# Patent

## Title
Adaptive transmit array for beam-steering

## Abstract

A method includes receiving a remote transmitter signal at an antenna array including a number of antenna elements, mixing the received signal with in-phase and quadrature-phase Local Oscillator (LO) signals from Voltage Controlled Oscillators (VCOs) of a coupled VCO array, and configuring each Phase Locked Loop (PLL) of a number of PLLs to receive an in-phase output of the mixing corresponding to a VCO and a quadrature-phase output of the mixing corresponding to another VCO adjacent to the VCO as inputs thereto. The method also includes feeding back an output of the each PLL to the VCO, driving the in-phase and the quadrature-phase outputs of the mixing from a transmit modulator, and transmitting, in a direction of the remote transmitter, an antenna array signal based on the driving. Further, the method includes sensing a servoed state related to LO phase relationships and holding thereof during the transmission of the signal.

## Background
CLAIM OF PRIORITY
This application is a conversion application of the U.S. provisional patent application Ser. No. 61/801,624 titled ADAPTIVE TRANSMIT ARRAY FOR BEAM-STEERING filed on Mar. 15, 2013
FIELD OF TECHNOLOGY
This disclosure generally relates to beam-steering and, more specifically, to a method, a circuit and/or a system of an adaptive transmit array for beam-steering.
BACKGROUND
Modern systems such as wireless, phased array, communication, radar, Global Positioning System (GPS) and signal gathering systems may require control and/or maintenance of a direction of a beam. The aforementioned systems may require costly physical alignment of antenna systems thereof; in the case of electronic beam-steering antenna systems, a high level of circuit and processing complexity may be required, in addition to constant monitoring.
A servo system utilized to determine the direction of a remote transmitter and then to transmit Radio Frequency (RF) signals back at the remote transmitter may require complete down-conversion and digital signal processing, which is time consuming and costly in terms of circuitry and power.
SUMMARY
Disclosed are a method, a circuit and/or a system of an adaptive transmit array for beam-steering.
In one aspect, a method includes receiving a signal from a remote transmitter at an antenna array including a number of antenna elements, mixing the received signal with in-phase and quadrature-phase Local Oscillator (LO) signals from Voltage Controlled Oscillators (VCOs) of a coupled VCO array, and configuring each Phase Locked Loop (PLL) of a number of PLLs to receive an in-phase output of the mixing corresponding to a VCO of the coupled VCO array and a quadrature-phase output of the mixing corresponding to another VCO adjacent to the VCO in the coupled VCO array as inputs thereto. The method also includes feeding back an output of the each PLL to the VCO of the coupled VCO array, and driving the in-phase and the quadrature-phase outputs of the mixing from in-phase and quadrature-phase outputs of a transmit modulator instead of the each PLL being driven by the in-phase and the quadrature-phase output of the mixing.
Further, the method includes transmitting, in a direction of the remote transmitter, a signal from the antenna array based on the driving of the in-phase and the quadrature-phase outputs of the mixing from the transmit modulator, and sensing a servoed state related to phase relationships between the LO signals and holding the servoed state through a sample and hold circuit coupled in a feedback path between the output of the each PLL and the VCO during the transmission of the signal in the direction of the remote transmitter.
In another aspect, a beam-steering system includes an antenna array including a number of antenna elements. The antenna array is configured to receive a signal from a remote transmitter thereat. The beam-steering system also includes a coupled VCO array including a number of VCOs coupled to one another, a number of mixers, a number of PLLs and a number of sample and hold circuits. Each mixer of the number of mixers is configured to mix the received signal at an antenna element with an in-phase and a quadrature-phase LO signal from a particular VCO of the coupled VCO array. Each PLL of the number of PLLs is configured to receive an in-phase output of the each mixer corresponding to the particular VCO and a quadrature-phase output of a mixer corresponding to another VCO adjacent to the particular VCO as inputs thereto.
An output of the each PLL is fed back to the particular VCO. The in-phase and the quadrature-phase outputs of the number of mixers are configured to be driven from in-phase and quadrature-phase outputs of a transmit modulator instead of the number of PLLs being driven by the in-phase and the quadrature-phase outputs of the number of mixers. The antenna array is configured to transmit a signal in a direction of the remote transmitter based on the driving of the in-phase and the quadrature-phase outputs of the number of mixers from the transmit modulator. Each sample and hold circuit of the number of sample and hold circuits is configured to sense a servoed state related to phase relationships between LO signals from VCOs of the coupled VCO array and hold the servoed state during the transmission of the signal in the direction of the remote transmitter. The each sample and hold circuit is coupled in a feedback path between the output of the each PLL and the particular VCO.
In yet another aspect, a wireless communication system includes a remote transmitter and a beam-steering system. The beam-steering system includes an antenna array including a number of antenna elements. The antenna array is configured to receive a signal from the remote transmitter thereat. The beam-steering system also includes a coupled VCO array including a number of VCOs coupled to one another, a number of mixers, a number of PLLs and a number of sample and hold circuits. Each mixer of the number of mixers is configured to mix the received signal at an antenna element with an in-phase and a quadrature-phase LO signal from a particular VCO of the coupled VCO array. Each PLL of the number of PLLs is configured to receive an in-phase output of the each mixer corresponding to the particular VCO and a quadrature-phase output of a mixer corresponding to another VCO adjacent to the particular VCO as inputs thereto.
An output of the each PLL is fed back to the particular VCO. The in-phase and the quadrature-phase outputs of the number of mixers are configured to be driven from in-phase and quadrature-phase outputs of a transmit modulator instead of the number of PLLs being driven by the in-phase and the quadrature-phase outputs of the number of mixers. The antenna array is configured to transmit a signal in a direction of the remote transmitter based on the driving of the in-phase and the quadrature-phase outputs of the number of mixers from the transmit modulator. Each sample and hold circuit of the number of sample and hold circuits is configured to sense a servoed state related to phase relationships between LO signals from VCOs of the coupled VCO array and hold the servoed state during the transmission of the signal in the direction of the remote transmitter. The each sample and hold circuit is coupled in a feedback path between the output of the each PLL and the particular VCO.
Other features will be apparent from the accompanying drawings and from the detailed description that follows.



