Conventional Branch-line Coupler Research Articles

Wide scan angle multibeam conformal antenna array with novel feeding for mm-wave 5G applications

This paper presents a low-profile wide scan angle multibeam conformal antenna array system with a novel feeding network for 28 GHz mm-wave 5G applications. The proposed antenna system utilizes two conventional branch-line couplers as its beamforming network. A novel feeding technique is applied to generate 7 beams with these couplers that are usually capable of generating 2 beams. The proposed solution provides a wide scanning range with a minimum realized gain of 5 dBi from −90° to 90° owing to this feeding approach and the peculiar placement of the array elements on a 0.15 mm thick R-F775 bendable substrate. The generated beams at their steer direction have the minimum and maximum gain values of 6.5 dBi and 9.7 dBi, respectively. A low-cost PCB manufacturing technique based on soft lithography and wet etching is used. The system dimensions excluding extra connector sections are 67×15×3mm3. The proposed flexible design is suitable for lightweight 5G communication systems and handsets with its compact low-complexity beamforming network, and wide 180° continuous covering angle.

Derivation of Generalized Design Formulas for Modified Branch-Line Coupler with the Second Harmonic Suppression Characteristics

We propose a modified branch-line coupler composed of the open stubs and stepped impedance lines. This structure allows the second harmonic suppression and size reduction. We present the steps to transform from a conventional branch-line coupler to the proposed structure using equivalent circuits and derive the generalized design formulas. From the results analysis of the design sample, we demonstrate the validity of the derived formulas. The fabricated branch-line coupler provides more than 30 dB the second harmonic suppression and about 30 % size reduction compared to a conventional branch-line coupler.

A novel branch line coupler with defected ground structure for Bone Density Measurement Analysis

Microwave Integrated Circuits play a vital role in the Medical field for sensing applications. Two hundred million people are affected globally by musculoskeletal diseases, a substantial healthcare burden and one of the most costly diseases. Our proposed design is dedicated to the Bone Density Measurement Analysis (BDAS) RF system. This paper investigates the development of a directional - Branch Line Coupler with Defected Ground Structure (DGS) to differentiate between transmitted and reflected signals in the split ring resonator (SRR) sensor for Bone Density Measurement Analysis using the HFSS V13 design tool. The Coupler operates within the range of 2 GHz - 3 GHz frequency band with a high directivity of 55 dB. The proposed design is compared with a conventional branch-line coupler, and S-Parameters are calculated. The design is optimized in HFSS to meet the required specifications.

A Novel Branch-Line Coupling Topology

This article presents a novel branch-line coupling topology, which offers superior performance to the conventional branch-line coupler. The structure of the proposed network is very simple; in fact, only one additional transmission line element is required to modify the ever-present branch-line coupler in such a way that the bandwidth is enhanced by roughly 25%. The proposed structure is analyzed using an even–odd analysis, and closed-form expressions for the dimensioning of the network parameters are given. The transmission-line impedances are equal or very close to the system’s impedance, and there is no need for very low or high transmission-line impedances.

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.

A compact coupler design using meandered line compact microstrip resonant cell (MLCMRC) and bended lines

In this paper, a novel branch-line coupler using meandered line compact microstrip resonant cell (MLCMRC) and bended lines is proposed. The presented coupler works at 0.9 GHz, with good specifications. The measured values of S12 and S13 at 0.9 GHz are 3.2 dB and 3.3 dB, respectively, which show better than 0.3 dB insertion loss in the pass band. The measured value of S14 is better than 36 dB and S11 is better than 31 dB. The proposed design can eliminate 3rd and 5th harmonic with high suppression level (more than 40 dB) and reduce the size of the circuit more than 64% compared to the conventional branch-line coupler. The presented coupler has a very simple structure, which can be used in modern communication applications.

Low-Cost Automated Design of Compact Branch-Line Couplers.

Branch-line couplers (BLCs) are important components of wireless communication systems. Conventional BLCs are often characterized by large footprints which make miniaturization an important pre-requisite for their application in modern devices. State-of-the-art approaches to design compact BLCs are largely based on the use of high-permittivity substrates and multi-layer topologies. Alternative methods involve replacement of transmission-line sections of the circuit, with their composite counterparts, referred to as compact cells (CCs). Due to the efficient use of available space, CC-based couplers are often characterized by small footprints. The design of compact BLCs is normally conducted based on engineering experience. The process is laborious and requires many adjustments of topology followed by manual or, semi-automatic tuning of design parameters. In this work, a framework for low-cost automated design of compact BLCs using pre-defined CCs is proposed. The low cost of the presented design technique is ensured using equivalent-circuit models, space mapping correction methods, and trust-region-based local optimization algorithms. The performance of the framework is demonstrated based on three examples, concerning the design of unequal-power split coupler, comparison of automatically generated compact BLCs, as well as rapid re-design of the coupler for different substrates. Furthermore, the approach has been benchmarked against the state-of-the-art methods for low-cost design of circuits.

