US2706778A

US2706778A - Cylindrical sleeve antenna

Info

Publication number: US2706778A
Application number: US169062A
Authority: US
Inventors: Andrew W Walters
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-06-19
Filing date: 1950-06-19
Publication date: 1955-04-19
Anticipated expiration: 1972-04-19

Description

April 19, 1955 A. w. WALTERS CYLINDRICAL SLEEVE ANTENNA Filed June 19, 1950 INVENT OR ANDREW W. WALTERS 10 Y W A'TORNEYS United States Patent O CYLENDRICAL SLEEVE ANTENNA Andrew W. Walters, Washington, D. C.

Application June 19, 1950, Serial No. 169,()62

Claims. (CI. 250--33) (Granted under Title 35, U. S. Code (1952), sec. 266) The present invention relates to short wave cylindrical sleeve antennas.

Antennas of the cylindrical sleeve type are well known in the art as shown in U. S. Patent 2,239,724 to Lindenblad and are known to produce broader band operation than the Simpler narrow conductor dipole types.

The more conventional sleeve antennas have often been found to be unsatisfactory because they have been unable to meet the requrements of a substantially undirectional response pattern, and at the same time providing a relatively small change of impedance with frequency characteristic, adaptability for use with the common sizes of coaxial transmssion lines and adaptability for use with relatively simple high frequency impedance matching network.

One object of this invention is therefore to provide an antenna suitable for the transmssion and reception of an extremely wide band of frequencies.

Another object of this invention is therefore to provide a sleeve type antenna suitable for the transmssion of an extremely wide band of frequencies without sacrifice of the omnidirectional characteristics thereof.

Another object of this invention is to provide a sleeve type antenna which is suitable for use with conventional coaxial cable sizes and which produces broad band operation without sacrificing the omnidirectional characteristics thereof.

Another object of this invention is to provide an antenna suitable for use With matching networks and coaxial transmssion lines of the common variety wherein a relatively satisfactory standing wave ratio results over a substantially wide frequency band.

These and other objects of the invention will became apparent from the drawings and specification to follow.

In the drawings:

Fig. l is a side elevational view of the cylindrical sleeve r antenna forming the present invention with the various important dimensions indicated thereon.

Fig. 2 is a cross sectional view of Fig. l along section line 2-2.

Fig. 3 is a side elevational view of a modification of the embodiment of Fig. 1.

For most commercial radio installations it is necessary to place the antenna an appreciable distance from the receiver or transmitter coupled thereto. Long transmssion lines are therefore required and under such conditions it is important to limit the standing waves on such a line to decrease power losses.

As is well known, when a transmssion line is terminated in its characteristic impedance no standing waves appear on the line.

Even if the transmssion lines were short, a terminatior of the lines in their characteristic impedance is' important so that the input impedance of the line remains substantially constant irrespective of frequency. This results in proper impedance matching which produces eicient operation and greatly simplifies the design of the receiver and transmitter circuit used with the transmssion line and attached antenna.

The ordinary simple dipole antenna, however, varies considerably in impedance With frequency, and so even though the transmssion line has a proper termination at one frequency, if the impedance varies much with frequency, broad band operation of the antenna becomes impossible.

The first requirement, therefore, for an antenna which is to simplify the impedance matching problem, is' one where the input resistance and reactance of the antenna varies only slightly with frequency change. The cylindrical sleeve antenna is such an antenna but there are other considerations.

Even if the resistance and reactance of the antenna do not vary appreciably, and since the characteristic impedance is a pure resistance for transmssion lines of the lossless variety (which includes all common and feasible Varieties) the antenna's reactance must be low as well as substantially constant in value. It might be thought that impedance matching networks could be used to cancel out the reactive Component. However, as' soon as the antenna reactance values are high Wherein the matching sections required become appreciable fractions of a quarter wave length in the lower range of frequencies to be used, the impedance variation of the matching section itself becomes so great as to make it impossible to eifectively cancel out the substantially constant value of antenna reactance over the same frequency band.

Even assuming that the reactance can be effectively cancelled out by matching networks, if the resistance of the antenna varies much from the characteristic impedance of the transmssion line to which it s to be attached within the frequency band to be used, the input impedance of the transmssion line will still vary over wide limits with change in frequency and no impedance match or low standing wave ratio (ratio of maximum to minimum voltage) will result. One may think of designing a transmssion line having the proper characteristic impedance to match an antenna which has' a substantially constant resistance vs. frequency characteristic. This is possible but often highly impractical because of the expense and time involved in designing and constructing new coaxial cable transmssion lines. To be practical, common Varieties of coaxial transmssion lines should be used. As an alternative, resistance could be added in parallel or in series with the antenna to properly match the transmssion line. This latter method of course would result in loss of energy and unless the resistance added would result in only a small loss as in the case where the resistance of the antenna is near the characteristic impedance of the line to be matched, this solution would be inpractical.

