US2293753A - Wide band traveling wave antenna - Google Patents

Description

N. E. LINDENBLAD 2,293,753 WIDE BAND TRAVELING WAVE ANTENNA Filed April l0, 1941 2 Sheets-Sheet l 70/5 LecZZ'on 1 l0 1/ l2 flnZ/vza, lenqzh in, Waredenqfiw INVENTOR ATTORNEY Patented Aug. 25, 1942 WIDE BAND TRAVELING WAVE ANTENNA Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April 10, 1941, Serial No. 387,830

18 Claims.

The present invention relates to multiple wavelength traveling wave radiators and, more particularly, to such radiators designed to cover a wide frequency band.

An object of the present invention is the provision of a radiator having a constant resistive input over a wide frequency spectrum.

Another object is to provide a traveling wave antenna which has a low factor of reflection over a wide frequency band.

Still another object of the present invention is the provision of a wide band short wave antenna suitable for producing energy concentration for either beam or broadcasting services.

In order to accomplish the above mentioned objects, and others which may appear from the following detailed description, in accordance with the principles of the present invention I propose to provide a radiator having a maximum diameter which is a large fraction of the length of the operating wave and which is several operating wavelengths in length. The radiator is gradually tapered at the end to which the transmission line is connected to the diameter of the transmission line conductor so as to provide a smooth transfer of energy from the transmission line to the antenna without reflection back into the transmission line. The remainder of the antenna is elliptically tapered to a much smaller diameter at the free end of the radiator.

While throughout the present specification I have particularly referred to the antenna as a radiator, it is to be clearly understood that the antenna may equally well be used forreceiving signals and in this service the same results are obtained as in the transmission of signals.

The present invention will be more fully understood by reference to the following detailed description, which is accompanied by drawings in which Figure 1 illustrates the ideal form of an antenna embodying the principles of the present invention, while Figure 2 illustrates a modification of the form shown in Figure 1, which is more easily constructed; Figures 3 and 4 illustrate by means of curves the percentage of reflection obtained in antennas constructed according to Figures 1 and 2 with variation in the wavelength of energy applied thereto; Figure 5 illustrates the horizontal directivity pattern obtained by using a single radiator as shown in Figures 1 and 2, while Figure 6 illustrates, in plan view, an antenna having a directivity characteristic with only a single major lobe.

Referring, now, to Figure 1, reference numeral N] indicates, generally, the radiator constructed according to the principles of my invention. The radiator in may consist of a plurality of separate conductors ll connected at one end to a small metallic cone l2 and at the other end to the inner conductor I3 of transmission line TL. The transmission'line TL is connected to a conventional source of high frequency ener y, not shown. The radiator I0 has a maximum diameter at l5 of the order of one wavelength at midband frequency. The diameter may vary from .6 of a wavelength up to one wavelength without a substantial variation in characteristics. The region of maximum diameter should preferably be spaced from the transmission line end of the antenna, a distance of approximately one wavelength at the midband frequency. From the region of maximum diameter the conductor tapers toward the far end where it is terminated by a small conductive cone. Preferably, the taper should be elliptical rather than purely conical. However, if the taper consists of a series of short conical sections the form approximates the ideal elliptical taper closely enough for all practical purposes. The first portion of the antenna between the region of maximum diameter and the transmission line should also be tapered in an elliptical manner so as to obtain as smooth a transition as possible between the impedance of the transmission line and the impedance of the antenna. The shaping of this portion of the antenna is far more critical than that of the other portion of the antenna and has an import ant influence on reflection at the input end.

The transmission line TL .preferably has its outer conductor [4 flared out around the expanding portion of conductor l3 where it connects to the radiator ll so as to aid in obtaining a smooth impedance transformation, according to the principles set forth in my prior application #208,573, filed May is, 1938, now Patent No.

2,239,724. The extreme end of the outer conductor l4 may be connected to a ground sheet as shown or other convenient means such as the quarter wave trap disclosed in my prior application #183,571, filed January 6, 1938, now Patent No. 2,238,904, may be employed to prevent high frequency energy from flowing over the outer surface of the conductor M.

