US 3475758 A
Description (OCR text may contain errors)
Oct. 28. 1969 G. DE VITO 3,475,758
WIDE BAND RADIATING SYSTEM EMBODYING DISC-TYPE DIPOLES Filed May 16, 1966 4 Sheets-Sheet l G/Qse J%ZZ INVENTOR By flu g age/11 Oct. 28, 1969 '6. DE vn'o 3,475,758
WIDE BAND RADIATING SYSTEM EMBODYING DIsc-TYPE DIPOLES Filed May 16. 1966 4 Sheets-Sheet 2 Fig.2
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Oct. 28, 1969 DE vrro 3,475,758
WIDE BAND RADIAHNG SYSTEM EHBODYING DISC-TYPE DIPOLES Filed May 16. 1966 I 4 Sheets-Sheet 5 Oct. 278, 1969 DE vrro 3,475,758
WIDE BAND RADIATING SYSTEM EHBODYING DISC-TYPE DIPOLES Filed May 16, 1966 4 Sheets-Sheet 4 @55 fie Zia wvmrm.
United States T 3,475,758 WIDE BAND RADIATING SYSTEM EMBODYING DISC-TYPE DIPOLES Giuseppe De Vito, Via Albani 61, Milan, Italy Filed May 16, 1966, Ser. No. 550,445 Int. Cl. H01q 9/28 U.S. Cl. 343795 1 Claim ABSTRACT OF THE DISCLOSURE This invention concerns a radiating system characterized by the presence of disc-type dipoles and having radiation and impedance characteristics which remain constant over a wide frequency band.
It is well known that for VHF and UHF in general and those employed for television broadcasting especially, it is desirable to have antennas with radiation and impedance characteristics appreciably constant over a wide fre quency band, which permits the use of a single antenna for different frequencies, as is the case with a whole set of television channels (e.g. either TV band IV and V, or MF and TV band III, or TV band I and MF).
In actual practice, the engineering problems involved by the manufacture of a single antenna element capable to satisfy the aforesaid requirements are extremely diflicult to solve, and it is for this reason that a combination of several elements is resorted to, preferably all identical, so as to achieve a satisfactory performance of the radiating assembly in terms of impedance and radiation.
According to said technique, known as a combination of basic elements, linear dipoles have been utilized arranged in sets of eight units, each dipole having a length approximately equal to M2, i.e. half the wavelength of the average frequency to be broadcast, coupled to reflectors set at about \/4 from the dipoles. Said arrangement is generally referred to as dipole curtain panel.
During the last years, said panels have been widely in use for manufacturing radiating systems for TV stations.
Their main features can be summarized as follows: (a) their input impedance remains practically constant as frequency varies within a -40% interval; (b) their radiation characteristics are suitable for the realization of a radiating system consisting of a plurality of basic elements suitably arranged around a supporting tower, generally square or triangular in section, so as to achieve the overall impedance and radiation characteristics wanted of the system; (c) from the structural viewpoint, it is possible to make them either with cylindrical dipoles, or simply from a thin rectangular metal plate supported by metal members at the point of null tension, or from a plate of a dielectric material to which the rectangular dipoles and the feedlines are fastened. In a preferred embodiment of the invention, the radiating system is characterized by the use of disc-shaped dipoles as the basic elements, supported by a common member of dielectric material and interconnected by means of a balanced line, the dipoles being positioned at approximately M4 (referred to the lowest frequency of operation) from a metal reflecting surface.
Said dipoles are preferably arranged in arrays of four atent O ,Q CC
per each face of the supporting tower, and in the same plane according to the vertices of a square. A dissymmetrizing device, generally termed a balun, is connected to the middle point of the balanced line that feeds the dipoles, for the termination of a 50 ohm coaxial cable.
In a preferred application of the invention a set of four dipoles is arranged in a vertical plane and a further set, also of four dipoles, is arranged in another vertical plane perpendicular to the former one.
The invention is further characterized by the fact that the antenna is fed through a 3 db hybrid.
Other characteristics and advantages offered by the invention will become apparent from the description which follows.
Reference is made to the enclosed drawings, where:
FIG. 1 is a perspective view of the radiating system according to a preferred embodiment of the invention, and reproduced herein solely for example purposes; the disk A is of conductive material, the support B is of insulating material and plate C can be of conductive material and can be a continuous plate or a net;
FIGS. 2 and 3 are an elevation view and a plan view of the same embodiment;
FIG. 4 is a schematic view showing the coupler in detail;
FIG. 5 is a diagram showing the coupler in basic principles, whereas FIGURES 6 to 11 represent the horizontal radiation patterns for three different frequencies and in two different operating conditions.