Even assuming that we have perfect impedance matching a problem of directivity patterns is present. For most communication purposes, it s undesirable to have a directive array because of the uncertainty from what direction a signal relative to the antenna orientation is coming. This is especially true of radio communication purposes where the radio equipment is on moving vehicles such as ships, airplanes, etc.

The present invention makes possible an antenna having substantially non-directional response patterns and at the same time providing broad band characteristics for use with transmssion lines having characteristic impedance of from 35-150 ohms. By broad band characteristics is meant that the antenna provides good impedance matching characteristic over extremely wide frequency ranges.

Figures 1-2, to which reference is now made, shows a novel type of a cylndrical sleeve antenna forming the present invention. It consists of a relatively narrow outer cylindrical sleeve portion 1, which is connected to the outer conductor 2 of a coaxial feeder cable by means' of metallic disc 6 at the feed point of radiator 4 (that is, at the base of radiator 4).

The inner conductor 3 of a coaxial cable extends through an insulator 5 to form a radiating element 4. A conventional ground plane 9 is attached to the bottom portion of sleeve 1 to increase the efiective length of the antenna there shown (i. e. Supplies the image thereof).

In constructing a sleeve antenna of the present type I have found that for both good omnidirectional and impedance matching characteristics there are certain antenna dimensions which are extremely critical. These dimensions are shown in Figure l to which reference is now made. These are the ratio of a to b (i. e. the ratio of the diameter of the radiating portion 4 to the diameter of sleeve 1), the ratio of c to d (i. e. the ratio of the length of the radiator 4 to the length of sleeve 1), and the ratio l/b (i. e. the ratio of the total length of the sleeve 1 plus the radiator 4 to the diameter of sleeve 1). All of these dimensions refer to the outer dimensions of the antenna elements.

The following are ranges of values found most suitable in providing a substantially omnidirectional, sleevetype array and also providing resistances which could be easily matched to transmission lines having characteristic impedance varying from 35 to 150 ohms in the embodiment of Figure 1 for an extremely wide frequency range (a band of frequencies where the overall antenna length l is .17 of a wavelength at the lower frequency end and .76 wavelength at the high frequency end) where satisfactory standing wave ratios (maximum to minimum voltage values) were obtained not greater than to 1 without the use of any impedance matching sections.

a/ b can be varied from 2 to 4 c/ d can be varied from 3 to 5 l/b can be varied from to 30 The above ratios are independent of the frequency band to be passed. For example, if a given design falling within the above ratio limit gave certain impedance and pattern characteristics found to be satisfactory from a frequency band of 65 to 300 megacycles, substantially the same impedance and pattern characteristics (and therefore the same standing wave ratio results), are obtained in the frequency band of 6.5 to 30 megacycles if the scale of the antenna is increased by a factor of 10. That is, the above mentioned ratios remain identical, but the diameter and lengths of the sleeve and radiator are increased by a factor of 10, The utility of the dimension relationship of the cylindrical sleeve antenna forming the present invention should therefore be apparent.

One example of an antenna found to give good results in a frequency range of from 90-300 megacycles wherein a substantially omnidirectional vertical plane pattern resulted with a standing wave ratio of not greater than about 5 with a 50 ohm coaxial line is as follows:

Each of the dimension relationships a/ b, c/d and l/ b, and l affects to some degree the impedance and pattern characteristics.

Fg. 3 shows a modification of the embodiment of Figure 1 where in a ground plane is not used but instead a dipole arrangement is utilized. The impedance values here of the antenna are twice that of the embodiment of Figure 1 and so can be used to match transmission lines having a characteristic impedance from about 70 to 300 ohms. The pattern characteristics are about the same as the embodiment of Figure 1 and the limits of the ratio of a/ b, c/d, and l are identical.

This embodiment basically consists of two symmetrical sections which are each similar to the embodiment of Figure l. Thus there are two radiator sections 4--4' and a sleeve portion 1 which extends between radiators 4 and 4' and are insulated therefrom by insulators 5. The input leads are conductors 3-3' which are fed respectively to radiators 4 and 4'. Insulator S' separates conductors 3-3'. The sleeve portion is not directly connected to conductors 3-3'. Many modificatons can be made without deviating from the scope of the present invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A broad band antenna comprising a first hollow cylindrical sleeve base member, a second cylindrical member having a diameter 2 to 4 times larger than said first sleeve member extending coaxially from and totally outside of one end of said first sleeve member and insulated therefrom, a first pair of antenna connecting leads coupled respectively to said first and second cylindrical members at adjacent points.

