US2111743A - Aerial system - Google Patents

Description

March 22, 1938.

A. D. BLUMLEIN ET AL AERIAL SYSTEM Filed Oct. '7, 1956 2 Sheets-Sheet 1 HUN INVENTORS ALAN DOWER BLIJMLEIN, EDWARD CECIL CORR AND.) EP ADE PAWSEY ATTORNEY March 22, 1938. A. D. BLUMLEIN E? AL 2,111,743

AERIAL SYSTEM Filed Oct. 7, 1936 2 Sheets-Shet 2 7/0 INVENTORS ALAN DOWER BLUMLEIN,EBWAKD CECIL CORK AND JOSE? LADE PAWSEY ATTORNEY 355 terminated, standing waves occur in the feeder In order that the invention may be more clearly 65 Patented Mar. 22, 1938 I r 2,111,743:

UNITED" STATES PATENT OFFICE AERIAL SYSTEM Alan Dower Blumlein and Edward Cecil Cork, Ealing, London, and Joseph Lade Pawsey, Hillingdon, England, assignors to Electric & Musical Industries Limited, Middlesex, England, a British company Application October 7, 1936, Serial No. 104,354

In=Great Britain October 19, 1935 '9 Claims. (01. 250-47) This invention relates to aerial and feeder and the impedance at the transmitter input will systems for short wave transmitting apparatus vary for any given aerial impedance and freand has particularrefercnce to aerial systems q y With the length o ef de If t e for use with signal frequencies of the order feeder s app x mat y an int al num er, of

employed in television transmission systems. half a e s long at h S bend q y, v

In the case of a short wave transmitter feedt e pe ce at t t a s tt r d of t e ing an aerial through a transmission line, it is feeder W a so be in error by 20%. If at thecarusual to match the resistive impedance of the e frequency the ed is a different integral aerial to the. characteristic impedance of the n m r of h lf w vel g, then at some der, and further, if possible, to match this frequency or frequencies between the carrier frecharacteristic impedance to the impedance of q n y nd th on me cy l id b n fr the transmitter. v quency, the feeder will be an integral number of When transmitting signals with a wide side -q a w v n h long and Will act as a band, such as television signals, it may be i transformer so that at these frequencies the practicableto match the transmitter impedance pe at the transmitter end will be less 15 to the feeder impedance and also to the aerial h the mp d n a t a -f qu n y. impedance, and at the sam tim btai th The response characteristic of the aerial, innecessary band width; in fact the load thrown stead o s o m e a d op t wa ds he exon the transmitter by .the aerial seen through treme d b frequencies. w also xhib t the feeder may be much lower than the impedalternatelises and falls 7 20 ance of the transmitter. Any small errors or If L IS e length of the feeder a f0 d f1 variations inthe impedance of the aerial as seen are the carrier d Side a q i s r through the feeder then affect the output. :If sp the numbers of s d wav s in the these errors are variable with frequency, the refeeder 2,it these tWO frequencies a sponse of the transmitter will also not be uniform, L ML 25 and will vary with the impedance of the aerial T a T as seen through the feeder. 1 V

Now, if the feeder is electrically long and the Where c Is the veloclty epe of waYes aerial impedance does not match the characterm feeder and eppitixlmatme to t istic impedance of the feeder, serious variations of hght' The feeder 15 defined as bemg electrl" of impedance seenby the transmitter may take long w respect to the highest modulation 30 place within. the working range of frequencies frequency and these variations of impedance: will cause QQZQ .variations in the response of the transmitter. c

Such failure of matching between the aerial and Th if (f -f )=i2 megacycles, the undet e f d r may be due o maladjustment t the sired effect will occur when L is greater than variation of the aerial impedance with frequency. about 75 meters Ev n if the aerial h s a n r l r q n It is the object of the invention to provide SDOHSe Curve adequately Wide for the bend in means for preventing variations of. the impedance 40 qu at Small departures from the tuning presented to a transmitter connected with an 40 frequency of the ia considerable reactance aerial by an electrically long feeder and so obmay be p e For example, if an aerial has tainin a substantially even response over a dea natural band width of :5'megacycles per secsired range of frequencies, 0nd} the band width being taken as the Width of According to the present invention, in ashort t e bend Within-Which the response does not wave transmitting system, variation in reactance fall more than 3 ibe below the maximum, of the aerial is corrected by the insertion at or then, t 5 ycles per Sec d from tuned near the aerial of circuits which convert the imfr qu y, h reactance of t aerial w ll qual edance of the aerial systemto a substantially its resistance- At One e ae 'p Second from constant resistance. In particular systems, acthe tim d q y, the reeetenee W be pcording to the invention, the aerial, by the addiproximately one-fifth of (or five times if contion of reactance with or without resistance, presidered in parallel) the resistance. This is a 20% sents a substantially constant terminating. reerror in matching impedance. sistance tothe feeder at all important frequencies It is well known thatif a feeder is not correctly within a. working range of frequencies.

