m; one GSM1800 system and one UMTS system. The analysis of co-location includes: wideband noise, spurious emissions, blocking and intermodulation. The solutions may come from: antenna isolation, use of filters (e.g. diplexer or triplexer). We assume the following reference output powers: 43 dBm out- put power at the antenna port of GSM900/1800 BTS, and 45 dBm output power at the antenna port of UMTS BS. Wide band noise: the frequency separation between the GSM900 and the UMTS, as well as between the GSM1800 and the UMTS bands is sufficiently large. Thus, it is frequently assumed that the transmit part of GSM900/1800 does not generate wideband noise in the receive part of UMTS. Spurious emissions: GSM recommendation 05.05 specifies a maximum level of spuri- ous emissions in the frequency band 1-12.5 GHz, including the UMTS receiving band. This maximum power should not be greater then -30 dBm at the base station RF output port, power measured in 3 MHz bandwidth, which is equivalent to -95 dBm/Hz. Looking at the maximum tolerable interference level in the Rx channel of -118 dBm, (i.e. -185 dBm/Hz, over 5 MHz worst case), we can calculate the required isolation to avoid interference for the Tx GSM/DCS Rx UMTS. Thus, assuming specified spurious emissions over 3 MHz of -30 dBm, specified spurious emissions per Hz of -95 dBm and maximum level of unwanted signal per Hz -185 dBm, the necessary isolation be- tween antenna connectors is 90 dB. GSM and UMTS band analysis indicates that a 2nd and 3rd order intermodulation product of GSM900 and 1800 transmission frequencies, respectively, fall into the UMTS uplink band. Thus, GSM 05.05 recommendation specifies that when the inter- modulation power level of the interfering signal gets injected into the antenna connector at a level of 30 dB lower than that of the wanted signal, the spurious emissions require- ments shall not exceeded, i.e. -30 dBm in the UMTS receiving band at the BS RF out- put port measured in 3 MHz bandwidth, which is equivalent to -95 dBm/Hz. Since this is a