Antenna Parameters.docx

Antenna Parameters 1. Radiation Pattern 2. Directivity 3. Gain 4. Return Losses 5. Bandwidth 6. Radiation Resistance and Efficiency 7. Polarisation

Radiation Pattern An antenna radiation pattern or antenna pattern is defined as a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates. • Defined for the far-field. • As a function of directional coordinates. • There can be field patterns Magnitude of the electric or magnetic field Or power patterns (square of the magnitude of the electric or magnetic field). • Often normalized with respect to their maximum value. • The power pattern is usually plotted on a logarithmic scale or more commonly in decibels (dB).

Directivity The ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. The average radiation intensity: total power radiated by the antenna divided by 4π

Gain The gain of the antenna is closely related to the directivity. The ratio of the intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically.

Return Losses Return Loss is the portion of a signal that is lost due to a reflection of power at a line discontinuity. There are two major causes of return losses in a network 1)discontinuities 2)impedance mismatches Discontinuities occur at connections where cable is terminated to plugs or jacks and within the plug/jack connection itself. A discontinuity can also occur if a cable is bent too much, kinked or otherwise damaged. When a transmitted signal hits one of these structural discontinuities, echo or RL occurs.

Bandwidth For broadband antennas, the bandwidth is usually expressed as the ratio of the upper-tolower frequencies of acceptable operation. For example, a 10:1 bandwidth indicates that the upper frequency is 10 times greater than the lower. For narrowband antennas, the bandwidth is expressed as a percentage of the frequency difference (upper minus lower) over the center frequency of the bandwidth. For example, a

5% bandwidth indicates that the frequency difference of acceptable operation is 5% of the center frequency of the bandwidth.

Polarization Polarization is the curve traced by the end point of the arrow (vector) representing the instantaneous electric field. The field must be observed along the direction of propagation.  Polarization is classified as linear, circular, or elliptical