Design of a two-LNAs-switch-module for biomedical applications in an L-band radiometric system

A thermally stable L-band switch module containing two very low noise amplifiers, high gain, low insertion loss, and high isolation between the amplifiers input ports is proposed for radiometric medical applications. The modified second stage of a Dicke radiometer front end consists of two low noise amplifiers followed by an SPDT switch. Grounded coplanar waveguides are used as transmission lines between the inputs and output. Negative image modeling technique was employed to design the impedance matching networks of the two low noise amplifiers. At room temperature, the integrated two-LNAs-switch-module has a noise figure below 0.58dB, an input return loss of less than -10dB and 20.5±0.6dB gain between 1.1GHz to 1.6GHz. The switching circuit has an insertion loss below 0.6dB and the measured isolation between input RF ports is less than -60dB. The noise figure of the module was validated at different temperatures. The results show 0.12dB increase in the noise figure when temperature is increased from 25°C to 60°C.