Branch-line Coupler Research Articles

Design of a Modified Compact Coupler with Unwanted Harmonics Suppression for L-Band Applications

This paper presents the design, analysis, and fabrication of a new miniaturized microstrip branch line coupler (BLC) with high harmonics suppression. The T-shaped resonators, open stubs cross-shaped resonators and radial stubs are used in the proposed coupler design. The designed BLC operates at 1 GHz frequency, which can suppress up to 5th spurious harmonics with a 20 dB level of attenuation. High miniaturization of about 86% is obtained for the proposed BLC, which is corresponding to the normalized size of 0.009 λg2. The measured values of isolation and return loss are obtained 28 dB and 29 dB, respectively, while the measured insertion loss of better than 0.2 dB is achieved at the operating frequency. Additionally, the operating bandwidth of the designed coupler ranges from 0.905 GHz up to 1.105 GHz, which shows a 200 MHz operating bandwidth or a fractional bandwidth (FBW) of 20%. The presented BLC is fabricated and measured, where the measurements confirm the simulated results. The designed coupler shows desirable performance compared to the recent designed couplers.

A compact 200° continuously variable phase shifter based on bridged-T circuit topology

An analog phase shifter using a bridged-T circuit topology is described in this paper. A conventional analog phase shifter employs a 3-dB 90° branch-line hybrid coupler applying four quarter-wavelength transmission lines. Herein, there are only two transmission lines in the proposed phase shifter, one of which is a quarter-wavelength long and the other is shorter than a quarter-wavelength. The structure of the phase shifter can be more compact by folding the quarter-wavelength transmission line. And the circuit can be miniaturized to less than one-fifth as compared to the conventional one. In addition, a large phase shift can be achieved by only two varactor diodes. Next, a phase shifter with an insertion loss of 2.29 ± 1.03 dB and a phase shift of more than 200° at the frequency range of 4.8 to 5.6 GHz was manufactured and tested. The size of the experimental phase shifter is less than 0.09 λg × 0.13 λg.

Design and Fabrication of a Compact Branch-Line Coupler Using Resonators with Wide Harmonics Suppression Band

The branch-line coupler (BLC) is an important device in radio frequency (RF) and microwave (MW) circuits. The main drawbacks of the conventional BLC are as follows: first, the four long quarter-wavelength (λ/4) transmission line sections occupy a large size, especially at the low frequencies, and second, the presence of unwanted harmonics. This research paper presents a compact 750 MHz BLC with harmonics suppression using resonators. The typical BLC consists of four λ/4 branches, two series arms of 35 Ω and two shunt arms of 50 Ω impedances. In the proposed BLC, these long branches are replaced with two types of compact resonators. The proposed resonators have the same responses at the operating frequency of 750 MHz and suppress higher frequencies. The designed BLC is simulated, fabricated and measured. The results show that the proposed BLC has good performance at 750 MHz with a bandwidth of 200 MHz, which provides more than 26% fractional bandwidth (FBW). It has a very compact size, about 84% size reduction, as compared with the typical BLC. Moreover, the fabricated BLC suppresses the 2nd up to 7th unwanted harmonics with a high suppression level.

Design of a miniaturized branch line microstrip coupler with a simple structure using artificial neural network

Abstract In this paper, a compact branch microstrip coupler with the simple structure using T-shaped resonators and open-ended stubs at 1.8 GHz is designed and fabricated. The proposed coupler creates two transmission zeros at 3.4 and 3.87 GHz, with more than 50 dB attenuation level, which resulted in a good harmonic suppression at 2nd harmonic. Artificial neural network (ANN) has been utilized to extract the transfer function of the proposed coupler resonator for the first time, so the values of the transmission zeros can be located in the desired frequency. This technique can also be used for the other electrical devices. The designed device has a small size of 28 mm × 30 mm (0.9 λ × 0.95 λ), which shows more than 35% size reduction compared to the typical branch-line coupler with λ/4 branch lines. The proposed coupler is simulated using Advanced Design System (ADS) software and fabricated on Rogers Duroid 5880 substrate (ε r = 2.2, h = 31 mil). The simulation and measurement results verify the correct performance of the designed coupler.

