Abstract :
A new lumped-circuit directional coupler is described for the 1-30 MHz frequency range. Directivity greater than 50 dB is achieved over this frequency range for coupling ratios of 30, 40, and 50 dB. Greater directivity can be achieved over a narrower frequency range, and the coupler can be tuned for essentially infinite directivity at a fixed frequency. The couplers, although resistive, can pass 100, 300, or 1000 watts for the coupling ratios of 30, 40, and 50 dB, respectively, with less than a 0.01-dB change in coupling ratio. The coupling ratios are constant with frequency to ±0.25 dB. Equations and curves are given for obtaining component values needed to design a resistive-divider-type coupler with any coupling from 3 to 60 dB.
