Embedded cavity based dielectric loss measurements for LTCC substrates up to 110 GHz

In literature there exists manifold techniques for measuring the permittivity of substrates. Printed circuit board (PCB) based methods like dielectric resonators are in general limited to determine the absolute value of the complex permittivity since e.g., a half wave resonator only provides information on the electrical length, which is inversely proportional to the square root of the absolute value of the permittivity. Additionally, dielectric loss measurements are more difficult, expensive and often limited to discrete frequency points due to resonance based measurement principles. In this paper, a PCB based dielectric loss measurement system is presented, operating from a few GHz up to 110 GHz, which is based on a differential measurement of a microstrip line on dense low temperature cofired ceramics (LTCC) and a microstrip on a LTCC layer with an embedded cavity. The cavity reduces the dielectric loss of the transmission line by replacing a certain amount of substrate with air. Subsequent electromagnetic time domain field simulations allow the dielectric loss assignment over the measured transmission frequency range.