Patent Description:
Electronic Circulator self-interference cancellation (SIC) is done today by coupling the transmit (TX) signal into a finite impulse response (FIR) filter for shaping post power amplifier (PA) and combining the canceling signal pre low noise amplifier (LNA). Such schemes are complex, not scalable to multiple-input and multiple-output (MIMO) systems, where self and mutual interferences are present and create transmit and receive losses, degrading power efficiency and receiver signal to noise ratio.

Simultaneous Transmit Receive (STR) single transmit/receive antenna wireless communication scenarios (such as Full Duplex (FD) or Frequency Division Duplex (FDD) without a Diplexer) require a Transmit-Receive SIC mechanism. Most implementations of SIC are done between the TX transmit output and the RX receive input, thereby loading both TX and RX channels, reducing the power efficiency and signal to noise ratio.

The article "<NPL>) describes how full-duplex operation can be integrated with multi-input multi-output operation using RF and baseband self-interference cancellation.

United States patent application <CIT> describes a non-reciprocal transceiver array architecture with a single non-reciprocal element.

The article "<NPL>) describes an acoustic four-port circulator based on two rat-race couplers and a non-reciprocal element.

It is an object of the present disclosure to describe a four-port circulator, as defined in claim <NUM> and its dependent claims, and methods of using the four-port circulator for radio frequency (RF) communication, as defined in claim <NUM> and its dependent claims.

Embodiments of the present disclosure provide a four-port circulator with lossless receive and SIC transfer functions. The four-port circulator (also denoted herein a quadrature circulator) includes a non-ideal four-point circulator (denoted herein a quasi-circulator) cascaded with a quadrature hybrid. Two ports of the quasi-circulator are respectively connected to two ports of the quadrature hybrid. The quadrature hybrid recovers perfectly the non-ideal characteristics of the quasi-circulator, resulting in a new transfer function of an ideal electronic quadrature circulator.

Embodiments of the quadrature circulator have the following transfer coefficients:.

All other pairs of ports are isolated from each other. These transfer coefficients are represented in the scattering matrix below: <MAT> Benefits of the quadrature circulator presented herein include:.

A first aspect of the disclosure provides a quadrature circulator device which includes:.

A benefit of the first aspect, is that quadrature circulator with an ideal transfer function is obtained with a small form factor.

In an implementation form of the first aspect, the quasi-circulator includes:.

A benefit of these implementations is that they provide a four-port device having the desired transfer function of the quasi-circulator.

In a further implementation form of the first aspect, the quadrature circulator device further includes an antenna connected to the second port of the quasi-circulator. A benefit of this implementation is that a quadrature circulator port may be used in wireless communication devices.

In a further implementation form of the first aspect, the quadrature circulator device further includes a first reflective element, wherein an output of the first reflective element is connected to the third port of the quadrature hybrid. Thus a self-interference cancellation signal may be input to Port <NUM> of the quadrature circulator device, while the signal from Port <NUM> is transferred to Port <NUM>. A benefit of this implementation is that it is suitable for many communication modes, such as full-duplex, half-duplex and frequency-division-duplex.

In a further implementation form of the first aspect, the quadrature circulator device further includes a second reflective element, wherein an output of the second reflective element is connected to the first port of the quasi-circulator. Thus transmitted signals may be input both to Port <NUM> and Port <NUM> of the quadrature circulator. A benefit of this implementation is that it is suitable for carrier-aggregation communication.

A second aspect of the disclosure provides a method of operating the quadrature circulator device by:.

A benefit of this aspect is that the quadrature circulator may be used as part of an RF front end for many forms of RF communications and system architectures.

In an implementation form of the second aspect, the quadrature circulator device is operated by:.

In further implementation form of the second aspect, the quadrature circulator device is operated by: inputting a transmit signal at the first port of the quasi-circulator;.

In further implementation form of the second aspect, the quadrature circulator device is operated by: inputting a transmit signal in a first frequency band at the first port of the quasi-circulator;.

In further implementation form of the second aspect, the quadrature circulator device is operated by: inputting a first transmit signal in a first frequency band at the first port of the quasi-circulator via a reflective element; inputting a second transmit signal in a second frequency band at the second port of the quadrature hybrid; and outputting the first transmit signal and the second transmit signal from the second port of the quasi-circulator. A benefit of this implementation is that it is suitable for an RF front end for carrier-aggregation communication.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments, exemplary methods and/or materials are described below.

