This is a part of the project “Radio telescope system” working at 1.42 GHz, which includes designing of patch antenna and LNA. The main objective of this project is to design a two stage low noise amplifier for a radio telescope system, working at the frequency 1.42 GHz. Finally our aim is to design a two stage LNA, match, connect and test together with patch antenna to reduce the system complexity and signal loss.
The requirements to design a two stage low noise amplifier (LNA) were well studied, topics including RF basic theory, layout and fabrication of RF circuits. A number of tools are available to design and simulate low noise amplifiers but our simulation work was done using advanced design system (ADS 2004 A). The design process includes selection of a proper device, stability check of the device, biasing, designing of matching networks and layout of total design and fabrication. A lot of time has been
spent on designing of impedance matching network, fabrication and testing of the design circuits and finally a two stage low noise amplifier (LNA) was designed. After the fabrication work, the circuits were tested by the spectrum analyzer in between 9 KHz to 25 GHz frequency range. Finally the resulting noise figure 0.299 dB and gain 24.25 dB are obtained from the simulation.
While measuring the values from the fabricated circuit board, we found that bias point is not stable due to self oscillations in the amplifier stages at lower frequencies like 149 MHz for first stage and 355 MHz for second stage.
Source: Halmstad University
Author: Aitha, Venkat Raman | Imam, Mohammad Kawsar