On Methods to Determine Bounds on the Q -Factor for a Given Directivity
This paper revisit and extend the interesting case of bounds on the Q-factor for a given directivity for a small antenna of arbitrary shape. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is sti...
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Published in | IEEE transactions on antennas and propagation Vol. 65; no. 11; pp. 5686 - 5696 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
IEEE
01.11.2017
Institute of Electrical and Electronics Engineers |
Subjects | |
Online Access | Get full text |
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Summary: | This paper revisit and extend the interesting case of bounds on the Q-factor for a given directivity for a small antenna of arbitrary shape. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is still not fully understood, not even for small antennas. Initial investigations in this direction have related the radius of a circumscribing sphere to the directivity, and bounds on the Q-factor have also been derived for a partial directivity in a given direction. In this paper, we derive lower bounds on the Q-factor for a total desired directivity for an arbitrarily shaped antenna in a given direction as a convex problem using semidefinite relaxation (SDR) techniques. We also show that the relaxed solution is also a solution of the original problem of determining the lower Q-factor bound for a total desired directivity. SDR can also be used to relax a class of other interesting nonconvex constraints in antenna optimization, such as tuning, losses, and front-to-back ratio. We compare two different new methods to determine the lowest Q-factor for arbitrary-shaped antennas for a given total directivity. We also compare our results with full electromagnetic simulations of a parasitic element antenna with high directivity. |
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ISSN: | 0018-926X 1558-2221 1558-2221 |
DOI: | 10.1109/TAP.2017.2748383 |