US 3918063 A
A composite antenna apparatus having a combination of a first element for a VHF signal formed in a modified loaded loop antenna and a second element for a UHF signal formed in a modified arraying antenna, both of which are disposed on their respective supports rotatable independently and compactly arranged.
Claims available in
Description (OCR text may contain errors)
Nov. 4, 1975 United States Patent Nakamichi et al.
ANTENNA HAVING COMSBINED  References Cited UNITED STATES PATENTS ELEMENTS FOR VHF AND UHF SIGNALS  Inventors: Koya Nakamichi, Chofu; Toshitada 3,623.110 11/1971 Doi et 3/[973 Gibson et 6/l973 Doi, Yokohama; Kosuke Akiba, Tama, all of Japan Callaghan SmalseruW...,..,,,.....r...,...n., 343/744  Assignee: Sony Corporation, Tokyo, Japan 22 Filed: u 13, 974 Primary Examiner-Eli Lieberman 1 J m Allorney, Agent. or FirmLewis H. Eslinger, Esq.; Alvin Sinderbrand, Esq.
Appl No.; 479,101
 ABSTRACT A composite antenna apparatus having a combination  Foreign Application Priority Data June l5, l973 48-67443 of a first element for a VHF signal formed in a mod:- fied loaded loop antenna and a second element for a 2 U. 7 2 4 7 44' t [5 l S C 343/ 2 3 3/ 3 7 8 UHF signal formed in a modified arra both of which are disposed on their r pons rotatable independently and co ranged a r nw HS el nv QIILC a e .mwm e 00 B2 17 AIL v Q2 7 m6 1, N5 32 3 04 3 J r am l...m pm te mm mm 55 6 Claims, 19 Drawing Figures QIJ Nov. 4,
Sheet 1 of 10 US. Patent Nov. 4, 1975 Sheet 2 of 10 3,918,063
US. Patent Nov. 4, 1975 Sheet 3 of 10 3,918,063
US. Patent Nov. 4, 1975 Sheet4 of 10 3,918,063
Reactance Kn) Prezmuma -(NHZ) US. Patent Nov. 4, 1975 Sheet 5 of 10 3,918,063
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U.S. Patent Nov. 4, 1975 Sheet 6 of 10 3,918,063
Nov. 4, 1975 Sheet 7 of 10 3,918,063
U.S. Patent d ['0 0 L0 i ent a) US. Patent Nov. 4, 1975 Sheet 9 of 10 3,918,063
US. Patent Nov. 4, 1975 Sheet 10 ofll) 3,918,063
aw W ET m w w ANTENNA HAVING COMBINED ELEMENTS FOR VHF AND UI-IF SIGNALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to an antenna apparatus having both elements for a VHF signal and a UHF signal. and more particularly to a compact composite antenna apparatus comprising a combination of a first element for the VHF signal and a second element for the UHF signal arranged compactly without mutual interference.
2. Description of the Prior Art In the field of television broadcasting. there have generally been two different systems in a view point of a signal used for transmitting informations, one of which uses a VHF (very high frequency) signal and the other of which uses a UHF (ultra-high frequency) sigml, for the transmission. Accordingly, it is necessary for receiving both types of transmitted television signals to provide two different kinds of antennae for receiving the VHF signal and for receiving the UHF signal. respectively.
Generally, it is annoying for people who want to enjoy watching television programs on their television receivers to have two separate antennae for receiving the VHF signal and the UHF signal. Further, these antennae separately provided require relatively large space. To avoid these troubles, the appearance of a compact composite antenna having both elements for the VHF signal and the UHF signal has been desired.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel composite antenna apparatus having both elements for a VHF signal and a UHF signal arranged compactly.
Another object of the present invention is to provide a compact composite antenna apparatus suitable for receiving both VHF and UHF television signals.
