In an effort to cover the relatively broad frequency ranges mandated by most modern EMC immunity standards, some amplifier vendors have resorted to combining two amplifier modules within a common enclosure. These so called dual-band amplifiers use frequency band switching to achieve an overall broader frequency band than either amplifier module could cover by itself. This application note will highlight both the benefits and drawbacks of this technique.
The most obvious benefit of a dual-band amplifier is the apparent simplification and possibly, the cost savings. Two amplifiers are replaced with one “box” with a single RF input and output and a bandwidth broader that either one of the amplifiers it has replaced. While on the surface the system may seem to have been simplified, a closer look within the “box” reveals a different story. While the two amplifier modules in a dual-band amplifier share a common power supply, the overall system is complicated by the fact that it now consists of not one, but two fairly complex amplifier modules. Furthermore, as can be seen in Fig. 2, additional RF switching, cabling and connectors are required which will adversely affect the RF output of both amplifiers. All of the additional components add insertion loss that may not present a problem at lower frequencies but can account for significant losses at higher frequencies.