A self-oscillating active filtering antenna with second and third harmonic suppressions

In this paper, a self-oscillating antenna is presented. The proposed circuit consists of an amplifier with positive feedback. In the feedback path, a two-way power divider is utilized for power splitting. One output of the power divider is electromagnetically coupled to the antenna for radiation, and the other is connected to the input of the amplifier through a delay line for positive feedback. To have a good frequency selectivity and harmonic suppression, coupled stepped impedance resonators are utilized to design the power divider. The proposed concept has been validated by simulating and measuring the open-loop gain of a designed circuit. An open-loop gain of 2.3 dB has been measured and shows the possibility of positive feedback for oscillation. A self-oscillating filtering antenna utilizing stepped-impedance resonators has been implemented. The measured harmonic suppression at the second/third harmonic frequency is 28/40 dB.