Reconfigurable Coupler Research Articles

A Bidirectional Long-Range IPT System based on Multi-Tap Parameter Reconfigurable Coupling Structure with Discrete Ferrite Bridge

A Bidirectional Long-Range IPT System based on Multi-Tap Parameter Reconfigurable Coupling Structure with Discrete Ferrite Bridge

Beyond-nearest-neighbour metamaterials

Engineering the dispersion of acoustic or elastic waves using coupling terms that spatially reach beyond the immediate local environment, or unit cell, is an “emerging topic” in Metamaterial design. In this talk, we present experimental studies in acoustic and elastic systems that realize beyond-nearest-neighbour coupling to introduce dispersion relations with extrema within the first Brilloun Zone. In acoustics, we use mixed waveguide-surfacewave coupling, while in elasticity we develop an elastic scaffold (made from meccano) with reconfigurable coupling elements and demonstrate the effects of structural symmetries on these exotic dispersion relations. Applications to enhanced energy harvesting structures are presented by leveraging zero-group-velocity modes.

Liquid-Crystal Reconfigurable Coupler for Millimeter-Wave Applications

A Substrate-integrated waveguide (SIW) coupler whose coupling ratio is controllable at millimeter-wave frequency is presented. To realize this unique property, the SIW coupler is loaded with a tunable liquid crystal (LC) in the central region. To increase, translate and shift the tuning range of the LC to the required permittivity, an artificial dielectric slab is introduced and validated. A new approach to locally increase the permittivity of the LC is presented, wherein the relative permittivity is increased over the desired band. Initially, the variation in the relative permittivity of the LC is 2.46 to 3.5; the slab offers an increment in the variation, from 8.82 to 14.7. Varying the permittivity of the slab in the central region enables coupling ratio control. Based on the investigation of the proposed model, the design requirements and physical parameters to achieve a wide range of reconfigurability are obtained at the millimeter-wave band. For experimental/demonstration purposes, two reconfigurable coupler prototypes with angles of 15°and 55°between the arms are fabricated and characterized. The results demonstrate a tunable operating frequency to a certain extend with a controllable coupling ratio between output ports from 0.5 to 15 dB. These results show very good agreement with the values determined via simulation.

A Butler Matrix-Based Antenna Array With Improved Gain Flatness and Sidelobe Levels by Using Pattern-Reconfigurable Subarrays

A pattern-reconfigurable subarray is proposed in this letter for the performance enhancement of Butler matrix (BM)-based antenna arrays. The reconfiguration is conducted at subarray-levels and therefore, requires much fewer lumped components than conventional methods. In the proposed design, the pattern of the subarray is switched to different modes for different scanning regions of the overall array, leading to an improvement of gain flatness and sidelobe levels. The reconfiguration is achieved by a novel reconfigurable coupler. By electronically controlling vias connected to a ground plane which severs as binary switches through PIN diodes, the proposed coupler is characterized by extremely low loss even with the capability of reconfiguration. For validation, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band prototype consisting of a 4 × 4 BM and four reconfigurable subarrays is designed, fabricated and measured. Measured results indicate that, the achieved gain fluctuation is only about 0.2 dB between the four scanning beams. The SLL is smaller than −12.1 dB while the gain is larger than 13.8 dB in the scanning plane, which are improved by 5.8 and 1.9 dB than its conventional counterparts, respectively.

A Coupler With Simultaneously Tunable Phase, Frequency and Coupling Coefficient

A novel coupled-line coupler with tunable frequency, coupling coefficient and phase difference is proposed with a reduced number of varactor diodes. The proposed coupler consists of two weakly coupled lines cascaded using varactors and two highly tunable coupled lines loaded with varactors. By varying the cascading capacitances between two weakly coupled lines, the phase difference between the output ports can be tuned with little effect on frequency and amplitude. More importantly, the operating frequency and coupling coefficient can also be independently controlled by choosing the proper combination of the loading capacitances between and on the highly tunable coupled lines. For demonstration, a highly reconfigurable coupler was designed, fabricated and measured. It exhibited a tunable operating frequency ranging from 1.15 GHz to 1.85 GHz with a relative bandwidth larger than 18%. The power division ratio and phase difference between the output ports are also tunable from 0 dB to 7.4 dB and from 65° to 130° respectively.

