Dielectric resonator antenna
A dielectric resonator antenna (DRA) is a radio antenna mostly used at microwave frequencies and higher, that consists of a block of ceramic material of various shapes, the dielectric resonator, mounted on a metal surface, a ground plane. Radio waves are introduced into the inside of the resonator material from the transmitter circuit and bounce back and forth between the resonator walls, forming standing waves. The walls of the resonator are partially transparent to radio waves, allowing the radio power to radiate into space.
An advantage of dielectric resonator antennas is they lack metal parts, which become lossy at high frequencies, dissipating energy. So these antennas can have lower losses and be more efficient than metal antennas at high microwave and millimeter wave frequencies. Dielectric waveguide antennas are used in some compact portable wireless devices, and military millimeter-wave radar equipment. The antenna was first proposed by Robert Richtmyer in 1939. In 1982, Long et al. did the first design and test of dielectric resonator antennas considering a leaky waveguide model assuming magnetic conductor model of the dielectric surface . Thus, they argued that the dielectric antenna behaved like a magnetic dipole antenna. The magnetic conductor model does not explain how current in the dielectric medium is transformed into electromagnetic waves which results in radiation. The electric field from oscillation of polarized dipole fall off inversely with cube of distance and cannot be responsible for far field radiation. There are no free currents in the system as is the case in metallic antennas. These questions have been addressed in a recent work by a group from the University of Cambridge where they proposed that dielectric resonator’s operation can be understood by looking at the system as an asymmetric resonator, i.e. a resonator whose symmetry has been explicitly broken by exciting from one end while leaving the other end floating which results in related broken symmetries of the electric field which results in radiation.  An antenna like effect is achieved by periodic swing of electrons from its capacitive element to the ground plane which behaves like an inductor. The authors further argued that the operation of a dielectric antenna resembles the antenna conceived by Marconi, the only difference is that inductive element is replaced by the dielectric material. 
Dielectric resonator antennas offer the following attractive features:
- The dimension of a DRA is of the order of , where is the free-space wavelength and is the dielectric constant of the resonator material. Thus, by choosing a high value of (), the size of the DRA can be significantly reduced.
- There is no inherent conductor loss in dielectric resonators. This leads to high radiation efficiency of the antenna. This feature is especially attractive for millimeter (mm)-wave antennas, where the loss in metal fabricated antennas can be high.
- DRAs offer simple coupling schemes to nearly all transmission lines used at microwave and mm-wave frequencies. This makes them suitable for integration into different planar technologies. The coupling between a DRA and the planar transmission line can be easily controlled by varying the position of the DRA with respect to the line. The performance of DRA can therefore be easily optimized experimentally.
- The operating bandwidth of a DRA can be varied over a wide range by suitably choosing resonator parameters. For example, the bandwidth of the lower order modes of a DRA can be easily varied from a fraction of a percent to about 10% or more by the suitable choice of the dielectric constant of the resonator material.
- Each mode of a DRA has a unique internal and associated external field distribution. Therefore, different radiation characteristics can be obtained by exciting different modes of a DRA.
- R. K. Mongia, and P. Bhartia, “Dielectric Resonator Antennas – A Review and General Design Relations for Resonant Frequency and Bandwidth”, International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering, 1994, 4, (3), pp 230–247.
- Antenova Antenova info
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- Richtmeyer, Robert (1939), "Dielectric Resonators,", Journal of Applied Physics 10: 391
- Long, S.; McAllister, M.; Shen, L. (1983), "The Resonant Cylindrical Dielectric Resonator Antenna,", IEEE Transactions on Antennas and Propagation 31: 406
- Sinha, Dhiraj; Amaratunga, Gehan (2015), "Electromagnetic Radiation Under Explicit symmetry Breaking,", Physical Review Letters 114: 147701
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