Multi-port S-parameter measurements with a VNA and switch matrix

With the increasing number of ports on RF components, testers need accurate and fast multi-port network analysis. The multi-port measurement capability of a VNA directly improves test throughput and cuts the cost per tested device — for design, verification and production of antennas, data-converter interfaces and automated RF component test.

Why multi-port testing is exploding

Mobile communication and microwave IC integration keep pushing complex multi-port devices to replace discrete parts: a phone's front-end module or a MIMO antenna packs many functions into one component. Characterising such a device as a long series of manual 2-port measurements is slow and error-prone — every re-connection costs time, adds wear and adds uncertainty. Devices with more ports than the analyzer's 2 or 4 need a better answer.

The solution: switch-matrix port expansion

The SSM5000A switch matrix expands the test ports of a network analyzer (and signal sources or spectrum analyzers) in a standard 19″ rack chassis. It contains 8 switch submodules — four 1-to-4 and four 2-to-6 — organised as two switch groups of 12 ports each; any path between the two groups can be measured, giving a 24-port system with 144 paths. The analyzer detects ports automatically and supports simplified multi-port calibration algorithms.

Step 1 — Connect and auto-detect

Connect the VNA (host) to the SSM matrix (slave) via USB, LAN or the direct-control interface. The analyzer detects the matrix type and assigns ports automatically — the info bar reports “The switch matrix plugged in”. Enable it under System → External Ports → Ext Port Enabled; the matrix identifier appears in the top-right of the UI. A 4-port SNA5000A with an SSM5144A can then be used as 24 single ports, 12 full 2-ports, 8 full 3-ports, 6 full 4-ports, 4 full 6-ports, 3 full 8-ports, 2 full 12-ports — or one full 24-port VNA.

Step 2 — Define the RF configuration

In Switch Matrix… → Switch Matrix RF Connections, map the VNA's physical ports to the matrix inputs: port 1 (A) → 1A, port 2 (B) → 1B, port 3 (C) → 1C, port 4 (D) → 1D. Click OK and the expanded ports are available everywhere — basic calibration, port extension, fixture simulation and port power all support them.

Step 3 — Measure any S-parameter, any pair

Under Measurement → S-Params → Other… you choose receiver and source port freely from drop-down lists — S0214 means receiver port 2, source port 14. Or type the port pair directly in the Edit box.

Step 4 — All-N-port calibration with ECal

Calibrating a 10- or 20-port system with mechanical standards is where multi-port projects traditionally die — the number of connections explodes. The SEM5000A electronic calibration kit (9 kHz–26.5 GHz, SMA/3.5 mm/N) solves it: one VNA port and one ECal port stay connected as the reference, and every other port is characterised with a single connection each. Solid-state switches give repeatable, consistent results with no operator error, and the VNA's multi-port calibration wizard walks you through every required port combination.

Complete configuration

• SNA5000A vector network analyzer — 2/4-port, 9 kHz–8.5 GHz or 100 kHz–26.5 GHz, 125 dB dynamic range
• SSM5000A switch matrix — 100 kHz–26.5 GHz, up to 4 inputs / 24 outputs, 3.5 mm female
• SNA5000-SWM licence — enables external switch-matrix port expansion on the VNA
• SEM5000A electronic calibration kit — 2/4-port, 9 kHz–26.5 GHz
• RF cables as required