Branch-line Balun Research Articles

Compact branch-line balun using coupled-line and open stubs fabricated on paper substrate

In this article, a novel transmission line model consisting of open stubs and a one-end connected coupled line is introduced as an alternative to the standard quarter wavelength transmission line (QWTL). The new transmission line unit is used to realize a highly compact branch-line balun. Even and odd mode analysis is employed to extract the closed-form design equations. To substantiate the theoretical analysis, a branch-line balun with f0 = 0.9 GHz is implemented on a biodegradable substrate material and tested. The developed prototype is having a relative circuit area of 11.2% of the conventional balun. The measured results exhibit that the return loss is better than 20 dB. A good match is found between the simulated and tested results.

Highly compact and harmonic suppressed branch line balun using artificial transmission lines

In this article, a compact and harmonic suppressed microstrip branch line balun is designed using artificial transmission line (ATL) units. The stopband response of open-stubs present in the ATL units has been utilized to suppress the spurious passbands. Design guidelines are given with graphs and equations based on the lossless transmission line model and an even-odd mode technique. To demonstrate the proposed design theory, an experimental prototype branch line balun operating at 0.9 GHz, having 10% relative circuit area and up to 5th harmonic suppression is presented.

Wideband bandpass filtering branch‐line balun with high‐isolation

The wideband bandpass filtering branch-line balun with high isolation is presented in this paper. The proposed balun can be designed for wideband performances by choosing a proper characteristics impedance of input vertical transmission line and odd-mode impedance of parallel-coupled lines. The proposed balun was designed at a center frequency (f0) of 3.5 GHz for validation. The measured results are in good agreement with the simulations. The measured power divisions are −3.31 dB and −3.24 dB at f0 and −3 ± 0.17 dB within the bandwidth of 0.95 GHz (3 GHz to 3.95 GHz). The input return loss of 24.09 is measured at f0 and higher than 20 dB over the same bandwidth. Moreover, the measured output losses are better than 11 dB within a wide bandwidth. The isolation between output ports is 20.32 dB at f0 and higher than 13.2 dB for a broad bandwidth from 1 GHz to 10 GHz. The phase difference and magnitude imbalance between two output ports are 180° ± 4.5° and ± 0.95 dB, respectively, for the bandwidth of 0.95 GHz.

A Novel Uniplanar Balun With Transparent Termination Impedance

In this letter, a novel planar branch line balun with transparent port impedance is presented. The balun is designed based on a symmetric four-port network with an open-ended transmission line stub in the middle of the branch at its unbalanced port side. From the even-odd mode analysis, the equivalent network is derived to be a short circuit under even-mode excitation, and the input impedance looking into the unbalanced port satisfies impedance matching under odd-mode excitation. Unlike previous designs, the equivalent cascaded impedance transformer in the proposed structure is independent to the system reference impedance in odd-mode excitation so that the termination at the unbalanced port is transparent to balanced ports. To prove the design concept, the closed-form equations are derived, and multiple prototypes with termination impedances 35, 50, and $75 ~\Omega $ are simulated, fabricated, and characterized.

A compact, wideband branch-line balun with small magnitude and phase imbalances

ABSTRACTThis paper presents the techniques to broaden the magnitude and phase bandwidth of a branch-line balun. Explicit equations based on S parameters are derived and presented by converting the 3-port network to a 2-port network, while compactness was achieved by meandering the branches. A demonstrator balun was developed and examined from numerical evaluations and experiments. Measurements agree well with the theoretical calculations and numerical predictions. Moreover, a figure of merit (FOM) has been proposed, for the first time, to comprehensively characterize the circuit performance of a microwave balun; and a very high FOM was found for the developed demonstrator balun.

Broadband branch-line balun with good isolation and impedance matching

ABSTRACTPrimary challenges of developing a branch-line balun lie in the output isolation and impedance matching. A two-order branch-line balun topology, featuring enhanced electric performance, is studied in this paper. Results show that by loading series resistors on the arm between the outputs, both impedance matching and port isolation can be achieved simultaneously. Moreover, with a two-section in cascade, small magnitude and phase imbalances are found within a wide frequency band. A prototype demonstrator, centered at 5 GHz, is further optimally designed, fabricated, and examined experimentally. Good results confirm the study of this contribution.

