Advantages of the Double Ridge Waveguide Design

Waveguides come in many varieties. The most common “shapes” for waveguide cross sections are rectangular and circular/oval. Waveguide can carry electromagnetic energy in several modes, though they are typically specified for a primary mode that presents the most desirable characteristics for loss and bandwidth. This mode is generally the transverse electric (TE) mode, where the direction of the electric field is perpendicular to the direction of travel. This mode has the electric field pointing toward, and away from, the sidewalls of the waveguide.

Adding an internal ridge to a waveguide changes the behavior of the electric field within the waveguide, as the walls of a waveguide are grounded. Hence, adding an internal ridge moves a ground plane and limits the distance the electric field has to travel within the waveguide, also increasing the capacitance between the walls compared to a waveguide without ridges. Like a single ridge waveguide, a double ridge waveguide uses this concept to further “pinch” the e-field within the waveguide.

The results of this are a reduction in impedance and also lowers the low frequency cut-off of the waveguide. This essentially allows for a waveguide of a smaller size to accommodate lower frequencies than would otherwise be possible without ridges within the waveguide. Moreover, adding ridges within a waveguide also leads to creating higher order waveguide modes that are possible with the new internal structures. With proper design and fabrication, the dimensions and depth of the ridges can be controlled to realize very specific behavior, including pushing undesirable modes to frequencies beyond that of interest and mitigating the need for filtering, in some cases.

The ability to control a waveguide’s impedance with ridges also allows for impedance matching without the need for additional components or devices, or reducing the impedance matching margins to something more easily managed. This can save substantially on design cost and complexity. Having a waveguide with smaller physical dimensions that can still operate at low frequency may be desirable in many applications where there are substantial space and weight constraints.

Main Benefits of Ridge Waveguide

• Lower cutoff frequency compared to similar sized non-ridge waveguide
• Extended higher order mode frequency, possible benefits for waveguide filter design
• Replacement for planar transmission lines where enhanced power handling is needed in a compact space
• Wider bandwidth than rectangular waveguides allows for a wide range of “transmission line” like use cases
• Switches

Another advantage of double ridge waveguides over non-ridge or even single ridge waveguides is the ability to place switching elements within the gap of the ridges to more easily create a switch. Double ridge waveguides have a much smaller gap region between the e-field ground planes, making them much easier to bridge with smaller, more reliable, and faster actuators. In some cases even microelectromechanical (MEMS) switch technologies may be used to create relatively compact and fast waveguide switches.

Learn more about Pasternack’s line of Double Ridge Waveguide Components:

• Pasternack Double Ridge Waveguide Switches