This paper presents a new architecture of a compact multimode FMCW radar for general purpose short-range applications. The radar can operate in CW as well as in FMCW modes. The transmitted RF frequency or frequency range can be arbitrarily selected using an inbuilt SPI control over 2.25-2.50 GHz with a frequency resolution of at least 100 kHz. A modified VCO-PLL loop with a stable reference source of 10 MHz improves the frequency stability. Other than the audio signal generator, all modules like RF blocks, base-band block DC power management block, and control and synchronization and data acquisition blocks are integrated into a single module using a three-layer PCB configuration. Fabrication and measurement of the radar unit in both the modes are presented.

An improved design of a cavity-backed slot ring antenna is presented. The antenna maintains its radiation characteristics and good impedance matching over at least 10 % frequency band. Over the band, the antenna does not show any beam tilt. Two higher order resonant modes are used to obtain high gain. The improved antenna characteristics is obtained by elevating a part of the top cavity plate containing the ring slot. A prototype antenna is designed and fabricated for 2.25-2.5 GHz short-range indoor radar applications. The antenna provides a measured gain of 7±0.5dBi over the entire band. The overall dimension of the antenna is 0.64λ0 × 0.64λ0 × 0.08 λ0, λ0 being the free space wavelength at the mid-band frequency. Design guidelines are provided for the frequency scaling.

This paper presents a compact continuous wave Doppler radar architecture at 2.4 GHz. The system provides a low-cost solution to remotely monitor vibrations of any object. In the RF system, two separate antennas are used for the transmitter and receiver. The receiver works in homodyne mode. A single microwave oscillator is used to transmit continuous wave signal as well as the synchronized local oscillator for the receiver. An opamp base band electronics separate the small receiver output signal from a large dc offset due to homodyne operation. In comparison to other approaches, number of components are minimized.