Abstract:
An antenna system is provided for receiving horizontal and vertical components of a transmitted RF signal and for minimizing the magnitude of one of the components prior to application to an RF utilization means, such as a TV receiver. The system includes a vertical antenna for primarily receiving the vertical components of the RF signal. A horizontal antenna serves to primarily receive the horizontal components of the RF signal. An adjustable time delay serves to adjust the time delay between the vertical and horizontal components. An adjustable phase adjuster serves to adjust the phase between the vertical and horizontal components. A combiner combines the adjusted horizontal and vertical components to obtain therefrom a combined RF signal for application to the RF utilization means.

Description:
BACKGROUND AND FIELD OF THE INVENTION 
     The present invention relates to antenna systems and, more particularly, to an antenna system particularly applicable for use in receiving RF signals including digital television (DTV) signals. 
     DESCRIPTION OF THE PRIOR ART 
     In the United States, the Federal Communications Commission (FCC) has established guidelines for broadcasting television signals. The established standard is known as the NTSC signal format which is an analog signal. The FCC is now permitting the broadcasting of digital television (DTV) as well as analog NTSC signals. 
     The digital television signals (DTV) being broadcast at this time are horizontally polarized signals. Circular polarized signals (CP) are being considered for future broadcasting of digital television signals. A problem noted with such horizontally polarized DTV signals arises in urban centers having tall buildings. The DTV signal may reflect off one or more buildings prior to being received at a subscriber&#39;s receiving antenna. If the receiving antenna is a “rabbit ear” di-pole antenna, the received signal may be comprised of the horizontal component (from the broadcasted horizontally polarized DTV signal) as well as a vertical component (the result of reflection). The reflected vertical component may lead or lag the horizontal component in time and be offset therefrom in phase, resulting in an erroneous “ghosting” signal being fed to the subscriber&#39;s DTV television receiver. The result will be a garbled picture on the television receiver. 
     It is understood that the same result will take place if the broadcasted signal is circularly polarized (CP). Such a signal, when received at a receiving antenna, will include a horizontal component and a vertical component together with a vertical reflection component and a horizontal reflection component resulting in erroneous signals being fed to the DTV television receiver. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, an antenna system is provided for receiving both horizontal and vertical components of a transmitted RF signal and for minimizing the magnitude of one of the components prior to application to an RF utilization means, such as a TV receiver. 
     The system includes a vertically oriented antenna for primarily receiving vertical components of the RF signal. A horizontally oriented antenna serves to primarily receive the horizontal components of the RF signal. An adjustable time delay serves to adjust the time delay between the vertical and horizontal components. An adjustable phase adjuster serves to adjust the phase between the vertical and horizontal components. A combiner combines the adjusted horizontal and vertical components to obtain therefrom a combined RF signal for application to the RF utilization means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the present invention will become more readily apparent from the following as taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is an elevational view of a circular polarized antenna together with a block diagram illustration of accompanying circuitry; 
     FIG. 2 is an omni-directional radiation pattern illustrative of the type of signal that may be transmitted by a transmitting antenna and intended to be received by the receiving antenna of the system herein; 
     FIG. 3 is a vector diagram illustrating the received horizontal component of the RF signal together with a reflected vertical component which lags that of the horizontal component; 
     FIG. 4 is a vector diagram similar to that of FIG. 3 but wherein the reflected vertical component leads the horizontal component; 
     FIG. 5 is a schematic-block diagram illustration of one embodiment of the receiving system in accordance with the invention herein; 
     FIG. 6 is a vector diagram useful in describing the operation herein; 
     FIG. 7 is a combined schematic-block diagram illustration of a second embodiment of the invention herein; 
     FIG. 8 is a graphical illustration of amplitude with respect to frequency and illustrating a waveform depicting the DTV channel  30  signal; and, 
     FIG. 9 is an elevational view similar to FIG.  1  and showing means for rotating the antenna. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to the drawings herein wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for limiting same. FIG. 1 illustrates an antenna system in accordance with the invention wherein the antenna system includes a circular polarized antenna  10  having a pair of vertically oriented di-pole elements  12  and  14  and a pair of horizontally oriented di-pole elements  16  and  18 . The antenna may be rotated about the vertical axis A-A′ extending through elements  12  and  14 , if desired. Also, the antenna may be rotated about the horizontal axis B-B′ extending through the horizontal elements  16  and  18 , if desired. This will be discussed in detail hereinafter. The RF signals received by the vertically oriented di-pole elements  12  and  14  are primarily the vertical components of the RF signal whereas the signals received by the horizontal di-pole elements  16  and  18  are primarily the horizontal components of the RF signal. 
