Microwave Tech - High frequency PCB board parameter extraction

High frequency PCB board parameter extraction

In the high-frequency simulation preset, the PCB material parameter is often a function of the frequency f, not a fixed value, and the PCB manufacturer specifications give a certain type of core or pp chip at the frequency of 1GHz and 10GHz The Dk and Df values.

In order to get the final result of the simulation and the final result of the actual test to be exactly the same as possible, in the sheet material verification stage, for a relatively fixed overlap and wiring structure, it is proposed to obtain the parameters that the sheet material changes with frequency. Office work that cannot be omitted in one item.

Generally, it can be considered appropriate and the Delta-L experimental method is used to propose to obtain the Dk(f) and Df values. The actual S parameter variable of the test sheet is preset in the test board after the preset SPP Coupon strip. This value overlaps with the specific and the board factory The PCB production process is different.

After the wrench returned, the VNA measured the S-parameters of the two coupons, and the AFR was used to embed and remove the parts of the branches introduced by the two SMA connectors. It was proposed to obtain the S-parameters of the naive PCB Trace.

In order to ensure the accuracy of de-embedding, it is necessary to verify the causality of the S-parameter variable after de-embedding. You can make a judgment by looking at the return loss, phase and the corresponding Smith chart. After there is no error, set up a channel simulation board type with a de-embedded board, and propose to obtain the S-parameter variable of a specified length PCB Trace, and check whether the insertion loss curve and phase are abnormal.

How does it meet the expectations in the 20GHz frequency band? At this time, the PCB manufacturer can perform the fitting of the dielectric constant of the sheet according to the overlap and wiring of the actual test version. The fitting process gives priority to debugging Dk and Df to ensure that the phase is basically consistent., And then fine-tune these two parameters to make SDD21 as possible as possible to maintain exactly the same measured value, you can get the Dk and Df values of the sheet material (10GHz) at a certain frequency.

On the basis of this fixed frequency (10GHz), the material properties are modeled according to the Svennsson Djordjevic theory, and the curve of the dielectric constant and the damage tangent of the sheet material with frequency is obtained.

The final function of Dk and Df changing with frequency is the actual parameter of the sheet material in the wide frequency band. This value can be used in subsequent simulations, so that the final simulation result and the actual measured value can be kept exactly the same as possible. Especially suitable for use in 3D full-wave simulation for precise and detailed simulation.

In the process of proposing to obtain the function, there is a basic calculation formula that is easily forgotten. Incorrect calculations often bring orders of magnitude of error. This formula is the polynomial algorithm of complex numbers.

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