CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119(e) to the subject matter of U.S. Provisional Patent Application Ser. No. 61/905,059 entitled “MICROWAVE OVEN USING SOLID STATE AMPLIFIERS AND ANTENNA ARRAY,” filed on Nov. 15, 2013, which is hereby incorporated herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a microwave oven, and more particularly, to a system and method for implementing beamforming techniques using solid state amplifiers and an array of antennas for heating materials in a microwave oven. 
       BACKGROUND 
       [0003]    A microwave oven (also referred to as a “microwave”) is a kitchen appliance that heats food using electromagnetic radiation in the microwave spectrum. Microwave ovens heat food quickly. Microwave ovens typically use magnetron technology to create microwave energy in a confined space, which causes a rapid rise in temperature of food placed in the confined space. Microwave ovens that use magnetron technology consume large amounts of power. 
         [0004]    Microwave ovens typically include a tube, such as a vacuum tube, and certain microwave ovens include only one vacuum tube. The use of the vacuum tube requires the food to be rotated to be cooked. This rotation is required for the material (i.e., food) to receive relatively uniform energy over the period of heating. To this end, microwave ovens include a mechanical motor to rotate the material to be heated or cooked. However, mechanical motors wear and are a source of frequent failures. 
         [0005]    The peak power draw of a magnetron of a microwave is typically about 1.0 kilowatts. An example microwave configuration may include a power supply unit (PSU) of 4 kilovolts (kV) and 300 milliamperes (mA). 
         [0006]    Microwave ovens also generally include a relatively large transformer, which increases the weight of the oven. A heavy microwave oven may be more difficult to mount to a wall than a lighter weight microwave, as it is harder to lift and stronger materials may be required to securely mount the oven above a cooking range, for example. The weight of a heavy microwave oven, compared to a lighter weight microwave, may also result in an increase in shipping or transportation costs. 
       SUMMARY 
       [0007]    A microwave oven may include a housing defining an oven cavity therein configured to receive material to be heated, and a plurality of solid state microwave generating cells carried by the housing. Each cell may include a microwave transmitting antenna to transmit electromagnetic (EM) energy in the microwave spectrum into the oven cavity at the material to be heated, and a respective phase shifter configured to alter a pattern of the EM energy transmitted by the antenna. At least one feedback circuit may be carried by the housing and configured to detect EM radiation within the oven cavity not absorbed by the material to be heated. A processor may be carried by the housing and coupled to the plurality of microwave beamforming cells and to the at least one feedback circuit. The processor may be configured to receive feedback from the at least one feedback circuit based upon the EM radiation not absorbed by the material to be heated, and control the phase shifters of the plurality of beamforming cells to change the patterns of EM energy transmitted by the antennas based upon the feedback received from the at least one feedback circuit. 
         [0008]    More particularly, the processor may be configured to control the phase shifters of the plurality of beamforming cells to reduce a power level associated with the EM energy not absorbed by the material to be heated. Furthermore, each beamforming cell may further include a solid state amplifier having an output coupled to the phase shifter. In accordance with another example embodiment, each beamforming cell may further include a solid state amplifier coupled between the phase shifter and the antenna. 
         [0009]    The housing may define the oven cavity with a plurality of sidewalls, and the plurality of beamforming cells may include a respective array of beamforming cells carried on a plurality of different sidewalls. Additionally, the at least one feedback circuit may include a respective feedback circuit for each of the arrays of beamforming cells. 
         [0010]    In an example embodiment, the microwave oven may further include a digital camera coupled to the processor for capturing digital images of the material within the oven cavity, and a communication interface coupled to the processor to communicate the captured digital images to a user display device. By way of example, the at least one feedback circuit may include a microwave receiving antenna carried by the housing, a buffer amplifier having an input coupled to the microwave receiving antenna and an output, and a power detector having an input coupled to the output of the buffer amplifier and an output coupled to the processor. 
