Abstract
Radiation pattern subtraction is a useful technique for narrowing a receiving antenna’s radiation pattern in a short-distance, non-destructive sensor. The sensor’s antenna was developed to be compact and light-weight as well as to operate in real-time. This work applied the principle of radiation pattern subtraction to narrow the beamwidth of an antenna. Our experimental data demonstrated that a simple narrow-beam three-element antenna with a 35° half-power beamwidth and a small size of $5.9\times 6.5\,\,\textrm {cm}^{2}$ could be realized. In the experiment, the radiation pattern of an array antenna (consisting of two halfwave dipoles with a reflector) was subtracted from the radiation pattern of an element antenna (consisting of a halfwave dipole with a reflector) for the three-element antenna to achieve a narrow beamwidth and compact size. The antenna had a simple feeding network that operated at 10.525 GHz and 35° half-power beamwidth. The angular resolution of the receiving antenna was tested with mango fruits: it was able to resolve an 80 mm separation between the fruit of interest and the nearby fruit, which was sufficient, in terms of practicality, for mitigating the interfering effect of nearby fruits to the fruit of interest. This type of antenna is useful as a short-distance, non-destructive sensor such as a pre-harvest sensor.
Highlights
The United Nations (UN) has announced 17 sustainable development goals (SDG) to make the world free of poverty, hunger, and disease [1]
An improved-angular-resolution, the pre-harvest sensor is necessary for quality control of fruits because there can be some fruits located near the fruit of interest on a tree, and the scattered waves from them and the fruit of interest can be much different from the scattered wave from an isolated fruit of interest alone
Radiation pattern subtraction method provides angular resolution improvement, especially under the constraints that the short-distance, non-destructive sensor being light-weight and able to operate in real-time
Summary
The United Nations (UN) has announced 17 sustainable development goals (SDG) to make the world free of poverty, hunger, and disease [1]. As the dielectric property of fruit flesh varies with time during the ripening process, its natural frequency can be used to predict a suitable harvest date Those previously mentioned papers are some fruit classification applications of non-destructive sensors that measure the radar cross-section (RCS) of a target at a short distance. ANALYSIS OF RADIATION PATTERN SUBTRACTION ANTENNA For a compact size antenna, beamwidth narrowing by radiation pattern subtraction can be explained by considering the case of two linear uniform arrays that have the same kind of element and same phase center, shown in Fig. 2 (a).
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