The other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the ac companying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing an embodiment of the antenna apparatus according to the present invention;
FIG. 2 is a partially cross-sectional view on the line l-l in FIG. 1;
FIG. 3 is a plane view of the antenna apparatus shown in FIG. 1;
FIG. 4 is a schematic diagram showing an electric construction of a VHF antenna according to the invention;
FIG. 5 is a cross-sectional view on the line II-ll in FIG. I;
FIG. 6 is a cross-sectional view on the line IIIIII in FIG. 3;
FIG. 7 is a front view showing a main part of a rod antenna for receiving two different signals according to the invention;
FIG. 8 is an equivalent trap circuit of the rod antenna shown in FIG. 7;
FIGS. 9A and 9B are schematic diagrams used for explaining the used state of the antenna shown in FIG. 7;
FIG. 10 is a graph showing the characteristics of the equivalent trap circuit;
FIG. 1] is a characteristic graph showing the gain and front to back ratio of a UHF antenna;
FIG. 12 is a SMith chart showing the characteristics of the UHF antenna;
FIGS. 13A and 13B are graphs showing the gain of a VHF antenna provided with a rod antenna;
FIGS. 14 and 15 are, respectively, graphs showing directional patterns of the VHF antenna;
FIG. I6 is a graph showing the gain and front to back ratio of the UHF antenna; and
FIG. 17 is a graph showing the directivity of the UHF antenna.
DESCRIPTION OF THE PREFERRED EMBODIMENT An antenna apparatus according to the present invention will be hereinbelow described with reference to the drawings. In order to better understand the invention, a general description will be now given on the antenna apparatus.
In FIG. 1, reference letter T shows an antenna apparatus according to the present invention as a whole. The antenna apparatus T comprises an antenna element 10 for a VHF signal which is arranged on a substantially horizontal plane and an antenna element 20 for a UHF signal which is arranged relatively close to the antenna element 10 and at a position above the antenna element 10, and also support 30 for holding the antenna elements 10 and 20 at predetermined positions. respectively. In making the arrangement of the antenna elements 10 and 20, which are different in frequency band to be received, compact with superior function, it is necessary to eliminate mutual interference between the antenna elements 10 and 20 for using them independently. That is. as well knowm, in the case where both the antenna elements 10 and 20 are used independently. if the antenna element 20 for the UHF signal were disposed ahead with respect to the coming direction of broadcasting electric signals and the antenna element 10 for the VHF signal were disposed in the same horizontal plane as that of the antenna element 20 and behind the same, or the antenna elements 10 and 20 were arranged in the vertical direction with a relatively large distance therebetween, influences or mutual interference between the antenna elements I0 and 20, especially the influence of the VHF antenna element 10 on the UHF antenna element 20 would pose no serious problem.
However, in such a case the antenna elements I0 and 20 would occupy a large space and hence they would not be preferred as a room antenna apparatus. Accordingly, it is necessary for a practical antenna apparatus provided with both UHF and VHF antenna elements. that the deterioration of antenna characteristics due to bad influences or mutual interference between the UHF and VHF antenna elements must be avoided at first. and that the antenna apparatus is small in size or compact.
The above problem is solved by the construction described hereinafter. Firstly, the structures of the antenna elements I0 and 20 for the VHF and UHF signals will now be described.
The VHF antenna element 10 is divided into a plurality of, for example eight conductive elements to 10/: as shown in FIG. 4. Selected ends of the conductive elements 10a to 10/1 are connected by trap circuits 1A to 1D for the UHF signal and a load 7, respectively, to form a loaded loop antenna as a whole. The trap circuits 1A to ID are formed to have such characteristics that they are low in impedance for a received frequency of the VHF signal, but high in impedance for that of the UHF signal, or such characteristics that they resonate in the received frequency band of the UHF signal. In practical embodiment, each of the trap circuits 1A to 1D is formed to be a parallel resonant circuit consisting of a capacitor 2 and a coil 3. If free ends of the conductive elements 100 and 1011 are selected as feeding terminals 40 and 4b as shown in FIG. 4, the trap circuits [A to ID are connected between the ends of the divided conductive elements shown in FIG. 4. In the embodiment shown in FIG. 4 rod antennae 5A and SB are attached to the VHF antenna element 10, so that trap circuits 6A and 6B are connected between the rod antennaes 5A, 5B and the conductive elements b, 10g, respectively, for trapping the UHF signal. For this reason, one ends of the conductive elements 100 and 10f adjacent to the conductive elements 10b and 10g are opened.
