Francesco Donzelli

Passive RFID at Millimeter Waves

This paper introduces a novel way to implement passive RF identification (RFID) at millimeter waves. Passive operation is achieved by adding an external mixing element between the tag antenna and a standard RFID chip. The mixing element converts the RFID reader signal from millimeter waves to RFID carrier frequency-the RFID chip operates as usual. Either passive or semipassive RFID circuits at any RFID carrier frequency can be used. The readers TX and RX ports are similarly equipped with external mixers to convert the reader output to millimeter waves and received millimeter-wave signal to RFID carrier frequency. The paper analyses the concept theoretically with a Schottky diode as the mixing element. The design and experimental demonstration of the operation at 10 GHz are presented. Using an EPC-compliant UHF tag integrated circuit and reader, a range of 30 cm is demonstrated, but range extension to over a meter is feasible.

Integration of numerical and field-theoretical techniques in the design of single- and multi-band rectennas for micro-power generation

We introduce an integrated design methodology for the optimization of RF-to-DC conversion efficiency of multi-band rectennas (rectifying antennas), with the aim of harvesting the RF energy available in humanized environments. Existing RF sources can either operate at known frequencies, power budgets, and locations, or can be ubiquitously available at different frequency bands, and with unknown directions of incidence and polarizations. In all cases, the RF link power budget may be extremely low. In order to harvest a significant quantity of energy, it is thus mandatory to place a very special care in the design of each part of the receiving/storing system. For this purpose, the receiving antenna must be optimized together with the rectifying circuit and the load. In our work, this is accomplished by a rigorous design tool based on the concurrent use of nonlinear/electromagnetic (EM) CAD tools and EM theory. The effectiveness of the method is demonstrated by comparing the computed and measured performance of single- and multi-band rectennas, both linearly and circularly polarized. Such antennas are designed to harvest RF energy from a variety of cellular and WiFi systems that are normally present in civil environments.

Transponders for millimeter wave identification

Radio frequency identification at millimeter waves enables new applications, such as high data rate short range communication, location sensing through narrow-beam antennas etc. In this paper two transponders designs for 60 GHz Millimeter wave identification (MMID) system are presented. One transponder consists of a Schottky diode and an antenna on LCP and the other of a backward tunneling diode and an antenna on LTCC. The design, fabrication and measurements of the two designs are presented, and compared to simulations and each other.

A CAD procedure for MIMO link estimation by the combination of nonlinear, electromagnetic and propagation analysis techniques

The paper demonstrates for the first time a CAD procedure for the circuit-level simulation of an entire MIMO link. The multiple transmitting and receiving antennas are treated as multiport radiating systems characterized by EM analysis. In this way the influence of mutual couplings on the frequency-dependent near-field and far-field performance of each element is fully accounted for. The set of transmitters is treated as a unique nonlinear system loaded by the multiport antenna, and is analyzed by nonlinear circuit techniques. In order to establish the connection between transmitters and receivers, the far fields incident on the receivers are evaluated by EM analysis and are combined by extending to the MIMO case an available ray tracing technique. EM theory is used to describe the receiving array as a linear active multiport network. The procedure is applied to several MIMO systems by varying antenna locations. The computation of BER performance at the circuit level is demonstrated.

Nonlinear modelling of reconfigurable microwave components based on resistive MEMS switches

We propose a nonlinear model of a resistive MEMS switch. We describe the nonlinear behaviour of the switch by exploiting an extended harmonic balance (HB) technique allowing the efficient calculation of distortion effects due to MEMS nonlinearities. A comparison with the corresponding capacitive model is also given. As an illustrative example, the results of the simulation of a reconfigurable integrated antenna operated by commercial MEMS switches are compared to measurements.

Efficient Circuit-Level Nonlinear Analysis of Interference in UWB Receivers

The paper demonstrates for the first time a circuit-level approach to the analysis of pulse-UWB receiver front ends in the presence of interfering communication signals. The procedure is based on a model-order reduction harmonic balance technique (MORHB) that has been especially devised to efficiently handle signal spectra including very large numbers of arbitrarily spaced lines. At each step of the nonlinear solution loop the GMRES iteration is used to find an approximate Newton update belonging to a suitable Krylov subspace, and a novel efficient algorithm for performing matrix-vector multiplications is exploited. The resulting simulation tool allows rigorous computation of interference effects on the nonlinear regime of UWB receivers and accurate circuit-level prediction of receiver sensitivity and channel capacitance. Simplifying assumptions typical of system-level approaches are overcome in this way, while keeping computational time at acceptable levels.