Analysis of a CSRR-Based S-Band Microstrip Patch Structure for Sensor and Tunable Antenna Applications

A square-shaped microwave patch structure with a defective ground plane configuration is reported to characterize engine oils and tunable antenna applications. The defect is created in the form of a CSRR structure. The proposed structure is designed with a Roger-RT Duroid 5880 substrate with a loss tangent of 0.004 and the dimensions of the antenna are 50 × 50 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>m</mml:mi> <mml:msup> <mml:mi>m</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>.</mml:mo> </mml:math> To obtain better efficiency, antenna parameters are optimized by the frequency domain solver tool in CST Microwave studio software. Under unloaded conditions, the sensor operates at a resonant frequency of 3.43 GHz. The sensor has a maximum dielectric sensitivity of 419 MHz/ε r , when it is immersed completely (100%) in used engine oil ( ε r = 2.74). As a liquid sensor, it has a sensitivity of 12.23%, greater than most existing sensors. Moreover, the advantage of the sensor is its simple design and fabrication. Further, the antenna is made tunable, where resonant frequency varies from 3.4 GHz to 2.90 GHz, i.e., 530 MHz, by immersing in different volumes of fresh engine oil ( ε r = 2.32).