Impedance, bandwidth, and Q of antennas

Abstract

I. INTRODUCTIONThe primary purpose of this paper is twofold: first, to derive an approximate expression for the bandwidth of a tuned antenna in terms of its input impedance that holds at every frequency, that is, throughout the entire antiresonant as well as resonant frequency ranges of the antenna; and second, to relate this expression for bandwidth to the antenna quahty factor Q. The definition of stored energy that we use to define the Q of an antenna is similar to that of previous authors [l]- [7]. However, the approximate expression for the bandwidth and its relationship to Q are both more generally applicable and more accurate than previous formulas. The validity and accuracy of the expressions are confirmed by the numerical solutions to straight-wire and wire-loop, lossy and lossless tuned antennas over a wide enough range of frequencies to cover several resonant and antiresonant frequency bands.

An Introduction to the Source Concept for Antennas

“…This strongly resembles the Foster theorem [21] where the reactance derivation produces a sum of energies. It should be stressed that the Foster theorem is valid only for a lossless reactance network, which is not the case of an radiating system.…”

“…Equation (10) is a departure point for the impedance quality factor [21]. It occurred many times, and in various forms and is known as the "EMF method" or EFIE for evaluating the impedance of an antenna using the prescribed current [20] or in the MoM formulation [22].…”

“…Therefore, modified finite energies have been proposed by many authors, see e. g. [14]. Unfortunately, deficiencies such as coordinate dependence [21] and negative values [23] exist.…”

Wideband Multiport Matching Phase I: Single-Feed Multiport Antennas

“…The Smith chart reveals the resonances of the input ports: A resonant frequency ω × is defined where s(jω × ) crosses the real axis in the upward direction. An anti-resonant frequency ω ⊗ is defined where s(jω ⊗ ) crosses the real axis in the downward direction [43]. For example, s 3,3 (jω) explains that two large spikes at 150 and 450 MHz in the admittance plot are resonant frequencies while the spike at 300 MHz is an anti-resonant frequency.…”

Selective Electron Beam Melting Manufacturing of Electrically Small Antennas

“…Generally, the radiation resistance decreases, while the reactive component of its impedance increases, leading to a poor match with the feed line or network. As such, there is a compromise between miniaturization and performance; small antenna theory dictates that a favourable compromise is reached when the antenna fully occupies a volume defined by the radius a [2][3][4][5][6][7][8]. Consequently, there is tremendous potential in the successful manufacture of novel, 3D antenna geometries -hitherto too complex to fabricate with traditional processes -using emergent technologies such as holographic photolithography, 3D printing, direct-write printing, direct transfer patterning, thermal transfer printing, and aerosol jet printing [9][10][11][12][13][14][15][16][17][18].…”