Antenna-independent analytical design of a decoupled monopole array antenna with broadband harmonic suppression

Abstract

• Design a coupler-based isolation network for any desired antenna-to-antenna distance using two phase regulators. • Design of a coupled structure as a new isolation system that does not connect two feed lines of the antennas to each other unlike many common methods. • Introducing a multi-functional via-less dual-stub-based network with ability to provide broadband very-advanced-matching and remove the harmonics. • A matrix-based step-by-step analysis of the proposed multi-step network is presented and required key closed-form equations are extracted. • An important feature is the coverage of all matching, isolation and harmonic-suppression conditions using the lowest number of the parameters in a compact structure. 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 0.039 λ 0 2 ( i . e . 0.12 λ 0 × 0.33 λ 0 ) and offers a highly improved matching with 25 dB S 11 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 S 11 .1 dB. This efficient design is promising for high conversion-efficiency Rectenna and low-interference medical applications.