Search

Butler Matrix networks are well established as beamforming networks for phased antenna arrays. The challenge we address in this work is to cover the entire (advanced 5G or 6G) FR3 band (7–24 GHz) with a single network, while retaining low losses and minimal size. The employed multilayer topology is also well established; however, the matching between the utilized hybrid couplers and the phase shifters constitutes a major challenge for such a wideband operation. This is achieved herein by employing meander lines with appropriate curvature and introducing two distinct design methods for the Butler Matrix. The first method focuses on designing individual components separately, followed by their integration into the overall Butler Matrix structure. This approach is demonstrated through the design, prototyping, measurements, and validation of an 8 × 8 Butler Matrix beamformer, which operates across the 6–16 GHz band (FR3 Low). The second method introduces a wideband-matching technique which simplifies the implementation process by designing the Butler Matrix as a single, unified structure. This technique is applied to both 4 × 4 and 8 × 8 Butler Matrices, which are implemented and simulated for the low FR3 band. Both design methods result in wideband operation and compact size and meet the desired performance criteria. [ABSTRACT FROM AUTHOR]

The study presents the successful design and implementation of a phase-controlled patch-fractal antenna using the Butler array. This work focuses on developing a laboratory prototype of a 4x4 array using microstrip technology. Theoretical conditions are established, and the theoretical basis of the microwave circuits that make up the matrix is described. Each element is individually designed, optimized, and simulated using specialized software (Ansoft Designer and Advanced Design System), and then its performance is verified by evaluating functional parameters. The tested designs are integrated into a single circuit to form the Butler matrix and are subjected to simulation and optimization before manufacturing. The functionality of the components is verified using a vector network analyzer. An analysis of the discrepancy between the measured values and the theoretical target parameters is performed, providing a comprehensive evaluation of the prototype's performance. Implementing the 4x4 Butler matrix together with the design of patch-fractal microstrip antennas has allowed practical phase control, demonstrating its viability in various applications. Results from both simulation and laboratory tests support the ability to direct the radiation lobe in various areas without the need for additional mechanical structures. The applicability of this antenna in short-range radar systems is highlighted, offering flexibility in addressing without compromising essential electromagnetic properties. For future applications requiring more precise control with a more significant number of radiation lobes, a Butler array with more ports is suggested.

In satellite remote sensing (SRS), there is a demand for large-power microwave components. A Butler matrix is essential to a transmitting antenna array in SRS. This article illustrates the electrical and mechanical design, simulation, and test results of a large-power planar beamforming network for SRS at C-band. It is a 4 × 4 Butler matrix based on square coaxial lines. Short-ended stubs are used in the Butler matrix to broaden its bandwidth by 10%, support inner conductors, and enhance heat transfer in vacuum environments. The simulation results are consistent with the measured results. The reflection coefficient is less than −18 dB, and the isolation is more than 23 dB from 3.8 GHz to 4.2 GHz. The insertion losses are less than 0.6 dB, and the phase errors are better than ±6°. The measured peak microwave power of the proposed Butler matrix is 9 kW. Its size is 440 × 400 × 40 mm3. The proposed Butler matrix beamforming network can be applied to SRS systems. [ABSTRACT FROM AUTHOR]

In this paper, a wideband Butler matrix for the uniform circular array antenna (UCA) generating multimode orbital angular momentum (OAM) vortex wave is designed. Firstly, the novel network topology of a Butler matrix is proposed. For the purpose of design and optimization convenience, the 8x8 Butler matrix is separated into two different sub 4x4 Butler matrix modules and one connection-output module. Then several wideband microwave components used in a Butler matrix, such as 3 dB directional coupler and stable phase shifter with composite right/left-handed (CRLH) transmission line, are designed. To demonstrate the effectiveness of the design process, a Butler matrix working in 5-7 GHz is designed and fabricated. It is found that the simulation results are in good agreement with the measured data. The constant amplitude distribution and progressive phase differences of ±45°, ±90° between the output ports are observed, hence the ±1, ±2 mode OAM waves can be generated by the proposed Butler matrix. [ABSTRACT FROM AUTHOR]

The paper proposes a four-directional beamforming switched antenna system based on Butler matrix for 28 GHz mmWave. It is made up of a 90-degree coupler, a crossover, and a 45-degree phase shifter. A $4\times 4$ Butler matrix is combined with a 28 GHz patch antenna to form a Butler network antenna. Four directions of the radiation beam can be changed when the input position is changed. From the simulation and measurement results, the measured reflection coefficients cover 27.9-29.3 GHz at all four ports with a standard reflection coefficient of -10 dB and four different angles of 15°, -46°, +44° and -13° for switching beam direction. The antenna’s compact size of $39.1\times 45.6\,\,{\mathrm {mm}}^{2}$ ( $3.65\lambda _{0}\times 4.26\lambda _{0}$ ) makes it ideal for use in millimeter wave bands for 5G NR n258, and n261 applications, while also providing a high gain of 11.5 dBi.

