# Microwave Engineering Questions and Answers – Striplines

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Striplines”.

1. Which mode of propagation is supported by a strip line?
a) TEM mode
b) TM mode
c) TE mode
d) None of the mentioned

Explanation: Since a stripline has 2 conductors and a homogeneous dielectric, it supports a TEM wave, and this is the usual mode of operation.

2. The higher order wave guide modes of propagation can be avoided in a strip line by:
a) Restricting both the ground plate spacing and the sidewall width to less than λd/2
b) Restricting both the ground facing plate spacing and the sidewall width to less than λd
c) Filling the region between 2 plates with di electric
d) Restricting both the ground plate spacing and the sidewall width between λg and λg/2

Explanation: When stripline is used as a media for propagation, it is always preferred that only certain modes of propagation are allowed. Hence, in order to avoid the higher order modes, it is achieved by restricting both the ground plate spacing and the sidewall width to less than λd/2.

3. Stripline can be compared to a:
a) Flattened rectangular waveguide
b) Flattened circular waveguide
c) Flattened co axial cable
d) None of the mentioned

Explanation: A stripline has an enter conductor enclosed by an outer conductor and are uniformly filled with a dielectric medium, these are similar to a coaxial cable. Hence it can be compared to a flattened coaxial cable.

4. If the dielectric material filled between the round plates of a microstrip line has a relative permittivity of 2.4, then the phase velocity is:
a) 1.3*108 m/s
b) 1.9*108 m/s
c) 3*108 m/s
d) 2*108 m/s

Explanation: Phase velocity is given by the expression C/√∈ for a stripline. Substituting the given values, the phase velocity for the above case is 1.9*108 m/s.

5. Expression for propagation constant β of a strip line is:
a) ω(√µ∈∈r)
b) ω(√µₒ/√∈r)
c) ω/(√µₒ∈ₒ∈r)
d)c/(√µₒ∈ₒ∈r)

Explanation: Propagation constant is associated with the propagating wave in the strip line. This propagation constant for a wave is defined by the expression ω(√µ∈∈r).

6. If the phase velocity in a stripline is 2.4*108m/s, and the capacitance per unit length of a micro stripline is 10pF/m, then the characteristic impedance of the line:
a) 50 Ω
b) 41.6 Ω
c) 100 Ω
d) None of the mentioned

Explanation: Characteristic impedance of a stripline is given by 1/ (vPc). Substituting the given values of phase velocity and capacitance, the characteristic impedance of the line is 41.6 Ω.

7. The expression for characteristic impedance Zₒ of a stripline is:
a) (30πb/√∈r)(1/We+0.441b)
b) (30πb) (1/We+0.441b)
c) 30π/√∈r
d) (1/We+0.441b)

Explanation: Characteristic impedance of a stripline is a function of the various parameters of the stripline. They are effective width, thickness and relative permittivity of the dielectric material. Changing any one of these parameters results in changing the characteristic impedance of the line The derived expression is hence (30πb/√∈r)(1/We+0.441b).

8. If the effective width of the center conductor is 3 mm and the distance between the two ground plates is 0.32 cm with the material of the dielectric used having a relative permittivity of 2.5, then what is the characteristic impedance of the strip line?
a) 50Ω
b) 71.071Ω
c) 43.24Ω
d) 121Ω

Explanation: The characteristic impedance of a stripline is given by the expression (30πb/√∈r)(1/We+0.441b). Substituting the given values in the given expression and hence solving, the characteristic impedance of the line is 43.24 Ω.

9. The wave number of a stripline operating at a frequency of 10 GHz is:
a) 401
b) 155
c) 206
d) 310

Explanation: The wave number of a microstrip line is given by the expression 2πf√∈r/c, c is the speed of light in space, ∈r is the relative permittivity of the dielectric medium. Substituting the given values in the equation, the wave number is 310.

10. If the loss tangent is 0.001 for a stripline operating at 12 GHz with the relative permittivity of the dielectric material being used equal to 2.6, then the conductor loss is:
a) 0.102
b) 0.202
c) 0.001
d) 0.002

Explanation: Conductor loss in a stripline is given by the expression k*tanδ/2. K is given by the expression 2πf√∈r/C which is the wave number. Substituting the values in the above two equations, conductor loss is 0.202.

11. If the dielectric material used between the grounded plates of a stripline is 2.2, when the strip line operating at 8 GHz, the wavelength on stripline is:
a) 1.2 cm
b) 2.52 cm
c) 0.15 cm
d) 3.2 cm

Explanation: The propagating wavelength on the stripline is defined by the relation C/f√∈r. substituting in the above relation, the propagating wavelength on the microstrip line is 2.52 cm.

12. Fields of TEM mode on strip line must satisfy:
a) Laplace’s equation
b) Ampere’s circuital law
c) Gaussian law
d) None of the mentioned

Explanation: If φ(x,y) is the function of potential in the stripline varying along the width and thickness, this potential function must satisfy the Laplace’s equation.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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