Patent Publication Number: US-2020281051-A1

Title: Six port power measurements

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention, in some embodiments thereof, relates to the field of controlling heating using sensors, and more particularly, but not exclusively, for using RF for the sensing and/or for the heating. 
     European patent application No. 2199753 is titled “Fluid cylinder with a microwave measuring assembly and method for recording at least one parameter”.  FIG. 2  in this patent application describes an evaluation device arranged on a printed circuit board. The evaluation device includes a six-port circuit comprising four power measurement ports. 
     SUMMARY 
     Some examples of embodiments of the invention follows. It should be noted that some embodiments of the invention include features from multiple examples and/or can include fewer than all features described in one example. 
     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 the present disclosure pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting. 
     As will be appreciated by one skilled in the art, aspects of the present disclosure may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system” (e.g., a method may be implemented using “computer circuitry”). Furthermore, some embodiments of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. Implementation of the method and/or system of some embodiments of the present disclosure can involve performing and/or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of some embodiments of the method and/or system of the present disclosure, several selected tasks could be implemented by hardware, by software or by firmware and/or by a combination thereof, e.g., using an operating system. 
     For example, hardware for performing selected tasks according to some embodiments of the present disclosure could be implemented as a chip or a circuit. As software, selected tasks according to some embodiments of the present disclosure could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In some embodiments of the present disclosure, one or more tasks performed in method and/or by system are performed by a data processor (also referred to herein as a “digital processor”, in reference to data processors which operate using groups of digital bits), such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile storage, for example, a magnetic hard-disk and/or removable media, for storing instructions and/or data. Optionally, a network connection is provided as well. A display and/or a user input device such as a keyboard or mouse are optionally provided as well. Any of these implementations are referred to herein more generally as instances of computer circuitry. 
     Any combination of one or more computer readable medium(s) may be utilized for some embodiments of the present disclosure. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, 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), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer readable storage medium may also contain or store information for use by such a program, for example, data structured in the way it is recorded by the computer readable storage medium so that a computer program can access it as, for example, one or more tables, lists, arrays, data trees, and/or another data structure. Herein a computer readable storage medium which records data in a form retrievable as groups of digital bits is also referred to as a digital memory. It should be understood that a computer readable storage medium, in some embodiments, is optionally also used as a computer writable storage medium, in the case of a computer readable storage medium which is not read-only in nature, and/or in a read-only state. 
     Herein, a data processor is said to be “configured” to perform data processing actions insofar as it is coupled to a computer readable memory to receive instructions and/or data therefrom, process them, and/or store processing results in the same or another computer readable storage memory. The processing performed (optionally on the data) is specified by the instructions. The act of processing may be referred to additionally or alternatively by one or more other terms; for example: comparing, estimating, determining, calculating, identifying, associating, storing, analyzing, selecting, and/or transforming. For example, in some embodiments, a digital processor receives instructions and data from a digital memory, processes the data according to the instructions, and/or stores processing results in the digital memory. In some embodiments, “providing” processing results comprises one or more of transmitting, storing and/or presenting processing results. Presenting optionally comprises showing on a display, indicating by sound, printing on a printout, or otherwise giving results in a form accessible to human sensory capabilities. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer readable medium and/or data used thereby may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for some embodiments of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider( 
     Some embodiments of the present disclosure may be described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present disclosure 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 of the present disclosure. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the present disclosure may be practiced. 
       In the drawings: 
       Each of  FIGS. 1, 2A, 2B, and 3  is a diagrammatic illustration of a solid state microwave module according to embodiments of the invention; 
         FIG. 4  is a diagrammatic representation of an apparatus for heating an object in a heating cavity by a heating unit, and comprising a module according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     In the present description, the word “exemplary” is used in the sense of may be serving as an example, instance, or illustration and not necessarily as deserving imitation. 
     The present invention, in some embodiments thereof, relates to the field of controlling heating using sensors, and more particularly, but not exclusively, for using RF for the sensing and/or for the heating. 
     Overview 
     An aspect of some embodiments of the inventions includes a solid state microwave module. The word module is used herein to refer to a functional assembly of electronic components. The module may be designed for use with other modules, of similar or different functionality. A solid state microwave module according to embodiments of the present invention includes one or more printed circuit boards (PCBs), connected to one another through mechanical fixtures with only TEM and/or quasi-TEM connections between components assembled on the one or more PCBs. 
     In some embodiments, a microwave solid state amplifier is assembled to the one or more PCBs, and connected to an antenna interface via a transmission line printed on the one or more PCBs. The transmission line is preferably a TEM and/or quasi-TEM transmission line. The antenna interface may include a connector to an antenna and/or make part of the antenna itself. In operation, signals amplified by the solid state amplifier may be transmitted by the antenna into an energy application zone having in it an object to be heated and/or sensed by those signals. The module also includes four ports printed on the one or more PCBs. The ports are configured to couple to at least one power meter different portions of microwave signals going through the transmission line. Each port is configured to couple to the at least one power meter a respective and different portion of the signal. As used herein, this arrangement may be referred to as a 6 point coupler, having one port coupled to the power amplifier, one port coupled to the antenna interface, and four measurement points, coupled to the one or more power meters. As for the “one or more power meters”, there may be a separate power meter for each measuring port (i.e., four power meters), there may be a single power meter, coupled (e.g., by a switch) at different times to different ones of the measuring ports, or there may be two or three power meters, with two switches. The one or more power meters may be assembled to the one or more PCBs, or may be separated therefrom. In some embodiments, some are assembled and some are not. 