This paper introduces an innovative $4 \times 4$ dual-band Butler matrix (BM) characterized by compactness and an enhanced frequency ratio (K). The design employs meandered lines and an interdigital capacitor (IDC) unit-cell-based composite right/left-handed transmission-line (CRLH-TL) metamaterial (MTM) structure. The BM integrates compact dual-band 3 dB branch-line couplers (BLC), a 0 dB crossover, and dual-band ±45° phase shifters on a single Rogers RT5880 substrate having relative permittivity $\varepsilon _{r}$ of 2.2 and thickness $h$ of 0.787 mm. Simulations and measurement results demonstrate reflection and isolation coefficients exceeding −20 dB at all ports, with obtained insertion loss of −6±3 dB over the 0.7 GHz and 3.5 GHz frequency bands. The achieved output phase differences of ±45°, ±135°, ±135°, and ±45° at the designed frequencies indicate a maximum average phase tolerance of ±4.5° concerning the ideal values. Importantly, the BM’s overall dimensions are 143 mm $ \times 186$ mm, resulting in an impressive 78% size reduction compared to traditional T-shaped BM designs. The proposed configuration is designed and simulated using CST Microwave Studio, with the agreement between simulated and measured parameters highlighting design reliability and effectiveness. Additionally, a performance evaluation comparing the proposed BM with existing circuits reveals its suitability for sub-6 GHz 5G dual-band antenna array beamforming networks (BFN) due to its compact size and improved band ratio.

Wireless communications with greater transmission capacities are possible in the millimeter wave (mmWave) region. However, to overcome the significant propagation losses in this frequency band, it is necessary to employ more efficient and intelligent antennas based on MIMO and beam-steering phased array technologies. This paper demonstrates the fabrication of a beam steerable array antenna using a $4\times 4$ Butler matrix at 60 GHz employing the metallic nanowire membrane (MnM) substrate. This substrate has the advantage of interconnecting two metallization layers by vias fabricated through its nanopores. Experimental characterization of the fabricated samples shows that the MnM platform represents a high-potential candidate for millimeter-wave front-ends supporting the beam-steering technique.

Current wireless communications urgently need to provide huge data rates, high gain and high directivity radiation pattern beams. Therefore, beamforming networks (BFNs) are introduced to provide these needs. Butler matrix (BM) is a type of beamforming network, which can be realized using fixed network circuits and feeds the antenna array. BM at high frequency suffers from components loss and phase error for massive network, especially when it is implemented using common microstrip structures. Different transmission lines such as waveguide and substrate integrated waveguide (SIW) are studied and introduced to realize Butler matrix. SIW structures are good candidate for the implementation of BM due to its property of low loss transmission line which comprises of properties of microstrip and waveguide technology. However, SIW antennas and structures at millimeter waves have unwanted radiation loss coming from the vias holes. In addition, the vias separation distance is dependent on waveguide size, which leads to a more massive beamforming network at 26-GHz. Hence, this thesis is proposing a more size-friendly and optimal SIW antenna beamforming structure to reduce the vias loss and provides higher bandwidth and gain at 26 GHz. The BM components such as 3 dB coupler, 0 dB crossover, and 45-degree phase shifter are designed by implementing metallic vias determination method. Size and distance of vias are the most important factors in determining the coupling ratio and phase shifts at output ports. Hence, the coupler is designed with different vias width and distance to obtain the correct phase and coupling at output ports. Then, the designed coupler is cascaded to form a 0-dB crossover. The phase shifter is designed with alerting vias distance inside the coupling area of SIW structure. The last component in beamforming is the design of SIW slot antenna based on longitude slot distributions. All the components are integrated to form a $4\times4$ BM with four slot antennas attached to BM networks. Microtrip separation feedline used to for coupler, crossover, BM and BFN. The proposed designs are simulated using CST software and fabricated by PCB LPKF ProtoMat printer. The outcomes of wide bandwidth with more than 1-GHz and high directive gain of more than 10-dB for the beamforming network are achieved. The output power of the BM is between −6-dB to −8-dB at all four ports with phase difference error less than 5°. Four directive beams are achieved at beam scanning of −14°, −41°, 40°, and −14° at port 1 to port 4 respectively. Hence, this $4\times4$ -BM with four slot antenna theses have introduced a successful design of an antenna beamforming network based on SIW technology with significant characteristics at 26-GHz.

In this article, a beam steering millimeter-wave antenna array operating in ka-band frequency has been proposed for 5G applications. Thus, to achieve a beam switching and to ensure a low side lobe level (SLL), a 4 × 4 Butler matrix (BM) and a Chebyshev array are used respectively. Moreover, to minimize the antenna array dimensions, a multilayer structure is used, where the BM and the antenna array are printed on the bottom and the upper layers respectively. The two radio frequency structures are connected by using via connectors. Furthermore, to reduce the mutual coupling between the antenna elements, we have used a metamaterial surface (metasurface) composed by periodic complementary split ring resonators (CSRRs) printed on the back side of the top layer. As a result, enhancements of the radiation pattern in the E-plane and an impedance matching improvement have been achieved. In addition, a beam steering in the range of − 6° to + 27°, with a variation of the main lobe magnitude from 11.5 to 13.5 dB, and a multi-band behavior in the frequency range 25–40 GHz, have been achieved. [ABSTRACT FROM AUTHOR]

In satellite remote sensing (SRS), there is a demand for large-power microwave components. A Butler matrix is essential to a transmitting antenna array in SRS. This article illustrates the electrical and mechanical design, simulation, and test results of a large-power planar beamforming network for SRS at C-band. It is a 4 × 4 Butler matrix based on square coaxial lines. Short-ended stubs are used in the Butler matrix to broaden its bandwidth by 10%, support inner conductors, and enhance heat transfer in vacuum environments. The simulation results are consistent with the measured results. The reflection coefficient is less than −18 dB, and the isolation is more than 23 dB from 3.8 GHz to 4.2 GHz. The insertion losses are less than 0.6 dB, and the phase errors are better than ±6°. The measured peak microwave power of the proposed Butler matrix is 9 kW. Its size is 440 × 400 × 40 mm3. The proposed Butler matrix beamforming network can be applied to SRS systems.

