MXPA00002428A - Rf receiving antenna system - Google Patents

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. A combiner combines the components to obtain therefrom a combined RF signal for application to the RF utilization means.

Description

RF RECEIVER ANTENNA SYSTEM The present invention relates to antenna systems and, more particularly, to an antenna system especially applicable for use in the reception of RF signals, including digital television (DTV) signals. In the United States, the Federal Communications Commission (FCC) has established guidelines for the broadcast of television signals. The established norm is known as the NTSC signal format which is an analog signal. The FCC now allows the broadcast of digital television (DTV) signals as well as analog NTSC. The digital television (DTV) signals that are now broadcast are horizontally polarized signals. Circular polarized (CP) signals are being considered for future digital television signal broadcasts. A problem observed with such horizontally polarized DTV signals arises in urban centers with tall buildings. The DTV signal may be reflected from one or several buildings before it is received at the subscriber receiving antenna. If the receiving antenna is a "rabbit ear" dipole antenna, the received signal may be composed of the horizontal component (from the horizontally polarized DTV signal emitted) as well as a vertical component (the result of the reflection) . The reflected vertical component can advance or retard the horizontal component in time and be deviated from it in phase, resulting in an erroneous "phantom" signal fed to the subscriber's DTV television receiver. The result will be a distorted image on the television receiver. The same result will be produced if the signal emitted is circularly polarized (CP). Such a signal, when received in a receiving antenna, will include a horizontal component and a vertical component together with a vertical reflection component and a horizontal reflection component that cause erroneous signals to be fed to the DTV television receiver. The present invention includes an antenna system for receiving horizontal and vertical components of a transmitted RF signal and for minimizing the magnitude of one of said components prior to the application of an RF utilization means and characterized by vertical antenna means for receiving primarily said vertical components of said RF signal, horizontal antenna means for receiving said horizontal components of said RF signal primary, time delay setting means for adjusting the time delay between said vertical and horizontal components, and a combiner for combining said components to obtain from them a combined RF signal for application to said RF utilization means. An antenna system has been conveniently 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 receiver. TV. Advantageously, the system includes a vertically oriented antenna for receiving primarily vertical components of the RF signal. A horizontally oriented antenna serves to receive primarily the horizontal components of the RF signal. An adjustable time delay adjuster circuit serves to adjust the time delay between the vertical and horizontal components. A combiner combines the components to obtain from them a combined RF signal for the application to the RF utilization means. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of a circular polaroid antenna together with a block diagram illustration of the accompanying circuitry. Figure 2 is an omnidirectional radiation configuration illustrative of the type of signal that can be transmitted by a transmitting antenna and intended to be received by the receiving antenna of the system. Figure 3 is a vector diagram illustrating the received horizontal component of the RF signal together with a reflected vertical component that retards the horizontal component. Figure 4 is a vector diagram similar to that of Figure 3, but where the reflected vertical component advances the horizontal component. Figure 5 is an illustration in schematic block diagram of an embodiment of the receiver system according to the present invention. Figure 6 is a vector diagram useful in describing operation. Figure 7 is a schematic block diagram combined illustration of a second embodiment of the invention. Figure 8 is a graphic illustration of the amplitude with respect to the frequency and illustrating a waveform illustrating the DTV channel signal 30. And Figure 9 is an elevational view similar to Figure 1 and showing means for rotating the antenna. Figure 1 illustrates an antenna system including a circular polarized antenna 10 having a pair of vertically oriented dipole elements 12 and 14 and a pair of horizontally oriented dipole elements 16 and 18. The antenna can be rotated about the vertical axis A-Ax which extends through elements 12 and 14, if desired. In addition, the antenna can be rotated about the horizontal axis B-Bx extending through the horizontal elements 16 and 18, if desired. This will be explained in detail later. The RF signals received by the vertically oriented dipole elements 12 and 14 are primarily the vertical components of the RF signal, while the signals received by the horizontal dipole elements 16 and 18 are primarily the horizontal components of the RF signal. The antenna 10 will be used to receive horizontally polarized signals that have been transmitted by a transmitting antenna, such as that which may be broadcasting digital television (DTV) signals. In an urban environment, tall buildings can interfere with the reception of such horizontally polarized signals since the signals can be reflected by several buildings resulting in signals being received with horizontal components along with reflections that are received as components see -ticas. This can produce "ghosts", resulting in loss of image in the subscriber's TV receiver. It is contemplated that the circular polarized antenna 10 be connected to a CC control circuit which minimizes the vertical components so that mainly the horizontal components of the horizontally polarized signal are supplied by the control circuit CC to a TV receiver R of the subscriber. Such TV receivers will typically employ adaptive equalizers that are capable of correcting some of the discrepancies, such as the vertical reflection components. However, the minimization of the vertical reflection components will ensure that such equalizers provide an appropriate image for the receiver R. It is contemplated that, in addition to such an equalizer, the receiver will be provided with a pilot light L that will illuminate whenever a signal is detected. pilot signal. This can be done by turning the antenna 10 around the axis A-Ax or B-Bx to tune the receiver. Reference is made to Figure 8 which shows a graphic waveform of the DTV signal for channel 30 extending from 566 MHz to 572 MHz, the pilot signal PS being located at approximately 566.31 MHz. Figure 2 illustrates a omnidirectional configuration that can be radiated by the emitting antenna. At present, it is contemplated that this signal is a horizontally polarized signal. Consequently, every vertical component received in the receiving antenna 10 would be the result of reflections, such as of a tall building in an urban environment. If the transmitted signal takes the form of a circular polarized signal, the reflections can result in a vertical reflection component as well as a horizontal reflection component. Figure 3 is a vector diagram illustrating the horizontal component H of the signal received in the antenna system 10 in response to the emission 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 VR. Said reflection component VR is spaced in time from the horizontal component H. Is an adjustment made so that the vertical component moves in time to approximately the position of the vertical component VR? The adjusted vertical component is still displaced in phase from the horizontal component H. Therefore, the adjusted component VXR is rotated towards the horizontal component when the components are combined in a way that results in an essentially horizontal, useful component, to be supplied to the receiver R. Figure 4 is similar to figure 3, but illustrates a second condition where the vertical reflected component VR is spaced in time from the horizontal component H. The CC control is used to move the vertical component Vx towards the position of the component VXR and then said adjusted component VRX is rotated towards the component H. Figure 5 illustrates the CC control circuit in more detail. In addition, the vertical antenna elements 12, 14 and the horizontal antenna elements 16, 18 are illustrated spaced apart from one another for the purpose of simplification. The antenna elements are normally positioned as illustrated in FIG. 1. The vertical antenna elements 12 and 14 are connected by means of a balun 50 to an adjustment path that includes a fine delay adjuster 52 and an adjuster of the antenna. approximate delay 54 and thence to a port A of a 90 ° hybrid combiner 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 adjuster 52 and the adjuster 54 can be adjusted manually. The horizontal dipole elements 16 and 18 are also connected to a balun 70 that includes a transformer 72 having a primary winding 74 connected to elements 16 and 18 and the secondary winding 76. The secondary winding 76 is connected between ground and an adjustment path which includes a fine delay adjuster 78 and an approximate delay adjuster 80. The adjuster 80 is connected to the B port of the hybrid 56. The phase and delay adjusters 78 and 80 can be adjusted manually. The port C of the hybrid combiner 56 is connected to a reject load 82 and the D port of the hybrid combiner is connected to the television receiver R. The user of the circuitry of figure 5 will adjust the fine delay adjusters 52 and 78 and the Approximate delay adjusters 54 and 80 to achieve the results explained above with reference to Figures 3 and 4. That is, the delay adjusters are manipulated to approximate the reflected component VR to the component V1R. During the signal combination, the hybrid combiner 56 rotates the com ponent? to the horizontal component H with the appropriate phase relationship, so that the output of port D is a single composite signal with the reflected component reduced in magnitude. The main vertical components and some 90 degree offset and attenuated horizontal components are applied to the reject load 82. By tuning the antenna system, the operator can adjust the antenna somewhat by rotating it around its axis A-A1 or its B axis -B1 in addition to adjusting the delay adjusters 52, 54, 78 and 80. For example, in a first form of tuning, the operator can use three steps including adjusting the approximate delay, adjusting the antenna and then adjusting both the approximate delay like the antenna. A second form of tuning may involve three steps that include adjusting the fine delay and then adjusting the antenna and then adjusting both the fine delay and the antenna. A third method of tuning the system could include three steps of first adjusting the approximate delay and fine delay, then adjusting the antenna, and fi nally adjusting the antenna and the approximate delay and fine delay. The fine time delay or fine delay can be considered as phase delay. In addition, the adjustments made by the adjusters are incremented each time.

