Abstract:
Provided is a steerable antenna for directing an RF output signal to a source from which an RF input signal was received. In particular, incoming phase measurements are used to calculate a phase offset. The phase offset is associated with the source and stored for subsequent use. The phase offsets are updated with each received message from the source to ensure accurate position tracking. A phase shifted oscillator uses a negated phase offset to create an output carrier signal that has the same frequency as the antenna master oscillator, but a phase shift adequate to allow the output signal or beam to form in the proper direction, i.e. toward the source. Each antenna element operates in both a transmit and receive mode, thereby ensuring that any time delays associated with the transmit and receive functions cancel one another.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority to U.S. provisional application Ser. No. 60/642,213 filed Jan. 7, 2005 and entitled RF Parameterized Steerable Antenna, which is hereby incorporated by reference to the same extent as though fully replicated herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to wireless communication networks, and in particular to steerable antennas. This invention defines an antenna system and method for determining the direction of arrival of a radio frequency (“RF”) input signal, and for determining an appropriate direction for a return RF signal.  
       BACKGROUND  
       [0003]     With the wide spread use of wireless communication today, especially in the unlicensed bands, methods are needed to maximize client coverage while minimizing noise and interference. SDMA (Space Division Multiple Access) is often used in a point to multi-point wireless system in order to maximize RF usage in a specific area, maximize useable distance to a client or source, and minimize power consumption by a client. SDMA incorporates antenna beam steering towards and from various transmit sources.  
         [0004]     Typically, the direction of arrival of an incoming radio signal, and a direction for sending a return signal, are calculated using digital signal processing (“DSP”) techniques. Many companies today are applying “smart” or steerable antenna techniques at the baseband level. These techniques often use the processing power of application specific integrated circuits to execute DSP algorithms and identify strong sources of interference, and to null these interfering sources accordingly. When a direction to the transmitting source of interest is not known, however, DSP specific antenna systems often nullify strong sources of interference, even if those interfering sources are not in the general vicinity of the transmitting source.  
         [0005]     Current “smart” or steerable antenna systems lack the ability to focus or “pre-steer” an RF input or output signal prior to the baseband digital signal processing. As such, a significant portion of the system processing resources are used to nullify or negate interfering signals that are irrelevant to the transmitting source. Hence, there is a need for a “smart” or steerable antenna capable of “pre-steering” an RF signal to address one or more of the drawbacks identified above.  
       SUMMARY  
       [0006]     The antenna system herein disclosed advances the art and overcomes problems articulated above by providing a system for directing an RF output signal to a source from which an RF input signal was received.  
         [0007]     In particular, and by way of example only, according to an embodiment, provided is an antenna system including: at least two antenna elements positioned to detect a radio frequency (“RF”) input signal from a source, and to transmit a corresponding phase-shifted RF output signal to the source; a master oscillator; a phase detector structured and arranged to measure a phase offset between the RF input signal and the master oscillator; a first input phase shifted oscillator, positioned to receive the phase offset from the phase detector for demodulation of the RF input signal to an intermediate frequency (“IF”); the RF input signal to generate an intermediate frequency (“IF”) signal; a second input phase shifted oscillator; an input RF/IF divider positioned to receive the phase offset from the phase detector and, in concert with the second input phase shifted oscillator, to demodulate the IF signal into an In-Phase (“I”) component and Quadrature (“Q”) component for base band processing; an output RF/IF divider positioned to receive a negated phase offset value; a first output phase shift oscillator, structured and arranged to modulate, in concert with the output RF/IF divider, the IF signal; and; a second output phase shift oscillator structured and arranged to receive the negated phase offset and modulate an RF component of the RF output signal, wherein the modulated IF signal and RF component combine to generate the RF output signal.  
         [0008]     In another embodiment, provided is a method for directionally transmitting an RF output signal to a source, the method including: detecting, with at least two antenna element, an RF input signal from the source; determining, for each antenna element, a phase offset between the RF input signal and a master oscillator; negating the phase offset in a processor; applying the negated phase offset in a phase shifted oscillator to shift a frequency of an output carrier signal from a first frequency to a second frequency for a predetermined number of cycles, thus shifting a phase of the output carrier signal; returning the output carrier signal to the first frequency; modulating the output carrier signal with an intermediate frequency to generate the RF output signal; and transmitting, through the at least two antenna elements, the RF output signal.  
         [0009]     In yet another embodiment, provided is a steerable antenna including: a transmit/receive means for receiving an RF input signal from a source, and for transmitting an RF output signal to the source; a determining means for determining a phase offset between the RF input signal and a master oscillator; an applying means for applying the phase offset to the RF input signal to derive an intermediate frequency; a negating means for negating the phase offset; and a generating means for applying the negated phase offset to an output carrier signal, and for modulating the output carrier signal with the intermediate frequency, to generate the RF output signal.  
         [0010]     In still another embodiment, provided is a method of directionally transmitting an RF output signal to a source, of the type wherein an RF input signal is received from the source, and a direction for transmission to the source is determined using data derived from the RF input signal, the improvement including: measuring a phase offset between the RF input signal and a master oscillator; negating the phase offset; applying the negated phase offset in a phase shifted oscillator to shift a frequency of an output carrier signal from a first frequency to a second frequency for a predetermined number of cycles, thus shifting a phase of the output carrier signal; returning the output carrier signal to the first frequency; and modulating the output carrier signal with an intermediate frequency to generate the RF output signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a top view of an incoming RF signal received by one or more antenna elements;  