         [0011]    The microwave oven may also include a local oscillator carried by the housing and having an output, and a buffer amplifier carried by the housing and having an input coupled to the local oscillator and an output. Furthermore, a power divider may be included having an input coupled to the output of the buffer amplifier and a plurality of outputs each coupled to a respective beamforming cell. 
         [0012]    A method for operating a microwave oven, such as the one described briefly above, is also provided. The method may include detecting EM radiation within the oven cavity not absorbed by the material to be heated using at least one feedback circuit carried by the housing, and controlling the phase shifters of the plurality of beamforming cells to change the patterns of EM energy transmitted by the antennas based upon the EM radiation detected from the at least one feedback circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram of a conventional microwave oven. 
           [0014]      FIGS. 2A  is a perspective diagram, and  FIG. 2B  is a corresponding block diagram, of a microwave oven according to an example embodiment. 
           [0015]      FIG. 3A  is a schematic circuit diagram of a beamforming circuit of the microwave of  FIGS. 2A and 2B  in accordance with an example embodiment. 
           [0016]      FIG. 3B  is a schematic circuit diagram illustrating an example solid state microwave generating cell of the beamforming circuit of  FIG. 3A . 
           [0017]      FIG. 4  is a schematic circuit diagram illustrating an example solid state microwave generating cell array for the beamforming circuit of  FIG. 3A . 
           [0018]      FIG. 5  is a schematic diagram of an example one-side cell array for a beamforming configuration in accordance with an example embodiment. 
           [0019]      FIGS. 6 through 8  are beamforming diagrams illustrating various beamforming configurations in accordance with example embodiments. 
           [0020]      FIG. 9  is a schematic block diagram of a system for monitoring and controlling a microwave in accordance with an example embodiment. 
           [0021]      FIG. 10  is a flow diagram illustrating a beamforming method for a microwave oven according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation and multiple prime notation are used to indicate similarly elements in different embodiments. 
         [0023]    Referring initially to  FIG. 1 , by way of background, a typical microwave oven  100  is first described. During operation, the microwave oven  100  heats material enclosed therein. The microwave oven  100  illustratively includes an oven cavity  110 , a rotary plate  120  that causes rotation of food  105  placed atop the rotary plate, and a magnetron  130  that generates electromagnetic waves in the microwave spectrum (also referred to as “microwaves”). A power supply unit (PSU) illustratively includes a transformer  140  that provides electricity to the electrical components of the microwave oven  100 , and a mechanical motor  150  rotates the rotary plate  120 . By way of example, the microwave oven  100  may consume 1.6 kilowatts (kW) of total power during operation, and the transformer  150  of the PSU  140  may output 4 kV at 300 mA, but other power ratings/levels may be used in different implementations, as will be appreciated by those skilled in the art. 
         [0024]    The microwave  100  in the example embodiment includes only a single magnetron  130 , which includes a relatively high-power vacuum tube. The microwaves emitted from the magnetron  130  are spread throughout the oven cavity  110 . A portion of the microwaves are absorbed by the food  105 , causing the food to heat up. The remainder of the microwaves are incident upon the walls and other surfaces of the oven cavity  110 , which reflect the microwaves. The reflection of this energy causes losses. Some of the microwaves are reflected several times before reaching the food  105  to be warmed. The magnetron  130  consumes much of the total power that the microwave consumes. Also, the efficiency of the magnetron  130  is typically in a range of 60-70%. During operation, the magnetron consumes a peak power of about 1.0 kW of the 1.6 kW of total power that the microwave oven consumes. 
         [0025]      FIGS. 2A and 2B  illustrate a microwave oven according to an example embodiment. The microwave oven  200  is configured to cook food and to heat materials placed in the oven cavity  210 . In certain embodiments, the microwave oven  200  is configured to cook multiple types of food simultaneously, although this is not required in all embodiments. Although certain details will be provided with reference to the components of the microwave oven  200 , other embodiments may include more, less, or different components, as will be appreciated by those skilled in the art. 
