US2656463A - Broad-band directive antenna - Google Patents

Description

Oct. 20, 1953 o. M. wooDwARD, JR 2,656,463

I BROAD-BAND DIRECTIVE ANTENNA Filed April s, 1951 2 Sheets-Sheet `l P'R/'OR TED 'o t w if Q k'x 17 2 .E2 Qa L) i 500 600 700 600 i000 400 500 600 700 600 $00 /000 Fffl/E/Vy//J Mii/76,1255 F16! dI/EA/C Y/A/ M5646 YCZES ATTORNEY Oct 20, 1953 o. M. WOQDWARD, JR

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INVENTOR ATTORNEY Patented Oct. 20, 1.95.3

UNITED STATES PATENT OFFICE BROAD-BAND DIRECTIVE ANTENNA poration of Dlwa VAppia-mm1 Aprile., 1951, se-rial No. vlaisses 4 claims. tol. 2stsassi 1 This invention relates to a broad-band antenna and more particularly to an antenna suitable for use in the ultra-high frequency band.

It is an object of this invention to vprovide an improved ultra-high frequency dipole antenna having separated arms and a broad frequency band characteristic.

It is a further object of this invention to provide a mechanically stable, all metal ultra-high frequency receiving antenna of the dipole type with electrically conducting bridging means between the effective electrical centers of the dipole arms.

According to one embodiment of this invention, two similarly constructed triangular sheets of conductive material are arranged substantially in the same plane with an apex of one sheet forming an acute angle adjacent to the corresponding apex of the other sheet ,also forming an acute angle. The dimension across both sheets is approximately in the range from 2/3 to 54 of the operating wave length. A conductive strap of approximately half this length is rigidly secured to the back of the sheets of material at'the centers thereof and the center section of the strap is spaced away from these elements. The strap serves a dual purpose, rst as a support for the antenna, and second as a shunt reactance in parallel with the antenna. The transmission line to the antenna is connected at or very near the adjacent apexes.

According to another embodiment of the invention, an array of these antennas is provided by arranging two or more of these antenna constructions in a single plane and mechanically and electrically connecting the lower outer points of the triangular sheets of one dipole antenna with the upper outer points of the triangular sheets of another dipole element, assuming that the antenna array is in the vertical plane. A short length of line is used to connectthe adjacent apexes of each dipole antenna in the array with those of the other dipole antennas. The transmission line extending from the antenna to suitable transducer apparatus, such as a transmitter or receiver, is connected to the center of this short length of line.

Other objects and advantages will be apparent from reading the following specication in connection with the accompanying drawing, in which:

Fig. 1 is a front elevation of the antenna;

Fig. 2 is a bottom view of the antenna;

Fig. 3 shows the gain over a portion of the ultra high frequency band;

Fig. 4 shows the standing wave ratio over the same portion of the band;

Fig.5 shows the `field patterns of the antenna at the lower end of the ultra high frequency band;

Fig. '6 shows the field pattern at a higher yfrequency;

Fig. 7 illustrates an array of the elements shown in Fig. 1;

Fig. 8 shows thegain over a portion of the ultra high frequency band for the array shown in Fig. 7;

Fig. 9 shows the standing wave ratio for the same array; and

Figs. 10 and 11 show the `field patternsgiven bythe array for the same frequencies shown in Figs. 5 and k6.

In the drawing, the same reference characters designate the same or similar parts in the several views.

In Fig. 1 there are shown two triangular sheets of conductive material I I having adjacently positioned apexes to which a transmission line may be connected at feed point I 3. Each sheet I I has diverging sides forming an acute angle A. The angle of each sheet determines the broad band frequency range. An electrically conductive strap I5 is secured to each sheet II at points Il and I9 approximately in the middle of the conductive sheets II. This strap I5 has a preferred electrical length equal to approximately one-half wavelength at mid-band frequency. The dimension across bothsheets, arranged end-to-end, in,- cluding thespacing between them is in the range of 273 to of the operating wave length.A

n Fig. 2,V there is shown more clearly the positionihg of the strap I5 which, while being joined at outer ends to plates II at approximately the midpoints I'I, I9, is spaced away from the sheets throughout the rest of its length by a small amount.