         [0012]      FIG. 2  is a top view of an incoming RF signal received by one or more antenna elements;  
         [0013]      FIG. 3  is a coordinate representation of an incident plane wave and the relative distances between antenna elements, according to an embodiment;  
         [0014]      FIG. 4  is a coordinate representation of an antenna element as related to the normal of the incident wave front;  
         [0015]      FIG. 5  is a coordinate representation of an antenna element as related to the normal of the incident wave front;  
         [0016]      FIG. 6  is a coordinate representation of the relationship of a return signal, according to an embodiment;  
         [0017]      FIG. 7  is a coordinate representation of the relationship of a return signal, according to an embodiment;  
         [0018]      FIG. 8  is a block diagram of multiple antenna element feeds into a central processing unit, according to an embodiment;  
         [0019]      FIG. 9  is block diagram of an antenna system, according to an embodiment;  
         [0020]      FIG. 10  is a block diagram of the receive path of an antenna system, according to an embodiment;  
         [0021]      FIG. 11  is a block diagram of the transmit path of an antenna system, according to an embodiment;  
         [0022]      FIG. 12  is a block diagram of a phase shifted oscillator or (“FShifter”), according to an embodiment;  
         [0023]      FIG. 13  is a block diagram of a method for receiving an RF input signal, and for transmitting an RF output signal, according to an embodiment; and  
         [0024]      FIG. 14  is an example of an output carrier signal from an FShifter, according to an embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0025]     Before proceeding with the detailed description, it should be noted that the present teaching is by way of example, not by limitation. The concepts herein are not limited to use or application with one specific type of antenna system. Thus, although the instrumentalities described herein are for the convenience of explanation, shown and described with respect to exemplary embodiments, the principles herein may be equally applied in other types of antenna systems.  
         [0026]     Disclosed is a system and method for acquiring a radio frequency (“RF”) signal from a source, and for determining the required direction for a reply transmission. Once the return direction to the source is known, an RF output signal may be generated and transmitted to the source.  
         [0027]     As illustrated in  FIG. 1 , the physics of an incoming RF signal  100  (or RF input signal) require that the phase of the RF input signal  100  is constant across the wave front  102  of the signal  100 , which is perpendicular to the direction of propagation  104 . The received phase is thus measured at each element in an array, of which elements  106 ,  108  and  110  of array  112  are exemplary. Of note, knowing the locations of elements  106 - 110  is not required, nor is it necessary to know the location of the source  114  of RF input signal  100  As discussed in greater detail below, each element  106 - 110  is used to receive and transmit corresponding RF signals, thereby ensuring substantially the same receive and transmit delay times as the signal propagates through the antenna circuitry in either a receive or transmit direction.  
         [0028]     If the direction of propagation  104  is normal to the array  112  of antenna elements  106 - 110 , as shown in  FIG. 1 , the distance between any given element and the wave front  102  will be substantially equal, i.e. d 11 =d 12 =d 13 . As represented in  FIG. 2 , however, the direction of propagation  200  of a signal  201  may not always be normal to the array  202 . In this instance, the distance between a given antenna element, such as elements  204 ,  206  and  208 , and the wave front  210  (i.e. d 21 , d 22  and d 23  respectively) will not be equal. Stated differently, there will be a temporal difference in detection of the incoming wave front  210  by elements  204 - 208 . As can be appreciated by those skilled in the art, this phase difference may be measured and used to determine an orientation of the wave front  210 , and hence a direction to source  212 .  
         [0029]     Referring now to  FIG. 3 , for a desired beam or wave front direction, the phase difference between antenna elements (e.g. elements  204 - 208  in  FIG. 2 ) can be determined. As discussed above, and graphically illustrated in  FIG. 3 , the phase difference is based on the distances, e.g. d 31 , d 32  and d 33 , between perpendicular planes or “wave fronts”  300 ,  302  and  304 , respectively, that intersect each antenna element. For the purposes of this disclosure, each antenna element may be treated as a point source  306  (an isotropic antenna or antenna element with no volume). Data from multiple point sources can be multipled (combined) to represent an entire antenna element array.  
         [0030]     Still referring to  FIG. 3 , the vector, rout represents the direction of propagation for wave fronts  300 - 304 . For an arbitarily chosen reference system, the r out  vector is defined in terms of θ out  and ρ out  (see also  FIGS. 4 and 5 ). The distances, d 31  through d 33 , represent the distances along r out  between the wave fronts  300 - 304  that intersect each of the antenna elements  306 . To determine the phase distance for an arbitary point P i , (of which points P 1 , P 2 , and P 3  are exemplary) the position vector to P i  must be projected onto the r out  vector.  
         [0031]     Referring now to  FIGS. 4 &amp; 5  of the present disclosure,  FIG. 4  represents what may be termed the “z-ρ out ”-plane. As shown, r i ′ is the projection of r i  into this plane, to a point identified as P i  (x i , y i , z i ). After determining a value for both r i ′ and the angle Ψ, the distance “d i ” may be calculated as d i =r i ′ cos(Ψ i ).  
         [0032]     Similarly,  FIG. 5  represents the “x-y” plane. The double primed vectors, i.e. r″ and r i ″ are the projections of these vectors into the “x-y” plane. The dashed lines marked as ρ, or more specifically ρ out  and ρ i , represent where the “z-ρ” plane would intersect the “x-y” plane.  
         [0033]     To aid in the trigonometric manipulations, a new angle, γ i =θ out +Ψ i , is defined The resulting equations are:  
         γ   i     =       tan     -   1       ⁡     [     tan   ⁢           ⁢     θ   i     ⁢     cos   ⁡     (       φ   out     -     φ   i       )         ]           
         d   i     =       r   i     ⁢       cos   ⁢           ⁢     θ   i         cos   ⁢           ⁢     γ   i         ⁢     cos   ⁡     (       γ   i     -     θ   out       )             
 
