# Patent

## Title
Antenna system and method for mitigating multi-path effect

## Abstract

An antenna system and method utilize a splitter electrically connectable to a single antenna for splitting an RF signal into two signals. A variable phase shifter shifts the phase of one of the signals. A combiner combines the phase shifted and non-phase shifted signals to produce a conditioned signal. A quality examiner circuit changes the amount of phase shift provided by the variable phase shifter to produce a plurality of different conditioned signals. The quality examiner circuit then determines a quality of each conditioned signal and changes the phase shift again to provide the highest quality conditioned signal to a receiver.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. provisional patent application Nos. 61/268,662, 61/268,663, 61/268,665, 61/268,673, 61/268,674, and 61/268,689, each filed on Jun. 15, 2009 and each of which is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The application generally relates to a system and method for providing a combined antenna signal to a receiver.
2. Description of the Related Art
The use of radio frequency (RF) receivers in vehicles, such as automobiles, is commonplace. In fact, many vehicles involve multiple RF receivers for different applications. These applications include, but are not limited to, terrestrial AM radio broadcasts, terrestrial FM radio broadcasts, satellite radio broadcast (e.g., SDARS), global position system (GPS) reception, and cellular telephone reception.
One challenge in RF signal reception in vehicles is known as the “multi-path effect”. This effect occurs when an RF signal is reflected off of an object, thus causing a phasing delay. The object may be a building, a mountain, or the ionosphere. Because of this reflection an antenna may receive the RF signal at two different times, i.e., in two different phases. The first phase may be received directly from the transmitting source while the second phase may be received after the RF signal is reflected off of the object. As such, the RF signal received by the antenna, and by the receiver, may be distorted.
As such, the subject disclosure provides an antenna system and method to overcome these and other deficiencies.
BRIEF SUMMARY AND ADVANTAGES
An antenna system for mitigating a multi-path effect on a radio frequency (RF) signal received by a single antenna is disclosed herein. The system provides a conditioned signal to a receiver. A splitter is electrically connectable to the antenna. The splitter splits the RF signal received by the antenna into a first non-phase shifted signal and a second non-phase shifted signal. A variable phase shifter is electrically connected to the splitter for receiving the second non-phase shifted signal. The phase shifter may phase shift the second non-phase shifted signal to produce a phase shifted signal. The system also includes a combiner having inputs electrically connected to the splitter and the variable phase shifter. The combiner receives and combines the first non-phase shifted signal and the phase shifted signal to produce the conditioned signal. A quality examiner circuit is electrically connected to an output of the combiner. The quality examiner circuit receives the conditioned signal and determines a quality of the conditioned signal. The quality examiner circuit communicates with the variable phase shifter for changing an amount of phase shift of the second non-phase shifted signal based on the quality of the conditioned signal to modify the phase shifted signal to mitigate the multi-path effect on the RF signal received by the antenna.
A method of conditioning an RF signal received by an antenna to mitigate a multi-path effect on the RF signal prior to providing a conditioned signal to a receiver is also disclosed herein. The method includes the step of splitting the RF signal received by the antenna into a first non-phase shifted signal and a second non-phase shifted signal. The phase of the second non-phase shifted signal is shifted to produce a first phase shifted signal. The first non-phase shifted signal and phase shifted signal are combined to produce a first conditioned signal. The method further includes the steps of determining and recording a quality of the first conditioned signal. The phase of the second non-phase shifted signal is then shifted to produce a second phase shifted signal different from the first phase shifted signal. The first non-phase shifted signal and the second phase shifted signal are combined to produce a second conditioned signal. The method also includes determining and recording a quality of the second conditioned signal. The quality of the first conditioned signal and the second conditioned signal are compared to determine which of the conditioned signals has a highest quality. The conditioned signal determined to have the highest quality is provided to the receiver.
By phase-shifting one branch of a split RF signal, then recombining phase shifted and non-phase shifted signals, the system and method mitigate a multi-path effect caused by reflections of the RF signal. The system and method perform well utilizing an input from just a single antenna and without numerous branch circuitry. As such, the system and method provides a cost effective technique to mitigate a multi-path effect on the RF signal especially in comparison to standard antenna diversity schemes.



BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages of the disclosed subject matter will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. 1 is a block electrical schematic diagram of a first embodiment of an antenna system;
FIG. 2 is a block electrical schematic diagram of a second embodiment of the system; and
FIG. 3 is a perspective view of a vehicle supporting an antenna for use with the system and method.



DETAILED DESCRIPTION
Referring to the Figures, wherein like numerals indicate like parts throughout the several views, an antenna system 10 and method is shown and described herein. The antenna system 10 and method are particularly effective for mitigating a multi-path effect on a radio frequency (RF) signal received by an antenna 12 and providing a conditioned signal to a receiver 14. However, those skilled in the art will realize other functional applications for the system 10 and method described herein. Furthermore, the method described herein may be implemented with devices other than those specific devices of the system 10.
In the illustrated embodiments, the system 10 and method are implemented in conjunction with a vehicle 16, such as an automobile, as shown in FIG. 3. However, it is appreciated that the system 10 and method may be implemented in other types of vehicles as well as non-vehicle environments. The system 10 and method described herein function well using only a single antenna 12. That is, the system 10 and method do not require multiple antennas, nor an antenna array, to achieve superior performance. However, those skilled in the art realize that the system 10 and method may alternatively be implemented with multiple antennas or an antenna array.
Referring now to FIGS. 1 and 2, an amplifier 17 may be electrically connected to the single antenna 12 for amplifying the RF signal received at the antenna 12. This amplifier 17 may be a low-noise amplifier (LNA) as is known to those skilled in the art. The amplifier 17 is preferably disposed in close proximity to the antenna 12, or, alternatively, is disposed somewhat distant from the antenna 12.
The system 10 includes a splitter 18 electrically connectable to the antenna 12. More specifically, in the illustrated embodiment, an input of the splitter 18 is electrically connected to an output of the amplifier 17. The splitter 18 splits the RF signal received by the antenna 12 into a plurality of non-phase shifted signals. The splitter 18 of the illustrated embodiments is implemented as a “two-way splitter”, i.e., the splitter 18 includes one input (not numbered) and two outputs (not numbered). As such, the splitter 18 of the illustrated embodiments splits the RF signal into a first non-phase shifted signal and a second non-phase shifted signal. The splitter 18 in the illustrated embodiments does not shift the phase of the RF signals. Instead, the splitter 18 merely splits the RF signal into multiple signals that are substantially identical to one another. However, in other embodiments (not shown), the splitter 18 may include more than two outputs to produce other non-phase shifted signals.
The splitter 18 may be implemented as a Wilkinson power divider or other suitable device. Preferably, the splitter 18 equally divides the power of the RF signal between the outputs, such that each non-phase shifted signals have about the same power level. However, those skilled in the art will realize certain situations where it may be advantageous to have differing power levels between the non-phase shifted signals.
The system 10 also includes a variable phase shifter 20 electrically connected to the splitter 18. More specifically, an input (not numbered) of the variable phase shifter 20 is electrically connected to one of the outputs of the splitter 18. In the illustrated embodiments, the variable phase shifter 20 receives the second non-phase shifted signal from the splitter 18 and may phase shift the second non-phase shifted signal to produce a phase shifted signal. In the illustrated embodiments, the amount of phase shift imposed on the second non-phase shifted signal is variable between 0 and 360 degrees. That is, the variable phase shifter 20 may impose no phase shift on the second non-phase shifted signal, thus, not changing the non-phase shifted signal in any meaningful way. Or, the variable phase shifter 20 may impose any amount of phase shift on the non-phase shifted signal, based on the technical limitations of the specific variable phase shifter 20 that is implemented. For example, the variable phase shifter 20 may be capable of shifting the phase of the RF signal by 0° (no phase shift), 2.5°, 5°, 7.5°, 10°, 12.5°, and 15°. Furthermore, those skilled in the art realize that the phase shift of a signal is analogous to a time delay of the signal.
The system 10 also includes a combiner 22 for combining signals. The combiner 22 includes inputs (not numbered) electrically connected to both the splitter 18 and the variable phase shifter 20. The combiner 22 receives and combines the first non-phase shifted signal from the splitter 18 and the phase shifted signal from the variable phase shifter 20 to produce the conditioned signal.
The system further includes a quality examiner circuit 24. The quality examiner circuit 24 is electrically connected to an output (not numbered) of the combiner 22 for receiving the conditioned signal. The quality examiner circuit 24 determines a quality of the conditioned signal and communicates with the variable phase shifter 20 for changing an amount of phase shift of the second non-phase shifted signal based on the quality of the conditioned signal. Signal quality refers to any of several aspects of a signal, including, but not limited to, high signal strength, low noise in the signal, and high signal-to-noise ratio.
The quality examiner circuit 24 may be implemented as a microprocessor (not separately numbered) operating as a digital signal processor. Those skilled in the art realize numerous suitable microprocessors to be utilized as the quality examiner circuit 24. Furthermore, those skilled in the art realize other non-microprocessor implementations for the quality examiner circuit 24.
