Dielectric resonator


Dielectric resonator

A dielectric resonator (also dielectric resonator oscillator, DRO) is an electronic component that exhibits resonance for a narrow range of frequencies, generally in the microwave band. The resonance is similar to that of a circular hollow metallic waveguide, except that the boundary is defined by large change in permittivity rather than by a conductor. Dielectric resonators generally consist of a "puck" of ceramic that has a large dielectric constant and a low dissipation factor. The resonance frequency is determined by the overall physical dimensions of the puck and the dielectric constant of the material.

Contents

Historical Overview

In the late 19th century, Lord Rayleigh demonstrated that an infinitely long cylindrical rod made up of dielectric material could serve as a waveguide.[1] Additional theoretical [2] and experimental [3] work done in Germany in early 20th century, offered further insight into the behavior of electromagnetic waves in dielectic rod waveguides. Since a dielectric resonator can be thought of as a truncated dielectric rod waveguide, this research was essential for scientific understanding of electromagnetic phenomena in dielectric resonators. In 1939 Robert D. Richtmyer published a study [4] in which he showed that dielectric structures can act just as metallic cavity resonators. He appropriately named these structures dielectric resonators. Richtmyer also demonstrated that, if exposed to free space, dielectic resonators must radiate because of the boundary conditions at the dielectric-to-air interface. These results were later used in development of DRA (Dielectric Resonator Antenna). Due to World War II, lack of advanced materials and adequate manufacturing techniques, dielectric resonators fell in relative obscurity for another two decades after Richtmyer's study was published. However, in the 1960s, as high-frequency electronics and modern communications industry started to take off, dielectric resonators gained in significance. They offered a size-reducing design alternative to bulky waveguide filters and lower-cost alternatives for electronic oscillator,[5] frequency selective limiter [6] and slow-wave [7] circuits. In addition to cost and size, other advantages that dielectric resonators have over conventional metal cavity resonators are lower weight, material availability, and ease of manufacturing. There is a vast availability of different dielectric resonators on the market today with unloaded Q factor on the order of 10000s.

Theory of Operation

Although dielectric resonators display many similarities to resonant metal cavities, there is one important difference between the two: while the electric and magnetic fields are zero outside the walls of the metal cavity (i.e. open circuit boundary conditions are fully satisfied), these fields are not zero outside the dielectric walls of the resonator (i.e. open circuit boundary conditions are approximately satisfied). Even so, electric and magnetic fields decay from their maximum values considerably when they are away from the resonator walls. Most of the energy is stored in the resonator at a given resonant frequency for a sufficiently high dielectric constant  \varepsilon_r . Dielectric resonators can exhibit extremely high Q factor that is comparable to a metal walled cavity.[8]

There are three types of resonant modes that can be excited in dielectric resonators: transverse electric (TE), transverse magnetic (TM) or hybrid electromagnetic (HEM) modes. Theoretically, there is an infinite number of modes in each of the three groups, and desired mode is usually selected based on the application requirements. Generally, TE01n mode is used in most non-radiating applications, but other modes can have certain advantages for specific applications.[9]

Approximate resonant frequency of TE01n mode for an isolated cylindrical dielectric resonator can be calculated as [10]:

 f_{GHz}=\frac{34}{a\sqrt{\varepsilon_r}}\left( \frac{a}{L}+3.45\right)

Where a is the radius of the cylindrical resonator and L is its length. Both a and L are in millimeters. Resonant frequency fGHz is in gigahertz. This formula is accurate to about 2% in the range:

 0.5<\frac{a}{L}<2

30 < εr < 50

However, since a dielectric resonator is usually enclosed in a conducting cavity for most applications, the real resonant frequencies are different from the one calculated above. As conducting walls of the enclosing cavity approach the resonator, change in boundary conditions and field containment start to affect resonant frequencies. The size and type of the material encapsulating the cavity can drastically impact the performance of the resonant circuit. This phenomenon can be explained using cavity perturbation theory. If a resonator is enclosed in a metallic cavity, resonant frequencies change in following fashion [11]:

- if the stored energy of the displaced field is mostly electric, its resonant frequency will decrease;

- if the stored energy of the displaced field is mostly magnetic, its resonant frequency will increase. This happens to be the case for TE01n mode.

Most common problem exhibited by dielectric resonator circuits is their sensitivity to temperature variation and mechanical vibrations.[12] Even though recent improvements in materials science and manufacturing mitigated some of these issues, compensating techniques still may be required to stabilize the circuit performance over temperature and frequency.

Common Applications

Most common applications,[13][14] of dielectric resonators are:

- Filtering applications (most common are bandpass and bandstop filters),

- Oscillators (diode, feedback-, reflection-, transmission- and reaction-type oscillators),

- Frequency-selective limiters,

- Dielectric Resonator Antenna (DRA) elements.

