Dual-band Coupler Research Articles

Theoretical designs and experiments on dual-band input coupler for gyrotron traveling wave tube

In this paper, a novel K/Ka dual-band input coupler for the gyrotron traveling wave tube is theoretically and experimentally investigated. This input coupler mainly consists of three modules, a Y-type power division coupler, a coaxial cavity coupler, and a Bragg reflector. When the dual-band coupler operates in K-band, the Y-type coupler couples out the TE11 mode, and simulation results show the −1 dB bandwidth is 3.3 GHz in the frequency range of 17.9–21.2 GHz. In Ka-band, the TE21 mode coupled out by the coaxial cavity coupler, the −1 dB bandwidth is 3.5 GHz within 33.7–37.2 GHz, and the reflection coefficient keeps a pretty low level. The prototype was fabricated and measured to further verify the designed dual-band input coupler's performance. The back-to-back cold test results show that the −3 dB bandwidth of the K-band is about 2.5 GHz, and the −3 dB bandwidth of the Ka-band is 2.44 GHz.

Dual-Band Coupling of Phonon and Surface Plasmon Polaritons with Vibrational and Electronic Excitations in Molecules

Strong coupling (SC) between light and matter excitations bears intriguing potential for manipulating material properties. Typically, SC has been achieved between mid-infrared (mid-IR) light and molecular vibrations or between visible light and excitons. However, simultaneously achieving SC in both frequency bands remains unexplored. Here, we introduce polaritonic nanoresonators (formed by h-BN layers on Al ribbons) hosting surface plasmon polaritons (SPPs) at visible frequencies and phonon polaritons (PhPs) at mid-IR frequencies, which simultaneously couple to excitons and molecular vibrations in an adjacent layer of CoPc molecules, respectively. Employing near-field optical nanoscopy, we demonstrate the colocalization of near fields at both visible and mid-IR frequencies. Far-field transmission spectroscopy of the nanoresonator structure covered with a layer of CoPc molecules shows clear mode splittings in both frequency ranges, revealing simultaneous SPP-exciton and PhP-vibron coupling. Dual-band SC may offer potential for manipulating coupling between exciton and molecular vibration in future optoelectronics, nanophotonics, and quantum information applications.

Dual-Band Branch-Line Coupler Based on Crossed Lines for Arbitrary Power-Split Ratios.

Dual-band branch-line couplers with arbitrary power-split ratios are presented. The use of crossed lines at the center of the dual-band coupler enables it to independently provide different power-split ratios to the two bands. Additionally, open stubs are utilized to enhance the stopband responses. The complete design procedure with example design curves is provided. For experimental verification, three dual-band couplers with power-split ratio combinations of +3 dB () and −3 dB (), −3 dB and +3 dB, and 0 dB () and +13 dB () at 1 GHz and 2.5 GHz were designed and fabricated. The measured results are in excellent agreement with the ideal and full-wave simulated results. The measured difference of −13.3 dB between the power-split ratios of the two bands is the largest reported for a dual-band branch-line coupler.

A Compact Dual-Band Coupler With Coupled Microstrip–Slotlines

In this letter, a novel dual-band coupler made of only three coupled microstrip–slotline (CMSL) sections is proposed to achieve a tight coupling with a high band ratio in a small size. A desired dual-band operation can be obtained by proper design of the coupling levels of the CMSL sections. Explicit design equations of the proposed coupler were derived by the method of even- and odd-mode excitations, and the characteristics of the CMSL were studied. For demonstration, a 3-dB dual-band CMSL coupler operating at 1 and 3 GHz is designed, fabricated, and measured. The proposed coupler has the advantages of small size, tight coupling, and high isolation.

3-D Printed Dual-Band Filter Based on Spherical Dual-Mode Cavity

A new dual-band bandpass filter (BPF) is designed and fabricated based on a pair of spherical dual-mode resonant cavities using 3-D printing technology. By elaborately introducing three-type metallic posts into each cavity to perturb the degenerated TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> modes in a reasonable way, a dual-band coupling topology is developed in the design accordingly. Owing to the cross-coupling paths in the designed topology, two transmission zeros (TZs) are successfully introduced between the passbands, bringing out a high band-to-band isolation. Even more, TZs can also be generated by creating additional internal coupling paths to the presented dual-band coupling topology. Besides, the spherical cavity provides a higher quality factor and wider stopband, compared to that of a square or cylindrical cavity. To validate the design concept, a dual-band BPF prototype, operating at 12.0 and 12.5 GHz with respective bandwidths of 120 and 240 MHz, is implemented by 3-D printing process. The measured results exhibit good agreement with the simulated ones, showing more than 20-dB return losses and 20-dB dual-band isolation.

