1 Gain and Power Gain An isotropic antenna simply beams its energy evenly in all directions The gain is the ratio of the maximum power received from a parabolic reflector to that from an isotropic antenna emitting the same total amount of energy The antenna or power Gain (in dB) is defined as: 10 log 10 (gain)

2 Antenna (Power) Gain of NRP Radars Typical weather antenna gains range from 20 to about 45 dB (Rinehart 1997) The antenna gain of operational weather radars is quite high…... CWSR 98-A : 46 dB CWSR 98-E : 43 dB WSR88D: 45 dB

3 Antenna-beam width relationship Beam width (deg) = 70  / (Antenna diameter) The diameter of the reflector of the new systems is 6.1m, compared to 3.7m for the retrofit systems Thus, the angular beam width (to half power) of the new systems is narrower than in the retrofit cases (0.65 deg vs 1.1 deg) This improves resolution and useful range A small beam width minimizes the effects of partial beam filling and beam blockage, the main reasons for poor performance with range

4 Gain and Beam width For circular reflectors, the expression relating gain and beam width is: g=     where  is the beam width in radians (Rhinehart 1997 quoting Battan, 1973)

5 Antenna Gain vs Beam width

6 Gain vs Beam width Thus, the smaller the beam width, the better the gain Improved gain means higher signal strength for distant objects or small targets –e.g. light precipitation may be detected at greater distances