     For example, one port may be configured to couple to the power meter a forward signal F (i.e., a signal going from the amplifier towards the antenna interface). Another port may be configured to couple to the power meter a backward signal B (i.e., a signal going from the antenna back towards the amplifier.) The third and fourth ports, in this example, may each couple to the at least one amplifier a respective linear combination of the forward and backward signals, e.g., a first linear combination of the forward and backwards signals (F+B) and a second linear combination of them (e.g., F+jB, where j is the square root of −1). 
     In another example, the four ports may be configured to couple to the at least one power meter the signals F, F+B, F+(2πj/3)B, and F+(4πj/3)B. This example may be advantageous over the former one in that it does not require coupling into the only one pure signal (the backward signal). On the other hand, the first example may be embodied in a smaller four-port coupler, that is, with smaller distance between the two furthers measurement ports. For example, the latter example may require spacing the two furthest ports λ/3 from each other, while in the former example, λ/8 suffices. Here and elsewhere in the description and the claims, λ stands for a wavelength in vacuum of the forward signal. 
     As used herein, if a machine (e.g., a port) is described as being “configured to” perform a particular task (e.g., configured to couple a signal to a power meter), the machine includes components, parts, or aspects (e.g., software) that enable the machine to perform the particular task. In some embodiments, the machine may perform this task during operation. 
     As used herein, the term measurement port refers to any conductive region printed on the PCB, which is significantly smaller (i.e., at least 10 times smaller) than the working signal wavelength in the PCB, in which the electric field is sufficiently strong to make the required measurement. The size of a conductive region is the longest straight line connecting two points on the edge of the region. 
     A measurement port coupled to a transmission line is a measurement port which is located near a transmission line such that the electrical field emanating from the transmission line is sufficiently strong to make the required measurement at the port. 
     The measurements of the signals coupled through the four measurement ports may enable one to characterize the entire microwave transmission system, e.g., including the antenna, the energy application zone, and the object. For example, the measurements may allow calculating the scattering parameters of the system, the voltages at any point along the transmission line, and the currents at any point along the transmission line. The voltages and currents (or, alternatively, the input power from the amplifier and the scattering parameters) may be used in some embodiments to protect the power amplifier from electrical and thermal over stress. For example, a processor controlling the power amplifier may be configured (e.g., by suitable programming) to ensure, based on the measurements, that critical voltages and/or currents don&#39;t arrive at the amplifier. Knowing the scattering parameters allows, in some embodiments, characterization of the object (e.g., by comparing the scattering parameters measured at a variety of frequencies to those measured in the same system for known objects). Then, heating of the object may be controlled based on the characterization of the object. For example, a first heating protocol may be applied to an object characterized as a frozen pizza, and a second heating protocol (different from the first) may be applied to an object characterized as not yet cooked bread. The heating itself may be by microwaves, generated using the same solid state amplifier, a different microwave source (e.g., a magnetron), or a combination thereof. Additionally or alternatively, the heating may be by means of hot air (e.g., convection), IR radiation, or any other heating means known in the art as such. In case microwaves from a solid state source are used to heat the object, a frequency-by frequency decision may be made to decide if to use any one of the frequencies for heating, and if so, for how long and/or at what power level. Such decisions may be made, for example, based on a desire to allow the same amount of energy to be absorbed by the system in each of the frequencies used. 
     As used herein, the term “processor” may include an electric circuit that performs a logic operation on input or inputs. For example, such a processor may include one or more integrated circuits, microchips, microcontrollers, microprocessors, all or part of a central processing unit (CPU), graphics processing unit (GPU), digital signal processors (DSP), field-programmable gate array (FPGA) or other circuit suitable for executing instructions or performing logic operations. 
     The instructions executed by the processor may, for example, be pre-loaded into the processor or may be stored in a separate memory unit such as a RAM, a ROM, a hard disk, an optical disk, a magnetic medium, a flash memory, other permanent, fixed, or volatile memory, or any other mechanism capable of storing instructions for the processor. The processor(s) may be customized for a particular use, or can be configured for general-purpose use and can perform different functions by executing different software. 
     The term “processor” is used to mean one or more processors. If more than one processor is employed, all may be of similar construction, or they may be of differing constructions electrically connected or disconnected from each other. They may be separate circuits or integrated in a single circuit. When more than one processor is used, they may be configured to operate independently or collaboratively. They may be coupled electrically, magnetically, optically, acoustically, mechanically or by other means permitting them to interact. 
