A Lowpass Filter Design Using Curved and Fountain Shaped Resonators

Abstract

In this paper a new lowpass filter (LPF) with curved line resonators and fountain shaped resonators is proposed. The proposed filter has achieved wide stopband, compact size, sharp roll-off rate and low return loss. Two tapered resonators are used to produce transmission zeros and widen the stopband. Also, a fountain shaped resonator is proposed using curved transmission lines to obtain good sharpness in the filter response. The cut-off frequency of the designed LPF is 1.74 GHz and the overall size of the designed LPF is 0.135 λg × 0.132 λg where λg is the guided wavelength at the cut-off frequency. The results show that the overall size of the lowpass filter could be reduced using curved line resonators and curved transmission lines.

A Compact Low-Pass Filter with Simple Structure and Sharp Roll-Off

“…Recently, microstrip filters are widely used in wireless circuits and systems [1][2][3][4][5]. Among the microstrip filters, compact LPFs with high performance are more attractive [1].…”

“…So far, several resonators have been presented for designing of the LPFS. For instance, triangular [1], rectangular [1] curved [2], T-shaped [11], π-shaped [13] resonators, stepped impedances [14] and open stubs [15] have been widely used to design different types of LPFs.…”

“…Despite of providing stop-band, resonators can also decrease the circuit size. For instance, curved Tshaped and π-shaped resonators can decrease the overall size of the filter [2,11]. Usually a suppressor cell is inserted in the LPF structure to provide wide stop-band.…”

A compact lowpass filter for satellite communication systems based on transfer function analysis

“…This is even more important for the communication-one-the-move, where in addition to all strict satellite communication requirements, there is a strong motivation to employ passive, affordable microwave and electromagnetic components in the portable satellite receivers [8][9][10][11]. Thus, various techniques have been studied to achieve LPFs with the mentioned features [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. A modified version of T-shaped resonators in conjunction with multiple open-stubs was proposed in [12] to realize a compact LPF with a large stopband.…”

“…In [22], a high-impedance transmission-line is loaded by multiple compact microstrip resonant cells to provide both high selectivity and wide stopband, while the circuit size is not equally weighted, resulting in a relatively large filter. In [23][24][25][26][27], numerical-based approaches were used to predict the transfer function of a lowpass filter and to extract its resonant frequencies.…”