Agilent Technologies 8935 series e6380a manual Swept Return Loss

Overview of theTest Set’s Built-In Tools

Using the RF Tools Program

Swept Return Loss

	Measurement Description
	Swept return loss is a measure of reflection characteristics. The
	purpose of the swept return loss test is to detect problems in the
	antenna feedline system and the antenna itself. A portion of the
	incident power will be reflected back to the source from each
	transmission line fault as well as the antenna. The ratio of the reflected
	voltages to the incident voltage is called the reflection coefficient. The
	reflection coefficient is a complex number, meaning it has both
	magnitude and phase information.
	The return loss is defined as the magnitude part of the reflection
	coefficient and is expressed in decibels (dB). Therefore, the return loss
	is a measure of how large the reflected wave is to the original incident
	wave. Remember that this measurement is in terms of loss, therefore a
	large number means that very little signal was reflected back. A loss of
	0 dB indicates that all of the incident wave is reflected, whereas a
	return loss of 40 dB, for example, would indicate that very little of the
	signal is reflected. When a device is frequency swept, a graph similar to
	Figure 4-14 on page 95 is obtained. This is an example of a radio
	transmitting at a particular frequency. It can be seen that the return
	loss at that frequency is a very large number which tapers off to small
	return losses at all other frequencies.
	Another way of looking at the same information is the SWR (also
	known as VSWR: Voltage Standing Wave Ratio). VSWR is stated as a
	ratio. For example: 1.2:1 or “one point two to one” VSWR. The first
	number in the ratio is a value between 1 and infinity. 1 indicates that
	none of the incident wave is reflected. Infinity implies that all of the
	incident wave is reflected. Therefore, the closer this number is to 1, the
	better the feedline system performance. The second number in the ratio
	is always one.
	Making the Measurement
	When testing antennas or cables with antennas attached to them, a test
NOTE
	signal is radiated. Verify that the level and frequency span used for the
	test cannot result in interference to other nearby systems.To minimize
	interference when running the program, set the power level at the
	DUPLEX OUT port to the minimum value needed for good
	measurement resolution. Set the frequency range carefully.
	1. Select Swept Return Loss from the Select Test (Main) Menu. The
	Swept Return Loss Information menu will appear.

92 Chapter 4

C:\Spk\Ref\RefGuideRevE\Tools.fm