Generalised MIT in a tri‐band LNA

In this study, the authors propose a generalised multiband impedance transformer (MIT), which can transform the frequency-dependent complex loads at multiple arbitrary bands simultaneously. The proposed transformer has two parts: the multiple frequency-selection sections consisted of the series–parallel branches and the π-shape impedance transformer is composed of the multiple series transmission lines. Analytical equations are derived for the closed-form solutions and the rules of electrical parameters. Numerical examples are examined to verify the validity. On the basis of printed circuit board, a single-stage tri-band low-noise amplifier (LNA) with the proposed MIT is designed, simulated, and measured for practical application. The measured LNA maintains the tri-band performance and the 3 dB bandwidths are 400, 250, and 50 MHz with the 15, 12, and 7 dB minimum gain, respectively. The minimum input return losses are −24, −13, and −11 dB corresponding to the three bands, and the output return loss is lower than −10 dB from 1.5 to 2.6 GHz. The minimum input third-order intercept points are 4.1, 6.2, and 14.7 dBm, respectively. Besides, the noise figures (NFs) are 1.9, 2.6, and 5.0 dB separately at the centre frequencies of 1.8, 2.23, and 2.47 GHz.