Using high permittivity ceramic substrates to fabricate a miniaturized bandpass filter with capacitive load

Using high permittivity ceramic substrates and capacitive coupling to miniaturize the sizes of Butterworth bandpass filters are investigated. The selectivity and stopband rejection of the designed filters can be improved significantly by utilizing a skew-symmetric (zero degree) feed structure. These factors result in reducing the size of the filter. The responses of the Butterworth filters using Al₂O₃ (ε_r = 10, Q × f = 20,000 GHz) and 0.85(M_80.95Zn_0.05)TiO ₃ - O.15Ca_0.6La_0.8/3TiO₃ ε_r = 26, Q × f = 86,000 GHz) ceramic substrates are designed at a center frequency of 2.4 GHz. The compact size, low-loss, sharp response, and performance of the filter are presented in this article.