The R&S ZVA24 network analyzer and the new R&S ZVAX24 extension unit combine to form a solution that adapts to user requirements. This combination facilitates faster and easier measurements on active components because it does not require any additional equipment or rewiring. Depending on the application, the extension unit can be equipped with combiners, harmonic filters, pulse modulators and power couplers. It is a scalable and compact test and measurement solution. Although the R&S ZVAX24 has been tailored to the R&S ZVA24, it can also be used with all other network analyzers of Rohde & Schwarz' R&S ZVA and R&S ZVT families.

Plug in and Measure

The combination of a network analyzer and the R&S ZVAX24 extension unit is suitable for use in the development and production of active components. This powerful and modular test solution especially benefits developers and manufacturers of amplifiers for mobile phones and base stations as well as of components for the automotive sector, e.g. car radar.

It facilitates complex measurements and can be used for measurements to satisfy aerospace and defense requirements or for tests on antennas or amplifiers under pulsed conditions. The R&S ZVAX24 occupies only two height units in a 19-inch rack and can be easily placed underneath the R&S ZVA. Semi-rigid cables connect the instruments so that they constitute a single unit.

Figure 1 Easy and convenient control of the R&S ZVAX24 extension unit using the graphical user interface of the R&S ZVA.

The extension unit and the components it contains are basically looped into the generator or receiver path by using the direct generator/receiver access. Only a USB cable (for path switching) and an LVDS (LAN) cable (for controlling the pulse modulators) are required as control lines. The unit is operated from the R&S ZVA network analyzer using a block diagram, shown in Figure 1, and dialog windows.

Depending on the measurement task, the required RF components such as combiners, pulse modulators or harmonic filters can be switched into the measurement path. The T&M solution's high level of integration means that both present and future functions of the R&S ZVA can be used to perform complex linear and nonlinear measurements, in particular on active components (intermodulation measurements, pulse profile measurements, etc.).

Intermodulation Measurements

Intermodulation products are unwanted spectral components that are caused by nonlinear circuit elements and a two-tone signal is required to measure them. If a conventional network analyzer with only one internal generator is used, an external generator and a combiner must be added to the test setup. This is not necessary with the R&S ZVA and R&S ZVAX24 combination because the internal combiner of the extension unit uses the two sources of the four-port network analyzer and generates a two-tone signal for intermodulation measurements. Figure 2 shows a typical intermodulation output signal from the Rohde & Schwarz solution in blue and from a conventional one in yellow.

This signal is directly output on one of the four ports. This feature plus the intermodulation wizard make it very easy and convenient to measure the intermodulation parameters of amplifiers or mixers as a function of frequency and power. The combiner can also be used to measure the group delay of mixers without LO access.

Pulse Modulators

Many applications require that DUTs be characterized by using pulsed signals instead of CW signals. The pulse width for these applications typically varies between a few hundred nanoseconds and the upper microsecond range. To be able to characterize the pulse profile distortion of components, the network analyzer must have a time resolution that is considerably higher than the pulse duration.

For applications where the DUT requires a pulse-modulated input signal, either a pulse modulator or a generator with pulse modulation can be used. Since the R&S ZVA-B16 hardware option enables direct access to the network analyzer generator path, the pulse-modulated RF signal (instead of the unmodulated signal) is directly fed to the network analyzer test set.

The pulse modulators of the R&S ZVAX24 offer even more measurement convenience. They are configured and controlled via the graphical user interface of the network analyzer, shown in Figure 3, so that no additional switches or trigger generators are required. For measurements with pulsed signals, the extension unit contains two modulators for pulse generation (see Figure 1). Single pulses, periodic pulses or variable pulse trains can be generated.

The R&S ZVA-K7 pulsed measurements option with easy setup enables direct recording of amplitude and phase versus time. This functionality makes it possible to analyze the time-dependent behavior in T/R modules, amplifiers and mixers with a resolution of 12.5 ns. This high resolution, ten times higher than any solution currently available on the market, enables a more accurate characterization of short pulses. At a maximum IF bandwidth of 30 MHz, the signal rise/fall time can be determined with a resolution of up to 33 ns.

