In a circular waveguide with radius r, the dominant mode is TM01 TE01 TM11 TE11

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Question
In a circular waveguide with radius r, the dominant mode is
Options
A. TM₀₁
B. TE₀₁
C. TM₁₁
D. TE₁₁

Correct Answer

TE₀₁

Explanation

Some applications require dual polarization capability. Circular waveguide has this capability.

These analysis uses cylindrical coordinates.

In circular waveguide TE₁₁ mode has the lowest cut off frequency and is the dominant mode.

If D is diameter of waveguide

?_c = 1.706 D for TE₁₁ mode

?_c = 1.029 D for TE₂₁ mode

?_c = 0.82 D for TE₀₁ mode

?_c = 1.306 D for TM₀₁ mode.

Microwave Communication problems

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1. Consider the following time parameters
1. Domain growth time constant.
2. Transit time.
3. Dielectric relaxation time in positive mobility regime.
Which of the above are used in connection width transferred electron device?
Options
A. 1, 2, and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only

2. A disadvantage of microstrip line as the connections of compared to strip line is that former
Options
A. do not lend themselves to printed circuit
B. are more likely to radiate
C. are bulky
D. are more expensive and complex

4. To ensure that only dominant mode TE₁₀ is allowed to propagate in an air filled rectangular waveguide, the lower frequency limit and upper frequency limit are
Options
A. about 25% above f_c for TE₁₀ and 5% below f_c for TE₂₀ mode respectively
B. about 50% above f_c for TE₁₀ and 25% below f_c for TE₂₀ mode respectively
C. about 25% above f_c for TE₁₀ and 25% below f_c for TE₂₀ mode respectively
D. none of the above

5. The external magnetic field in a magnetron is such that lines are
Options
A. parallel to the axis of cathode
B. perpendicular to the axis of cathode
C. inclined to the axis of cathode
D. either (b) or (c)

8. A circular waveguide carries TE₁₁ mode whole radial electric field is given by
E_r = E₀j₁(r) sin ? V/m
where r is radial distance in cm from the axis
The cut off wavelength is
Options
A. 10 cm
B. 3 p cm
C. 2 p cm
D. 8 cm

9. A 75 ohm line is first short terminated and minima locations are noted. Then the short is replaced by resistive load and minima location are again noted. If minima location are not altered and VSWR is 3, the value of resistive load is
Options
A. 25 ?
B. 50 ?
C. 225 ?
D. 250 ?

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