Wave transmission lines and networks – Coupling networks – Delay lines including long line elements
Reexamination Certificate
2000-10-26
2003-04-01
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Delay lines including long line elements
C333S101000
Reexamination Certificate
active
06542051
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a phase shifter, and in particular, to a phase shifter for a microwave or millimeter wave band which is used as part of a phase control element of a phased array antenna etc.
DESCRIPTION OF THE RELATED ART
A typical conventional switched line phase shifter is composed of two main lines, two or more switched lines (a reference line and one or more delay lines), and two or more RF (Radio Frequency) switches. Each end of a switched line is connected to one of the main lines through an RF switch. By the operation of the RF switches, the connection between the two main lines changes and thereby a desired phase shift is given to an RF signal which is passing through the phase shifter.
FIG. 1
is a circuit diagram showing a conventional switched line phase shifter. Referring to
FIG. 1
, the conventional switched line phase shifter includes two switched lines S and L and four RF switches SWa~SWd. Each switched line (S, L) is connected between two main lines ML
1
and ML
2
, and each RF switch (SWa, SWb, SWc, SWd) is connected between a main line and a switched line. The length of the switched line L is set longer than that of the switched line S. The connection between the main lines ML
1
and ML
2
through the switched line S or L is changed by the operation of the RF switches SWa~SWd. When the RF switches SWa~SWd, which operate together, are (OFF, OFF, ON, ON), the switched line L is connected with the main lines ML
1
and ML
2
and the switched line S is disconnected from the main lines ML
1
and ML
2
(hereafter referred to as “state L”). When the RF switches SWa~SWd are (ON, ON, OFF, OFF), the switched line S is connected with the main lines ML
1
and ML
2
and the switched line L is disconnected from the main lines ML
1
and ML
2
(hereafter referred to as “state S”). By the switching of the RF switches SWa~SWd between the states L and S, a phase shift corresponding to the length difference between the switched lines L and S is realized.
However, in the conventional switched line phase shifter which has been described above, phase shift deviation (deviation of phase shift when the frequency of an input RF signal varies) occurs as will be described below.
FIG. 2
is a plan view showing a conventional 90° switched line phase shifter which is composed of microstrip lines, and
FIG. 3
is an explanatory drawing which explains the operation of the conventional 90° switched line phase shifter of
FIG. 2
simply.
FIGS. 2 and 3
are equivalent in electrical meanings. Referring to
FIGS. 2 and 3
, the lengths of the switched lines L and S are L=&lgr;g
0
/2 and S=&lgr;g
0
/4, therefore, the designed phase shift of the 90° switched line phase shifter becomes &Dgr;&PHgr; 90° corresponding to the length difference (L−S=&lgr;g
0
/4) between the switched lines L and S.
FIG. 4
is a graph showing the phase shift deviation (phase shift-frequency relationship) of the conventional 90° switched line phase shifter of
FIGS. 2 and 3
(simulation result). In
FIG. 4
, the vertical axis denotes phase shift of the 90° switched line phase shifter in the state S relative to the state L (&Dgr;&PHgr;=&PHgr;S−&PHgr;)L (&PHgr;S:transmission phase delay in the state S, &PHgr;L: transmission phase delay in the state L)). Incidentally, a transmission phase delay of ¼ &lgr;g
0
is usually expressed as −90° (negative), for example. The lengths (L, S) of the switched lines L and S are set based on the wavelength &lgr;g
0
at the (designed) center frequency f
0
. For example, in the case of
FIG. 3
, the switched line lengths L and S are set so that L−S will be &lgr;g
0
/4 (L=&lgr;g/2, S=&lgr;g
0
/4), thereby the phase difference between the states L and S becomes &Dgr;&PHgr;
32
90° at the center frequency f
0
.
However, in the frequency range higher than the center frequency f
0
, the wavelength is shorter than &lgr;g
0
and thus the phase shift becomes larger than 90°
0
. On the other hand, in the lower frequency range, the wavelength is longer than &lgr;g
0
and thus the phase shift becomes smaller than 90° . Consequently, the phase shift-frequency relationship of the 90° switched line phase shifter becomes a straight line having a positive slope as shown in FIG.
4
. In the case of
FIG. 4
, the phase shift &Dgr;&PHgr; is precisely 90° at the center frequency f
0
, however, the phase shift &Dgr;&PHgr; deviates from 90° and the phase shift deviation becomes larger as the frequency of the input RF signal deviates from the center frequency f
0
.
Further, in the conventional switched line phase shifter which has been shown in
FIGS. 1 through 3
, four RF switches are necessary for switching the connections of the two switched lines L and S of different lengths and thereby obtaining the phase shift &Dgr;&PHgr;. The number
4
of the RF switches is larger in comparison with other types of phase shifters. For example, a loaded line phase shifter can be implemented by only two RF switches.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide a phase shifter that can reduce the phase shift deviation and thereby enlarge the usable frequency range.
Another object of the present invention is to provide a phase shifter that can be implemented by a smaller number of RF switches.
In accordance with a first aspect of the present invention, there is provided a phase shifter for digitally shifting the phase of an RF (Radio Frequency) signal by changing a switched line which is connecting two main lines into another switched line. In the phase shifter, at least one of the switched lines is always connected to one of the main lines so as to operate as an open stub when the RF signal is not passed through the switched line.
In accordance with a second aspect of the present invention, in the first aspect, the phase shifter comprises a first main line, a second main line which is placed a predetermined distance apart from the first main line, a first switched line which is placed between the first main line and the second main line, a second switched line which is placed between the first main line and the second main line and which is always connected to the second main line, a first switch for controlling the connection/disconnection between the first main line and the first switched line, a second switch for controlling the connection/disconnection between the second main line and the first switched line, and a third switch for controlling the connection/disconnection between the first main line and the second switched line.
In accordance with a third aspect of the present invention, in the second aspect, the length of the first switched line is set to ¼ of the wavelength of the RF signal and the length of the second switched line is set to ½ of the wavelength and thereby a 90° phase shifter is implemented.
In accordance with a fourth aspect of the present invention, in the second aspect, the length of the first switched line is set to ½ of the wavelength of the RF signal and the length of the second switched line is set to the wavelength and thereby a 180° phase shifter is implemented.
In accordance with a fifth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by microstrip lines.
In accordance with a sixth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by slot lines.
In accordance with a seventh aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by co-planer lines.
In accordance with an eighth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by coaxial lines.
In accord
Chang Joseph
McGinn & Gibb PLLC
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