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Transmission and phase-shift characteristics of dichroic high-pass filters with cutoff frequencies as high as 1.11 THz and of a cross-shaped grid bandpass filter with a resonance frequency of 280 GHz were measured with an electro-optic sampling terahertz time-domain spectrometer operating between 0.1 and 2 THz. Good agreement with transmission theories is found. We also compare the transmission performance of cascaded dichroic filters with that of cross-shaped grid bandpass filters. Both types of bandpass filter permit frequency-selective ultrafast experiments in the far-infrared spectral region. In the millimeter and the submillimeter wavelength regions, which are difficult to access by conventional means, knowledge of the frequency response of frequency-selective components is important for applications in frequency mixing, multiplying, and multiplexing in quasi-optical systems.

A flexible waveguide system has been simulated using the field calculation program MAFIA, for the first time realised for frequencies up t o 150 GHz and operated in two applications. The flexible waveguide system consists of a rectangular, dielectric fibre made of polyethylene combined with optimised tapers and waveguide adapters, which makes the flexible waveguide easy to use in combination with conventional waveguides.A minimum attenuation of 4dB/m at 140 GHz has been obtained with the dielectric waveguides, which is about 6dB less than the measured attenuation of D-band waveguides operated at the same frequency. Additionally the phase shift of the flexible waveguides for different bending radii as well as the influence of different tapered fibre terminations was measured and is reported.

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