Design and testing of frequency-doubling microstrip antenna sensor for wireless monitoring of high temperatures

In order to solve the shortcomings of wireless passive sensors based on label chips for signal transmission, which cannot withstand high temperatures, and the problem of the short transmission distance of wireless passive sensors without chips, a wireless passive high-temperature frequency-doubling microstrip antenna sensor based on a high-temperature-resistant Schottky diode is proposed. The sensor utilizes the characteristic of the resonant frequency of the microstrip antenna changing with temperature. The high-temperature-resistant platinum sensitive structure integrated on alumina ceramic adapts to temperature measurement in harsh environments such as high temperatures, oxidation, and corrosion. A high-temperature-resistant Schottky diode was designed, and on this basis, a high-temperature-resistant frequency doubling circuit was designed and implemented. Through this circuit, the network analyzer can transmit a fundamental frequency signal and receive a modulated double frequency signal, while limiting ambient noise to the fundamental frequency band, eliminating interference, and significantly improving the signal-to-noise ratio, thereby enabling wireless transmission. In addition, a high-temperature-resistant, miniaturized broadband coplanar waveguide antenna was designed to replace the traditional horn antenna as the interrogation antenna, which realized the wireless transmission of sensor signals. A high-temperature testing system was set up to test the sensor performance in the range of 15-800 °C. The results showed that the maximum transmission distance of the sensor is 20 cm, and the transmission performance is best at 10 cm away from the interrogation antenna. It can accurately characterize the temperature during the heating process, with a sensitivity of up to 181 KHz/°C and a frequency error of no more than 0.2%.