Very compact 3D-printed folded branch-line hybrid coupler based on loaded helical-microstrip transmission lines

This paper presents a 3D topology for high miniaturization of the well-known hybrid branch-line coupler at the UHF band. A preliminary work already proposed the use of helical-microstrip TLs combined with a folded structure for this purpose. This extended work includes a compactness enhancement by loading the TL segments with capacitors. An study of loaded helical-microstrip TL is reported as well. The coupler prototypes have been simulated and fabricated by using a combination of Additive Manufacturing and copper electroplating. The performance results have been compared to the conventional model showing a good agreement. In order to place the designed devices within the state of the art a figure of merit that combines the compactness and the relative bandwidth has been proposed, showing very good results in terms of miniaturization.

A quad-band branch line coupler with high frequency ratio

A quad-band branch line coupler with high frequency ratio

A miniature TSV-based branch line coupler using π equivalent circuit model for transmission line

A miniature TSV-based branch line coupler using π equivalent circuit model for transmission line

Recent Developments of Butler Matrix From Components Design Evolution to System Integration for 5G Beamforming Applications: A Survey

Beamforming networks for multiple beam antennas are believed to be in the vanguard of technological developments in mmWave for 5G wireless applications. The basic idea of beamforming technique is the application of multiple antenna elements radiating the same signal at an identical phase and wavelength, into one strong signal pointed to a specific direction. For low cost and power consumption, radio frequency beamforming networks (RF-BFNs) such as Blass matrices, Butler matrices, and Nolen matrices will play a critical role in achieving the ever-increasing demands in wireless technology. Therefore, this study aims to present a comprehensive survey and developments of RF-BFNs with (particular focus in Butler matrices). From the fundamental perspectives of the beamforming techniques and progress over time, component evolution includes branch-line coupler (BLC), Phase shifter (PS), and Crossovers to complete system Butler matrix (BM) integration. Different design techniques to improve bandwidth, size reduction, multi-band, and other performance characteristics are discussed extensively. Furthermore, the paper also discusses different geometry of Butler matrices in open microstrip transmission lines, substrate integrated waveguide (SIW) and gap waveguide (GWG) technologies highlighting key developments and research challenges from single band to dual-band operations.We expect this paper to provide more profound insights into the designs processes and suggest suitable ways to facilitate further developments of RF-beamforming networks at mmWave and sub-mmWave frequency ranges.

A compact microstrip coupler using T-shape and open stubs for fifth generation applications

The paper presents a new design of a compact branch-line coupler (BLC) operating at 3.5 GHz, that is suitable for 5G applications. In order to miniaturize the proposed coupler, two miniaturization methods are combined where a T-shaped structure is used instead of quarter wavelengths parallels, as well as open stubs are introduced into the series lines resulting in a size reduction of 52.56% with 25.05% fractional bandwidth (FBW). The frequency responses indicate that the presented coupler is able to operate at 3.04 GHz to 3.91 GHz with a low return loss and high isolation that is improved to -28.9 and -31.1 dB in 3.5 GHz, insertion loss and coupling of -3.6 dB and -3.5 dB, respectively, and a phase difference of about 90°±1°. The strong agreement of measurement and simulation results indicated the suitability of this proposed design for 5G microwave integrated circuits (ICs) that require a small size.

Wideband Highly-Selective Bandpass Filtering Branch-Line Coupler

This paper presents a novel design of a wideband highly-selective bandpass filtering branch-line coupler (FBLC). By integrating a coupled microstrip line, and an open-ended stub at each port of a single-section BLC, bandpass filtering characteristics with excellent selectivity and broad operating bandwidth have been achieved. The proposed circuit has been verified through EM simulations and physical measurements of the fabricated prototype. Experimental results demonstrate over 71-percent fractional bandwidth (2.25 GHz to 4.74 GHz) with a power imbalance lower than 0.5 dB. At the same time, the measured return loss and isolation are better than 15dB with the phase imbalance of 5 ± 5°. This level of performance, especially in terms of bandwidth and selectivity, has not been reported in the literature thus far.