In a first embodiment of the system 10, as shown in FIG. 1, the quality examiner circuit 24 includes an input (not numbered) for receiving the conditioned signal and an output (not numbered) electrically connectable to the receiver 14 for providing the modified signal to the receiver 14. As such, the modified signal is passed through the quality examiner circuit 24. The quality examiner circuit 24 may further modify the modified signal with digital signal processing techniques as is realized by those skilled in the art.
In a second embodiment of the system 10, as shown in FIG. 2, the output of the combiner 22 is electrically connectable to the receiver 14 for providing the conditioned signal to the receiver 14. As such, modified signal is not passed through the quality examiner circuit 24, and is not further modified by the quality examiner circuit 24.
The system 10 may also include an analog-to-digital converter (ADC) 26. The ADC 26 is electrically connected to the combiner 22 and the quality examiner circuit 24 for receiving the conditioned signal from the combiner 22 and providing a digital representation of the conditioned signal to the quality examiner circuit 24. Use of the ADC 26 is especially advantageous when either signal strength or noise are being examined as an aspect of signal quality. In the first embodiment, as shown in FIG. 1, the ADC 26 is integrated with the quality examiner circuit 24. In the second embodiment, as shown in FIG. 2, the ADC 26 is shown separate from the quality examiner circuit 24. Furthermore, those skilled in the art realize that the system 10 may be implemented without the ADC 26.
As stated above, the method of conditioning the RF signal provides a technique to mitigate a multi-path effect. The multi-path effect, as realized by those skilled in the art, occurs when an RF signal is reflected off of an object, thus causing a delay. The object may include, but is not limited to, a building, a mountain, and the ionosphere. Because of this reflection, and subsequent delay, the antenna 12 may receive the RF signal in two different phases. The first phase may be received directly from the transmitting source while the second phase may be received after the RF signal is reflected off of the object.
Particularly, to determine the best combination of phase shifted and non-phase shifted signals to make up the conditioned signal that is delivered to the receiver 14, the conditioned signal is analyzed using a plurality of different phase shifts of the phase shifted signal. The different phase shifted signals may, for convenience, be referred to as a first phase shifted signal, a second phase shifted signal, a third phase shifted signal, and so on.
In the illustrated embodiments the quality examiner circuit 24 changes the phase of the amount of phase shift provided by the variable phase shifter 20. For each different amount of phase shift, the quality examiner circuit 24 analyzes the quality of the resulting conditioned signal. The quality examiner circuit 24 then determines which of the resulting conditioned signals provides the highest quality signal and changes to the phase shift of the variable phase shifter 20 to match the phase shift of the highest quality signal. The conditioned signal is then provided to the receiver 14. Preferably, the quality examiner circuit 24 repeats this cycle only when needed, such as when the signal quality falls below a predetermined threshold. However, in other embodiments, the quality examiner circuit 24 may repeat this cycle based on other considerations.
In one particular example, the variable phase shifter 20 first produces a first phase shifted signal by phase shifting the second non-phase shifted signal by a first amount. This first phase shifted signal is combined with the first non-phase shifted signal to produce a first conditioned signal. The quality examiner circuit 24 determines and records the quality of the first conditioned signal. The variable phase shifter 20 then produces the second phase shifted signal by phase shifting the second non-phase shifted signal by a second amount, which is different than the first amount. As such, the second phase shifted signal is different from the first phase shifted signal. This second phase shifted signal is combined with the first non-phase shifted signal to produce a second conditioned signal. Accordingly, the second conditioned signal is different from the first conditioned signal. The quality examiner circuit 24 determines and records the quality of the second conditioned signal. The quality examiner circuit 24 then determines which of the first or second conditioned signals provides the highest quality signal and changes the phase shift of the variable phase shifter 20 to match the phase shift of the highest quality signal.
Of course, the method may utilize more than a first and second conditioned signal. For instance, the variable phase shifter 20 may also produce a third phase shifted signal by phase shifting the second non-phase shifted signal by a third amount, which is different than the first and second amounts. As such, the third phase shifted signal is different from the first and second phase shifted signals. This third phase shifted signal is combined with the first non-phase shifted signal to produce a third conditioned signal. Accordingly, the third conditioned signal is different from the first and second conditioned signals. The quality examiner circuit 24 determines and records the quality of the third conditioned signal. The quality examiner circuit 24 then determines which of the first, second, or third conditioned signals provides the highest quality signal and changes the phase shift of the variable phase shifter 20 to match the phase shift of the highest quality signal.
Thus, the method provides a cost effective technique to mitigate a multi-path effect on the RF signal, especially in comparison to antenna diversity schemes, where multiple antennas are required. Accordingly, the system 10 also provides a cost effective technique to mitigate a multi-path effect on the RF signal when the quality examiner circuit 24 is properly programmed to execute the method described herein.
The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.

