Resonant Modes of a Parallel-plate Waveguide and Radiated Coupling of IC Chips

Abstract

This dissertation proposes a method for using a parallel-plate waveguide to measure the permittivity and thickness of a dielectric plate, explores newly recognized higher-order modes in a parallel-plate waveguide, and presents methods to measure IC chip radiation.The dielectric constant of a dielectric plate with known length, width, and thickness was obtained by measuring the phase difference of the propagating wave in a PPW. A 750 MHz PPW cavity of which both ends are shorted was designed for measuring the thickness of scales formed on steel plates. This measurement method uses the change of the resonance frequency as a function of the thicknesses of the scales on the steel plates inserted at the open sides of the cavity. The dielectric constants were obtained with a 5% tolerance, and the thicknesses of the scales were measured at a 10 µm resolution. When the two plates of a PPW are infinite, transverse higher order modes do not occur, however, if the width is finite, the TEm0 modes that change m times in the transverse direction can be generated. It is found that the cut-off frequencies of the TEm0 modes are even lower than those of the TE1 mode, which are the lowest higher-order modes that change in the vertical direction. Therefore, the TEm0 modes must be considered when using PPWs. The TEm0 modes were evaluated assuming that the boundaries at both sides of the PPW are perfect magnetic conductors

the existence of the modes was verified using a PPW cavity resonating at 1.48 GHz. The effect of the fringing field was analyzed by considering the width-to-height ratio of a PPW. The mechanisms by which the TEm0 modes are generated in PPWs and the effects of these modes are explained. An example is presented that demonstrates how to exploit these modes when designing an RFID tag antenna that operates in stacked steel plates. As the clock speed, power consumption, and circuit density of the high-speed digital circuits increase, the radiated emissions from the IC chips deteriorate the sensitivity of the antennas in mobile equipment. The equivalent current components of the IC chips mounted on a ground plane consist of one electric dipole moment orthogonal to the plane and two magnetic dipole moments tangential to the plane. These three dipole moments were obtained by measuring an IC chip using a TEM cell and a hybrid coupler. A new method to obtain the three dipole moments using a cube-shaped cavity was proposed and simulated. Approximate formulas to estimate the power transmission are proposed when an IC chip and a receiver antenna are in the near-field region. These formulas are expressed in terms of the dipole moments of the IC chip and the effective area of the receiver antenna. To validate these formulas, power transmission experiments were performed at a separation of 50 mm for the 900 MHz band.