2. A broad band antenna comprising a first hollow cylindrical sleeve base member, a second cylindrical member having a diameter 2 to 4 times larger than said first sleeve member extending eoaxially from and totally outside of one end of said first sleeve member and insulated therefrom, a coaxial cable having inner and outer conductors entering said first sleeve member from the other end thereof, the inner conductor coupled to said second cylindrical member at the base thereof, and the outer conductor of said coaxial cable connecting with said first cylindrical member at a point adjacent the connection of the inner conductor to the second cylindrical member.

3. A broad band antenna comprising a first hollow cylindrical sleeve base member, a second cylindrical member having a diameter 2 to 4 times larger than said first sleeve member eXtending coaxially from and totally outside of one end of said first sleeve member and insulated therefrom, a coaxial cable having inner and outer conductors entering said first sleeve member from the other end thereof, the inner conductor coupled to said second cylindrical member at the base thereof, and the outer conductor of said coaxial cable connecting with said first cylindrical member at the said one end.

4. A broad band antenna comprising a first metallic cylindrical sleeve base member having a length d and a diameter b, said sleeve electrically coupled to a first connecting lead, a radiating element having a length c and a diameter a extending concentrically from and totally outside of one end of said cylindrical sleeve and insulated therefrom, said radiating element electrically coupled to a second connecting lead, the ratio of a/b being within a range of from 2 to 4, the ratio of c/d being within the range of from 3 to 5, and the ratio of the sum of c and d to the sleeve diameter b being within a range of from 10 to 30.

5. A broad band antenna comprising a first hollow metallic cylindrical sleeve base member having a length d and a diameter b, a pair of connecting leads entering said sleeve from one end, one of said leads connecting with the end of said sleeve remote from said one end, a radiating element having a length c and a diameter a extending concentrically from the latter end of said sleeve and insulated therefrom, said radiating element electrically coupled to the other connecting lead, the ratio of a/ b being within a range of from 2 to 4, the ratio of c/d being within the range of from 3 to 5, and the ratio of the sum of c and d to b being within a range of from 10 to 30.

6. A broad band antenna comprising a first hollow metallic cylindrical sleeve base member having a length d and a diameter b, a coaxial cable having an inner and outer conductors entering said sleeve from one end, the outer conductor of said coaxial cable electrically connected with the other end of said sleeve, a radiating element having a length c and a diameter a extending concentrically from the latter end of said sleeve and insulated therefrom, said radiating element connected to the inner conductor of said coaxial cable, the ratio of a/ b being within a range of from 2 to 4, the ratio of c/d being within the range of from 3 to 5, and the ratio of the sum of c and d to b being within a range of from 10 to 30.

7. A broad band antenna comprising a first hollow, metallic cylindrical sleeve having a diameter b and length d, one end of said sleeve electrically connected to relatively large conducting surface forming a ground plane, a radiating element having a length c and a diameter a extending coaxially from the other end of said sleeve and insulated therefrom, a pair of connecting leads, one lead connecting to said sleeve, and the other to said radiating element, the ratio of a/ b being within a range of from 2 to 4, the ratio of c/d being within the range of from 3 to 5, and the ratio of the sum of c and a' to b being within a range of from 10 to 30.

8. A broad band antenna comprising a first metallic cylindrical sleeve base member having a length d and a diameter b, a radiating element having a length c and a diameter a extending concentrically from and totally outside of one end of said cylindrical sleeve and insulated therefrom, the ratio of c/ b being within a range of from 2 to 4, the ratio of c/d being within the range of from 3 to 5, and the ratio of the sum of c and d to the sleeve diameter b being within a range of from 10 to 30.

9. A broad band antenna comprising a first hollow cylindrical sleeve base member, one end of said sleeve member being electrically connected to a relatively large conducting surface forming a ground plane, a second cylindrical member having a diameter 2 to 4 times larger than said first sleeve member extending coaxially from and totally outside of the other end of said first sleeve member and insulated therefrom, said antenna having first and second feed terminals on said first and second cylindrical members respectively at adjacent points at said other end of said first sleeve member.

10. A broad band antenna comprising a first hollow cylindrical sleeve base member, one end of said sleeve member electrically connected to a reiatively large conducting surface forming a ground plane, a second cylindrical member having a diameter 2 to 4 times larger than said first sleeve member extending coaxially from and totally outside of the other end of said first sleeve member and insulated therefrom, a pair of antenna connecting leads extending through said first sleeve member and coupled respectively to said first and second cylindrcal members at adjacent points at said other end of said first sleeve member.

References Cited in the file of this patent UNITED STATES PATENTS Gothe May 16, 1933 Baley Dec. 26, 1939 Lindenblad Apr. 29, 1941 Roosensten Dec. 30, 1941 Kraus Nov. 2, 1948 Gilbert Aug. 16, 1949 Shanklin Sept. 27, 1949 Schriefer Nov. 28, 1950