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ECal: an electronic calibration system.

Introduction

ECaL[TM] provides a new, hands-off method for calibration of vector network analyzers. The ECal electronic calibration system replaces the error-prone time-consuming mechanical process with a single connection to an extremely repeatable, variable impedance, solid-state calibrations standard. With this single connection, ECal can create a 12-term, two-port error model and then provide a confidence check or verification of the calibration. This result is achieved in a single connection for all types of connector configurations, including insertable, noninsertable and even transitional. The accuracy of the calibration is enhanced by the reduction in connector nonrepeatability. Also, due to the one time connection, the product is physically more convenient, less prone to operator error and less damaging to the measurement system.

A traditional coaxial calibration, when done carefully, can take 10 minutes or more for an insertable device. Noninsertable device calibrations are more complex and can take significantly longer. Electronic calibrations for both insertable and noninsertable devices can be done in a minute. The convenience and simplicity of this procedure should be of great interest to network analyzer users.

Background

The ECal tuner was derived from the solid-state tuner used in noise parameter and load pull measurement systems. In trying to quantify the repeatability of the tuners for the device characterization application, it was determined that the tuner was at least as repeatable as the network analyzer, if not better. Therefore, if the tuner was more repeatable than the network analyzer, then the tuner could be used to calibrate the network analyzer. The tuner's application was evaluated as a transfer calibration standard. ECal's resettability was evaluated at two parts in [10.sup.5] or -94 dB in return loss with a six-port analyzer. This repeatability, 30 dB better than a torqued 7 mm connector, enables ECal to be used in this application.

Technique

The ECal technique presents a number of well known, repeatable states or standards to the network analyzer. By measuring three uncorrected reflection coefficients by the VNA from three known states at port 1, ECal can determine the directivity, source match and reflection tracing errors for the forward direction. This comprises the one-port error model for the VNA. The same process is repeated at port 2 for the reverse directivity, source match and reflection tracking. ECal then presents greater than 100 dB isolation between its ports and measures the forward and reverse isolation coefficients. Using the calibrated one-port error coefficients and the known ECal thru, ECal can determine the forward and reverse load match error coefficients. Measuring known ECal forward and reverse thru states, ECal determines the forward and reverse transmission tracking errors, completing the calibrations. At this point, a unique feature of ECal is implemented. ECal presents a verification state, which is not used in the calibration. This state is then measured and compared to its known value. The system checks itself. A complete description of this technique has been presented previously.[1]

ECal Product Description

ECal is comprised of a mainframe controller unit and one or more two-port, solid-state calibration standards, depending upon the connector type. For sexed connector types, three units are provided, including female/female, male/male and male/female. Having a noninsertable standard eliminates the tedious process of two complete calibrations and adapter removal. For APC-7 connectors, one unit is provided.

The mainframe controller unit controls the network analyzer, exercises ECal and generates the calibration. It is actuated from the front panel of the VNA. Each ECal module comes with a characterization disc generated at the factory calibration laboratory. This disc contains the known values of ECal and its verification states. These data are generated with the greatest accuracy possible, namely with a precision TRL cal kit. ECal can then transfer that high level of accuracy to any network analyzer. Metrology level accuracy can be achieved in any laboratory setting.

Other products in the ECal product family include ECal characterization software for calibration laboratories to maintain their own ECal characterizations, and Custom ECals. Custom ECals can be built in any connector types, for example, type N to waveguide or nonstandard connectors, such as blindmate. In addition, ECals can be made for multiport device test sets to reduce the complexities of multipath S-parameter calibration.

References

[1.] Vahe Adamian, "A Novel Procedure for Network Analyzer Calibration," ARFTG Digest, Spring 1993.

[2.] Glenn F. Engen, Robert Judish and John Juroshek, "The Multi-State Two-Port, A Transfer Calibration Standard," ARFTG Digest, Spring 1993.
COPYRIGHT 1993 Horizon House Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Publication:Microwave Journal
Date:Sep 1, 1993
Words:733
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