In this paper, a miniaturized circularly polarized (CP) continuous wave Doppler radar system operating at 2.4 GHz is presented. The radar front end consists of one left-handed CP (LHCP) antenna and ...one right-handed CP (RHCP) antenna, which share a single patch antenna aperture. Orthogonal polarization is achieved through a modified ring-shaped quadrature hybrid coupler (QHC), and the resulting isolation between the two CP antennas is better than 30 dB. With 0 dBm input power to the transmitting antenna, the proposed radar system can accurately detect heartbeat and respiration movements of human test subjects under 1 m and over a wide angular range. The single dual CP antenna achieves 280% size reduction compared to a traditional two linear polarization patch antenna array with the same isolation level.
A novel coupled line structure is studied based on two layers of crossing strips with dense interconnecting vias. The two arrays of vias resembling fence walls in substrate integrated waveguides help ...enhance the inductive coupling significantly. Dispersion characteristics of both odd and even modes are investigated with emphasis on phase equalization and impedance design as well as coupling enhancement. A specific slow-wave coupled-line structure with enhanced coupling is designed, fabricated and tested as an example. Good agreements are found between measured and simulated results of slow-wave factors, line impedances, and coupling level.
A novel coupled line structure based on two inter-wound right-handed metamaterial transmission lines is investigated. The basic approach is to compress, twist, and fragment (CTF) metal strips or ...discs periodically in a multi-layer structure to form a four port structure that carries the feature of a large slow-wave factor with a band selection capability. Dispersion characteristics of both odd and even modes are investigated with emphasis on phase equalization and impedance design. A specific metamaterial couple-lines structure is designed, fabricated and tested as an example. The measured results of the slow-wave factor and line impedance are in good agreement with those of simulated results. Potential applications of the proposed coupled line structure are also discussed.
The design and analysis of a miniaturized transmission line transformer/balun for RF applications are presented in this paper. A novel right-handed slow-wave line using three-dimensional periodic ...substrate metallization is proposed, where each unit cell is made up of a multilayer loop as a series inductor and parallel strips as a shunt capacitor. DC isolated single-end primary and differential secondary are constructed using three quarter-wave slow-wave lines. A design example is given for a 1:3 voltage ratio at 1.9GHz with slow-wave factors (SWF) between 8~9 for the quarter-wave lines on a three-layer FR4 substrate. The planar dimensions of the electrically small balun are 10mm by 6mm. Details of the designs with simulated and measured data are discussed.
Recently, the demand for small RF front ends has been ever increasing for modern compact versatile wireless systems. It brings new design challenges to RF engineers, as the dimensions of antennas and ...passive circuits are proportional to a guided wavelength. Coupled-line circuits still remain the bottleneck for miniaturization due to their more complexity over other passive circuits. In this thesis, novel slow-wave coupled line circuits and antennas are proposed to address the above-mentioned bottleneck. Initially, a complete theoretical study is conducted on both right-handed and left-handed artificial coupled transmission lines. Design criteria and tradeoffs are illustrated for right-handed slow-wave coupled lines through guided-wave characteristics in terms of propagation constants, line impedances, slow-wave factors, and cut-off frequencies under even- and odd-mode excitations. High-density 3D metallization on multilayer substrate can help to enrich inductive and capacitive effects periodically within a small unit cell. New slow-wave coupled and isolated lines are designed with least dispersion and attenuation based on the three-layer inverse mushroom topology. In succession, high-performance miniaturized coupled line circuits with DC isolation are demonstrated with over 80% planar area reduction, in contrast to their conventional microstrip counterparts. Apart from directional coupler, two low-order coupled line band-pass filters are presented in both regular and folded configurations. A Marchand balun is shown with an impedance transformation ratio of 1:3 from source to load impedances. A novel coupled line 180° hybrid coupler is developed with equal power splitting and excellent isolation at outputs. In addition, circuit architectures, analyses, and syntheses are provided. Finally, miniaturized printed folded helical dipole and monopole antennas at GSM1800/1900 bands are investigated as two examples of electrically small antennas with self resonance, sufficient bandwidth, and self impedance matching. Their radiation Q-factor reductions of about 40% and 62% are observed, respectively, over their non-folded helix counterparts.
This paper presents a folding scheme to address fundamental issues of planar electrically small resonant antennas with small radiation resistance, high Q factor, and narrow bandwidth. Two printed ...folded helical antennas are investigated as examples of small antennas for GSM1800/1900 bands. Dramatic bandwidth enhancements of as much as 66% and 163% are found, respectively, for folded helical dipole and its monopole version over their non-folded counterparts. The proposed folding method facilitates integrated antenna miniaturization with self resonance, sufficient bandwidth, and self impedance matching.
A novel coupled line structure based on two inter-wound right-handed metamaterial transmission lines is investigated. The basic approach is to compress, twist, and fragment (CTF) metal strips or ...discs periodically in a multi-layer structure to form a four port structure that carries the feature of a large slow-wave factor with a band selection capability. Dispersion characteristics of both odd and even modes are investigated with emphasis on phase equalization and impedance design. A specific metamaterial couple-lines structure is designed, fabricated and tested as an example. The measured results of the slow-wave factor and line impedance are in good agreement with those of simulated results. Potential applications of the proposed coupled line structure are also discussed.
This paper investigates equity with respect to one component of welfare in China--the provision and use of health services. Based upon a large-scale survey of almost 16,000 individuals in eight ...provinces in China, we examine a sub-sample of working-age adults who have identified themselves as injured or ill during the four weeks prior to being interviewed. We found that, beyond the level of severity of the reported condition, very few individual-level factors are related to the use of services when ill or injured. Only gender (female) and employment in state-run enterprises are associated with higher patterns of use. These results suggest that China has achieved a very wide distribution of clinics and other services at the local level, and that they are widely used by those who identify need for them. It is rare to be over half an hour away by bike from some form of care and the majority of care appears to be reasonably inexpensive. This broad availability of services contrasts with recent reports from China stressing declining accessibility, and paints a picture of relatively equal access to health care.
Diets and activity patterns are changing rapidly in low-income countries, and problems of undernutrition and overnutrition commonly exist side by side. China has conquered problems of food scarcity ...at the national level and has undergone a remarkable transition in the structure of its diet in the last decade. In this paper, we use data from the 1989 China Health and Nutrition Survey and national data from the State Statistical Bureau to explore China's recent history with respect to nutrition and to identify patterns of under- and overnutrition. In particular, we see that higher income levels, particularly in urban areas, are associated with consumption of a diet higher in fat and with problems of obesity. At the same time, undernutrition is a problem in important segments of Chinese society. There is a need for the Chinese government to consider ways to address these problems of deficit and excess jointly.
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