Differentially fed multilayer antennas with harmonic filtering for push-pull Class B Power Amplifier integration

In this paper, a contactless method of spatially coupling differential signals from a transmission line with harmonic trap filtering to an antenna structure is described. A differential signal is used to generate a maximum current (short circuit) under the antenna and electromagnetic energy is efficiently coupled from the transmission line to the antenna via a single aperture. In this case, the transmission line is like a power divider/combiner into the antenna feed. As this circuit is to be co-integrated with a Class B Power Amplifier, the harmonic trap or bandstop filter (BSF) is essential for harmonic termination within the transmission line. It is to work in parallel to suppress 2^nd and 3^rd harmonics respectively. Further mismatch at fundamental (f₀ = 2.062 GHz) occurs when a simple stub based dual BSF is employed. Hence, electrical length adjustment or tuning has been done to match the fundamental to 50Ω. This technique offers advantages of tight and very neat integration for Class B Push-pull amplifier with better antenna performance, and enhanced immunity from common mode interference.