Hybrid Coupler Used as Tunable Phase Shifter Based on Varactor Diodes

Area of Science:

• Electrical Engineering
• Microwave Engineering
• Electromagnetics

Background:

• Hybrid couplers are fundamental components in microwave circuits.
• Controlling phase differences is critical for applications like phased array antennas.
• Existing couplers often have fixed phase differences, limiting flexibility.

Purpose of the Study:

• To design and demonstrate a hybrid coupler with a continuously variable output phase difference.
• To utilize reconfigurable transmission lines and varactor diodes for electrical tuning.
• To achieve a wide tunable phase range while maintaining a stable coupling coefficient.

Main Methods:

• The coupler design is based on quadrature and asymmetric hybrid structures.
• Electrically tunable transmission lines are implemented using varactor diodes.
• Two biasing voltages control the varactor diodes to adjust line lengths.
• A prototype operating at 3.5 GHz was fabricated and tested.

Main Results:

• The coupler achieves a tunable output phase difference from 52° to 128°.
• A consistent coupling coefficient of -3 dB (± 0.5 dB) was maintained.
• Measurement results closely matched simulations, with a phase mismatch under 7° for non-90° cases.
• The prototype validated the design's effectiveness.

Conclusions:

• The proposed hybrid coupler offers a flexible and continuously variable phase difference.
• This technology is highly suitable for antenna feeding arrays and Butler matrices.
• The design provides a valuable solution for advanced microwave and antenna systems.