Simple antenna characterisation using multiple VNAs: Page 5 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.

Outdoor antenna ranges

Antenna measurement sites or antenna ranges can be categorised as outdoor ranges or indoor ranges (anechoic chambers). According to the principle of measurement, they can also be categorised as reflection ranges, free-space ranges, and compact ranges. For this type of project, a reflection-free propagation free-space range like the so-called elevated or slanted range is applicable.

For measurements, the antenna is placed at the Fraunhofer distance, which approaches far-field conditions. Separating the antenna under test and the instrumentation antenna by this distance reduces the phase front variation of the received wavefront enough for a plane wave approach.


Antenna test setup

Based on the given outdoor environment, a slanted range was adapted based on an equilateral triangle having a side length of 10.35 m with the antenna under test located at the downhill apex. One of the single-port VNA modules was directly connected to the USLP 9143 log-periodic antenna, which was installed on a Zaber rotary stage, and the other was connected to a tripod-mounted TDK precision log-periodic antenna (acting as the illuminator), also fixed on a tripod.

The aim was to verify antenna pattern and gain at four individual frequencies: 700, 800, 1000 and 2000 MHz.

The antenna under test was mounted in the apex of the triangle, with the “illuminator” on one opposing side and a standard gain horn antenna on the other. This arrangement ensures that no mechanical changes are required for the later planned gain measurements. The distance and therefore the free space loss (FSL) is constant and just a re-alignment with a laser is necessary to switch from antenna pattern to antenna gain measurements.

A MATLAB script was used to control the ShockLine VNA modules through the ShockLine GUI software and the Zaber stepper motor.

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