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If we talk about dipoles or any other antenna, we discuss the electric field as well as the magnetic field. But while discussing micro-strip antennas, only the electric field is explained.

Why?

EM waves are made of both fields and antennas radiate both fields.

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while discussing Micro strip antenna only electric field is explained

It's because it's well understood that the magnetic part of an EM field can be deduced from the electric field part and vice versa. Hence, engineers usually only bother talking about one or the other. What I've just said applies to the far-field of the radiating EM wave. If we are talking about the near-field then analyzing quantities of either is complex and you cannot assume that there is an easily deducible ratio at any close-by point in space.

But, like I said, in the far field and in free space, the ratio of electric field to magnetic field is approximately 377:1.

This is because the square root of the ratio of the permeability of free space to permittivity of free space is 377 or \$\sqrt{\dfrac{\mu_0}{\epsilon_0}}\$. This is naturally called the impedance of free space.

Knowing that \$\mu_0\$ is in henries per metre and that \$\epsilon_0\$ is in farads per metre, the equation for impedance can be re-written as \$\sqrt{\dfrac{L}{C}}\$ because the "per metre" parts cancel. This is of course is the characteristic impedance of a lossless transmission line.

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