A novel frequency doubling active microstrip transponder

A new frequency doubling active microstrip transponder is presented. The frequency doubling is achieved from harmonics generated by non-linear devices connected in push-push configuration. Two rectangular half wavelength microstrip antennas are used for transmitting and receiving. The frequency doubling circuit and receiving antenna are integrated to minimise the losses and for compactness of the transponder. Two outputs in anti-phase from the receiving patch antenna are amplified non-linearly using MMICs and combined in phase, which suppresses the fundamental and enhances the second harmonic which is transmitted from a second patch antenna. The experimental results achieved are presented in the paper