Improve mm-wave measurement repeatability and accuracy by increasing coaxial connector pin gap

For decades, we were taught that connector pin gap must be kept to a minimum to reduce reflection and hence improve device performance and measurement accuracy. Yet, measurement inconsistencies were observed between calibration methods, such as sliding load, TRL and offset short, especially at frequencies above 18 GHz. Measurement repeatability was another frustrating experience for practitioners of high precision measurements, such as TRL calibration. The root cause of these measurement inconsistencies wasn't identified until recently. The "connector and gap effect" was discovered and finally these measurement inconsistencies can be explained with an appropriate model. This paper will review the observed measurement issues, present the theoretical base of the connector effect and show how measurement accuracy can be improved.