This paper proposes a compact 4 × 4 Butler matrix (BM) with broadband characteristics within the 5G NR frequency range (3 GHz ~4.5 GHz). To achieve broadband performance, 3 dB broad-side coupler with optimal parameters was implemented, and the circuit was designed with a strip line based on the FR-4 four-layer structure to reduce the size. The average implementation loss was measured as −1.5 dB, and the reflection coefficient was measured as over 15 dB across the entire frequency range. Phase differences of −45°, 135°, −135°, and 45° were confirmed, with an average phase error of ±3°. When the antenna was mounted, beam steering angles were measured as 10.29° ± 1°, −32.41° ± 1.5°, 32.41° ± 1.1°, and −10.29° ± 2.5°. The size of the manufactured compact BM was 40×38.6×1.2 mm3, and it achieved a size reduction of 30% and a bandwidth improvement of 2.54 times compared with the legacy BM using the same frequency. Ansys HFSS was used to design and simulate the BM, and the results suggested that this wideband compact BM could be used for the miniaturization of 5G beamforming systems. [ABSTRACT FROM AUTHOR]

A novel broadband three‐input four‐output (3 × 4) Butler matrix (BM) without crossover is presented for the wider band operation. The proposed 3 × 4 BM is composed of three 3 dB branch‐line directional couplers, one T‐splitter power divider, and two 90° phase shifters. Unlike the traditional BM, the proposed BM network has successfully eliminated the crossover connection for simplifying the network, which operates in a wide operating range. For the validation of the design, a planar single‐layer 3 × 4 BM working at the frequency band of 1.69–2.69 GHz is designed, fabricated, and measured. The measurement result gives bandwidth up to 46% with return loss better than 14.3 dB at the full operating frequency band. [ABSTRACT FROM AUTHOR]

An 8 × 8 butler Vivaldi beam-steering antenna array is introduced for X-band application. Circularly polarized array is made of eight Vivaldi elements with 1×8 platform and an 8×8 beam feeding network. Vivaldi radiating element is used in array form to enhance impedance bandwidth and overall efficiency such as gain. Using microwave passive components, for instance, 3 dB branch line couplers and crossover help to have orthogonal modes for feeding each of the elements, hence circular polarization property is achieved. Extracted results show that the array has an impedance bandwidth over 7–12.7 GHz (~58%) for VSWR≤2 and an axial-ratio bandwidth of 3.15 GHz that is between 8.15 and 11.3 GHz (~33%). The peak gain of antenna array is 18 dBi at 10 GHz. The proposed beam-steering antenna with compact size and good operation is capable to cover an angle range from −42 to 55 degree in whole operation frequency. [ABSTRACT FROM AUTHOR]

In this work, we present a compact four-direction beamforming 5G antenna based on a stacked $4\times4$ Butler matrix and a microstrip patch array antenna. The proposed beamforming antenna is a stacked-up structure using the low temperature co-fired ceramics (LTCC) process and thus its size can be significantly reduced by compared to a conventional beamforming antenna with a single-layer $4\times4$ Butler matrix. Moreover, spurious radiation generated from the Butler matrix can be effectively suppressed due to shielding effects inherent to the multilayer substrate. The fabricated beamforming antenna is composed the stacked $4\times4$ Butler matrix with striplines and the $4\times1$ array microstrip patch antenna. The overall size of the fabricated antenna system is 22.02 mm $\times5.93$ mm $\times1.20$ mm. The beam steering angles are measured to be −16°, 45°, −45° and 16°.

This article provides for the first time a detailed discussion of the optimal assignment of adjacent output phase differences in terms of matrix performance out of all possible combinations in generalized one-dimensional parallel switching matrices with four beams. In this specific case, the topology of the proposed matrix reduces to that of a single-layer Butler matrix, connecting hybrid couplers and crossovers with adequate phase shifters. The values of the phase shift required are dependent on the assignment of the output phase differences, which in turn is shown to have an impact on the radiation characteristics of the linear array fed by such networks when imposing constraints on the matrix layout for a more generic implementation. The configuration having the smallest phase difference with reference to the transmission phase of a straight waveguide with the same length as the coupled region of the crossover is chosen and compared with the conventional well-known Butler matrix. The two matrix configurations are implemented using post-wall waveguides designed to operate over the band 20 GHz – 24 GHz. The prototypes are manufactured and tested, using transitions to standard waveguide WR42. The measured results confirm the benefits of the identified optimal adjacent phase difference assignment in terms of transmission coefficients, reflection coefficients, phase differences between adjacent output ports, and frequency dependence of the array factor. These results will also benefit the design of larger generalized one-dimensional parallel switching matrices.