     An aspect of some embodiments of the present invention includes an apparatus for heating an object by a heating unit using a module as described above. In some embodiments, the apparatus further includes a processor, configured to control the heating unit based on measurements received from the four measurement ports. For example, the processor may be configured to process the measurement results using non-iterative processing methods, and send control signals to the heating unit based on the processed results. Alternatively or additionally, the processor may be configured to calculate, based on the input received from the above-described microwave module, the real forward and backward signals, their amplitude, and/or the phase difference between them. The real signals are characterized by amplitude and phase at the entrance to the energy application zone, rather than at any point along the path between the amplifier and the antenna interface, as may be measured by the module. The real phase may be, for example, a phase difference between forward and backward signals and/or relative phase between different signals, in case more than one antenna is used. In embodiments where several antennas are used, each antenna may be connected to a feeding amplifier via a six-port measurement device as described above. Calculating the real values may be important for comparing with previously measured signals, for example, previously measured signals to be used as “finger prints” to the object inside the energy application zone. In another example, the real values of the signals may be used to carry out a pre-determined heating scheme. Providing heating schemes in real values (rather than measured values) may be beneficial, because the differences between measured and real values may change during the operation of the oven, e.g., because of heating of the amplifier, heating of any other component, age of the module, etc. 
     In some embodiments, the processor may be configured to determine the actual power of the forward and backward signal by a method comprising (or being mathematically equivalent to) multiplying a predetermined 2×4 matrix by a measured 4 dimensional vector, each component of which is a result received from a respective one of the measuring ports. The determination of the matrix may be referred to as a calibration of the module. The matrix may be determined (i.e., the module may be calibrated) by measuring the actual forward and reverse waves, when RF power is applied through the module to four different calibration loads (e.g., open, short, and two different loads; or non-reflective load and three fully reflective loads with 0, 120, and 240 degrees phase, or any other four mutually different calibration loads), and solving the appropriate equations. 
     Exemplary Microwave Modules 
       FIG. 1  is a diagrammatic illustration of a solid state microwave module  100  according to some embodiments of the invention. Module  100  includes one printed circuit boards (PCB)  102 , but the invention is not limited to modules that lie on a single PCB, and a module may also include a plurality of PCBs. Module  100  includes a microwave solid state amplifier  104  and an antenna interface  106  assembled to PCB  100 . Amplifier  104  receives an RF signal (via input  104 ′) and a DC signal from a power source (via input  104 ″), and outputs an amplified RF signal to transmission line  108 . In some embodiments, the RF signal source (not shown), whose output is inputted to amplifier  104  via input  104 ′ may be assembled to PCB  102 . In some embodiments, it may be external to the PCB. Similarly, the DC power source (not shown), whose output is inputted to amplifier  104  via input  104 ″ may be assembled to PCB  102  in some embodiments, or external to the PCB in some embodiments. Antenna interface  106  may include a connector configured to connect to an antenna, or the antenna itself, connected directly (e.g., by soldering) to the PCB. Amplifier  104  and antenna interface  106  are interconnected via transmission line  108 . Transmission line  108  may be a TEM or semi-TEM transmission line, or may include TEM parts and semi-TEM parts. Finally, PCB  100  includes four measurement probes ( 110 ,  120 ,  130 ,  140 ) configured to couple respective different portions of microwave signals going through transmission line  108  to at least one power meter (not shown in  FIG. 1 ). To be so configured, the measurements are disposed along transmission line  108  so that a distance between the two furthest ports ( 110  and  140 ) is smaller than a wavelength. In some embodiments, measurement ports  120  and  130  form together a bidirectional coupler. The directivity of the bidirectional coupler is preferably worse than 20 dB, e.g., 15 dB or worse. Each of the measurements ports  110 ,  120 ,  130 , and  140  includes a conductive region printed on the PCB, which is significantly smaller (i.e., at least 10 times smaller) than the quasi-TEM working signal wavelength in the PCB, provided that the electrical field generated by signals running between the amplifier and the antenna interface is sufficiently strong in this region to allow the at least one power meter measurement to measure the power of these signals. While  FIG. 1  is not necessarily to scale, it does show that the distance between the two furthest measurement ports ( 110  and  140 ) is ⅛ of a wavelength of a frequency of a signal running in transmission line  108 . It is noted that module  100  may be configured to work with various frequencies, for example, with an entire ISM bands (e.g., between 2400 MHz and 2500 MHz, and/or between 900 MHz and 928 MHz) or even at broader frequency ranges, for example, when the module is used for working at low powers which do not impose too strict regulatory restrictions. Such a sensing frequency range may be, for example between 0.5 GHz and 10 GHz, e.g., between 1 and 5 GHz. Whenever the module is described herein in relation to “the wavelength”, this is the central wavelength (e.g., 2450 MHz and 915 MHz in the above examples of ISM bands, or 5.25 GHz and 3 GHz in the above examples of sensing frequency bands, respectively). 
     In some embodiments, one or more of the measurement ports include an insulator between transmission line  108  and the at least one power meter. For example, in  FIG. 1 , port  110  may include a gap between transmission line  108  and transmission line  112  going from that gap towards the at least one power meter. This gap is insulating, for example, if it has air in it, or is filled with any other dielectric material. 
       FIG. 2A  is a diagrammatic illustration of a microwave module  200  according to some embodiments of the invention. The module of  FIG. 2A  is similar to that of  FIG. 1 , but includes four power meters:  210 ,  220 ,  230 , and  240 , assembled to the one or more PCBs that make module  200 . The four measurement ports  110 ,  120 ,  130 , and  140 , couple the signals going through transmission line  108  to the four power meters  210 ,  220 ,  230 , and  240 , respectively. 
     The measurement ports may be positioned so as to couple to the at least one power meter four different linear combinations of measured forward and backward signals. As used herein, a forward signal is one that goes in transmission line  108  along a direction going from power amplifier  104  to antenna interface  106 . The term “measured signal” is used to refer to the size of the signal as measured. As the measurement device (e.g., each of the power meters) may be influenced by signals additional to the one that the measurement device is supposed to measure, there may be room to calculate an actual signal, which is the forward signal that actually reached the antenna interface from the amplifier or the backward signal that actually emanated towards the amplifier from the antenna interface. For example, the measured signals coupled to the power meters in  FIG. 2A  are: the forward signal to port  120 ; the backward signal coupled to port  130 , a sum of the forward and backward signal is coupled to port  110 , and a sum of the forward signal and 90 degrees shifted backwards signal, as summarized in Table 1, where F stands for forward; B for backwards, and j for the square root of −1. The parameters α and β are the coefficients in the linear combinations 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Port 
                 Signal 
                 α 
                 β 
               
