The typical setup for the modular BB system is shown in Figure: System Setup for Modular BB Mode below. In contrast to the classical BB/mm-Wave setup discussed previously, external synthesizers are not used but conditioned versions of internal VNA source and LO signals are instead routed to the modules. An option on the VNA, Option 08x provides these connection points that the test set (3739x) uses for routing to the modules (see Table: Option 08x Descriptions). Much like in the classical setup discussed before, control and power connections are provided by the test set to the modules and IF signals are taken from the modules for routing to the VNA. As with the classical mode, Option 007 (frequency offset) is required for the more elaborate frequency programming.
Two additional rear panel connections are used in this system: an external ALC connection is used between the test set and the VNA to enable leveled power control at the heads and the VNA external analog out function is used to assist in LO leveling. Note that when in Modular BB mode, the normal function of the Ext Analog Out connector is suspended.
When in Modular BB mode, the frequency plan calculations are automatically changed to account for the multiplier behavior and the allowed frequency ranges. For ME7838A and related systems (using the 3743A modules), the range is 70 kHz to 125 GHz if option 070 is installed (10 MHz start frequency otherwise). For ME7838D and related systems (using the MA25300A modules), the maximum frequency is 145 GHz.
System Setup for Modular BB Mode
The VNA in this figure has Option 08x which provides the Src, LO1, and LO2 connectors shown in the figure.
1. MS4647A VNA with Option 080/081
2. VNA Test Port 1 V (m)
3. VNA Test Port 2 V (m)
4. 3739x Test Set
5. MA25300A Modules, 2 each, or 3743x Modules, 2 each, or 3744x-xx Modules, 2 each Note: When using MA25300A BB/mm-Wave modules, the 3739C Test Set is required
6. Heavy lines are RF and LO Cables
7. Light dashed lines are IF Cables
8. Heavy dashed lines are DC/control cables
Option 08x Descriptions
Option
Description
080
For ME7838A and ME7838D systems, used for single source VNAs withoutOption 051, 061, or 062 where broadband operation is desired (to 125 GHz or 145 GHz with the appropriate modules).
081
For ME7838A and ME7838D systems, used for single source VNAs with Option 051, 061, or 062 where broadband operation is desired (to 125 GHz or 145 GHz with the appropriate modules).
082
For ME7838A and ME7838D systems, used for single source VNAs without Option 051, 061, or 062 where only banded operation broadband operation is desired (E and W band).
083
For ME7838A and ME7838D systems, used for single source VNAs with Option 051, 061, or 062 where only banded operation broadband operation is desired (E and W band).
In terms of completing the connections, the power/control cable ends at the module side with a snap-in microD connector. The two IF connectors are SSMC and the reference connector is closest to the middle of the module (this is also marked on the module). The V cable coming from the VNA port routes to the module V connector in the middle of the module. The K (LO) and V (Src) cables from the test set route to the appropriate outer connectors on the module. All coax connectors should be torqued properly.
The rear panel connections are shown in Figure: Rear Panel Connections for the Modular BB System. Two BNC-connectorized coax cables are used for routing Ext. ALC (External Automatic Level Control) and analog control signals between the test set and the VNA. A DB-25 connectorized cable is used for routing digital control signals and the IFs are routed using four SMA-connectorized coax cables.
Rear Panel Connections for the Modular BB System
1. MS4647A VNA with Option 080/081 Rear Panel
2. 3739x Test Set Rear Panel
3. IF I/Os
4. Ext Analog
5. Ext ALC
6. External I/O
A block diagram of the system is shown in Figure: Modular BB Block Diagram. The 3739x test set provides several distinct functions:
• Source power amplification and transfer switching
• LO leveling and distribution
• Generating control signals for the modules from VNA input and supplying power
• Routing and processing IF signals as necessary.
The 3739x test set includes higher power amplifiers and further LO condition circuits for use with higher mm-wave bands. The B model also includes an AUX POWER connector for a third module. This connector supplies power to the module and mimics the control signals sent to the Port 1 module. This makes the port very useful for IMD and mixer measurements. The second tone (for IMD) or the LO (for mm-wave mixers requiring a high frequency LO) can be supplied this way. The second tone for these applications could be supplied by an external synthesizer (see multiple source in Multiple Source Control (Option 007)).
