DESIGNING A REFLECTION-TYPE NGD NETWORK USING OPEN AND SHORT SHUNT STUBS FOR WIDEBAND ELECTRICALLY SMALL ANTENNAS
Wireless communication devices such as mobile phones play a vital role in our daily life. They need to cover an increasingly wide frequency band with low profile antennas. Electrically small antennas (ESAs) comply with these requirements. However, they are subject to gain-bandwidth limits when matched with passive matching networks. Non-Foster reactive elements have been proposed to bypass those restrictions. This paper addresses designing negative group delay NGD-based non-Foster networks to overcome stability problems when using Negative Impedance Converters (NICs) in order to realise on-Foster reactive circuits. The NGD network model was designed using open short stubs to achieve a non-Foster behaviour, and to act as a negative capacitor in the frequency range of interest. This technique of compensating the inherent loss of the proposed NGD network in the reflection mode was to realise a new structure of reactive non-Foster elements. It involves a negative resistance amplifier and a Lange coupler. The proposed technique is applicable to antenna matching where both transmit and received capabilities are required. It was simulated and the experimental results of the new NGD network circuit were introduced.