Design Of Balun Research Articles

A Unified-Mode Analysis Method for Symmetric Networks and Its Application to Balun Design

A Unified-Mode Analysis Method for Symmetric Networks and Its Application to Balun Design

Design and Analysis of Balun for 3-4 GHz Ultra-Wide Band Receiver Front End for Wireless Communication

Design and Analysis of Balun for 3-4 GHz Ultra-Wide Band Receiver Front End for Wireless Communication

Miniaturised integrated passive device balun design with balanced amplitude and phase for Wi‐Fi applications

AbstractA miniaturised integrated passive device (IPD) balun design with low insertion loss and balanced amplitude and phase is proposed for Wi‐Fi/Bluetooth applications. In this design, a novel topology based on the modified T‐type filter structure is introduced to offset the parasitic and coupling effects that cause poor balance in IPD design. The proposed balun design is fabricated on a GaAs substrate. The measured insertion loss is lower than 0.9 dB and the measured return loss is >16 dB in the frequency range of 2.2–2.9 GHz. The measured results of amplitude and phase show rather minor imbalances, which are lower than ±0.67 dB and ±1.8° respectively. The fabricated device size is 0.9 mm × 0.6 mm only.

Miniature and flexible Bazooka balun for high-field MRI

Flexible coils offer improved patient comfort and better imaging quality. However, rigid and bulky baluns in RF coils limit flexibility and manufacturing. A miniaturized and flexible balun design was proposed to address this issue. It replaced rigid components with an ultra-flexible rubber tube and a flexible coaxial capacitor. Simulations validated the concept, and bench tests confirmed its performance, including a measured common-mode rejection ratio of −15.8 dB. The flexible balun was integrated into a 4-channel coil array, evaluating impedance changes caused by the “hand effect.” Compared to coils without the balun, the flexible coil with the proposed balun showed improved robustness in impedance matching and inter-element couplings. Transmit efficiency of the flexible coil with the balun was compared to coils without a balun and with a rigid, shielded cable trap. Results demonstrated that the proposed balun circuit maintained high transmit efficiency. Overall, the flexible balun design offers a promising solution for improving the flexibility and performance of RF coil arrays in MRI applications.

Design of compact and broadband filtering balun based on N-shaped spoof surface plasmon polaritons

This paper presents a novel compact and broadband filtering balun using N-shaped spoof surface plasmon polaritons (SSPPs). The N-shaped SSPP unit cell’s lateral size has a 48% reduction compared to the rectangle-shaped counterpart. The proposed filtering balun is constructed by periodically etching N-shaped and mode-matching SSPP unit cells into the slotline balun consisting of the microstrip-to-slotline transition (MST) structures. The combination of the N-shaped SSPP unit cells and slotline balun realize the compactness and the broadband bandpass filtering response. Moreover, we can individually adjust the passband’s lower and upper cut-off frequencies. Due to the larger phase constant of the N-shaped SSPP unit cell, the field-confined ability of the proposed filtering balun is enhanced. The proposed design is fabricated and measured. It has advantages in bandwidth, stopband performance, size, and degree of design freedom compared with existing SSPP filtering baluns.

Compact Filtering Balun-Diplexer Using Coupled-Line-Loaded Hairpin Ring Resonator

A filtering balun-diplexer (FBD) with compact size and high channel isolation is proposed based on the dual-mode coupled-line-loaded hairpin ring resonator (C-HRR). The special features of C-HRR are presented and concluded. The out-of-phase current distribution of the C-HRR at the odd-mode resonant frequency is noticed and utilized in the balun design. By carefully arranging the resonant frequencies and coupling topology, the two channels of the FBD can share one common C-HRR to reduce the circuit size. The lower and higher channel filtering baluns are designed separately and integrated directly into the FBD without extra impedance matching network because of the low loading effect. For validation, an FBD is fabricated with circuit size of 0.24 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda }_{\mathrm{ g}}\,\, {\times }\,\,0.14{\lambda }_{\mathrm{ g}}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda }_{\mathrm{ g}}$ </tex-math></inline-formula> is the guide wavelength at the center frequency of the lower passband. The isolation between the lower and higher channels is greater than 39 dB with the common mode rejection better than 34 dB over the passbands.

