A 3-dB 90 degrees microstrip hybrid directional coupler at 2.27 GHz

Abstract

A 90° hybrid-coupler in the 2.27 GHz range, offering high performance despite its size of 115.64 mm2 (18.36 λg), is introduced. The main factor that distinguishes this proposed design, positively, is that the device demonstrates high fabrication tolerances due to its simplicity, and uncomplicated length dimensions. At the center of the structure are 9 metal squares, all of equal size and equidistant. It has been observed that the S-parameters remain relatively the same after increasing or decreasing the side lengths, substrate parameters, and the vertical separation dimensions. Based on these results, it has been shown that the design will provide a successful fabrication tolerance. According to the simulation results, the S-parameters are as follows: S11 = −24.01, S12 = −3.063, S13 = −3.063, and S14 = –23.47 (all in dB). The phase deviation is only 0.8°. After the simulation studies, a prototype of the coupler was fabricated, and laboratory measurements were made. The simulated and measured results, have desirable agreement. Finally, a few similar studies presented in the literature are discussed with a comparative table, in terms of overall size, isolation, phase deviation, and structure complexity. Thus, the advantages of this presented structure, compared to these studies, have been revealed.