Research On Directional Coupler Using Element Compensation

Directional couplers are widely used as an integral part of many microwave networks and systems, such as amplitude controller, balanced amplifier, power splitter and combiner. They have matched characteristics at all four ports, making them ideal for insertion in a circuit or subsystem.First, a directivity-enhancement technique of microstrip directional couplers is designed, which is realized by compensation element. By loading the coupler with shunt inductors, the phase velocities of the even and odd modes are altered in such a way that an isolation null is achieved.Then a directivity-enhancement technique of micro-strip directional couplers is designed, which is loaded the coupler with capacitance. At last, a directional coupler using three-element compensation is designed, which can also enhance the directivity Compared with other compensation techniques for directivity enhancements, its biggest advantage is its simply realization. But the parasitic effects are not taken into account, which is critical for the directivity-enhancement technique, so a new method is provided to model the the parasitic effects.With the proposed method which is mentioned in the front, a 20 dB microstrip directional coupler is designed at 2.8GHz. A maximum directivity of 50dB has been acquired, which is an improvement of 40 dB over a conventional microstrip directional coupler. A 15% bandwidth at 2.8GHz has been acquired in which the directivity remains above 20 dB, while the maximum variation in the coupling level is 0.5 dB, which has the excellent performance.