Inverse-Designed Metastructures Together with Reconfigurable Couplers to Compute Forward Scattering

Inverse-Designed Metastructures Together with Reconfigurable Couplers to Compute Forward Scattering

Reconfigurable fiber-to-waveguide coupling module enabled by phase-change material incorporated switchable directional couplers

In silicon photonics, grating-assisted fiber-to-waveguide couplers provide out-of-plane coupling to facilitate wafer-level testing; however, their limited bandwidth and efficiency restrict their use in broadband applications. Alternatively, end-fire couplers overcome these constraints but require a dicing process prior usage, which makes them unsuitable for wafer-level testing. To address this trade-off, a reconfigurable fiber-to-waveguide coupling module is proposed and designed to allow for both grating-assisted and end-fire coupling in the same photonic circuit. The proposed module deploys a switchable directional coupler incorporating a thin layer of phase-change material, whose state is initially amorphous to render the coupler activated and hence facilitate grating-assisted coupling for wafer-level testing. The state can be altered into crystalline through a low-temperature annealing process to deactivate the directional coupler, thus facilitating broadband chip-level coupling through end-fire couplers. All the components encompassing conjoined switchable directional couplers as well as the grating and end-fire couplers were individually designed through rigorous simulations. They were subsequently assembled to establish the proposed reconfigurable coupling module, which was simulated and analyzed to validate the selective coupling operation. The proposed module gives rise to a low excess loss below 1.2 dB and a high extinction ratio over 13 dB throughout the C-band, when operating either under grating-assisted or end-fire input. The proposed reconfigurable coupling module is anticipated to be a practical solution for flexibly expediting the inspection of integrated photonic circuits on a wafer scale.

Reconfigurable Spoof plasmonic Coupler for Dynamic Switching between Forward and Backward Propagations

AbstractA reconfigurable coupler constructed using two spoof surface plasmon polariton (SSPP) waveguides and a spoof localized surface plasmon (SLSP) resonator to achieve switching between the forward and backward coupling of SSPP waves is proposed. By changing the bias voltage applied to the varactor diodes loaded in the SSPP waveguide, the dispersion of the plasmonic structure is adjusted to achieve a reversed group velocity. Consequently, the direction of the coupled SSPP waves can be dynamically controlled at the same operating frequency. The tunability of this coupler can be further improved by incorporating varactor diodes into the SLSP resonator, where forward–backward coupling can be achieved at multiple frequencies.

A Novel Circular Reconfigurable Metasurface-Based Compact UWB Hybrid Coupler for Ku-Band Applications

A novel circular reconfigurable metasurface (MS) based compact ultra-wideband (UWB) hybrid coupler is developed for Ku-band applications. The coupler is developed using the substrate-integrated gap waveguide (SIGW) technology. The coupler structure consists of two layers, the bottom layer represents the artificial magnetic surface of the periodic structures and the ridges in between that guide the wave in the required direction with minimum dispersion. It involves the coupling section with a centered etched slot and two additional vias to achieve the basic hybrid coupler properties. This layer is nominated as the ridge layer. The second layer is a circular shape of a dielectric gap loaded with the top ground. The top ground is left solid for a non-reconfigurable coupler. Concerning the reconfigurable coupler, this layer contains an artificial metasurface of Jerusalem cross elements where the copper is etched around. This layer is nominated as the gap layer. This MS surface is mechanically rotated to offset the magnitude and phase of the signal going to the through and coupled ports. The findings obtained from the simulations show that the reconfiguration can be accomplished by rotating the MS around the source coupler’s central axis. The rotation is tested between 0° to 180° in the counter-clockwise direction. The operating frequency range of the coupler is between 11.94 to 16.91 GHz, which covers approximately the whole Ku-band. The coupler delivers continuously adjustable amplitude between 2.6 and 4.8 dB while the phase differences within 77° to 105° over a fractional bandwidth (FBW) of 34.45%. It is manufactured using PCB technology and measured using network analyzer. A strong agreement is achieved between simulations and measurements. The proposed coupler can be used in traditional beam-forming and beam-steering networks by changing the rotation angle or the operating frequency. The developed coupler can replace the Butler and Bless matrices with their complication, heavy number of phase shifters, and crossover problems. The current work can be extended to operate in the mm-Wave band by changing the dimension and the material of the unit cell of the ridge layer of the coupler.

Π-type reconfigurable coupler based on a complementary tunable method

A complementary tunable method is proposed based on the Hybrid coupler. The odd-even mode analysis shows that the method can achieve continuously tunable power division ratio by changing two transmission lines in the circuit, and it can achieve larger tunable range by improving the complementary tunable method based on the cascaded Hybrid coupler. Using the improved method, a novel π-type reconfigurable coupler, which works at 2.45 GHz, is designed by replacing transmission lines with π-type circuit. The power division ratio of the fabricated reconfigurable coupler is changed in the range of −20.5–21.3 dB, with the bias voltage being 0∼6 V; meanwhile, the isolation and return loss are above 20 dB.

