Jari-Matti Hannula

On Design and Evaluation of Harmonic Transponders

Performance and characterization of harmonic transponders is investigated both theoretically and experimentally. The harmonic response of a transponder based on a Schottky diode is analytically derived in the case when the excitation power is low. Theoretical calculations prove that at high frequencies, capacitive nonlinearity contributes more to frequency multiplication than resistive nonlinearity. This means that the feasibility of a particular diode for harmonic transponder applications largely depends on its varactor properties. Figures-of-merit (FOM) are derived both for the mixing diode and the transponder antenna. The validity of the proposed theoretical model is investigated experimentally using a harmonic transponder operating at 1 GHz fundamental frequency.

Harmonic Transponders: Performance and Challenges

Performance of a harmonic transponder strongly depends on the properties of the antenna and diode used, which makes finding a good combination of them very important. For a transponder with a fixed antenna geometry, the effect of different diodes is analyzed through electromagnetic simulations and theoretical calculations. The antenna used in the transponder is directly matched to the impedance properties of a particular diode. Effects of both detector and varactor diodes on the return loss characteristics of the antenna and the obtainable transponder response are observed. Criteria for selecting a suitable diode are given. Benefits and drawbacks of using different antenna matching techniques are discussed, and principal design steps are given both for transponders matched directly to the antenna and for transponders with external matching circuits.

Concept for Frequency-Reconfigurable Antenna Based on Distributed Transceivers

This letter presents a new concept for frequency-reconfigurable antennas. The concept involves a multiport antenna, whose elements are mutually coupled. By properly weighting the excitation signals in each port, the total reflected power can be minimized, and radiation efficiency maximized. Different frequency components of the transmitter can be weighted differently to obtain broad instantaneous band. The concept is studied by simulations.

Characterization of Transponder Antennas Using Intermodulation Response

The intermodulation measurement technique enables measuring transponder antennas without any cable connections. This contactless technique exploits the inherent nonlinearity of the transponder to generate intermodulation products that can be measured. In this paper, we relate the transponder antenna properties to the intermodulation response, and use this relation to calculate the gain and impedance matching of the transponder antenna. Additionally, we consider the limitations of the measurement method and present three different measurement geometries for measuring the radiation pattern. The presented equations and methods are experimentally verified by measuring an example harmonic transponder.

Designing Harmonic Transponders Using Lumped-Component Matching Circuits

Design of harmonic transponders is presented in a case when the harmonic operating frequencies are implemented with a separate matching circuit based on lumped components. The required frequency multiplication is generated by a diode, and both varactor and detector diodes are investigated. Benefits and drawbacks of the proposed design compared to completely self-resonant transponder antennas are considered. Transponders are designed for three different diodes. Based on the obtained results, it can be seen that when using a matching-circuit-based transponder, antenna design is more straightforward. The main design challenge in this approach becomes finding a suitably well-performing matching circuit and circuit topology.