As mentioned above, the VHF antenna element or member 10 is a loop antenna which consists of eightdivided conductive elements 100 to 103. Its various characteristics and antenna characteristics will be described later together with those of the UHF antenna element or member 20.
The VHF antenna member 10 is fixedly arranged on the horizontal plane as shown in the figure and the UHF antenna member is disposed on the plane above the VHF antenna member 10. As may be seen in FIG. 3, the UHF antenna member 20 consists of three conductive elements. The embodiment shown in FIG. 3 is intended for expanding a frequency band to be received. To this end, the UHF antenna member 20, which consists of a wave-guide 20A, a radiator 20B and reflector 20C arranged in this order with respect to the incoming direction of the broadcasting wave shown by an arrow 0 in FIG. 3, is not a well known Yagi antenna consisting of rod-shaped conductive elements, but consists of conductive plate elements of desired shape. That is, the radiator 20B comprises a pair of conductive sector plates 90 and 9b which are attached separately and from the ends of inner faces of which feeding terminals are led out. Ahead of the radiator 208, there is disposed the waveguide 20A made of a V-shaped conductive plate apart from the radiator 208 with a predetermined distance, while behind the radiator 208 there is disposed the reflector 20C formed of an arc-shaped conductive plate with a predetermined distance from the radiator 208. All the conductive plates may be formed of aluminum. As shown in FIG. 3, the UHF antenna member 20 is so selected in its maximum outer diameter that it is located within the inner diameter of the loop of the VHF antenna member 10 and that the outer configurations of the radiator 20B and the reflector 20C are selected to be parts of the outermost circle thereof.
The VHF and UHF antenna members 10 and 20, constructed as above, are assembled by means of the support with the mutual distance mentioned above. As shown in FIGS. I and 2, the support 30 includes a cone-shaped rotary body II for supporting the VHF antenna member 10 and a rotary shaft 12 disposed within the rotary body 11 for supporting the UHF antenna member 20. The rotary body 11 and the rotary shaft 12 are assembled such that they can be rotated independently. To this end, a disc-shaped base 13 made of, for example, rubber or the like is provided under the rotary body 11, and a rotatable cylinder 14 is provided on the base 13 rotatable with respect to the base 13. The rotary shaft 12 is fixedly inserted into the rotatable cylinder 14, so that the rotary shaft 12 is rotated externally through the cylinder 14. The rotary shaft 12 has a suitable length projected upwardly beyond the rotary body 11 and has attached thereto a holder 40 which holds the UHF antenna member 20 together with the rotary body 11.
To the outer periphery of the rotary body 11, which can be freely rotated, near its upper end, the conductive elements 10a to 10k forming the VHF antenna member 10 are attached with the predetermined distance. The manner of the attachment is, for example, as follows. As shown in FIG. 5, projections 28a and 28b are provided at both ends of the conductive element 10a made of, for example, aluminum conductive plate, while apertures 29a and 29b are bored through the rotary body II at the position, where the element 10a is attached, for passing therethrough the projections 28a and 28b, respectively. After the projections 28a and 2812 are passed through the apertures 29a and 29b from the outside of the rotary body 11 to its inside, they are bent on an inner surface 31 of the body 11 to be attached to the body 11. The other elements 10b to 10h are attached to the body 11 similarly. Thus, all the elements 10a to 10h of the VHF antenna member 10 are arranged on the substantially same horizontal plane. The trap circuits 1A to 1D, 6A, 6B and the load 7 are connected to the conductive elements to 1011 on the inner surface 31, respectively. Line-shaped conductors 32 provided on the inner surface 31 serve to improve the impedance characteristic of the VHF antenna member 10, and accordingly they are provided between the conductive elements 100 to 10h, respectively.
The feeding portion of the VHF antenna member 10 is electrically connected through a connector 33 to a feeder wire 34 and the conductive elements 10f and 103, as shown in FIG. 1. It is, of course, possible to use adhesive upon the attachment of the elements to ensure the attachment.
