Design of a multimode tunable low noise amplifier for software defined radios

This Letter presents the design and analysis of a tunable low noise amplifier (LNA) capable of achieving single band, dual band and wideband operations. The circuit features a modified tunable open stub matching to achieve a reconfigurable multiband response. The LNA adopts a varactor diode in the input matching stage to achieve reconfigurable modes. Two bias conditions for the varactor diode are analysed. The forward bias condition yields a wideband mode (1.6 to 2.5 GHz) and zero bias results in a concurrent dual band mode (0.9 and 1.7–2.5 GHz). In reverse bias condition, the bias voltage of varactor diode ( V d − rb) can be tuned to achieve one single band mode (1 GHz), and a tunable concurrent dual band mode, where the first band is fixed at 1 GHz and the second band is continuously tunable from 1.7 to 2.5 GHz. The LNA is fabricated in microwave integrated circuit process on an FR‐4 board. The measured power gain is 7–15 dB and noise figure is 1.2–2.2 dB across all bands. The measured 1 dB compression ( P 1dB) is − 4 , − 3 and − 6dBm at 0.9, 1 and 2.4 GHz, respectively.