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 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.

A non-coherent passive six-port receiver system is presented for accurate amplitude, phase and frequency measurement of a RF signal. The system uses the six-port network and a new wideband phase delay line with known phase profile. The phase delay unit uses a number of openstubs connected to a microstrip line. Detail design steps of the phase delay line is presented. The whole receiver is fabricated in PCB technology. No local oscillator or DC biasing are used. Thus, it is an all-passive system, which does not require any power source. It can be used as a real time and fast demodulator for both analog and digital signals.

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.

This paper presents a broadside radiating wideband array antenna at 26.5 GHz. Both the TM ₁₁ and the next higher order mode, TM ₂₁ are excited on a single circular patch sitting on a large ground plane. The combination of these two modes provides elliptical beam in the broadside direction. Then, this patch is used as the basic radiating element for an array antenna. Because of the shaped radiation pattern, a 1 × 2 half wavelength array of the proposed antenna provides similar pattern like a 2 × 2 array of circular patches operating in only TM ₁₁ mode. With same inter element distance, a 1 × 2 array gives better performance in terms of gain bandwidth and size requirement as compared to conventional 2 × 2 array. Individual element size is slightly larger than the conventional TM ₁₁ mode antenna but the overall size of the array antenna is reduced to 50% without degrading the gain value. Further, the mode mixing technique provides a wide bandwidth and lower side lobe level. A prototype array element is fabricated in 1.52 mm thick RO4003C substrate. It provides an average broadside gain of 7.1 dBi with gain variation less than 0.8 dBi over 25.3527.65 GHz. The side lobe level is less than -14 dB from the broadside gain. Average total efficiency of the antenna is 86.6%.