December 23, 2014
In our previous post, we discussed the benefits of an advanced vector network analyzer (VNA) architecture based on Nonlinear Transmission Line (NLTL) technology. For engineers, this emerging generation of VNAs addresses the economic constraints and time-to-market pressures they face by more accurately and efficiently measuring devices and systems operating at microwave and millimeter wave (mm-wave) frequencies. In this post, we will detail just how NLTL-based VNAs can save engineers time and money.
The benefits outlined above can be realized at every stage of the wireless communication lifecycle. VNA architectures with NLTL are now integrated into instruments that can be used during design and development, on the production line, and in the field for deployment, installation, and maintenance. In each of these applications, measurements are being conducted more accurately, efficiently, and with greater confidence.
A major advantage of NLTL-based VNAs is the high level of monolithic integration of the various constituents, such as sampling receivers, distributed harmonic generators, directional bridges, and other key components. The resulting reflectometer modules share the same thermally stable mass, and are miniature in size, thus greatly reducing temperature variations. Engineers experience highly optimized short- and long-term stability, and less frequent VNA calibration. In addition, eliminating microwave connectors between the various reflectometer components enhances performance – e.g. lower loss, less reflections – while improving system reliability.
The compact nature of the NLTL-based reflectometers brings advantages in several key VNA applications, including:
- High-frequency on-wafer testing. By directly connecting the reflectometer to the wafer probe, directivity, port power, and system stability are enhanced.
- Dense multi-port on-wafer measurements.
- Very low-cost solutions for testing components in production environments.
- High-frequency handheld VNAs for field applications.
What makes VNAs with an NLTL-based architecture superior to their older, Step-Recovery Diode (SRD)-based sampling VNA brethren? Here are three main reasons:
Maximum Dynamic Range Across Broad Frequency Ranges
NLTL samplers exhibit extremely wide RF bandwidth (figure 1) that is scalable to sub-millimeter-wave frequencies. The continuous frequency coverage is limited only by the bandwidth of the coaxial connector and the number of NLTL frequency multiplier chains. When combined with a directional bridge, NLTL samplers enhance VNA directivity.
Figure 1
In contrast, older architectures require implementing a large external combiner to concatenate two frequency bands to extend VNA frequency range. Such implementation deteriorates the raw directivity and output power of the VNA.
Unmatched Stability
A key advantage of the NLTL-based reflectometer is its inherent temperature and time stability, which simplifies obtaining stable, quality measurements (figure 2). The stability is a result of the monolithic construction of the NLTL-based sampler and reflectometer components. Monolithic integration results in a vanishing thermal gradient across the reflectometer module and the sampling directional bridge, thus delivering improved measurement stability and lower temperature drift when compared with SRD samplers and classical mixers.
Figure 2a
Figure 2b
Improved Capability-to-Cost Ratio
The NLTL-based VNA-on-a-chip advances the capabilities of a VNA and introduces a number of new application spaces. Cost-sensitive component manufacturers face increasing demand but must meet lower price points to enable less expensive components. NLTL-based VNAs offer component manufacturers very affordable VNAs without compromising performance.
A white paper on the NLTL-based VNA architecture has been published. You can download it for free to learn more about its development and advantages.