The strap I5 in conjunction with the antenna forms effectively a shunt reactance in parallel with the antenna. This reactance is high over the mid-band portion, similar to the action of a short-circuited quarter-wave stub. The reactance becomes inductive at frequencies below mida band vfrequency and capacitive at frequencies above mid-band frequency. It is therefore posi sible by proportioning the strap I5 properly in its cross-sectional dimension or configuration to affect the impedance of the antenna, and give the antenna'a highly desirable impedance characteristic over the band of frequencies desired. The voltage distribution in the strap I5 will always have a nodal point in the center of the strap, opposite the middle of the terminals I3.

one embodiment of this antenna successfully ltried out in practice which was designed for the frequency band from 500 to 900 megacycles per second, the antenna had the following dimensions: The angle A in Fig. 1 was 70, and the width across both sheets was inches including a inch spacing between the sheets at the adjacent apeXes, which is convenient spacing for terminating ordinary parallel-lay inch line. The strap I5 was 8@ inches long and the center section was spaced 'V3 of an inch from the Sheet II. The sheets II were made of als inch brass, while the strap I5 was 1A; by 1/2 inch brass. It will be seen that the' spacing of the strap I5 from the sheets II varied between 1/15 and 1/27 of a wavelength for the band of frequencies for which the antenna was designed.

Fig. 3 graphically illustrates the frequency versus gain characteristic of the antenna of Fig. 1 under the foregoing conditions, compared with a simple half-wave dipole matched throughout the frequency band to 300 ohm output, the half-wave dipole considered as having a gain of unity; .that is, being always zero on the decibel scale. It should be noted that the antenna exhibits a slowly rising gain characteristic with a maximum occurring at the upper end of the frequency band.

Fig. 4 illustrates the frequency versus standing wave ratio of the antenna of Fig. l under the foregoing conditions. The standing wave ratio is lowest near the middle of the band where the operating frequency gives approximately one wavelength across the width of both elements.

Figs. 5 and 6 graphically illustrate the azimuthal field patterns of the antenna of Fig. 1 at the two extremes of frequency at both ends of the band. These figures illustrate the desirable directional characteristics of the antenna over the entire band for which it is designed. In both illustrations the larger lobe occurs in the front of the antenna while the smaller lobe occurs in the rear of the antenna where the strap is located.

Fig. '7 shows an array of two dipole antennas II and II' of the construction illustrated in Fig. 1 joined mechanically and electrically at the outer lower points of the upper set II and the outer upper points of the lower set II', respectively designated 2| and 23. The dipoles of Fig. 'I are substantially identical to each other and to the dipole of Fig. l. Straps I5, I5 identical with those described in connection with Figs. 1 and 2 are provided for each antenna dipole in the array. A short length of transmission line is shown connected between the feed point I3 of the upper elements Il and the feed point I3 of the lower elements II'. The transmission line extending to the receiver or transmitter is coupled .to the center 2l of the short section of transmission line 25.

Fig. 8 graphically illustrates the gain versus frequency characteristic of the antenna array of Fig. 7, when tested over a band of frequencies ranging from 5ml-900 me., also compared with a simple half-wave dipole matched throughout the frequency band to 300 ohms, and considered as having a gain of unity. Comparing Fig. 8 with Fig. 3, it can be readily seen that a considerable increase irl/gain is obtained by use of the array shown in Fig. 7, and that a peak is exhibited in the upper end of the band.

Fig. 9 graphically illustrates the standing wave ratio versus frequency characteristic of the array of Fig. 7. An inspection of Fig. 9 and a comparison with Fig. 4 shows that the standing wave characteristic is also altered and that the low point for the array is shifted upwardly.

Figs. 10 and 11 respectively show a graphical representation of the azimuthal field patterns of the antenna array of Fig. 7 for the low and high ends of the band for which they were designed. An inspection of Figs. 10 and 1l and a comparison with Figs. 5 and 6 will show that .the field patterns are identical.

