Dielectric resonator

A dielectric resonator (DR) is an electronic component, which has sharp resonance frequencies. These are in the microwave range and are determined by the geometric dimensions and the dielectric constant. Its resonance behavior is similar to a waveguide, but it has no metallic walls. Therefore, it can radiate electromagnetic energy and are used as an antenna.

Historical

Lord Rayleigh predicted that an infinitely long cylinder of a dielectric can act as a waveguide. This was confirmed by subsequent theoretical and experimental research.

In a 1939 published study was derived that dielectric structures can act as metallic cavity resonators. The term was coined and dielectric resonator shown that unshielded dielectric resonators emit and receive energy due to the reversibility also. This led to the development of dielectric antennas, which won after 1960 with the advent of modern communications technology in importance.

Dielectric resonators can be made smaller and lighter than the large and heavy waveguide, they are cheaper and require less volume.

Operation

Although dielectric resonators in many respects behave like metallic cavity resonators, there is one important difference: whereas the electromagnetic fields can not penetrate the metal walls, they are detectable outside of dielectric resonators, although they are considerably weaker with increasing distance. At sufficiently high dielectric constant most of the energy in the resonator remains. The quality factor can be well over 10,000 and reach the value of metallic resonators.

In dielectric resonators, three different modes can be excited: TE, TM, or HEM. It 's right for the application sub- group must be selected. For applications in which it does not depend on the radiation, the mode is preferred. In this mode, the resonant frequency of a cylindrical dielectric resonator approach are calculated using the following formula:

Here, a is the cylinder radius and L is its length, both measured in millimeters. The result is given in GHz and is accurate to 2% when

When the dielectric resonator is sealed in a metal casing, deviations may occur which increase with decreasing distance. By means of a perturbation theory can be set up the following rules for the fashion:

  • When the cut-off volume is preferably stored electrical energy, the resonant frequency decreases.
  • When the cut-off volume is preferably stored magnetic energy, the resonant frequency increases.

Dielectric resonators are very sensitive to temperature fluctuations and mechanical vibrations. Despite some progress, appropriate stabilization measures are still required.

Applications

The most common applications are:

  • Frequency filter, preferably bandpass and bandstop filters,
  • Resonator oscillators in different designs,
  • Frequency -sensitive limiters and ..

Antennas from dielectric resonators ( DRA)

An unshielded dielectric resonator loses radiant energy, so he can act as an antenna. Compared to other antenna designs offers a DRA benefits:

  • An antenna of dielectric resonators is about the size, the wavelength in free space and the relative dielectric constant of the cavity material is. With sufficiently large values ​​can be built very small antennas.
  • Since there are no losses by ohmic resistors, the efficiency of the antenna increases. This is particularly advantageous in millimeter waves, where the conduction losses in the metal can be quite large.
  • In the millimeter wave strip lines are often used as a waveguide, which can be very easy couple to DRAs. The degree of coupling can be optimized simply by moving.
  • At low modes of the DRA can be achieved with an appropriate choice of a relative bandwidth of 10%.

Swell

  • Antenna design
  • High Frequency Technology
  • Vibration
  • Filter ( Electrical Engineering)
Waveguide (electromagnetism)
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