Range detection of moisture plume with miniaturized microwave sensor

Abstract

Range detection and tracking of moisture plume in the microwave spectrum (L-band: 1–2 GHz) has been successfully achieved using compact sensors. Range detection is advantageous over point sensors due to its long range tracking capability as well as its immunity from adverse weather conditions. Hexagonal Microstrip antenna (HMSA) and its miniaturized shorter versions (4X) are investigated as potential sensor candidates. HMSA is modified by shorting along the zero field to yield Quarter Hexagonal Microstrip Antenna (QHMSA). QHMSA acts as a shorted 90° sectoral antenna. There is a size reduction by a factor of four without any significant change in resonant frequency. The sensing is based on the principle of loss in attenuation in the presence of moisture plume. As moisture is known to absorb microwave frequency, there is a reduction in S21 which is a measure of the device sensitivity. Effective aperture size of the antenna in compact shorted mode is reduced and accordingly the gain. Since loss in attenuation (S21) is unchanged even with reduced gain, the sensitivity to moisture and thereby sensor's performance remains unaffected. The frequency with an insignificant variation of about 2–3% and an enhanced bandwidth (∼ 60%) of the QHMSA over HMSA further adds to its sensitivity.