As can be seen from the drawing in FIG. 1, the radiating panel according to the invention is basically composed of four basic-shaped dipoles I placed side by side in pairs, supported by members 2 made of a dielectric material and interconnected by a balanced line 3. A symmetrizing device not shown, generally termed a balun, is connected to the middle point of said line, for termination to a 50 ohm coaxial cable.
The four disc-dipoles are positioned at approximately 7\/ 4 (referred to the lowest frequency of operation) from reflecting metal surface 4.
In this way, a basic element is obtained which permits the realization of a system of antenna both for horizontal and vertical polarization, being composed as it is of four dipoles instead of eight and therefore capable to admit perfect symmetry of the horizontal and vertical directions. Moreover, an operating band of one octave is achieved (ratio 2 to 1) for what concerns the impedance and radiation characteristics of the panel.
This is a very important point regarding the possibility to arrange the elementary panels, or basic panels, to obtain omnidirectional antennae with radiated field intensity constant within :2 db in every direction.
On the attached drawings, FIGURES 6, 7 and 8 show the horizontal radiation patterns as plotted for a system comprising two of the aforesaid panels, located on two adjacent sides of a square tower.
The omnidirectional antenna comprises four of the aforesaid panels located on the four faces of the tower.
It is common, moreover, with radiating systems of this type, in order to compensate for the reflection inherent in each panel and for the effects due to the mutual coupling of the panels, to feed the various panels forming the radiating system with signals the phases of which are displaced with respect to each other by whole multiples of increments: e.g. 0, +90, +270 for a four-panel system.
In this way, a dissymmetry occurs in the radiation pattern which, however, is compensated by a suitable displacement or rotation of the panels in such a direction as to correct the rate of phase retardation or advance introduced by the cables.
This compensating effect, however, can be achieved efficiently only for a rather limited frequency band (20- 25%), since the electrical length varies with the frequency. According to the invention, to achieve an efficient compensation over a bandwidth of at least one octave, a constant-phase dephaser is employed. To this end, in the radiating system subject of the invention, in lieu of different cable lengths a hybrid circuit has been adopted, generally called 3 db coupler, which permits to achieve the required constant phase displacement as the frequency varies.
The aforesaid hybrid circuit, shown schematically in FIG. 5, is a four-gate circuit. The power admitted through gate A is distributed in equal amounts to port B and D provided the corresponding loads are matched, and between these signals there exists a 90 phase displacement which remains constant as frequency varies. If, as shown in figure, the B and D terminations are matched, there occurs no power output at port C. When on the contrary, ports B and D are not perfectly matched, there occurs an energy backflow which is transferred to mouth C. In other words, impedance as seen from port A remains constant within limits of mismatching of port B and C which are appreciably wide.
It is therefore evident how by utilizing, for instance, this particular two-way power divider to feed a pair of basic panels, it becomes possible to achieve radiation patterns that are practically uniform over a frequency band of one octave.
FIGURES 9, and 11 show patterns corresponding to those in FIGURES 6, 7 and 8 but plotted experimentally, for a system utilizing this type of dephaser.
The frequency in the case of FIGURES 6 and 9 is of 470 mHz., for FIGURES 7 and 10 is 650 mHz., for FIG- URES 8 and 11 860 mHz.
The use of this particular type of dephaser offers other important advantages, such as for instance that of reducing, at the antenna input, the asymmetrical impedance variations of the panel due to different snow and/or ice formations on the various panels on the various faces of a square tower, On the contrary the known'system utilizing a common power divider is much more sensitive to this type of impedance variation.
Moreover, by employing said type of hybrid the phase distortion due to the multiplepaths within the long (in terms of wavelengths) cables is also eliminated, since the energy flowing back from the operating circuit is absorbed by the load terminating port C of the hybrid.
1. A broad band radiating system, especially for television broadcasting, comprising at least a pair of basic panels each having four disc-dipoles and radiation and impedance characteristics which are constant over a broad frequency band, said disc-dipoles being supported by members made of a dielectric material and interconnected by a balanced feedline, a reflecting metal surface, said disc-dipoles being spaced by said supporting members from said reflecting metal surface at about M4 referred to the lowest operating frequency intended, said basic panels are fed through a single hybrid by which a phase difference is achieved between adjacent panels which phase difference remains constant as the frequency varies, for an interval of approximately one octave, said basic panels are disposed on two adjacent faces of a square tower.
References Cited UNITED STATES PATENTS 2,939,143 5/1960 Zisler 343-807 3,273,158 9/1966 Fouts et al. 343-797 3,329,959 7/1967 Laub et al. 343-890 FOREIGN PATENTS 867,563 2/1953 Germany.
867,565 2/1953 Germany.
883,351 3/1943 France. 1,359,037 3/1964 France.
ELI LIEBERMAN, Primary Examiner 11.5. C1. X.R. 343799, 853, 890