Design and Evaluation of Harmonic Transponder

Abstract

Wearable harmonic tags have gained considerable attention as it can be easily worn on the cloths and can easily collect vital information in real time. Harmonic tag is battery- free and lightweight wireless sensor which can benefit various applications like military, detection of objects, tracking of insects etc. This report demonstrates the design and evaluation of compact, low profile harmonic transponder (tags) as a marker for detecting objects or any person. This harmonic transponder consists of symmetrical meandered line antenna operating at two different frequencies and Schottky diode for frequency doubling operation. Transmitting antenna is operating on fundamental frequency i.e., 900 MHz and receiving antenna is operating at second harmonic of fundamental frequency i.e., 1800 MHz. Whenever radio waves impinge on the harmonic tag, the radio waves are then converted into twice of the operating frequency i.e., 1800 MHz using frequency Doubler circuit and then first harmonic signal gets re-radiated back towards the reader. In this project performance analysis and characterization of harmonic tag is investigated both theoretically and experimentally. These harmonic tags can generate response at harmonic of incident radar signal. The dual-ridged broadband horn antenna radiates signals at fundamental frequency of 900 MHz though signal generator which falls on the harmonic tag and scatters off and is then collected by the receiving broadband horn antenna which was connected to the spectrum analyser to detect the reflected signal at fundamental frequency (900 MHz) and twice the fundamental frequency (1800 MHz). The harmonic tag collects incident signals, generate harmonics of incoming signals using diode (SMV2019-079LF) which re-radiate the first harmonic signal towards the receiver. Harmonic tag can eliminate clutter from the surface of the ground and can also enhance signal to noise ratio of received signal. The nonlinear diode is embedded into the substrate and coupled to the antenna for generating higher order harmonics. The polarization of antenna is used to determine the location and direction of the object.