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Agilent Technologies Pulsed Measurements with the Agilent 8720ES and 8753ES Network Analyzers Product Note Introduction High-performance vector network analyzers are used to characterize the frequency responses of various RF and microwave components. While most network analyzers are used to measure continuous signals, some users have a need to pulse the RF signal on and off. The need for pulsed signals arises for various reasons. It might be because the total power input to the device under test must be limited to prevent overheating, or because the component will only operate under pulsed conditions, or because the component behaves differently in response to pulses than it does to steady state inputs. Whatever the reason, pulsed RF creates a unique set of conditions that must be addressed in order to produce reliable measurement results. It is commonly presumed that only network analyzers such as the Agilent 8510C or the 85108A that incorpo- rate sophisticated timing circuits, dual reference chan- nels, and wide IF bandwidths are suitable for measurements of pulsed systems. However, the aim of this product note is to show that under certain condi- tions, network analyzers such as the 8720ES and 8753ES can produce good results at a much lower cost. The principles in this product note apply to either model, and to some earlier models as well; for brevity we will refer only to the 8720ES throughout the rest of this product note. In general, for a standard network analyzer to be able to make pulsed measurements, there are three conditions that must be met. The first condition is that the RF source must be externally modulated, since a standard network analyzer lacks any modulating circuitry. The second condition is that if the pulse is a single or ran- domly timed pulse, it must exceed a width of 400 microseconds. Also for this case, the user must supply external triggering circuitry with variable delay between the trigger signal and the RF pulse. The third condition is that if the RF signal is a continuous pulse train, the minimum pulse width must exceed 500 nanoseconds and the pulse repetition frequency must be 20 Hz or greater. The reasons for these constraints will be explained later. (Note: the techniques described in this product note cannot determine the impulse response of a device.) 2 Measurement theory In general two types of pulse measurements may be Two types of low PRF measurements are possible. The made: Those with a pulse width greater than the net- first type is commonly referred to as the pulse-profile work analyzer's response time, and those with a pulse mode of operation. In this mode the source is operating width less than the network analyzer's response time. at a CW frequency, and the analyz