임피던스 매칭을 포함하는 소형 광대역 집중소자-분산 발룬의 설계

In this paper, the design of a compact broadband lumped-distributed balun, including impedance matching, is suggested. For the broadband impedance characteristic of the suggested balun design, the even-mode impedances of the balun were analyzed using the differential port impedance (Zin). The proposed balun enables broadband impedance matching without an additional impedance-matching network, thereby reducing the circuit size and passive loss. The suggested balun was fabricated using FR4-based PCB and its performance was verified. The balun was designed to match a single-ended port impedance of 50 Ω and a Zin of 25 Ω. The fabricated balun has a −10-dB return loss from 550 to 950 MHz. Zin was measured to confirm impedance transformation and matching of the fabricated balun. The measured real value of impedance was 25±5 Ω and the imaginary value was 0±5 Ω from 640 to 870 MHz. The electrical length of the balun was reduced to 18°

Analysis and fabrication of a small-scale radio-frequency balun for magnetic resonance imaging amplifier.

In this study, the authors report the design and fabrication of a small mixed-integrated balun for magnetic resonance imaging (MRI). The device was designed by using the positive anti-symmetric coupling method, which applies the lump surface-mount technology capacitors as well as mirror-symmetric coupling strips that were etched on the top and bottom layers of a printed circuit board. The capacitors reduced the length of the coupling strips and compensated for imbalances in the phase and gain due to errors in the fabrication process. The structure and equivalent even-odd circuit model of the device was modeled and examined using commercial software to optimize the design parameters. Following this, the device was fabricated and its performance was assessed through measurements using a network analyzer. The results showed that imbalances in the gain and phase were lower than 0.1 dB and 1°, respectively, and the insertion loss and the input voltage standing-wave ratio (VSWR) were lower than 0.4 dB and -25 dB, respectively. More importantly, the device was small, with dimensions of 50 × 60 × 1.5mm. This makes it suitable for MRI applications involving highly integrated miniaturized systems. The proposed device was integrated into a 3.0T radio-frequency power amplifier (RFPA) and reduced the dimensions of its power modules by 20% compared with the traditional balun. Finally, the RFPA module was used in an 3.0T MRI system for imaging experiments, and the results showed that the balun can help obtain high-quality scanning images.

3-D Compact Marchand Balun Design Based on Through-Silicon via Technology for Monolithic and 3-D Integration

An original concept of 3-D through-silicon via (TSV)-based Marchand baluns and its design methodology is proposed for on- chip and 3-D integration. By utilizing a 3-D packaging process that includes a TSV and redistribution layer (RDL), a meander coupling path is established and embedded in the vertical direction of the substrate for balun design. The 3-D structure can effectively reduce the on- chip area while maintaining good balance characteristics. Furthermore, the structure can be flexibly integrated with 3-D integrated circuits (3-D ICs) to realize signal conversion between different stacking tiers. An equivalent circuit model based on the TSV-to-TSV coupling channel and coupled transmission line has been established for initial estimation before electromagnetic (EM) optimization. To shorten the design cycle, a specific flow is proposed to meet the structural particularity and different application scenarios. To verify the design method and flow, a design case is analyzed and EM simulated with the antenna feeding network as the target application. The EM simulation results show that the design can work at 43–82 GHz with an amplitude imbalance of less than 0.3 dB and a phase imbalance of less than 1.3°, which meets the requirements of balanced feeding. It only costs a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.084\,\,\lambda _{\text {g}}\,{\times }\,0.009\,\,\lambda _{\text {g}}$ </tex-math></inline-formula> footprint, which is far lower than that of the conventional planar types.

Dual-Tuned Lattice Balun for Multi-Nuclear MRI and MRS.

Balun or trap circuits are critical components for suppressing common-mode currents flowing on the outer conductors of coaxial cables in RF coil systems for Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS). Common-mode currents affect coils' tuning and matching, induce losses, pick up extra noise from the surrounding environment, lead to undesired cross-talk, and cause safety concerns in animal and human imaging. First proposed for microwave antenna applications, the Lattice balun has been widely used in MRI coils. It has a small footprint and can be easily integrated with coil tuning/matching circuits. However, the Lattice balun is typically a single-tuned circuit and cannot be used for multi-nuclear MRI and MRS with two RF frequencies. This work describes a dual-tuned Lattice balun design that is suitable for multi-nuclear MRI/MRS. It was first analyzed theoretically to derive component values. RF circuit simulations were then performed to validate the theoretical analysis and provide guidance for practical construction. Based on the simulation results, a dual-tuned balun circuit was built for 7T 1H/23Na MRI and bench tested. The fabricated dual-tuned balun exhibits superior performance at the Larmor frequencies of both 1H and 23Na, with less than 0.15 dB insertion loss and better than 17 dB common-mode rejection ratio at both frequencies.