Trapezoid-shaped resonators to design compact branch line coupler with harmonic suppression

This article proposes a new branch-line coupler design using two trapezoid-shaped resonators, applied in side and center. The standard 35 and 50 Ohms λ/4 transmission lines (TLs) are attained through the variations of the resonator’s TLs width. Since there are not explicit formulas for the suggested trapezoidal shape resonator, the design procedure will include the derivation of new formulas to configure the LC equivalent circuit. The proposed branch-line coupler, operating at 0.95 GHz, has achieved 79% of size reduction if compared to the conventional designs. Furthermore, the suggested design has successfully diminished the first six harmonics with a suppression level of (41, 29, 29, 28, 20, and 20) dB, respectively. The bandwidth is from 800 MHz to 1 GHz and The fractional bandwidth is 22.2%.

A novel balanced‐to‐unbalanced branch‐line coupler with large power division ratio

A novel balanced-to-unbalanced branch-line coupler with a large power division ratio (PDR) is proposed in this paper. The proposed coupler consists of six transmission-line sections, which can be easily synthesized with the prescribed PDR. By changing the electrical lengths of two transmission lines, a large PDR range can be obtained without the use of high-impedance transmission lines. The closed-form design equations are provided and discussed. To verify the proposed circuit, a coupler prototype with the PDR of 20 dB and the center frequency of f0 = 1.0 GHz is designed and fabricated. Simulation and measurement results are in good agreement. When the balanced port A is excited, the measured differential-mode to single-ended transmission coefficients at f0 for the unbalanced ports D and C are |SsdDA| = −0.28 dB and |SsdCA| = −20.02 dB, respectively, which meet the desired PDR. The measured |SddAA| at f0 is −33.6 dB with a −10-dB bandwidth of about 12.7% from 0.933 to 1.059 GHz. The |SscDA| and |SscCA| are less than −29.5 dB with a −18-dB bandwidth of 22.4% from 0.924 to 1.157 GHz.

Constrained multi-objective optimization of compact microwave circuits by design triangulation and pareto front interpolation

Development of microwave components is an inherently multi-objective task. This is especially pertinent to the design closure stage, i.e., final adjustment of geometry and/or material parameters carried out to improve the electrical performance of the system. The design goals are often conflicting so that the improvement of one normally leads to a degradation of others. Compact microwave passives constitute a representative case: reduction of the circuit footprint area is detrimental to electrical figures of merit (e.g., the operating bandwidth). Identification of the best available trade-off designs requires multi-objective optimization (MO). This is a computationally expensive task, especially when executed at the level of full-wave electromagnetic (EM) simulation. The computational complexity issue can be mitigated through the employment of surrogate modeling methods, yet their application is limited by a typically high nonlinearity of system responses, and the curse of dimensionality. In this paper, a novel technique for fast MO of compact microwave components is proposed, which allows for sequential rendition of the trade-off designs using triangulation of the already available Pareto front as well as rapid refinement algorithms. Our methodology is purely deterministic; in particular, it does not rely on population-based nature-inspired procedures. The three major benefits are low computational cost, possibility of handling explicit design constraints, and a capability of producing a visually uniform representation of the Pareto front. The algorithm is demonstrated using a compact branch-line coupler and a three-section impedance matching transformer. In both cases, considerable savings are obtained over the benchmark, here, the state-of-the-art surrogate-assisted MO technique.

A 28-GHz Switched-Beam Antenna with Integrated Butler Matrix and Switch for 5G Applications.