         [0026]    The microwave oven  200  illustratively includes a user control panel  202  for receiving user selections. A user may press buttons of the user control panel to instruct the microwave  200  to perform desired functions. For example, a user may press a door opening button  202  that causes the door  204  of the microwave to open, as well as control buttons  206  to control cooking operations (time, power levels, etc.) as well as other operations (e.g., clock, timer, etc.). 
         [0027]    The door  204  opens to allow the user to place food into the metal oven cavity  210  to be heated. The microwave  200  may be configured not to operate while the door  204  is open to avoid microwave exposure to the user. That is, the user may be required to close the door  204  (as seen in  FIG. 2A ) before the microwave  200  will heat the food  205   a,    205   b  inside. 
         [0028]    In certain embodiments, the microwave door  204  includes a metal safety net or mesh  206  disposed across some or all of the door  204 . The safety net  206  catches microwaves incident upon the door that were not absorbed by the food, thereby helping to prevent those microwaves from traveling through the door  202  or otherwise escaping the oven cavity. For example, in certain embodiments, the door  204  may include a clear window fully covered by the safety net  206 , allowing the user to look into the oven cavity while the microwave  200  warms the food. 
         [0029]    As seen in  FIG. 2B , the microwave  200  is configured for heating of multiple types of food  205   a,    205   b  at the same time. The microwave oven  200  may heat foods that require high power at the same time and in the same oven cavity  210  as foods that require low power. For example, chicken and a cup of soup may require the same amount of time to cook. To cook the chicken may require higher power during that amount of time than the lower power required to cook the soup in the same time period. This may be accomplished using the beamforming techniques described below to change the shape and/or intensity of the microwave energy directed at the given food items  205   a,    205   b.    
         [0030]    The oven cavity  210  may be a rectangular prism shape, having a top sidewall, a left sidewall, a right sidewall, a back sidewall, and a bottom  220 . For proper use, the user places food on the oven cavity surface of the bottom  220 , and not in contact with any sidewalls. In the present disclosure, the sidewalls are referred to as foodless. 
         [0031]    The microwave oven  200  includes beamforming circuitry  300  that causes high powered microwaves to be incident upon the food  205   a  that requires high power for cooking (e.g., chicken). At the same time, the circuitry  300  causes low powered microwaves to be incident upon the food  205   b  that requires low power for cooking (e.g., water in a kettle). In certain embodiments, the circuitry  300  receives input from a user making selections using the user control panel  206 . The input can indicate a level of power to be supplied to food disposed a specified area of the microwave. For example, the user may specify that food  205   a  placed on a rack  215  (located in a upper level area) in the oven cavity  210  requires high power, while the food  205   b  placed on a bottom  220  of the oven cavity  210  requires low power, or vice-versa. In another example, the food  205   a  placed on the left side of the oven cavity  210  requires high power, and that food  205   b  placed on the right side of the oven cavity  210  requires low power, or vice-versa. The user may specify the level of power by a number of watts, a power level (e.g., 1-10), etc. That is, the oven cavity  210  may be divided into a plurality of different zones or sections in which different levels of microwave intensity is applied to food items therein. 
         [0032]    Referring additionally to  FIG. 3A , a top level block diagram of a beamforming circuitry  300  which may be used for the microwave  200  to provide the above-noted zones of different microwave intensity is now described. The beamforming circuitry  300  controls internal components of the microwave oven  200 . Although certain details will be provided with reference to the components of the beamforming circuitry  300 , it should be understood that other embodiments may include more, less, or different components. 
