RFhex is developing a compact, host-connected, two-port vector network analyzer (VNA) with a frequency target up to 26 GHz. The goal is to deliver professional-grade S-parameter measurement at a price that individual engineers, startups, research groups, and small design teams can justify.
This article outlines the intended applications, the system architecture, the calibration approach, and how performance will be verified.
The gap in the current VNA market
VNA options today fall into two groups. Laboratory-grade instruments from established vendors offer excellent directivity, dynamic range, and calibration support, but their cost puts them out of reach for many teams. Low-cost analyzers have made basic S-parameter measurement widely available, but they are generally limited in frequency coverage, dynamic range, and measurement repeatability.
For engineers working on microwave designs, neither option fits well. RFhex is being developed to sit between these two groups: professional measurement capability without laboratory-instrument pricing.
Target applications
The planned frequency range covers most RF and microwave development and verification work, including:
- Antennas: input match, return loss, and resonant frequency (S11)
- Filters: passband response, rejection, and insertion loss (S21, S11)
- Cables and interconnects: loss, mismatch, and connector quality
- Matching networks: tuning and verification against simulation
- Amplifiers and RF front ends: gain, input match, and output match (S21, S11, S22)
A two-port design is being prioritized because it supports full reflection and transmission analysis. With full two-port calibration, all four S-parameters (S11, S21, S12, S22) can be measured and error-corrected, which is required for accurate characterization of most passive and active devices.
Design priorities
The development effort is focused on the parameters that determine measurement quality in practice:
- Directivity: the ability of the test port to separate the reflected wave from the incident wave. It sets the floor for how accurately small reflections can be measured, which matters for well-matched antennas and filters.
- Dynamic range: the span between the maximum measurable signal and the noise floor. It determines how deep a filter stopband or how high an isolation can be measured.
- Sweep repeatability: consistent results from sweep to sweep and over time. Without it, calibration cannot be trusted and small design changes cannot be resolved.
- Characterized calibration standards: the accuracy of any calibrated VNA depends on how well the standards are defined.
These are the areas where low-cost analyzers typically fall short, and they are the areas RFhex is designed to address.
Host-connected architecture
A conventional benchtop VNA integrates a display, embedded computer, front-panel controls, and operating system. These add significant cost but do not contribute to the RF measurement itself.
RFhex uses a host-connected architecture. The instrument contains the microwave signal path and data acquisition hardware. The host computer handles:
- Display and user interface
- Instrument control and sweep configuration
- Measurement processing
- Calibration and error correction
This reduces non-RF hardware in the instrument and allows more of the hardware budget to go into the microwave signal path, which determines directivity, dynamic range, and stability. It also means that processing and calibration features can be improved through software updates.
Calibration
Raw VNA measurements include systematic errors from directivity, source match, load match, reflection and transmission tracking, and isolation. Calibration measures known standards to characterize these errors and remove them from device measurements.
RFhex is planning to support the following calibration methods:
- SOLT (Short, Open, Load, Thru): the standard method for coaxial measurements, relying on well-characterized standards.
- TRL (Thru, Reflect, Line): suited to fixtured and on-board measurements, where precise coaxial standards are not practical. TRL depends mainly on the quality of the transmission line standard rather than on lumped standard models.
- Unknown-thru: useful when the two ports cannot be connected with a known thru, such as when connector genders or types differ between ports.
Verification plan
Performance claims will be verified against calibrated laboratory VNAs. Testing will use documented fixtures, reference devices, and test conditions, so that results can be reviewed and reproduced.
When RFhex specifications are published, the measurement method behind each figure will be published with them.
Development status
RFhex is currently in development. Final frequency coverage, dynamic range, accuracy, calibration performance, pricing, and availability will be published after prototype verification.
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