US 2704811 A
Description (OCR text may contain errors)
March 22, 1955 A. W. WALTERS CYLINDRICAL ANTENNA Filed June 19. 1950 v INVENTOR JAV ANDREW w. WALTERS W ATTORNEYS United States Patent C) CYLINDRICAL ANTENNA Andrew W. Walters, Washington, D. C.
Application June 19, 1950, Serial No. 169,061
3 Claims. (Cl. 250-33) (Granted under Title 35, U. S. Code (1952), see. 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 have been known to produce broader band operation than the simpler narrow conductor dipole types.
The more conventional sleeve antennas however, have often been found to be unsatisfactory because they have been unable to meet the requirements of a substantially omni-directional response pattern, and at the same time provide a relatively small change of impedance with frequency characteristic, adaptability for use with the common sizes of coaxial transmission lines, and adaptabiilty for use with relatively simple high frequency impedance matching network.
One object of this invention is therefore to provide an antenna suitable for the transmission and reception of an extremely wide band of frequencies.
Another object of this invention is to provide a sleeve type antenna suitable for the transmission of an extremely wide band of frequencies without sacrificing the near omni-directional characteristic 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 near omni-directional characteristic thereof.
Another object of this invention is to provide an antenna suitable for use with conventional matching networks and coaxial transmission lines of the common variety wherein a relatively satisfactory standing wave ratio results over a substantially wide frequency band.
Still another object of this invention is to provide an antenna giving broad band response and in which a ships smokestack or the like can be used as an element of the antenna structure.
Another object of the present invention is to provide an anetnna giving broad band response which utilizes common existing ship and submarine structures as elements thereof.
These and other objects of this invention will become apparent from the drawings and specification to follow.
In the drawings:
Figure l is a side elevational view of the cylindrical sleeve antenna forming the present invention with the various important dimensions indicated thereon.
Figure 2 is a top view of the antenna shown in Figure 1.
Figure 3 is a cross sectional view of Figure 2 along section 33.
Figure 4 is a side elevational view of a modification of the embodiment of Figure 1.
Figure 5 shows the present invention applied to a Smokestack on a ship.
Figure 6 shows the present invention applied to the conning tower of a submarine.
In most commercial radio installations it is necessary to place the antenna an appreciable distance from the receiver or transmitter coupled thereto. Long transmission lines are therefore required and under such conditions it is important to limit the standing waves on such lines to decrease power losses.
As is well known, when a transmission line is terminated in its characteristic impedance no standing waves appear on the line.
Even if the transmission lines are short, a termination "ice of the lines in their characteristic impedance is still of great importance in order that the input impedance of the line will remain substantially constant irrespective of frequency. This resultes in proper impedance matching which produces efiicient operation and greatly simplifies the design of the receiver and transmitter circuits used with the transmission line and attached antenna.
The ordinary simple dipole antenna, however, varies considerably in impedance with frequency, and, so even though the transmission 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 does not vary appreciably, since the characteristic impedance is a pure resistance for transmission lines of the lossless variety (which includes all common and feasible varieties), the antennas 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 effectively cancel out the substantially constant value of antenna reactance over the same frequency band.
Even assuming that the reactance can be etiectively cancelled out by matching networks, if the resistance of the antenna varies much from the characteristic impedance of the transmission line to which it is to be attached within the frequency band to be used, the input impedance of the transmission line will likewise vary over wide limits with changes in frequency and no impedance match or low standing wave ratio will result. One may think of designing a transmission 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 transmission lines. To be practical, common varieties of coaxial transmission lines should be used. As an alternative resistance could be added in parallel or in series with the antenna to properly match the transmission 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 impractical.
Even assuming that perfect impedance matching is obtained a problem of directivity patterns is present. For many communication purposes, it is 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 transmission lines having characteristic impedance of from 50-200 ohms. By broad band character istics is meant that the antenna provides good impedance matching characteristic over extremely wide frequency ranges.
Figs. 1-3, to which reference is now made, show one type of cylindrical sleeve antenna with which the present invention deals. The antenna there shown comprises a relatively wide outer cylindrical sleeve portion 1 which is electrically connected with the outer conductor 2 of coaxial feeder cable by means of metal conductors 6 at the feed point of radiator 4 (that is at the base of radiator 4). Conductors 6 could be replaced by a metallic disc if desired.
