24 GHz Flexible Antenna for Doppler Radar based Human Vital Signs Monitoring
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Noncontact monitoring of human vital signs is an emerging research topic in recent years. A key approach to this monitoring is the use of the Doppler radar concept which enables real-time vital signs detection, resulting in a new class of radar system known as bio-radar. Unlike traditional techniques that use contact electrodes for vital sign measurement, bio-radar is non-intrusive and less perturbing for infants and patients with critical injuries. The bio-radar can even detect life under rubble in the aftermath of disasters. The antennas are a key component of any bio-radar module and their designs should meet the common requirements of bio-radar applications such as high directivity, circularly polarized, and flexibility. This thesis presents the design of a 24 GHz four-element antenna array on a low-cost and flexible liquid crystal polymer (LCP) substrate with a thickness of only 100 m, low-loss tangent (tan=0.0021), stable dielectric constant (r=3.35) and low moisture permeability. The designed antenna array can be used with a bio-radar for vital signs monitoring in a non-contact manner. To the best of our knowledge, the design of flexible antenna arrays for bio-radar and the use of LCP for such applications have not been explored in literature. Any antenna array will require a unit element to be designed first. The unit element was designed with an input impedance of 50 Ω on LCP substrate, which is then used to construct a two- and four-element array with an overall dimension of 29.5×25.4 mm, and 5336.5 mm, respectively. The simulated gain obtained is 4.39 dB, 5.46 dB, and 6.68 dB for unit cell, two-element array, and four-element array, respectively. Other measured and simulation results showed close agreement. The two vital signs: breathing rate (BR) and heart rate (HR) of two human subjects are detected with relatively good accuracy using the fabricated antenna arrays and RF output power of -3 dBm from a distance of approximately 60 cm.