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85072A 10-GHz Split Cylinder Resonator

Technical Overviews

Part of the complete turn-key solution for the IPC test method TM-650 2.5.5.13

Features

  • Measures complex permittivity and loss tangent of thin film, un-clad substrates and low loss sheet materials
  • Complies with IPC test method TM-650 2.5.5.13
  • Works with Keysight Technologies, Inc. resonant cavity software
  • Innovative design is robust and easy to use
  • Depending on sample properties, higher frequency modes may also be measured

The Keysight 85072A split cylinder resonator measures relative permittivity and loss tangent of thin film, un-clad substrates and low loss sheet materials. An Keysight vector network analyzer, cables and software, purchased separately, complete the test system.

The split cylinder resonator is a cylindrical resonant cavity separated into two halves. The sample is loaded in a gap between the two cylinder halves. One cylinder half is fixed, and the other adjusts allowing the gap to accommodate varying sample thicknesses. In order to measure the TE0np modes in the resonator, a small coupling loop is introduced through a small hole in the side of each cylinder half.

Electric Field Orientation

The electric field is parallel to the sample and perpendicular to the z axis of the cylinder halves. To achieve the highest sensitivity of the split cylinder resonator, the sample is placed where the electric field is at its maximum. Because of the symmetry of the cylinders, this occurs in TEOnp modes where p, the number of half wavelengths along the cylinder z axis, is an odd integer.

The real part of permittivity, ε’, and loss tangent or tan delta, tanδ, are calculated from the sample thickness, cylinder length, and S-parameter measurements of the split cylinder resonator, both empty and loaded with the sample. Using a mode matching model developed at NIST in Boulder, Colorado, permittivity and loss tangent can be calculated at the TE011 mode as well as higher order TE0np modes [2].

When the sample is loaded into the split cylinder resonator, the resonant frequency will shift downward so the measurement frequency is always lower than the frequency of the empty split cylinder resonator. The amount of frequency shift is dependent on the real part of permittivity and thickness of the sample. By varying the thickness of the sample, it may be possible to target a specific measurement frequency. It is also possible that the measurement frequency may shift down into a range where interference from other non-TE modes can cause distortion and decrease the accuracy of the measurement. Increasing or decreasing the thickness of the sample may shift the measurement frequency away from the interfering mode.

The quality factor, or Q factor, of the split cylinder resonator will also decrease when the sample is loaded into the split cylinder resonator. The amount of decrease is dependent on the loss tangent and the thickness of the sample. Thick or lossy materials can decrease the Q factor enough to cause the split cylinder resonator not to resonate properly making it difficult or impossible to measure these materials. Making samples thinner may help increase the Q factor, but for some lossy samples it may not be possible to make them thin enough to measure. Therefore the split cylinder resonator is only recommended for low loss materials.

Keysight’s split cylinder resonator is designed for robustness and ease of use

The 85072A has lightweight aluminum cylinders are diamond turned for the best possible surface finish and then plated with copper and gold for better conductivity and durability. They have a kinematic mount for precise, rigid alignment of the cylinders. These features allow for a high Q cavity and the best loss tangent resolution. The side mounting of the cylinders allows for large samples to be measured. An integrated digital micrometer measures the sample thickness at the time of the measurement. Electrical coupling into the cavity is adjustable with large dials on the top of the fixture, while the coupling loops and cabling itself is protected under protective covers.

Keysight’s resonant cavity software guides you through the whole setup and measurement process

Keysight’s resonant cavity software, purchased separately, calculates permittivity and loss tangent using algorithms developed at NIST’s Electromagnetics Division in Boulder, Colorado [2]. It provides an intuitive user interface, controls the network analyzer, guides the user through the setup and measurement process and displays the results. Special features developed for the split cylinder resonator help the user select the correct TE0np modes, determine if they useable, and set the optimum input coupling. It has an application programmable interface (API) which allows the user to develop customized software for their individual needs.

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