Agilent Technologies 8753ET, ES Learning to Make Reflection Measurements, = Γ, = 1 + ρ / 1 − ρ

Quick Start: Learning How to Make Measurements

Learning to Make Reflection Measurements

Learning to Make Reflection Measurements

This example procedure shows you how to measure the reflection response of a 175 MHz bandpass filter. The measurement parameter values listed are unique to this particular test device.

For further measurement examples, refer to the "Making Measurements" chapter in the User's Guide.

NOTE	Reflection measurements monitor only one port of a test device. When a test
	device has more than one port, you must ensure that the unused port(s) are
	terminated in their characteristic impedance (for example, 50Ω or 75Ω). If
	you do not terminate unused ports, reflections from these ports will cause
	measurement errors. Figure 2-8 on page 2-15illustrates two ways to
	terminate an unused device port with the proper characteristic impedance.

The signal reflected from the device under test is measured as a ratio of the reflected energy versus the incident energy. It can be expressed as reflection coefficient, return loss, or standing-wave-ratio (SWR). These measurements are mathematically defined as follows:

reflection coefficient (Γ)	= reflected voltage / incident voltage
	= S11 or S22 (magnitude and phase)
magnitude of reflection	= Γ
coefficient (ρ)
return loss (dB)	= −20 log (ρ), where ρ = Γ
standing-wave-ratio (SWR)	= V maximum / V minimum
	= (1 + ρ) / (1 − ρ)

2-14 Chapter 2