M.R. Kirillova1, Yu.V. Raevskaya2, V.A. Redkina3, T.S. Ryzhakova4

1 LLC «Radio Gigabit» (Nizhny Novgorod, Russia)

2–4 Nizhny Novgorod State Technical University (Nizhny Novgorod, Russia)

This article is devoted to the modeling of directional Lange couplers with the maximum possible overlap in frequency. Lange directional couplers are widely used in various branches of radio electronics, which requires their constant improvement, the development of new designs, and the improvement of their characteristics. At the same time, the development of microstrip directional couplers is a promising direction.

A literature review was conducted to identify promising designs of directional couplers from the point of view of broadband. Based on the conducted research, it was concluded that from the point of view of increasing broadband, the models of the Lange coupler with a suspended substrate, as well as the models of the coupler with an additional sample in the housing, are promising.

In the course of the work, it was supposed to simulate a directional Lange coupler with the maximum possible overlap in frequency, while the frequency range of the directional coupler was supposed to be in the microwave range.

Initially, it was found out that due to the selection of parameters of the unmodified standard design of the directional coupler, it is not possible to significantly increase the operating frequency band. Therefore, modifications were made to its design to expand the operating frequency band of the directional Lange coupler.

The first simulated design represented the initial topology of the coupler, but on the reverse side of the substrate, in a thin layer of a grounded conductor, there is a window, and a sample is also made in the module housing in the form of a pyramid. It was found out that in this model the frequency response unevenness exceeds the permissible limits.

The second design under study also had a cutout in a thin layer of a grounded conductor, but did not have a pyramidal sample in the housing. With this design, the band is divided into two bands (from 2 GHz to 13 GHz and from 20 GHz to 24 GHz).

The third variant of the simulated structure was a standard topology of the coupler pattern on the board, but with a cut-out window in a thin layer of metallization in the connection area of the coupler lines. This modified design of the directional Lange coupler has good broadband with low frequency response unevenness. The following characteristics of the device were obtained for it: the operating frequency range is 4,4–26,1 GHz, the frequency response is ±1 dB uneven, the reflection coefficient is below –11 dB, the phase difference in the output arms is 90±3°.

For this structure, modeling was also carried out in the presence of a screen (a thin aluminum screen that imitated the body of a real device, and a screen in the form of transition holes along the perimeter of the topology of the coupler). In addition, the characteristics of the directional coupler were compared when connected to an isolated arm of an ideal resistor (50 ohms) and when connected to the same arm of a real resistor.

Kirillova M.R., Raevskaya Yu.V., Redkina V.A., Ryzhakova T.S. Computer simulation of the Lange directional coupler with maximum possible frequency overlap. Achievements of modern radioelectronics. 2022. V. 76. № 10. P. 67–81. DOI: https://doi.org/10.18127/ j20700784-202210-07 [in Russian]

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