Design of Highly Reconfigurable Couplers

高度可重構耦合器的研究

Student thesis: Doctoral Thesis

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Award date30 Mar 2022

Abstract

Reconfigurable components have become more and more attractive due to its flexible control of certain characteristics. Tunable characteristics for reconfigurable coupler design include frequency, coupling coefficient and phase difference. However, shortcomings such as narrow tuning range, limited tunabilities and single band operating shown in conventional reconfigurable couplers are obvious. This thesis proposes several reconfigurable couplers with wide phase tunable range, high tunability integration and independent dual-band tunability. The wide tuning range and flexible reconfigurabilities of the designed circuits will be more favorable for next generation wireless communication.

To solve the limited phase tunable range from 45° to 135° of the traditional phase tunable couplers, a 0°-180° phase reconfigurable coupler is presented as the first design of this thesis. To realize such a wide tuning range, a phase tunable unit consisting of two open stubs, one shorted stub and two tunable capacitors is investigated and verified. By using the tunable units at both sides of a coupled line coupler, the phase difference can be tuned from 45° to 135°. To enlarge the tuning range, the phase difference can be reconfigured within a range from 0° to 180° by using two phase tunable units. The investigated reconfigurable couplers can maintain equal power division during the phase tuning, which demonstrate its wide tuning ability in phase control.

In the next chapter, a highly reconfigurable coupler with simultaneously tunable frequency, phase difference and coupling coefficient is proposed. Between two coupled line sections, four varactors used to adjust the frequency and phase difference are connected with two transmission lines. Between the two transmission lines, another tuning capacitor is employed to tune the coupling coefficient. To further improve the matching characteristics during the coupling coefficient tuning, two shorted stubs are connected at each side of the central varactor by two PIN diodes. Based on the topology, theoretical analysis is proposed to explain the working principle and the circuit is fabricated and measured to verify the concept.

To improve the matching responses and tuning flexibility of the all-tuned mechanism, a coupler with simultaneously tunable frequency, phase difference and coupling coefficient is proposed based on a single circular patch. According to the analysis of the circular patch, a cross-shaped slot with different lengths is introduced at the center of the circular patch. To realize the reconfigurability, two pairs of varactor diodes are placed at the four feeding lines for frequency and phase difference tuning. While another two pairs of varactors are loaded at the four ends of the slot to tune the coupling coefficient. For demonstration, the coupler is designed, fabricated and measured. Good agreement between measured and simulated results verify that the proposed coupler can realize tunable frequency from 1.3 to 1.9 GHz, tunable phase difference from 50° to 130°, and tunable coupling coefficient from 3 to 10 dB at 1.3, 1.5 and 1.7 GHz.

The last design of this thesis presents a highly reconfigurable dual-band coupler with independently tunable frequency and coupling coefficient at the lower band. As the characteristics at lower band of a stub-loaded dual-band circular patch coupler can be varied by simply changing the parameters of the stubs, a coupled line loaded with varactors structure is designed to replace the open stubs for realizing the independent tunabilities at the lower. To verify this, a reconfigurable coupler is designed, fabricated and measured, whose frequency at the lower band can be tuned from 2.9 to 3.2 GHz by decreasing the values of the two pairs of varactors. Its coupling coefficient can be tuned from 3 dB to 10 dB at the lower band by changing the capacitance ratio of the two pairs of varactors. Characteristics at the upper band remain the same during the tuning mechanisms.