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Harmonic Distortion Suppression Technique for Varactor-Loaded Parasitic Radiator Antennas
Qing HAN Keizo INAGAKI Kyouichi IIGUSA Robert SCHLUB Takashi OHIRA Masami AKAIKE
IEICE TRANSACTIONS on Electronics
Publication Date: 2002/12/01
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Low-Distortion,High-Power,High-Efficiency Active Device and Circuit Technology)
ESPAR antenna, varactor diode, nonlinear, harmonic distortion, reactive near-field measurement,
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Harmonic distortions of a recently developed lightweight film-type ESPAR (Electronically Steerable Passive Array Radiator) antenna are investigated experimentally. These distortions arise from the nonlinearity of the varactor diodes that are directly integrated with the parasitic radiator elements to control the antenna's radiation pattern. A reactive-near-field measurement technique that employs low-interference probes in an ultra-small anechoic box is used to reduce experimental time and cost. An anti-series varactor pair is introduced and compared with the conventional single varactor. Consequently, an ESPAR antenna equipped with the anti-series varactor pair exhibits remarkable suppression of nonlinear distortion. In particular, the second- and the third-order harmonic is reduced by approximately 20 dB and 12 dB from the level of a single varactor type ESPAR antenna, respectively.