Directional coupler and wireless communication device

Abstract

A directional coupler according to the present invention includes a primary line for transmitting a transmission signal; an input port for inputting the transmission signal to the primary line; an output port for outputting the transmission signal from the primary line; a secondary line for electromagnetically coupling with the primary line to extract part of the transmission signal; a coupling port provided at one end of the secondary line; an isolation port provided at the other end of the secondary line; and a low pass filter unit having a function of low pass filter, disposed between the secondary line and the coupling port.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a directional coupler and a wireless communication device, and more particularly, to techniques for providing a flat frequency characteristic for the degree of coupling in the directional coupler.[0002]A directional coupler (hereinafter simply referred to as the “coupler”), which enables extraction of part of power propagated on a transmission line, has become an indispensable component for designing a transmitter circuit of a variety of wireless communication devices such as portable telephones, wireless LAN communication device, communication devices of Bluetooth standard, and the like.[0003]Specifically, a coupler forms part of an adjuster means for controlling a transmission signal to maintain at a certain level. The adjuster means comprises a power amplifier (hereinafter referred to as the “PA”) capable of controlling a gain; a coupler for detecting the level of a transmission signal; and an automatic output cont...

AI Technical Summary

Benefits of technology

The present invention is related to a small coupler for multi-band communication devices. The technical effects of this invention include reducing the number of parts and manufacturing costs, as well as reducing the size of the device. Additionally, the coupler provides a flat degree of coupling in both the forward and reverse directions, which improves the accuracy and precision of power detection. The coupler includes an LPF unit that forms a resonant point to mitigate the influence of other circuit elements and improve isolation and directivity. Overall, the coupler exhibits a wide band width with excellent performance in isolation and directivity.

Problems solved by technology

However, in a semi-micro wave mainly used by mobile radio devices such as portable telephones, one quarter wavelength is very long, approximately 25 cm to 3 cm (for example, 3 cm for 10 GHz), so that it is not feasible from a viewpoint of the size to provide a coupling line of this length in a coupler for use in mobile radio devices such as portable telephones and the like which are required to be reduced in weight, thickness, length, and size.

Also, the use of a long coupling line equal to or larger than several centimeters would result in an extremely large insertion loss, which can cause a signification degradation of the battery life, which is a fatal disadvantage for mobile radio devices.

However, such a coupling line generally tends to suffer from varying characteristics depending on the frequency and to exhibit the degree of coupling which increases as the frequency is higher (for example, see FIG. 6(b) of Patent Document 1 cited above).

On the other hand, in third-generation portable telephone systems such as UMTS (Universal Mobile Telecommunications System) and 3G, the degree of coupling must be maintained constant over a wide range of 800 to 2200 MHz in roder to cover, for example, from Band 1 (1920-2170 MHz) to Band 5 (824-894 MHz), however, couplers which satisfy such specifications are not currently available on the market.

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