Abstract:
A combined VHF/UHF active antenna, suitable for indoor use, includes a common element that serves as a reflector for UHF signals and as a director for VHF signals. The VHF element is bent upon itself to permit its packaging as a consumer product accessory.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This invention is related to commonly assigned application serial No. 09/469,420, filed Dec. 23, 1999, entitled Dipole UHF Antenna in the name of the inventor. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to VHF/UHF antennas and particularly to VHF/UHF antennas that are intended for indoor use. With the recent adoption of television signal transmission standards for HDTV (High definition television) signals and ATSC (Advanced television systems committee) type signals, the need for significantly improved VHF/UHF antennas, primarily for indoor use, has become apparent. The most popular form of prior art VHF antenna was the ubiquitous “rabbit ears”, which took up a great deal of space when fully extended and was difficult to adjust properly. Similarly, the “bow tie” UHF antenna was sensitive to adjustment and left a great deal to be desired in terms of performance. What is needed is an indoor antenna to replace both the rabbit ears and bow tie of the prior art and, hopefully do so with improved reception characteristics, since the transmitted signals are digital, which makes it imperative that signal reception be optimized to prevent data corruption. 
     Conventional VHF/UHF indoor antennas are limited in gain and directivity, and in some instances, very sensitive to the direction of the received signals. In an analog multipath environment, signal reflections and reduced gains are more tolerable in that, while the quality of the picture may be compromised, the viewer is presented with a viewable, though less than ideal, picture. With digital signals, these same signal impairments most often result in no viewable picture. Further, these transmitted digital signals require a lower voltage standing wave ratio (VSWR), between the antenna and receiver RF input terminals, than their analog counterparts and it is also very important to maintain a high signal to noise ratio. 
     Another draw back of the prior art rabbit ears and bow tie antennas was esthetic. The indoor antenna ideally should not be visible, or at least not look like the prior art devices. The combined antenna of the invention arranges the various elements such that the antenna may be conveniently packaged, in an unobtrusive way, with the television receiver. This is especially important due to the new, higher, aspect ratio of the picture tubes that are specially designed for HDTV receivers. 
     The combined Low VHF, High VHF and UHF antenna of the invention uses a UHF antenna as disclosed and claimed in the above-mentioned copending application in combination with a Low and High VHF antenna, in which the reflecting backplate of the UHF antenna also serves as a directing element for the VHF antennas. As fully discussed in the copending application, the increased width/length ratio of the UHF antenna improves its wideband performance, whereas the reflector guarantees a 10 to 15 dB front to back ratio in addition to providing excellent decoupling between the UHF output and the dipole elements. While the copending application also discloses and claims different configurations of active versions of the UHF antenna only a single version of the antenna is disclosed in the combination VHF/UHF antenna of the present invention. The inventive antenna also includes a “folded” dipole VHF element for enabling compact packaging of the antenna, without undue performance deterioration. The folded arrangement, for example, adapts itself for integration with HDTV television receivers that incorporate picture tubes of the new, higher, aspect ratio. 
     OBJECTS OF THE INVENTION 
     A principal object of the invention is to provide a novel combination VHF/UHF antenna. 
     Another object of the invention is to provide an improved indoor VHF/UHF antenna. 
     A further object of the invention is to provide conveniently packaged indoor VHF/UHF antenna. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawings in which: 
     FIG. 1 is a front perspective view of the antenna of the invention; 
     FIG. 2 is a plan view of the antenna of the invention; 
     FIG. 3 is a schematic diagram of the amplifier and diplexer portions of the antenna of the invention; 
     FIG. 4 illustrates the frequency response of the antenna of the invention, and; 
     FIG. 5 illustrates a possible packaging arrangement for the antenna of the invention with a HDTV television receiver. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, the combined VHF/UHF antenna of the invention includes a VHF dipole comprising elements  12  and  14 , an intermediate element  16  and a UHF dipole comprising elements  18  and  20 . The intermediate element  16  and the UHF dipole elements  18  and  20  and the conductive supports  22  and  24  therefor are fully disclosed and claimed in the above-mentioned copending application and will not be discussed in detail. In the UHF dipole arrangement, intermediate element  16  serves as a reflector for UHF signals. In this invention, intermediate element  16  also serves as a director for VHF signals and thus performs a double function. The VHF dipole is folded or bent upon itself to reduce its overall “footprint” which enhances its ability to be integrated into various designs for use with television receivers that incorporate the new, higher aspect ratio picture tubes. Specifically, left hand element  12  is bent to form a generally V-shaped section comprising elements  12   a,    12   b  and  12   c.  Similarly, right hand element  14  is bent to form a generally V-shaped section comprising elements  14   a,    14   b  and  14   c.  Elements  12   a  and  14   a  are angled to be parallel with the corresponding portions  16   a  and  16   b,  respectively, of intermediate element  16 . 