         [0034]     The resulting phase shift for the ith antenna element is  
         τ   i     =     -       2   ⁢   π   ⁢           ⁢     d   i       λ           
 
 where λ is the wavelength of the carrier wave in free space. 
 
         [0035]     In  FIGS. 6 and 7 , the dashed vectors represent the incoming direction, r in , or as shown r in  and r″ in . Similarly, the return signal “r out ” is represented as a solid vector in the opposite directions of r in  and r″ in . These return signal vectors have been labeled, i.e. r out  and r″ out  respectively. From these figures ( FIGS. 6 and 7 ) it can be appreciated that the following relationships may be determined: 
 
φ out =φ in +180°
 
θ out =180° −θ in  
 
         [0036]     Comparing the equations from the previous discussion, a summary is provided in Table 1.  
                         TABLE 1                           Summary of Calculations for Incoming/Outgoing Signals            Incoming   Outgoing                                             γ   i   in     =       ⁢       tan     -   1       [     tan   ⁢           ⁢     θ   i     ⁢           ⁢     cos   (       φ   in     -                               ⁢     φ   i     )     ]     ⁢                                                 γ   i   out     =       tan     -   1       ⁡     [     tan   ⁢           ⁢     θ   i     ⁢           ⁢     cos   ⁡     (       φ   out     -     φ   i       )         ]                   =       tan     -   1       ⁡     [     tan   ⁢           ⁢     θ   i     ⁢           ⁢     cos   ⁡     (       (       φ   in     +     180   ⁢   °       )     -     φ   i       )         ]                   =       tan     -   1       ⁡     [     tan   ⁢           ⁢     θ   i     ⁢           ⁢     cos   ⁡     (       φ   in     -     φ   i       )         ]                   =     -     γ   i   in                                                 d   i   in     =       r   i     ⁢           ⁢       cos   ⁢           ⁢     θ   i         cos   ⁢           ⁢     γ   i   in         ⁢   cos   ⁢           ⁢     (       γ   i   in     -     θ   in       )                                 d   i   out     =       r   i     ⁢           ⁢       cos   ⁢           ⁢     θ   i         cos   ⁢           ⁢     γ   i   in         ⁢           ⁢     cos   ⁡     (       γ   i   out     -     θ   out       )                     =       r   i     ⁢           ⁢       cos   ⁢           ⁢     θ   i         cos   ⁢           ⁢     (     -     γ   i   in       )         ⁢           ⁢     cos   ⁡     (       -     γ   i   in       -     (       180   ⁢   °     -     θ   in       )       )                     =       r   i     ⁢           ⁢       cos   ⁢           ⁢     θ   i         cos   ⁢           ⁢     γ   i   in         ⁢           ⁢     cos   ⁡     (       γ   i   in     -     θ   in       )                     =     -     d   i   out                                          
 
