An improved two-tier L-L method for characterizing symmetrical microwave test fixtures

An improved two-tier L-L method for characterizing symmetrical microwave test fixtures is introduced in this paper. The improved two-tier L-L method is implemented with two uniform transmission lines having the same characteristic impedance and propagation constants, but different lengths. The ABCD parameters of the test fixture and the embedded device under test (DUT) can be determined by measurements of the two lines and the DUT. To validate the improved L-L method, the two-tier thru-reflect-line (TRL) calibration technique is used. High correlation between the S-parameter data de-embedded with the TRL and with the proposed two-tier L-L validates the method. Moreover, the improved L-L method is not only useful for characterizing the test fixture, but is also useful for determining the line characteristic impedance. The main advantage of the two-tier L-L method over the two-tier TRL is the number of calibration elements. The former method uses two and the latter method uses three.

► The two-tier L-L method allows the characterization of symmetrical test fixtures.
► The two-tier L-L method requires two uniform equal transmission lines, but different lengths.
► The improved two-tier L-L method also allows determine the line characteristic impedance.
► The two-tier L-L method is useful when the impedance of line is different from 50 Ω.
► The two-tier L-L method overcomes the two-tier TRL method when the characteristic impedance is arbitrary and unknown.