Text preview for : 5965-7708E.pdf part of HP 5965-7708E HP Publikacje 5965-7708E.pdf
Back to : 5965-7708E.pdf | Home
Agilent AN 1287-2
Exploring the Architectures of
Network Analyzers
Application Note
Table of Contents
2 Introduction
2 Network Analyzer Architecture
3 Coupling Signals
6 Directional Bridges
6 Network Analyzer Detection
8 Comparing Dynamic Range
9 The Spectrum Analyzer Alternative
9 The Test Set
10 Other Considerations
10 Suggested Reading
Introduction Network Analyzer Architecture
Network analyzers have become one of the most Network analyzers differ in form and function
important measurement tools for characterizing from another tool commonly used to characterize
the performance of high-frequency components communications systems and components, the spec-
and devices. A modern vector network analyzer trum analyzer (see Figure 1). Spectrum analyzers
can measure a component's magnitude, phase, and measure unknown external signals. In contrast,
group delay, show port impedances on a Smith network analyzers utilize synthesized-frequency
chart, and, with time-domain capability, show the sources to provide a known test stimulus that can
distance from a test port to an impedance mismatch sweep across a range of frequencies or power levels.
or circuit fault. Understanding a network analyzer's Network analyzers also can perform ratioed meas-
capabilities and operation can help an operator urements (including phase), which require multi-
derive optimum performance from the instrument. ple receivers. These measurements cannot be per-
formed with a spectrum analyzer, even when it
Agilent Technologies offers an extensive line of RF is complemented by a tracking generator.
and microwave network analyzers for applications
from DC to 110 GHz. These analyzers are available Spectrum analyzers are generally employed to
with a variety of test sets and calibration kits and measure signal characteristics such as carrier
can be equipped with such options as time-domain level, sidebands, harmonics, and phase noise. They
capability for making distance-to-fault evaluations are usually configured as a single-channel receiver
in transmission lines. Agilent also supplies linear without a source. These instruments have a wide
and nonlinear computer-aided-engineering (CAE) range of IF bandwidths available in order to analyze
software tools such as the Agilent EEsof Microwave diverse types of signals and are often used with
Design System (MDS) and Series IV Suite, useful in external sources for nonlinear stimulus/response
creating device and component models based on testing. When combined with a tracking generator,
vector network analyzer measurements. spectrum analyzers can be used for scalar compo-
nent testing to show magnitude versus frequency
information but not phase information.
Amplitude Ratio
8563A
Power
Measures Measures
known unknown
signal signals
Frequency Frequency
Network analyzers: Spectrum analyzers:
measure components, devices, measure signal amplitude characteristics
circuits, sub-assemblies (carrier level, sidebands, harmonics, etc.)
contain source and receiver can demodulate (& measure) complex signals
display ratioed amplitude and phase are receivers only (single channel)
(frequency or power sweeps) can be used for scalar component test (no
offer advanced error correction phase) with tracking gen. or ext. source(s)
Figure 1. Differences between Network and Spectrum Analyzers
2
Network analyzers can provide a wealth of knowl- Coupling Signals
edge about a device under test (DUT), including its Directional couplers are useful for measuring both
magnitude, phase, and group-delay response. To the incident and reflected signals present at the
accomplish this, a network analyzer must provide input of the DUT. Directional couplers consist of a
a source for stimulus, signal-separation devices, "through" path and a "coupled" path, which diverts
receivers for signal detection, and display/process- a small amount of the power traveling along the
ing circuitry for reviewing results (Figure 2). The through path (Figure 3). The amount of coupled
source is usually a built-in phase-locked (synthe- power is determined by the coupling factor:
sized) voltage-controlled oscillator.
Coupling factor (in dB) =