Abstract
This paper presents the development of a PC-based microwave five-port reflectometer for the determination of moisture content in oil palm fruits. The reflectometer was designed to measure both the magnitude and phase of the reflection coefficient of any passive microwave device. The stand-alone reflectometer consists of a PC, a microwave source, diode detectors and an analog to digital converter. All the measurement and data acquisition were done using Agilent VEE graphical programming software. The relectometer can be used with any reflection based microwave sensor. In this work, the application of the reflectometer as a useful instrument to determine the moisture content in oil palm fruits using monopole and coaxial sensors was demonstrated. Calibration equations between reflection coefficients and moisture content have been established for both sensors. The equation based on phase measurement of monopole sensor was found to be accurate within 5% in predicting moisture content in the fruits when compared to the conventional oven drying method.
Highlights
The principle of the six-port reflectometer for measuring reflection coefficients was introduced byEngen [1] in 1977
The sensors used in this work were the open ended coaxial and monopole sensor [7,8] constructed from an RG 402 semi-rigid cable
The performance of the five-port reflectometer was tested by comparing reflection coefficient S11 values of eight different offset shorts using both the reflectometer and a commercial Vector Network Analyzer (VNA)
Summary
Many papers have been published to simplify or extend the application of the instrument [2,3,4,5,6]. An interesting variant of the six-port unit is provided by the five-port reflectometer where the reflection coefficient of the device under testing can be determined by using only three power detectors [5,6]. We proposed the use of an open ended coaxial sensor to determine moisture content in oil palm fruits [7] by measuring the reflection coefficient with a Vector Network Analyzer (VNA).
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