Massive Multiple-Input Multiple-Output (Massive MIMO), which uses a large number of antenna, has been investigated to realize high-speed wireless communications. However, as the number of antenna increases, the number of components also increases. In addition, it has the problem that circuit mounting becomes difficult due to the narrow antenna spacing and increased loss and phase deviation. To solve these problems, this paper proposes a compact configuration for concurrent multi-beams. The proposed antenna is composed of a one-dimensional patch array antenna and a Butler matrix, which are stacked on top of each other in a staircase configuration. The proposed antenna is fabricated by stacking several identical substrates, reducing design and manufacturing costs. Fixed beam steering can be realized depending on the input port of the Butler matrix. In addition, the phase shifter can steer beams in the direction orthogonal to beam steering by the Butler matrix. To verify the design results, the prototype antenna, an $8 \times 8$ patch array antenna consisting of eight substrates, is fabricated at 28 GHz. Beam steering was achieved in the range of −55° to 55° by inputting the outputs to the respective ports of the Butler matrix and in the range of −29° to 25° by phase shifter.

This paper creates a compact design of a 4×4 butler matrix integrated with an array of antenna elements at 38 GHz frequency. The antenna simulation performance is acceptable, approaching the ideal one. The butler matrix can generate four beams through the output port directly. Each input port 1, 2, 3, and 4 has beam direction, which is 42°, -19°, 19°, and -42°, respectively. The phase difference between output ports of the butler matrix is approaching 45° and 135°. Besides, antenna patch simulation has a good performance. The results are still acceptable after combining the butler matrix and four linear array antenna.

This paper proposes a low loss 4 × 4 Butler matrix based on rectangular waveguide cavity resonators technology for millimeterwave beamforming network using iris coupling method. This method has the advantage of controlling the electrical fields and the coupling factor inside a complex medium such as waveguide cavity resonators. The coupling factor of 6 dB for 4 × 4 Butler matrix is achieved by tuning the iris coupling k-value between the waveguide cavity resonators. Thus, avoiding a higher phase difference losses and component losses at upper millimeterwave bands. To validate the proposed method, CST software simulations are performed under several iris coupling k-values to achieve a 6 dB coupling factor. Then, the proposed 4 × 4 Butler matrix is 3D metal printed using selective laser melting (SLM) technique. The measured reflection and isolation coefficients are observed below −10 dB, with coupling coefficients ranging between −6 and −7 dB. The phase differences of −42.02°, 42.02°, −130.95°, and 133.3° are achieved at the outputs. It confirmed that using this proposed method has the superiority over the conventional microstrip and waveguide coupling methods by a 1 dB coupling factor loss and a 3° phase difference error. [ABSTRACT FROM AUTHOR]

In this paper, a sub-6 beam-steerable antenna array system is introduced. The main radiating element in the proposed array is a gain-enhanced Vivaldi antenna, whose overall realized gain is improved by introducing near-zero-index metamaterial (NZIM) with broadband characteristics at 3.6 GHz. The proposed system is intended to be integrated with fifth-generation automotive applications. The 4 × 4 butler matrix is resonating at 3.6 GHz to feed the designed antenna array elements and steer the radiating beam. When altering the phase of the input signal, the primary beam direction is steered at an angle from 45° to 135°. So, by choosing the butler matrix input port, the phase of each radiating element is changed, which leads to precise beam direction control. All the system components, including antenna elements and the [4 × 4] butler matrix, are designed, simulated, and optimized. In order to verify the proposed design, the system is fabricated using the photolithographic technique. The experimental results show very good agreement with the simulated ones. The NZIM-loaded antenna element achieves a − 10 dB bandwidth of 2.9 GHz, while the overall array system achieves a 600 MHz bandwidth. The steered beam of the proposed system has an overall realized gain of 11.2 dB. [ABSTRACT FROM AUTHOR]

This paper introduces a miniaturized Butler matrix design method using a folded structure. The Butler matrix was fabricated in multi-layers using low-temperature co-fired ceramics (LTCC) and designed to operate at 28 GHz. The conventional one-plane Butler matrix has a major disadvantage in that the length and volume of the system inevitably have to be increased. By using the proposed folded structure, the length can be reduced more than two times compared to the general one-layer Butler matrix. In order to minimize the loss of the Butler matrix, it was designed in a stripline structure by forming a ground plane on the upper and lower surfaces of each layer. A signal is transmitted between the layers through via holes. A 4 × 4 Butler matrix was fabricated and measured for the demonstration of the proposed concept. The proposed Butler matrix was measured through a precisely calibrated antenna chamber with closed cell absorbers. The dimensions of the fabricated Butler matrix are 14 mm × 20 mm × 1.52 mm. The beam of the fabricated Butler matrix can be properly steered in a total of four directions.

