TABLE OF CONTENTS Microwave systems have an enormous impact on modern society. Applications are diverse, from entertainment via satellite television, to civil and military radar systems. In the field of communications, cellular radio is becoming as widespread as conventional telephony. Microwave and RF filters are widely used in all these systems in order to discriminate between wanted and unwanted signal frequencies. Cellular radio provides particularly stringent filter requirements both in the base stations and in mobile handsets. A typical filtering application is shown in Figure 1.1 which is a block diagram of the RF front end of a cellular radio base station.
The GSM system uses a time division multiple access technique (TDMA) [1]. Here the base station is transmitting and receiving simultaneously. Mobile propagation effects require a system dynamic range in excess of 100 dB. The transmit power amplifier produces out-of-band intermodulation products and harmonics. These must be filtered to prevent leakage into the receiver and to satisfy regulatory requirements on out-of-band radiation. Therefore the transmit filter must have a high level of attenuation in the receive band. Furthermore, the transmit filter must have low passband insertion loss, to satisfy power amplifier linearity and efficiency requirements. Similarly the receiver must be protected by a filter with high attenuation in the transmit band to isolate the high power (30 W) transmitter. This filter must have low passband insertion loss to preserve system sensitivity. A typical specification...