The UHF antenna member 20, which may be attached to the rotary shaft 12, is attached to a holder 40 with a plane shape substantially same as that of the UHF antenna member 20 as shown by one-dot chain line in FIG. 3. This attachment will be described, by way of example. As shown in FIG. 6, ends of a conductor 35 are bent to be fixed to the holder 40. The holder 40 is provided with a cylindrical engaging member 41 (refer to FIG. 2) which may engage with the rotary shaft 12. Thus, a distance it, between the antenna members l0 and 20 is determined.
A feeding wire 36 of the antenna member 20 passes through the inside of the rotary shaft 12 and then led out to the outside through a bore (not shown) formed in the rotatable cylinder 14. Reference letter S (refer to FIGS. 1 and 2) indicates a cover which may cover the UHF antenna 20. Thus, the UHF antenna 20 is formed of a cup-shape as a whole.
The rod antennae 5A and 53 shown in FIG. 2 are provided for improving the gain upon the reception of the VHF signal, especially in its low frequency band,
but in this embodiment they are formed to be of practical use for the case where a frequency band of the VHF signal to be received is relatively wide (for example, 50MH2 to 220MHz). In other words, the rod antennae 5A and SB are made to be a so-called two-frequency type antenna with which one of antennae can receive the VHF signals of different bands.
FIG. 7 shows the essential construction of one of the rod antennae 5A and 5B, for example, 5A. In the figure, reference numeral 50A indicates a main antenna member which may be rotatably mounted on the outer periphery of the rotary body 11 shown in FIGS. 1 and 2. In order to receive a signal with a relatively low frequency band of about SOMHZ to 90MHz, a subantenna member 508 is slidably mounted on the main antenna member 50A to form a low frequency band receiving antenna together with the antenna member 50A. The sub-antenna member 508 is formed of a wire conductor 51 with a diameter of 2.00mm which consists of an iron wire that is chromium plated, by way of example. On end portion of the wire conductor 51 is wound on an outer periphery of an insulator 52 made of synthetic resin and mounted on the main antenna member 50A, as shown in FIG. 7. To this end, a spiral groove 52a is formed on the outer periphery of the insulator 52 with a desired pitch, and the wire conductor 51 is wound on the spiral groove 52 0. Thus, the subantenna member 508 is slidably connected to the main antenna member 50A. In FIG. 7, reference numeral 53 generally shows the above connecting member.
By connecting the sub-antenna 508 with the main antenna 50A by means of the insulator 52, the electric equivalent circuit of the connecting member 53 can be shown as a trap circuit 54 in FIG. 8. That is, a capacitor 54a is formed between the main antenna 50A and the wire conductor 51 wound thereon, and a coil 54b is formed by the wound wire conductor 51. Accordingly, if the respective constants of the equivalent trap circuit 54 are selected to make the trap circuit 54 resonate to a VHF signal with a relatively high frequency band which is received by the main antenna 50A, the trap circuit 54 shows a high impedance for the VHF signal of a high frequency band, but shows a low impedance for the VHF signal of a low frequency band.
For this reason, in the case where the rod antenna 5A is used under the condition that the connecting member 53 is moved to a top end 55 of the main antenna 50A, the main antenna 50A and the sub-antenna 50B are electrically connected as shown in FIG. 9A for a low frequency band of the VHF signal and the rod antenna 5A acts as an antenna with a total length L. However, for a high frequency band of the VHF signal, since the impedance of the equivalent trap circuit 54 is high, the sub-antenna 50B is electrically isolated from the main antenna 50A as shown in FIG. 9B and hence the effective length as an antenna becomes a length L of the main antenna 50A.
From the above description, it may be apparent that since the rod antenna 5A is superior in trapping effect, it can be used as the so-called two-frequency type antenna to improve the directivity or directional characteristic of the VHF antenna described later.
