3 GHz [56], 2 GHz and 3 GHz [57], and 2 GHz and 4 GHz [2], [58] as illustrated in Table 5. In this section, a review of state-of-the-art research on commonly used types of radars for vital sign detection was presented. The CW, UWB, FMCW, SFCW have all been used in this application, and each radar has its own advantages and disadvantages. The selection of the radar type in the research is subject to practical and detection environment requirements. Atten. FPGA OPAMP Pulse Generator 10 MHz CLK FPGA ADC I Agilent 83622B Signal Generator LPF LPF Mixer I Mixer 0° L Power Divider 2 Gain Block ADC Tx. ANT. PA Power Divider 1 Gain Block FPGA R L 90° L R Power Divider 1 R LNA Rx. ANT. Mixer LPF LPF I Figure 12. UWB radar system [2] and [49] © 2016 IEEE. Two-Channel DDS Board 1.2 GHz Ref Clock DDS1 Mini-Circuits Analog Device ZAPD-4+ HMC833 PLL Power PLL Splitter Mini-Circuits ZAV-8G PA Multiplexer DDS2 Transmitting Antenna Power Splitter PLL Quadrature 0° 90° Quadrature 0° 90° NI USB-6009 ADC LPF PC MultiChannel ADC Mini-Circuits ZAPDQ-4+ Power Splitter Multiplexer LPF LPF Analog Device HMC753 LNA Receiving Antenna Power Splitter LPF Figure 13. Multi-channel SFCW radar in [2]. FIRST QUARTER 2021 IEEE CIRCUITS AND SYSTEMS MAGAZINE 55