Notes

  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, “Ueber elektromagnetische Drahtwelle,” Annalen der Physik, Vol. 30, pp. 905-949, 1909.
  3. ^ H. Zahn, “Ueber den Nachweis elektromagnetischer Wellen an dielektrischen Draehten,”, Annalen der Physik, vol. 37, pp. 907-933, 1916.
  4. ^ R.D. Richtmyer, “Dielectric Resonators”, J.Appl. Phys., Vol. 10, pp. 391-398, June 1939.
  5. ^ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  6. ^ Marian W. Pospieszalski, “Cylindrical Dielectric Resonators and Their Applications in TEM Line Microwave Circuits”, IEEE Trans. Microwave Theory Tech., Vol. MTT-27, pp. 233-238, March 1979.
  7. ^ Marian W. Pospieszalski, “Cylindrical Dielectric Resonators and Their Applications in TEM Line Microwave Circuits”, IEEE Trans. Microwave Theory Tech., Vol. MTT-27, pp. 233-238, March 1979.
  8. ^ A. Okaya and L.F. Barash, “The Dielectric Microwave Resonator”, Proc. IRE, Vol. 50, pp. 2081-2092, October 1962.
  9. ^ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  10. ^ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  11. ^ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  12. ^ M.J. Loboda, T.E. Parker and G.K. Montress, "Temperature sensitivity of dielectric resonators and dielectric resonator oscillators," Proc. of the 42nd Annual Freq. Cont. Symp., pp.263-271, Jun 1988.
  13. ^ Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  14. ^ J.K. Plourde and C. Ren, “Application of Dielectric Resonators in Microwave Components”, IEEE Trans. Microwave Theory Tech., Vol. MTT-29, pp. 754-769, August 1981.

References

  • Lord Rayleigh, “On the Passage of Waves Through Tubes, or the Vibration of Dielectric Cylinders”, Philosophical Magazine, Vol. 43, pp. 125–132, February 1897.
  • D. Hondros, “Ueber elektromagnetische Drahtwelle,” Annalen der Physik, Vol. 30, pp. 905–949, 1909.
  • H. Zahn, “Ueber den Nachweis elektromagnetischer Wellen an dielektrischen Draehten,”, Annalen der Physik, vol. 37, pp. 907–933, 1916.
  • R.D. Richtmyer, “Dielectric Resonators”, J.Appl. Phys., Vol. 10, pp. 391–398, June 1939.
  • Darko Kajfez and Piere Guillon, Dielectric Resonators, Artech House, Dedham, MA, 1986.
  • Marian W. Pospieszalski, “Cylindrical Dielectric Resonators and Their Applications in TEM Line Microwave Circuits”, IEEE Trans. Microwave Theory Tech., Vol. MTT-27, pp. 233–238, March 1979.
  • A. Okaya and L.F. Barash, “The Dielectric Microwave Resonator”, Proc. IRE, Vol. 50, pp. 2081–2092, October 1962.
  • M.J. Loboda, T.E. Parker and G.K. Montress, "Temperature sensitivity of dielectric resonators and dielectric resonator oscillators," Proc. of the 42nd Annual Freq. Cont. Symp., pp. 263–271, Jun 1988.
  • J.K. Plourde and C. Ren, “Application of Dielectric Resonators in Microwave Components”, IEEE Trans. Microwave Theory Tech., Vol. MTT-29, pp. 754–769, August 1981.

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • dielectric resonator — dielektrinis rezonatorius statusas T sritis radioelektronika atitikmenys: angl. dielectric resonator vok. dielektrischer Resonator, m rus. диэлектрический резонатор, m pranc. résonateur diélectrique, m …   Radioelektronikos terminų žodynas

  • Dielectric Resonator Antenna — If the dielectric resonator is placed in an open environment, power is lost in the radiated fields. This fact makes dielectric resonators useful as antenna elements. Dielectric resonator antennas (DRA) offer following attractive features: The… …   Wikipedia

  • Dielectric wireless receiver — is a type of radiofrequency receiver front end featuring a complete absence of electronic circuitry and metal interconnects. It offers immunity against damage from intense electromagnetic radiation, produced by EMP and HPM sources. This receiver… …   Wikipedia

  • Dielectric — A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their …   Wikipedia

  • Resonator — A resonator is a device or system that exhibits resonance or resonant behavior, that is, it naturally oscillates at some frequencies, called its resonance frequencies, with greater amplitude than at others. Although its usage has broadened, the… …   Wikipedia

  • dielektrischer Resonator — dielektrinis rezonatorius statusas T sritis radioelektronika atitikmenys: angl. dielectric resonator vok. dielektrischer Resonator, m rus. диэлектрический резонатор, m pranc. résonateur diélectrique, m …   Radioelektronikos terminų žodynas

  • Split Ring Resonator — A split ring resonator (SRR) is a component part of a negative refractive index material. SRRs are a pair of concentric annular rings with splits in them at opposite ends. The rings are made of nonmagnetic metal like copper and have small gap… …   Wikipedia

  • Microwave cavity — A microwave cavity is a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. Such cavities act as resonant circuits with extremely low loss at their frequency of operation. Their Q factor may reach… …   Wikipedia

  • dielektrinis rezonatorius — statusas T sritis radioelektronika atitikmenys: angl. dielectric resonator vok. dielektrischer Resonator, m rus. диэлектрический резонатор, m pranc. résonateur diélectrique, m …   Radioelektronikos terminų žodynas

  • résonateur diélectrique — dielektrinis rezonatorius statusas T sritis radioelektronika atitikmenys: angl. dielectric resonator vok. dielektrischer Resonator, m rus. диэлектрический резонатор, m pranc. résonateur diélectrique, m …   Radioelektronikos terminų žodynas


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.