Resonance Frequency and Cavity Resonators

Resonance Frequency

Resonance is, is the frequency, response of system’s to the affects depending on the frequency for which system responses with greater amplitude. When the system has the maximum amplitude response (relatively), we can call these frequencies as resonance frequency. For resonance frequencies small effects causes greater changes. Also resonance occurs in the system when the system have capacity of two or more different types of energy which can be stored and transferred energy easily. [1]

Cavity Resonators

At the lower mode of frequencies, the oscillation and amplification is carried out by conventional wires and transistors networks. At the higher mode of frequencies above 3 MHz conventional wires and transistors networks are not applicable due to the skin effect and stray inductance/capacitance. The cavity resonator has been used for the system which has frequencies above than 3 Mhz. Most resonant cavities are made from closed (or short-circuited) sections of waveguide or high-permittivity dielectric material. The input and output ports are designed to carry RF signals. Resonator’s conducting sides works as inductors and it’s open sides works as capacitors specified length of the microwave frequencies. With explained information cavity resonators works as an amplifier for it increases the frequency of the system. Besides electric and magnetic energy is stored in the cavities, the only losses are due to finite conductivity of cavity walls and dielectric losses of material filling the cavity.[2]

For the resonance frequency , the frequencies should supply the boundary condition( will be explained above). These boundary conditions can be supplied by the numerous resonance frequencies.

For resonance frequency ;

1_These boundary conditions that must be satisfied at resonance (tangential electric fields must be zero at cavity walls)

2_Cavity length must be an integer multiple of half-wavelength at resonance. [3]

Cavity resonators losses energy ;

1_ Apertures in the walls of the cavity and if these apertures intersect the lines of current, then an electromagnetic field will be generated outside the cavity, which causes energy losses by radiation.

2_ There are energy losses within the dielectric and losses caused by coupling with external circuits.

To find the quality of the cavity resonators we can use figure of merit, or quality factor, or Q, of the cavity resonator that gives the ratio of energy that is stored in a cavity resonator to the total losses in the resonator taken over one. The higher the figure of merit, the better the quality of the resonator. By analogy with waveguides, the oscillations that occur in a cavity resonator are classified in groups. In this classification, the grouping depends on the presence or absence of axial and radial (transverse) components in the spatial distribution of the electromagnetic field. (TE-TM or TEM)[4]

The most widely used cavity resonator type is ‘cylindrical cavity resonators’.  The cavity can be characterized by three subscripts m, n, and p that refers the diameter, circumference, and length of the resonator.