Narrow-Beam Antenna for Short-Distance Non-Destructive Sensor in Fruit-Ripeness Monitoring

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 × 6.5 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.