Design of a Dual-Band Power Amplifier Using a Simple Method

This letter presents a simple method to design dual-band high-efficiency power amplifiers (PAs). The dual-band coupler is exploited to design the output circuits of the PA. By proper selection of impedance conditions of terminal ports, the dual-band coupler can convert the fundamental impedance of transistor to the standard 50- $\Omega $ load at two frequencies. At the same time, the second harmonic impedance is also controlled without the need for additional tuning. For validation, a dual-band high-efficiency PA is designed and fabricated by using CGH40010F GaN HEMT. Measurements indicate that the designed PA can deliver saturated output power of 41.6 and 42.1 dBm at 1 and 2.3 GHz, respectively. Also, the obtained drain efficiency exceeds 72% at both frequencies.

Novel Dual-Band Beam-Scanning/Switching Network Based on a Hybrid Coupler With Synchronously Tuned Phase Differences

This paper proposes a novel feeding network that enables the antenna array to perform dualband continuous beam scanning and beam switching between forward and backward directions. Specifically, the switchable beam is controlled by the network input and the beam in each direction is continuously steerable at either frequency. To support a wide range of beam-scanning angles, a novel dual-band coupler with synchronously tuned differential phases is applied to the feeding network, together with a pair of phase shifters. The operating principles and design equations of the dual-band beam-scanning/switching network, coupler, and phase shifters will be given in detail. As a proof-of-concept, a 0.9-GHz/1.8-GHz beamscanning/switching network was prototyped alongside a 1W4 linear array. Experimental results show that the array can scan and switch its main beam from -24° to -42° in the backward direction and from 24° to 34° in the forward direction at 0.9 GHz, while the beam scanning is from -12° to -24° and from 12° to 22° at 1.8 GHz.

Highly Reconfigurable Dual-Band Coupler With Independently Tunable Frequency and Coupling Coefficient at the Lower Band

To satisfy the stringent requirements of the emerging wireless communication system, the dual-band operation and reconfigurability are both desired for the front end. However, few works can realize them simultaneously. In addition, the flexibility of the implemented reconfigurability is limited. In this article, a reconfigurable dual-band quadrature coupler with independently tunable characteristics at the lower band is proposed. Based on the investigation of an ideal model, the design requirements to achieve the previous reconfigurability can be obtained. Thus, the coupled line loaded with varactor is proposed on a patch coupler to implement the desired functionality. By varying the voltages applied on the varactors, the frequency and coupling coefficient at the lower band of the proposed coupler can be tuned independently with the characteristics at the upper band fixed. For validation, a prototype was designed, fabricated, and measured. Measured results show that the frequency of the coupler at the lower band can be tuned from 2.9 to 3.2 GHz. Meanwhile, the corresponding coupling coefficient can be tuned from 3 to 10 dB. During the lower band tuning, 3 dB coupling coefficient and quadrature phase difference can be always maintained for upper band, which is fixed at 4.7 GHz.

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.

Tight Coupling Dual-Band Coupler With Large Frequency Ratio and Arbitrary Power Division Ratios Over Two Bands

To satisfy the requirements of the emerging wireless communication system, the simultaneous implementation of large frequency ratio and tight coupling is demanded for a dual-band coupler. But most of the existing dual-band coupler structures can only achieve one of them. In this paper, a new coupled line based dual-band coupler structure is proposed. The detailed theoretical analysis is conducted for different ranges of frequency ratio. It was shown that a wide frequency ratio from 1.4 to 11.7 can be achieved even for the designs which require a tight coupling of 3 dB. For higher flexibility, the same circuit topology is further investigated to implement the arbitrary power division ratios over the two bands. More importantly, the design parameters for the large frequency ratio and arbitrary power division ratio are found to be almost independent resulting in a simple design procedure. For demonstration purposes, a dual-band 3 dB coupler with a large frequency ratio of 6 is designed, fabricated and measured. Furthermore, another dual-band coupler with coupling coefficients of 3 dB and 6 dB at 2 GHz and 4 GHz is designed, fabricated and measured. Good agreement between simulation and measurement can be observed for both prototypes.

