a point intermediate the ends thereof for tuning said stubs to resonance at the meanoperating frequency, a transmission linefor coupling said antenna to a translation device and an impedance transformer substantially a quarter 5 wave length of said mean frequency coupling the open circulted end of said antenna and said trans-- transformer being accommodated within one of said conducting cylinders and further including means for suppressing standing waves on the transmission line.

8. A radio dipole antenna system as'claimed claim '7, said means comprising a short circuiting conductor between the screen of said balanced transmission line and said one cylinder at substantially a quarter of the mean operating wave length from the inner end of said cylinder.

ER1C OSBORNE WILLOUGHBY.

REFERENCES CITED The following references file of this patent:

are of record in the UNITED STATES PATENTS Number Name Date 2,067,337 Polatzek Jan. 12, 1937 2,158,271 Buschbeck May '16, 1939 40 2,167,709 Cork Aug. 1, 1939 2,226,686 Alford Dec. 31, 1940 2,239,700 Carter Apr. 29, 1941 2,311,364 Buschbeck Feb. 16, 1943 2,321,454 Brown June 8, 1943 2,368,298 Harris Jan. 30, 1945 FOREIGN PATENTS Number Country Date 878,564 France Jan. 25, 1943 260,005 Great Britain Mar. 24, 1927 7. A radio dipole antenna system as claimed in claim 2, in which the transmission line is screenedand approaches the dipole antenna along the longitudinal axis of the antenna, said impedance

Images