A low-loss, compact, ultra-thin, passive, 77 GHz, 8 × 8 microstrip Butler matrix on a 200 μm thick high-purity fused-silica (HPFS) glass substrate embedded in 0.8 μm thick patterned gold conducting layers was developed for low power automotive radars. The first-of-its-kind, HPFS, glass-based Butler matrix comprised 12 hybrid couplers, 16 crossovers, and 8 phase shifters in a footprint area of 19.1 mm × 26.6 mm. The device and the corresponding building blocks were designed and optimized using 3D electromagnetic finite element method (FEM) simulations using the Advanced Design System (ADS) from Keysight™ Technologies. Due to the very-low-loss tangent of the HPFS glass substrate (0.0005 @77 GHz) compared to other common substrate materials and rigorous design optimization, the return loss and isolation of the input ports are both below −20 dB, respectively, as verified by 3D FEM simulations. Due to the absence of any published data on a 77 GHz 8 × 8 Butler matrix, the design was validated by developing a 4 × 4 version of the Butler matrix using the same building blocks and comparing the 3D simulation results in ADS with results published elsewhere that showed that the developed Butler matrix offers lower insertion loss in a 10% smaller footprint area. A low-cost microfabrication method has been developed to fabricate the devices using a standard lift-off process. A scaled version of the device can be used for 5G beamforming applications. [ABSTRACT FROM AUTHOR]

A wideband and low‐profile H‐plane horn antenna array is proposed to achieve a tilted‐beam in H‐plane based on the theory of maximum power transfer efficiency (method of maximum power transfer efficiency (MMPTE)), which is built on bent corrugated substrate integrated waveguide structure. The horn array is implemented in the substrate with the thickness of 0.13 λ0 ${\boldsymbol{\lambda }}_{\mathbf{0}}$ at the centre frequency. The arc‐shaped aperture is employed to achieve smooth transition from horn aperture to the free space, which also improve the front‐to‐back ratio of the radiation pattern. In order to realise a tilted‐beam, MMPTE is used to obtain the excitation distribution of array elements. A double‐layer butler matrix feed network is built based on the calculated excitation, maintaining the characteristic of broadband and miniaturisation simultaneously. Measured VSWR parameter of the proposed antenna is less than 2.0 from 6 to 18 GHz. The antenna achieves a beam titling of ±6° in H‐plane. It is observed that the measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

This work proposes and analyzes a low-cost fixed microstrip beamforming system based on a uniform linear array with four rectangular patch antennas controlled by a Butler matrix that operates in the 2.4 GHz ISM band. A 4×4 Butler matrix consisting of four hybrid quadrature directional couplers, two crossovers, and two 45° phase shifters was designed and implemented to control the beam direction of the entire system. Similarly, a comparative study is performed between two different antenna arrays, the first consisting of a conventional linear antenna array and the second antenna array consisting of four patch antennas loaded with metamaterial structures on the ground plane. Finally, the electrical performance of both smart beamforming systems was evaluated, and their potential application as a wireless power transmitter was evaluated. Four beams with distinct orientations were created in each situation. The smart antenna based on a conventional array has a higher gain, while the smart antenna based on metamaterial structures has a higher HPBW. [ABSTRACT FROM AUTHOR]

A design of millimeter wave (mm‐wave) dual‐polarized multibeam antenna array (MAA) with a boresight beam is presented. In order to generate a boresight beam, a 5 × 6 Butler matrix based on three‐way directional couplers is designed as the beamforming network, which achieves equal power division and −60°, +120°, 0°, −120°, +60° progressive phase differences among the output ports when the five input ports are excited, respectively. By four‐layer design, the two 5 × 6 BMs for horizontal polarization (HP) and vertical polarization (VP) are constructed. The patch is used as radiator element, and the HP and VP wave are excited by aperture coupling and microstrip feed, respectively. A prototype is fabricated and measured to verify the design. The measured results show that the designed mm‐wave dual‐polarized MAA can generate five radiation beams including a boresight beam and the five beams with HP and VP cover the range of ±50° at 28 GHz. In addition, the designed mm‐wave dual‐polarized MAA can be a potential option for mm‐wave multibeam application. [ABSTRACT FROM AUTHOR]

This work presents a two-axis beamsteering system designed for WLAN millimeter-wave frequencies. The system comprises a wideband Butler matrix and series-fed arrays. The Butler matrix, implemented with microstrip lines, features a wideband crossover with low phase imbalance, enabling four discrete beamsteering directions on the radiation H-plane. The series-fed arrays enable frequency-dependent beamsteering on the E-plane. The entire system was fabricated on a nanoporous alumina substrate using metallic-nanowire-membrane technology. Measurement results indicate an impedance bandwidth of 17.71%, which accommodates typical requirements for 60 GHz WLAN applications. Additionally, beamsteering in the desired directions was achieved. The presented Butler matrix structure stands out as one of the most compact found in the reviewed literature. The produced device successfully balances wideband behavior, compactness, and fabrication simplicity. [ABSTRACT FROM AUTHOR]

This paper presents a butler matrix-based microstrip hexagonal patch antenna with a direction of arrival (DOA) estimation approach for mm-wave application. The hexagonal-shaped patch antenna had been designed with a Z-shaped slot with an eight-port butler matrix. The DOA estimation is also done for the switched beam antenna using a novel direction of arrival (DOA) estimation algorithm known as Cramer-Rao lower bound (CRLB). The proposed design leads to significant size reduction and loss minimization. In addition to this, the design had the advantages of being low-cost, lightweight, and small-volume. The entire proposed design provides an operating frequency range of 28 GHz to 39 GHz with a center frequency of 33 GHz. The proposed work makes use of two butler matrices with two 45° phase shifters and 120° phase shifters. The effectiveness of the proposed algorithm and antenna design using the Butler matrix is evaluated for various performance metrics separately. The antenna is designed using Rogers RT/duroid 5880(tm) substrate, and the fabricated prototype is studied. The designed antenna attains high radiation efficiency, and it ranges between 97 and 98 % under both the measures and simulated scenarios under the operating frequency range of 28 GHz to 39 GHz. [ABSTRACT FROM AUTHOR]

