Modulator and oscillator for microwave and milliwave use

Details Modulator and oscillator for microwave and milliwave use Modulator and oscillator for microwave and milliwave use

2001-12-18

2004-04-13

Mis, David C. (Department: 2817)

Oscillators

With distributed parameter resonator

C331S1170FE, C331S1070DP, C331S17700V, C333S219100, C333S235000

Reexamination Certificate

active

06720833

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-speed modulator and oscillator for microwave and milliwave use, and more particularly to a modulator which is superior in terms of high-frequency stability and which has a high degree of modulation.
2. Description of Related Art
Conventional modulators for microwave and milliwave use have been described in the literature (H. Mitsumoto, et al. “GaAs FET Direct Frequency-Modulators for 42-GHz-Band HDTV Radio Cameras and 7-GHz-Band Field Pick-up Transmitters”, IEEE MALE TYPE TERMINAL-S Digest, pp. 663-666, 1993).
The structure of the modulators disclosed in the above literature is shown in FIG.
5
. The modulator
100
comprises an oscillating circuit
102
and a resonator portion
104
. The resonator portion
104
comprises a reflective circuit board
106
, a coupling line
108
which is formed on the surface of this board
106
, a coupled load
110
which is coupled to one end
108
a
of the coupling line
108
, a dielectric resonator
112
which is disposed on the surface of the board
106
so that said resonator is magnetically coupled with the coupling line
108
, a &lgr;/2 line (&lgr; is the wavelength)
114
which is magnetically coupled with the dielectric resonator
112
, and two varactor diodes
116
and
118
which are respectively connected to both ends
114
a
and
114
b
of the &lgr;/2 line
114
. The &lgr;/2 line
114
is disposed in a position which is located on the surface of the board
106
, and which is located on the opposite side of the dielectric resonator
112
from the abovementioned coupling line
108
.
The oscillating circuit
102
supplies a negative resistance to the output port of the resonator portion
104
constituting the other end
108
b
of the coupling line
108
in the desired oscillation frequency band. As a result, the dielectric resonator
112
resonates, so that a high-reflection signal wave appears at the output port
108
b
from the coupling line
108
. On the other hand, in frequency bands other than the desired oscillation frequency band, the dielectric resonator
112
does not resonate. Accordingly, a low-reflection signal wave appears at the output port
108
b
as a result of the action of the coupled load
110
.
Furthermore, in this modulator
100
, the dielectric resonator
112
is disposed on the upper surface of the board
106
between the coupling line
108
and the &lgr;/2 line
114
. This dielectric resonator
112
is magnetic coupled with both the coupling line
108
and the &lgr;/2 line
114
. Accordingly, the resonance frequency of the dielectric resonator
112
is affected by the &lgr;/2 line
114
. Furthermore, varactor diodes
116
and
118
are coupled to both ends
114
a
and
114
b
of the &lgr;/2 line
114
. Accordingly, the capacitances of the varactor diodes
116
and
118
vary according to the magnitude of the modulating wave that is input into the &lgr;/2 line
114
, and as a result, the resonance frequency of the dielectric resonator
112
varies. Accordingly, the frequency and phase of the peak of the reflected wave that appears at the output port
108
b
vary according to the modulating signal. The oscillation frequency that is output from the oscillating circuit
102
can be modulated by this variation.
In this modulator
100
described in the literature, the frequency width of the oscillation frequency that is modulated is broadened as a result of the provision of two varactor diodes
116
and
118
. Specifically, this modulator is advantageous in that a high degree of modulation can be obtained.
However, the following problems occur in the abovementioned modulator
100
:
The dielectric resonator
112
is magnetically coupled with the coupling line
108
and &lgr;/2 line
114
. Since the &lgr;/2 line
114
is formed by a strip line with a low resonance Q value, the Q value of the dielectric resonator
112
is affected by the Q value of the &lgr;/2 line
114
so that the Q value of the dielectric resonator
112
is lowered. As a result, the stability of the peak frequency of the reflected wave that appears at the output port
108
b
of the resonator portion
104
is lost. Accordingly, the stability of the oscillation frequency is also lost. This means that the modulation sensitivity drops.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a modulator which has a high degree of modulation and a good modulation sensitivity.
Furthermore, a further object of the present invention is to provide a modulator which is capable of modulation at a stable oscillation frequency.
In order to achieve these objects, the modulator of the present invention comprises a resonator portion and an oscillating circuit which have the constructions described below. Furthermore, the resonator portion comprises a reflective circuit board, a coupling line which is disposed on a reflective circuit board, a coupled load which is coupled to one end of the coupling line, a dielectric resonator which is disposed on the reflective circuit board and which is magnetically coupled with the coupling line, a window portion which is formed in the undersurface of the reflective circuit board directly beneath the coupling line, a waveguide resonator which is disposed on the undersurface of the reflective circuit board in the area that includes the window portion, and which is magnetically coupled with the coupling line, and a varactor diode which is inserted between the opposite signal conductor surfaces of the waveguide resonator, and to which the input signal terminal is connected. Furthermore, the other end of the coupling line constitutes the output port of the resonator portion, and this output port is connected to the input port of the oscillating circuit. Moreover, the side of the coupled load that is not coupled to the coupling line is grounded.
The operating principle of the modulator constructed as described above is similar to that of a conventional modulator. In the desired oscillation frequency band, a negative resistance is supplied to the output port of the reflective circuit board from the oscillating circuit. As a result, so that a high-reflection wave appears at the output port from the coupling line. This magnitude and phase of this reflected wave are determined by the dielectric resonator, which has a high Q value. Furthermore, this reflected wave is also affected by the waveguide resonator that is magnetically coupled with the coupling line.
Specifically, both the dielectric resonator and the waveguide resonator are magnetically coupled with the coupling line. As a result, the resonance frequency of the dielectric resonator and the resonance frequency of the waveguide resonator coincide with the desired frequency. Accordingly, the impedance of the resonator portion with respect to the desired frequency (nearby frequencies) is increased. Consequently, the reflection to the coupling line is increased.
On the other hand, the magnetic coupling of the waveguide resonator and dielectric resonator to the coupling line is decreased with respect to frequencies that are not the desired frequency. As a result, the impedance of the resonator portion is also decreased, so that the coupling line shows impedance matching with the coupled load. Consequently, the reflection at the output port of the reflective circuit board is reduced, so that the oscillating circuit does not oscillate.
Thus, by making the resonator that causes coupled modulation with the dielectric resonator a waveguide resonator which has a Q value that is higher than that of the &lgr;/2 line, it is possible to maintain the Q value of the resonator portion in a high state. Accordingly, the oscillation frequency can be stabilized. Furthermore, the capacitance of the varactor diode of the waveguide resonator varies according to the modulating signal. Modulation is accomplished by means of this variation in capacitance. Accordingly, modulation at a stable oscillation frequency can be realized.


REFERENCES:
patent: 4488124 (1984-12-01), Yoshimura
H. M

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