This paper presents a novel design for a four-port transmitter antenna circuit tailored for an ambient backscatter communication system (ABCS) operating at 433 MHz, aimed at enhancing human activity recognition (HAR) in healthcare monitoring applications. The proposed system captures the ability of the ABCS to utilize ambient radio frequency (RF) signals, such as those from Wi-Fi, to transmit data without the need for active RF sources. This feature is particularly advantageous in low-power, data-intensive environments. The paper introduces the development of the ABCS framework, comprising a four-port antenna circuit and a Nooelec NESDR Mini USB RTL-SDR receiver, to accurately detect eight specific human activities, including new healthcare monitoring activities like “standing while dizzy,” “standing and suddenly collapsing,” and “sitting while shaking.” The experiment was conducted with five participants performing eight activities, and the results demonstrated distinct signal patterns corresponding to each activity. The findings show that the proposed system is a promising solution for the real-time, non-intrusive monitoring of human activities, which is crucial for early detection and intervention in healthcare scenarios.