Some embodiments are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments may be practiced.

Some embodiments described in the present disclosure relate to a quadrature circulator and, more specifically, but not exclusively, to a four-port quadrature electronic circulator.

Embodiments of the present disclosure provide a lossless and fully matched quadrature circulator. The quadrature circulator) includes a quasi-circulator cascaded with a quadrature hybrid as described herein.

Before explaining at least one embodiment in detail, it is to be understood that embodiments are not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. Implementations described herein are capable of other embodiments or of being practiced or carried out in various ways.

Embodiments may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the embodiments.

A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, and any suitable combination of the foregoing.

Computer readable program instructions for carrying out operations of embodiments may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of embodiments.

Aspects of embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments.

Reference is now made to <FIG>, which is a schematic block diagram of a quadrature circulator according to embodiments of the invention. Quadrature circulator <NUM> includes quasi-circulator <NUM> and quadrature hybrid <NUM>, which are connected in cascade. Quasi-circulator <NUM> and quadrature hybrid <NUM> have the same characteristic impedance Z<NUM>.

Quadrature circulator <NUM> includes quasi-circulator <NUM> and quadrature hybrid <NUM>.

Quasi-circulator <NUM> has four ports: first port (<NUM>), second port (<NUM>), third port (<NUM>), and fourth port (<NUM>). Quadrature hybrid (<NUM>) has four ports: first port (<NUM>), second port (<NUM>), third port (<NUM>), and fourth port (<NUM>). The quasi-circulator's fourth port (<NUM>) is connected to the quadrature hybrid's fourth port (<NUM>) and the quasi-circulator's third port (<NUM>) is connected to the quadrature hybrid's first port (<NUM>).

The remaining four ports (ports <NUM>, <NUM>, <NUM> and <NUM>) serve as the ports of quadrature circulator (<NUM>) as follows:.

As used herein, Port <NUM>, Port <NUM>, Port <NUM> and Port <NUM> denote the four ports of the quadrature circulator.

The scattering matrix (S1) of quasi-circulator <NUM> is: <MAT> Each entry S<NUM>xy of S1 represents a portion of a square root of a power of a signal that is directed by quasi-circulator (<NUM>) from the yth port to the xth port, wherein x and y each can be <NUM>, <NUM>, <NUM>, and <NUM> and x is not equal to y, and each entry S<NUM>xx represents a portion of a square root of a power of a signal that is reflected at the xth port.

The scattering matrix (S2) of quadrature hybrid <NUM> is: <MAT> Similarly to the notation of S1, each entry S<NUM>xy of S2 represents a portion of a square root of a power of a signal that is directed by quadrature hybrid (<NUM>) from the quadrature hybrid's yth port to the xth port, wherein x and y each can be <NUM>, <NUM>, <NUM>, and <NUM> and x is not equal to y, and each entry S<NUM>xx represents a portion of a square root of a power of a signal that is reflected at the quadrature hybrid's xth port.

Surprisingly, the inventors have found that a signal entering Port <NUM> is fully transmitted to Port <NUM> of quadrature circulator (<NUM>). This is despite the -<NUM>/<NUM> reflection coefficients at quasi-circulator ports <NUM> and <NUM> and the transfer coefficients of -j/<NUM> and j/<NUM> between ports <NUM> to <NUM> and ports <NUM> to <NUM> respectively. While quadrature hybrid <NUM> divides the signal entering at Port <NUM> equally in amplitude, the skilled person would not deduce that these two signal portions will add perfectly at Port <NUM>. It is also unexpected that a signal entering Port <NUM> will reconstruct at Port <NUM>, since quasi-circulator ports <NUM> and <NUM> have reflection coefficients of -<NUM>/<NUM>.

