The cutoff frequency (in GHz) for the dominant TE10 mode of an air-filled rectangular waveguide of ...
Q. The cutoff frequency (in GHz) for the dominant TE10 mode of an air-filled rectangular waveguide of inner dimension 0.28 inch×0.14 inch is __. (rounded off to two decimal places).
Given Information
- Waveguide dimensions = 0.28 inch × 0.14 inch
- Wider dimension (a) = 0.28 inch
- Smaller dimension (b) = 0.14 inch
- Medium = Air
- Dominant mode = TE10
- Speed of light (c) = 3 × 108 m/s
Step 1: Cutoff Frequency Formula
The cutoff frequency of a rectangular waveguide is:
fc = (c / 2) √[(m/a)2 + (n/b)2]
For the dominant TE10 mode:
m = 1, n = 0
fc = c / 2a
Step 2: Convert Inch into Meter
We know that 1 inch = 0.0254 meter.
a = 0.28 × 0.0254
a = 0.007112 m
Step 3: Calculate Cutoff Frequency
Substitute the values into the formula:
fc = c / 2a
= (3 × 108) / (2 × 0.007112)
= 21.0911 × 109 Hz
= 21.0911 GHz
Final Answer
21.09 GHz
Cutoff frequency of the dominant TE10 mode
Important Note
For the dominant TE10 mode, the cutoff frequency depends only on the wider dimension (a), not on the smaller dimension (b).