Design of Dual-band Bandpass Filter for GSM 950 MHz and GSM 1850 MHz Applications using Lumped Component

Abstract

Filter is an electrical circuit that designed to pass the signal generated at certain frequencies and block the signal generated by all other frequencies. Dual-band filter is a filter designed to work on two frequency bands simultaneously. This research aims to design a dual-band bandpass filter for GSM applications, to pass signals on two frequency bands simultaneously, namely GSM900 with 950 MHz center frequency and bandwidth of 25 MHz and GSM1800 with 1850 MHz center frequency and bandwidth of 75 MHz. The steps taken to design a bandpass filter dual-band is starting to make a normalized lowpass filter Butterworth, then transform the lowpass filter into a bandpass filter with a center frequency of 950 MHz and 1850 MHz, then combining the two bandpass filters are to be filter dual-band with center frequency 950 MHz and 1850 MHz, and finally analyze the performance of the dual-band bandpass filter. Performance filter parameters to be analyzed is the return loss (S11), insertion loss (S21) and Voltage Standing Wave Ratio (VSWR). From the analysis and discussion for dual-band bandpass filter is obtained that: center frequency of the filter is at 950 MHz and 1850 MHz. Filter bandwidth at center frequency of 950 MHz is 25 MHz (962.5 MHz - 937.5 MHz) and filter bandwidth at center frequency of 1850 MHz is 75 MHz (1812.5 MHz - 1887.5 MHz). Return loss (S11) filter at frequency of 950 MHz and 1850 MHz < -10 dB. Insertion loss (S21) filter at frequency of 950 MHz and 1850 MHz > -3 dB. VSWR at frequency of 950 MHz and 1850 MHz < 2.