We are developing a spatial multiplexing technique based on orbital angular momentum (OAM) that is capable of 1 Tbit/s point-to-point wireless transmissions for the sixth generation mobile communication system. In this paper, we describe a demonstration of 100 Gbit/s wireless transmission over a range of 100 m that used OAM multiplexing of 15 streams with a 1.5 GHz bandwidth ( $39.5-41$ GHz). The OAM modes of this system were generated using a Butler matrix that allows discrete Fourier transform (DFT) operations to be performed in analog circuits. We designed $8\times 8$ Butler matrices to generate OAM modes by combining hybrid couplers and phase shifters. Since this Butler matrix was connected to 16 element antennas, two $8\times 8$ Butler matrices were connected to make an $8\times 16$ matrix. Furthermore, since these inputs were in 7 OAM mode, one port was terminated to create a $7\times 16$ Butler matrix. It was confirmed that the mode isolation was more than 15 dB in the 1.5 GHz bandwidth. Next, we designed microstrip antennas for a horizontal and vertical polarization uniform circular array (UCA) to radiate the OAM modes. Then, we implemented radio frequency (RF) chains and digital signal processing, including single carrier-frequency domain equalization and adaptive modulation and coding. A transmission experiment conducted in a field line-of-sight environment showed that the system could transmit at 119.45 Gbit/s at a distance of 100 meters, thereby demonstrating the feasibility of wideband OAM transmission in the millimeter-wave band.

In this paper, a detailed sensitivity study of Butler matrices is proposed. In particular, a Monte Carlo analysis is carried out on each block constituting the matrix to estimate its impact on the overall performance. The isolation level of the crossover transmission path is hence proved to be a critical part of the Butler matrix design. As it will be shown using both full-wave analysis and analytical equations, an isolation of 30 dB should be reached in order to guarantee proper operation of the matrix. These outcomes were experimentally proved by designing two 28 GHz Substrate Integrated Waveguide (SIW) $4\times 4$ Butler matrices as a demonstrator in the framework of the extended beam concept. Thanks to the crossover transmission path high isolation, the measured results show an insertion loss of 2.13±0.7 dB and a maximum output progressive phase deviation of −15.5° and +16.9°. Based on 0.5 $\lambda $ _0 evenly spaced isotropic antennas, those results enable a spatial coverage from −89.4° to 83.1° with a maximum loss of 2.2 dB and a ripple of 1.1 dB for the array factor as compared to the −48.6°/+48.6° spatial coverage, 3.7-dB of ripple of the conventional $4\times 4$ Butler matrix array.

This paper proposes the $2.45~GHz$ planar Beam Steering Antenna Array for Indoor Positioning Systems. The antenna array consists of a phase shifter based on a $4\times 4$ Butler matrix, and an array of four dipole Yagi antennas. By choosing one of four beams using a switching controller, the main beam of the antenna can steer in four directions from +37°, −12°, +12° to −36°. The antenna has a narrow fan beam with a beamwidth in the azimuth plane of from +21.5° to +24.5° and in the elevation plane of approximately 90° which effectively minimizes multipath signals. These advantages are suitable for positioning systems to increase location accuracy. The antenna achieves a peak gain of from 9.1 to $9.8~dBi$ in four directions, a wide band of $400~MHz$ . The fully electronically steerable antenna prototype has been designed using CST software, simulated based on the finite element method, and fabricated on the RO4003C substrate as well as measured. The antenna is implemented in the Indoor Positioning System using three different location methods, including trilateration, triangulation, and fingerprinting, to highlight the antenna’s advantages in improving location accuracy with the ratio between the mean location error and area of 0.051, 0.033, and 0.023 respectively.

For fifth-generation (5G) millimeter-wave (mmWave) beamforming, a fully planar 2 × 2 2-D multibeam antenna operating at 24–28 GHz is proposed. The proposed antenna is fed by a compact dual-layer 4 × 4 Butler matrix in substrate-integrated waveguide (SIW). In this fully planar and compact configuration, SIW coupling slot is used to facilitate the output ports of the Butler matrix on the same planar layer, and the via-based phase shifters are designed to generate wideband phase performance with compact size. The measured impedance bandwidth is 15.4%, and the measured maximum beam pointing angle is 55°. These results are in good agreement with simulation. The proposed configuration can be extended with more radiating elements for higher gain, and it is promising for beamforming scenarios, including communications. [ABSTRACT FROM AUTHOR]