Design of an Ultrawideband Planar Guanella Balun

This article presents the design and implementation of an ultrawideband multioctave planar Guanella balun (balanced-to-unbalanced) using double-sided parallel strip lines (DSPSLs). The operating frequency of the balun is found to be 0.5–2.6 GHz. The DSPSL is a type of balanced transmission line where two metal strips are present on the opposite sides of a flat dielectric substrate. Wideband transition between these balanced lines to a microstrip line has also been implemented. The measured amplitude and phase imbalance between the output signals at the balanced ports are less than 0.75 dB and 7°, respectively. The impact of these amplitude and phase imbalances on the combining loss of the balun has been presented. In order to understand the behavior of the balun with respect to differential and common mode signals, the mixed-mode <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters have been calculated. The physical size of the fabricated balun is 27.25 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times\,\,49$ </tex-math></inline-formula> mm. The design has been validated with the help of its measurement results.

Active Balun with Center-Tapped Inductor and Double-Balanced Gilbert Mixer for GNSS Applications

A new 1.575 GHz active balun with a classic double-balanced Gilbert mixer for global navigation satellite systems is proposed herein. A simple, low-noise amplifier architecture is used with a center-tapped inductor to generate a differential signal equal in amplitude and shifted in phase by 180°. The main advantage of the proposed circuit is that the phase shift between the outputs is always equal to 180°, with an accuracy of ±5°, and the gain difference between the balun outputs does not change by more than 1.5 dB. This phase shift and gain difference between the outputs are also preserved for all process corners, as well as temperature and voltage supply variations. In the balun design, a band calibration system based on a switchable capacitor bank is proposed. The balun and mixer were designed with a 110 nm CMOS process, consuming only a 2.24 mA current from a 1.5 V supply. The measured noise figure and conversion gain of the balun and mixer were, respectively, NF = 7.7 dB and GC = 25.8 dB in the band of interest.

Design and analysis of low-insertion-loss G-band CMOS four-way Wilkinson power dividers and dual balun

We present the design and analysis of G-band CMOS Wilkinson power dividers and dual balun for G-band communication and imaging systems. Miniature spiral and U-shaped four-way Wilkinson power dividers, which are based on three two-way Wilkinson power dividers, are designed and implemented. Miniature spiral dual balun, which is equivalent to an upper balun and a lower balun in parallel, is also designed and implemented for comparison. These devices are planar and symmetrical, and their main structure is implemented by the 2.34-µm-thick topmost metal to minimize the resistive loss. This leads to low insertion loss, and small amplitude imbalance (AI) magnitude and phase difference (PD) deviation. For instance, the spiral four-way Wilkinson power divider occupies 0.033 mm2 chip area and achieves S11 of − 11.4 dB, S21 of − 6.271 dB, S31 of − 6.445 dB, S41 of − 6.676 dB, and S51 of − 6.111 dB at 180 GHz, one of the smallest chip areas and lowest insertion losses for four-way power dividers with similar operation frequency. The corresponding AI magnitude and PD deviation are 0.565 dB and 3.2°, respectively. Moreover, the spiral dual balun occupies 0.026 mm2 chip area and achieves S11 of − 10.6 dB, S21 of − 7.549 dB, S31 of − 7.1 dB, S41 of − 7.598 dB, and S51 of − 7.352 dB at 180 GHz. The corresponding AI magnitude and PD deviation are 0.498 dB and 5.7°, respectively. The prominent results of the spiral and U-shaped four-way Wilkinson power dividers, and the spiral dual balun indicate that they are suitable for power division/combination in G-band systems.

A Review of Passive and Active Ultra-Wideband Baluns for Use in Ground Penetrating Radar

Microwave ultra-wideband technology has been widely adopted in instrumentation and measurement systems, including ground-penetrating radar (GPR) sensors. Baluns are essential components in these systems to feed balanced antennas from unbalanced feed cables. Baluns are typically introduced to avoid issues with return signals, asymmetrical radiation patterns and radiation from cables. In GPR systems, these issues can cause poor sensitivity due to a reduction in radiated power, blind spots due to changes in the radiation pattern and additional clutter from common mode radiation. The different balun technologies currently available exhibit a wide variation in performance characteristics such as insertion loss, reflection coefficient and phase balance, as well as physical properties such as size and manufacturability. In this study, the performance of two magnetic transformer baluns, two tapered microstrip baluns and an active balun based on high-speed amplifiers were investigated, all up to frequencies of 6 GHz. A radio frequency current probe was used to measure the common mode currents on the feed cables that occur with poor performing baluns. It was found that commercially available magnetic transformer baluns have the best phase linearity, while also having the highest insertion losses. The active balun design has the best reflection coefficient at low frequencies, while, at high frequencies, its performance is similar to the other baluns tested. It was found that the active balun had the lowest common mode current on the feed cables.