               
                   
               
             
            
               
                 110 
                 F + B 
                 1 
                 1 
               
               
                 120 
                 F 
                 1 
                 0 
               
               
                 130 
                 B 
                 0 
                 1 
               
               
                 140 
                 F + jB 
                 1 
                 j 
               
               
                   
               
            
           
         
       
     
     It is noted that the signals coupled to the various power meters are not necessarily as detailed in Table 1: the calculation detailed below is valid, for every signal combination at which the M matrix defined below is invertible. 
       FIG. 2B  is a diagrammatic illustration of a microwave module  200 B according to some embodiments of the invention. The module of  FIG. 2B  is similar to that of  FIG. 1 , and includes four measurement ports  110 ,  120 ,  130 , and  140 , spaced away from each other so as to couple to the at least one power meter (not shown) different signals. However, none of the ports in  FIG. 2B  form together a bidirectional coupler. Port  120  is connected to a short conducting strip  125  parallel to transmission line  108 . Strip  125  is terminated by a load  226 . 
     The measurement ports in  FIG. 2B  are positioned so as to couple to the at least one power meter four different linear combinations of measured forward and backward signals. The distances between port  110 ,  130 , and  140  are λ/6, and port  120  is between port  110  and port  130 , for example, at a distance of λ/12 from each of them. The measured signals coupled to the power meters in  FIG. 2B  are: the forward signal to port  120 ; and three different complex summations of the forward and backward signals to ports  110 ,  130 , and  140 . The signals coupled to the measurement ports in  FIG. 2B  are summarized in Table 1, where F stands for forward; B for backwards, and j for the square root of −1. The parameters α and β are the coefficients in the linear combinations 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Port 
                 Signal 
                 α 
                 β 
               
