Antenna Quality Factor Research Articles

The influence of complex material coverings on the quality factor of simple radiating systems

The influence of material coverings on the antenna quality factor is investigated for radiators formed by thin electric or magnetic line sources. It is shown that thin uniform and symmetric layers of arbitrary passive materials (including Veselago, left-handed, or double-negative materials) cannot help to overcome the bandwidth limitations imposed by the amount of energy stored in the antenna reactive field. Alternative possibilities offered by complex composite materials in the antenna design are identified.

Physical limitations of antenna

A discussion of minimum possible antenna quality factor (Q) is first presented . Based on the spherical wave function theory, the maximum possible ratios of gain to Q for both directional antenna and omnidirectional antenna are examined and new upper limits for both cases have been obtained. Universally applicable numerical results and some related discussions are also included.

A method for the evaluation of small antenna Q

A method is presented to calculate the quality factor (Q) of small antennas, which is based on the understanding that for a small antenna the total energy in Poynting theorem can be easily separated into the stored energy and radiated energy by using the low frequency expansions. The Poynting theorem in frequency domain provides an equation on the stored electric and magnetic energy while the Poynting theorem in time domain can be used as another independent equation for the stored electric and magnetic energy. By solving these equations the stored electric and magnetic energy can be obtained, thus, making the Q calculation possible.

Radiation quality factor and resonant resistance of rectangular microstrip antennas

AbstractA new very simple radiation quality factor expression is presented for a rectangular microstrip antenna. The theoretical resonant resistance results obtained by using this new radiation quality factor expression are in very good agreement with the experimental results available in the literature. © 1994 John Wiley & Sons, Inc.

Transmission Line Model Analysis of Rectangular Patch Antennas

ABSTRACT The transmission line model has been utilized to determine the input performance of a rectangular patch antenna excited by a coaxial probe. Approximate expressions have been developed for the resonant propagation constant (or the resonant frequency), quality factor and input resistance of such antennas which clearly indicate the effects of the various antenna parameters including the feed on these quantities under dynamic conditions. The results of computations based on the expressions developed are compared with available measured values. The present work establishes the transmisson line model as a valid representation of rectangular patch antennas, and would facilitate the design of such antennas without elaborate numerical computation. The model has also been applied to determine the resonant parameters for a similar antenna tuned by passive metallic posts. Validity of an approximate expression derived for the resonant frequencies of such tunable antennas has also been established by comparison with available measured results.

The pattern space factor and quality factor of cylindrical source antennas

For the first time the quality factor of cylindrical source antennas is derived by a plane wave expansion. The evanescent energy (and therefore the quality factor) as defined by a plane wave expansion is shown to be different from Collin and Rothschild’s [IEEE Trans. Antennas Propagation AP-12, 23 (1964)] quality factor.

On the quality factor of strip and line source antennas and its relationship to superdirectivity ratio

Exact formulas are derived for the quality factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> of strip and line source antennas. Contrary to popular opinion, none of them is equal to Taylor's superdirectivity ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma</tex> or to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma - 1</tex> . But in the case of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> -plane strip sources (the complement of the type of strip source treated by Woodward and Lawson) the value of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> is precisely equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma_{\alpha}^{-1/2}- 1</tex> , where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma_{\alpha}^{\beta}</tex> is a generalized superdirectivity ratio that reduces to Taylor's <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma</tex> when the edge exponent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> and the pattern weighting exponent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\beta</tex> are both zero. In the case of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -plane strip sources the value of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> is approximately equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma_{\alpha}^{1/2} - 1</tex> , and for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -plane line sources of vanishing width <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</tex> it is approximately equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[(2/\pi) \ln (2.516\lambda/\pi a)]\gamma_{\alpha}^{1}</tex> .

Quality factor of general ideal antennas

An expression for the quality factor of an ideal antenna with both TE and TM modes excited is derived and applied to several special cases.