understood and readily carried into effect, some aerial and feeder systems embodying the invention will now be described by way of example with reference to the accompanying drawings, wherein Figs. 1 and 6 are given for purposes of exposition and Figs. 2 to 5, inclusive, and '7 to 10, inclusive, illustrate various applications of the invention considered, respectively, first from the 7 angle of equivalent constants for the antenna circuits, and then actual antenna constructions. Referring to the drawings, Fig. 1 illustrates diagrammatically a known dipole aerial system fed from a potential antinode, in this case one end of the aerial. The aerial as represented includes a resistance R, a condenser C, and an inductance L connected in shunt with one another between earth and a common point. A concentric feeder F of characteristic impedance Z is connected at one end to a transmitter (not shown) and at its other end has its central conductor G connected to a point H which is one end of the aerial. The outer conductor of the feeder F is earthed. R, C and L represent the resistance, capacity and inductance, respectively, of the aerial. It will be seen that at frequencies off resonance, even when the reactance of L and C is still considerably greater than R, the feeder of impedance Z, assumed to be substantially resistive, will not be correctly terminated by the aerial. Fig. 2 illustrates the application of the invention to the aerial system shown in Fig. 1. An inductance L2 and condenser C2 are connected in series between the aerial and the feeder. Condenser C2 and inductance L2 are shunted by the resistance 1' equal in magnitude to the resistance of the feeder and have the values Under these conditions the impedance facing the feeder will be invariant with frequency and equal to R, i. e., equal to Z. If only comparatively small departures from the resonant frequency of the aerial are considered, the resistance r may be omitted altogether since the variation of resistance presented to the feeder will not be seriousand the only effect which it is necessary to correct is the reactance introduced by L and C. This can be corrected for small departures from resonance by the reactances L2 and C2.

If the impedance of the feeder does not match the impedance of the aerial directly, i. e., if Z is not equal to R, which is usual in practice when the end fed aerial is one-half of a wavelength long, it is necessary to insert a transformer between the feeder and aerial. This may take the form of a tuned circuit connected between the earth and the end of the aerial, the central conductor of the feeder being connected to a tapping point on the inductance of the tuned circuit while the sheath of the feeder is earthed. The inductance and capacity of the tuned circuit are in parallel with the corresponding inductance and capacity of the equivalent aerial circuit. The resultant inductance and capacity are shown by L1 and C1 in Fig. 3, which shows the application of the invention to the aerial and transformer system. The inductance L3 and condenser C3 are connected in series between the aerial end of the central core G of the feeder F, and the tapping point on the inductance L1. The resistance 1', equal in magnitude to the resistance of the feeder, shunts the condenser C3 and inductance L3 as in Fig. 2. If it is assumed that the transformer ratio is the square root of n, where n is equal to then the apparent inductance value of L1 at the tapping point will be and the apparent value of C1 at the same point will be nC. L3 is then made equal to nC1Z and C3 is made equal to Under these conditions, assuming a perfect transformer, the impedance facing the feeder will be equal to Z. As in the case of the arrangement shown in Fig. 2, the resistance r may be omitted if only small departures from the resonant frequency of the aerial are considered. Correction for the reactance introduced by L1 and C1 for small departures from resonance can be corrected by the reactances L3 and C3. In this case L3 may be composed of the leakage inductance of the transformer so that in some cases only C: need be added.

Fig. 4 illustrates the case of an aerial fed at its centre, the aerial system being represented by an inductance L, a condenser C and a resistance R, connected in series with one another and between the aerial end of the feeder F and earth. It is assumed that the feeder impedance has been made equal to R. The present invention is shown applied to this arrangement by the addition of a shunt load comprising an inductance L4 and capacity C4 and resistance r. The lower terminal of resistance r is earthed and its upper terminal is connected to one terminal of condenser C4 and to one terminal of inductance L4. The other terminals of the inductance L4 and condenser C4 are connected to the aerial end of the central conductor G. In this case it is arranged that 6 is equal to R,

E, is equal to R and T is equal to R. This is a counterpart of the arrangement described with reference to Fig. 3, and again, as a first approxi mation, resistance 1 may be omitted and for this purpose may be short circuited.

Fig. 5 shows another method of applying the invention to the aerial system described with reference to Fig. 3. The tapping point on the inductance L remains directly connected to the end of the central conductor G of the feeder F, and a shunt load is connected between the central conductor G of the feeder and earth at a point I located a quarter wavelength or an odd number of quarter wavelengths from the aerial end of the feeder. The shunt load is of the type deand C5 is equal to 110. As before, as a first approximation close to resonance r may be effectively omitted by short circuiting it. If this type bf correction is employed; it is advisable-to' put the correcting"circuit-wily a" small *number-jof quarter wavelengths away from the"aerial, if correction-oyer a wide frequency band is. required. By putting theload-a-quarter wavelength away, the impedanceerrors ar'iriverted so that the type of circuit required is altered.