Experimental Demonstration of a Reconfigurable Coupled Oscillator Platform to Solve the Max-Cut Problem

In this work, we experimentally demonstrate an integrated circuit (IC) of 30 relaxation oscillators with reconfigurable capacitive coupling to solve the NP-Hard maximum cut (Max-Cut) problem. We show that under the influence of an external second-harmonic injection signal, the oscillator phases exhibit a bipartition that can be used to calculate a high-quality approximate Max-Cut solution. Leveraging the all-to-all reconfigurable coupling architecture, we experimentally evaluate the computational properties of the oscillators using randomly generated graph instances of varying size and edge density ( $\eta $ ). Furthermore, comparing the Max-Cut solutions with the optimal values, we show that the oscillators (after simple postprocessing) produce a Max-Cut that is within 99% of the optimal value in 28 of the 36 measured graphs; importantly, the oscillators are particularly effective in dense graphs with the Max-Cut being optimal in seven out of nine measured graphs with $\eta =0.8$ . Our work marks a step toward creating an efficient, room-temperature-compatible non-Boolean hardware-based solver for hard combinatorial optimization problems.

Using synchronized oscillators to compute the maximum independent set

Not all computing problems are created equal. The inherent complexity of processing certain classes of problems using digital computers has inspired the exploration of alternate computing paradigms. Coupled oscillators exhibiting rich spatio-temporal dynamics have been proposed for solving hard optimization problems. However, the physical implementation of such systems has been constrained to small prototypes. Consequently, the computational properties of this paradigm remain inadequately explored. Here, we demonstrate an integrated circuit of thirty oscillators with highly reconfigurable coupling to compute optimal/near-optimal solutions to the archetypally hard Maximum Independent Set problem with over 90% accuracy. This platform uniquely enables us to characterize the dynamical and computational properties of this hardware approach. We show that the Maximum Independent Set is more challenging to compute in sparser graphs than in denser ones. Finally, using simulations we evaluate the scalability of the proposed approach. Our work marks an important step towards enabling application-specific analog computing platforms to solve computationally hard problems.

Tunable Plasmon-Induced Transparency through Bright Mode Resonator in a Metal–Graphene Terahertz Metamaterial

The combination of graphene and metamaterials is the ideal route to achieve active control of the electromagnetic wave in the terahertz (THz) regime. Here, the tunable plasmon-induced transparency (PIT) metamaterial, integrating metal resonators with tunable graphene, is numerically investigated at THz frequencies. By varying the Fermi energy of graphene, the reconfigurable coupling condition is actively modulated and continuous manipulation of the metamaterial resonance intensity is achieved. In this device structure, monolayer graphene operates as a tunable conductive film which yields actively controlled PIT behavior and the accompanied group delay. This device concept provides theoretical guidance to design compact terahertz modulation devices.

A Flexible Quadrature Coupler With Reconfigurable Frequency and Coupling Ratio in Switchable Coupling Direction

A highly reconfigurable and switchable quadrature coupler with simultaneous control in terms of operating frequency, coupling ratio, and coupling direction is presented. To start with, a prototype coupler based on an ideal admittance-inverter model is investigated, and a method to obtain the admittance-inverter values for an arbitrary coupling ratio is described. Next, a tunable-admittance-inverter network implemented with lumped inductors and varactors, which features reconfigurable operating frequency, and tunable-admittance-inverter value is discussed. The conceived reconfigurable coupler is then realized by replacing the ideal admittance inverters with the proposed tunable-admittance-inverter circuit to provide it with operating-frequency and coupling-ratio controllability. Furthermore, when exchanging the admittance-inverter values in the coupler, the coupling direction is switched from forward to backward. The proposed technique is further developed into a general design procedure for reconfigurable-coupler implementations with an arbitrary admittance-inverter-based network. Wilkinson power dividers with equal and unequal power-division ratios are also shown as examples. For experimental/demonstration purposes, a reconfigurable coupler prototype is fabricated and characterized. It demonstrates a tunable operating frequency from 1 to 1.5 GHz, a controllable power-division ratio between output ports from 1 to 0.7, and switchable operational direction between forward and backward.

Extension of Butler Matrix Number of Beams Based on Reconfigurable Couplers

A scheme to extend the beam number of Butler matrices (BMs) by utilizing reconfigurable couplers is presented and illustrated with experimental verification. The beam number of a traditional $2^{N} \times 2^{N}$ BM can be increased to $3\cdot 2^{N}$ by substituting reconfigurable couplers for all hybrids while maintaining the structure and other components as the original. Moreover, only N sets of different parameters are required for these couplers. The principle, properties, and the generalized expressions for the N sets of parameters are discussed and exhibited. The properties of the extended beams are illustrated in terms of beam directions and crossover levels. As an example, a switchable 12-beam forming network extended from a $4\, \times \, 4$ BM for 2.4 GHz applications is fabricated and tested. Over a 30% relative bandwidth is achieved with phase errors less than ±12°, amplitude unbalances lower than ±1.7 dB, isolations better than −15.5 dB, and a return loss better than 11.5 dB.