     FIG. 3 illustrates the electronic parts arrangement for the combined antenna of the invention. A symmetrical VHF push-pull amplifier  40  receives both Low VHF and High VHF band signals at its input from VHF antenna elements  12  and  14  by means of a stripline  26  and has its output leads  42  and  44  coupled to a ferrite core balun  46 . Output leads  42  and  44  couple DC power to push-pull amplifier  40  and also convey signals from the amplifier. The “hot” output lead from balun  46  supplies an inductor  52 , which is connected to the junction of a capacitor  54 , that is connected to ground, and a series connection of a capacitor  56  and an inductor  58 . Inductor  58  is connected to ground through a notch circuit comprising an inductor  60  and a capacitor  62 . Inductor  58  is also connected to a junction A through an inductor  64 . 
     On the UHF side, an amplifier  75  supplies signal to a capacitor  74  that is connected to an inductor  72 , which is returned to ground through an inductor  70 . Inductor  72  is also connected to an inductor  68  that is connected through a capacitor  66  to junction A. Junction A is the input for DC power and the output for the antenna signal, which is coupled to a coaxial cable  88 . 
     DC power is supplied to amplifiers  40  and  75  from junction A as follows: For push-pull amplifier  40 , the path is through a choke  80 , (with the RF bypassed to ground through a capacitor  78 ) through a choke  76 , (again with the RF bypassed to ground through a capacitor  48 ) to the “cold” end of balun  46 , while the hot end of balun  46  is supplied with DC power through a choke  50 . For amplifier  75 , the path is through a choke  82 , (that is RF bypassed to ground through a capacitor  84 ), through a choke  86  to the output of amplifier  75 . It will be appreciated that the UHF amplifier may be formed directly on the surfaces of the UHF antenna dipole elements as described in the copending application while the VHF amplifier may be carried by director/reflector element  16 . Similarly, the inductances and capacitance may be implemented on the printed circuit board materials of the antenna element  16 . 
     The combined VHF/UHF antenna of the invention has a “folded” dipole VHF element having a width that is preferably around sixty centimeters. While the bending of the element upon itself somewhat increases the VSWR of the VHF antenna, the reduced footprint gives it greater mechanical design flexibility. Further, the directivity supplied by the intermediate element increases the gain of the VHF elements at 175 to 215 MHz (high VHF) by a few dB. The front to back ratio for the Low VHF spectrum is 0 dB. The front to back ratio for the High VHF spectrum is 3 to 4 dB, whereas the front to back ratio for UHF is 10 to 15 dB 
     FIG. 4 indicates the general spectrum response of the combination antenna of the invention over the VHF/UHF frequency range. The Low VHF and High VHF response is indicated by reference  90  and the UHF response is indicated by reference  92 . The crossover point  94  of the two response curves is approximately 20 dB down from the maximum response. 
     In FIG. 5, a cabinet structure  99  includes a television receiver  96 , having a picture tube  97  of the new, higher, aspect ratio, and a speaker system  98  in the lower portion of television receiver  96 . An upper portion  100  of the cabinet  99  conveniently houses a combination VHF/UHF antenna that is constructed in accordance with the invention. Since, in all probability, the orientation of the antenna will need to be changed for best reception among different signals, it may be rotatably mounted in portion  100 , or portion  100  itself may be rotatably mounted, detachable or positioned on television receiver  96 . It will be appreciated that other structures may be used to house the antenna, the illustration merely represents a possible form of housing. 
     What has been described is a novel combination indoor VHF/UHF antenna that includes a common element that functions as a reflector for UHF signals and as a director for upper end VHF signals. It is recognized that numerous changes to the described embodiment of the invention will be apparent to those skilled in the art without departing from its true spirit and scope. The invention is to be limited only as defined in the claims.