On-chip unidirectional dual-band fiber-chip grating coupler in silicon nitride

We report, for the first time, a single state polarization (TE) dual-band grating fiber-chip coupler on a 700 nm thick silicon nitride platform that couples to both O and C band channels. Dual-band coupling with a single grating coupler is achieved using cross mode k-space equalization. By phase matching the first-order vertical TE01 mode and the fundamental TE00 mode in two distinct bands, we observe simultaneous co-directional dual-band coupling to a single waveguide. Experimental peak efficiency per coupler is measured to be −7.3 dB in the O-band and −8.2 dB in the C-band and the combined 1 dB bandwidth is observed to be 82 nm.

Grating-Assisted Fiber to Chip Coupling for SOI Photonic Circuits

Fiber to chip coupling is a critical aspect of any integrated photonic circuit. In terms of ease of fabrication as well as wafer-scale testability, surface grating couplers are by far the most preferred scheme of the coupling to integrated circuits. In the past decade, considerable effort has been made for designing efficient grating couplers on Silicon-on-Insulator (SOI) and other allied photonic platforms. Highly efficient grating couplers with sub-dB coupling performance have now been demonstrated. In this article, we review the recent advances made to develop grating coupler designs for a variety of applications on SOI platform. We begin with a basic overview of design methodology involving both shallow etched gratings and the emerging field of subwavelength gratings. The feasibility of reducing footprint by way of incorporating compact tapers is also explored. We also discuss novel grating designs like polarization diversity as well as dual band couplers. Lastly, a brief description of various packaging and wafer-scale testing schemes available for fiber-chip couplers is elaborated.

Reply to “Comments on ‘An Analytical Design Method for a Novel Dual-Band Unequal Coupler With Four Arbitrary Terminated Resistances’”

The phase-difference performance at two desired frequencies of the generalized dual-band unequal coupler is discussed and presented in this comment as supplementary information. The condition of ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1}}} + {\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_2}}} = \pi $ and the analytical equations for ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1} \,\text{or}\, f_{2}}}$ are provided. It can be concluded that the dual-frequency output phase differences are constant and equal to 90° when ${R_2} = {R_3},$ but the values of ${R_1}$ and ${R_4}$ can be varied. Finally, the calculated results show that the phase-difference variations about $ \pm 11\% $ in the whole useful bandwidths of these branch-line couplers are objective and acceptable in common practical applications when ${R_2}$ and ${R_3}$ are in the range of 30–100 Ω $({R_2} \ne {R_3})$ .

Compact dual-band coupler with independent control of band positions and power-split ratios based on circular patch with DGS

In this paper, we propose a novel dual-band coupler based on circular patch structure perturbed with slits, shorting posts and defected ground structures. It is shown that the proposed perturbations allow size reduction and independent control of the operating bands in terms of their position and power-split ratio between the output ports. To demonstrate the potential of the proposed structure, two dual-band 3-dB couplers operating at 2.4/5.2 and 2.4/5.8 GHz have been designed, fabricated and measured. The couplers are characterized by excellent in-band performance and compact size of only 0.41λg × 0.41λg. Additionally, three couplers operating at 2.4/5.8 GHz with different combinations of coupling coefficients at the two operating bands have been designed and fabricated.

Computationally‐efficient surrogate‐assisted dimension scaling of compact dual‐band couplers

Reusing existing results in order to facilitate optimisation of structures for various sets of performance requirements such as operating frequencies is an attractive concept. When implemented properly, it can lead to considerable speedup of the microwave design process. In general, re-design of microwave structures is a challenging task, particularly for compact components where considerable electromagnetic (EM) cross-couplings make the relationships between geometry parameters and the structure responses complex. In this study, the authors address geometry scaling of miniaturised dual-band couplers by means of inverse surrogate modelling. It allows for fast estimation of the optimum values of structure dimensions corresponding to required operating frequencies, independently for each band. The inverse surrogate is constructed based on a set of reference designs obtained by optimising the equivalent circuit model of the coupler, and subsequently corrected using output space mapping to accommodate the discrepancies between the network model and the EM-simulation one. As demonstrated using a compact dual-band microstrip branch-line coupler example, geometry scaling is possible in a wide range of operating frequencies and at a very low cost of just a single EM simulation of the structure at hand. Numerical results are validated through physical measurements of fabricated coupler prototypes for several test cases.

