Harmonics suppression of microstrip antenna using open ended stubs
Harmonic suppression is an important study for microstrip patch antenna that radiates harmonic frequencies. In an active microstrip patch antenna, severe surface waves perturb the impedance parameters of the patch element, which cause pattern anomalies associated with the higher harmonics. In this study, the higher order modes including 1st harmonic and a subharmonic (which exist in between fundamental and 1st harmonic) have been removed by using open ended stubs. The subharmonic and the 1st harmonic have been suppressed by using a pair of quarter wave length stubs placed on either sides of the feed line. The introduction of stubs on the feed line does not affect antenna characteristics associated with the fundamental frequency. Simulated and measured results show that the harmonic components existing at 7.9 GHz (subharmonic) and 10.0 GHz (1st harmonic) of the fundamental frequency of 5.20 GHz have been successfully suppressed. The harmonic properties of microstrip antenna with and without stubs have been studied and the result indicates that the 1st and the subharmonic of the patch antenna have been well eliminated because of the effect of the tuning stubs. A parametric study has been done to optimize the stub dimensions. Finally, the influence of other antenna parameters at the presence of stubs in the antenna structure has been studied. Prototype antennas of different combination of stubs have been fabricated, measured and the idea has been verified. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1340 1345, 2016