For a given input power, a two-way splitter will typically decreases output by 3.5 db, three-way by 5.3 db and four-way by 7.5 db.
Example 1: PC Card with 1 Watt amplifier, three way splitter and three 11 dBi external antennas.
Each tap off the splitter goes to one sector antenna, the output power is the same for each antenna:
+ amplifier - splitter + antenna = ? Total output power
30 dBm - 5.3 dB + 11 dBi = 35.7 dBm