Unidirectional Slot-Loaded Loop Antenna With Wideband Performance and Compact Size for Congestive Heart Failure Detection

A slot-loaded meandered loop antenna for congestive heart failure (CHF) detection system is presented. To meet the requirements for a CHF detection system, the antenna is designed to have a compact size, wideband at the ultra-high frequency band and unidirectional radiation. To that end, several techniques are applied to the main utilized structure, which is a conventional loop antenna. To lower the resonant frequency and enhance the directivity within a compact size, the loop is capacitively loaded using a pair of slots. To compensate for the effect of the capacitive coupling on the input impedance matching, an inductive reactance is added by meandering the loop's structure. With the applied modifications, the proposed antenna has a compact size of 0.21 × 0.21 with respect to the wavelength at the lowest operating frequency. The realized dimension represents only a quarter of the size of its counterpart planar designs. The proposed antenna achieves a wide measured fractional bandwidth of 50% (0.66-1.1 GHz), 9 dB peak front-to-back ratio and 4.1 dBi gain. The antenna is then used as part of a CHF detection system that also includes a compact transceiver, scanning platform, and laptop for control and processing. Using a suitable frequency-domain processing and imaging algorithm, the system successfully detects an early CHF in an artificial torso phantom.