A Wideband MNG-TL Dipole Antenna With Stable Radiation Patterns

This paper presents the successful design and physical realization of a wideband MNG-TL dipole antenna. An artificial mu-negative transmission line (MNG-TL) structure is realized by employing periodically loaded parallel-plate lines. It is known that the current reversal, which occurs at frequencies much beyond the dipole natural frequency, disturbs the omnidirectional radiation pattern in the azimuth plane. The MNG-TL has a unique property to support a zero propagation constant <formula formulatype="inline"><tex Notation="TeX">$(\beta =0)$</tex></formula> with non-zero group velocity at the zeroth-order resonance. Due to the unique property of an infinite wavelength, the current distribution of the dipole antenna can be improved. Furthermore, the MNG-TL dipole is also useful to achieve a wide impedance bandwidth. A prototype of the proposed MNG-TL dipole is fabricated and measured. It can provide a wide effective bandwidth of about 1.55 GHz (1.85–3.40 GHz) with VSWR 2:1 (<formula formulatype="inline"><tex Notation="TeX">${\rm S}_{11}< -10$</tex></formula> dB) impedance matching and stable omnidirectional radiation patterns in the azimuth plane.

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