BRIEF DESCRIPTION OF THE FIGURES
Example embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
FIG. 1 is a schematic view of a beamforming system involving Local Oscillator (LO) scanned arrays.
FIG. 2 is a schematic view of servoing a beamforming system.
FIG. 3 is a schematic view of mixing of a received RF signal with in-phase (I) and quadrature-phase (Q) LO signal components from a coupled VCO array of the beamforming system of FIG. 2.
FIG. 4 is a schematic view of a modified servo arrangement of the beamforming system of FIG. 3, according to one or more embodiments.
FIG. 5 is a schematic view of a sample and hold circuit of the modified servo arrangement of FIG. 4, according to one or more embodiments.
FIG. 6A is a process flow diagram detailing operations involved in realizing an adaptive transmit array for beam-steering, according to one or more embodiments;
FIG. 6B is a continuation of the process flow diagram of FIG. 6A.



Other features of the present embodiments will be apparent from the accompanying drawings and from the disclosure that follows.
DETAILED DESCRIPTION
Example embodiments, as described below, may be used to provide a method, a circuit and/or a system of an adaptive transmit array for beam-steering. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments.
Beamforming may be a technique for electronically setting a direction of a Radio Frequency (RF) beam using fixed arrays of antenna apertures or antenna elements. The aforementioned antenna arrays may be one-dimensional, two-dimensional or three-dimensional. The electronic pointing of the RF beam may be performed for either transmission or reception of signals. Beamforming, or electronic direction setting of the RF beam, may typically be achieved through the introduction of differential phase shifts in signal paths coupled to each of the antenna apertures or antenna elements.
It should be noted that exemplary embodiments to be discussed herein are to be placed within the context of a receiver (e.g., wireless receiver), where Local Oscillator (LO) signal generation is required.
A common technique to introduce the requisite phase shift in the signal path may involve generation of LO signals to mixers located in the signal paths. The aforementioned configuration may be called an LO scanned array. FIG. 1 shows a beamforming system 100 involving LO scanned arrays; LO scanned arrays may also be utilized to sense the direction from which a transmitter 102 is radiating energy. The antenna system including antenna array 106 and antenna electronics 107 may be utilized to reflect back the incident RF radiation in the direction of the source transmitter 102. The aforementioned antenna array 106 may be called a retro-directive array. FIG. 1 shows the automatic adaptive alignment of the receive beam (e.g., receive beam 160) toward the direction (e.g., rotating an angle β) of the transmitted RF signal.
In the LO scanned arrays of FIG. 1, LO signals 108 with differential phases may be generated and the differential phase LO signals 108 may be input to mixers 111 located in the signal paths. Antenna array 106 may be utilized in beam-steering or directing and/or focusing of transmitted/received signals. By directing the energy from or concentrating the energy incoming thereto, a higher efficiency may be achieved compared to a standard antenna implementation. This may result in the capability to transmit or receive signals corresponding to or from more distant receiving or transmitting radios, as discussed above.
A voltage controlled oscillator (VCO) 101 (see, e.g., FIGS. 1-5) may be an electronic oscillator configured to vary oscillation frequency thereof based on a voltage input. FIGS. 1-5 serve to describe the receiver (e.g., wireless receiver) context in which exemplary embodiments discussed herein may be practiced. The function of VCO 101 in LO signal generation (e.g., LO signal 108) as applied to receivers is well known to one of ordinary skill in the art. In order to generate differential phase LO signals, a coupled VCO array may be utilized. FIG. 1 shows beamforming system 100 including a coupled VCO array 150. Here, coupled VCO array 150 may include two or more VCOs 101 mutually injection locked to each other. Injection locking may be the state in which the two or more VCOs 101 exchange oscillatory energy sufficient enough to lock to a same frequency. Injection locking may be accomplished based on coupling VCOs 101 together through a bidirectional coupling circuit (e.g., resistor 103; other bidirectional coupling circuits 103 may also be used instead).
The outputs of mixing of LO signals 108 with signals from antenna elements of antenna array 106 may be combined at combiner 112 (e.g., a combiner circuit). There may be various ways to sense the direction of the remote transmitter 102, and to servo the LO phase relationships in the LO scanned array to better receive the remote signal, or to transmit energy back in the direction of the remote signal. The aforementioned ways may also be employed to track a remote transmitter in motion relative to the retro-directive array discussed above.