         [0033]    The beamforming circuitry  300  illustratively includes a local oscillator  305  coupled to array controlling circuitry  365 . The array controlling circuitry illustratively includes a buffer  310  coupled to the local oscillator  305 , a power splitter  315  (also referred to as a power divider or radio frequency (RF) coupler) coupled to the output of the buffer, and an array of cells  320   a,    320   b  coupled to respective outputs of the power slitter. Each cell  320   a,    320   b  illustratively includes an amplifier  325   a,    325   b  coupled to a respective output of the power divider  315 , a phase shifter circuit block  330   a,    330   b  coupled to the output of the respective amplifier, and a patch antenna  335   a,    335   b  coupled to the respective phase shifter circuit block. 
         [0034]    The beamforming circuitry  300  further illustratively includes a feedback circuit  360 , and a processing circuit block  355  coupled to the feedback circuit and the array controlling circuit  365 . The feedback circuit  360  illustratively includes a sensing antenna  340 , a buffer  345  having an input coupled to the sensing antenna, and a power detector  350  coupled to the output of the buffer. The array controlling circuit  365  illustratively includes a single buffer  310 , a single power splitter  315 , and the two cells  320   a  and/or  320   b,  although different numbers of these components may be used in different embodiments. For example, the present disclosure is not limited to a cell array where N equals two, rather any suitable number N of cells may be used, as indicated by the “N(t)” in the Nth phase shifter circuit block  330   b.    
         [0035]    The local oscillator  305  is coupled to the buffer  310 , which is a low power amplifier that buffers signals sent to the power splitter  315 . That is, the buffer  310  (e.g., a low power amplifier) distributes power to the power splitter  315 . The power splitter  315  sends a signal to each cell  320   a,    320   b  in the array. More particularly, the power splitter  315  sends a first signal  370   a  to the first cell  320   a  and sends a second signal  370   b  to the second cell  320   b.  The first and second signals  370   a ,  370   b  include an amount of power and a phase. 
         [0036]    In each respective cell  320   a,    320   b,  the amplifier  325   a,    325   b  receives the signal  370   a,    370   b.  Each amplifier  325   a ,  325   b  amplifies the received signal  370   a,    370   b  and outputs the amplified signal to the respective phase shifter circuit block  330   a,    330   b.  That is, the first amplifier  325   a  amplifies the first signal  370   a,  and the second amplifier  325   b  amplifies the second signal  370   b.  In response to receiving the amplified first signal, the first phase shifter circuit block  330   a  selectively adjusts the phase of the amplified signal and outputs an amplified, phase shifted signal to the first antenna  335   a.  In response to receiving the amplified second signal, the second phase shifter circuit block  330   b  selectively adjusts the phase of the amplified signal and outputs an amplified, phase shifted signal to the second antenna  335   b.  The patch antennas  335   a  and  335   b  are transmitter antennas that transmit electromagnetic waves into the oven cavity  210 . 
         [0037]    Another example cell embodiment is shown in  FIG. 3B , in which the amplifier  325 ′ is coupled between the phase shifter circuit block  330 ′ and the patch antenna  335 ′. For example, in the cell  320 ′, the phase shifter circuit block  330 ′ is directly coupled the amplifier  325 ′, and the amplifier  325 ′ is directly coupled to the patch antenna  335 ′. That is, phase shifter circuit block  330 ′ is indirectly coupled to the patch antenna  335 ′ through the amplifier  325 ′ (as an intermediary). In each respective cell  320 ′, the phase shifter circuit block  330 ′ receives the signal  370 ′ from the power splitter  315 ′. In response to receiving the signal  370 ′, the phase shifter circuit block  330 ′ selectively adjusts the phase of the signal  370 ′ and outputs a phase shifted signal to the power amplifier  325 ′. The power amplifier  325 ′ amplifies the received phase shifted signal and outputs an amplified, phase shifted signal to the patch antenna  335 ′. The patch antenna  335 ′ is a transmitter antenna that transmits electromagnetic waves into the oven cavity  210 ′. 
