Waveguides are some of the most important transmission lines used in microwave applications, especially in millimeter-wave systems, due to its low loss and high-power handling characteristics. However, the waveguide has a defined operating bandwidth due to its inherent structural limitations. For example, the standard operating frequency of a WR-10 rectangular waveguide is 75 to 110 GHz. It is well known that the lower side frequency is limited by the cutoff frequency of the waveguide dominant mode, TE10:
Fc ≥ C/2A
Where C is the speed of light and A is the dimension of the wider side, or width of the rectangular waveguide.
The WR-10 waveguide cut off frequency is 59.01 GHz, therefore, frequencies higher than 60 GHz can pass. In order to avoid the excessive insertion loss and rapid phase frustrations near the cut off frequency, the practical low side operation frequency limit can be set at 65 GHz.
The high side frequency limit is set by the first high order model. In the case of the WR-10 rectangular waveguide, the first high order mode is TE20 mode with a cutoff frequency of two times of the TE10 mode cut off frequency, i.e., 118.02 GHz. Leaving a proper guard bandwidth to accommodate for mechanical tolerance, the high side frequency limit of the WR-10 rectangular waveguide is set at 110 GHz. For a similar reason to the low side frequency limit, the high side operation frequency of the WR-10 waveguide can be pushed to 116 GHz. Furthermore, the high side frequency limits can be extended further given that the mechanical structure of the component prevents the TE20 mode excitement.
Because of the considerations discussed above, customers are using waveguide components beyond the recommended frequency range of the standard waveguides and asking if SAGE Millimeter’s components can likewise support. Fortunately, SAGE Millimeter has manufactured and designed many of our full waveguide bandwidth products with good margins on the frequency range of operation. In other words, the actual operating frequency range is wider than what the industry has specified. The STF, STA, STZ, SFB and SWD models are a few product families that belong to this category. These products have about a 10% extended bandwidth on the low side and a greater than 10% extended bandwidth on the high side.
Several products with extended bandwidth performance are presented below (Figures 1 through 5) as examples to demonstrate the potential operating frequency range of SAGE Millimeter’s standard models. The data presented is for illustration only. Detailed data collection for more extended product models with upper and low frequency limits are in progress. Please contact us for performance of the product of interest.
- Faraday Isolator, STF Series
2. Direct Reading Attenuator, STA Series
3. Noise Source, STZ Series
4. Full Band Balanced Mixer, SFB Series
5. Full Band Directional Coupler, SWD Series
6. End Launch Waveguide to Coax Adapters, SWC Series
In general, the end launch waveguide to coax adapters can easily extend the operation frequency of the waveguide band by 10%. The example shown below is the Ka Band.