Since the pulse generators support user-configurable pulse trains (see Figure 3), the user can generate arbitrary sequences of any width, duration and power, and also characterize components under real-world conditions. Significantly, this measurement does not require a repetitive signal because the user can work with any pulse trains.

The high dynamic range and measurement speed of the new solution are complemented by an easy test setup and straightforward operation. In addition to typical measurements such as high-PRF-mode or point-in-pulse measurements, the R&S ZVA-K7 option offers a very convenient pulse profile measurement facility.

A third modulator in the receiver path, shown in Figure 1, 'chops' the pulses. This can be useful in antenna measurements (e.g. in the case of pulsed radar cross-section [RCS] measurements), for example, because time gating allows direct crosstalk between transmit and receive antennas with short delay and high amplitude. Pulse profile measurements can be implemented very easily by using the conventional high-PRF-mode.

The pulse modulators of the R&S ZVAX24 can be controlled either via an external trigger generator or directly by the R&S ZVA24 using the new R&S ZVA-K27 internal pulse generator option. The trigger signals are fed in via BNC connectors (if an external trigger generator is used) or via an RJ-45 cable (if the internal R&S ZVA pulse generators are used).

Group Delay Measurements

Mixers and frequency converters form the core of wireless and satellite communications systems. Especially in satellite systems, these frequency converters have to satisfy ever more demanding requirements regarding frequency response and phase linearity. Therefore, the measurement of relative and absolute group delay, of relative phase and of the group delay derivations (dispersion and scattering) in T/R modules is playing an increasingly important role.

Since there is no access to the local oscillator (LO), Rohde & Schwarz has developed the R&S ZVA-K9 option as a new method for characterizing the group delay and derived parameters without exactly knowing the LO signal. This option makes it possible to determine absolute and relative group delay, relative phase and scattering (group delay derivations).

This innovative method requires a four-port network analyzer with two sources for feeding a two-tone signal to the converter. The R&S ZVA24 measures the phase deviation between the two signals at the input and at the output of the DUT and determines the group delay. Neither the frequency drift nor the frequency modulation of the internal and unknown LO influences the measurement results. The R&S ZVA-K9 calculates the relative phase by integrating the group delay, and it calculates the DUT scattering by group delay derivation.

The conventional methods for determining group delay require a complicated test setup and a calibration. They are also associated with a significant level of uncertainty because they depend on the stability of the LO. Moreover, it is almost impossible to perform group delay measurements on converters having multiple mixer stages. This new approach, however, offers easy setup and calibration, and is independent of the LO's frequency stability. This method is ideal for investigating DUTs with multiple mixer stages.

Harmonic and Interference Test Filters

Two harmonic filters in the generator paths, shown in the block diagram of Figure 1, improve the spectral purity of the signals. Harmonic suppression is typically 60 dBc for the second and 70 dBc for the third harmonic. An additional filter in the receive path (see Figure 1) expands the receiver's dynamic range at test port 2, which is a crucial advantage when measuring harmonics or interference signals. The filter also allows very low harmonic levels to be measured. Harmonic measurements are carried out using the R&S ZVA-K4 option.

Couplers

The R&S ZVAX24 can also be equipped with two high-power couplers, shown in Figure 1, to cover power levels up to 43 dBm (standard test port: 27 dBm). Preamplifiers can be inserted into the source path using connectors on the unit's rear panel in order to further increase the available power levels. A coupler in the measurement path allows the signals of port 2 to be monitored in parallel using a spectrum analyzer or power meter. Signal monitoring is a very helpful feature for complementary measurements or when controlling signals during S-parameter or intermodulation measurements. All these features enable the user to measure DUTs without reconnecting them.

Conclusion

The scalable T&M solution that consists of the R&S ZVAX24 extension unit and the R&S ZVA24 vector network analyzer (or any other R&S ZVA or ZVT network analyzer) enables linear and nonlinear measurements on active components without extra equipment and without reconnecting the DUT. This is a big step toward higher efficiency and measurement accuracy. Depending on the measurement task to be solved, users can customize a powerful test solution by adding combiners, harmonic filters, pulse modulators and high-power couplers in line with their needs.