     As will be brought out hereinafter, it is contemplated that the antenna  10  will be employed for receiving horizontally polarized signals which have been transmitted from a broadcasting antenna such as that which may be broadcasting digital television (DTV) signals. In an urban atmosphere, large buildings may interfere with the reception of such horizontally polarized signals because the signals may be reflected by various buildings resulting in the signals being received with horizontal components together with reflections which are received as vertical components. This may cause “ghosting”, resulting in picture loss at the subscriber&#39;s TV receiver. 
     It is contemplated that the circular polarized antenna  10  be connected to a control circuit CC that minimizes the vertical components so that mostly the horizontal components of the horizontally polarized signal are supplied by the control circuit CC to a subscriber&#39;s TV receiver R. Such TV receivers will typically employ adaptive equalizers which are capable of correcting for some of the discrepancies, such as the vertical reflection components. However, minimizing the vertical reflection components will assure that such equalizers will provide a proper picture for the receiver R. It is contemplated that in addition to such an equalizer, the receiver is provided with a pilot light L which is illuminated whenever a pilot signal is detected. This can be accomplished by rotating the antenna  10  about either the axis A-A′ or B-B′ for tuning the receiver. Reference is made to FIG. 8 which shows a graphical waveform of the DTV signal for channel  30  which extends from 566 MHz to 572 MHz with the pilot signal PS being located at approximately 566.31 MHz. 
     FIG. 2 is illustrative of an omni-directional pattern which may be radiated by the broadcasting antenna. At present, this signal is contemplated as being a horizontally polarized signal. Consequently, any vertical component received at the receiving antenna  10  would be the result of reflections, such as from a tall building in an urban environment. If the transmitted signal takes the form of a circular polarized signal, the reflections may result in a vertical reflection component as well as a horizontal reflection component. 
     Reference is now made to FIG. 3 which is a vector diagram illustrating the horizontal component H of the received signal at the antenna system  10  in response to the broadcasting of a horizontally polarized signal. The vertical component is the result of a reflection between the transmitting antenna and the receiving antenna  10  as indicated by the vertical reflection component V R . It is to be noted that this reflection component V R  is spaced in time from the horizontal component H. In accordance with the present invention adjustments are made so that the vertical component is displaced in time to approximately the position of vertical component V R ′. The adjusted vertical component is still displaced in phase from that of the horizontal component H. Accordingly, in accordance with another aspect of the present invention, the adjusted component V′ R  is rotated toward the horizontal component so that when these components are combined there will result a useful, essentially horizontal component to be delivered to the receiver R. 
     FIG. 4 is similar to that of FIG. 3 but illustrates a second condition wherein the reflected vertical component V R  is spaced in time from the horizontal component H. The control CC in accordance with the invention is employed for displacing the vertical component V R  toward the location of component V′ R  and then this adjusted component V R ′ is rotated toward that of the component H. 
     Reference is now directed to FIG. 5 which illustrates the control circuit CC in greater detail. Also, the vertical antenna elements  12 ,  14  and the horizontal antenna elements  16 ,  18  are illustrated as being spaced from each other for purposes of simplification. It is to be understood that the antenna elements are normally positioned as is illustrated in FIG.  1 . 
     The vertical antenna elements  12  and  14  are connected by way of a balun  50  to an adjustment path including a phase adjuster  52  and a delay adjuster  54  and thence to port A of a 90° hybrid  56 . The balun includes a transformer  58  having a primary winding  60  connected between antenna elements  12  and  14  and a secondary winding  62  connected between ground and the phase adjuster  52 . The phase adjuster  52  and the delay adjuster  54  may be manually adjusted. 
     The horizontal di-pole elements  16  and  18  are also connected to a balun  70  which includes a transformer  72  having a primary winding  74  connected to elements  16  and  18  and secondary winding  76 . The secondary winding  76  is connected between ground and an adjustment path including a phase adjuster  78  and a delay adjuster  80 . The phase adjuster  80  is connected to the B port of the hybrid  56 . The phase and delay adjusters  78  and  80  may be manually adjusted. The C port of the hybrid  56  is connected to a reject load  82  and the D port of the hybrid is connected to the television receiver R. 