         [0038]    The cell  320 ′ shown in  FIG. 3B  may potentially be less costly than the cell  320   a  shown in  FIG. 3A . When the amplifier  325 ′ is coupled between the phase shifter circuit block  330  and the patch antenna  335 ′, the signal  370 ′ received by the phase shifter circuit block  330 ′ has a lower power level compared to the amplified signal received by the phase shifter circuit block  330   a  output from the amplifier  325   a.  That is, a phase shifter circuit block  330   a  which is configured to phase shift high powered signals may cost more than a power phase shifter circuit block  330  configured to phase shift relatively lower powered signals. 
         [0039]    The microcontroller  355  controls the amplified, phase-shifted signals sent to each antenna  335   a - 335   b.  The microcontroller  355  sends a signal  375   a - 375   b  to each phase shifter control block  330   a - 330   b.  In response to receiving the control signal  375   a,    375   b,  the phase shift circuit block  330   a ,  325   b  determines an amount by which to adjust the amplified signal. In response to receiving the control signal  375 , the phase shift circuit block  330  determines an amount by which to adjust the amplified signal. 
         [0040]    The microcontroller  355  monitors the microwave energy within the oven cavity  210  based upon feedback signals  380  received from the feedback circuit  360 . The sensing antenna  340  is a receiving antenna that receives the microwave energy that reflects in the oven cavity  210 , or that is not incident upon the food  205   a - 205   b.  In response to receiving microwave energy, the sensing antenna  340  sends a signal to the power detector  350  through the buffer  345 . The power detector sends feedback signals  380  to the microcontroller  355  indicating the amount of power received by the sensing antenna  340 . The feedback signal may also include information such as the location of the sensing antenna. 
         [0041]    As noted above, the microcontroller  355  outputs a control signal  375   a  to the phase shifter circuit block  330   a  and outputs a control signal  375   b  to the phase shifter circuit block  330   b.  The control signal  375   a  may be different from the control signal  375 . To instruct the phase shifter control circuit block  330   a,    330   b  of a specific phase angle to select, the microcontroller  355  performs calculations “on the fly” using the feedback signal  380 . For example, in response to receiving the feedback signals  380  indicating that microwave energy is being sensed from sensing antennas  340  of different sidewalls, the microcontroller  355  sends control signals  375   a - 375   b  to control the relative phase delay of the array of cells to narrow the beamform of microwave energy transmitted from the transmit patch antennas  335   a - 335   b  toward small dimensioned food, for example. Alternatively, the microcontroller  355  may send control signals  375   a - 375   b  to further spread the beam of microwave energy transmitted from the transmit patch antennas  335   a - 335   b  toward wide dimensioned food, for example. 
         [0042]    In certain embodiments, the feedback circuit  360  may include at least one sensing antenna  340  per sidewall of the microwave. More particularly, the microwave oven  200  may include at least one sensing antenna  340  per sidewall that also includes a cell array of transmit patch antennas  320   a,    320   b.  That is, the microwave oven  200  may be configured for a cell array of transmit patch antennas  320   a,    320   b  to be on each sidewall. In certain embodiments, the door  204  may be considered a sidewall that may include a cell array of transmit patch antennas  320 ,  320   a,    320   b.  The safety net  206  on the door  204  may optionally be omitted in embodiments when the door  204  includes a cell array of transmit patch antennas. That is, certain embodiments of the microwave oven  200  need not include a safety net  206 . 
         [0043]    Referring now to  FIG. 4 , another example cell array  400 ″ for the microwave oven  200  is now described. The cell array  400 ″ creates a beamform by changing the phases of each one of the output signals from the patch antennas  320 ″. The beamform points to food  205   a - 205   b  that needs to be cooked. The cell array  400 ″ illustratively includes a number N of low power cells  320 ″. The number N may be an integer value of at least one. It should be understood that other embodiments may include more, less, or different components. 
         [0044]    The microwave oven  200  may include a cell array  400 ″ per sidewall. Using several low power amplifiers in the beamforming circuit may result in lower costs compared to a beamforming circuit that includes a single high power amplifier. Moreover, the required transmitted power of the microwave oven  200  is lower than a microwave  100  using a magnetron  130 . 
