Sen-Kuei Hsu

A Novel Compact Forward-Wave Directional Coupler Design Using Periodical Patterned Ground Structure

A novel forward-wave directional coupler with periodical patterned ground structures is proposed. The input impedance of the even and odd mode of the proposed coupler can be matched, and the phase difference between the even and odd mode is also strongly enhanced. The equivalent models are constructed to predict the propagation properties based on the Bloch-Floquet theorem. A completed design procedure is also proposed based on the equivalent models. This two-layer structure is fabricated on Duroid substrate. 0.5-dB coupling level can be measured at 1.5 GHz, and the coupler length is 0.5 λg. Compared to previous studies, the proposed coupler can be designed at a lower frequency range with a smaller size.

A Novel Miniaturized Forward-Wave Directional Coupler With Periodical Mushroom-Shaped Ground Plane

A novel miniaturized forward-wave directional coupler with periodical mushroom-shaped ground plane is proposed. The coupler can be designed with identical characteristic impedances for even and odd mode and enhanced the difference of propagation constants between the even and odd mode. These distinct propagation characteristics can be predicted by the equivalent-circuit model of a unit-cell using the Bloch-Floquet theorem. A tested sample is designed and fabricated on the FR4 substrate. We designed a 0-dB coupler with the length about 1.28 λg, and 1.0-dB coupling is measured at 2.9 GHz due to the loss. Compared with previously studies, the proposed coupler can be implemented to attain the highest coupling level with a smaller size.

A Broadband Forward-Wave Directional Coupler Using Periodic Y-Shaped Ground Via Structures With Arbitrary Coupling Levels

A broadband forward-wave directional coupler loaded with periodic Y-shaped ground via structures is proposed. Broadband impedance matching of the even and odd modes can be approximately achieved. The proposed coupler can provide an almost constant phase difference between the even and odd modes over a wide frequency range. Therefore, a forward coupler with broad bandwidth can be expected. Based on the Bloch-Floquet theorem, the Bloch impedances and the electrical lengths of both modes can be predicted with the aid of our simple equivalent models. Also, a complete design procedure for arbitrary coupling level is provided. A test sample is fabricated on a low-temperature co-fired ceramic substrate with coupled-line length 2.02 λg. The coupling level over 1.5 dB can be measured from 4.5 to 10.4 GHz, which corresponds to the fractional bandwidth of 79.2%. To our knowledge, the proposed coupler is the smallest design with such a broad bandwidth.

Bandwidth Enhancement of 4

A broadband Butler matrix by combining the proposed broadband forward-wave directional coupler and a broadband middle network is proposed. Test samples of both the proposed coupler and Butler matrix are fabricated on Ro4003 and the sizes are 0.4 λ_g × 0.14 λ_g and 1.02 λ_g × 1.17 λ_g, respectively. For the Butler matrix, the amplitudes of the output signals and the phase imbalances between output ports can be kept at an approximately constant level. The errors of phase imbalances can be kept within ±6^° from 1.96 GHz to 3.15 GHz and the corresponding fractional bandwidth is 47%.

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We propose a novel, eight-port, forward-wave directional coupler with periodically patterned ground structures. The input impedances of the four modes for the proposed coupler can be matched, and the phase difference between the even–even and the other three modes is also strongly enhanced. Equivalent models have been constructed to predict the propagation properties based on the Bloch–Floquet theorem. A design procedure is also proposed completely based on the equivalent models. The proposed couplers, with both equal and unequal power divisions, are fabricated on a Duroid substrate. Then, there is good agreement between theoretical simulations and measurements.

4 Butler Matrix Using Broadband Forward-Wave Directional Coupler and Phase Difference Compensation

A compact forward-wave directional coupler using periodic capacitive loadings has been proposed. The phase difference between the even and odd modes can be significantly enlarged, which makes the size of the coupler more compact. A simple equivalent model of the unit cell is developed to predict the electrical lengths and the Bloch impedances for both even and odd modes. A test sample is fabricated on an FR4 substrate. The coupling level of 3.4 dB can be measured at 1.7 GHz with a small electrical length of 0.19λg.