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Keywords
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Harmonic suppression,
Isolation,
Microstrip array,
Monopole antenna,
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Abstract
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A hybrid microstrip-based network is proposed to simultaneously cover a multi-functional performance including
high single-antenna matching, improved array isolation and higher-order harmonics suppression. Unlike most
inductance-based isolators with destructive direct connection of two feed lines, the proposed isolator is
comprised of only a thin dual-coupled-lines coupler with the ability to design for any desired antenna-to-antenna
distance. A multi-variable via-less Π-shaped network is then introduced with dual-band filtering capability to
significantly remove the antenna-isolator harmonics independently. A step-by-step matrix analysis with appropriate
circuit conversion and equivalence is presented to easily extract closed-form equations of the key parameters
as an overall design guideline. Full-wave simulations of two commercial software provide more validity
for theoretical calculations. Furthermore, the bandwidths of the notch filters are investigated to obtain a broad
harmonic-suppressed band. The fabricated array with optimal network occupies an area of only 0.039λ02(i.e.
0.12λ0 × 0.33λ0) and offers a highly improved matching with 25 dB S11 bandwidth of 7.2% (2.39 ~ 2.57 GHz). In
this well-matched band, the isolation is over 22 dB with significant improvement of 36 dB compared to the
primary one. Moreover, all harmonics are suppressed up to 9 GHz with measured<1|S11|.1 dB. This efficient
design is promising for high conversion-efficiency Rectenna and low-interference medical applications.
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