Directional coupler

Details Directional coupler Directional coupler

2002-10-16

2004-08-03

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Plural channel systems

Having branched circuits

C333S109000

Reexamination Certificate

active

06771141

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a directional coupler which, for example, extracts portions of output signals, and outputs the extracted portions of signals as feedback control signals, and particularly relates to a directional coupler used for an output monitor of mobile communication equipment such as a cellular telephone, and other such devices.
2. Description of the Related Art
Conventionally, directional couplers take advantage of a phenomena wherein, in the event that two conductor patterns with ¼ wavelength of the usage frequency are arranged so as to be mutually parallel with one of the conductor patterns as a main line, applying signals to the main line results in signals that are proportionate to the voltage propagating the main line being output at one end of the other line. Such directional couplers are in widespread use as output adjusting monitors for cellular telephones, and other suitable devices.
FIG. 27
is a model plan view illustrating an example of a directional coupler. This directional coupler
100
includes an insulating member
200
, and a main line
300
and sub line
400
formed on the insulating member
200
. The main line
300
and sub line
400
are partially parallel with a gap therebetween, and it is at this parallel portion that coupling occurs. The sub line
400
can extract a portion of the signals flowing along the main line
300
by the coupling.
For example, in the event that such a directional coupling is assembled into a cellular telephone, the directional coupler
100
is used at the high-frequency amplifier circuit of the transmitting side. One end
300
&agr; of the main line
300
is connected to the high-frequency amplifier circuit, while the other end
300
&bgr; is connected to an antenna. Also, one end
400
&agr; of the sub line
400
is connected to a circuit that controls the high-frequency amplifier circuit, and the other end
400
&bgr; is terminated at a terminating resistor. The sub line
400
extracts (detects) a portion of the voltage passing through the main line
300
, and the detected signals are sent to the circuit for controlling the high-frequency amplifier circuit, where high-frequency voltage output from the high-frequency amplifier circuit is controlled by this circuit, thereby maintaining the intensity of signals emitted from the antenna within a predetermined range.
Incidentally, loss which occurs upon being input from the one end
300
&agr; of the main line
300
and output at the other end
300
&bgr; is referred to as “insertion loss”, and voltage input from the one end
300
&agr; of the main line
300
and output at the other end
400
&agr; of the sub line
400
is referred to as “degree of coupling”. Also, the minute voltage observed at the other end
400
&agr; of the sub line
400
, as opposed to the voltage output at the input end
300
&agr; which is voltage input from the one end
300
&agr; of the main line
300
but reflected within the coupler or at the output end (other end)
300
&bgr; and output at the input end
300
&agr;, is referred to as “isolation”. Further, the ratio of the “degree of coupling” and “isolation” is referred to as “directivity”.
Now, directional couplers
100
are being reduced in size, due to the devices in which they are being assembled, such as cellular telephones, being reduced in size. This reduction in size requires reduction in the length of the parallel portion between the main line
300
and the sub line
400
. This causes a problem in that a sufficient degree of coupling cannot be obtained.
Accordingly, an arrangement can be conceived to reduce the gap between the main line
300
and sub line
400
, in order to obtain sufficient coupling. However, excessively narrowing the gap may result in insulation destruction between the main line
300
and sub line
400
, so there is a limit to how narrow the gap between the main line
300
and sub line
400
can be, and satisfactory coupling cannot be obtained by this arrangement. Accordingly, a directional coupler
100
such as shown in
FIG. 28
has been proposed. With this directional coupler
100
, sub lines
400
A and
400
B are arranged in parallel on both sides of the main line
300
with gaps therebetween, and both ends of the sub lines
400
A and
400
B are each short-circuited. This configuration attempts to obtain satisfactory degree of coupling by increasing the sub line portion that is parallel to the main line
300
.
Also, as another proposal, an arrangement can be conceived wherein the width of the lines
300
and
400
are narrower, thereby disposing long lines on the insulating member
200
. However, in this case, an increase of loss of line increases the insertion loss, resulting in increased electric power consumption of the equipment in which the directional coupler
100
is assembled. This leads to the problem of reduced driving time with cellular telephone terminals and other devices which are generally driven by batteries.
Also, an arrangement can be conceived wherein the lines are longer in order to raise the degree of coupling, but making the lines longer causes the problem of increased insertion loss occurring.
On the other hand, as a result of a reduced permissive area for forming the conductor patterns due to reduction in size, there are problems in that securing sufficient line length is difficult, and in that consistency with circuits to which connection is made becomes poor, leading to deterioration in reflection properties. That is, the size of directional couplers is being reduced by forming the lines to have meandering, spiral, or helical configurations, thereby reducing the area and volume necessary for forming the conductor patterns.
Particularly, in the event of forming the lines (conductors) to have spiral or helical shapes, the inductance component can be efficiently obtained, and thus is advantageous in that the length of the lines to be formed can be reduced.
However, in the event that the lines (conductors) are formed to have spiral or helical shapes, there is the problem that deterioration in isolation properties occurs. Isolation properties can be improved by adjusting the gap between the main line and the sub line, and so forth, but in this case, the coupling between the main line and the sub line is low, so in practice, it is difficult to improve the directivity, which is the ratio between the degree of coupling and the isolation.
SUMMARY OF THE INVENTION
In order to solve the above-described problems, preferred embodiments of the present invention provides a small and high-capability directional coupler which has excellent isolation properties and directivity while maintaining a desired degree of coupling, with minimal deterioration in insertion loss and reflection properties.
According to a preferred embodiment of the present invention, in a directional coupling device, line coupling (distributed constant coupling) is effected between a main line and a sub line by positioning at least a partial region of a main line and sub line substantially parallel with one another when viewed in a planar manner, and the line length of the sub line is longer than the line length of the main line.
With a side edge type directional coupler wherein line coupling (distributed constant coupling) is effected between the main line and the sub line by positioning at least a partial region of a main line and a sub line substantially parallel with one another, forming the line length of the sub line to be longer than the line length of the main line improves isolation properties, and the desired degree of coupling can be obtained while securing directivity.
Also, there is no lengthening of the main line, so the insertion loss is not increased and deterioration in reflection properties is prevented, and the electric power consumption in battery-driven mobile communication equipment is minimized.
Note that the phrase “line coupling (distributed constant coupling) is effected between the main line and sub line” in preferred embodiments of the present i

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