In this paper, the gap waveguide technology is examined for packaging liquid crystal (LC) in tunable microwave devices. For this purpose, a line based passive phase shifter is designed and implemented in a ridge gap waveguide (RGW) topology and filled with LC serving as functional material. The inherent direct current (DC) decoupling property of gap waveguides is used to utilize the waveguide surroundings as biasing electrodes for tuning the LC. The bed of nails structure of the RGW exhibits an E-field suppression of 76 dB in simulation, forming a completely shielded device. The phase shifter shows a maximum figure of merit (FoM) of 70 • /dB from 20 GHz to 30 GHz with a differential phase shift of 387 • at 25 GHz. The insertion loss ranges from 3.5 dB to 5.5 dB depending on the applied biasing voltage of 0 V to 60 V. INDEX TERMS Liquid crystals (LC's), tunable phase shifter, phased array, gap waveguide, bed of nails.

The passivation behaviour of e-brass (Cu : Zn = 67: 33) in alkaline solutions was studied using cyclic voltammetry and potentiostatic current transient measurements. The recorded cyclic voltammograms exhibited the main features usually observed for pure copper and zinc, and one additional anodic peak on the reverse potential scan. The height, sharpness and location of the different peaks depended greatly on the alkali concentration and the scan rate. The results show that the formation of Cu20 and Cu(OH)2 films proceed under ohmic resistance control following a dissolution-precipitation mechanism. The effect of F-, C1-and Br-ions on the passivity was also studied. The pitting potential was found to decrease with logarithm of halide ion concentration. The current transients in the absence and presence of halide ions were analysed. In the absence of pitting the current, after a few seconds, was found to increase linearly with the reciprocal of the square root of time while in the presence of pitting it was found to fit the Engell-Stolica equation.

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