Novel Compact Coupler with Tunable Frequency, Phase Difference, and Power-Dividing Ratio

This letter proposes a novel compact coupler with simultaneously and continuously tuned frequency, output differential phase, and power-dividing ratio (PDR). In addition to multifunctionally tunable capabilities, this microstrip coupler is only one-tenth the size of the state-of-the-art coupler based on the coupled-line structure. Coupler analysis and design equations will be provided with thorough discussion. The fabricated prototype achieved the frequency, differential phase, and PDR tuning ranges of 1.2-2.4 GHz, -64° to -112°, and 0-12 dB, respectively. Moreover, the same coupler can be reconfigured to be a 180° coupler with the measured frequency tuning range of 1.3-2 GHz and PDR tuning range of -8.3 to 11.1 dB.