The Effect of Phase Continuity on Synchronous Antenna Tuning

Synchronously tuning a narrowband antenna at the symbol rate of a frequency shift keyed (FSK) modulation has been shown to increase the efficiency of the transmitter. When tuning by switching between a set of matching networks, it is important to not only have phase continuity between the symbols but to also switch at a precise phase in the transmitted signal, which restricts the usable FSK frequencies. When tuning by changing the reactance of a single tuning circuit, it is not obvious that strict phase control between symbols is necessary. This paper investigates the importance of the phase of a FSK signal at symbol transitions when synchronously tuning by changing the capacitance of a varactor diode on the antenna.