A multiband monopole antenna with an embedded reactance-cancelling transmission-line matching network

Abstract

A series reactance-canceling (SERCA) transmission-line (TL) matching network is proposed, which replaces the series resonant circuit of a double-tuned Wheeler matching network with a λg/2 TL in order to achieve a broadband double-tuned matching response around the design frequency f0 while also introducing additional matching bands at harmonic frequencies of f0. The reactance cancellation property of the λg/2 TL is first outlined, followed by simple equations for the design of multiband SERCA-TL matching networks. A SERCA-TL matching network is subsequently embedded within a printed circular monopole antenna, and it is demonstrated that the lowest frequency of operation can be reduced from 4.43 GHz for the unmatched monopole to 2.1 GHz. Thus, a compact, multiband, and highly efficient antenna is achieved that operates in the frequency ranges of 2.14.31 and 6.356.78 GHz. The total size of the antenna is 20 × 50.3 × 1.59 mm3, and the measured efficiency is on the order of 80%90% within the bands of operation. © 2006 IEEE.