Cheap Waveguides can Ruin your Day

Though there are many reputable and high quality waveguide vendors, some vendors, specifically offshore vendors, may use machining techniques that reduce time and cost of manufacture. These short-cuts could have dramatic impact on a waveguide component and system performance. Any misalignments or machined geometries beyond specified levels can reduce the VSWR performance of a waveguide, cause RF leakage between the flanges, and increase maintenance/service costs.

One such example is the drilling of fastening holes in a waveguide flange. In order to achieve high precision alignment, the waveguide flange needs to be attached to the waveguide prior to drilling. However, some machining houses will drill the waveguide flanges prior to attachment. This could lead to x,y, and rotational displacement between the waveguide flange holes and the specified hole locations for the waveguide size and flange type. The errors may be so slight that there aren’t visually discernible or measurable with a pair of calipers. There are x,y, coordinate machines used to measure hole dimensions that are highly precise, and can be used to evaluate incoming parts.

Some high microwave and millimeter-wave waveguides also use guide pins with detailed specifications provided in MIL-DTL-3922. At higher frequencies these pins are specified at 0615, where some companies will use 0612 pins, as they are a standard stock pin. The pin sizes are not visually discernible and can also lead to misalignments.