March 14, 2017
Vector network analyzers (VNAs) are general purpose measurement instruments that have been used in a wide variety of applications ranging from aerospace and military to commercial wireless networks. Their importance in helping bring about new technologies can be seen in the history books as well as in today’s R&D labs. A case in point is how engineers are now relying on VNA measurement capabilities to verify designs of products that are being developed for 5G communication systems, such as the one shown in figure 1.
Figure 1. Simple illustration of a 5G communication system.
To achieve the high speed expected from 5G, the data cannot be constrained or degraded by the channels in which it is being transmitted. Another important element to remember is that while the information being sent is digital, the signals are fundamentally analog. This makes analog behavior important to monitor as the data rates increase.
VNAs are an excellent tool to measure signal integrity and diagnose issues when expected data rates are not achieved. Here are a few examples of how they are being used:
- Analyze real-world channel defects, such as exceeded tolerances on printed circuit board (PCB) artwork, and plating and dielectric thickness variations
- Evaluate connector performance, construction and mounting
- Analyze multilayer PCB stack ups and find imperfect vias or ground plane issues
- Measure the distance to a fault to pinpoint where issues occur by converting frequency measurements to the time domain
For the last example, the Anritsu ShockLine™ MS46500B VNA series offers an Advanced Time Domain option. This innovative tool enables signal integrity engineers to measure parameters such as time domain reflection (TDR), time domain transmission (TDT), and crosstalk, as well as display an eye diagram based on simulated data being transmitted over a measured channel.
Verifying Optical Modules
To move the massive amount of data traffic expected in 5G systems between data centers and base stations, the digital signals will often be converted from electrical to optical and back to electrical. VNAs can be used to help determine the efficiency at which these conversions happen. Used in conjunction with a well characterized optical modulator or photodiode, VNAs can determine the transfer function of optical transmitters, receivers, and transceivers. Key parameters, such as bandwidth, flatness, phase linearity, and group delay, can be verified with a VNA.
5G Base Stations
At the base station, unparalleled performance will be required of the 5G transmitters and the RF components designed into them. To ensure this level of operation is achieved, a thorough understanding of component behavior is required. Once again, the VNA is up to the task.
Engineers use VNAs to conduct measurements as early in the design process as at the wafer stage. S-parameter measurements can be made on devices under test (DUTs) to ensure expected performance or build device models. Wafer-level measurements pose unique challenges, so VNAs need to de-embed the effects of fixtures and probes. More accurate models lead to shorter design cycles, helping be first to market in the all-important race to rollout the initial 5G radio solutions.
The Anritsu VectorStar® VNA can cover frequency ranges from 70 kHz to 40, 70, 110, and 145 GHz in a single coaxial connection for either single-ended or differential devices, and utilize the widest range of standard embedding/de-embedding techniques to realize the most accurate device models. In addition, for challenging differential device characterization, all frequency models provide the ability to independently control and adjust power and phase at the differential ports with calibrated accuracy.
5G radios will need to handle much wider bandwidths, forcing them to operate at higher frequencies than traditional communication systems. The move to microwave and millimeter wave (mmWave) frequencies will require considerably more cell sites to account for greater path losses. Combined with historically more expensive microwave and mmWave instrumentation, there is a need for much lower cost measurement equipment, including VNAs. To address this market condition, dedicated cost-effective VNAs, such as the Anritsu ShockLine MS46500 series of VNAs, have emerged. The MS46522B with option -082 (Figure 2) offers an unprecedented price point for an E-band VNA covering frequencies from 55 GHz to 92 GHz in an instrument ready to use right from the box for mass production of E-band components.
Figure 2. Anritsu MS46522B with Option -082 E-band VNA.
High Frequency Transmission
The last stage of the 5G communication systems is the transmission of the microwave and mmWave signals to the devices that will use them. In anticipation of 5G, many infrastructure companies are employing multiple input, multiple output (MIMO) technologies with antenna systems utilizing large numbers of array elements, a.k.a. massive MIMO. The geometries associated with microwave and mmWave components are much smaller than traditional RF components, forcing engineers to conduct over-the-air (OTA) measurements. Combined with the abundance of array elements and significantly greater path losses at these high frequencies, VNAs for these applications must be more compact and account for the multiple array elements.
To address this challenge, there has been an emergence of small, microwave/mmWave measurement modules tethered to a base VNA model to get closer to the DUTs. An example is the MA25300A broadband mmWave module that is about the size of a deck of playing cards yet enables measurements up to 145 GHz, making it a perfect enabler for the VectorStar ME7838D Broadband Vector Network Analyzer System.
Innovative VNA Architecture
To address the numerous challenges noted above for utilizing VNAs to make measurements for 5G communication systems, VNA suppliers must develop innovative technologies. For example, Anritsu’s innovative application of non-linear transmission line (NLTL) technology in vector network analysis and other test instrumentation has proven to provide high performance, robust, frequency-scalable, and cost-effective test solutions. NLTL technology redefines the level of performance and size of instrumentation while breaking down the cost barriers usually associated with high frequency test and measurement equipment. Anritsu’s patented application of this technology enables the next wave of microwave/mmWave instruments - accelerating next-generation product development and lowering production costs with the portability to install and maintain next-generation radio systems.
VNAs are an essential tool for enabling 5G communication systems. They can be used in applications ranging from data center signal integrity measurements, through characterization of the devices and components used in the fiber connectivity and mmWave radios in next-generation base stations, to OTA measurements required to address massive MIMO technologies. Anritsu’s broad portfolio of VNAs utilize patented NLTL technology to address both existing and emerging technology trends.
To learn more about VNA technology and test solutions for emerging high-frequency applications such as 5G, download this free white paper entitled Scaling Test Equipment Size to Match Millimeter Wave Test Needs.
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