FIG. 10 is a graph showing the characteristics of the equivalent trap circuit 54 in which the abscissa respresents the frequency F in MHz and the ordinate the reactance Re in KO. In the graph of FIG. 10, a dotted line curve 60 shows the trapping chracteristic of an ordinary trap circuit, while a solid line curve 61 shows that of the trap circuit 54. From this graph, it is obvious that the trap circuit 54 shown in FIG. 8 has a greatly improved ideal trapping characteristic. In the trap circuit with the trapping characteristic shown by the dotted line curve 60, the capacitor (corresponding to the capacitor 54a) is selected of ZpF and the coil (corresponding to the coil 54b) is made of a formal wire with the diameter of 0.6 mm and wound by 13 turns to form a resonant circuit. The resonant frequency of the trap circuit 54 is determined by the number of turns of the coil 5411, the winding pitch of the coil 54b, the coil 54b itself or its diameter and so on.
As described above, the antenna apparatus T is formed of the VHF and UHF antenna members 10 and 20 and the support 30 which are shaped desirably, as mentioned above. The respective characteristics of the antenna apparatus T will be now described in order.
The characteristic of the UHF antenna 20 will be now described. With the present invention, since the antenna elements or conductive elements are not made of rod-shaped conductors as in the prior art, but made of wide conductive plates with the predetermined width and shape, the frequency band to be received is widened to provide a so-called wide band antenna, which is ascertained by experiments. That is, the compared results on the gain and front to back ratio of the directivity between an ordinary Yagi antenna consisting of three elements and the UHF antenna 20 of the present invention are shown in the graph of FIG. 11 in which the abscissa represents the frequency F in MHz, the positive ordinate the gain G in dB, and the negative ordinate the front to back ratio Ra, respectively. In the graph of FIG. 1 I, curves 62 and 64 show the characteristics of the ordinary Yagi antenna, while curves 63 and 65 show those of the UHF antenna 20. It will be obvious from the curves that the solid line curve 63 which shows the gain of the UHF antenna 20 is wider in frequency band than the solid line curve 62 and that the front to back ratio of the UHF antenna 20 is relatively high in a wide frequency band. As a result, the UHF antenna 20 of the invention eliminates the narrow band characteristic of the prior art antenna and proposes an antenna of a wide band. Further, with the prior UHF antenna, it is found that as antenna elements increase in number, the frequency characteristic of its impedance is greatly deteriorated. The UHF antenna 20 of the invention can improve such a deterioration also. That is, with the Smith chart (FIG. 12) which may show an admittance characteristic, a dotted line curve shows the case where no element is provided except the radiator 20B. According to this curve, the standing wave ratio (S.W.R.) is 3 or more than 3 in a frequency band of about 500MHz, but the S.W.R. becomes close to I in a frequency band of about 700MHz. However, if experiments are performed under the condition that the number of antenna elements in the UHF antenna 20 are increased to be three for the same frequency band (about 470 to 770MHz), the results are counter to the above, that is the S.W.R. becomes lower than 3 (shown by solid line curves). In other words, as the elements of the U.H.F antenna of this invention increase in number, the coupling characteristic is improved to also improve the frequency characteristic. From this, it will be apparent that the UHF antenna 20 performs the effect that it acts as a wide band antenna.
The respective characteristics of the UHF antenna 20 are mentioned as above, but a description will be now given on the VHF antenna l0. When the rod antennae A and 58 provided with the equivalent circuits 54 mentioned above are attached to the VHF antenna 10, the gain of the VHF antenna 10 itself is improved, which will be described with reference to the graphs shown in FIGS. l3A and 138 in which the ordinates represent the gain G in dB and the abscissas the frequency F, respectively. In the graphs of FIGS. 13A and 13B, dotted line curves 67 and 68 show the characteristics of a prior art rod antenna which is not contemplated to form a two-frequency antenna and hence in which the whole length L (refer to FIG. 9) is formed by the main antenna, while solid line curves 66 and 69 show the characteristics of the rod antennae 5A and 58. It may be apparent from the comparison therebetween that the gain is approximately same in the low frequency band of the VHF signal in the invention and the prior art as shown by the curves 66 and 67 in FIG. 13A, but in its high frequency band a marked difference appears. That is, with the prior art rod antenna the gain decreases as shown by the dotted line curve 68 in FIG. 138, but with the rod antennae 5A and 5B of the invention there is no decrease in gain as shown by the solid line curve 69 in FIG. 138. This fact means that the equivalent trap circuit 54 shown in FIG. 8 performs with a superior effect.
