Microwave Sensor Antenna for Soil Moisture Measurement

The paper presents a compact sensor antenna for soil moisture measurement. With a simple measurement setup, the method is valid for all types of soil. Overall structure of the antenna is 12mm × 12mm × 1.6mm. A 10 arm spiral antenna is embedded onto a 50 Ω Asymmetric Coplanar Strip transmission line. The antenna is fabricated on a substrate with ε_r =4.4 and loss tangent 0.02. The antenna resonates at 2.48 GHz with a bandwidth of 25 MHz. The resonant frequency of the antenna shifts depending on the material in which the antenna is placed. The soil moisture content is found by the relative shift of S₁₁ of the sensor antenna. Sensors can be used in real environment especially in the agricultural domain to find the dry or humid nature of the soil in the field at any particular time of the year. It can also be used to sense the presence of water in remote areas.