This work presents a 28-GHz Butler matrix based switched-beam antenna for fifth-generation (5G) wireless applications. It integrates a 1 × 4 microstrip antenna, a 4 × 4 Butler matrix, and a single-pole four-throw (SP4T) absorptive switch in a single planar printed circuit board and is housed in a metal enclosure. Co-integration of a packaged switch chip with the Butler matrix based switched-beam antenna greatly enhances the form factor and integration level of the entire system. A wideband two-section branch line coupler is employed to minimize the phase and magnitude errors and variations of the Butler matrix. The aluminum metal enclosure stabilizes the electrical performances, reduces the sidelobes, and improves the structural stability. The fabricated antenna with the metal enclosure assembled has a dimension of 37 × 50 × 6.2 mm3. With an RF input signal fed to the antenna’s input port through a single Ka-band connector, and the switching states chosen by 2-bit dc control voltages, the antenna successfully demonstrates four directional switched beams. The beam switching operations are verified through the over-the-air far-field measurements. The measured results show that the four beam steering directions are −43°, −17°, +10°, +34° with side lobe levels < −5.3 dB at 28 GHz. The antenna also shows reasonably wideband radiation patterns over 27–29 GHz band. The 10-dB impedance bandwidth is 25.4–27.6 GHz, while a slightly relaxed 8-dB bandwidth is 25.2–29.6 GHz. Compared to previous works, this four-directional switched-beam antenna successfully exhibits the advantages of high integration level and satisfactory performances for the 28-GHz 5G wireless applications.

Dual-Band/Dual-Mode Rat-Race/Branch-Line Coupler Using Split Ring Resonators

A novel dual-band/dual-mode compact hybrid coupler which acts as a dual-band branch-line coupler at the lower band and as a rat-race coupler at the higher band is presented in this paper. One of the most interesting features of the proposed structure is that outputs of the proposed coupler in each mode of operation are on the same side. This unique design is implemented using artificial transmission lines (ATLs) based on open split ring resonators (OSRR). The low-cost miniaturized coupler could be operated as a dual-band 90° branch-line coupler at 3.3 and 3.85 GHz and 180° rat-race coupler at 5.3 GHz. The proposed coupler could be utilized in the antenna array feeding circuit to form the antenna beam. The structure’s analytical circuit design based on its equivalent circuit model is provided and verified by measurement results.

A novel design of compact broadband 4 × 4 Butler matrix-based beamforming antenna array for C-Band applications

In this paper, a compact broadband 4 × 4 Butler matrix (BM) as a feeding network for antenna array is presented and studied. The broadband performance of the BM occurs when it operates in the almost equal difference of phases and coupling throughout the operating band. The different components of the proposed design such as branch-line coupler, crossover, and Schiffman line phase shifter are designed and optimized to be low loss and wideband. The total size of the BM is 37 mm × 47 mm, equal to 0.64λ0 × 0.81λ0 in design frequency at 5.2 GHz. The measurement bandwidth for fabricated structure on the FR4 substrate is 24 % achieved from return loss lower than −10 dB. The beam directions are measured at −15, −43.2, +43, and +15° at 5.2 GHz for each input port 1–4 excitation respectively with the gain value of 10.2 ± 0.2 dB and sidelobe levels of −8.2 ± 1.2 dB. The Final BM exposures phase errors of 3 ± 1.7° with the amplitude imbalance of less than ±1 dB over the operational band.

Compact Size, and Highly Sensitive, Microwave Sensor for Non-Invasive Measurement of Blood Glucose Level

None-invasive blood glucose measurement enables effective diagnosis and treatment of diabetic patients. The existing microwave sensors suffer from low sensitivity and large size. This article presents a highly sensitive and compact size non-invasive microwave sensor for real-time blood glucose measurements. We have developed a new sensing technique using directly connected Branch Line Coupler and Split Ring Resonators. This technique significantly improves the sensitivity by mitigating the limited coupling between transmission lines and resonators. In addition, using Split Ring Resonators reduces the sensor size due to capacitive and inductive effects, which are loaded to the Branch Line Coupler. The proposed sensing function is based on shifting the transmission notch frequency in coupled arm of the Branch Line Coupler, which is caused by loading the Split Ring Resonators with varying glucose concentration. A prototype sensor is fabricated and successfully tested using several glucose concentrations in deionized water. Experimental results demonstrate 0.72 MHz/mgdL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> measurement sensitivity, which is higher in comparison with available sensors in PCB technology. The prototype sensor size is 3.5×3.5×0.16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