         [0045]    A one-side cell array  500  according to an example embodiment is shown in  FIG. 5 . The one-side cell array  500  illustratively includes sixteen cells. In the present example, each square represents a transmit patch antenna  335 ′ of a cell. The microwave oven  200  may include a plurality of one-side arrays  500 , each for a respective sidewall. A combination of the sixteen cells in the array  500  will provide the beamform from one sidewall. The combination of multiple cells  320  in an array  500  allows each cell  320  to transmit less power. For example, if each cell  320  can produce  20  watts of power, then in combination, the 16 cells of the one-side array  500  produce a beamform of 320 watts of power (20 W×16=320 Watts). 
         [0046]    The one-side antenna may have a flat shape, for example. The arrangement of the antenna array may vary in terms of the number of patch antennas  335 ′ in the array  500 , as well as the distance between antennas in the array, as will be appreciated by those skilled in the art. 
         [0047]      FIGS. 6-8  illustrate example embodiments of beam-forming using the above-described configurations. The examples of  FIGS. 6-8  show that the beamform may be adjusted to be more directional by increasing the number of antennas in the array of cells. These examples also show that adjusting the phase at the output of the amplifier causes the beam direction to adaptively change directions. The graphs shown in  FIGS. 6-8  were obtained by running a MATLAB script obtained at
   http://staff.washington.edu/aganse/src/index.html. The spacing between elements and phase delay are in radians.   
 
         [0049]    More particularly, the example waveform  600  of  FIG. 6  was formed using five transmit patch antennas (such as patch antenna  335 ′, and also referred to as elements) spaced 10 units of length apart (e.g., millimeters or centimeters). The relative phase delay is controlled at −7 radians. The beamform  600  includes microwave signals concentrated along two paths  610  and  620 . The direction of the paths  610  and  620  are angled apart by the angle  630 , which is an acute angle. The paths  610  and  620  are also angled apart by a second angle  640 , which is a reflex angle. 
         [0050]    The example waveform  700  of  FIG. 7  was formed using five transmit patch antennas (such as patch antenna  335 ′) spaced 10 units of length apart (e.g., millimeters or centimeters). The relative phase delay is controlled at −2 radians. The beamform  700  includes microwave signals concentrated along two paths  710  and  720 . The direction of the paths  710  and  720  are angled apart by the angle  730 , which is an obtuse angle. The paths  710  and  720  are also angled apart by a second angle  740 , which is an obtuse angle. 
         [0051]    In the above-noted example, the microwave oven  200  has a fixed number of transmit patch antennas  335  that are spaced a fixed distance apart. Comparing the beamform  600  to beamform  700  reveals that decreasing the relative phase delay from −2 radians to −7 radians reduces the angle between of the paths of the beamform. Furthermore, increasing the relative phase delay from −7 to −2 radians increases the angle between the paths of the beamform. That is, the angle  730  is greater than the angle  630  as a result of the adjustment of relative phase delay from −2 radians to −7 radians. The beamform  600  may accordingly be applied to cook a wide dimensioned food in the oven cavity  210 , for example. The beamform  700  may be applied to cook multiple foods spaced apart from each other in the oven cavity  210 , for example. 
         [0052]    The waveform  800  of  FIG. 8  was formed using three transmit patch antennas (such as the patch antenna  335 ′) spaced 10 units of length apart. The relative phase delay is controlled at −7 radians. The beamform  800  includes microwave signals concentrated along two paths  810  and  820 . The direction of the paths  810  and  820  are angled apart by the angle  830 , which is an acute angle. The paths  810  and  820  are also angled apart by a second angle  840 , which is an acute angle. 
