Simple antenna characterisation using multiple VNAs: Page 2 of 7

May 25, 2017 //By Ing. C. Culotta-Lopez, Dipl.-Ing. T. Dallmann, IHF RWTH, Aachen, Germany and Dipl.-Ing. F. Gerhardes, Anritsu, Germany
This article shows how a set of two single-port vector network analysers (VNAs) that can be remotely operated via a LAN interface can be used for low-cost scalar transmission measurements for simple antenna characterisation. Practical results are included to show how antenna pattern and antenna gain measurements can be carried out with a very limited investment.

Experimental set-up

The MS46121A is a full-featured single-port USB vector analyser module including time-domain measurement capabilities. By adding a second module, the test engineer can carry out scalar transmission measurements such as S21 testing. In such a set-up, either of the modules can be used as the stimulus source, with the other behaving as a fully vector corrected (calibrated) receiver. For the antenna measurement concept, two of these modules are sufficient. For complex applications such as multi-band antenna test, it is possible to employ up to 16 VNA modules, with one acting as a stimulus and the remaining 15 as receivers.

The system is controlled from user an external PC or laptop with the Windows 7 or higher operating system and the ShockLineTM VNA software available free of charge from Anritsu. MS46121A option 021 enables the scalar measurement (|S21|,|S12|) capability, in which each attached module appears as a separate physical measurement channel. The active selected channel is always the stimulus source. The receive port(s) can be selected via the response menu (S11, S22 … S16 16).

A further option (002) offers bandpass and lowpass time-domain measurements with time gating capability for measuring parameters such as distance to fault or impedance.

For antenna measurements the VNA benchmarks are dynamic range, stimulus power and measurement sweep. One of the main drivers limiting dynamic range is the use of long VNA test port cables with their inherent high insertion loss and the limited VNA stimulus power.

The ideal set-up is for the VNA hardware to be linked directly to the antennas without any cable and for measurement data to be transferred by means of a low-cost USB hub extended with an Ethernet LAN link to a PC. In this way, undesired losses can be avoided and the money for expensive long test port cables can be saved. As a result, the dynamic range is improved. With a stimulus power of +3 dBm (>23.2 MHz to 4 GHz), antenna side lobes down to a level of -30 dB up to frequencies of 3 GHz with an antenna distance of up to 10 m can be characterised.

Design category: