Myun-Joo Park

It is shown that the analysis by Zerfaine et al. (2023) is based on the incorrect S₁₁ expression and leads to erroneous results. The S₁₁ errors are proved through the exact solution of the analysis equations by Zerfaine et al. (2023) and the correct S₁₁ expression is provided.

Some erroneous results are found in the analysis results presented in 1 and its corrections 2. The errors associated with the isolation resistor in 1 and the impedance expression in 2 are indicated, and the exact equations are presented.

In the above article (Pan et al., 2023), it is shown that the solution given for the –90 $^\circ$ directional coupler with adjustable phase difference slope is inadequate for equal power division purposes. The proposed solution results in a significant error between the two outputs of the coupler. Exact, correct solutions are derived for the coupler, which proves that the proposed solution in Pan et al. (2023) corresponds to the coupler for an unequal power division case rather than the equal power division.

It is shown that the two-section branch-line coupler proposed in Liu and Lin (2021) corresponds to the cascade connection of two conventional couplers. The design of the two-section coupler can be reduced to that of a conventional single-section branch-line coupler. The wide-range phase-differences of the two-section couplers become ineffective toward larger power-dividing ratios and the two-section couplers have a much-reduced range of power-dividing ratios as compared with the conventional single-section couplers.

In the title paper, the authors proposed the model of the directional coupler using electrical balance based on a pair of coupled lines and presented its analysis. It is shown that the proposed equivalent circuit is incomplete without additional transmission line sections, and the analysis based on it cannot justify the claimed coupler performance or the design equations. A correct circuit model and the design equations are presented for the proposed coupler.

The power-dividing ratio analysis by Ye et al. is based on an inadequate equivalent circuit and neglects the effect of the isolation resistor. It is shown that the isolation resistor should be included for the power-dividing analysis and the exact analysis results are presented for the power-dividing ratio. According to the exact analysis, the wide tuning range of the power division ratio claimed by Ye et al. is sharply reduced including the effect of the isolation resistor.

A new method is presented to obtain arbitrary coupling levels of the branch-line couplers through the simple modification of the 3-dB coupler. It is shown that the coupling of the conventional 3-dB branch-line coupler can be adjusted to arbitrary values by varying the electrical length of the branches without changing the impedances. A very wide range of coupling values can easily be obtained using the same line impedances as the conventional 3-dB couplers based on the proposed method.

The synthesis and design method for the dual-band, dual transmission line branch-line coupler in [1] involves equivalent circuit transformations that are single-banded in nature and not suitable for the dual-band operations. The proposed equivalent dual transmission line transform has been applied only in the middle of the dual-band operation frequencies and its validity has not been confirmed at the two band frequencies. As the result, the proposed circuit equivalence can be quite poor and the coupler design in [1] based on it can be quite erroneous at the dual-band operation frequencies.

Asia-Pacific Microwave Conference Proceedings, 2005, APMC 2005, vol. 4, 4-7. doi: 10.1109/APMC.2005.1606887 ©2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. This Article is brought to you for free and open access by the Department of Electrical and Computer Engineering at OpenSIUC. It has been accepte

A new equivalent circuit model is proposed for an asymmetric coupled line based on a symmetric coupled line. The proposed equivalent circuit consists of a symmetric coupled line and two ideal transformers to represent an asymmetric coupled line and can be easily incorporated into the existing microwave and RF circuit simulators. This makes it easier to model and simulate the asymmetric coupled line circuits in terms of simple symmetric coupled lines. Using the proposed equivalent circuit model, it is shown that an asymmetric coupled line coupler is electrically equivalent to a symmetric coupled line coupler with transformed port impedances and the relation between the two couplers is investigated through the established equivalence. The validity of the proposed model is confirmed through the analysis of the directional couplers and the impedance transformers involving the asymmetric coupled lines. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:277–282, 2016.