A travelling wave amplifier (TWA) with a widened frequency bandwidth is disclosed. The TWA include input transmission lines, amplifier units connected in parallel between the input terminal and the out terminal of the TWA. Each of the amplifier units configures an emitter follower in the front end thereof and an amplifying section. A feature of the TWA is that compensation units that compensates the high frequency performance of the TWA are implemented in the input transmission lines and/or integrated with the amplifier units.

There is provided an amplifier device for a CATV network comprising a first amplifier element for upstream signals and a second amplifier element for downstream signals, wherein the first and second amplifier elements are disposed between first and second directional couplers. The combined isolation of the first and second directional couplers is greater than the sum of the gain of the first and second amplifier elements. The first directional coupler has one port attached to an input of the downstream amplification element and one port attached to an output of an upstream amplification element (38) and the second directional coupler has one port attached to an output of the downstream amplifier and one port attached to an input of the upstream amplifier.

Disclosed are systems, devices, and methodologies to reduce harmonics in a radio frequency output signal. A power amplifier system comprises a power amplifier and a tunable output matching network electrically connected between the output of the power amplifier and an output of the tunable output matching network. The tunable output matching network reduces second-order harmonics in an amplified radio frequency signal when the power amplifier operates in a low frequency mode. The tunable output matching network includes traps such as a series inductor and a first capacitor in series with a first switch, a second capacitor in series with a second switch, and a third capacitor in series with a third switch, where the traps are tuned to selected harmonic frequencies when the power amplifier operates in the low frequency band of the operating band of frequencies.