Further applications of the invention are illustrated in- Figs. 7, 8, 9 and 10, and will be more clearly understood when considered in relation to the following explanation of Fig. 6. In this figure a dipole aerial l is represented diagrammatically and includes a parallel line circuit 2. If it is assumed that the dipole aerial is a line of characteristic impedance Zn and of a length 9a with a radiation resistance R1 in series, and that the line'2 has an impedance Z0, an electrical length 9 and has in series a resistance R2, then the impedance between the points A and B may be obtained by the following equation:-

12,122+ z,,z,, cot 0,, tan ow -(121a, tan Z tan 04 If, in this equation is inserted:

and tan 9A=tan 9, then Z=R, from which it is seen that the reactance variation has disappeared.

Referring to Fig. 7, a concentric feeder havin inner and outer conductors 3 and 4 is connected to a dipole aerial 5, 6. The parallel line corresponding with the line 2 in Fig. 6 is constituted by an outer sheath I enclosing the sheath 4 of the feeder. sheath 4 at a point 8 approximately one electrical quarter of a wavelength from the aerial 5, 6.

In Fig. 8 a symmetrical arrangement is'shown in which the parallel line is formed by adding an inner conductor 9 to a hollow line In used normally as a dummy line serving the same purpose as an interference suppressing line of the kind described in the specification of British Patent No. 438,506. This interference suppressing line renders the end of the feeder connected to the aerial electrically symmetrical with respect to earth, and also acts so that interference picked up by and propagated along the outside of the feeder acts equally on each half of the dipole aerial so that no potential difference due to inter ference is established between the conductors of the feeders 3, 4.

In Fig. 9 a symmetrical arrangement is shown, but in this case two parallel lines 'H and I2 are used as the correcting lines, the dummy line H] shown in Fig. 8 being retained.

In Fig. 10 a further symmetrical arrangement is shown but in this case two auxiliary concentric lines having inner and outer conductors I3 and I4, and I and I6, respectively, are used for correction purposes.

It will be understood that the invention may be carried out in further ways which will occur to those skilled in the art, and it is further to be understood that the invention may be applied to aerials of other types than dipoles, the correction in certain cases being made at the junction of the aerial and its feeder.

What is claimed is:

1. In a short Wave transmitting system, an

aerial, a source of high frequency energy, a feeder coupling said aerial to said source, and a circuit coupled to said feeder near the coupling point of said aerial and feeder for presenting a R Z tan 9 The sheath I is connected directly to the *2. In a short wave transmitting system, an

aerial, asource of high frequency energy; a feeder coupling said aerial to said source,"and acircuit coupled to -said feeder near the coupling point of said aerial and feeder for presenting a substantially pure resistance of constant magnitude to said feeder over a range of frequencies which said aerial is adapted to radiate.

3. In a short wave transmitting system, an aerial, a source of high frequency energy, a feeder coupling said aerial to said source, and a circuit inserted in series between said aerial and feeder and located near the coupling point of said aerial and feeder for presenting to said feeder a substantially pure resistance over a range of frequencies which said aerial is adapted to radiate.

4. In a short wave transmitting system, an aerial, a source of high frequency energy, a feeder coupling said aerial to said source, and a circuit including a concentrated reactance coupled to said feeder near the coupling point of said aerial and feeder for presenting a substantially pure resistance to said feeder over a range of frequencies which said aerial is adapted to radiate.

5. In a short wave transmitting system, an aerial, a source of high frequency energy, a feeder coupling said aerial to said source, and a circuit including a capacitance and an inductance effectively arranged in series inserted between said aerial and feeder near the coupling point of said aerial and feeder, said capacitance and inductance having such values as to present to said feeder a substantially pure terminating resistance over a range of frequencies.

6. In a short wave transmitting system, an aerial, a source of energy, a feeder a plurality of wavelengths long at the operating frequencies coupling one end of said aerial to said source, and a circuit including a capacitance and an inductance effectively arranged inseries inserted between said aerial and feeder near the coupling point of said aerial and feeder, said capacitance and inductance having such values as to present to said feeder, a substantially pure terminating resistance over a range of frequencies.

'7. In a short wave transmitting system, an aerial, a source of high frequency energy, a feeder coupling the center of said aerial to said 7 source, and a circuit including a capacitance and an inductance effectively arranged in parallel coupled between said feeder and ground at a point near the coupling point of said aerial and feeder, said capacitance and inductance having such values as to present to said feeder a substantially pure terminating resistance over a range of frequencies which said aerial is adapted to radiate.

'8. In a short wave transmitting system, an aerial, a source of high frequency energy, a feeder coupling the center of said aerial to said source, and a circuit including a capacitance and inductance effectively arranged in parallel coupled between said feeder and ground at a point a multiple of a quarter wavelength, including unity, from the coupling point of said aerial and feeder, said capacitance and inductance having ductance are substantially uniformly distributed such values as to present to said feeder a suband in the form of portions of concentric transstantially pure terminating resistance over a mission lines.

range of frequencies which said aerial is adapted ALAN DOWER BLUMLEIN. to radiate. EDWARD CECIL CORK.

9. A system in accordance with claim 5, char- JOSEPH LADE PAWSEY.

acterized in this that said capacitance and in-

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