An Integrated Millimeter-Wave Broadband Microstrip-to-Waveguide Vertical Transition Suitable for Multilayer Planar Circuits
An integrated broadband vertical microstrip-to-rectangular waveguide (RWG) transition at Ka-band is presented. This transition is especially suitable for multilayer planar circuits, by utilizing a section of multilayer three-dimensional (3-D) stepped substrate integrated waveguide (SIW) structure, along with a taper transition. A simplified initial transition model from 3-D stepped SIW to waveguide is first optimized, thereafter, a full microstrip-to-waveguide transition is constructed and further optimized. For demonstration, some back-to-back transition prototypes are fabricated by multilayer PCB processing. The experimental results show that the return loss better than 15 dB is obtained from 33 to 36.7 GHz, with the minimum net insertion loss about 0.7 dB for a single transition at 35 GHz.
Substrate Integrated Waveguide Cavity-Backed Wide Slot Antenna for 60-GHz Bands
A wide slot antenna backed by a substrate integrated waveguide (SIW) cavity is presented and investigated for the enhancement of operating bandwidth at 60-GHz band. The 10-dB return loss impedance bandwidth of the antenna increases from 3% to 11.6% with consistent radiation performance as the width to length ratio (WLR) of the rectangular slot cutting from the SIW increases from 0.12 to 0.71. Its dual-resonance operation mechanism is verified by a parametric study. Three 2 × 4 antenna arrays with different slot WLRs are designed and fabricated with a printed circuit board (PCB) process at the 60-GHz bands. The measured results show that the antenna array with slot WLR of 0.71 achieves the gain of 10-12 dBi and the cross-polarization levels of better than 25 dB in both E- and H-planes over the enhanced operating bandwidth of about 11.6%.
Optical rotatory dispersion and absolute configuration—III
Abstract Optical rotatory dispersion measurements on pyrrolidine, piperidine, and tetrahydro-isoquinoline alkaloids indicate that the absolute configuration of the α-asymmetric center may be assigned directly from the dispersion curve, provided either that the nitrogen atom is not protonated, or that the compound contains a chromophore absorbing above 200 mμ.