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The Q factor is a parameter that describes the resonance behavior of an underdamped harmonic oscillator (resonator). Sinusoidally driven resonators having higher Q factors resonate with greater amplitudes (at the resonant frequency) but have a smaller range of frequencies around that frequency for which they resonate; the range of frequencies for which the oscillator resonates is called the ...
In electrical engineering and telecommunications the Chu–Harrington limit or Chu limit sets a lower limit on the Q factor for a small radio antenna. [1] The theorem was developed in several papers between 1948 and 1960 by Lan Jen Chu, [2] Harold Wheeler, [3] and later by Roger F. Harrington. [4]
Clearly this is not the case and it is well known that a dielectric perturbation may either increase or decrease the Q factor. The problems stems from the fact that a cavity is an open non-Hermitian system with leakage and absorption. The theory of non-Hermitian electromagnetic systems abandons energy, i.e. |.
The quality of the resonance (how long it will ring when excited) is determined by its Q factor, which is a function of resistance: =. An idealized, lossless LC circuit has infinite Q , but all actual circuits have some resistance and finite Q , and are usually approximated more realistically by an RLC circuit .
The linewidth is inversely proportional to the Q factor, which is a measure of the sharpness of the resonance. In radio engineering and electronics engineering , this approximate symmetric response is known as the universal resonance curve , a concept introduced by Frederick E. Terman in 1932 to simplify the approximate analysis of radio ...
The ultra-low electrical resistivity of a superconducting material allows an RF resonator to obtain an extremely high quality factor, Q. For example, it is commonplace for a 1.3 GHz niobium SRF resonant cavity at 1.8 kelvins to obtain a quality factor of Q=5×10 10. Such a very high Q resonator stores energy with very low loss and narrow bandwidth.
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The Q factor of a particular mode in a resonant cavity can be calculated. For a cavity with high degrees of symmetry, using analytical expressions of the electric and magnetic field, surface currents in the conducting walls and electric field in dielectric lossy material. [14]