               
                   
                   
               
             
            
               
                   
                 110 
                 F + B 
                 1 
                 1 
               
               
                   
                 120 
                 F 
                 1 
                 0 
               
               
                   
                   
               
               
                   
                 130 
                 
                   
                     
                       
                         F 
                         + 
                         
                           
                             e 
                             
                               j 
                                
                               
                                 
                                   2 
                                    
                                   
                                       
                                   
                                    
                                   π 
                                 
                                 3 
                               
                             
                           
                            
                           B 
                         
                       
                     
                   
                 
                 1 
                 
                   
                     
                       
                         e 
                         
                           j 
                            
                           
                             
                               2 
                                
                               
                                   
                               
                                
                               π 
                             
                             3 
                           
                         
                       
                     
                   
                 
               
               
                   
                   
               
               
                   
                 140 
                 
                   
                     
                       
                         F 
                         + 
                         
                           
                             e 
                             
                               j 
                                
                               
                                 
                                   4 
                                    
                                   
                                       
                                   
                                    
                                   π 
                                 
                                 3 
                               
                             
                           
                            
                           B 
                         
                       
                     
                   
                 
                 1 
                 
                   
                     
                       
                         e 
                         
                           j 
                            
                           
                             
                               4 
                                
                               
                                   
                               
                                
                               π 
                             
                             3 
                           
                         
                       
                     
                   
                 
               
               
                   
                   
               
            
           
         
       
     
     The four different measurements may be useful for solving four linear equations for telling the real powers based on the measured ones. Such a set of four equations is developed, for example, below. 
     The outputs at coupler ports  110  to  140  are each a unique combination of the forward (denoted by F) and backward (denoted by B) waves present at the antenna interface and can be written as V i =α i F+β i B where all the quantities are complex numbers. 
     The values of the four α i  and β i  in the above example are also summarized in Table 1. 
     The resulting powers measured at each power meter are 
         P   i   =|V   i | 2 =∥α i   ∥F|+γ   i   |B |exp[ i (θ( B )−θ( F ))]| 2  
 
     where we have defined the fixed quantity 
       γ i =|β i |exp[ i (θ(β i )−θ(α i ))]
 
     and θ(c) denotes the angle of the complex number c. We now define two fixed real valued quantities 
         u   i =Re(γ i )=|β i |cos(θ(β i )−θ(α i ))
 
         v   i =Im(γ i )=|β i |sin(θ(β i )−θ(α i ))
 
     and two real valued quantities that depend only on the forward and backward waves 
         X =Re(| B |exp[ i (θ( B )−θ( F ))])=| B |cos(θ( B )−θ( F ))
 
         Y =Im(| B |exp[ i (θ( B )−θ( F ))])=| B |sin(θ( B )−θ( F ))
 
     This results in the following expression for the measured powers 
     
       
         
           
             
               
                 
                   
                     P 
                     i 
                   
                   = 
                     
                    
                   
                     
                        
                       
                         
                           
                              
                             
                               α 
                               i 
                             
                              
                           
                            
                           
                              
                             F 
                              
                           
                         
                         + 
                         
                           
                             ( 
                             
                               
                                 u 
                                 i 
                               
                               + 
                               
                                 iv 
                                 i 
                               
                             
                             ) 
                           
                            
                           
                             ( 
                             
                               X 
                               + 
                               iY 
                             
                             ) 
                           
                         
                       
                        
                     
                     2 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                        
                       
                         
                           ( 
                           
                             
                               
                                  
                                 
                                   α 
                                   i 
                                 
                                  
                               
                                
                               
                                  
                                 F 
                                  
                               
                             
                             + 
                             
                               
                                 u 
                                 i 
                               
                                
                               X 
                             
                             - 
                             
                               
                                 v 
                                 i 
                               
                                
                               Y 
                             
                           
                           ) 
                         
                         + 
                         
                           i 
                            
                           
                             ( 
                             
                               
                                 
                                   u 
                                   i 
                                 
                                  
                                 Y 
                               
                               + 
                               
                                 
                                   v 
                                   i 
                                 
                                  
                                 X 
                               
                             
                             ) 
                           
