Broadband RF power amplifiers often create two additional problems:

1. The overall gain must be relatively flat over the operating frequency range f _min. . . f _max. The required flatness usually varies from tenths of a dB to 1 to 2 dB.

2. The input VSWR of the amplifier must be kept within a specified range (for example, 2:1 or lower) over the operating frequency range.

Although these two problems are sometimes discussed separately, they cannot be completely divorced from each other. Both problems can be solved by including various R, C and L components at the amplifier input or in a feedback path. A circuit designed for input VSWR correction will, to some extent, affect the overall gain of the amplifier and vice versa. For example, if some of the driving power is lost in the compensating input network, the amplifier gain will decrease. In fact, this could be helpful at low frequencies, where the amplifier gain is usually higher.

This discussion intends only to present a qualitative approach and some basic design ideas. More detailed explanations and design equations can be found in the literature. Since some of the design equations are only approximate, some of the design parameters are difficult to estimate from the manufacturers data sheets, and it is almost impossible to consider all the parasitic elements in the circuits, numerical optimization and experimental adjustments are often required.

The gain disparity in a broadband amplifier can be greater than 10...