Accordingly, the directivity of the rod antennae SA and SB of the invention in a high frequency band of the VHF signal is, of course, improved as compared with that of the prior art. The graph of FIG. 14 shows the directivity of the prior art rod antenna which is already shown in FIG. 13. In the graph of FIG. 14, a solid line curve 70 indicates the directivity in 170 MHz, a dotted line curve 71 that in 190MHz and a one-dot chain line curve 72 that in 220MHz, respectively. FIG. 15 is a graph showing the directivity of the rod antennae 5A and 5B of the invention in which the same reference numerals indicate the directivities in the same frequency bands as those of FIG. 14. From the comparison of FIG. 14 with FIG. 15, it is obvious that the VHF antenna 10 of the invention has greatly improved directivity.
As described previously, the VHF antenna 10 has as one object to avoid the deterioration due to the UHF antenna caused by the close arrangement of both antennae adapted to receive different frequency bands and also to reduce the size of the antenna apparatus T. To this end, as described previously, the loop antenna is divided into eight parts and the trap circuits IA to 1D, which may resonate with received UHF signals, are provided. Thus, when the UHF signal arrives at the antenna, it is not induced in the conductive elements IOa to 10h because of the trap circuits 1A to ID with the result that the conductive elements 100 to 1011, by way of example, have no deleterious affect as reflectors for the UHF antenna 20 and hence the directivity is not disturbed. By the way, if the prior art VHF antenna (loop antenna) consisting of eight divided elements but having no trap circuits is used, the divided elements act as a reflector for the UHF signal to disturb its directivity and hence to deteriorate the gain. The VHF antenna I0 of the invention, however, has negligible reflector effect.
During reception of the VHF signal, even if the UHF signal arrives, it does not act as ajamming wave for the VHF signal because the respective trap circuits 1A to 1D have high impedance therefor. Accordingly, even if both the antennae l0 and 20 are arranged close to each other, there is almost no mutual interference and they achieve the same effects as if they are disposed far apart. yet the antenna apparatus T is formed as a compact structure.
In order to ascertain that the embodiment of the VHF antenna having eight divided elements has less affect on the gain for the UHF signal than an embodiment which is not eight divided (for example, divided into four or less sections), the inventors of the invention carried out the following experiments. In this case, a VHF antenna divided into four elements is typified as an antenna to be compared with the embodiment of the invention. As shown in the graph of FIG. 16 in which the abscissa represents the frequency F in MHz, the positive ordinate the gain G in dB and the negative ordinate the front to back ratio Ra, the gain for the UHF signal decreases for the case where the four divided element antenna is used as shown by a solid line curve 73, but for the case where the eight divided element VHF antenna 10 of the invention is used the gain is superior in a received frequency band as shown by a solid line curve 74. In the graph of FIG. 16, a dotted line curve shows the front to back ratio of the invention and a dotted line curve 76 that of the prior art.
It is described that since the VHF antenna 10 is divided into eight parts and the trap circuits 1A to ID are connected thereto, the UHF signal is hardly induced in the conductive elements 10a to 10h to thus improve the gain for the UHF signal. However, the above signal induction cannot be eliminated entirely by provision of the trap circuits IA to 1D. As a result, the VHF antenna l0 acts minimally as a reflector for the UHF antenna 20. For this reason, if the UHF antenna 20 is located above the VHF antenna 10, the optimum direction in which the directivity of the UHF antenna 20 can be orientated is upward because this directivity is opposite to the reflector. If, in the graph of FIG. 17, its XX axis is taken as the horizontal plane of the UHF antenna 20 and the reflector 20B of the UHF antenna 20 is located at the center point 3 of the graph, the directivity in the vertical plane is orientated upward shown by a solid line curve 77. The graph of FIG. 17 shows the case where a frequency of the UHF signal is selected as 600MHz. In this case, the maximum directivity is inclined from the vertical plane by about 20 to the side of the waveguide (in the graph to the left side).
Accordingly, with the existence of the VHF antenna 10, the directivity of the UHF antenna 20 is orientated to the vertical direction with the result that the maximum direction of the directional pattern coincides with the wave incoming direction (in general, the wave comes from the upper side due to diffraction) to improve the directivity much more.
