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Introduction

As Over-the-Air (OTA) testing is becoming standardized and is being adopted by network providers, more pressure is being exerted on the RF engine in a mobile device to improve its performance in real-world scenarios. No formal specifications have been standardized as of yet for the performance results of a mobile device that has undergone OTA testing. However, the Cellular Telecommunications Industry Association (CTIA) has established the methods for OTA testing and some network providers have set their own specifications. OTA testing methods that are used to test a mobile device will be discussed with the concentration being on the performance parameter that more closely relates to the power amplifier (PA) in a GSM (Global System for Mobile Communications) system, the Total Radiated Power (TRP). A method of testing which presents conditions to the PA that closely imitate the conditions presented during OTA testing is also discussed. This allows the TRP performance of the PA to be evaluated. Test results from two GSM PA modules are presented and compared, one being TRP compliant and the other being non-compliant.

Overview

As OTA testing requirements are developing, the TRP of the power amplifier is becoming increasingly important. Classically, the output power of a PA has been measured and evaluated into a 50 ohm load impedance; however, the load impedance presented to the PA by the antenna of a mobile device can vary significantly in real world applications. The cellular industry has realized that a better evaluation of the RF performance of a mobile device can be achieved through OTA testing. The TRP performance associated with the PA is significantly affected by varying load impedance, and these affects can be measured by simulating an OTA testing environment for the PA. Currently, the most advanced specification on this matter has been put forth by CTIA. The current specification published by CTIA is revision 2.1 of the Test Plan for Mobile Station Over the Air Performance. The 3rd Generation Partnership Project (3GPP) and the European Telecommunication Standards Institute (ETSI) appear to also be working on a specification standard, but there is no known publication date as of this writing. The CTIA specification only describes the method of testing and does not, at this point, state any kind of numerical results.

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