Microwave and characteristics
    Microwave is the electromagnetic wavelength of about 1m-10mm , often divided into UHF , centimeter waves , millimeter and submillimeter four bands. Microwave and visible light , infrared , ultraviolet , x-rays , are electromagnetic waves, except that they have different wavelengths and frequencies. Microwave frequencies (300Mh a 300 GH2) between radio frequency ( VHF ) and far -infrared frequency ( low frequency ) . Because of its high frequency, in some cases , also known as ultra-high frequency electromagnetic waves. Microwave frequency close to the frequency of radio waves and radar frequencies overlap , interfere Communications . Therefore , the microwave frequency range of international industrial , scientific and medical use , there are stringent requirements. Currently the industry is only 915MHz ( 896M compared with the U.S. ) , and the two frequencies are widely 2450Mh . In some high frequency , since the power of the microwave tube , efficiency, cost yet able to meet industry requirements, it is seldom used.
    Microwave with electromagnetic wave characteristics , such as the fluctuation characteristics reflection, transmission and interference , diffraction, polarization and accompanying electromagnetic energy transmission , which determines the generation, transmission , amplification, microwave radiation and other issues are also different from ordinary radio , AC . In the microwave system , the electrical properties of a few can not be considered lumped microwave system is not the wire -type circuits , AC and DC transmission parameters discharge capacitors and inductors concept has lost its exact meaning. In the microwave field , usually applied concept called " field" to analyze the structure of the system of electromagnetic waves . And the use of power, frequency , impedance, VSWR measurement , etc., as a substantial amount of microwave . Specifically , ① issues in the study of the microwave , you should use the concept of electromagnetic fields , many of the high-frequency alternating electromagnetic field effects can not be ignored. For example, the diameter of the wavelength of the microwave and the circuit is the same order of magnitude , phase lag has been very clear that this must be taken into account when ② microwave propagation is a straight line . Encounter reflective metal surface will occur , in line with the direction of the reflected light reflection law . ③ high microwave frequencies, the radiation effect is more obvious , and it means that the microstrip conductor on a common , constant energy is accompanied by radiation to the surrounding space , the transmission will quickly attenuate fluctuations , so the transmission part there are special requirements. ④ When the superposition of incident and reflected waves encounter interference wave can be formed , including the standing wave phenomenon . In the microwave waveguide or resonator , standing microwave electromagnetic field distribution of the phenomenon is very common. In microwave devices, we also use a variety of modes of electromagnetic field distribution of the electromagnetic field is superimposed to improve the uniformity of the total . ⑤ spatial distribution of microwave energy with the general electromagnetic energy , like spatial distribution properties . Where the presence of electromagnetic fields, where there is energy. The secondary side of a point in space , for example a microwave energy transmission direction, the value of the electric field energy , and the size of the space where the field strength is related to the sum of the total energy of the microwave electromagnetic energy of the electromagnetic field point in space .
    The same straight line as the optical microwave , reflected by the metal , and other substances through the air ( such as various glass, paper and plastic ) , may be well absorbed by the type of food ingredients ( including water ) . When the microwave is reflective material , does not increase the thermal mass ; material to absorb microwave energy , is caused by the position becomes hot .
    Usually the transmission of microwave energy with high frequency electromagnetic wave is different, it is an ultra-high frequency electromagnetic waves , and an alternating magnetic field transmitted in the form of mutual induction . In order to transmit large capacity power and reduce power losses during transmission , and often in a certain size microwave waveguide ( referred to as a waveguide ) within the transmission. Common waveguide hollow conductive metal tube filled with medium or internal , such as a circular waveguide , a ridge waveguide of rectangular waveguide and the like . The size and structure of the waveguide, the transmission of electromagnetic waves according to the actual needs of specialized nature and design and manufacturing .