         [0037]     It can be seen in Table 1 that the return phase shift, i.e. −γ i   in , is simply the negative of the incident phase shift at a given antenna element, i.e. γ i   in . This relationship is independent of the location of the antenna element, and the location of the source is not required to determine the phase shift.  
         [0038]     The phase shift mathematically represented and described above is determined at the antenna element terminal. Referring now to  FIG. 8 , for a system of the present disclosure, an incoming signal is delayed as it travels from a given antenna element, of which antenna elements  800 ,  802 ,  804  and  806  are exemplary, to a processing section or processor  808 . As shown in  FIG. 8 , each antenna element  800 - 802  is connected to processor  808  via a transmit/receive line, e.g. lines  810 ,  812 ,  814  and  816  respectively. For the purposes of this disclosure, a given receive signal, and a corresponding transmit signal, are carried via the same transmit/receive line (e.g. line  810 ), and are received or transmitted via the same antenna element (e.g. element  800 ). In this manner, each receive signal and corresponding transmit signal will have the same delay circuitry, and the same delay time traveling through the circuitry.  
         [0039]     Still referring to  FIG. 8 , the received phase at an antenna element, e.g. element  800 , is represented as  A τ i   in . Likewise, the phase delay due to the feed from antenna element  800  to processor  808  is represented as  F τ i   in  . It can be said, therefore, that the phase as received at processor  808  is given by  P τ i   in = A τ i   in , − F τ i   in . In the operation of the antenna system disclosed herein, the phase of a signal transmitted from processor  808  , i.e.  P τ i   out , is determined such that the phase of the signal transmitted at element  800  is represented as  A τ i   out =− A τ i   in . Stated differently, the phase of the transmitted or output RF signal at element  800  is the inverse or negative of the phase of the incoming or input RF signal. Of note, the antenna elements  800 - 806  are used for both receive and transmit, therefore, for lines  810 - 816 ,  F τ i   out = F τ i   in .  
         [0040]     Thus, it can be determined that  
                 A     ⁢     τ   i   out     ⁢     =   P     ⁢         τ   i   out     ⁢     -   F     ⁢     τ   i   out       ⇒                     P     ⁢     τ   i   out     ⁢     =   A     ⁢       τ   i   out     ⁢     +   F     ⁢     τ   i   out                   =         -   A     ⁢     τ   i     i   ⁢           ⁢   n         ⁢     +   F     ⁢     τ   i     i   ⁢           ⁢   n                     =       -   P     ⁢     τ   i     i   ⁢           ⁢   n                       
 
 and the proper transmit phase shift is achieved by negating the phase measured at processor  808 , with the line  810 - 816  delays for receive and transmit canceling each other. 
 