2-섹션 분기선 결합기를 이용한 동시 정보 및 전력 전송용 고효율 정류기 배열

This study presents a rectifier array with a two-section branch-line coupler for simultaneous wireless information and power transfer (SWIPT). The branch-line coupler-based power recycling technique is introduced to combine two sub-rectifiers to maintain high rectification efficiency within a wide input power range. A U-shaped 2nd order band stop filter is proposed to reflect a power signal and transmit an information signal to the isolated port of the coupler. A voltage doubler topology is adopted for the sub-rectifiers to minimize the impedance change to the input power. The proposed rectifier array achieves a wide input power range of 13 dBm～32 dBm for a power conversion efficiency (PCE) &gt; 50 %, with a peak PCE of 74.7 % at 2.45 GHz.

Development of a new wideband heterodyne receiver system for the Osaka 1.85 m mm–submm telescope: Receiver development and the first light of simultaneous observations in 230 GHz and 345 GHz bands with an SIS-mixer with 4–21 GHz IF output

Abstract We have developed a wideband receiver system for simultaneous observations in CO lines of J = 2–1 and J = 3–2 transitions using the Osaka 1.85 m mm–submm telescope. As a frequency separation system, we developed multiplexers that connect three types of diplexers, each consisting of branch-line couplers and high-pass filters. The radio frequency (RF) signal is eventually distributed into four frequency bands, each of which is fed to a superconductor–insulator–superconductor (SIS) mixer. The RF signal from the horn is divided into two frequency bands by a wideband diplexer with a fractional bandwidth of $56\%$, and then each frequency band is further divided into two bands by each diplexer. The developed multiplexers were designed, fabricated, and characterized using a vector network analyzer. The measurement results showed good agreement with the simulation. The receiver noise temperature was measured by connecting the SIS-mixers, one of which has a wideband 4–21 GHz intermediate frequency (IF) output. The receiver noise temperatures were measured to be ∼70 K in the 220 GHz band, ∼100 K in the 230 GHz band, 110–175 K in the 330 GHz band, and 150–250 K in the 345 GHz band. This receiver system has been installed on the 1.85 m telescope at the Nobeyama Radio Observatory. We succeeded in simultaneous observations of six CO isotopologue lines with the transitions of J = 2–1 and J = 3–2 toward the Orion KL as well as on-the-fly mappings toward the Orion KL and W 51.

Coupled-line co-directional coupler with inherent harmonic suppression and its wideband implementation

In the study, a novel implementation of the coupled-line co-directional (CL-COD) coupler is proposed for the first time, and the wideband realizations are also demonstrated. The CL-COD coupler, which is composed of inductor loaded parallel coupled line and a pair of open-circuited stubs, has the advantages of smaller size and inherent harmonics suppression compared with the traditional λ/4 branch line coupler. Design equations of the single-section CL-COD coupler are derived by the even-odd mode decomposition analysis and a prototype is designed for validation. The experimental results indicate that compared with the traditional single-section λ/4 branch line coupler, the designed single-section CL-COD coupler shows a size reduction of 64.1%, a bandwidth enhancement of 13%, and a second harmonic suppression of more than 20 dB. By cascading multi-sections of the CL-COD couplers, wideband CL-COD coupler with harmonics suppression is also realized. A computer-aided program is applied for solving the circuit parameters of the multi-section cascaded CL-COD coupler. Besides, the two- and three-section cascaded 3-dB CL-COD couplers are designed for guidance. Finally, a 3-dB three-section cascaded CL-COD coupler is fabricated and measured. Compared with the traditional three-section cascaded λ/4 branch line coupler, the prototype shows a size reduction of 61.9% with an additional second order harmonic suppression.