## Claims

1. A method of conditioning an RF signal received by a single antenna to mitigate a multi-path effect on the RF signal prior to providing a conditioned signal to a receiver, said method comprising the steps of:
splitting the RF signal received by the single antenna into a first non-phase shifted signal and a second non-phase shifted signal;
shifting the phase of the second non-phase shifted signal to produce a first phase shifted signal;
combining the first non-phase shifted signal and phase shifted signal to produce a first conditioned signal;
determining and recording a quality of the first conditioned signal;
shifting the phase of the second non-phase shifted signal to produce a second phase shifted signal different from the first phase shifted signal;
combining the first non-phase shifted signal and the second phase shifted signal to produce a second conditioned signal;
determining and recording a quality of the second conditioned signal;
comparing the quality of the first conditioned signal and the second conditioned signal to determine which of the conditioned signals has a highest quality; and
providing the conditioned signal determined to have the highest quality to the receiver.

2. A method as set forth in claim 1 further comprising the step of shifting the phase of the second non-phase shifted signal to produce a third phase shifted signal different from the first and second phase shifted signals.

3. A method as set forth in claim 2 further comprising the step of combining the first non-phase shifted signal and the third phase shifted signal to produce a third conditioned signal.

4. A method as set forth in claim 3 further comprising the step of determining and recording a quality of the third conditioned signal.

5. A method as set forth in claim 4 wherein said step of comparing the quality is further defined as comparing the quality of the first, second, and third non-phase shifted signals to determine which of the conditioned signals has a highest quality.

6. A method as set forth in claim 5 wherein said step of providing the conditioned signal is further defined as providing the conditioned signal determined to have the highest quality to the receiver.

7. A method as set forth in claim 6 wherein said step of providing the conditioned signal is further defined as shifting the phase of the second non-phase shifted signal to the phase shift associated with the conditioned signal having the highest quality.

8. A method as set forth in claim 1 wherein said step of providing the conditioned signal is further defined as shifting the phase of the second non-phase shifted signal to the phase shift associated with the conditioned signal having the highest quality.