For each channel defined above, from 1 (one) to 16 trace graphs (called “traces”) can be defined where each trace is a data display within a specific channel. Each trace is defined by a response parameter (such as S11), a graph type display (such as a rectilinear graph, a polar display or Smith chart), a scale, and possibly post-processing elements such as time domain and smoothing. There are four general graph types available and within each general type are multiple sub-types:

The data types generated by the VNA (real, imaginary, magnitude, phase) are used in the display graph to show the possible ways in which S-Parameter data can be represented. For example, complex data, that is data in which both phase and magnitude are graphed, may be displayed in any of the following ways:

A separate graph can be assigned to each active channel and display area. The following available display graph types are listed in Table: Available Trace Display Types below.

 

Each graph type is described in greater detail below with sample graphs, and explanation of supporting trace displays.

Each trace (i.e. each graph display) is labeled with information such as its trace number, the graph type, scaling, reference delay, and S-parameter associated with that trace. Depending on the trace settings and the graph type, other information may be displayed.

The general format of trace label consists of the following parameters and their associated abbreviations appearing from left to right in the trace label. Some parameters may not appear depending on the instrument settings.

Trace labels can be customized by the user in the DISPLAY SETUP menu and toggled on or off as an alternate trace name.

The trace label abbreviations are described in the three tables below:

 

 

A rectilinear graph is a display of a Cartesian coordinate system or plan consisting of an X-axis and a Y-axis. The X-axis displays the independent variable (such as frequency or time) and the Y-axis displays the dependent value.

 

 

As above, but paired with a phase rectilinear graph below. Useful to save a channel, or provide immediate comparison with a function value and its phase.

 

The power reflected from a DUT has both magnitude and phase because the impedance of the device has both a resistive and a reactive term of the form r+jx. We refer to the r as the real or resistive term, while we call x the imaginary or reactive term. The j, which we sometimes denote as i, is an imaginary number. It is the square root of –1. If x is positive, the impedance is inductive, if x is negative the impedance is capacitive. The size and polarity of the reactive component x is important in impedance matching. The best match to a complex impedance is the complex conjugate which means an impedance with the same value of r and x, but with x of opposite polarity. This term is best analyzed using a Smith Chart, which is a plot of r and x.

To display all the information on a single S-parameter requires one or two traces, depending upon the format we want. A very common requirement is to view forward reflection on a Smith Chart (one trace) while observing forward transmission.

The Smith Chart with impedance (Smith R + jX) has four display options:

The impedance is the measure of a circuit’s opposition to alternating current which consists of the circuit resistance and the circuit reactance, together they determine the magnitude and phase of the impedance.

 

The admittance (Y) is the inverse of the impedance (Z) and is a measure of how easily a circuit will allow current to flow, a combination of conductance (the inverse of resistance) and the dynamic susceptance (the inverse of reactance). Smith Chart graph display showing admittance (conductance and susceptance) has four read out style options are available:

 

A polar graph represents a two-dimensional coordinate system where each point is determined by an angle and a distance. The polar coordinate system is especially useful in situations where the relationship between two points is most easily expressed in terms of angles and distance such as in phase relationships in antenna and feedline design. The magnitude parameter can use either a linear or log scale. As the coordinate system is two-dimensional, each point is determined by two polar coordinates: the radial coordinate (distance from the center) and the angular coordinate (degrees counterclockwise from the right edge). Polar displays are used for transmission measurements, especially for cascaded devices in series. The transmission result is the addition of the phase and log magnitude (dB) information in the polar display of each device.

 

The quantity group delay is displayed using a modified rectilinear-magnitude format. In this format the vertical scale is in linear units of time (ps-ns-s). With one exception, the reference value and reference line functions operate the same as they do with a normal magnitude display. The exception is that they appear in units of time instead of magnitude.