The reason why the outer diameter of the UHF antenna 20 is selected smaller than the inner diameter of the VHF antenna 10 and the former is disposed within the latter is to reduce the size of the antenna apparatus T and also to minimize the affect of the VHF antenna 10 on the UHF antenna 20 as much as possible.
In the above embodiment, the VHF antenna I0 is divided into eight parts or conductive elements, but the same effect can be performed by dividing the VHF antenna l0 into more than eight parts. Further, in the above embodiment the length of the divided conductive elements is selected equal with one another, but it is also possible to divide the VHF antenna 10 into conductive elements different in length. It is only necessary to arrange to avoid that the UHF signal is induced in the VHF antenna 10.
As may be apparent from the foregoing, with the antenna apparatus T according to the present invention, the VHF antenna 10 is disposed on the substantially horizontal plane and the UHF antenna is disposed within the VHF antenna 10 and above the same spaced a predetermined distance therefrom as shown in FIGS. 1 and 2, so that the VHF antenna 10 acts to a minimum degree as a reflector of the UHF antenna 20 and hence the directivity of the UHF antenna 20 is directed to the vertical direction thereof as shown in FIG. 17. As a result, the maximum direction of the directivity coincides with the wave incoming direction to provide the antenna apparatus T with superior directivity qualities as compared with the prior art.
With the antenna apparatus T of the present invention, the UHF antenna 20 can be located close to the VHF antenna 10, so that the antenna apparatus T itself can be reduced in size and thus be formed as a compact structure. Accordingly, the antenna apparatus T is preferred as a room antenna for use with a television receiver which room antenna is often disposed on the cabinet of the television receiver.
In the foregoing, only one preferred embodiment of the present invention is shown and described, but it will be obvious that many modifications and variations could be effected by those skilled in the art without departing from the spirit and scope of the novel concepts of the invention.
We claim as our invention:
1. Antenna apparatus having combined elements for receiving VHF and UHF signals, comprising:
a VHF antenna member disposed in a loop formed of plural, spaced apart conductive plates, a first pair of adjacent plates being connected to feeding terminals, a second pair of adjacent plates opposite said first pair of plates being interconnected by a load impedance, and at least third and fourth pairs of adjacent plates being interconnected, respectively, by at least first and second respective UHF signal trap means, each of said trap means comprising a parallel resonant circuit for presenting maximum impedance to received UHF signals;
a UHF antenna member spaced from said VHF antenna member and extending within a circular area having a diameter less than the diameter of said VHF antenna loop, said UHF antenna member including a wave-guide conducting plate, a radiator conducting plate and a reflector conducting plate, and having optimum directivity in a direction substantially normal to the plane of said VHF antenna loop;
first rotatable support means mechanically coupled to said VHF antenna member for rotating same in the plane of said loop; and
second rotatable support means coaxial with said first rotatable support means and mechanically coupled to said UHF antenna member for rotating same in a plane parallel to said loop.
2. The antenna apparatus of claim 1 wherein said first rotatable support means comprises a ring-shaped body to which said spaced apart conductive plates are coupled; said first and second rotatable support means being rotatable independently of each other.
3. The antenna apparatus of claim 2 wherein said second rotatable support means comprises a sphericalshaped body to which said wave-guide, radiator and reflector conducting plates are coupled.
4. The antenna apparatus of claim 2 wherein said VHF antenna member further includes at least one conductive rod coupled to one of said conductive plates by a further UHF signal trap comprising a parallel resonant circuit for presenting maximum impedance to received UHF signals.
5. The antenna apparatus of claim 4 wherein two conductive rods are coupled to two of said conductive plates, each of said conductive rods comprising a main antenna portion and a sub-antenna portion slidably mounted on said main antenna portion by a slidable insulating member, an end portion of said sub-antenna portion being wound about said insulating member to form a parallel resonant trap circuit for presenting a higher impedance to VHF signals above a predetermined frequency.
6. The antenna apparatus of claim 5 wherein said VHF antenna member is formed of at least eight conductive plates having at least four UHF signal trap means coupled thereto.