Kimmo Rasilainen

Mobile Terminal Antenna Performance With the User's Hand: Effect of Antenna Dimensioning and Location

This letter reports a systematic simulation study of the performance of mobile terminal antennas in the vicinity of the users hand. The effects of antenna dimensioning and antenna location on the ground plane of the device are demonstrated. The studied performance parameters are quality factor, radiation efficiency, and frequency detuning. Based on the results, beneficial approaches and general guidelines for antenna designs with a reduced effect of the users hand can be given. For instance, it is shown that the radiation efficiency with the users hand stays nearly constant (variation <;0.2 dB) despite the changes in the antenna element height (2-6.6 mm at 900 and 2000 MHz).

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.

Implementation of Sensor RFID: Carrying Sensor Information in the Modulation Frequency

An approach that can be used for exploiting the sensing capabilities of RF identification (RFID) is presented and formulated. In this approach, sensor information is carried through the modulation frequency of RFID. The aim of this work is to investigate the sensor concept and to characterize the sensor performance both theoretically and experimentally. Furthermore, the operation of the sensor RF parts and oscillator are described analytically, and the equations are verified by simulations and measurements. The concept is experimentally demonstrated at a single carrier frequency to test its suitability for ultra-high-frequency RFID applications, and shown to be feasible for implementing sensors that can be read across distances up to 14 m.

Antenna Matching at Harmonic Frequencies to Complex Load Impedance

Analysis of a self-resonant, dual-frequency-matched antenna is presented. The operating frequencies of the antenna are harmonically separated, and 1-GHz fundamental and 2-GHz second harmonic frequencies are used. This type of antenna can be used, e.g., in harmonic transponder applications, where the antenna is loaded with a nonlinear element, which is typically a Schottky diode. In this letter, the impedance properties of the studied antenna are investigated using an example Schottky diode. Compared to conventional 50- Ω environments, the frequency-dependent impedance of the Schottky diode provides additional challenges for antenna matching, which are also addressed. Rather than providing a design for an application-specific antenna, the current study presents certain “building blocks” that may be useful for particular antenna designs.

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.

Optimization of RFID Sensor With Frequency Modulation

Sensing capabilities of radio frequency identification (RFID) have recently been investigated both theoretically and experimentally. Frequency-modulated sensors utilize the modulation frequency for carrying sensor information when interrogated by a reader device. This paper derives analytical expressions for optimizing the electrical circuitry of such a sensor, as well as a figure of merit for selecting a suitable diode for rectification. A novel design strategy for optimizing an RFID sensor based on frequency modulation is presented, and it is used to design, fabricate, and experimentally characterize an optimized sensor. The result of this paper shows that a change in the sensor capacitance can be detected across a distance of 15 m with low uncertainty.

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.

Extension to Characterization Model for GPS Antenna Performance in Mobile Terminals

A new, extended model to evaluate the performance of Global Positioning System (GPS) antennas in mobile terminals is introduced. The new model is demonstrated using three different antennas with two orientations, and it is shown to give a more reliable prediction of the GPS antenna performance compared to the earlier model. Also, a new parameter for characterizing the ability of the GPS antenna to reject the reflected waves from the ground is introduced.

Transponder utilizing the modulated re-scattering communication principle

In this work, the performance of a re-scatter transponder is investigated. The transponder is based on a 90° hybrid coupler, and it provides independent amplitude and phase modulation as a function of the bias voltage. The structure operates at a frequency of 3.42 GHz, and the performance of the transponder is investigated using simulations and measurements. The results show that the proposed approach is a viable candidate to implement wireless connectivity for simple, passive and low-cost devices.

Carrier Aggregation Compatible MIMO Antenna for LTE Handset

This paper proposes a two-element LTE MIMO handset antenna with physically different main and diversity antennas. The performance of the design is studied theoretically and experimentally. The investigated design utilises physically different main and diversity antennas to improve especially the low-band MIMO performance. A Combined Parasitic-coupled, Aperture-Matched (CPAM) antenna is used as the main antenna, and the diversity antenna is a simple Capacitive Coupling Element (CCE) design. The antenna covers the LTE bands from 698–960 MHz and 1710–2690 MHz with fixed matching circuits suitable for low-band (LB) Carrier Aggregation (CA). Measured total efficiency of the antennas is from −3 to −6 dB and −2 to −5 dB at the low and high bands, respectively. In the MIMO case, envelope correlation coefficient (ECC) and multiplexing efficiency (η̃mux) are studied also from measurements.