Automatic phase control
Disclosed are methods and apparatuses for heating an object in a cavity by feeding the cavity with RF signals. One of the disclosed methods includes simultaneously feeding the cavity with at least two RF signals. Of the at least two RF signals, a first RF signal is fed to the cavity via a first antenna and a second RF signal is fed to the cavity via a second antenna. The first and second RF signals have a common frequency and differ in phase by a first phase difference. The method also includes measuring the first phase difference and adjusting the feeding based on measurements of reflected RF signals reflected from the cavity. Conducting the measurements of the reflected RF signals may also be part of the disclosed method. A disclosed apparatus includes the structure required for carrying out the above method.
1. A method of cooking, thawing, or drying food in a cavity by feeding the cavity with RF signals having phase differences of target values, the method comprising:
setting a target value for a phase difference;
simultaneously feeding the cavity with at least two RF signals comprising a first RF signal fed to the cavity via a first antenna and a second RF signal fed to the cavity via a second antenna, said first and second RF signals having a common frequency and differ in phase by a first phase difference;
measuring the first phase difference; and
adjusting the feeding based on measurements of reflected RF signals reflected from the cavity so that the phase difference between the first and second signals fed to the cavity via the first and second antennas approaches the target value.
2. The method according to claim 1 , wherein adjusting the feeding is based on measurements of a ratio between a first forward RF signal fed to the cavity via a first antenna and a signal reflected from the cavity via the first antenna when the first forward RF signal is fed into the cavity.
3. The method of claim 1 , wherein the reflected signals are reflected from the cavity when an RF signal is fed into the cavity via one antenna at a time.
4. The method of claim 1 , wherein measurements of the first phase difference are taken more often than measurements of the signals reflected from the cavity.
5. The method of claim 1 , wherein the first phase difference is measured using a coupler having directivity worse than −30 dB.
6. The method of claim 1 , wherein said first and second RF signals differ in amplitude by a first amplitude ratio, and the method comprises measuring the first amplitude ratio and adjusting the feeding so that the actual amplitude ratio between the first and second RF signals approaches an amplitude ratio target value.
7. The method of claim 1 , wherein adjusting the feeding is based on:
measurements of reflected RF signals reflected from the cavity;
the value of the first phase difference; and
error correction terms indicative of systematic errors in a measurement system used for measuring the first phase difference.
8. The method of claim 1 , wherein said feeding is at power levels and for time durations sufficient to cook, thaw, or dry the food in the cavity.
9. The method of claim 1 , further comprising heating the food by energy other than RF energy, and said feeding is at power levels and for time durations sufficient to shorten the cooking, thawing, or drying of the food, in comparison to not applying the RF energy, by at least 15%.
10. The method of claim 1 , wherein said setting is based on the food.
11. The method of claim 1 , wherein said setting is based on RF absorption in the food.