The antenna shown in Figure 2 follows, generally, the principles set forth above with reference to Figure 1. However, the construction is somewhat more easily accomplished since the taper from the region 25 of the maximum diameter to the minimum diameter regions is.

conic in form, the conductor wires being maintained in their proper relative relationship one to the other by means of spacing rings 25. Likewise, the first portion of the expansion of the radiator between transmission line TL and the portion of maximum diameter 25 is, instead of being continuously tapered, tapered in steps. The steps should, however, be sufficiently closely spaced so as to obtain an approximation of an elliptic expansion.

Figure 3 is a curve in which is shown percentage reflection back into the transmission line plotted against radiator length measured in wave multiples. The relationships shown were obtained by utilizing a fixed length antenna and varying the frequency applied to the antenna. The curve represents the results obtained with a radiator of a length equal to about 8 wavelengths at the middle frequency. It will be seen that within the limits of 7 to 10 wavelengths the percentage of reflection was maintained below 20 percent.

Figure 4 shows a curve similar to that shown in Figure 3 wherein the antenna length is a greater multiple of the operating wavelength. The antenna length in this case is about 11 wavelengths at the midband frequency. As may readily be seen the longer radiator achieves the desired results much more efiectively. Over the entire range from 7 /2 to 14 wavelengths a maximum reflection of only 14 percent is encountered, and it will further be evident that much lower reflection is encountered over the major portions of this range. For example, between 8 and 12 wavelengths the reflection does not rise above 10 percent.

Figure shows the directivity obtained with an antenna of the form shown in Figures 1 and 2. It will be noted that this directivity pattern shows two maximum lobes one'at each side of the antenna axis. The pattern is not entirely symmetrical due to the presence of unavoidable conductive objects within the field of the radiator tested. This pattern is somewhat similar to that obtained by the conventional long wire antenna.

A directivity pattern having only a single maximum lobe may be obtained in the same way as that with previously known traveling wave antennas. One way in which this may be done is shown in Figure 6 wherein a pair of radiators and 36 are disposed at an angle to one another, the b-isector of the angle being in the direction of the maximum desired radiation. The magnitude of the angle is determined by the angle between the two maximum lobes shown in Figure 5. The two radiators 35 and 3b are so disposed the right-hand maximum lobe of the left-hand antenna and the left-hand maximum directivity lobe of the right-hand antenna add to form a single large lobe in the desired direction while the other lobes are correspondingly reduced. The two antennas 35 and 36 are energized in the desired phase relationship from any desired energy source by means of transmission lines TL.

While I have particularly shown and described several modificationsof the present invention, it is to be distinctly understood that my invention is not limited to these particular embodiments but that modifications and alterations within the scope of the invention may be made.

I claim:

1. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a maximum transverse dimension of the order of one wavelength near one end, means for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end.

2. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several. wavelengths of any frequency within said band, said conductor having a maximum transverse dimension greater than one-half wavelength near one end, means for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end.

3. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a maximum transverse dimension of the order of one wavelength near one end, means for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end, and said conductor being sharply tapered from said maximum transverse dimension at said one end.

4. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several wavelengths of any fre quency within said band, said conductor having a maximum transverse dimension greater than one-half wavelength near one end, means 'for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end, and said conductor being sharply tapered from said maximum transverse dimension at said one end.

5. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a maximum transverse dimension of the order of one wavelength near one end, means for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end, and said conductor being sharply tapered from said maximum transverse dimension at said one end, said tapers being elliptical in form whereby a smooth change in characteristic 'impedances is obtained.

6. A wide band traveling wave antenna comprising a radiating conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a maximum transverse dimension greater than onehalf wavelength near one end, means forenergizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end, and said conductor being sharply tapered from said maximum transverse dimension at said one end and said tapers being elliptical in form whereby a smooth change in characteristic impedances is obtained.

'7. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any frequency within said band-said conductor having a maximum transverse dimension of the order of one wavelength a distance substantially equal to one wavelength at midband frequency from one end, means for energizing said conductor at said one end, said conductor gradually tapering to a small transverse dimension at said other end, and said conductor being sharply tapered from said maximum transverse dimension at said one end, said tapers being elliptical in form whereby a smooth change in characteristic impedances is obtained.

