HP 8530A, Руководство по эксплуатации и программированию, Страница: 232 / 439

Time Domain RCS Measurements
Time Domain Digital Resolution
Digital Resolution is dened as the ability to locate a single response in time . In other words , if
only one response is there , this is how closely you can pinpoint the peak of that response . The
Digital Resolution is equal to the digital resolution of the CRT (which is the time span displayed
divided by the number of points). Maximum Digital Resolution is achieved by centering the
response on the display and then reducing the time span. Therefore , the Digital Resolution is
always much ner than the Down-Range Resolution.
The digital resolution of the Time Domain trace is determined by the Number of P oints
measured in the Frequency Domain and by the time span that is displayed. The HP 8530A
digital Inverse F ourier Transform method applies these points to the time span that is
displayed. Therefore , it is possible to obtain increasingly higher digital resolution of the Time
Domain trace by reducing the displayed time span. This is an advantage the Chirp Z F ast
F ourier Transform (FFT) has over standard FFT processing methods . Standard FFT methods
require the Number of P oints to be spread across the entire Time Domain Alias-Free Range ,
thereby limiting the digital resolution.
By reducing the displayed time span, you can usually obtain sucient digital resolution for
viewing the RCS responses , even with a low number of Frequency Domain points . Note that
increasing the digital resolution does not increase the ability to resolve individual target
scatterers . Higher digital resolution simply gives better point-to-point resolution of a Time
Domain trace .
Figure 13-4. Typical Aliased Response
Introduction to Time Domain RCS and
Antenna Measurements
13-7