The resulting antenna, either with a single pair of elements or in an array, was found to be mechanically very stable due to the presence of the strap I5 joining the two triangular sheets and overcoming the diculty of providing suicient support encountered in prior art antennas supported by rigid feed lines joined at the apexes. The actual mounting brackets for fastening the antenna to the mast or reflector (not shown in the drawing) are preferably secured to the middle of the strap I5 which is a point of zero voltage.

Since the strap I5 is electrically conductive, and is connected at its mid-point to the antenna mast, not shown, the entire assembly can be grounded by grounding the mast, giving simple and effective lightning protection without the necessity for separate lightning arrestor devices.

Although conductive sheets II are shown in the figures of the drawing as being of solid material, the sheets iI may have apertures therein or be constructed of conductors spaced apart, with the ends of such conductors electrically connected. The term sheet in this specification and the appended claims is deemed to include this perforated type of sheet.

Although there is illustrated and described an antenna having triangular sheet elements, it will be understood that by proper dimensioning, the same invention could be utilized in an embodiment having elements shaped like sectors of a circle, wherein the outer edges would be curved.

The antennas of the invention are particularly suitable for the reception of television and other signals requiring a broad band of frequency.

claim:

1. A broad band antenna structure comprising two separate triangular sheets of conductive material having apexes of acute angles adjacent to each other, the dimension across both sheets being substantially one wave-length at mid-band frequency, a strap of conductive material, said strap having a length of substantially one-half one wave-length at mid-band frequency, the width of said strap being considerably narrower than both the length thereof and widest dimension of said sheets, sai-d straps being connected to the centers of said sheets and supporting said separate sheets at the ends of said strap, said strap being closely spaced from said sheets, and terminals at said adjacent apexes of said sheets.

2. Broad band antenna structure comprising two separate triangular sheets of conductive material in the same plane, having apexes of acute angles adjacent to each other, the dimension across both sheets being substantially i/SA- to EAA at the operating frequency, a strap of conductive material, said strap having a length substantially ll to 5/8A at the operating frequency, and being connected to and supporting said separate sheets at the ends of said strap, the width of said strap being considerably narrower than both the length thereof and the widest dimension of said sheets the center of said strap being physically spaced from said sheets a distance not substructure comprising a plurality of triangulary sheets of conductive material, each p-air of said triangular sheets having apexes of acute angles adjacent to each other, the dimension across bothv sheets being substantially one Wave-length at mid-band frequency, a strap of conductive material having a length of substantially one-half one wave-length at mid-band frequency the Width of said strap being considerably narrower than both the length thereof and the widest dimension of said sheets, said straps being connected to -each pair of said sheets at the ends of said strap, said strap being spaced a distance not substantially greater than 1/{151 from said sheets, and terminals at said adjacent apexes of said sheets.

4. Broad band ultra high frequency antenna structure comprising a plurality of similar triangular sheets of conductive material, each pair of said triangular sheets having apexes of corresponding angles adjacent to each other, the dimension across both sheets being substantially one wave-length at mid-band frequency, a strap of conductive material, having a length of substantially one-half one wave-length at mid-band frequency the width of said strap being considerably narrower than both the length thereof and the widest dimension of said sheets, said straps being connected to each pair of said sheets at the ends of said strap, said strap being spaced a distance not substantially greater than k from said sheets, the outer lower points of each pair of said sheets being connected to the outer upper points of the next lower pair of said sheets, and terminals at said adjacent apexes of said sheets.

OAKLEY M. WOODWARD, Ja.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,163,770 Von Radinger June 27, 1939 2,175,253 Carter Oct. 10, 1939 2,175,254 Carter Oct. l0, 1939 2,274,149 Lubeke Feb. 24, 1942 2,430,664 Bradley Nov. 1l, 1947 2,433,183 Wolf Dec. 23, 1947 2,507,225 Scheldorf May 9, 1950 2,519,209 Wheeler Aug. 15 1950 2,596,389 Ercolino May 13, 1952

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