gain & directivity slides

Gain & Directivity<br />

P Available<br />

P Reflected<br />

Radiation efficiency<br />

or loss<br />

AUT<br />

P IN<br />

P RAD<br />

Directivity<br />

• Directivity is given by,<br />

Gain<br />

Realized Gain<br />

power radiated per unit solid angle in direction<br />

D = 4π<br />

total power radiated by antenna<br />

• Gain is given by,<br />

power radiated per unit solid angle in direction<br />

G = 4π<br />

total power accepted from source<br />

• In practice, many people measure realized <strong>gain</strong> which is affected by VSWR and<br />

internal ohmic losses.<br />

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Gain, Directivity & Efficiency<br />

• Gain in a direction is given by,<br />

power radiated per unit solid angle in direction<br />

G = 4π<br />

total power accepted from source<br />

• Directivity in a direction is given by,<br />

power radiated per unit solid angle in direction<br />

D = 4π<br />

total power radiated by antenna<br />

• Taking e r to denote radiation efficiency, when expressed in decibel form,<br />

<strong>directivity</strong> and <strong>gain</strong> can be related through,<br />

G<br />

dB<br />

= D<br />

• According to the IEEE standards, <strong>gain</strong> does NOT include losses arising from:<br />

• Impedance mismatches (reflection losses),<br />

• Polarization mismatches (losses).<br />

• In general <strong>gain</strong> is measured and <strong>directivity</strong> is calculated.<br />

dB<br />

− e<br />

r dB<br />

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