In fact quadrature circulator (<NUM>) attains the ideal scattering matrix of: <MAT> where each entry |S<NUM>-Port_circ-XY| represents a portion of a square root of a power of a signal that is directed by quadrature circulator (<NUM>) from the Port X to Port Y of quadrature circulator (<NUM>), wherein X and Y each can be <NUM>, <NUM>, <NUM>, and <NUM> and X is not equal to Y, and each entry |S<NUM>-Port_circ-XX| represents a portion of a square root of a power of a signal that is reflected at Port X of quadrature circulator (<NUM>). As can be seen from|S<NUM>-Port_circ|, quadrature circulator (<NUM>) offers "circular" full transmission from port to port in one direction and zero transmission in the reverse direction as well as to non-adjacent ports, with perfect matching at all ports.

These results were validated by Mason's Flow-Graph analysis and by simulation. <FIG> is a schematic diagram of the simulated quadrature circulator. Both the Mason's Flow-Graph analysis and the simulation results show that the cascading the quasi-circulator and quadrature hybrid results in the |S<NUM>-Port_circ-XY| prepresented above. In particular, ideal transmission between Port <NUM> and Port <NUM> was demonstrated (i.e. |S<NUM>-Portcirc-<NUM>| = <NUM> ).

Technologies for implementation of quadrature circulator (<NUM>) include but are not limited to:.

Optionally, the quadrature circulator is designed to operate in frequency bands ranging from <NUM> to <NUM>. Alternately or additionally, the quadrature circulator operates in optical frequencies.

Quadrature circulator <NUM> may be integrated into many types of communication system architectures and may be used for many types of communication techniques. Exemplary embodiments of communication techniques utilizing these architectures are presented below.

Optionally, Port <NUM> of the quadrature circulator is configured to be connected to an antenna.

Optionally, Port <NUM> of the quadrature circulator is configured to be connected to a reflective element. Alternately or additionally, Port <NUM> of the quadrature circulator is configured to be connected to a reflective element.

As used herein the term "reflective element" means a circuit element which reflects the signal transferred from the previous port to the following port. Optionally, the reflective element has an input for transferring an input signal (e.g. a SIC signal) to the port it is connected to.

Examples of reflective elements include but are not limited to:.

Optionally, Port <NUM> of the quadrature circulator is configured to be connected to a circuit element which enables carrier aggregation with full-duplex (FD) communication. Examples of this circuit element include but are limited to:.

Exemplary embodiments are described below with reference to <FIG>.

Reference is now made to <FIG>, which is a schematic diagram of a quasi-circulator with scattering matrix S1. The quasi-circulator has non-ideal transfer between most pairs of ports <NUM>-<NUM>, with reflection at ports <NUM> and <NUM>.

Reference is now made to <FIG>, which is a simplified block diagram of a quasi-circulator according to an exemplary embodiment of the invention. Quasi-circulator <NUM> comprises a first port <NUM>, a second port <NUM>, a third port <NUM>, and a fourth port <NUM>. The port impedances are all Z<NUM>.

A phase shifter is an electronic device that changes the phase of a propagating signal. A reciprocal phase shifter (RPS) introduces the same phase shift into signals propagating in both directions. A non-reciprocal phase shifter (NRPS) introduces different phase shifts into signals propagating in opposite directions.

In addition, the quadrature quasi-circulator device <NUM> further comprises a first <NUM> degree RPS <NUM> between the first port <NUM> and the second port <NUM>; a second <NUM> degree RPS <NUM> between the second port <NUM> and the third port <NUM>; a <NUM> degree NRPS <NUM> between the third port <NUM> and the fourth port <NUM>; and a third <NUM> degree RPS <NUM> between the fourth port <NUM> and the first port <NUM>. According to embodiments of this disclosure, the third port <NUM> and/or the fourth port <NUM> is isolated from the first port <NUM>. In particular, a characteristic impedance of the first RPS <NUM> a first value, and a characteristic impedance of the second RPS <NUM> and the third PRS <NUM> is a second value, wherein the second value equals the first value divided by √<NUM> (square-root of <NUM>). In particular, the first value, i.e., the characteristic impedance of the first RPS <NUM>, is equal to an impedance (i.e., a port impedance) of the first port <NUM>.

It should be noted that, according to some embodiments, a phase of a forward signal path from the first port <NUM> through second port <NUM> to the third port <NUM> is <NUM> degrees, resulting from the -<NUM> degree RPS <NUM> and the -<NUM> degree RPS <NUM>. Similarly, a phase of a forward signal path from the first port <NUM> through fourth port <NUM> to the third port <NUM> is <NUM> degrees, as a result of the <NUM> degree NRPS <NUM> and the -<NUM> degree RPS <NUM>.

