This suggests that a resonant frequency tuning range of 240 MHz in this study for the constructed DR antennas is obtained.Also, the impedance bandwidth for the case with l ϭ 20 mm was measured to be 3.5%, which is greater than that of a corresponding regular DRA (2.8%). This behavior is largely owing to the embedded slots in the ground plane, which causes the lowering of the quality factor of the DR antenna. Radiation characteristics of the constructed prototypes were also studied. Figure 4 plots measured radiation patterns of the prototypes. Good broadside radiation characteristics are observed, and the obtained antenna gain was about 6 dBi.
CONCLUSIONSMicrostripline-fed frequency tunable DR antennas have been demonstrated. Experimental results of the constructed prototypes show a resonant frequency tuning range of more than 10% of the antenna's resonant frequency. Also, the proposed antenna allows post-manufacturing resonant frequency tuning to compensate for manufacturing tolerances or possible fabrication errors, and thus meet precise frequency specifications in practical designs.
A new balanced two-wire shielded transmission line is presented. The wires are arcshaped thick conductors that are shielded by a circular pipe. This structure allows implementation of a relatively wider range of characteristic impedance as compared to that of the conventional two-wise line. Possible applications of the proposed line include antenna feeds and communication links, The characteristic impedance of the proposed line is found using an efficient moment method (MM) in which the M M expansion functions contain the exact singular behavior of the electric fields near the right angle wedges ofthe arc shaped conductors.
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