FIG. 2 shows servoing a beamforming system (e.g., beamforming system 100). Here, RF signals 202 (e.g., from transmitter 102) may be incident on antenna array 106. RF signals 202 may be received and mixed (e.g., through mixer 111(s); see also FIG. 3) with in-phase (I) and quadrature-phase (Q) LO signals 108 from coupled VCO array 150. Appropriate elements are analogous to the counterparts thereof in FIG. 1. The resulting in-phase (I) outputs may be compared to the quadrature-phase (Q) outputs of a neighboring element in a Phase Locked Loop (PLL) 220. PLL 220 may include a phase detector and a filter; the constituent elements of PLL 220 are well known to one skilled in the art. Detailed discussion thereof, therefore, has been skipped for the sake of convenience and brevity. The output of PLL 220 (OP 222) may then be fed back as an input to coupled VCO array 150 (e.g., to a corresponding VCO 101).
The process of I/Q down-converting RF signals, comparing phases of a 0 degree output of one down-converted RF input to the 90 degree output of an adjacent down-converted RF input, filtering, and feeding back into one of the VCOs 101 of coupled VCO array 150 may create a servo loop that senses the direction of a remote transmitter 102 and electronically points antenna array 106 to better receive the remotely transmitted signal (e.g., RF signal 202).
In one or more embodiments, concepts related to the abovementioned automatic receive system may also be utilized in transmitting signal(s) back to the remote transmitter 102. By utilizing the servoed array setting, the same system may be utilized to transmit energy back at the remote transmitter 102. FIG. 4 shows a modified servo arrangement of the beamforming system of FIG. 3, according to one or more embodiments. Here, in one or more embodiments, a sample and hold circuit 402 may be coupled in series with OP 222. In one or more embodiments, sample and hold circuit 402 may be implemented with merely a switch (S) and a capacitor (C) (see FIG. 5); alternately, in one or more embodiments, sample and hold circuit 402 may be more complex. In one or more embodiments, sample and hold circuits 402 may sense the state of the servoed array and then hold the servoed state during the transmission back to the remote transmitter 102.
In one or more embodiments, a switch 404 may be added to each of the I and Q outputs of I/Q mixers 111. In one or more embodiments, instead of driving PLLs 220, the I and Q outputs of mixers 111 may instead be driven from I and Q outputs of a transmit modulator 406. Here, the I and Q outputs of mixers 111 may become I and Q inputs, and mixers 111 may be utilized in a reverse direction to transmit. Thus, in one or more embodiments, it may be possible to transmit signals/information in the direction of the remote transmitter 102.
Exemplary embodiments, therefore, may provide for automatic servoing of and transmission from antenna array 106, with the servoing being fast and consuming low power. It will be appreciated that concepts disclosed herein may also be applied to two-dimensional or three-dimensional arrays of coupled VCOs 101, in addition to one-dimensional arrays thereof.
FIG. 6 shows a process flow diagram detailing operations involved in realizing an adaptive transmit array for beam-steering, according to one or more embodiments. In one or more embodiments, operation 602 may involve receiving a signal (e.g., RF signal 202) from a remote transmitter (e.g., transmitter 102) at antenna array 106 including a number of antenna elements. In one or more embodiments, operation 604 may involve mixing the received signal with in-phase and quadrature-phase LO signals 108 from VCOs 101 of coupled VCO array 150. In one or more embodiments, operation 606 may involve configuring each PLL 220 of a number of PLLs 220 to receive an in-phase output of the mixing corresponding to a VCO 101 of coupled VCO array 150 and a quadrature-phase output of the mixing corresponding to another VCO 101 adjacent to the VCO 101 in coupled VCO array 150 as inputs thereto.
In one or more embodiments, operation 608 may involve feeding back an output (e.g., OP 222) of the each PLL 220 to the VCO 101 of coupled VCO array 150. In one or more embodiments, operation 610 may involve driving the in-phase and the quadrature-phase outputs of the mixing from in-phase and quadrature-phase outputs of transmit modulator 406 instead of the each PLL 220 being driven by the in-phase and the quadrature-phase output of the mixing. In one or more embodiments, operation 612 may involve transmitting, in a direction of the remote transmitter 102, a signal from antenna array 106 based on the driving of the in-phase and the quadrature-phase outputs of the mixing from transmit modulator 406.
In one or more embodiments, operation 614 may then involve sensing a servoed state related to phase relationships between the LO signals 108 and holding the servoed state through a sample and hold circuit (e.g., sample and hold 402) coupled in a feedback path between the output of the each PLL 220 and the VCO 101 during the transmission of the signal in the direction of the remote transmitter 102.
Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

