Novel RF Slow-Wave Coupled-Line Circuits and Antennas for Compact Wireless Systems
thesisposted on 15.04.2014, 00:00 by Haijiang Ma
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 180o 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.