Defected ground structures (DGSs) are often utilized in planar filters and antennas for compactness and spurious frequency suppressions by creating defects or slots on the ground planes. One disadvantage of conventional DGS filters is that the overall dimension increases as the order of the filter increases. In this research, we proposed an asymmetric finger-shape DGS which created multiple equivalent LC resonators when combining with a capacitive microstrip gap on the top. In contrast to the conventional high-order DGS filter by generating many DGSs on the ground plane, the finger-shape DGS provided a high-order bandpass response with one single DGS due to the capacitances between the top metallic strip and the ground plane. Therefore, we developed a wide-band, high-order, and spurious frequency suppressed microstrip bandpass filter with a compact size. To achieve these features, different filter design techniques were exploited including stepped impedance resonator (SIR), series-coupled resonator, and nger-shape DGSs. The main advantage of our DGS filter was that it had a higher-order and wider bandpass responses than other harmonic-suppressed work. A prototype was designed, fabricated, and measured with a calibrated vector network analyzer (VNA) where the simulations matched with the measurements. The finger-shape DGS filter demonstrated a passband centered at 2.35 GHz with a fractional bandwidth of 72.3%, the spurious frequency suppression up to 8.5f0 where f0 was the center frequency of the passband, and a compact size of 0.034λ02 where λ0 was the wavelength corresponding to f0.
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