## Claims

1. A method comprising:
receiving a signal from a remote transmitter at an antenna array comprising a plurality of antenna elements;
mixing the received signal with in-phase and quadrature-phase Local Oscillator (LO) signals from Voltage Controlled Oscillators (VCOs) of a coupled VCO array;
configuring each Phase Locked Loop (PLL) of a plurality of PLLs to receive an in-phase output of the mixing corresponding to a VCO of the coupled VCO array and a quadrature-phase output of the mixing corresponding to another VCO adjacent to the VCO in the coupled VCO array as inputs thereto;
feeding back an output of the each PLL to the VCO of the coupled VCO array;
driving the in-phase and the quadrature-phase outputs of the mixing from in-phase and quadrature-phase outputs of a transmit modulator instead of the each PLL being driven by the in-phase and the quadrature-phase output of the mixing;
transmitting, in a direction of the remote transmitter, a signal from the antenna array based on the driving of the in-phase and the quadrature-phase outputs of the mixing from the transmit modulator; and
sensing a servoed state related to phase relationships between the LO signals and holding the servoed state through a sample and hold circuit coupled in a feedback path between the output of the each PLL and the VCO during the transmission of the signal in the direction of the remote transmitter.

2. The method of claim 1, comprising implementing the sample and hold circuit with a switch and a capacitor.

3. The method of claim 1, further comprising coupling a switch each in a path of the in-phase output of the mixing corresponding to the VCO of the coupled VCO array and in another path of the quadrature-phase output of the mixing corresponding to the VCO, the path being coupled to the each PLL and the another path being coupled to another PLL.

4. The method of claim 1, further comprising injection locking two or more VCOs of the coupled VCO array to each other.

5. The method of claim 1, further comprising coupling a VCO of the coupled VCO array to another VCO thereof through a bidirectional coupling circuit.

6. The method of claim 1, comprising providing one of: a one-dimensional, a two-dimensional and a three-dimensional VCO array as the coupled VCO array.

7. The method of claim 1, comprising beam-steering the signal from the remote transmitter back thereto, the beam-steered signal being the signal transmitted from the antenna array in the direction of the remote transmitter.

