A Dual-band Balanced Amplifier with CRLH Transmission Lines Fully Implemented

The topology of balanced amplifiers has conventionally been one of good solutions for broadband amplifiers. Although feedback amplifiers have broader band characteristics than normal single-ended amplifiers, balanced amplifiers have been more popular with their additional technical advantages such as high output power, redundancy, and many productive applications in wireless systems. However, in most cases, the wide operating band of the balanced amplifiers contain not only the practically required multiple narrow bands, but the frequency bands in the vicinity of the practically used bands. So it is normal that the balanced amplifiers operate at the un-required bands within their broad operating band, which can cause the problems of channel capacity, interference, and so on. In this work, a dual-band balanced amplifier, which has been composed of dual-band couplers and amplifier, is discussed (Fig. 1). The couplers operate at dual-bands and implemented by composite right/left handed (CRLH) transmission lines. In addition, the amplifier is also designed for the dual-band operation using the CRLH structure, while its topology is just like a single-ended amplifier (Fig. 2). As the design example, in this work, a dual-band balanced amplifier has been designed, fabricated, and measured with the target frequencies of 1800MHz and 2300 MHz. It is shown that the gain performances appear clearly only at the required dual frequency bands, while the gain at other bands in the vicinity of the required bands are well rejected (Fig. 3). The rejection in the gain seems to be excellent due to the dual-band performances of CRLH transmission line structure. It is believed that the selective dual-band gain performances of the proposed dual-band balanced amplifier are promising for improving the performances of wireless systems.