US2683808A

US2683808A - Broad band antenna

Info

Publication number: US2683808A
Application number: US728986A
Authority: US
Inventors: Shumaker Clifton
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-02-17
Filing date: 1947-02-17
Publication date: 1954-07-13
Anticipated expiration: 1971-07-13

Description

y 1954 c. SHUMAKER 2,683,808

BROAD BAND ANTENNA Filed Feb. 17, 1947 OF COAXIAL LINE OFCOAXIAL LINE FREQUENCY INVENTOR. CLIFTON SHUMAKER ATTORNEY Patented July 13, 1954 UNETED STATES PATENT QFFICE (Granted under Title 35, U. S. Code (1952),

sec. 266) 4 Claims.

This invention relates in general to antennas and more particularly to an antenna providing wide band frequency response characteristic.

It is an object of this invention to provide a means for extending the frequency response band of a conventional antenna system, such as a half Wave antenna.

It is a further object of this invention to provide an antenna system whose frequency response characteristic is maintained substantially con stant over a wide band of frequencies.

Other objects and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawing in which there is illustrated a preferred embodiment of the invention, and in which:

Fig. 1 shows an embodiment of the contemplated antenna arrangement and Fig. 2 shows diagrammatically how the ire quency response band is widened by the arrange ment shown in Fig. 1.

In accordance with the present invention, a wide frequency response band is contemplated for an antenna by causing, in a sense, the antenna to be resonant at two different frequencies. This result is accomplished by causing part of the antenna to present a very great impedance to signals having a certain frequency. Separate frequency response patterns may be considered to result from the antenna having, in effect, two different lengths. If, now, the dimensions for the antenna are properly chosen, these patterns may be so combined that a composite frequency pattern will result which will be substantially constant in amplitude for all the frequencies intermediate the two resonant frequencies.

In Fig. 1, to which reference is now had, one exemplary embodiment of the antenna arrangement is shown. This includes a half-wave antenna comprising two quarter-wave conductors ill and ii. Attached to one end of each of the conductors it and ii respectively is a cylindrical cup-like member l2 and i3. The quarter-wave conductors as and H are excited, by means not shown, from the ends is and 15, these ends facing each other, and the free ends of these conductors are physically attached to the cylindrical cups l2 and it such that they extend back to envelope partially the conductors it and H, re-

spectively. The cu-ps i2 and 3 are so shaped that they are the same distance from the perimeters of the conductors Iii and H along the whole length of the cups. Since, additionally, cylinders 12 and 13 are made concentric with the conductors IE and II, respectively, and since they are closed at their free ends, a shorted concentric line is formed, for the length of the cylindrical cups [2 and It. If now the resonant frequency of this shorted concentric line be made sufficiently different from the resonant frequency of the conductors Ill and H the impedance of the shorted concentric line will be low as compared to the impedance of the conductors it and ii themselves and the response of the conductors it and II will not be disturbed. Instead, the frequency response band of the conductors It and M will be slightly widened around their resonant frequency because the cylindrical cups l2 and i3 serve to increase the effective diameter of the conductors l6 and H with respect to th ir length. As shown in Fig. 1, the conductors it and ii are generally tubular in shape with an irregular diameter. That is, the diameter of each member i6 and H increases to a maximum at its mid-portion and tapers away to smaller diameters at its end, so as to increase the ratio of diameter to length. This proportion of the members it and H acts to widen further the frequency response band of the conductors I8 and H about their resonant frequency. As thus constructed, response patterns of conductors it and H will be similar since the two conductors are dimensionally equal and each will act like a quarterwave antenna at the resonant frequency. The response patterns of the conductors iii and. i I are shown in curve is of Fig. 2.

Curve I9 of Fig. 2 shows the response pattern which results from the reaction of the shorted concentric line formed by the conductors i2 and I3 surrounding the conductors it and l l, respectively. At their resonant frequency, these lines will present a very great impedance to any signals and thus in effect a new half-Wave antenna will be formed whose length is shorter than the conductors It and H by the length of the concentric lines. Thus a new resonant frequency will re sult from this shorter antenna, as shown in the curve 19. If now the curves l8 and is are combined, a curve '28 will result which will give a frequency response band that is wider than the response bands of the curves :8 and is and this response band will be the frequency response pattern of the antenna arrangement shown in Fig. 1. The dimensions of the conductors i9 and ii, and of the cylinders 12 and 13, may be so chosen that a substantially constant response will be obtained for all frequencies intermediate to the resonant frequencies of the curves l8 and it.

It should be noted that although the shorted concentric lines formed along the length of the cylindrical cups [2 and I3 presents a very great impedance at the resonant frequency of the line, it tends to become inductive at frequencies below the resonant frequency and capacitive at frequencies above the resonant frequency. Thus, at frequencies below the resonant frequency, the effective length of the line is increased with respect to the diameter and at frequencies above the resonant frequency, the ratio of diameter to length is increased.

It should be further noted that the half-wave antenna arrangement shown in Fig. 1 is composed of two similar quarter-wave components. Thus, if one of these quarter-wave components is. eliminated and the remaining component is placed close to a ground plane, an image antenna will result from the reflection produced on the ground plane by the quarter-wave antenna. Thus the quarter-wave arrangement located close to a ground plane will act like the half-wave arrangement shown in Fig. 1.

While certain preferred embodiments of this invention have been described, it is realized that many modifications and variations of this invention may be made and no. limitations upon this invention are intended other than may beimposed by the scope of the appended claims.

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

What is claimed is:

1. An antenna system comprising: at least one radiating element resonant at a given frequency; and a sleeve of conducting material concentrically disposed about the end of said radiating element and shorted thereto at the end of said radiating element to form a section of line resonant at a second higher frequency, said sleeve being operative to effectively shorten the electrical 4 length of said radiating element in response to said second higher frequency.

2. An antenna system comprising: a pair of radiating elements resonant at a given frequency and arranged in the form of a center fed dipole, each of said radiating elements being generally tubular in shape with an irregular diameter which increases gradually from each end thereof to a maximum at its mid portion; and a cup-shaped member resonant at a second higher frequency, fitted over the free end of each of said radiating elements, said last named members extending for a predetermined length back along the respective radiating elements toward the feed ends thereof.

3. A wide band antenna comprising: a dipole antenna resonant at a given frequency; and an electrically conducting member resonant at a second higher frequency, physically attached to the dipole only at the end thereof opposite the end to which excitation is applied and surrounding the dipole along part of its length.

4. A Wide band antenna comprising: a center fed half wave antenna resonant at a given frequency; and an electrically-conducting member resonant at a second higher frequency physically attached to the free end of each half of said antenna opposite the end to which excitation is applied and surrounding each half of the antenna along part of its length such that the member is concentric with the half wave antenna.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,287,220 Alford June 23, 1942 2,321,454 Brown June 8, 1943 2,480,172 Willoughby Aug. 30, 1949 2,487,567 Lindenblad Nov. 8, 1949 FOREIGN PATENTS Number Country Date 446,441 Great Britain Apr. 30 1936'