8. A beam-steering system comprising:
an antenna array comprising a plurality of antenna elements, the antenna array being configured to receive a signal from a remote transmitter thereat;
a coupled VCO array comprising a plurality of VCOs coupled to one another;
a plurality of mixers, each of which is configured to mix the received signal at an antenna element with an in-phase and a quadrature-phase LO signal from a particular VCO of the coupled VCO array;
a plurality of PLLs, each of which is configured to receive an in-phase output of the each mixer corresponding to the particular VCO and a quadrature-phase output of a mixer corresponding to another VCO adjacent to the particular VCO as inputs thereto, an output of the each PLL being fed back to the particular VCO, the in-phase and the quadrature-phase outputs of the plurality of mixers being configured to be driven from in-phase and quadrature-phase outputs of a transmit modulator instead of the plurality of PLLs being driven by the in-phase and the quadrature-phase outputs of the plurality of mixers, and the antenna array being configured to transmit a signal in a direction of the remote transmitter based on the driving of the in-phase and the quadrature-phase outputs of the plurality of mixers from the transmit modulator; and
a plurality of sample and hold circuits, each of which is configured to sense a servoed state related to phase relationships between LO signals from VCOs of the coupled VCO array and hold the servoed state during the transmission of the signal in the direction of the remote transmitter, the each sample and hold circuit being coupled in a feedback path between the output of the each PLL and the particular VCO.

9. The beam-steering system of claim 8, wherein the each sample and hold circuit is implemented with a switch and a capacitor.

10. The beam-steering system of claim 8, further comprising a switch coupled each in a path of the in-phase output of the each mixer corresponding to the particular VCO of the coupled VCO array and in another path of the quadrature-phase output of the each mixer corresponding to the particular VCO, the path being coupled to the PLL and the another path being coupled to another PLL.

11. The beam-steering system of claim 8, wherein two or more VCOs of the coupled VCO array are configured to be injection locked to each other.

12. The beam-steering system of claim 8, further comprising a plurality of bidirectional coupling circuits, each of which is configured to couple a VCO of the coupled VCO array to another VCO thereof.

13. The beam-steering system of claim 8, wherein the coupled VCO array is one of: a one-dimensional, a two-dimensional and a three-dimensional VCO array.

14. The beam-steering system of claim 8, wherein the signal from the remote transmitter is configured to be beam-steered back thereto, the beam-steered signal being the signal transmitted from the antenna array in the direction of the remote transmitter.

15. A wireless communication system comprising:
a remote transmitter; and
a beam-steering system comprising:
an antenna array comprising a plurality of antenna elements, the antenna array being configured to receive a signal from the remote transmitter thereat;
a coupled VCO array comprising a plurality of VCOs coupled to one another;
a plurality of mixers, each of which is configured to mix the received signal at an antenna element with an in-phase and a quadrature-phase LO signal from a particular VCO of the coupled VCO array;
a plurality of PLLs, each of which is configured to receive an in-phase output of the each mixer corresponding to the particular VCO and a quadrature-phase output of a mixer corresponding to another VCO adjacent to the particular VCO as inputs thereto, an output of the each PLL being fed back to the particular VCO, the in-phase and the quadrature-phase outputs of the plurality of mixers being configured to be driven from in-phase and quadrature-phase outputs of a transmit modulator instead of the plurality of PLLs being driven by the in-phase and the quadrature-phase outputs of the plurality of mixers, and the antenna array being configured to transmit a signal in a direction of the remote transmitter based on the driving of the in-phase and the quadrature-phase outputs of the plurality of mixers from the transmit modulator; and
a plurality of sample and hold circuits, each of which is configured to sense a servoed state related to phase relationships between LO signals from VCOs of the coupled VCO array and hold the servoed state during the transmission of the signal in the direction of the remote transmitter, the each sample and hold circuit being coupled in a feedback path between the output of the each PLL and the particular VCO.

16. The wireless communication system of claim 15, wherein the each sample and hold circuit of the beam-steering system is implemented with a switch and a capacitor.

17. The wireless communication system of claim 15, wherein the beam-steering system further comprises a switch coupled each in a path of the in-phase output of the each mixer corresponding to the particular VCO of the coupled VCO array and in another path of the quadrature-phase output of the each mixer corresponding to the particular VCO, the path being coupled to the PLL and the another path being coupled to another PLL.

18. The wireless communication system of claim 15, wherein two or more VCOs of the coupled VCO array of the beam-steering system are configured to be injection locked to each other.

19. The wireless communication system of claim 15, wherein the beam-steering system further comprises a plurality of bidirectional coupling circuits, each of which is configured to couple a VCO of the coupled VCO array to another VCO thereof.

20. The wireless communication system of claim 15, wherein the signal from the remote transmitter is configured to be beam-steered back thereto through the beam-steering system, the beam-steered signal being the signal transmitted from the antenna array of the beam-steering system in the direction of the remote transmitter.