                         
                       
                        
                     
                     2 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         
                            
                           
                             α 
                             i 
                           
                            
                         
                         2 
                       
                        
                       
                         
                            
                           F 
                            
                         
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           
                             u 
                             i 
                             2 
                           
                           + 
                           
                             v 
                             i 
                             2 
                           
                         
                         ) 
                       
                        
                       
                         ( 
                         
                           
                             X 
                             2 
                           
                           + 
                           
                             Y 
                             2 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       2 
                        
                       
                          
                         
                           α 
                           i 
                         
                          
                       
                        
                       
                         u 
                         i 
                       
                        
                       
                          
                         F 
                          
                       
                        
                       X 
                     
                     + 
                     
                       2 
                        
                       
                          
                         
                           α 
                           i 
                         
                          
                       
                        
                       
                         v 
                         i 
                       
                        
                       
                          
                         F 
                          
                       
                        
                       Y 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         
                            
                           
                             α 
                             i 
                           
                            
                         
                         2 
                       
                        
                       
                         
                            
                           F 
                            
                         
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           
                             u 
                             i 
                             2 
                           
                           + 
                           
                             v 
                             i 
                             2 
                           
                           + 
                           
                             v 
                             i 
                             2 
                           
                         
                         ) 
                       
                        
                       
                         
                            
                           B 
                            
                         
                         2 
                       
                     
                     + 
                     
                       2 
                        
                       
                          
                         
                           α 
                           i 
                         
                          
                       
                        
                       
                         u 
                         i 
                       
                        
                       
                          
                         F 
                          
                       
                        
                       X 
                     
                     + 
                     
                       2 
                        
                       
                          
                         
                           α 
                           i 
                         
                          
                       
                        
                       
                         v 
                         i 
                       
                        
                       
                          
                         F 
                          
                       
                        
                       Y 
                     
                   
                 
               
             
           
         
       
     
     By defining the column vector {right arrow over (W)} to be 
     
       
         
           
             
               W 
               → 
             
             = 
             
               [ 
               
                 
                   
                     
                       
                          
                         F 
                          
                       
                       2 
                     
                   
                 
                 
                   
                     
                       
                          
                         B 
                          
                       
                       2 
                     
                   
                 
                 
                   
                     
                       
                          
                         F 
                          
                       
                        
                       X 
                     
                   
                 
                 
                   
                     
                       
                          
                         F 
                          
                       
                        
                       Y 
                     
                   
                 
               
               ] 
             
           
         
       
     
     and a matrix M with line i equal to 
         M   i =[|α i | 2 ( u   i   2   +v   i   2 )2|α i   |u   i 2|α i   |v   i ]
 
     one can obtain all the power readings for a single set of forward and backward waves by the following matrix multiplication 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       P 
                       1 
                     
                   
                 
                 
                   
                     
                       P 
                       2 
                     
                   
                 
                 
                   
                     
                       P 
                       3 
                     
                   
                 
                 
                   
                     
                       P 
                       4 
                     
                   
                 
               
               ] 
             
             = 
             
               
                 P 
                 → 
               
               = 
               
                 
                   M 
                    
                   
                     W 
                     → 
                   
                 
                 = 
                 
                   M 
                    
                   
                     [ 
                     
                       
                         
                           
                             
                                
                               F 
                                
                             
                             2 
                           
                         
                       
                       
                         
                           
                             
                                
                               B 
                                
                             
                             2 
                           
                         
                       
                       
                         
                           
                             
                                
                               F 
                                
                             
                              
                             X 
                           
                         
                       
                       
                         
                           
                             
                                
                               F 
                                
                             
                              
                             Y 
                           
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
     It is noted that M is a matrix that characterizes the module (e.g., module  200 ) and is independent on the signals. This is evident from the matrix M being related only to the parameters α i  and β i  of the six port coupler. When the matrix M can be inverted, the actual forward and backward waves can be obtained by a simple matrix multiplication 
     
       
      
       {right arrow over (W)}=M 
       −1 
       {right arrow over (P)} 
      
     
     which can be written explicitly in order to obtain forward and backward wave powers as 
     
       
         
           
             
               
                  
                 F 
                  
               
               2 
             
             = 
             
               
                 ∑ 
                 
                   k 
                   = 
                   1 
                 
                 4 
               
                
               
                 
                   
                     [ 
                     
                       M 
                       
                         - 
                         1 
                       
                     
                     ] 
                   
                   
                     1 
                     , 
                     k 
                   
                 
                  
                 
                   
