Luso Electronics, a supplier and installer of microwave systems and components, has introduced a low-loss alternative to standard WR75 and WR62 for cross-site runs between switching networks and antennas. The Signal Wave System (SWS), which also offers increased power handling capability over traditional waveguides, gives worthwhile savings on runs as short as 10 m.
The improvement is achieved by adding an electroformed taper transition from WR75 to SWS75, a mode suppressor and a length of over-sized waveguide in the run. The over-sized section is made from precision drawn waveguide and it is terminated with special flanges to minimize mismatch in the waveguide run.
For standard waveguide frequency bands, traditional waveguide dimensions are chosen so that only the single mode TE10 will propagate. Even with precise electroformed components, no matter how insignificant the mode conversion energy, some unwanted higher order waveguide modes may be excited. Without some form of mode suppression, the unwanted higher order modes are trapped between the two transition ends.
In Signal Wave System installations, the SWS run length is many times the signal wavelength, so the trapped resonant frequencies form comb lines. Even though these higher order modes are very weak (typically -60 dB or less), trapped mode conversion affects linearity whenever the operating frequency coincides with one of the comb lines. The exact process causes small wiggles in the group delay at the comb line frequencies. The mode suppressor absorbs these. Importantly, SWS is no more complicated to install than standard waveguide and no special tools or alignment are necessary.