In addition to the broadband measurements described in the previous section, the 3739x test set supports a number of different banded mm-wave measurement setups that are described in this section.

The first group has been alluded to and uses banded versions of the 3743x mm-wave modules described above and are sold as the 3744x. These modules allow operation in extended E (54-95 GHz) or extended W (65 GHz to 110 GHz) bands and are convenient for purely waveguide-based applications. The corresponding options on the VNA are 082 (without step attenuators) and 083 (with step attenuators). All of the 08x options are mutually exclusive.

The broadband selection allows operation from the low frequency limit of the instrument (70 kHz or 10 MHz depending on option 070 presence/absence) to the upper limit of the mm-wave module. For ME7838A systems (using 3743A modules), the Broadband to 125 GHz selection should be used. For ME7838D systems (using MA25300A modules), the Broadband to 145 GHz selection should be used. NOTE: The system cannot tell which modules are connected (between 3743A and MA25300A) so the user MUST select the correct broadband option when one is offered.

The extended E and extended W band modes operate very similarly to the 3739 broadband mode discussed previously except that the frequency ranges of operation are more restricted. The same RF and power calibration methodologies apply and there are no other substantive user interface changes when in these modes. On the 3744x modules, the center RF connector (used for the RF pass-thru on the 3743x module) is now only used as a bias connector. The port is low-pass filtered so bias can be applied without RF leakage.

The second group is based on OEM mm-wave modules much like the 3738 test set-based systems, except the internal VNA sources are used to drive the modules and additional leveling capabilities are enabled. The 3739-based setup menu is shown below and has additions (see Figure: The 3739-based setup menu is shown here.) relative to the 3738 setup for the E and W banded solutions, as well as for a leveling calibration that will be discussed shortly. The external equation dialog has the same structure as for the 3738 setup and example for a WR-2.2 (24 GHz) module is shown in Figure: An example equation dialog box is shown here for a WR-2.2 setup..

The 3739-based mm-Wave systems have some power control options available that are not present on the 3738-based systems and they are illustrated by the mmWave ALC Cal menu shown in Figure: mmWave ALC Cal Menu.

 

To understand the leveling/power control options, consider the very simplified block diagram in Figure: A simplified block diagram of a 3739-based mm-wave setup is shown here to help illustrate power control and leveling concepts.. The key point is that there are multiple locations to sample the power, but because of the very high frequencies involved, there is potentially no one ideal location.

In the ‘VNA’ mode, the standard VNA ALC calibrations are used with the existing detection system in the VNA so that the power menu settings correspond roughly to the actual RF levels being delivered to the 3739x test set. One can then have a general idea of the levels driving the module and may know the corresponding mm-wave output power levels based on data from the manufacturer. The leveling loop is closed, but in this mode the instrument has no knowledge of the relationship between mm-wave power levels and the instrument settings.

In the RF leveling mode, the same detection circuitry is used as in the VNA mode, but now a means of relating the actual mm-wave power levels is available. Because of the paucity of readily-available power measurement methods in these higher frequency ranges, the method used is somewhat indirect, but relies on the established linearity of the measurement system. The concept is illustrated in Figure: The concept of RF mm-wave leveling is illustrated here.. From the manufacturers’ measurements (often based on quasi-optical or other techniques), a value is generally known for the saturated mm-wave power. The saturation breakpoint can be found by locally sweeping the VNA RF power until the measured IF power leaves saturation (Pvna1). The IF reading can be noted at this point (IF1) and it can be linked to the known mm-wave saturated power. Now the VNA plane power can be dropped and the IF magnitude recorded as a function of this setting. Based on the known receiver linearity, we can now link the IF changes to the mm-wave power level (note this is only done during the calibration step. The leveling is based on finding the needed VNA setting to get the requested mm-wave power level, and then relying on the VNA leveling loop). So if the IF level has decreased to IF1-10 dB at some input level Pvna2, then we can state the mm-wave power is Psat-10 dB with some reasonable level of uncertainty. The concept is to level on the VNA power plane while establishing a link to the mm-wave power so that user entries can be in the latter form.

Since this leveling method only relies on the detection system at the VNA plane, it is useful for all measurement classes including converter and IMD measurements. Because it is leveling prior to the multipliers, it is less stable than the IF leveling to be discussed next and will provide a lower level of long term accuracy.

The calibration is accomplished using the dialog shown in Figure: The mm-wave ALC calibration dialog as configured for a single frequency point of RF calibration on Port 1 is shown here.. The concept is that the saturated power is known at some frequencies in the band and the user is allowed to enter those values discretely. When the calibration is executed, the above power sweep and iteration scheme is executed individually at each of the frequencies requested. Note that Port 1 and Port 2 calibrations are separate since modules are rarely identical. When the calibration is completed, the calibration may be saved and recalled later using the buttons shown in Figure: The mm-wave ALC calibration dialog as configured for a single frequency point of RF calibration on Port 1 is shown here..

The IF leveling scheme relies on sensing the IF amplitude coming out of the module directly and using that IF signal as the leveling signal. This requires that an IF be present on the reference channels so it is not appropriate for mixer or IMD measurements. Since the IF is derived post-multiplication, however, it is much more stable over time and temperature than is the RF leveling scheme discussed before. The block diagram of Figure: A simplified block diagram of a 3739-based mm-wave setup is shown here to help illustrate power control and leveling concepts. still applies except now the Ext ALC path shown is used for leveling.

The calibration proceeds in the same way as discussed for the RF leveling scheme and the same dialog is used (with different button selections). In both cases, since the leveling is analog, it is very fast so that the DUT rarely sees transient power spikes that can occur under purely software leveling schemes. The detected transient response time for one measurement is shown in Figure: An example transient response of the mm-wave ALC system is shown here. and illustrates that a ~5 dB power request step is resolved in a few microseconds in an overdamped manner.

Both leveling schemes enable power sweeps as well as finer power control when sweeping frequency. Both modes of control can be useful for active device measurement or for other RF-sensitive or potentially non-linear situations. An example of a power sweep at 400 GHz is shown in Figure: An example power sweep measurement is shown here. to illustrate the range that may be possible.