Loop-Dipole Composite Antenna for Wideband Microwave-Based Medical Diagnostic Systems With Verification on Pulmonary Edema Detection

Abstract

A unidirectional and compact antenna for wideband microwave-based medical diagnostic applications is presented. The main part of the antenna is formed from the combination of loop and dipole interleaved structures. To enable the antenna to resonate at a low frequency within a compact substrate area, a pair of slots is created on the loop’s vertical arms, whereas the dipole’s structure is tapered to compensate for the negative effect of the capacitively loaded slots. With the proposed configuration, the antenna acts as an array of two dipoles and a quasi-Yagi antenna at lower and higher frequencies, respectively, and thus radiates mainly in one direction. The antenna has a compact size (with respect to the wavelength at the lowest operating frequency) of $0.23 \times 0.23$ , making it 50% smaller than similar designs. It has a measured fractional bandwidth of 55% at 0.65–1.15 GHz and peak gain and front-to-back ratio of 3.8 dBi and 11 dB, respectively. To verify the practicality of the antenna, it is applied in an array configuration and successfully tested in detecting pulmonary edema in realistic simulation and experimental environments.