VNA Reflections is an educational blog sponsored by Anritsu Company, a leader in vector network analyzers for more than four decades. The goal of VNA Reflections is to discuss leading trends in vector network analysis, emerging VNA applications, fundamentals of VNA measurements, and technological advances in VNAs.

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Vector Network Analysis

Ensuring Large Vehicle Comms System Performance Using VNAs with NLTL Technology

February 14, 2022

Large vehicles, such as aircrafts, ships, and trains, rely on advanced wireless technology for communications, systems control, and sensor interconnects. Successful operation of these systems on large commercial and military vehicles requires interference mitigation. Often, vector network analyzers (VNAs) are used to ensure signal transmission. In today’s post, we explain how VNAs can ensure systems on large vehicles operate according to specification.

Interference can be caused by numerous devices. Laptops, electronic games, and mobile devices are common examples. There are also nefarious acts designed to intentionally create interference. Autopilot disconnects, erratic indicators, and vehicles veering off course are potential consequences that may be caused by interference.

Testing Cabling on Large Vehicles

RF/µW cabling is used throughout modern vehicles. Checking cable phase and magnitude performance over frequency becomes more important – and challenging. This is especially true as systems used in larger vehicles are increasingly sophisticated and complex, and connections between different parts of the vehicle are often well over several meters in length.

Once installed, fully characterizing long RF/µW cables with vector S-parameter measurements creates a connection challenge between a traditional VNA and the widely spaced cable ends. The interconnect cables required to attach the VNA ports to the cable under test adds significant insertion loss and phase instability to the measurements over the distances involved.  Cable replacement due to wear-and-tear adds considerable expense to the test setup, as well.

Figure 1 shows how to conduct cable measurements on ships and aircraft using the Anritsu ShockLine™ ME7868A VNA. As depicted, the portable port modules connect directly to the cable under test.

Cable measurements on airplane and ship using the ShockLine ME7868A VNA.
Figure 1: Cable measurements on airplane and ship using the ShockLine ME7868A VNA.

Four advantages are realized using the ME7868A VNA-based solution:

  1. Eliminates coax cable insertion loss and phase instability
  2. Complete vector S-parameter characterization
  3. Full wide band frequency sweep coverage
  4. Easier and faster setups for more efficient testing

The configuration can be used to conduct the following tests on cabling used in large vehicles:

  • RF/µW vector S-parameter characterization
  • Test phase matched cabling
  • Group delay cable testing
  • Insertion loss measurements
  • Cable fault detection

Eliminating EMI

With so much cabling and wireless equipment now aboard large vehicles, electromagnetic interference (EMI) is a critical factor that must be considered. It can cause equipment performance to degrade or even malfunction. EMI can affect radios and radar signals, interfering with communication between the aircraft or ship and the control tower and ports, respectively.

As a result, EMI effects must be considered in all aspects of large vehicle design and certification. Standards such as RTCA DO-160 for environmental conditions and test procedures for airborne equipment or MIL-STD-461, developed by the Department of Defense (DoD) to control EMI issues, are often used as the basis of evaluation.

One major method to combat EMI is to provide shielding of various line replaceable units (LRUs) and harnesses. Shielding a device or system not only reduces EMI emissions, it improves susceptibility performance. With advances in wireless technology and increased device signal sensitivity, shielding becomes even more important to maintain the functionality and safety of equipment.

OTA Solution Brings Benefits

Engineers often use VNAs to test RF/µW shielding and propagation on large vehicles. Typically, the configuration requires very long test port cables to reach around the vehicles. At the distances required for these tests, coax cables introduce insertion loss and phase instability so significant that different transmission media (such as optical cabling) must be used to enable S-parameter measurements. The additional hardware and setup complexity significantly raise the cost and time required to make the propagation and shielding measurements.

To alleviate additional expense and improve test times, the ME7868A VNA (figure 2) can be used to conduct OTA measurements on large vehicles, including aircraft and ships.

The Anritsu ShockLine ME7868A 2-port VNA.
Figure 2: The Anritsu ShockLine ME7868A 2-port VNA.

The ME7868A is configured with portable port modules that eliminate the need for long test port cables. It supports typical large vehicle tests, including:

  • RF/µW shielding characterization
  • RF/µW propagation studies
  • Vehicle antenna pattern measurement

Figure 3 shows the difference between a traditional complex configuration and the more efficient, streamlined ME7868A OTA set-up to conduct measurements on aircraft.

Comparison of testing aircraft using traditional VNA vs. ME7868A setups.
Figure 3: Comparison of testing aircraft using traditional VNA vs. ME7868A setups.

The ME7868A solution provides four key benefits in these OTA environments:

  1. Eliminates coax cable insertion loss and phase instability
  2. No different transmission media (E/O, O/E) required; additional costly hardware to overcome coax cable issues unnecessary
  3. Full wide band sweep coverage
  4. Easier and faster setups for more efficient testing

Unique VNA Architecture

The Anritsu ShockLine ME7868A has a unique design that makes it well suited for conducting measurements on systems used on large vehicles. As outlined in the examples described, it is a chassis-less 2-port VNA with portable port modules that supports a frequency range from 1 MHz to 43.5 GHz.

It can conduct tests with port modules spaced up to 100 meters apart. The ability of the VNA ports to be connected directly to each end of long cables in large vehicles optimizes dynamic range and improves phase stability in vector S-parameter testing. VNA ports can be physically placed close to large DUTs or at widely placed test antennas without the need for additional complex test hardware.

Many of the advantages are realized due to the patented nonlinear transmission line (NLTL) technology used in all ShockLine VNAs. It delivers wider bandwidth and higher dynamic range than competing technologies, enabling better measurement accuracy and repeatability with longer intervals between calibrations. NLTL is also employed on Anritsu’s VNA-on-chip design, which has inherent temperature and time stability advantages. NLTL technology also enables cost-effective, high-frequency measurements.

To learn more about large vehicle testing using a VNA, download leaflets on large vehicle OTA tests and cable tests.