Miniaturisation of branch line couplers with a compact transmission line topology based on coupled line section

This study presents a compact transmission line topology to reduce the circuit size of single- and two-section branch line couplers (BLCs). The proposed transmission line is composed of a high impedance series line and one coupled line section. The coupled line section consists of two high impedance series lines and one coupled line. The proposed line is analysed with even-odd mode analysis to derive closed-form design equations. To validate the equations, a compact single- and two-section BLCs are designed at 0.85 GHz based on the proposed line. The physical size occupied by the proposed single- and two-section BLCs is 23 and 19.5%, respectively, compared to conventional BLCs. Moreover, the proposed transmission line demonstrates the harmonic suppression characteristic due to the coupled line section. As a result of which, the second- and third-order harmonic of the proposed BLCs are suppressed. The proposed BLCs are designed, fabricated, and tested.

Designs of Branch-Line Couplers by Considering the Parasitic Effects of P-I-N Diodes

Branch-line couplers (BLCs) are commonly used in the wireless systems. To achieve reconfigurable applications, switchable BLCs with p-i-n diodes can be used. Several studies have used diode parasitic reverse-biased capacitor and forward-biased inductor to approach off and on states. Although the capacitance and inductance are usually low, the parasitic effect may degrade predicted switching responses. This study proposes five reconfigurable switching microstrip BLCs. Each of the first two presented BLCs uses shunt to ground diodes for realizing two switching modes. The first mode with reverse-biased capacitors for perfect matching design is equivalent to a conventional branch-line coupler (BLC). The second mode uses low forward-biased inductances to approach shunt to ground, which transfers most signal power from Port 1 to Port 2/4; however, parasitic inductors produce some mismatches. To improve this problem, the proposed third or fourth BLC achieves two perfect matching modes by using shunt stub-loaded diodes. Specifically, by using four stub-loaded diodes, the proposed final BLC exhibits three perfect matching modes and one perfect isolation mode under a lossless ideal circuit condition.

Design of Compact Hybrid Branch Line Coupler (BLC) for GSM Application

This paper presents a compact design of a hybrid branch line coupler (BLC) operating at 1.8 GHz frequency for the global system for mobile communication (GSM) applications. The miniaturization is achieved by using two short circuited stubs and one series transmission line (TL) instead of series quarter wavelength line of conventional BLC. The characteristic impedance of the shunt quarter wavelength section is optimized to improve the overall performances. Therefore, the proposed technique is 59% compact in size is compared to conventional BLC. The outputs at two ports (|S21| = |S31|) are 3.5 ± 0.3 dB with return loss (|S11|) and isolation (|S41|) is better than 20 dB. The prototype coupler is simulated using ANSYS HFSS EM simulator and fabricated on a substrate of dielectric constant (er) = 2.2, thickness (h) = 0.787 mm and loss tangent of 0.0009 and tested. The measured result is completely compiled with the simulated one.

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.

Compact Design of Planar Quadrature Coupler With Improved Phase Responses and Wide Tunable Coupling Ratios

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 $0.21\lambda \text{g}\,\,\times \,\,0.08\lambda \text{g}$ 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.

Analytical modeling of conventional and miniaturization three-section branch-line couplers

Analytical modeling of conventional and miniaturization three-section branch-line couplers

Design of compact microstrip branch line coupler using semi-circular and rectangular resonators with wide range suppressed harmonics

In this paper, a novel compact branch line coupler (BLC) with 10 suppressed harmonics is proposed. To achieve small size, four semi-circular and eight stepped impedance resonators are used instead of 35 Ω and 50 Ω conventional branch line coupler transmission lines. The operational frequency of the presented branch line coupler is 0.85 GHz. The size of the proposed circuit is reduced about 78% in compared with the conventional branch line coupler. To verify the design and analysis, the proposed coupler is simulated using full-wave EM simulator Advanced Design System and fabricated. Simulation results are in good agreement with measurement results.