Each increment by the fine adjusters is of the order of 12 nanoseconds, while each increment by the approximate adjusters is 96 nanoseconds. The vector diagram of Figure 6 illustrates two horizontal components Hi and H2. In this example, no vertical reflection component is illustrated. If the normal horizontal component is the Hi component, the reflected horizontal component can be considered H2 In this case, the delay adjusters 52, 54, 78 and 80 are manipulated by the operator to move the Hi and H2 components. The embodiment described here is intended for use with digital television. The goal of the delay settings is to place the reflected components for cancellation in the hybrid re-load load. In practice, only partial cancellation is needed to adjust the adaptive equalization of the receiver to an operational state. Figure 7 illustrates this embodiment which is useful in correcting several reflections of a signal emitted before the signal is received by the receiving antenna. This embodiment is similar to that of Figures 1 and 5, and analogous reference characters are used in Figure 7 when describing analogous 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 Figure 5, the baluns 50 and 70 of figure 7 are respectively connected to signal dividers 100 and 102. Said dividers divide the received signal into two paths representative of two reflections for which correction has to be performed. The two paths obtained from the divider 100 include a first path having a fine delay adjuster 104 connected in series with an approximate delay adjuster 106 and therefore an input of a summing device 108. Likewise, the second path includes a fine delay adjuster 110 connected in series with an approximate delay adjuster 112 and thence to summing device 108. The output of summing device 108 is applied to a fine tuning adjuster 114, whose output is supplied to port A of hybrid 56. The divider 102 supplies its output signals to two paths, the first path including a fine delay adjuster 120 connected in series with an approximate delay adjuster 122 and thence to an input of a summing device 124. A second path from the The splitter includes a fine delay adjuster 126 connected in series with an approximate delay adjuster 128 and thence to a second input of the device. summation volume 124. The output of the summing device 124 is applied to a fine tuning fade adjuster 130 whose output is supplied to the B port of the hybrid 56. The embodiment of FIG. 7 provides an independent adjustment delay for each one of the paths (or reflections) of the signals supplied to the antenna elements 12 and 14. Similarly, independent delay adjustment is provided for each of the paths (or reflections) of the signals applied to the horizontal elements antenna 16 and 18. Additional tuning can be achieved with the fine tuning delay adjusters 114 and 130. Figure 9 illustrates means for achieving movement of the antenna 10 for rotation about the axis A-A1 or B-B1 or for rotate the antenna around an axis perpendicular to the paper in a clockwise or counterclockwise direction around a cube 200. The cube is connected to the antenna elements, as with non-conductive materials. The hub can be moved by an engine 202, while the vertical antenna elements 12 and 14 can be moved around the axis A-A1 by a suitable motor 204. Similarly, the horizontal antenna elements 16 and 18 can be moved around the axis B-B1 by means of a motor 206. It is contemplated that these motors can be controlled individually with suitable motor controls 208. An antenna system is provided for receiving horizontal and vertical components of a transmitted RF signal and for minimize the magnitude of one of the components before application to an RF utilization means, like a TV receiver. The system includes a vertical antenna to receive primarily the vertical components of the RF signal. A horizontal antenna serves to receive primarily the horizontal components of the RF signal. An adjustable time delay serves to adjust the time delay between the vertical and horizontal components. A combiner combines the components to obtain a combined RF signal for application to the RF utilization means.

