Balanced-type Circular Disk Resonator Research Articles

A Novel FDTD Approach Considering Frequency Dispersion of FR-4 Substrates for Signal Transmission Analyses at GHz Band

High-speed digital signaling can cause various signal integrity and electromagnetic interference problems. Signal attenuation and distortion can be observed in the gigahertz band owing to the frequency dispersion of substrates. In this article, we propose a frequency-dependent finite-difference time-domain (FDTD) approach for the numerical analyses of flame-retardant type-4 (FR-4) substrates. The proposed FDTD approach provides accurate broadband solutions because it can take into account the frequency dispersion of the substrate. First, the broadband complex permittivity of FR-4 substrates was measured using a balanced-type circular disk resonator and fitted into a Djordjevic model for the FR-4 substrates. Second, we adapted the fast inverse Laplace transform and Prony methods to find the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -domain expressions and incorporate them into the FDTD formulation.The validity of the proposed approach was demonstrated by comparing the numerical and experimental results of the differential insertion loss and phase constant of differential microstrip lines. Both results were in good agreement, indicating the validity and usefulness of the proposed approach for simulations of broadband signal transmission in FR-4 substrates.

Broadband complex permittivity and conductivity measurements in the millimeter-wave bands over variable temperatures using a balanced-type circular disk resonator

A broadband measurement system is developed to address the issue of temperature dependence of the complex permittivity and conductivity of low-loss substrates in the millimeter-wave bands for fifth/sixth generation wireless communication applications. The developed system can provide broadband material measurements from less than 20 GHz to over 100 GHz over variable temperatures by utilizing higher order mode resonances of a balanced-type circular disk resonator (BCDR). The broadband measurement capability of the developed system is attributed to the mode-selective behavior of the BCDR over a wideband. To demonstrate the developed system, we measure the complex permittivity of the following three substrate materials over variable temperatures from 25 °C to 100 °C: cyclo-olefin polymer (COP), ceramic-filled polytetrafluoroethylene composites, and fused silica. Furthermore, the temperature dependence of the conductivity of the surface-mounted metal is characterized for the COP substrate. The measurements indicate that the loss tangents and conductivities of the substrates increase and decrease, respectively, with the temperature and frequency in the millimeter-wave bands. The full-wave simulations using the measured complex permittivity and conductivity of the COP substrate reveal that the propagation loss of the microstrip line using the COP substrate increases with the temperature and frequency and that the increase in the loss is primarily attributed to the decrease in the conductivity.

PTFEを装荷した平衡形円板共振器を用いたマイクロ波・ミリ波帯における中損失基板の厚み方向複素誘電率測定

PTFEを装荷した平衡形円板共振器を用いたマイクロ波・ミリ波帯における中損失基板の厚み方向複素誘電率測定

D-Band Perfect Anomalous Reflectors for 6G Applications

We demonstrate anomalous reflectors at 140 GHz for the application of 6G communication coverage expansion. The reflectors are designed on cyclo-olefin polymer (COP) substrates on the basis of measured complex permittivity and conductivity at millimeter frequencies obtained with the balancedtype circular disk resonator method. From full-wave simulations, we confirm that nearly perfect anomalous reflection characteristics are realized with suppressed parasitic reflections in undesired directions. The simulated efficiencies excluding the material losses of the reflectors designed with the reflection angle θR = 30°, 45°, 60°, and 75° are 99.5%, 98.9%, 99.7%, and 99.8%, respectively. In addition, we fabricate the designed reflectors on the COP substrates and experimentally evaluate their anomalous reflection performances. The measured overall efficiencies of the reflectors with θR = 450, 600, and 750 are 88.0%, 83.6%, and 81.6%, respectively. This is the first demonstration of highly efficient anomalous reflectors in the D-band.

Broadband Conductivity Measurement Technique at Millimeter-Wave Bands Using a Balanced-Type Circular Disk Resonator

We propose a broadband conductivity measurement method in the millimeter-wave bands using a balanced-type circular disk resonator (BCDR). Because of the unique feature of the BCDR's mode selective behavior over a wide band, the proposed technique can provide broadband conductivity measurements from less than 20 GHz up to over 100 GHz with a single closed-type resonator utilizing higher order mode resonances. We consider three measurement scenarios for the proposed BCDR-based broadband conductivity measurements. First, we discuss the absolute measurements of copper conductivity and then consider the relative conductivity measurements for metallic disks with reference to copper conductivity obtained in the first scenario. Finally, the second scenario is extended to the interface conductivity measurements of copper-clad substrates. The proposed measurement scenarios are demonstrated both numerically and experimentally in the millimeter-wave bands with uncertainty evaluations. The proposed technique can contribute to the development of advanced materials and implementation processes of planar circuits for various millimeter-wave applications, including 5G and 6G.

Broadband Permittivity Measurements up to 170-GHz Using Balanced-Type Circular-Disk Resonator Excited by 0.8-mm Coaxial Line

This paper describes the broadband permittivity measurements up to 170 GHz of plate samples by using a balanced-type circular-disk resonator (BCDR) excited by a 0.8-mm coaxial line. Because only the TM ${_{0m0}}$ modes are selectively excited in the BCDR and their resonant frequencies largely change by changing the size of the circular disk that constitutes the resonator, the BCDR method provides permittivity measurements at an almost arbitrary frequency across a wideband. We have increased the maximum measurable frequency of the BCDR method to 170 GHz by developing a BCDR excited by a 0.8-mm coaxial line and by improving the analysis method. We demonstrated that highly stable and rather simple permittivity measurements up to 170 GHz can be realized by the BCDR method by confirming that the measured complex permittivities of a low-loss material from 11.3 to 167 GHz at 59 frequency points obtained with five circular disks of different radii are consistent within the uncertainties.

Microwave Characterization of Copper-Clad Dielectric Laminate Substrates

Microwave measurement methods necessary to characterize copper-clad dielectric laminate substrates are reviewed to realize more precise design of planar circuits: that is, the balanced-type circular disk resonator method for the relative complex permittivity in the normal direction e rn and tan δ n , the cavity resonator method and the cut-off waveguide method for one in the tangential direction e rt and tan δ t , and the dielectric resonator method for the surface and interface conductivity of copper foil σ s and σ ι . The measured results of the frequency and temperature dependences of these parameters are presented for a PTFE substrate and a copper-clad glass cloth PTFE laminate substrate.