High selectivity and wideband bandpass filtering impedance transformer

Abstract

An impedance transformer (IT) with wideband and high selectivity is presented in this paper. Three transmission poles were obtained within the passband and provides a wide passband response. Moreover, there are two transmission zeros (TZs) close to the passband that were achieved by a shunt parallel coupled line and provide high selectivity. For validation of proposed circuit, the ITs were designed at a center frequency (f0) of 3.5 GHz using an impedance‐transforming ratio (r) of 5 and 10. For r = 5, |S21| and |S11| are 0.36 dB and 28 dB at f0, respectively. Within the passband, |S21| and |S11| are better than 0.65 dB and 18 dB, respectively. The TZs at 2.65 GHz (0.76f0) and 1.22f0, close to the passband, were measured with attenuation better than 37 dB. The out‐of‐band attenuations are higher than 20 dB from DC to 2.77 GHz of the lower stopband and from 4.16 GHz to 9.73 GHz of the higher stopband. For r = 10, |S21| = −1.4 dB and |S11| = −23 dB were measured at f0. An 18 dB return loss was obtained from 3.415 GHz to 3.694 GHz (FBW = 7.96%).

A Dual-Band Dual-Output Filtering Power Amplifier Based on High-Selectivity Filtering Impedance Transformer

“…To clarify the differences between this work and the previous works, the comparison of FITs is summarized in Table 2. One coupled-line (CL) and two stubs constitute the FIT to realize the impedance transformation with low termination impedance in [5]. Also, two CLs and one stub are utilized to realize the impedance transformation with International Journal of RF and Microwave Computer-Aided Engineering low termination impedance in [9].…”

“…Impedance transformer (IT), as one of the basic components of radio frequency (RF)/microwave systems, can be utilized to achieve the desired impedance matching and the efficient power transmission. To improve the frequency selectivity, various ITs with bandpass response have been widely investigated [1][2][3][4][5][6][7][8][9][10][11] and applied to matching network designs of power amplifiers (PAs) [8][9][10][11]. In [1][2][3][4][5], different coupled-line structure filtering impedance transformers (FITs) with ultrahigh transforming ratio realize low/high termination impedance transformations, respectively.…”

“…To improve the frequency selectivity, various ITs with bandpass response have been widely investigated [1][2][3][4][5][6][7][8][9][10][11] and applied to matching network designs of power amplifiers (PAs) [8][9][10][11]. In [1][2][3][4][5], different coupled-line structure filtering impedance transformers (FITs) with ultrahigh transforming ratio realize low/high termination impedance transformations, respectively. Also, cross-shaped [6] and coupled-line structure [7] ITs are presented, both of which can implement an extremely low/high impedance transformation.…”