Compact Filtering Balun With Wide Stopband and Low Radiation Loss Using Hybrid Microstrip and Substrate-Integrated Defected Ground Structure

In this letter, a novel hybrid microstrip and substrate-integrated defected ground structure (SIDGS) are proposed for filtering balun design. Coupled microstrip and SIDGS resonators can not only achieve 180° phase imbalance with filtering response but also realize wide stopband and wideband low radiation loss. In addition, the feature of stacked substrate packaging could reduce the size of the circuit and be flexible for integration. To verify this mechanism, a filtering balun operating at 3.08 GHz with 3-dB fractional bandwidth (FBW) of 45% is proposed based on hybrid microstrip and SIDGS, which exhibits the in-band amplitude- and phase-imbalances of ±0.5 dB and ±0.4°, respectively. The stopband extends to 18 GHz with the rejection level of 20 dB, whereas the measured total loss (i.e., including radiation, metal, and substrate loss) is less than 15% up to 15.3 GHz.

Triaxial Balun With Inherent Harmonic Reflection for Millimeter-Wave Frequency Doublers

This article presents the design and utilization of a triaxial balun as a harmonic reflector (HR) for millimeter-wave frequency doublers (FDs). The triaxial structure consists of two vertically integrated transmission lines (TLs). The impedance of the asymmetric couplers can be tuned to independently control the reflection coefficients at the fundamental and second-harmonic frequencies. The performance of this reflector is analyzed in detail, and the effects of parasitics and nonideal terminations are investigated. Two FDs utilizing this approach were implemented in a 90-nm silicon-germanium (SiGe) BiCMOS platform, both with and without an output buffer. The bufferless design achieves a record peak output power and efficiency of 9.4 dBm and 12.1% at 130 GHz, respectively, with a bandwidth of 128-140 GHz. The buffered design achieves a peak output power of 8.85 dBm and 8.8% efficiency while operating over a 118-146-GHz bandwidth.

A compact wideband balun design using double‐sided parallel strip lines with over 9:1 bandwidth

A simplified miniaturized wideband balun design covering (0.38-3.5 GHz) is presented. The broadband balun structure occupies a small area of 20.7 mm × 20.8 mm. The balun is designed using low loss double-sided parallel strip lines and is comprised of a two-stage Wilkinson divider followed by loading, symmetrically, the two output ports. One port with a phase inverter circuit; while a very similar but non-inverting circuit is placed in the other port for loading-balance compensation. To realize the balun's function, different smooth transitions have been employed and were accounted for. The fabricated balun circuit demonstrated phase and amplitude imbalance of less than ±5° and ± 0.4 dB, respectively, over the band.

An Ultraminiaturized Bandpass Filtering Marchand Balun Chip With Spiral Coupled Lines Based on GaAs Integrated Passive Device Technology

The integrated passive device (IPD) technology has become a new research hotspot, and it depends on electrical characteristics of GaAs, NiCr, and Si3N4 to construct radio frequency (RF) components. RF elements constructed by the IPD technology have features of high quality and ultra-small size, especially for capacitors and inductors. In order to realize the miniaturization of RF circuits, dimensions become as small as possible. Consequently, the layout of a spiral coupled line (SCL) cannot be drawn freely, so that it has uncontrollable odd- and even-mode impedances and a large coupling coefficient, which may limit the design of the traditional Marchand balun negatively. This article solves this problem by designing a GaAs IPD Marchand balun with 1/8-wavelength coupled lines (CLs) and using a capacitor termination to replace the open end in the conventional Marchand balun. Meanwhile, a filter is added to realize a filtering function. The proposed bandpass filtering Marchand balun (BFMB) chip has a size of 1.49 mm $\times1.39$ mm, and measured results indicate that it has an operation band of 2.39–5.68 GHz with a phase imbalance of 5.26° and a magnitude imbalance of less than 0.35 dB.

An Enhanced Frequency Ratio Dual Band Balun Augmented With High Impedance Transformation

Design of a dual-band balun achieving simultaneous high impedance ratio (> 20) and band-ratio (> 10) is reported in this brief. The presented design, augmented with closed-form design equations and a systematic design procedure, achieves excellent isolation between output ports and good matching at all the ports. A number of case studies are included to demonstrate the capability of the presented approach for varying design specifications and port-terminations. A prototype is developed for impedance transformation ratio (k) of 5 and frequency ratio (r) of 5 concurrently to evaluate the presented design approach show excellent agreement between the simulation and experimental results and thus validate the proposed design strategy. A comparative analysis with a number of recently reported dual-band impedance transforming components demonstrates superior performance of the proposed design.

Guest Editorial for the special issue on devices and circuits for millimeter‐wave and THz applications

Guest Editorial for the special issue on devices and circuits for millimeter‐wave and THz applications