A Semi-Elliptical Wideband Directional Coupler

Abstract

Abstract-A new design of wideband directional couplers using a semi-elliptical edge-coupled structure is presented. This structure consists of two semi-elliptical patches on the top layer and an elliptical defected ground plane on the bottom layer to increase the coupling coefficient and operating bandwidth. Even and odd mode analysis is performed, and sets of design graphs are formulated to facilitate the design of the coupler on substrate with dielectric constants of 2.2 and 3.38. The operating frequency and coupling are controlled by the dimensions of the elliptical patch and the size of the air gap. Compared to the conventional parallel-microstrip coupler which requires extremely narrow air gap to achieve tighter coupling factor, the semi-elliptical coupler allows for wider air gap to be used, and it reduces fabrication difficulty. Both simulation and measurement results show that the proposed design exhibits wideband characteristic with a bandwidth ratio of more than 2.4 with a coupling deviation of ±1 dB.

Miniaturized and Folded Multisection Quadrature Hybrid for Uwb Applications

“…Conventional single section quadrature hybrid with equal power division has a limited bandwidth about 15% over which the power balance is within 0.5 dB. Bandwidth can be increased using coupled lines [1][2][3][4][5][6] and multisection structures [7][8][9][10][11][12][13]. However, hybrids using coupled lines are hard to be implemented on microwave monolithic integrated circuit (MMIC), and multisection hybrids occupy large size due to its planar multisection structure, shown in Figure 1(a).…”