         [0053]    From  FIGS. 6 and 8  it may be seen that in comparing the beamform  600  to beamform  800 , increasing the number of transmit patch antennas from 3 to 5 increases the directionality of the paths of the beamform. Increasing the number of transmit patch antennas from 3 to 5 also causes the paths of the beamform to be narrower and more pointed toward the food to be warmed. 
         [0054]    Referring additionally to  FIG. 9 , a system  900  for monitoring and controlling the microwave  200  according to an example embodiment is now described. The system  900  allows a user to view images captured by a camera  905  in the microwave  200  on a device such as a user mobile device  950  (e.g., mobile phone or tablet computer), and/or a display  960  (for example, a television screen). One or more of the cameras  905  may be disposed within the oven cavity  210  to allow a user to visually monitor the food  205  while it is being cooked in the microwave oven  200 . The camera  905  may be a video camera that captures real time images of the food  205 , for example. 
         [0055]    The system  900  further illustratively includes a communication interface  910  that allows the microwave oven  200  to communicate with a user mobile device  950  (e.g., mobile smartphone, tablet, laptop computer, desktop computer, etc.). A user may control the functions of the microwave  200  using the mobile user device  950  which executes computer readable code configured to generate and send control signals to the microwave oven  200 . Communication may be by wireless data transfer, local area network Internet communication, or through an access port provided in the microwave oven  200 , such as Universal Serial Bus (USB) port, for example. Communication with the user mobile devices  950  external to the microwave oven  200  allows the user to start or halt operation of the cooking function of the microwave oven  200  without standing near the microwave oven  200 . The user may accordingly reduce exposure to microwave energy that may escape the microwave oven  200  by using the monitoring and control system  900  to determine whether the food is thoroughly cooked by viewing real-time images of the food  205  being cooked. 
         [0056]    Turning now to  FIG. 10 , a beamforming method  1000  for operating the microwave oven  200  in accordance with an example embodiment is now described. The beamforming circuitry  300 , and more particularly the processor  355 , may be implemented with appropriate hardware (e.g., microprocessor, etc.) and a non-transitory computer-readable medium having computer-executable instructions to perform the beamforming operations described herein. At Block  1010 , the material  205  to be heated in the oven cavity  210  is inserted into or received in the microwave  200 . At Block  1020 , an antenna array of N transmit antenna cells transmits electromagnetic (EM) waves in the microwave spectrum within the oven cavity  210 . At block  1030 , the microprocessor  355  creates one or more beamforms using the EM waves. At the same time, at block  1050 , the microprocessor  355  sends control signals  375   a,    375   b  to direct the path of each beamform toward the material by adjusting a relative phase delay of the antenna array, as discussed further above. 
         [0057]    Furthermore, the sensing receiver antenna  340  of the feedback circuit(s)  360  receives a portion of the EM waves not absorbed by the material, at Block  1040 . The microprocessor  355  receives feedback signals from the feedback circuit  360  indicating an amount of power sensed by the at least one sensing receiver antenna and a location of the at least one sensing receiver antenna, at Block  1060 . At Block  1070 , in response to receiving the feedback signals, the microprocessor  355  selectively adjust the relative phase delay to reduce at least one of a number EM waves received by the feedback circuit, and a power of the portion of the EM waves not absorbed by the material. The microwave  200  may repeat the functions described above with reference to Blocks  1020 - 1070  until the microprocessor  355  executes a command to stop operating the cooking function of the microwave oven  200 . 
         [0058]    Various features and advantages may be provided by the above described system and techniques. Such technical advantages may include: 1) reduction of energy consumption; 2) increases of mean time between failures (MTBF) of a microwave oven; 3) decreases the vibration failure rate present in microwave ovens; 4) elimination of a mechanical motor; and 5) elimination of the need of very high power amplifiers (1000 Watts and beyond). Thus, instead of magnetron technology, embodiments of the present disclosure use solid state technology, which is generally more reliable and consumes less power. Stated alternatively, embodiments of the present disclosure may include semiconductors and antenna arrays instead of tubes (for example, magnetron). This may also avoid the requirement for a relatively large and/or heavy transformer. In addition, the microwave  200  may not require the use of a rotary plate, as even cooking may be achieved through controlling the beamforming arrays rather than having to rotate the food items through an unselective RF field. 