It is noted that NRPS <NUM> (between the third port <NUM> and the fourth port <NUM>) is "impedance transparent". Typically, the four ports of quasi-circulator <NUM> (<NUM>-<NUM>) have the same impedance value, for instance, a common value of the impedance is <NUM> ohm. However, other impedance values may also be used.

A quadrature hybrid is a four port device that splits an input signal at one of the ports equally between two output ports with a <NUM> degree phase difference between them. When quadrature signals are input to two of the ports, they combine constructively at one of the ports and combine destructively at the other port. The quadrature hybrid is a symmetric device, in which each port may serve as an input and/or output port. Many implementations of quadrature hybrids are known in the art.

<FIG> is a schematic diagram of an exemplary quadrature hybrid. The quadrature hybrid includes two branches with a characteristic impedance Z<NUM>, and two more branches with a characteristic impedance of Z<NUM>/√<NUM>. Quadrature hybrid <NUM> ideally divides the input power equally between two of the other three ports, wherein the remaining port is fully isolated, in accordance with S2 above.

In some embodiments of the invention, a radio frequency (RF) signal is input into one of the quadrature circulator ports and an RF signal is output from at least one of the quadrature circulator ports as illustrated in <FIG>.

In some of the exemplary embodiments described herein the reflective element is a reflective power amplifier. Other embodiments may use different types of reflective element(s), such as reflective isolator(s).

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for full-duplex (FD) communication according to an exemplary embodiment of the invention. The signal to be transmitted is input to Port <NUM>. The received signal is input to Port <NUM> and the SIC signal is Input to Port <NUM>. Port <NUM> is the RX output.

Port <NUM> of quadrature circulator <NUM> is connected to an antenna. Port <NUM> of quadrature circulator <NUM> is connected to the output of reflective SIC amplifier <NUM> (or alternately an isolator). Port <NUM> is fully reflective and functions as a SIC input that directs its full power to the RX Port <NUM> for TX leakage cancellation. Both Port <NUM> and Port <NUM> are isolated from the TX signal at Port <NUM> (S<NUM> =<NUM>, S<NUM> =<NUM>).

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for half-duplex (HD) communication, according to an exemplary embodiment of the invention. Port <NUM> of quadrature circulator <NUM> is connected to an antenna. Port <NUM> of quadrature circulator <NUM> is connected to the output of reflective SIC amplifier <NUM>. In transmit mode, the TX input at Port <NUM> is transferred completely to the antenna. In RX mode, all the antenna input signal power is reflected at Port <NUM> and directed to Port <NUM>.

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for Frequency Division-Duplex (FDD) communication, according to an exemplary embodiment of the invention. Port <NUM> of quadrature circulator <NUM> is connected to an antenna. Port <NUM> of quadrature circulator <NUM> is connected to the output of reflective SIC amplifier <NUM>. Port <NUM> is fully reflective and functions as a SIC input that directs its full power to the RX Port <NUM> for TX leakage cancellation. In TX mode, Port <NUM> transmits all the TX power to the antenna at frequency f<NUM>. In RX mode, all the power of a signal at frequency f<NUM> input from the antenna is reflected at Port <NUM> and directed to Port <NUM>. A SIC signal to cancel frequency f<NUM> at Port <NUM> is injected from Port <NUM>.

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for MIMO communication, according to an exemplary embodiment of the invention. RFFE <NUM> is suitable for a MIMO architecture operating in half-duplex, simultaneous transmit-receive\FDD and FD modes.

In FDD and FD, no RF coupling between different antennas is required for cancelling mutual TX leakages because all SIC functionality may be lumped into the Port <NUM>. The SIC signal counteracts all the leakages for adjacent MIMO antennas and transmitters.

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for Carrier Aggregation communication, according to an exemplary embodiment of the invention. RFFE <NUM> is suitable for CA architecture. An RF transmit signal TX<NUM> with a carrier frequency of f<NUM> is input to reflective PA<NUM> <NUM>. An RF transmit signal TX<NUM> with a carrier frequency of f<NUM> is input at Port <NUM> of circulator <NUM>. The aggregated signal is output to an antenna at Port <NUM>.

