Abstract
As many emerging technologies require the use of high-speed signals, the understanding of dielectric properties of materials used in manufacturing printed circuit boards (PCBs) is an essential aspect for accurate high-speed circuit designs, especially at millimeter-wave (mm-wave) frequencies. This work demonstrates a methodology for extracting complex relative permittivity of dielectric substrates covering mm-wave frequencies. For this purpose, low-temperature cofired ceramic (LTCC) substrate was measured up to 85 GHz and its complex relative permittivity was extracted. The approach used in this work is based on multiline thru–reflect–line (TRL) calibration for measuring the propagation constant and electromagnetic (EM) simulations to estimate the losses contributed by the conductor while accounting for surface roughness. An estimate of complex relative effective permittivity is obtained, from which the actual relative dielectric constant and the loss tangent of LTCC substrate are extracted. The estimated values for the relative dielectric constant and the loss tangent show an excellent agreement compared with the results obtained via split cavity resonator measurements.
Highlights
W ITH the increasing usage of higher frequencies in modern communication systems, it becomes necessary to have broadband measurements of the complex relative permittivity of dielectric substrates used to manufacture Printed Circuit Boards (PCBs)
The approach used in this work is based on the multiline TRL (Thru-Reflect-Line) calibration DeGroot2002, Marks1991a for measuring the propagation constant, and electromagnetic (EM) simulations to estimate the losses contributed by the conductor while accounting for surface roughness
As alluded to in the introduction section, methods to measure the complex permittivity of dielectric substrates is hard to generalize at mm-wave frequencies
Summary
W ITH the increasing usage of higher frequencies in modern communication systems, it becomes necessary to have broadband measurements of the complex relative permittivity of dielectric substrates used to manufacture PCBs. E.g., Popovic2020, Marks1991, they assume that the loss tangent tanδ of the dielectric is very low, allowing them to neglect the term G/(ωC) They would assume that the distributed capacitance C is frequency-independent, measuring its value in the quasi-static sense Williams1991. These assumptions are generally valid if we discuss near-lossless materials and TEM propagation. We should mention that other methods to characterize a dielectric substrate are based on model optimization, e.g., Zhang2010 In such cases, the objective is to fit the frequency-dependent RLGC model to S-parameter measurements. Sec. ?? and ?? present the conducted experiment and finish with a conclusion
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