THz technology makes possible imaging of phenomena, inaccessible to both visible and infrared radiation, but the
imaging is still in its early stages of development. This paper draws attention to the aspects of speckle reduction to
improve the image quality. Because all existing THz sources are coherent - speckle is an ultimate limiting factor of the
free-space imaging techniques. Speckle arises when coherent light scattered from a rough surface is detected by an
intensity detector with a finite aperture, hiding the image information. This problem is of special importance for THz
imaging, because surface roughness is closer to the object dimension as in optical imaging. The reduction of speckle is
highly desirable and we propose here a Hadamard matrix solution. Hadamard diffuser for mm-wave frequency range
have been designed, built and tested. We report 50% speckle reduction measurements using a free-space vector network
analyzer over the full W-band (75-110 GHz). The advantage of the mm-wave Hadamard technology over optical: the
diffuser doesn't have to be moved (vibrated) any more to accomplish the technology of speckle reduction. Temporal
optical effect is substituted here by spatial quasi-optical: Hadamard coding in each scan pixel. Second method delivers
realistic system parameters for the speckle reduction with polychromatic light for aviation security.
Lumped circuit and 3D-electromagnetic models are presented for a photo-induced plasma that induces local changes in the dielectric properties of a coplanar waveguide transmission line to switch millimeter waves, propagating along transmission lines on BCB coated high resistive silicon substrates. Measurements up to 110 GHz are compared with the various developed models. The insertion loss of these transmission lines was only 1 dB/mm at 100 GHz. The modulation of S21 was about 40 dB at 110 GHz for an optical power of 60 mW focused on one slot between signal and ground. S11 could only be fitted with a lumped circuit model when introducing a frequency dependent impedance was introduced.