                     P 
                     → 
                   
                   k 
                 
               
             
           
         
       
       
         
           
             
               
                  
                 B 
                  
               
               2 
             
             = 
             
               
                 ∑ 
                 
                   k 
                   = 
                   1 
                 
                 4 
               
                
               
                 
                   
                     [ 
                     
                       M 
                       
                         - 
                         1 
                       
                     
                     ] 
                   
                   
                     2 
                     , 
                     k 
                   
                 
                  
                 
                   
                     P 
                     → 
                   
                   k 
                 
               
             
           
         
       
     
     In some embodiments of the invention, the linear combinations (or, equivalently, the values for α i  and β i ) are selected so as to control (e.g., minimize) the overall size of the module. 
     One useful measure of the size of a module is the minimal total length of transmission lines needed in order to build it. A length is “minimal” if it does not include transmission line portions the lengths of which do not affect the functioning of the module. For example, in the modules of  FIGS. 1 and 2 , the size of the module is, under that definition, λ/8, where λ is the wavelength of the signals in the PCB. In some embodiments of the invention, the module is designed to have a size of between about λ/8 and about λ/4. In some embodiments, the module is designed to have a minimal possible size, e.g., by selecting positions to the measurement so as to minimize the size of the module. 
     In some embodiments, the four ports (e.g.,  110 ,  120 ,  130 ,  140 ) are arranged to allow transforming power levels measured by the at least one amplifier to actual power levels by a linear transformation (e.g., embodied in matrix M −1  above) having a condition number between 4 and 5. 
     The solid state microwave module described herein may be included in a microwave oven, for example, for heating objects in the oven&#39;s cavity. In such embodiments, the solid state amplifier is configured to output microwaves having power of at least 100 W, for example, 100 W, 150 W, 200 W, 500 W, 1000 W, 2000 W, or any other power in between 100 W and 2000 W. 
     In some embodiments, the solid state microwave module described herein may be used for sensing, for example, for sensing objects to be heated in a cavity. The heating itself may be carried out by microwave, convection, IR radiation, or any other heating method known in the art. Sensing may be achieved with much lower power levels than those required for heating. Accordingly, in some embodiments (e.g., where the module is used for sensing), the solid state amplifier is configured to output microwaves having power of between 0.1 mW and 100 mW. Some possible powers include 0.1 mW, 0.5 mW, 1 mW, 2 mW, 10 mW, 50 mW, 100 mW, or any other power in between. 
       FIG. 3  is a diagrammatic illustration of a microwave module comprising one or more PCBs  302  according to some embodiments of the invention. While in  FIG. 2A , each port connects transmission line  108  to a corresponding voltmeter, in  FIG. 3 , two ports ( 120  and  130 ) are connected to a single voltmeter  250  via switch  260 , that has at least one state at which one of the ports is connected to the voltmeter and the other is disconnected from the voltmeter, and at least one state at which the other port is connected to the voltmeter, and the one of the ports is disconnected from the voltmeter. The two other ports ( 110  and  140 ) are connected each to a different (dedicated) voltmeter ( 210  and  240 ). In some embodiments, all the voltmeters are connected to the same ground. 
     Exemplary Heating Apparatus 
       FIG. 4  is a diagrammatic representation of apparatus  400  for heating an object  402  in a heating cavity  401  by a heating unit  406 . Apparatus  400  includes a solid state microwave module  500 , processor  404 , configured (e.g., by proper programming) to receive measurement results from module  500  and send control signals to heating unit  406  based on the received inputs. In some embodiments, cavity  401  is a resonator, that resonates in one or more frequencies of microwaves supplied via module  500 . The control signals sent to heating unit  406  based on the received inputs may include for example, at what power to heat, for how long, at what frequency (e.g., if heating unit  406  is a variable frequency microwave heater), etc. The processor may be configured to change the control signals based on changes in the measurements received from module  500 . In some embodiments, the measurements received from module  500  may be frequency dependent, and the measurements in the different frequencies may form a pattern (e.g., a pattern of scattering parameters vs. frequency). In some embodiments, such patterns are identified in advance to be indicative to the object being heated and/or to a property of the object. A pattern recognition module in the processor may then recognize the pattern of the received measurements to match a pattern indicative of a certain object and/or property thereof, and send the control signals accordingly. In some embodiments, the processor may receive (e.g., via a user interface) information regarding the object (e.g., that it is a frozen pizza), and use the measurements to tell a property of the object (e.g., that the frozen pizza is at a certain temperature, for example, −20° C., −4° C., etc.). In some embodiments, module  500  provides microwave output at low power (e.g., between 0.0001 W and 0.01 W), and used only for sensing, in the sense of transmitting these low power microwave signals into cavity  101 , receiving feedback from the cavity in the form of signals returning from the cavity to the module, and providing data indicative of said transmitting and receiving to the processor. The processor may process such data to identify, e.g., kind and/or property of the object in the cavity. 
