tenna designs in present products when used close to the head have negative gains of -8dB or more. 4.5.3 The Antenna TX/RX Switch Module for GSM, Duplexers for UMTS Another option for improving sensitivity is not to transmit and receive at the same time. This is used in GSM-only phones where there is a two-slot offset between transmit and receive frames. Switching is normally implemented with a GaAs device or pin diodes. WCDMA/UMTS and LTE FDD phones, however, send and receive at the same time, and therefore require a duplexer. Making Telecoms Work GSM/WCDMA/UMTS/LTE phones therefore typically end up with a duplexer and a GSM TX/RX switch in the front end of the phone. Each additional UMTS/LTE band requires an additional duplexer. 4.5.4 Other Front-End Switch Paths In addition, there is a need to band switch and mode switch. In an ideal world you would not introduce these switch paths. They create loss and distortion and dissipate power. More bands and additional modes therefore add direct costs in terms of component costs and indirect costs in terms of a loss of sensitivity on the receive path and a loss of transmitted power on the transmit path. 4.5.5 MEMS Devices One alternative is to use MEMS (microelectrical mechanical system) -based switches. The idea of building microelectrical mechanical switches has been around for twenty years or SO but is now becoming increasingly practical and has the benefit of sharing available semiconductor fabrication techniques. MEMS components are manufactured using microma- chining processes to etch away parts of a silicon wafer or to construct new structural layers that can perform mechanical and electromechanical functions. A MEMS-based switch would have low insertion loss, good isolation and linearity and would be small and power efficient. In addition, it is essentially a broadband device. It is electrostatically activated SO needs a high voltage which is inconvenient, but low current (so practical). MEMS devices are sensitive to moisture and atmospheric contaminants SO hav