Claims (9)

Claims

1. An antenna system for receiving horizontal and vertical components of a transmitted RF signal and for minimizing the magnitude of one of said components prior to application to an RF utilization means and characterized by antenna vertical means for receiving said vertical components primarily of said RF signal, horizontal antenna means for receiving said horizontal components of said RF signal, means for adjusting the time delay for adjusting the time delay between said vertical and horizontal components, and a combiner for combining said elements. components to obtain from them a combined RF signal for application to said RF utilization means.

2. A system as claimed in claim 1, characterized in that said combiner includes means for combining said components in such a manner that phase displacement of said vertical component occurs so that said combined RF signal is primarily for reducing the reflected components.

3. A system as claimed in claim 2, characterized in that said combination means is a 90 degree hybrid combiner, said time delay means are manually adjustable, and said combination means is a hybrid circuit.

4. A system as claimed in claim 3, wherein said combining means is a 90 ° hybrid circuit, said time delay adjusting means include a vertical time delay adjuster coupled to said vertical antenna means and a horizontal timer adjuster coupled to said horizontal antenna means.

5. An antenna system as claimed in claim 1, characterized in that said time delay adjusting means includes a vertical fine time delay adjuster coupled to said vertical antenna means and a horizontal adjuster of fine time delay coupled to said horizontal antenna means and each indicated adjuster is incrementally adjusted so that each increment of fine delay is given a given increase in time.

6. An antenna system as claimed in claim 5, characterized in that said time delay adjusting means also include a vertical adjuster of approximate time delay coupled to said vertical antenna means and a horizontal adjuster of approximate time delay coupled to said horizontal antenna means and wherein each indicated approximate delay adjuster is incrementally adjusted in such a manner that each approximate delay increase is substantially greater than each indicated fine delay increment.

7. A system as claimed in claim 6, characterized in that said vertical fine time delay adjuster and said vertical time delay adjuster are connected in series between said vertical antenna means and said combiner, and said horizontal adjuster Fine time delay and said horizontal adjuster of approximate time delay are connected in series between said horizontal antenna means and said combiner.

8. An antenna system as claimed in any of claims 1 to 7, including vertical signal dividing means coupled to said vertical antenna means for dividing any received RF signal into N correction paths, and horizontal dividing means coupled to said means antenna horizontals to divide any RF signal divided into N correction paths where N represents the number of signal reflections that are corrected.

9. A system as claimed in claim 8, wherein said time delay adjusting means includes a vertical time delay adjuster located on each of said N paths provided by said vertical divider, and a horizontal time delay adjuster located in each of said N paths provided by said horizontal divider.