8. A wide band traveling wave antenna system comprising a radiating conductor having a length equal to at least several wavelengths of any frequency Within said band, said conductor having a maximum transverse dimension at a distance substantially equal to one wavelength at midband frequency from one end of the order of one wavelength, 3, transmission line having an inner conductor and an outer shell for connecting said antenna to a transducer, the inner conductor of said transmission line being connected to said conductor at said one end, said conductor smoothly tapering from said maximum transverse dimension to the diameter of said inner conductor whereby energy is transferred along said tapering portion without reflection.

9. A wide band traveling wave antenna system comprising a radiating conductor having a length equal to at least several Wavelengths of any frequency within said band, said conductor having a maximum transverse dimension at a distance substantially equal to one wavelength at midband frequency from one end of the order of one wavelength, a transmission line having an inner conductor and an outer shell for connecting said antenna to a transducer, the inner conductor of said transmission line being connected to said conductor at said one end, said conductor smoothly tapering from said maximum'transverse dimension to the diameter of said inner conductor whereby energy is transferred along said tapering portion without reflection, said outer shell being flared at its end and surrounding a portion of said taper.

10. A wide ban-:1 traveling wave antenna system comprising a radiating conductor having a length equal to at least several wavelengths of any frequency within said band, said conductor having a maximum transverse dimension at a distance substantially equal to one wavelength at midband frequency from one end of the order of one wavelength, a transmission line having an inner conductor and an outer shell for connecting said antenna to a transducer, the inner conductor of said transmission line being connected to said conductor at said one end, said conductor smoothly tapering from said maximum transverse dimension to the diameter of said inner conductor whereby energy is transferred along said tapering portion without a reflection, said outer shell being flared at its end and surrounding a portion of said taper, means surrounding said outer shell for preventing the flow of energy along the outer surface thereof, said radiating conductors being tapered from its region of maximum transverse dimension throughout its length to said other end.

11. A wide band traveling wave antenna system comprising a radiating conductor having a length equal to at least several wavelengths of any frequency Within said band, said conductor having a maximum transverse dimension at a distance substantially equal to one wavelength at midband frequency from one end of the order of one wavelength, a transmission line having an inner conductor and an outer shell for connecting said antenna to a transducer, the inner conductor of said transmission line being connected to said conductor at said one end, said conductor smoothly tapering from said maximum transverse dimension to the diameter of said inner conductor whereby energy is transferred along said tapering portion Without reflection, said outer shell being flared at its end and. surrounding a portion of said taper, means surrounding said outer shell for preventing the flow of energy along the outer surface thereof, said radiating conductors being tapered from its region of maximum transverse dimension through* out its length to said other end, said tapers being elliptical in form.

12. An antenna as set forth in cl-aim'8, wherein said radiating conductor is comprised of a plurality of longitudinal Wires defining the surface thereof, said wires being connected to met-allic end pieces and supported in position along the length of said conductor by spacing rings.

13. An antenna as set forth in claim 9, Wherein said radiating conductor is comprised of a plurality of longitudinal wires defining the surface thereof, said wires being connected to metallic end pieces and supported in position along the length of said conductor by spacing rings.

14. An antenna as set forth in claim 10, Wherein said radiating conductor is comprised of a plurality of longitudinal wires defining the surface thereof, said wires being connected to metallic end pieces and supported in position along the length of said conductor by spacing rings.

15. An antenna as set forth in claim 11, wherein said radiating conductor is comprised of a plurality of longitudinal wires defining the surface thereof, said wires being connected to metallic end pieces and supported in position along the length of said (conductor by spacing rings.

16. An antenna array comprising a pair of antennae as set forth in claim 3, lying in a common horizontal plane with their one ends adjacent and storming an angle, the bisector of said angle being directed in the desired direction of communication.

17. An antenna array comprising a pair of antennae as set forth in claim 8, lying in a common horizontal plane with their one ends adjacent and forming an angle, the 'bisector of said angle being directed in the desired direction of communication.

18. An antenna array comprising a pair of antennae as set forth in claim 11, lying in a common horizontal plane with their one ends adjacent and forming an angle, the bisector of said.

angle being directed in the desired direction of communication.

NJLS E. LINDENBLAD.

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