Highly Reconfigurable Dual-Band Coupler With Independently Tunable Operating Frequencies

To support different standards simultaneously within a wireless communication system, research on dual-/multi-band components has been conducted extensively. However, the operating frequencies of existing works are usually fixed resulting in a low flexibility. To solve this problem, a highly reconfigurable coupler whose two operating frequencies can be controlled independently is proposed for the first time in this paper. Based on the analysis of a basic configuration, the conditions for realizing the desired independent frequency tuning can be obtained. To realize this unique property, varactors loaded coupled line sections are introduced on a conventional branch line coupler. Owing to the symmetrical structure of the proposed coupler, explicit theoretical analysis can be conducted. For demonstration, two reconfigurable couplers are designed, fabricated, and measured. The first coupler can provide frequency tunability from 3.4 to 4.2 GHz at the upper band with the lower band fixed at 2.4 GHz. The other one can not only provide a tunable frequency from 1.3 to 1.6 GHz at the lower band with the higher band fixed at 3.4 GHz, but also give a tunable higher band from 2.9 to 3.4 GHz with the lower band fixed at 1.55 GHz. The measured results agree well with the simulated results, validating the proposed design methodologies.

Robust Self-Interference Cancellation for Microstrip Antennas by Means of Phase Reconfigurable Coupler

We propose a robust self-interference cancellation (SIC) technique for microstrip antennas. A microstrip antenna operates as a transmitter located between two identical receiver antennas having orthogonal polarization with respect to each other. The microstrip antennas show out-of-phase electric field distribution in the H-plane. We exploit this characteristic to cancel self-interference (SI) signals through a rat-race circuit, and we achieved more than 50 dB (60 dB) SIC over 180 MHz (120 MHz) at 2.45 GHz. Furthermore, we propose a new phase-reconfigurable rat-race circuit to adjust the SI signals phase response. The proposed technique is robust and resilient to the potential phase offset of SI signals caused by fabrication errors or scatterers nearby the antennas. As a result, the 50 dB (60 dB) SIC bandwidth spreads over 280 MHz (150 MHz). This technique is a good candidate for in-band full-duplex communication systems with dimensions of $\mathbf {1.4\lambda _{0}\times 0.4\lambda _{0}\times 0.05\lambda _{0}}$ and antennas edge-to-edge separation $\mathbf { , and is easily applied to other frequency bands.

Coupling Coefficient Reconfigurable Wideband Branch-Line Coupler Topology With Harmonic Suppression

The need for a flexible coupler topology to support a wide variety of coupling coefficients and robust suppression of harmonics often results in severely increased insertion loss, system size, and fabrication complexity. In this paper, we propose a two-section branch-line coupler (BLC) topology that simultaneously achieves a wide bandwidth, reconfigurable coupling coefficient, and harmonic suppression. Closed-form equations and a design methodology are provided. To verify the proposed technique, a BLC prototype operating at 3 GHz was designed, fabricated, and measured. The circuit can work under four configurations providing the coupling coefficients of 4, 6, 8, and 10 dB. The prototype achieved a 15-dB harmonic suppression up to 7.5 GHz. The measured fractional bandwidth, defined by 1-dB amplitude imbalance and 5° phase stability, is 30% from 2.55 to 3.45 GHz, the widest of reported reconfigurable couplers.

Coupling coefficient reconfigurable quadrature coupler based on mechanical switches

The conventional reconfigurable quadrature coupler configuration usually requires an external supply voltage which reduces its robustness. A new quadrature coupler with reconfigurable coupling coefficient is implemented using a mechanical control approach to simultaneously satisfy high performance and reliability requirements. Two mechanical switches are firstly implemented on a circular patch to realize two states with different coupling coefficient. To further increase the flexibility in reconfigurability, two more mechanical switches are employed. For demonstration purposes, two patch quadrature couplers were designed, simulated, and measured. The coupling coefficient of coupler I can be switched between 9 dB and 3 dB from 4.9 GHz to 5.3 GHz. Coupler II gave a reconfigurable coupling coefficient, which can be switched between 4 dB, 6 dB, and 11 dB at 3.5 GHz.

A Compact Reconfigurable Coupler with Tunable Coupling Coefficients and Frequencies

A compact microstrip coupler with tunable frequencies and coupling coefficients is presented. The calculation equations for capacitances under two different reconfigurable situations are derived. The design procedures are also given upon different requirements. To demonstrate the design strategies, a prototype with center frequency of 2 GHz is fabricated and measured. The measured results show a tunable frequency range from 1 to 3 GHz with 3 dB coupling, and a tunable coupling coefficient range from 0.86 dB to 9.5 dB at center frequency.