Abstract
This paper presents a compact planar tunable quadrature coupler with improved phase responses. Wide coupling-Tuning ratio is achieved by using two varactors loaded on the center of the transmission lines of the modified coupler. Closed-form equations are derived for design parameters. For verification, a 1-GHz tunable coupler is designed and measured. The measured results agree well with the simulated ones. The measured power-dividing ratio can be tuned in a range from 16.2 to ?35 dB (from 42 to 3.2E-4) with better than 20-dB return loss and isolation, while the phase imbalance is smaller than 10°. The coupler size is 0.21λg × 0.08λg and reduced by 73.1% compared with the conventional branch-line coupler. The theoretical analysis shows that the phase imbalance and insertion loss are mostly caused by the loss from varactors. Then, a tunable coupler with improved phase and loss responses is proposed, where the additional phase difference and insertion loss resulting from the varactors are compensated for by introducing a negative resistance from the negative impedance converter. Measured results of a demonstrative 1-GHz coupler show a power-dividing ratio tuning range from 24.4 to ?22.2 dB (from 275.4 to 6E-4) while maintaining 20-dB return loss and isolation. The phase imbalance is smaller than 1° and the insertion loss is improved by 1 dB and nearly close to theoretical values across the tuning range.
Original language | English |
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Pages (from-to) | 1263-1272 |
Number of pages | 10 |
Journal | IEEE Transactions on Microwave Theory and Techniques |
Volume | 66 |
Issue number | 3 |
DOIs | |
Publication status | Published - Mar 2018 |
Keywords
- Coupler
- microstrip
- planar circuits
- power-dividing ratio
- reconfigurable