A Compact Wideband Bandpass Filter Based on Stepped Impedance Line Sections

This paper presents a design of compact wideband bandpass filter (BPF). The BPF is based on the traditional highpass filter formed by three short-circuited stubs separated by uniform impedance lines. Since the uniform impedance line sections of the traditional filter are replaced by the stepped impedance lines, the size of the filter can be miniaturized. For a demonstration, a compact BPF with center frequency of 1.3 GHz and fractional bandwidth of 85% has been designed and implemented in microstrip technology. The size of the fabricated BPF is only about $\mathbf{0.45}\ \lambda_{\pmb{g}}$ by $\mathbf{0.8}\ \lambda_{\pmb{g}}$. Moreover, the experimental results are in good agreement with the simulation predictions.