The modules themselves have several unique aspects
• A bypass path for use at low frequencies. The internal VNA source and couplers/bridges are used for lower frequency measurements.
• At higher frequencies, separate reflectometers in the module handle the measurements
• Also at higher frequencies, multipliers in the modules provide source power.
• Leveling circuitry (both source and LO) is built into the modules
There are two main breakpoint frequencies that are helpful in understanding the performance of the system:
• The break where the module receivers take over from the internal VNA receivers. This is nominally at 25.4 GHz
• The break where the module source multipliers take over for the main VNA multipliers. This is nominally at 54 GHz.
As with the classical approach discussed previously, this mode can also be invoked from within multiple source control for a more customized setup. Details of this approach are covered in Multiple Source Control (Option 007).
Modular BB Block Diagram
The modular BB block diagram is shown above. Relative to the classical setup, the MUXing is performed in a different location and different multiplier and downconverter technologies are used.
1. 3739x Test Set
2. Src from VNA
3. LO from VNA
4. To VNA IFs
5. Source Amp and Switching
6. Control
7. LO Leveling Loop
8. From VNA Port
9. MA25300 Module or 3743A Module
10. Multipliers
11. Src Drive MUX
12. LO Chain
13. IFs to Test Set
14. Control
15. Downconverters
16. Test Port
Full power control and power sweeps are available in this mode due to the integrated leveling circuitry in the modules and test set. Flat power calibrations/linear power calibrations are also available and function as described in other chapters. An important point is that the standard Anritsu power meters are used up to 70 GHz while separate waveguide-based power meters are needed above 70 GHz. Normally an Agilent W8486A W-band sensor or equivalent is used for 70 GHz-125 GHz (for ME7838A and related systems) and an Elva‑1 power meter with D-band sensor is used for higher frequencies (for ME7838D and related systems). For traceability and accuracy information, contact the factory.
The calibration routines will prompt when a different meter/sensor needs to be connected. Because of the need for adapters in many cases, the manual power offset feature may be employed on the power meters to correct for adapter loss (e.g., a W1-WR10 coax-to-waveguide adapter typically has 0.5 dB of loss at 110 GHz).
Full ALC calibrations are performed at the diagnostics menu level of the firmware and are normally only employed in service situations. When moving between Standard and Modular BB modes, the ALC calibration files automatically switch to properly handle the hardware being used in those modes.
From a troubleshooting point-of-view, miscabling of the system is the most common problem. A typical symptom is non-ratioed parameters that are very low (< – 90 dB; when at default power, a1/1 and a2/1 will typically be in the –10 to –30 dB range (uncalibrated) depending on frequency). Very low received signals can sometimes also be due to requesting a leveled power too far below specified ranges (the system will allow lower entries than specified since they may be achieved at certain frequencies).
The normal ALC range when above 54 GHz reaches down to -60 dBm, although there may be some significant drop-offs below –55 dBm (and below –50 dBm above 110 GHz for those systems operating to higher frequencies). This is possible because of the highly linear integrated UIF leveling loop based within the modules. A separate RF leveling loop is also available for frequency translating measurements (discussed in Multiple Source Control (Option 007)). Because no step attenuators are in the mm-wave part of the system, this extended ALC range is particularly useful. Since the power structures are fairly different above and below 54 GHz (with or without step attenuator possibilities), two different ALC entries are used and are labeled as such on the Power menu. An example of the wide power range and wide power sweep range is shown in Figure: An example of the wide power sweep range available with the modular BB system. (the curve flat lines at the upper end of the sweep as it reaches maximum power of ~+3 dBm for this frequency). To achieve a constant low power level in a broadband sweep, it will be necessary to use step attenuators below 54 GHz and a low base setting above 54 GHz.
An example of the wide power sweep range available with the modular BB system.
Example:
• Broadband sweep with port power of -50 dBm
• Set the ALC level (<54 GHz) to -20 dBm and engage 30 dB of source step attenuation (assumes Option 061 or 062)