     It is contemplated that the user of the circuitry in FIG. 5 will adjust the phase adjusters  52  and  78  and the delay adjusters  54  and  80  to achieve the results discussed hereinbefore with reference to FIGS. 3 and 4. That is, the delay adjusters are manipulated to move the reflected component V R  toward that of component V′ R  and the phase adjusters are manipulated to rotate component V′ R  toward that of the horizontal component H. 
     In tuning the antenna system described herein it is contemplated that the operator may adjust the antenna somewhat by rotating it about it&#39;s axis A-A′ or it&#39;s axis B-B′ in addition to adjusting the phase and delay adjusters  52 ,  54 ,  78  and  80 . For example, in a first form of tuning, the operator may use three steps including adjusting the delay, adjusting the antenna and then adjusting both the delay and the antenna. A second form of tuning may involve three steps including adjusting the phase and then adjusting the antenna and thereafter adjusting both the phase and the antenna. A third method of tuning the system might include three steps of first adjusting the delay and the phase, then adjusting the antenna, and finally adjusting the antenna and delay the and the phase. 
     Reference is now made to the vector diagram of FIG. 6 which illustrates two horizontal components H 1  and H 2 . No vertical reflection component is illustrated in this example. If the normal horizontal component is component H 1  then the reflected horizontal component may be considered H 2  In this case, the phase and delay adjusters  52 ,  54   78  and  80  are manipulated by the operator to move the reflected horizontal component H 2  toward and then ideally coincide with the correct horizontal component H 1 . Alternatively, the horizontal component H 2  may be the normal horizontal component and component H 1  may be the reflected component and, in such case, the phase and delay adjusters are adjusted to move the horizontal component H 1  toward that of component H 2 . 
     Reference is now made to the embodiment illustrated in FIG.  7 . This embodiment is particularly useful when correcting for several reflections of a broadcasted signal prior to the signal being received by the receiving antenna. This embodiment is similar to that of FIGS. 1 and 5 and like character references are employed in FIG. 7 when describing like components. 
     In this embodiment, the vertical antenna elements  12  and  14  are connected to a balun  50  and the horizontal antenna elements  16  and  18  are connected to a balun  70 . However, unlike the embodiment of FIG. 5, the baluns  50  and  70  of FIG. 7 are respectively connected to signal splitters  100  and  102 . These splitters split the signal into two paths representative of two reflections for which correction is to be accomplished. The two paths obtained from the splitter  100  include a first path having delay adjuster  104  connected in series with phase adjuster  106  and thence to one input of a summation device  108 . Similarly, the second path includes a delay adjuster  110  connected in series with a phase adjuster  112  and thence to the summing device  108 . The output of the summing device  108  is applied to a fine tune phase adjuster  114 , the output of which is supplied to port A of the hybrid  56 . 
     Splitter  102  supplies it&#39;s output signals to two paths with the first path including a delay adjuster  120  connected in series with a phase adjuster  122  and thence to one input of a summation device  124 . A second path from the splitter includes a delay adjuster  126  connected in series with a phase adjuster  128  and thence to a second input of the summation device  124 . The output of the summation device  124  is applied to a fine tune phase adjuster  130  the output of which is supplied to the B port of the hybrid  56 . 
     The embodiment of FIG. 7 provides independent adjustment of both phase and delay for each of the paths (or reflections) of the signals supplied to the antenna elements  12  and  14 . In a similar manner, independent adjustment of both delay and phase is provided for each of the paths (or reflections) of the signals applied to the horizontal antenna elements  16  and  18 . Additional tuning may be achieved with the fine tuning phase adjusters  114  and  130 . 
     Reference is now made to FIG. 9 which illustrates means for achieving movement of the antenna  10  for rotation about axis A-A′ or B-B′ or for rotating the antenna about an axis perpendicular to the paper in either a clock-wise or counter-clock-wise direction about a hub  200 . The hub is suitably connected to the antenna elements, as with non-conductive materials. The hub may be driven by a motor  202  whereas the vertical antenna elements  12  and  14  may be driven about axis A-A′ by a suitable motor  204 . Likewise, the horizontal antenna elements  16  and  18  may be driven about axis B-B′ by means of a motor  206 . It is contemplated that these motors may be individually controlled with suitable motor controls  208 . 
     From the foregoing description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.