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.