Dielectric resonator

A dielectric resonator ( DR ) is an electronic component that 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 that of a waveguide , but it has no metallic walls. Therefore, it can radiate electromagnetic energy and can be used as an antenna .

Historical

John William Strutt, 3rd Baron Rayleigh , previously said that an infinitely long cylinder made of a dielectric can act as a waveguide . This was confirmed by later theoretical and experimental research.

In a study published in 1939 it was deduced that dielectric structures can act like metallic cavity resonators . The term dielectric resonator was coined and it was shown that unshielded dielectric resonators radiate energy and, because of their reversibility, also receive it. This led to the development of dielectric antennas, which gained in importance after 1960 with the beginning of modern communication technology .

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

functionality

Although dielectric resonators behave like metallic cavity resonators in many ways, there is one important difference: while the electromagnetic fields cannot penetrate the metal walls, they are detectable outside of dielectric resonators, although they become considerably weaker with increasing distance. If the dielectric constant is high enough , most of the energy remains in the resonator. The quality factor can be well over 10,000 and reach the value of metallic resonators. ${\displaystyle \varepsilon _{\mathrm {r} }}$

Three different modes can be excited in dielectric resonators : TE, TM or HEM. The appropriate subgroup for the application must be selected from this. In applications where radiation is not important, fashion is preferred. In this mode, the resonance frequency of a cylindrical dielectric resonator can be approximately calculated using the following formula: ${\displaystyle TE_{01n}}$

${\displaystyle f_{\mathrm {GHz} }={\frac {34}{a{\sqrt {\varepsilon _{\mathrm {r} }}}}}\left({\frac {a}{L}}+3{,}45\right)}$

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

${\displaystyle 0{,}5<{\frac {a}{L}}<2}$

${\displaystyle 30<\varepsilon _{\mathrm {r} }<50}$

If the dielectric resonator is enclosed in a metallic housing, deviations can occur which increase with decreasing distance. With the help of a perturbation calculation, the following rules can be established for the mode: ${\displaystyle TE_{01n}}$

• If the cut volume has preferably stored electrical energy, the resonance frequency decreases.
• If the cut volume has preferably stored magnetic energy, the resonance 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 uses are:

• Frequency filter , preferably bandpass and bandstop ,
• Resonator in oscillators of different types,
• Frequency sensitive limiters and ..

Antennas made from dielectric resonators (DRA)

An unshielded dielectric resonator loses radiant energy , which is why it can function as an antenna. Compared to other antenna designs, a DRA offers advantages:

• An antenna made of dielectric resonators is about the size , where the wavelength is in free space and the relative permittivity of the resonator material is. With sufficiently large values , you can build very small antennas. ${\displaystyle {\tfrac {\lambda _{0}}{\sqrt {\varepsilon _{\mathrm {r} }}}}}$ ${\displaystyle \lambda _{0}}$ ${\displaystyle \varepsilon _{\mathrm {r} }}$ ${\displaystyle (\varepsilon _{\mathrm {r} }\approx 10-100)}$
• Since there are no losses due to ohmic resistances, the efficiency of the antenna increases. This is particularly advantageous for millimeter waves, where conduction losses in the metal can be quite large.
• In the millimeter wave range, striplines are often used as waveguides, which can be very easily coupled to DRAs. The degree of coupling can be optimized simply by moving it.
• With low modes of the DRA, a relative bandwidth of 10% can be achieved with a suitable choice . ${\displaystyle \varepsilon _{\mathrm {r} }}$

swell

1. ↑ Lord Rayleigh, "On the Passage of Waves Through Tubes, or the Vibration of Dielectric Cylinders," Philosophical Magazine, Vol. 43, pp. 125-132, February 1897.
2. ↑ D. Hondros, “On Electromagnetic Wire Waves,” Annalen der Physik, Vol. 30, pp. 905-949, 1909.
3. ↑ H. Zahn, "On the detection of electromagnetic waves on dielectric wires," Annalen der Physik, vol. 37, pp. 907-933, 1916.
4. ↑ RD Richtmyer, “Dielectric Resonators”, J.Appl. Phys., Vol. 10, pp. 391-398, June 1939.
5. ^ A. Okaya and LF Barash, "The Dielectric Microwave Resonator", Proc. IRE, Vol. 50, pp. 2081-2092, October 1962.
6. ↑ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
7. ^ MJ Loboda, TE Parker and GK Montress, "Temperature sensitivity of dielectric resonators and dielectric resonator oscillators," Proc. of the 42nd Annual Freq. Cont. Symp., Pp. 263-271, Jun 1988.
8. ↑ JK Plourde and C. Ren, “Application of Dielectric Resonators in Microwave Components”, IEEE Trans. Microwave Theory Tech., Vol. MTT-29, pp. 754-769, August 1981.
9. ^ Rajesh K. Mongia, Prakash Bhartia: Dielectric resonator antennas — a review and general design relations for resonant frequency and bandwidth. In: International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering. 4, 1994, p. 230, doi : 10.1002 / mmce.4570040304 .