Introduction:

Standing waves are formed when a wave reflects back and forth between two points with a fixed boundary condition. In the context of electrical engineering, standing waves occur when an incident wave encounters an impedance mismatch, resulting in partial reflection and transmission. Standing wave analysis is a commonly used technique to characterize transmission lines and waveguides.

Parameter Calculation:

Several parameters can be calculated from the standing waves, but in this question, we need to identify the parameter that cannot be calculated. Let's analyze each option:

a) Peak voltage and peak current:

Peak voltage and peak current can be easily calculated from the standing wave patterns. By measuring the maximum and minimum values of voltage and current at any point in the standing wave pattern, we can determine their peak values.

b) SWR (Standing Wave Ratio):

SWR is a measure of the mismatch between the characteristic impedance of a transmission line and the load impedance. It is calculated by dividing the maximum amplitude of the standing wave by the minimum amplitude. SWR can be determined by measuring the voltage or current at multiple points along the transmission line.

c) Reflection and transmission coefficients:

Reflection coefficient (Γ) and transmission coefficient (T) are important parameters that characterize the behavior of standing waves. Reflection coefficient represents the ratio of the amplitude of the reflected wave to the incident wave, while transmission coefficient represents the ratio of the amplitude of the transmitted wave to the incident wave. Both coefficients can be calculated from the standing wave pattern by measuring the voltage or current at different points.

d) Attenuation constant:

Attenuation constant (α) is a parameter that quantifies the rate at which the power of a wave decreases as it propagates through a medium. It is typically measured in decibels per unit length. However, the attenuation constant cannot be directly calculated from the standing wave patterns. It requires additional information about the medium and its properties, such as the material's conductivity and dielectric constant.

Conclusion:

Based on the analysis above, the correct answer is option 'D' - Attenuation constant. While peak voltage, peak current, SWR, and reflection/transmission coefficients can be determined from the standing wave patterns, the attenuation constant requires additional information about the medium and its properties.