     Module  500  may include a solid state microwave power amplifier (e.g.,  104 ) assembled to one or more PCBs. In some embodiments, the solid state power amplifier is configured to be fed with RF signals having a variety of different frequencies, and amplify them. A six port coupler may be printed on the one or more PCBs, and this six port coupler may include one port connected to the power amplifier via a TEM or quasi-TEM transition line. In some embodiments, another one of the six ports of the coupler is connected to an antenna interface ( 106 ), e.g., via a TEM or quasi-TEM transmission line. The six port coupler may also include four measurement ports, each connected to a power meter, and the processor receives these measurements as inputs. In some embodiments, module  500  is the same as described above, for example, the same as module  100 ,  200 , or  300 . In some embodiments, the output of module  500  may be used for heating object  402 . In some such embodiments, heating unit  406  is the same as module  500 . In some embodiments, module  500  is used for heating, and heating unit  406  is an additional heating unit. 
     In some embodiments, processor  404  is configured to process the measurement results using a non-iterative processing method to obtain processed results, and send the control signals based on the processed results. The non-iterative processing method may include, determining, based on the received measurement results, an actual power of the forward signal and an actual power of the backward signal by multiplying a predetermined 4×4 matrix by a measured 4 dimensional vector, each component of which is a result received from a respective one of the four ports. 
     The predetermined matrix may characterize the six port coupler, for example, as the above-mentioned matrix M (or M −1 ) does. An example of the measured four dimensional vector may be the above-mentioned results vector {right arrow over (P)} and matrix M −1 . In some embodiments, other mathematical methods, mathematically equivalent to such a multiplication of a result vector by a predetermined matrix may be similarly used. 
     In some embodiments, the processor may be configured to determine a property of the object being heated in the oven based on the received measurement results. For example, the frequency dependence of the return loss of the heating chamber with the object therein may be indicative to a property of the object, if, for example, the object itself is known, e.g., based on input received from a user. The return loss may be the real return loss, that is, the ratio between real forward and real backward signals. In some embodiments, more than one module  500  is provided (e.g., two such modules), and coupling between them may be used for evaluating, for example S parameters (e.g., a ratio between a real forward signal going out of an antenna of one module, and a real backward signal going into an antenna of another module at the same time and frequency, and when no module other than the first is outputting signals at that frequency). 
     In some embodiments, heating unit  406  heats object  402  by microwaves, e.g., microwaves generated by a magnetron and/or by microwaves amplified by a solid state amplifier, e.g., the solid state amplifier of module  500 . In some embodiments, in addition to or instead of heating by microwave, heating unit  406  heats object  402  by means other than microwave, e.g., blowing hot air into the cavity, radiating infrared radiation, etc. 
     General 
     As used herein with reference to quantity or value, the term “about” means “within ±10% of.” 
     The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean: “including but not limited to.” 
     As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. 
     The word “optionally” is used herein to mean “is provided in some embodiments and not provided in other embodiments”. Any particular embodiment of the present disclosure may include a plurality of “optional” features except insofar as such features conflict. 
     Throughout this application, embodiments may be presented with reference to 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 descriptions of the present disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as “from 1 to 6” should be considered to have specifically disclosed subranges such as “from 1 to 3”, “from 1 to 4”, “from 1 to 5”, “from 2 to 4”, “from 2 to 6”, “from 3 to 6”, etc.; as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. 
     Whenever a numerical range is indicated herein (for example “10-15”, “10 to 15”, or any pair of numbers linked by these another such range indication), it is meant to include any number (fractional or integral) within the indicated range limits, including the range limits, unless the context clearly dictates otherwise. The phrases “range/ranging/ranges between” a first indicate number and a second indicate number and “range/ranging/ranges from” a first indicate number “to”, “up to”, “until” or “through” (or another such range-indicating term) a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numbers therebetween. 
     Although descriptions of the present disclosure are provided in conjunction with specific embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 
     All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present disclosure. To the extent that section headings are used, they should not be construed as necessarily limiting. 
     It is appreciated that certain features which are, for clarity, described in the present disclosure in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features, 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 of the present disclosure. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.