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A wide-band test fixture is designed for the measurement of parasitic effects of RF passive SMD (surface mounted devices) components. Two calibration methods, TRM (Thru-Reflect-Match) from 45 MHz to 2 GHz and TRL (Thru-Reflect-Line) from 2 GHz to 12 GHz, are used for error correction. The measurement standards and fixture are designed based on these two calibration methods. For experimental verification, the multilayered ceramic SMD capacitors of Johanson Technology are measured. The parasitic effects of the SMD capacitors are analyzed. The designed fixture is feasible and applicable for quick and accurate measurement of RF passive SMD components.

With the development of electronic technology, SMD components have been widely used in the design of microwave circuits and wireless communication systems. Therefore, studying the SMD component measurement methods and extracting accurate high-frequency component characteristic parameters in high frequency are very important. However, for conventional SOLT (Short-Open-Load-Thru) calibration method, with the increase of the operating frequency, the parasitic effects caused by the calibration standards increase, especially by the fringing capacitance of the open standard. The fringing effect of open standard can be adjusted by using EM modeling and inputting the model value into the VNA. For TRL (Thru-Reflect-Line) calibration method, the calibration bandwidth is limited by the line standard due to the line phase ambiguity, where the eigenvalue matrix becomes unitary and can cause measurement inaccuracy, if only one LINE is used [

TRL calibration is based on the ten-term error model (shown in Figure

The ten-term error model of a two-port network.

For reflection calibration, the reflect standards (open-circuited or short-circuited) are connected to the measurement ports. The reflection coefficient is

Besides the ten error terms, the reflection coefficient Γ_{R} of the reflect standard and the phase constant

Then the real

Since the calibration algorithm has been determined, the next step is to design the measurement fixture. In our work, the measurement standards are designed firstly. For an ideal thru standard, its impedance should match the standard characteristic impedance of the system. The impedance and electrical length of a microstrip line can be calculated as [

The structure of the thru standard.

As for the reflect standard, the phase of the reflection coefficients of the two ports should be the same. Therefore, the reflect standard should be symmetrical. In real applications, the reflect standard can be either open-ended or short-ended. But for the open-ended structure, the fringing capacitance cannot be neglected, especially at high frequency range, which can deteriorate the measurement results considerably. So in order to achieve better calibration, the short-ended structure is adopted. The reflect standard is shown in Figure

The structure of the reflect standard.

Compared with the thru standard, the line standard should have the same characteristic impedance but with a longer phase delay. For measurement accuracy, the phase delay should be controlled between 20° and 160° to avoid phase ambiguity [

The structure of the line standard.

The final measurement standard is the match standard. The key to designing a good match standard is to avoid reflection at the ports [

The structure of the match standard.

SMD components have many different packaging types. The 1210 packaging with length of 2.0 mm, width of 1.25 mm, and height of 0.5 mm is most commonly used. Therefore, in our experiment, the SMD capacitors with 1210 packaging type are measured and analyzed. The structure for measuring SMD components is shown in Figure

The structure for measuring SMD component.

Based on the calibration standards and the measurement structure, the measurement fixture is designed and shown in Figure

The structure of the measurement fixture.

The photograph of the designed measurement equipment.

An SMD capacitor is not an ideal capacitor due to its parasitic effects. The equivalent circuit model of the SMD capacitor is shown in Figure

The equivalent circuit model for SMD capacitors.

When the working frequency exceeds

The next step is measurement. The measurement is performed using the vector network analyzer HP8510B and the photograph of the measurement setup is shown in Figure

Calibrate the VNA from 45 MHz to 12 GHz.

Measure the

Measure the SMD capacitors on the measurement structure. Copy the measurement data into the computer.

Calculate the corrected data using Matlab based on (

The photograph of the measurement setup.

In our experiment, multilayered ceramic SMD capacitors with the values of 2.0, 3.9, 5.6, 8.2, 10, 18, 30, 47, and 100 pF have been measured. Here, we take the 2.0 pF capacitor as an example to show the measurement results. The measured

The measured

The reference

From Figure

The effective capacitance of the capacitor.

In our experiment, other capacitors with values of 3.9, 5.6, 8.2, 10, 18, 30, 47, and 100 pF are also measured, and the results are shown in Figure

The measured results of other capacitors.

In this paper, a wide-band test fixture is designed for the measurement of parasitic effects of RF passive SMD components. Two calibration methods (TRM and TRL) are used. Good results have been achieved. The proposed test fixture can be applied to measure SMD components from VHF band up to X band.

The authors declare that there are no conflicts of interest regarding the publication of this paper.

This work is supported by the National Natural Science Foundation of China (Grant nos. 61301022 and U1430102).