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This work presents a single-antenna self-injection-locked (SIL) radar to reduce the hardware complexity of continuous-wave (CW) Doppler systems. The theory provides a basis for determining the signal-to-noise spectral density ratio (SNDR) with the effects of clutter. Experimental results agree closely with the theoretical predictions, showing that the clutter does not affect the optimal SNR performance in an SIL radar. A single-antenna SIL radar array is designed to detect vital signs with random body movement cancellation. To this end, a subject is placed between two single-antenna SIL radars to measure the rates of respiration and heartbeat using Doppler shift, and the effects of random movement of the subject are cancelled by wireless mutual injection locking (MIL) of the two radars. In an experiment, a prototype of such a two-radar array with a spacing of 2 m was implemented at 2.4 GHz, providing accurate and reliable cardiopulmonary monitoring of a subject who jogged on a treadmill with random body motion of many centimeters.

on 0.508-mm-thick (20 mil) RT/Duroid 5870 substrate with a relative dielectric constant of 2.33. The chip components include Panasonic surface mount capacitors (1.0 ϫ 0.5 mm) of value 2C N ϭ 12 pF and inductors (1.6 ϫ 0.8 mm) of value L N ϭ 15 nH. The dimensions of the resonator with an inner diameter greater than zero as shown in Figure 1 are l 1 ϭ 6.2 mm, W ϭ 1.47 mm, and d ϭ 1.02 mm. The dimensions of the resonator with an inner diameter of zero as shown in Figure 2 are l 2 ϭ 6.93 mm and W ϭ 1.47 mm. The coupling gap spacing for both resonators is s ϭ 0.2 mm.The measurements are made using an Agilent 8510C network analyzer and the results are shown in Figure 3. The measured responses of the proposed resonators are almost identical. The loaded Q for both resonators is about 48, which approximately equals the Q for the lumped inductor at 1.2 GHz. Therefore, if the design requires a higher Q, a lower loss inductor can be used. At 1.2 GHz, the proposed resonator offers 6-dB lower insertion loss and has a maximum dimension 32% more compact than the gap coupled NRI line resonator in [5]. Compared to a conventional half-wavelength ring resonator at 1.2 GHz, the total circumference of the proposed resonator (including both upper and lower paths) is reduced by 84%. Also, due to the lumped elements there are not higher-order resonances as in the conventional ring resonator [7]. CONCLUSIONSA compact gap-coupled ring resonator using an NRI TL section has been realized. It was demonstrated that the proposed structure resonates with an inner diameter of zero. Resonance occurs when the phase delay of the upper path equals the phase advance of the lower path. It is expected that this new resonator will have many applications in the design of compact microstrip filters and oscillators. ACKNOWLEDGMENTSThe authors would like to thank M.-Y. Li of Texas A&M University for technical assistance.

Abstract-This paper presents a self-injection-locked (SIL) radar with ranging and tracking capabilities to see through walls for discovering hidden people. Characterized by low complexity and high sensitivity, the proposed SIL radar merges the frequency-modulated continuous-wave and sum-difference pattern detection approaches to determine the distance and azimuth from the radar to each individual in a scene behind a wooden partition wall. An individual can be distinguished from a stationary object by using dynamic spectral subtraction to extract human motions or vital signs. Additionally, two or more individuals can be distinguished from each other by decomposing the Doppler signal into contributions of individuals in a polar domain. Consequently, a see-through-wall imaging system is constructed with the proposed SIL radar to position different individuals concealed behind a wall.