Rohde & Schwarz ZVB 4, Manual

Page: 61 / 156

Instrument Construction and Function Description R&S ZVB
1145.1078.82 3.4 E-1
Description of the Block Diagram
The block diagram shown in Fig. 3-1 applies to the ZVB4 4 ports and the ZVB8 4 ports, Fig. 3-2 to the
ZVB4 2 ports and the ZVB8 2 ports
The ZVB is a vector network analyzer covering 300 kHz to 4 GHz (ZVB4) or 300 kHz to 8 GHz (ZVB8).
The models ZVB4 and ZVB8 are available in a 2-port or in a 4-port version. The signal generator
(including the LO signal for the receiver) is implemented, according to the number of ports, using one or
two synthesizer boards. The signal processing path comprises a reflectometer board, an IF board, a
network controller and a processor section, comprising a Pentium-PC, I/O interface and graphics board.
The instrument can be expanded to handle future digital and analog requirements by retrofitting options.
The generator signal (300 kHz to 4 GHz or 300 kHz to 8 GHz) is generated on synthesizer board 1,
amplified in the generator section of the reflectometer board and then passes via the bridge to the port
(port1 to 4) and so to the DUT. The reference signal (Ref1 to 4) is split in the bridge and fed to the
receiver section (Receiver Ref1 to 4) on the reflectometer board.
The signal reflected or transmitted by the DUT (Meas1 to 4) is fed to the port, coupled out in the bridge
unit and fed to the receiver section (Receiver Meas 1 to 4) on the reflectometer board.
The internal reference frequencies are generated on the frequency reference board the128-MHz
reference frequency is generated there as an internal device reference.
The following sections describe the various boards in greater detail.
Reflectometer
A reflectometer board comprising a
bridge unit
, a
generator section (Generator)
and a
receiver
section (Receiver)
are incorporated in every port (Port1 to 4). These three components are screwed
together to form a compact unit.
Bridge unit
The bridge unit is a resistive coupler which is used to separate the signal going to the DUT from the
signal coming from the DUT. The reference signal (= measure of the signal to the DUT) is also obtained
from the bridge unit. The reference signal provides a reference for relative measurements.
Generator
The generator contains three broadband amplifier stages which boost the signal coming from the
synthesizer to a level > 20 dBm. Limiter diodes protect the output stage from ESDs. A total of three
adjustable attenuators form the setting element to keep the output level constant and to attenuate it
electronically.
Receiver
The receiver section has two channels (measurement channel and reference channel) and uses single
conversion. Every channel contains a buffer amplifier, for each of the frequency ranges 300 kHz to
4 GHz and 4 GHz to 8 GHz (ZVB8 only) a mixer with LO amplifiers and an IF amplifier. In the mixer, the
input signal is directly converted to the IF range,
approx 15 to 21 MHz. The inputs are protected by
limiter diodes.