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Agilent AN 1287-4 Network Analyzer Measurements: Filter and Amplifier Examples Application Note Table of Contents 2 Introduction 2 Measuring a Filter 3 Error Correction for Accurate Passband Measurements 4 Swept-Power Amplifier Measurements 5 Evaluating AM-to-PM Conversion Introduction The network analyzer is used for a variety of device and component charac- terization tasks in both laboratory and production environments. This highly accurate instrument can evaluate both active and passive components for measurements of a filter and amplifier, as will be demonstrated in this applica- tion note. With the addition of time-domain capability, a network analyzer can also gate out unwanted responses during measurements, leaving only the desired information. Agilent Technologies offers a wide range of RF and microwave network analyz- ers for measurements from DC to 110 GHz. These instruments are available with a wide range of options and test sets to simplify measurements in stand- alone and automatic-test-equipment (ATE) setups. Often, both the magnitude and phase behavior of a component can be critical to the performance of a communications system. A vector network analyzer can provide information on a wide range of these devices, from active devices such as amplifiers and transistors, to passive devices such as capacitors and filters. This application note illustrates swept-frequency measurements on an RF filter, and swept-power measurements on a communications-band amplifier. The amplifier is typical of those used in Global System for Mobile Commun- ications (GSM) service. Measuring a Filter Complete characterization of filters is typically achieved with swept-frequency measurements. Shown in Figure 1 are the frequency responses of a filter. On the left and bottom we see the transmission response in log magnitude format, and on the right we see the reflection response (return loss). The most commonly measured filter characteristics are insertion loss and bandwidth, shown on the lower plot with an expanded vertical scale. Another common measured parameter is out-of-band rejection. This is a measure of how well a filter passes signals within its bandwidth while simultaneously rejecting signals well outside that same bandwidth. A test system's dynamic range generally determines how well it can evaluate this characteristic. CH1S11 log MAG 5 dB/ REF 0 dB CH1S21 log MAG 10 dB/ REF 0 dB Cor Stopband 69.1 dB rejection CENTER 200.000 MHz SPAN 50.000 MH