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for Carrier Aggregation communication and concurrent full-duplex operation, according to a first exemplary embodiment. RFFE <NUM> is also suitable for HD and STR\FDD communication modes and for MIMO systems.

In order to support simultaneous transmit-receive for CA FD communications, RFFE <NUM> includes two quadrature circulators, <NUM> and <NUM>. Port <NUM> of quadrature circulator <NUM> is connected to Port <NUM> of quadrature circulator <NUM>.

RF transmit signal TX<NUM> with a carrier frequency of f<NUM> is input via reflective PA<NUM> <NUM> to Port <NUM> of quadrature circulator <NUM>. RF transmit signal TX<NUM> with a carrier frequency of f<NUM> is input to Port <NUM> of quadrature circulator <NUM>. Quadrature circulator <NUM> also inputs an SIC signal at Port <NUM> and outputs an RX signal at Port <NUM>. The aggregated signal is output to an antenna at Port <NUM> of quadrature circulator <NUM>.

RFFE <NUM> has a simultaneous transmit/receive operation for Port <NUM> of quadrature circulator <NUM> and therefore supports CA FD communications.

RFFE <NUM> includes a second reflective power amplifier <NUM> for transferring an SIC signal to Port <NUM>.

Reference is now made to <FIG>, which is a schematic block diagram of an RF front end for Carrier Aggregation communication and concurrent full-duplex operation, according to a second exemplary embodiment of the invention. RFFE <NUM> is also suitable for operating in HD and STR\FDD modes and for MIMO communications.

In order to support simultaneous transmit-receive for CA FD communications, RFFE <NUM> includes QBPA <NUM>.

An RF transmit signal TX<NUM> with a carrier frequency of f<NUM> is input to reflective PA<NUM> <NUM>. QBPA <NUM> provides a combined SIC signal and RF transmit signal TX<NUM> with a carrier frequency of f<NUM> to Port <NUM> of circulator <NUM>. The aggregated signal is output to an antenna at Port <NUM> of quadrature circulator <NUM>.

The RX output of QBPA <NUM> enables a simultaneous transmit/receive operation for Port <NUM> of quadrature circulator <NUM> and therefore supports CA FD communications.

Embodiments of the invention cascade a quasi-circulator and a quadrature hybrid to obtain an ideal quadrature circulator with full transmission and no power loss between consecutive ports. The quadrature circulator has a small form factor and on-chip integration compatibility. The quadrature circulator may be integrated into RF front ends that are suitable for many system architectures and modes of RF communication.

The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Any particular embodiment may include a plurality of "optional" features unless such features conflict.

Throughout this application, various embodiments may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of embodiments.

It is appreciated that certain features of embodiments, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of embodiments, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment.

Claim 1:
A four-port circulator device comprising:
a quasi-circulator (<NUM>) comprising:
a first port (<NUM>), a second port (<NUM>), a third port (<NUM>), and a fourth port (<NUM>), wherein a scattering matrix S1 of said quasi-circulator (<NUM>) is represented as: <MAT>
wherein each entry S<NUM>xy of the scattering matrix S1 represents a portion of a square root of a power of a signal that is directed by the quasi-circulator (<NUM>) from the yth port to the xth port, wherein x and y each can be <NUM>, <NUM>, <NUM>, and <NUM> and x is not equal to y, and each entry S<NUM>xx represents a portion of a square root of a power of a signal that is reflected at the xth port; and
a quadrature hybrid (<NUM>) comprising a first port (<NUM>), a second port (<NUM>), a third port (<NUM>), and a fourth port (<NUM>), wherein a scattering matrix S2 of said quadrature hybrid (<NUM>) is represented as: <MAT>
wherein each entry S<NUM>xy of the scattering matrix S2 represents a portion of a square root of a power of a signal that is directed by the quadrature hybrid (<NUM>) from the yth port to the xth port, wherein x and y each can be <NUM>, <NUM>, <NUM>, and <NUM> and x is not equal to y, and each entry S<NUM>xx represents a portion of a square root of a power of a signal that is reflected at the xth port,
and wherein said fourth port of said quasi-circulator (<NUM>) is connected to said fourth port of said quadrature hybrid (<NUM>) and said third port of said quasi-circulator (<NUM>) is connected to said first port of said quadrature hybrid (<NUM>).