# Microwave Engineering Questions and Answers – Lange Coupler

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

1. The major disadvantage of coupled line coupler is:
a) complex construction
b) low power gain
c) higher loss
d) none of the mentioned

Explanation: Coupling in a coupled line coupler is too loose to achieve coupling factors of 3 or 6 dB. Since higher efficiency is not achievable, this a major disadvantage. One method of improving coupling is designing in such a way that the fringing field contributes to coupling.

2. Lange couplers consist of four parallel lines that are ______ coupled.
a) tightly
b) loosely
c) partially
d) none of the mentioned

Explanation: Lange couplers consist of four parallel lines. These parallel lines are tightly coupled to achieve 3 dB coupling ratio. Achieving 3dB coupling implies that 70% of the applied power is coupled.

3. Lange coupler is a type of Quadrature hybrid.
a) true
b) false

Explanation: Lange coupler ha two output ports. The output voltage measured at these ports is 900 out of phase with one another. Hence, they are called a type of Quadrature hybrid.

4. A major disadvantage of Lange coupler is:
a) high power loss
b) complex construction
c) low gain
d) none of the mentioned

Explanation: The main disadvantage of Lange coupler is probably practical, as the lines are very narrow and close together, and the required bonding wires across the lines increases complexity.

5. For even mode excitation of a Lange coupler, all the four lines of the Lange coupler are at:
a) equal potential
b) zero potential
c) unequal potential
d) negative potential

Explanation: during the analysis of Lange coupler, when they are excited in the even mode, all the four conductors of the coupler are at equal potential. Hence the capacitance Cm has no effect and need not be considered for further analysis.

6. Even mode characteristic impedance of a Lange coupler:
a) (Vp.Cep)-1
b) Vp.Cep
c) (Vp.Lep)-1
d) Vp.Lep

Explanation: The even mode characteristic impedance of a Lange coupler is given by (Vp.Cep)-1. Here Vpp is the phase velocity and Cep is the capacitance of any of the four conductors of the Lange coupler measured during even mode of analysis.

7. In a Lange coupler having 4 lines, the adjacent lines are connected so as to act as two conductors in parallel.
a) true
b) false

Explanation: In a Lange coupler consisting of 4 lines, the alternating lines are connected together. This simplifies the computation effort for finding equivalent capacitance and the construction is simpler. Also ports are easily distinguished and helps in flow of power in required direction.

8. For a 4 wire Lange coupler, if the odd mode and even mode capacitances are 12pF and 9pF respectively, then the equivalent capacitance in terms of two wired coupled line in even mode is:
a) 15.1 pF
b) 16.7 pF
c) 12 pF
d) 9 pF

Explanation: Equivalent capacitance in terms of two wired coupled model is Ce (3Ce+C0)/(Ce+C0), Where Ce and C0 are the equivalent capacitances in even mode and odd mode for 4 wire model. Substituting the given values in the above expression, the equivalent capacitance is 16.7 pF.

9. For a 4 wire Lange coupler, if the odd mode and even mode capacitances are 12pF and 9pF respectively, then the equivalent capacitance in terms of two wired coupled line in odd mode is:
a) 18.56 pF
b) 25.71 pF
c) 42 pF
d) 31.6 pF

Explanation: Equivalent capacitance in terms of two wired coupled model is C0 (3C0+Ce)/ (Ce+C0), Where Ce and C0 are the equivalent capacitances in even mode and odd mode for 4 wire model. Substituting the given values in the above expression, the equivalent capacitance is 25.71 pF.

10. The phase velocity of the waves in both even and odd mode of a Lange coupler is equal.
a) true
b) false

Explanation: The phase velocity of the waves in the even mode and odd mode are not practically equal and there are lot of variations. But only for theoretical analysis, they are assumed to be equal.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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