A monolithic miniature multi-conductor strip-resonator bandpass filter

A new monolithic design of a miniature bandpass filter for manufacture by means of multilayer printed-circuit-board technology has been developed. It is demonstrated using a fourth-order filter that multi-conductor strip resonators used in the design ensure both miniaturization and high selectivity of the device. The passband center frequency of the manufactured filter is $f_0$ = 546 MHz, the fractional bandwidth is $\Delta f/f_0$ = 25%, and the insertion loss is 0.8 dB. The filter has a wide high-frequency stopband, which extends up to a frequency of 10 $f_0$ at a level of –30 dB. The filter dimensions are 15.0 $\times$ 12.0 $\times$ 4.3 mm (0.027 $\lambda_{0}$ $\times$ 0.021 $\lambda_{0}$ $\times$ 0.007 $\lambda_{0}$, where $\lambda_{0}$ is the wavelength in vacuum at frequency $f_0$) and the mass is only 1.8 g. The performances of the filter and the accessibility of its design for surface mounting show that the device has great potential.