Ultra-Compact Band-Pass Filter at Low Frequency of Operation

An ultra-compact band-pass filter is presented in this paper. The filter is designed to operate in the medical implants communication service (MICS) band ranging from 401 MHz to 406 MHz. The filter is designed on a Rogers RT/duroid substrate with e(r) = 2.94 and tans = 0.0012. The overall size of the proposed filter is only 30.6 mm x 18.5 mm (0.058?(g) x 0.035?(g)), making it suitable for compact, portable devices. An equivalent circuit model is also proposed for the analysis of the filter geometry. From the circuit model, it can be concluded that the filter exhibits the characteristics of a dual-composite right left-handed (D-CRLH) transmission line. This is also confirmed from the dispersion characteristics. The salient features of the proposed filter include ultra-compactness at low operating frequency, harmonic suppression of 3.7 times of the passband frequency, fractional bandwidth of 4.45%, and good roll-off rate of 297.6 dB/GHz in the lower stopband and 116.4 dB/GHz in the upper stopband.