铁电薄膜可调带通滤波器

铁电薄膜的介电常数随外加电场强度的增加而减小.依据铁电薄膜的这一特性,提出了一种新颖的基于共面传输线结构的铁电薄膜可调带通滤波器.为了减小传输损耗,滤波器的导体部分由超导薄膜构成.滤波器的输入输出采用抽头线的方式分别与谐振器相接,外加电压通过输入输出端口直接施加到共面谐振器缝隙处的铁电薄膜上,用以改变铁电薄膜的介电常数,从而改变谐振器的谐振频率,实现带通滤波器通带频率的移动.这种新型可调带通滤波器具有结构紧凑、尺寸小及施加外加偏压容易等优点.仿真结果表明:铁电薄膜的介电常数在外加偏压下从250减小到150时,带通滤波器的传输特性曲线的形状基本保持不变,通带的中心频率从10.283GHz增加到10.518GHz,其3dB带宽保持在0.150GHz左右,反射损耗始终小于-17dB.

A CPW TUNABLE BANDPASS FILTER USING FERROELECTRIC THIN FILM

The dielectric constant of the ferroelectric thin film depends strongly on the applied bias electric field. Based on this principle, a novel CPW (coplanar waveguide) tunable bandpass filter is proposed in this paper, whose input/output structure adopts tapped lines connected with resonators. Bias voltage is applied directly to ferroelectric thin film through tapped lines. The variable dielectric constant of the ferroelectric thin film under different bias voltages results in the resonant frequency shift for the resonator, thus the passband of the filter is shifted with different voltages. The tunable bandpass filter with this novel structure is compact, small size and easy to apply bias voltage. Simulation results show that: when the dielectric constant of the ferroelectric thin film is decreased from 250 to 150 under the external bias voltage, the shape of the transmission response of the bandpass filter is almost unvaried, and its central frequency increases from 10.283 GHz to 10.518 GHz, its 3dB bandwidth keeps at 0.150 GHz, and simultaneously its return loss is thoroughly less than -17 dB.