         [0059]    With respect to using solid state solutions in microwave ovens instead of using tubes, the challenge of using solid state components is a conventional configuration is the general lack of radio frequency (RF) transistors to support high dissipation and to provide enough irradiated power. However, the present approach may advantageously overcome this challenge by using relatively small power transistors instead of such high power transistors. The amount of energy necessary to cook or warm a dish of food is obtained by a combination of multiple low power components plus beam-forming techniques. 
         [0060]    With regard to a reduction of energy consumption during the cooking process, microwave ovens generally spread energy inside a metallic cage (i.e., inside of the oven cavity). By spreading this energy, there is a loss inherent to the bouncing around of this energy. Some of this energy will be reflected several times before it reaches the food to be heated or cooked. The use of beam-forming will provide a microwave beam in the direction of the material (e.g., food) to be heated or cooked. This use of beam-forming mitigates energy losses. Therefore, a lesser amount of energy is required to be irradiated to warm a certain material (e.g., food). 
         [0061]    With respect to increasing the mean time between failure (MTBF) of microwave ovens, solid state devices (e.g., transistors) generally have a much better MTBF than an electronic tube (e.g., magnetron). Embodiments of the present disclosure provide a microwave that does not require a mechanical motor that rotates the material (e.g., food) to be warmed. Removing a mechanical component from the microwave  200  also removes the errors or failures caused by that mechanical component. That is, a microwave that does not include a mechanical motor will not be subject to the failures caused by the mechanical motor. Consequently, compared to the microwave with a mechanical motor, the frequency of failures of the microwave without a mechanical motor is reduced, and the time between failures is improved. 
         [0062]    As for decreasing the vibration failure rate of microwave ovens, which microwave ovens are subjected to vibrations (e.g., during transportation), their failure rate increases. These vibration-related failures are mostly caused by the failure of the microwave tube installed inside the oven. During transportation of the microwave oven by its owner and without proper packing, the tube is more likely to state failing. Embodiments of the present disclosure use solid state amplifiers instead of vacuum tubes, which help significantly reduce vibration-related failure issues. 
         [0063]    With regard to elimination of the mechanical motor, as note above, with the antennas installed on internal sides of the oven cavity and the use of beam-forming methods, the microwave beams will be electronically formed in the direction of the material to be warmed. The techniques of the present disclosure, using beam-forming and placing antennas on the internal walls of the oven, may provide uniform energy for the material to be warmed or cooked relatively easily controlling phases at the output of the amplifiers. 
         [0064]    Moreover, the above-described approach may eliminate the need for using very high power amplifiers (e.g., 1000 W and beyond). Here again, the above-noted techniques combine the low irradiated power of each amplifier into the required amount of power necessary to warm up or cook the given material. The techniques of the present disclosure may help eliminate the need to use relatively expensive high amplifiers in 2.4 GHz bands, for example. The techniques described herein accordingly provide an avenue for the transition from vacuums tubes to solid state microwave ovens. 
         [0065]    Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
A microwave oven may include a housing defining an oven cavity therein configured to receive material to be heated, and a plurality of solid state microwave generating cells carried by the housing. At least one feedback circuit may be carried by the housing and configured to detect EM radiation within the oven cavity not absorbed by the material to be heated. A processor may be carried by the housing and coupled to the plurality of microwave beamforming cells and to the at least one feedback circuit. The processor may be configured to receive feedback from the at least one feedback circuit based upon the EM radiation not absorbed by the material to be heated, and control phase shifters of the beamforming cells to change the patterns of EM energy transmitted by antennas of the beamforming cells based upon the feedback received from the at least one feedback circuit.