Design of a Dual-Band Low-Noise Amplifier with a Novel Matching Structure

This paper proposes a method for designing a dual-band low-noise amplifier (DB-LNA) using a new improved complex impedance dual-band transformer (IDBT). This complex IDBT is composed of parallel-coupled lines and two sections of series microstrip lines. The parallel-coupled lines are used to complete the transformation from complex impedances at two different frequencies to a pair of conjugate complex impedances, meanwhile eliminating the need for DC blocking capacitors. The transformation to real impedances is achieved by series microstrip lines at dual frequency points. A single-stage DB-LNA was designed using the BFP840ESD transistor in combination with the proposed IDBT. The fabrication and testing of the Printed Circuit Board (PCB) were then completed. The measured results of the proposed 2.4/5.5 GHz DB-LNA show an S21 parameter of 20.3/14.7 dB, an S11 of -29.8/-20.3 dB, an S22 of -15.2/-16.4 dB, and a noise figure (NF) of 1.6/1.6 dB. The whole DB-LNA has a simple structure, low cost, and excellent performance and is easy to tune.