The inner conductor 3 of a coaxial cable extends through an insulator 5 to form a radiating element 4. A ground plane 9 is provided at the bottom portion of sleeve 1 to increase the efiective length of the antenna there shown, i. e. provide an image).
On ship installations, to make most effective use of the ship structure, the smokestack has been found to be useful for sleeve 1 and the ships deck has served as ground plane 9.
n submarine installations (Figure 6) the conning tower 1" could be used as the sleeve of the antenna corresponding to sleeve 1 in Figure 1. (By conning tower is meant the superstructure in the vicinity of the periscope of the submarine.)
To achieve broad band omni-directional operation with a sleeve type antenna there are several dimensions which I have found 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 radiaetor 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 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 providing reactances which could be easily matched to transmission lines having characteristic impedances vary ing from 50 to 100 ohms for the embodiment of Figure 1 for extremely wide frequency range (a band of frequencies where the overall antenna length l is about .25 of the wavelength at the lower frequency end and is about .75 of a wavelength at the upper frequency end) where satisfactory standing wave ratios (maximum to minimum voltage values) were obtained not greater than 5 to 1.
a/ b can be varied from A to c/d can be varied from 1.4 to 2.0, and l/ b can be varied from 3.8 to 7.5
In the situation where the sleeve 1 corresponds to a ships smokestack and thus has a fixed diameter, the value of the radiator 4 diameter is of course fixed by the ratio of a to b.
The above factors are independent of the frequency band to be passed. For example, if a given design gave certain impedance and pattern characteristics found to be satisfactory from a frequency band of 90 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 8 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 98-290 megacycles wherein a substantially omni-directional vertical plane pattern resulted with a standing wave ratio not greater than 5 with a 50 ohm coaxial line is as follows (with no matching sections):
Each of the dimension relationships a/ b, old, [I b and l etftecitisg) some degree the impedance and pattern charac e cs.
Fig. 4 shows a modification of the embodiment of Figure 1 wherein a ground plane is not used but instead a dipole arrangement is utilized. The impedance value here of the antenna is twice that of the embodiment of Figure 1 and so can be used to match transmission lines having a characteristic impedance from about to 200 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/ b are identical.
This embodiment basically consists of two symmetrical sections which are each similar to the embodiment of Figure 1. The feeding is accomplished by means of a two-wire coaxial line wherein the inner conductors 3'-3 are respectively connected to radiator 44'. Insulator 5 separates conductors 33. The outer conductor 2 0f the coaxial line connects sleeves 1-1.
Many modifications 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:
l. A broad band antenna comprising a smokestack having a conductive surface thereon and having a diameter b and a length d, a conducting surface forming a ground plane, one end of said smokestack electrically connected to and extending from said ground plane, a radiating element having a length 0 and a diameter a extending from the other end of said smokestack and insulated therefrom, a pair of connecting leads, one lead connecting to said smokestack, and the other to said radiating element, the ratio of a/ b being within a range of from A to 1 the ratio of c/ d being Within the range of from 1.4 to 2.0 and-the ratio of the sum of c and d to b being within a range of from 3.8 to 7.5.
2. A broad band antenna comprising a smokestack having a conductive surface thereon, and having a diameter b and a length d, a conducting surface forming a ground plane, one end of said smokestack electrically connected to and extending from said ground plane, a coaxial cable having an inner and outer conductor, conductive means connecting the outer conductor of said coaxial cable to the other end of said smokestack, a radiating element having a length c and a diameter a extending concentrically from the said other end of said smokestack 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 A to /30, the ratio of c/d being within the range of from 1.4 to 2.0, and the ratio of the sum of c and a to b being within a range of from 3.8 to 7.5.
3. In a vessel having an electrically conductive deck and an electrically conductive smokestack electrically connected thereto. a broadband cylindrical sleeve antenna comprising, a radiating element extending coaxially from the unconnected end of said smokestack for a predetermined distance and electrically insulated therefrom, said smokestack forming the outer cylindrical sleeve portion of said cylindrical sleeve antenna and said deck forming a ground plane.
References Cited in the file of this patent UNITED STATES PATENTS 842,146 Goldsborough Jan. 22, 1907 2,078,234 Buschbeck Apr. 27, 1937 2,235,139 Bruce Mar. 18, 1941 2,239,909 Buschbeck et al. Apr. 29, 1941 2,239,724 Lindenblad Apr. 29, 1941 2,267,951 Roosenstein Dec. 30, 1941 2,286,179 Lindenblad June 9, 1942