         [0041]     In  FIG. 9 , a top level block diagram of a steerable antenna/antenna system  900  of the present application is presented. Also depicted is a source  902  for transmitting a signal  904  toward system  900 , and for receiving a signal  906  transmitted from system  900 . As can be appreciated by those skilled in the art, as either signal  904 ,  906  is eventually received by receiver elements, the signal  904 ,  906  will appear to be a substantially linear wave front. Multiple received signals may be used to maintain/update position data related to the source.  
         [0042]     System  900  may include an antenna array  908 , which may include two or more antenna elements, e.g. elements  910  and  912 . Further, system  900  includes both a receive link or pathway, represented by arrow  914 , and a transmit link or pathway, represented by arrow  916 . As represented by arrow  918 , both links may include one or more of the same components, as discussed in greater detail below.  
         [0043]     Receive and transmit links  914 ,  916  may be interconnected electronically to a processor  920  for processing signals (to include digital signal processing), and for deriving data from signals received by system  900 . Further, system  900  may include additional support electronics and hardware  922  for facilitating operation, and for integrating with a base station (not shown) or other host.  
         [0044]     Considering now the receive link in greater detail, it can be seen in  FIG. 10  that the link  1000  includes two or more antenna elements  1002 ,  1003  interconnected to the remaining link architecture. As shown in  FIG. 10 , system  900  may include “n” number of antenna elements. The receive link architecture is structured substantially the same for each antenna element. A master oscillator  1004  is interconnected to each antenna element architecture, and tuned to a correct carrier frequency, f c .  
         [0045]     A phase detector  1006 , of a type well known in the art, is interconnected to master oscillator  1004  to compare the carrier phase to a phase of master oscillator  1004 , and to convert the phase difference into a constant voltage level. Interconnected to phase detector  1006  is an analog-to-digital or A/D converter  1008 . A/D converter  1008  is also connected to a data storage device  1010 , which in turn is connected to a processor  1012 . Also, an RF applicable phase shifted oscillator, or RF “FShifter”  1014  is positioned to receive a voltage output from phase detector  1006 . As discussed below, the present disclosure includes at least two FShifters, which may be identified as RF or IF (“Intermediate Frequency”) FShifters, depending on whether an RF or IF signal is involved. The specific elements of a FShifter, e.g. RF FShifter  1014 , are described in greater detail below. RF FShifter  1014  interconnects to a mixer  1015 , which also receives the input carrier signal and, in turn, transmits signals to a filter  1017 , wherein demodulation to the IF frequency may occur.  
         [0046]     Still referring to  FIG. 10 , an RF/IF or radio frequency (RF)/Intermediate Frequency (IF) divider  1016  is aligned with A/D converter  1008  to receive an output from the converter  1008 , and to relay a signal to a digital-to-analog or D/A converter  1018 . D/A converter  1018 , in turn, connects to an IF applicable FShifter  1020 . In at least one embodiment, the inputs to both RF/IF divider  1016  and IF Fshifter  1020  are analog, therefore A/D and D/A conversions are not required.  
         [0047]     The output of IF FShifter  1020  is input into an I/Q splitter  1022 . The output of IF FShifter  1020  is in phase with the output of  1017 , and is at the IF frequency. In at least one embodiment of the present application, the components of RF Fshifter  1014  and IF FShifter  1020  are substantially the same.  
         [0048]     As noted above, connected to processor  1012 , and to filter  1017 , is I/Q splitter  1022 , wherein the RF input signal, demodulated to the IF frequency, is split into its I and Q components for data processing. One or more outputs from I/Q splitter  1022  feed into processor  1012  for digital signal processing as necessary and/or desired. As previously noted, each antenna element in an “n” antenna element array has a receive link or pathway substantially the same as that described above. In the processing of multiple RF input signals, a combining or addition of the discrete signals received by each element is performed to generate an entire received signal.  
         [0049]     Referring now to  FIG. 11 , the transmit link  1100  or pathway is substantially the reverse of the transmit link  1000 , and it includes a modulation module  1102  for receiving the IF signal. The stored, digitized offset value (in voltage form) is transmitted to two separate D/A converters  1104  and  1106 . The signal transmitted to D/A converter  1104  first passes through an RF/IF divider  1108 . An IF FShifter  1110  is interconnected to D/A converter  1104  and modulation module  1102 . The digitized voltage is also directed to an RF FShifter  1112 . Outputs of both IF FShifter  1110  and RF FShifter  1112  are inputs to a mixer  1114 .  
         [0050]     An integral element of the present disclosure is the phase shifted oscillator or FShifter. Referring now to  FIG. 12 , an FShifter  1200  (which may be either an IF FShifter or an RF FShifter) may include a voltage controller or “VShifter”  1202  for receiving an analog signal  1204  indicative of the phase offset, or alternatively the negated phase offset. Further, a voltage control oscillator or “VCO”  1206  is interconnected to voltage controller  1202 . In addition to periodically receiving an input from VShifter  1202 , VCO  1206  receives base frequency input  1208  from master oscillator  1004  ( FIG. 10 ). As shown in  FIG. 12 , a shift register or counter  1210  is interconnected to both VCO  1206  and VShifter  1202 . The output of FShifter  1200  is a phase-shifted carrier signal  1212 . As noted in  FIG. 12 , other input/control signals, such as a clocking signal “Clk” or reset signal “Rst” are inputs or directions to FShifter  1200 .  
         [0051]      FIG. 13  is a flow diagram of the functional operation of at least one embodiment of a steerable antenna system of the present application, e.g. system  900 . In the operation of the system  900 , an RF input signal or carrier signal is received at each antenna element, block  1300 . A phase detector compares the carrier phase to the master oscillator&#39;s known phase, block  1302 . The offset, or delta phase derived from this comparison is converted into a constant voltage level by the phase detector, block  1304 . Of note, each antenna element will have a phase voltage or phase offset unique to that antenna element. The converted voltage(s) are stored by antenna system  900  (for example in the processor), or alternatively a base station or host, and are associated with a specific source for future reference and use, block  1306 .  
         [0052]     The constant phase voltage is also directed to the RF version of the Fshifter, block  1308 . With this input voltage, the RF Fshifter aligns the master oscillator phase to the specific antenna element phase for proper demodulation, block  1310 . RF demodulation follows, block  1311 . For proper IF demodulation, the IF phase must also be shifted. The amount of IF phase shift is determined by the ratio of RF/IF frequencies. This ratio value is inputted to the IF version of the Fshifter (block  1312 ), which is followed by phase alignment, block  1313 . Output from the IF FShifter is used as input for proper extraction of the I and Q base band components, block  1314 . These components are provided to the base band processing (block  1316 ) wherein they may be combined directly, resulting in some minor ISI (inter-symbol interference), or the phase delay information may be used for shifting any base band processing, such as the CDMA code generator, prior to combining the separate signals.  
         [0053]     Considering now the transmit portion of system  900  operation, the phase delay information, that was stored in the receive cycle, is provided to the modulation module. For the I/Q modulation, this value is adjusted to the proper IF frequency and phase, again using the RF/IF ratio (block  1318 ), and converted from a digital value to an analog voltage, block  1320 . The stored value is then inputted to the IF version of the Fshifter, block  1322 , the output of which is input into the I/Q modulation module, block  1324 .  
         [0054]     Of note, the operation of the IF FShifter creates a carrier signal that is the same frequency as the IF frequency, however the carrier signal has a phase shift relative to the master oscillator that allows the beam to form in the proper direction. To accomplish this task, a window is defined where the frequency of the carrier signal is either higher or lower than the IF frequency for a specific number of cycles. The frequency is determined by  
           f   Shift     =       K   ⁢           ⁢     f   carr           -     V   θ       +   K         ,       
 