Design of a dual‐band microstrip branch‐line balun using T‐shaped coupled lines

ABSTRACTThis article presents the development of a novel dual‐band branch line balun with design flexibility. The T‐shaped coupled line structure is constructed by two series short‐ended coupled lines and one open‐ended stub to obtain the dual‐band characteristics. The proposed dual‐band structure has the capability to design a conventional microstrip line with arbitrary impedances and electrical lengths at two different operating frequencies. In addition to this, different range of frequency ratios is obtained by varying the length of the stub. The required explicit design equations are derived analytically to compute the physical dimensions of the coupled lines and stub. Based on these equations, closely and widely spaced frequency bands useful for many wireless communication systems are devised. To prove better agility, three examples of dual‐band branch line baluns are designed. Finally, a prototype of dual‐band balun is demonstrated for GSM and WiMAX applications at 0.9 and 3.5 GHz, respectively. Good agreement is found between the theoretical predictions and experimental results. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1197–1202, 2017

High‐gain low‐cost broadband 60 GHz differential integrated patch array antennas with wire‐bonding packaging and on‐board compensation network

Two high-gain broadband 60GHz integrated planar patch array antennas, without and with air cavity, are designed and implemented on Rogers 5880 substrate. The differential antenna structure is used to improve the signal integrity at millimetre-wave frequencies. The antennas are co-designed with bonding wires of which the parasitic effect is compensated using a passive network. The proposed antennas have the advantages of symmetrical radiation pattern, wide bandwidth and low insertion loss. In the measurement, a differential transmission line based de-embedding structure is developed on silicon, mimicking the real chip packaging environment and providing reliable terminations for antennas. The measured fractional bandwidths (| S 11 | <; -10dB) are 13.8 and 26.2%, respectively, for the two structures without and with air cavity, including the effect of a waveguide-to-microstrip line transition and a branch-line balun. Both antennas have measured gain of about 12 dBi. After de-embedding the return loss, the measured insertion loss of the bond wire compensation network is only 0.07dB at 61GHz.

Design of a Quad-Band Branch Line Balun Using Extended Pi-Shaped Coupled Lines

In this letter, a quad-band balun employing Pi-shaped and series connected coupled lines is proposed. The closed form design equations are derived analytically. Based on these equations, a quad-band balun operating at 1.8/3.6/5.8/7.8 GHz is designed, fabricated and tested. The measurement result shows that, the return loss and isolation are better than 18 dB and the bandwidth obtained is more than 150 MHz at each operating frequency band, which is feasible for most applications. Good agreement is found between the theoretical predictions and experimental results.

Broadband Branch Line Balun using Meander line on Silicon Substrate

This article presents the design of L-band branch line balun using microstrip configuration on high resistive silicon substrate (ρ>8KΩ-cm). In comparison to earlier designs better performance is achieved by meandering all the four branches and appending a quarter wavelength short circuited stub at the upper right corner of the structure. The circuit is designed using circuit simulator of Agilent's advanced design system (ADS) and further verified using Ansoft's FEM and ADS's MoM based electromagnetic solvers. Comparative study is carried out among various simulation techniques and analyzed. Fabrication methodology along with design steps are detailed in this article. Proposed design saves around 60% print area as compared to conventional topology. Further comparison with other reported topologies have also been discussed. Keywords - Branch line balun, high resistive silicon, microstrip line, short circuited stub, via hole.

A Compact Log-Periodic Branch-Line Balun with an Octave Bandwidth

Conventional half-wavelength branch-line baluns are bulky and suffer from narrow operating bandwidth. The use of log-periodic type can extend the bandwidth greatly at the expense of the circuit area. In this article, a planar branch-line balun, characterizing a wide operating bandwidth and a compact size, is developed. The analysis of such a kind of three-port network starts from its symmetric four-port network. Even- and odd-mode analyzing methods are adopted to determine the line impedance of the branches. The size reduction of the developed balun is achieved by periodically loading a slow-wave structure on the transmission line itself. Also, the slow-wave factor is studied to give design guides in practical designs. With five-section topology, an octave bandwidth log-periodic balun is developed, where its circuit area is approximately halved as compared with the traditional log-periodic balun for the same operating bandwidth. To validate the study, a demonstration balun, operating from 2 to 4 GHz, is optimally designed, built and tested. Results from measurements confirm the predicted performance with good consistency.

Stubbed Branch Line Balun

A new impedance transforming balun scheme is presented based on the branch line structure with stubs on the vertical branches. The stubbed vertical branch eliminates the unwanted even mode output and provides only the required balun output with opposite phase. Also, the use of stubs reduces the branch lengths by two times the stub length and therefore, helps to reduce the total size of the proposed balun

Miniaturised branch-line balun with bandwidth enhancement

A miniaturised branch-line balun with bandwidth enhancement is investigated. The improved performance is achieved by meandering the branches and attaching a quarter-wavelength stub at the upper right corner of the conventional branch-line balun. Centred at 1.5 GHz, the introduced balun is optimally designed and validated by experiments. A circuit size of 20% is achieved as compared to the conventional type, and good electrical performance is observed.