Wave transmission lines and networks – Resonators
Reexamination Certificate
2001-03-06
2003-12-09
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Resonators
C333S134000, C333S204000
Reexamination Certificate
active
06661315
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resonator having an electrode formed on a dielectric substrate, a filter, an oscillator, a duplexer, and a communication apparatus employing these devices.
2. Description of the Related Art
Resonators formed using a dielectric substrate and designed to exhibit resonance in the frequency band of microwaves or millimeter waves include a resonator realized with a slot line.
In a conventional slot-line resonator, one resonator is realized with a straight half-wave slot line. Such a resonator realized with a slot line is structured to have an electrode continuously formed around a slot line, and can therefore confine electromagnetic energy in the slot line with high efficiency. When the resonator is included as a module in a high-frequency circuit, it hardly interferes with any other circuit. This is advantageous.
FIG.
18
A and
FIG. 18B
show an example of a half-wave slot-line resonator having both ends thereof short-circuited. In
FIG. 18A
, an electrode
2
having a slot
3
bored as part thereof is formed on the upper side of a dielectric substrate
1
.
FIG. 18B
shows the distribution of the electromagnetic field on the slot-line resonator. In
FIG. 18B
, solid lines denote the electric field and dashed lines denote the magnetic field.
The efficiency of the resonator realized with a slot line in confining the electromagnetic field depends on the width of the slot. In other words, the larger the width of the slot
3
(slot line), the wider the spread of the electromagnetic field in the slot-line resonator.
The foregoing phenomenon will be interpreted below from a physical viewpoint.
For example, the electric field distribution in a slotted section is as shown in FIG.
19
A. When the electric field distribution is expressed as an equivalent circuit, the equivalent circuit is like that shown in
FIG. 19B
or FIG.
19
C.
FIG. 19B
shows an equivalent circuit for a large-width slot, while
FIG. 19C
shows an equivalent circuit for a small-width slot. In the equivalent circuit, if the ratio of an electrostatic capacitance C
2
(C
2
′) or C
3
(C
3
′) to the total electrostatic capacitance is large, or in other words, if the electrostatic capacitance C
2
(C
2
′) or C
3
(C
3
′) contributes greatly to the total electrostatic capacitance, the spread of the electromagnetic field is thought to be wide. In contrast, if the ratio is small or if the electrostatic capacitance C
2
(C
2
′) or C
3
(C
3
′) contributes little, the degree of concentration of the electromagnetic field in the slot is thought to be high.
Assuming that the lengths of electric lines of force drawn to pass through points at which the electrostatic capacitances C
1
(C
1
′), C
2
(C
2
′), and C
3
(C
3
′) are detected are w
1
(w
1
′), w
2
(w
2
′), and w
3
(w
3
′), respectively, the electrostatic capacitances are inversely proportional to the lengths of the electric lines of force.
The lengths of the electric lines of force drawn to pass through the points at which the electrostatic capacitances are detected are assumed to change from those shown in
FIG. 19B
to those shown in FIG.
19
C. This signifies that the width of the slot is decreased by a length &Dgr;w. In this case, the following relationships are obtained:
w
1
′=
w
1
−&Dgr;
w
w
2
′=
w
2
−&Dgr;
w
w
3
′=
w
3
−&Dgr;
w
In addition, a relationship of w
1
<w
2
<w
3
holds. Among the changes from the capacitances C
1
, C
2
, and C
3
to the capacitances C
1
′, C
2
′, and C
3
′, the change from C
1
to C
1
′ is the largest. Namely, when the width of the slot is small, the electrostatic capacitance C
1
(C
1
′) contributes most greatly to the total electrostatic capacitance. This means that a smaller width of a slot or a slot line leads to a higher degree of concentration of the electromagnetic field.
Therefore, for improving the efficiency of a slot-line resonator in confining the electromagnetic field, the width of a slot or a slot line should be decreased. A high-frequency circuit module is assumed to be composed of a slot-line resonator and another conductive line which are formed using a dielectric substrate. In this case, once the efficiency of the slot-line resonator in confining the electromagnetic field is improved, even if the distance from the slot-line resonator to the conductive line is decreased, undesirable coupling will hardly occur. The high-frequency circuit module can therefore be designed compactly.
When the width of a slot line in a slot-line resonator is decreased, the degree of current concentration at the edges of an electrode increases. Consequently, the edge effect becomes significant and conductor loss increases. The unloaded Q-factor (Qo) exhibited by the resonator decreases. Therefore, if the resonator is employed in a filter or the like, a new problem such as increased insertion loss will occur.
SUMMARY OF THE INVENTION
Addressing these problems, the present invention provides a resonator, a filter, an oscillator, a duplexer, and a communication apparatus employing these devices which exhibit improved efficiency in confining an electromagnetic field in an opening of an electrode, suppressed concentration of currents, and minimized conductor loss.
According to an aspect of the present invention, a resonator has a slot-like opening formed in a dielectric substrate. Electrode patterns are formed in the slot-like opening so that the slot-like opening will be divided into smaller-width slot lines. The electrode patterns by which the slot-like opening is divided into the smaller-width slot lines have a width permitting suppression of an edge effect occurring in the electrode patterns.
Owing to the above structure, since the slot lines into which the slot-like opening is divided by the electrode patterns have a small width, the efficiency in confining the electromagnetic field improves. Moreover, the resonator is structured to have a plurality of slot lines, which serve as resonators, juxtaposed and separated by the electrode patterns. The direction of a current flowing along one edge of each of the electrode patterns by which the slot-like opening is divided into the smaller-width slot lines is opposite to the direction of a current flowing along the other parallel edge thereof. The currents flow close to each other in mutually opposite directions. Therefore, loss hardly occurs in each electrode pattern. However, conductor loss occurs at both the edges of each electrode pattern. Assuming that resistors Ra and Rb cause the conductor loss at the edges of each electrode pattern, an unloaded Q-factor Qo exhibited by each slot line is expressed as Qo=&ohgr;L/(Ra+Rb). Since the plurality of slot lines is juxtaposed, &ohgr;L gets larger in proportion to the number of juxtaposed slot lines. This results in an improved unloaded Q-factor Qo.
Moreover, according to an aspect of the present invention, the electrode patterns are preferably formed only in short-circuited or equivalently short-circuited portions of the slot-like opening so that adjoining slot lines will communicate with a portion of the slot-like opening. Owing to this structure, conduction loss occurring in part of each electrode pattern which exhibits a high current density is minimized effectively. Moreover, the adjoining slot lines into which the slot-like opening is divided communicate with the portion of the slot-like opening devoid of the electrode patterns. Consequently, occurrence of a spurious pulse mode in each of the slot lines into which the slot-like opening is divided by the electrode patterns can be suppressed. Moreover, a portion of the slot-like opening in which the electrode patterns, by which the slot-like opening is divided into the smaller-width slot lines, are formed is so limited that the electrode patterns can be formed easily.
Moreover, according to an aspect of the present invention, t
Ham Seungsook
Murata Manufactuing Co. Ltd
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