This study presents a compact, wideband, 4 × 4 Butler matrix using a two‐metal‐layer thin‐film process for millimeter (mm)‐wave 5G radio applications. Size reduction techniques are thoroughly discussed for size and performance optimization. A size‐reduced quadrature coupler is designed with coplanar waveguide based length‐reduced branch lines using capacitive loading effect from the ground bridges. A compact crossover is designed for a return loss of 20 dB or more with negligible crosstalk over a wide frequency range. The circuit components are arranged in an optimized space, allowing negligible coupling between nearby elements. The Butler matrix is fabricated on a quartz substrate at the center frequency of 28 GHz. The fractional bandwidth is 15.4% at a 15‐dB return loss and insertion loss is measured in the range of 7.8–8.7 dB at the center frequency. The size of the core circuit is 3.375 × 2.100 mm2 ${\rm{m}}{{\rm{m}}}^{2}$, which corresponds to 0.469 × 0.292 λg2 ${\lambda }_{g}^{2}$. [ABSTRACT FROM AUTHOR]

A 24-GHz frequency modulated continuous wave (FMCW) radar system with self-packaged six-port Butler matrix receiver using substrate integrated suspended line (SISL) platform is proposed in this article. Since all active and passive components are integrated on the SISL platform using the standard printed circuit board (PCB) process, the proposed system is highly integrated with low cost. The system is composed of a transmitting (TX) antenna, a Butler matrix with a receiving (RX) antenna array, a single pole four throw (SP4T) switch, a low noise amplifier (LNA), and a six-port receiver. The Butler matrix and SP4T switch are implemented for beam scanning, which has the advantages of low loss and compact size. The SISL-based six-port receiver is designed for quadrature downconversion. The supporting digital signal processing algorithms are also proposed for the calculation and display of multiple targets information. The radar system has shown excellent performance in the measurement of indoor environment, including range, velocity, and direction of arrival (DOA). The proposed radar provides a new solution for a transceiver system. [ABSTRACT FROM AUTHOR]

This article presents the design of a Ka-band beam-switchable and beam-steerable endfire planar Yagi–Uda antenna array fed by a wideband Butler matrix, combining continuously tunable phase shifters based on a liquid crystal (LC) technology. The proposed array consists of four wideband 3 dB 90° branch-line couplers, two novel wideband via-less crossovers, LC-based 135° microstrip (MS) delay line phase shifters, and planar endfire Yagi–Uda antennas. The Butler matrix realizes beam switching, while LC phase shifters enable continuous beam steering inbetween the discrete beam positions. In this way, long delay line phase shifters are avoided for achieving 360°, reducing the phase shifter insertion losses (IL). Besides, such a hybrid beam steering method is expected to respond faster and more accurate. The array has two metallized layers, which can be easily fabricated by standard photolithography procedures. The fabricated array demonstrator is measured in terms of $S$ -parameters and far-field patterns. The measured return loss and isolation of the array are both ≥15 dB from 26 to 30 GHz. The beam is switchable among ±15° and ±45° in E-plane. By applying bias voltage up to 5 V to the LC phase shifters, the beam can be further continuously steered, covering almost −60° to +60° with acceptable sidelobe level. The maximum gain of the array is estimated to be 5.6 dBi. The radiation efficiency is 12%. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a miniaturized beam steering network that produces broadside beams when it is fed with a compact antenna array. Butler Matrix (BM) was used as the beam steering network. It was completely built from a miniaturized 3 dB hybrid-couplers in planar microstrip technology. It was configured by feeding the BM with a Planar Inverted-E Antenna (PIEA) array separated at 0.3 λ as against the 0.5 λ separation. This makes the BM produce a major radiation pattern at the broadside. Apart from the miniaturization, no modification was made from the BM side. However, employing effective mutual coupling reduction techniques helped to design the compact PIEA array. The validity of this BM based multibeam PIEA array was demonstrated by comparing the simulation results of the reflection coefficients, transmissions coefficients and the radiation pattern with measurements. The measurement results showed good agreement with simulations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Butler matrix adalah beamforming network yang umum digunakan pada antena multibeam karena memiliki struktur yang sederhana dan efisiensi yang tinggi. Namun, Butler matrix memiliki dimensi yang relatif besar. Struktur meander line merupakan pendekatan yang banyak digunakan untuk mereduksi dimensi dari berbagai peranti gelombang mikro. Makalah ini memaparkan tentang implementasi struktur meander line pada Butler matrix 2 × 2 untuk mereduksi dimensi. Metode yang digunakan adalah dengan menerapkan struktur meander line pada bagian through arm. Butler matrix 2 × 2 dengan struktur meander line dirancang menggunakan material dielektrik epoxy FR4 dengan dimensi 17,9 mm × 36,4 mm untuk beroperasi pada frekuensi 2,4 GHz. Hasil pengukuran menunjukkan bahwa Butler matrix 2 × 2 dengan struktur meander line memiliki koefisien refleksi kurang dari -10 dB pada frekuensi 1,88 GHz sampai 2,93 GHz (fractional bandwidth 43,75%). Pada frekuensi 2,4 GHz, dicapai isolasi sebesar -6,15 dB, koefisien transmisi sebesar -3,70 dB dan beda fase pada port keluaran sebesar 91,37o. Penerapan struktur meander line dapat mereduksi dimensi Butler matrix 2 × 2 sebesar 34,54%.