Coupling coefficient range extension technique for broadband branch-line coupler

In a conventional branch-line coupler (BLC), high coupling coefficients require very narrow lines, which results in high fabrication complexity and reduction in power handling capacity. In addition, changes in multiple design parameters are required to realize arbitrary coupling coefficients. In this paper, we present the design, fabrication, and characterization of a novel broadband branch-line coupler that extends the range of arbitrary coupling coefficients. The proposed structure is also able to achieve different coupling through tuning only one design parameter, and therefore can be used as a tunable coupler. Closed-form design equations are presented for the synthesis of broadband BLCs based on the proposed structure. To validate the proposed structure and the corresponding design methodology, a variety of broadband BLCs with different coupling coefficients have been designed, fabricated, and measured. Measurements show that couplers with 6, 9, and 12 dB coupling coefficients provide wide fractional bandwidths of 49, 49, and 52%, respectively.

Wide bandwidth arbitrary phase difference branch line coupler

As a conventional branch line coupler (BLC) is limited to a phase difference of 90°, different phases have typically been realized by cascading additional phase-shifters, which inevitably increase the circuit size. This article presents a BLC capable of achieving a combined wide bandwidth and arbitrary phase difference. This is achieved by inserting a phase compensation network directly in each of the series branch lines, which effectively modifies the electrical lengths. A prototype 60°/–120° coupler has been fabricated and experimentally characterized to achieve a 0.5-dB magnitude imbalance, 5° phase stability, return loss better than −15 dB, and isolation better than −14 dB from 2.3 to 3.5 GHz.

Wideband Branch Line Coupler with Open Circuit Coupled Lines

This paper focuses on the design of a Wideband Branch Line Coupler by using open circuits coupled lines technique. The design is implemented by adding four open circuits coupled lines to the structure of the Conventional Branch Line Coupler. The proposed design of Wideband Branch Line Coupler is simulated using CST microwave software. The simulation results show that the coupler is operated at 3.8 GHz with coupling factor of -3dB and 90̊ phase difference between the two output ports. The prototype is fabricated and measured to validate the simulated results. A similar Wide Bandwidth is observed on simulation and measurement. The structure achieved a fractional bandwidth of 42.63%, and return loss of 21 dB compared to the Conventional Branch Line Coupler (BLC).

Miniaturization of a 90° Hybrid Coupler with Improved Bandwidth Performance

This letter presents a compact hybrid coupler having wider bandwidth compared to a conventional 90° branch line coupler. Coupling between two closely spaced branches is utilized for the improvement. Closed form expressions are derived using a lossless transmission line theory. Further, graphs are presented to determine size of the coupler with the required bandwidth specifications. In the bandwidth calculation, input matching, isolation, phase and amplitude imbalances, all conditions are considered simultaneously. A coupler is fabricated on a 1.58 mm thick FR4 substrate. It occupies 33% area of a conventional branch line coupler. The measured fractional bandwidths for the input matching, isolation, phase and amplitude imbalance conditions are 19.6%, 12.4%, 41.9% and 35.2%, respectively, which is higher than a conventional one.

Thin Film Ferroelectric Compact Branch-Line Coupler Based on D-CRLH Unit Cell and YBCO HTS Microstrip

In this paper, two new compact branch-line couplers (BLCs) are proposed. The first is designed and implemented using D-CRLH unit cells made of copper microstrip line. The new design occupies only 52 % of the area of the conventional BLC that operates at 1.8 GHz. The structure has been fabricated and the experimental results have been compared to the simulated ones and very good agreement has been obtained. Advanced design system circuit simulator and the CST full wave EM simulator have been used to simulate the proposed BLCs. The second BLC is designed using YBCO high-temperature superconducting (HTS) microstrip rather than copper to achieve low insertion loss, and more compact size. Three cases of this coupler with different substrate materials are studied. The design of YBCO on lanthanum aluminate (LAO) substrate attains an optimum BLC performance compared to the one using D-CRLH. All parameters of the second design are enhanced compared to the first one, the insertion loss is enhanced from ?0.1268 to ?0.007 dB, return loss is enhanced from ?35 to ?41 dB, isolation is enhanced from ?25 to ?36 dB, and the area is reduced from 246 to 53.55 mm2. Moreover, the tunable frequency BLC is designed using thin film layer of BST ferroelectric material, the layer is sandwiched between the LAO substrate and HTS microstrip line, the response shows a variation of the center frequency work with the applied electric field, and the ferroelectric thickness.

A Compact Branch-Line Coupler Using Substrate Integrated Suspended Line Technology

A novel compact branch-line coupler using substrate integrated suspended line (SISL) technology is proposed in this letter. In order to reduce the size of conventional branch-line coupler, we propose a novel slow wave structure, which is composed of high-low impedance lines cascaded in meander line configuration, and a 62% size reduction has been achieved. Moreover, fabricated by using standard printed circuit board process, the proposed compact SISL branch-line coupler has advantages of self-packaging, low cost and light weight.