Compact Dual-Band Coupler for Vehicular Beam-Forming Array

A novel kind of compact dual-band quadrature patch coupler for vehicular beam-forming array is proposed for the first time in this paper. To keep the performance of the first operating frequency 2.4 GHz (for Bluetooth Low Energy (BLE)) and generate the second operating frequency 5.9 GHz (for Dedicated Short Range Communications (DSRC)) simultaneously, complementary triangular split resonant rings (CTSRRs) and splitting gaps are employed to improve the performance of this new coupler; final size of the proposed coupler is 0.24λg (for 2.4 GHz). To validate the performance and design method of the coupler this paper proposed, a 3D model is constructed and optimized with ANSOFT HFSS firstly and then a coupler prototype is fabricated and measured. The measured results show that the amplitude unbalance (AU) is 0.54 dB and 0.44 dB for 2.4 GHz and 5.9 GHz, respectively, and the corresponding phase unbalance (PU) is 93.5 and 92 degrees, respectively.

Miniaturized dual-band coupler using three-branch-line structure and dual transmission lines

Miniaturized dual-band coupler using three-branch-line structure and dual transmission lines

Rapid simulation‐driven design of miniaturised dual‐band microwave couplers by means of adaptive response scaling

One of the major challenges in the design of compact microwave structures is the necessity of simultaneous handling of several objectives and the fact that expensive electromagnetic (EM) analysis is required for their reliable evaluation. Design of multi-band circuits where performance requirements are to be satisfied for several frequencies at the same time is even more difficult. In this work, a computationally efficient design of dual-band microstrip couplers is demonstrated by means of an adaptive response scaling (ARS) technique. ARS is a surrogate-assisted method that exploits a fast surrogate of the high-fidelity EM-simulation model of the coupler at hand constructed from its corrected equivalent circuit. ARS identifies nonlinear frequency and amplitude response scaling that accommodates the misalignment between the low- and high-fidelity models. Due to exploiting the knowledge embedded in the low-fidelity model ARS surrogate exhibits excellent generalisation capability. It is demonstrated here by optimisation of a dual-band microstrip coupler with enhanced bandwidth, working at 1 GHz and 2 GHz frequencies. The optimised design has been obtained at the cost of just a few high-fidelity EM simulations of the structure. Numerical comparisons indicate superiority of ARS over competitive surrogate-assisted techniques. Experimental validation is also provided.

Design of dual‐band −3 dB couplers with a wide range of dual‐band frequency ratios

A novel topology for designing dual-band couplers with −3 dB coupling and a wide range of dual-band frequency ratios is presented. The proposed structure consists of two coupled-line sections connected by two uncoupled lines and four tapped stubs. This coupler can achieve a high frequency ratio of up to 5 by adjusting the impedance of tapped stubs. An experiment coupler operating at 0.7/2.6 GHz with a frequency ratio of 3.71 and −3 dB coupling was fabricated for demonstration.

Design of Microwave Dual-Band Rat-Race Couplers in Printed-Circuit Board and GIPD Technologies

In this paper, the dual-band $\pi $ -section is proposed to design three types of dual-band rat-race couplers. Except for the experimental verification by the printed-circuit board process, the miniaturized dual-band coupler is also implemented in the glass integrated passive device (GIPD) technology to reveal the practical value. The $\pi $ -section is realized by a section of the transmission line (TL) with two reactive shunt elements at the bilateral ends. The design formulas of the 90° and 270 $^{\circ }\pi $ -sections are derived, and their corresponding design figures are then plotted for simplifying design procedures. Moreover, the reactive shunt elements of the 90 $^{\circ }\pi $ -section can be implemented by series $LC$ resonators, while those of the 270 $^{\circ }\pi $ -section can be realized by series or parallel $LC$ resonators. As six 90 $^{\circ }\pi $ -sections are integrated to form a dual-band coupler, the band ratio, which is defined as the center frequency of the second passband dividing by that of the first passband, covers from 1.38 to 3.16. By setting the band ratio to 2 and constructing the dual-band rat-race coupler by three 90 $^{\circ }\pi $ -sections and one 270 $^{\circ }\pi $ -section with parallel $LC$ resonators, two sets of the adjacent series and parallel resonators can cancel each other to reduce the power loss. Consequently, this dual-band coupler uses only two series $LC$ resonators. In addition, the proposed dual-band coupler can be miniaturized by replacing microstrips with the complementary-conducting-strip TLs. It only occupies a 10% circuit size of the conventional one at the center frequency of the first passband. This miniaturized approach is also demonstrated in the GIPD technology.