A 7 × 8 Butler matrix (BM) beam‐forming network operating at Ka‐band is proposed to feed a 8 × 8 slot array. By merging the two central input ports of the BM into one port, the BM can provide output signals with equal phase, thereby generating a boresight beam. Measured results show that the proposed antenna has impedance bandwidth of 29.5–30.5 GHz, while the gain lies in the range of 14.7–21.8 dBi. Seven beams are realized, including a boresight beam, covering the range from −58° to 58°. In order to verify this concept, the feeding network and antenna are designed and manufactured. The measured results are in good agreement with simulation. It is a capable candidate for 5G mobile terminal applications. [ABSTRACT FROM AUTHOR]

In this article, a 2-D $16 \times 16$ Butler matrix-based passive multibeam antenna array (MBAA) and a 2-D active–passive hybrid MBAA (APHMBAA) are both presented for fifth-generation (5G) millimeter-wave (mmWave) applications, which demonstrate that a 2-D coverage can be achieved by two types of 1-D beamformers in two orthogonal planes at analog beamforming level. For the 2-D passive MBAA (PMBAA), the 16 beams are controlled by two stages of substrate integrated waveguide (SIW) Butler matrices placed orthogonally. A novel 2-D interconnection method for connecting these two-stage Butler matrices is implemented based on the flexibility of the SIW without any connectors, cables, and soldering operations and then possesses the advantages of low cost, extensible, and integrated easily in the mmWave bands. The measured results exhibit that the operating bandwidth is 15.38% for the single-stage Butler matrix-based antenna array. Meanwhile, the maximal beam gain of the 2-D PMBAA is 9.4 dBi and its accurate beam directivity is also observed. For the 2-D APHMBAA, the multiple beams are generated by the Butler matrix-based passive beamformers in the vertical direction, whereas the beamforming on the horizontal direction is realized by the active networks utilizing mmWave active beamformer chips. Compared to the proposed 2-D PMBAA, the horizontal scanning performance of the hybrid framework is more flexible. What is more, its costs and complexity are both reduced tempestuously in comparison with an active multibeam array. The measured results show that the maximum measured beam gain of the array is 10.9 dBi and the chip channel gain is 27 dB. A wide 2-D spatial angle is covered simultaneously by the proposed hybrid beamforming scheme. [ABSTRACT FROM AUTHOR]

A design of planar dual‐polarized differentially fed multibeam patch antenna array (DFMPAA) is presented in this article. The dual‐polarized DFMPAA is composed of two circular 4 × 4 butler matrixs (BMs) and a 1 × 4 dual‐polarized patch antenna array. The two BMs are designed in the top and bottom layer as the feeding network of horizontal polarization (HP) and vertical polarization (VP), respectively. The patch is designed as the radiation element of the dual‐polarized DFMPAA, which is fed by the slot and aperture coupling to generate the HP and VP wave, respectively. To achieve high cross‐polarization discrimination (XPD), the antenna element is fed differentially. A prototype working at 5.5 GHz is fabricated and measured in order to validate the performance of the proposed dual‐polarized DFMPAA. The dimension of the dual‐polarized DFMPAA is 3.8 λ0 × 1.7 λ0. Measured results show that when the beam scan to the maximal pointing angle, the XPD of the dual‐polarized DFMPAA in HP and VP are higher than 27 and 29 dB, respectively. Additionally, the beams of the dual‐polarized DFMPAA can cover the range of ±42° in horizontal plane. [ABSTRACT FROM AUTHOR]

In this letter, an endfire double dipole antenna fed from double-ridge gap waveguides (DRGWG) is proposed and designed for multibeam array application. Two dipoles with different lengths are connected to the extension of the ridges of DRGWG in series. Different resonances can be generated by these two dipoles, which contributes to a wide impedance bandwidth, high gain, and stable radiation patterns across the working band. The double dipole antenna is vertically polarized and has a wide H-plane beamwidth suitable for beam scanning application. To verify the performance of the double dipole antenna, a Butler matrix is designed based on ridge gap waveguides to feed a 1 × 4 double dipole array arranging in H-plane. The maximum gains achieved for Ports 1 and 2 are 13.94 and 12.68 dBi, respectively. Besides, the simulated radiation efficiencies for Ports 1 and 2 are both above 83%. [ABSTRACT FROM AUTHOR]

In this article, the design and realization of a planar microstrip array antenna with a 4 × 4 modified Butler matrix is presented. The proposed switched‐beam smart antenna operates at 4.95 GHz. The significant purpose of this research is mutual coupling reduction between antennas of the array. Therefore, the microstrip array antenna is arranged as E‐plane mode and the novel decoupling network is used to reduce the mutual coupling. The mutual coupling of the proposed structure is measured −35 dB at 4.95 GHz frequency. The mutual coupling reduction of 17 dB is achieved by using the decoupling network. Also, the impedance bandwidth of the proposed structure with |S11| < −10 dB is about 300 MHz (6%) operating at the center frequency of 5.05 GHz and the average gain of 10.6 dB is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a detailed design and realization of a switched‐beam network. The concept is verified using planar microstrip technology. Beam forming network is constructed by a 4 × 4 Butler matrix on a single‐layer substrate. The proposed design is centered at 5.5 GHz (C‐band) for commercial WLAN applications. Individual components of the Butler matrix are discussed here and further integrated system analysis is outlined in this article. The whole architecture is realized on low‐loss FR4 substrate. Design aspects, measured results and comparative study are summarized here. Key Points: Planar, switch beam, Butler matrix, wireless communication [ABSTRACT FROM AUTHOR]