 where K is the window length, f carr  is the carrier frequency, and V θ  is the voltage measurement for the phase. 
 
         [0055]     In particular, the voltage control oscillator or VCO generates the carrier frequency based on the master oscillator frequency and phase. The output cycles of the VCO are also shifting “1” s in the shift register or counter. After the K cycles, the output of the shift register goes to zero. During this window of “1”s, the Vshifter is outputting a delta voltage change based on the inputted phase voltage. The Vshifter is an implementation of the equation for f Shift −f carr  or  
           f   Shift     -     f   carr       =         V   θ       K   -     V   θ         ⁢       f   carr     .           
 
 After the window, the V shifter goes to zero and maintains its shifted phase. 
 
         [0056]     The RF modulation is done in a similar manner. The stored digital value is converted to an analog voltage, block  1326 . This value is inputted to the RF version of the Fshifter for proper frequency and phase generation, block  1328 . The outptut of the RF FShifter is mixed with the output of the I/Q Modulation to create the RF output signal, block  1330 , and RF modulation (block  1331 ) is the final step prior to transmitting to the source, block  1332 .  
         [0057]      FIG. 14  is a representation of the shifted output of the IF or RF Shifter as discussed above. As shown, the output shifts from the phase of the master oscillator (as depicted by curve  1400 ) to the shifted phase of the output carrier or RF output signal (as depicted by curve  1402 ) over a predetermined number (“K”) cycles. As can be appreciated by referring to  FIG. 14 , once the phase has shifted the output signal returns to the original frequency and maintains the phase shift. In this manner, the RF output siganl, which is transmitted through the same antenna element as originally received, is directed or steered toward the source. Directional transmission of the RF output signal is accomplished using RF signal parameters, as opposed to digital signal processing to calculate a return direction.  
         [0058]     Changes may be made in the above methods, devices and structures without departing from the scope hereof. It should thus be noted that the matter contained in the above description and/or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method, device and structure.