Wave transmission lines and networks – Coupling networks – Delay lines including long line elements
Reexamination Certificate
1999-11-19
2002-06-04
Pascal, Robert J. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Delay lines including long line elements
C333S139000
Reexamination Certificate
active
06400237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase compensation circuit which is incorporated into a radar system or a communication system in a microwave band to compensate change in phase due to the temperature of these devices, and a frequency converter device using the phase compensation circuit, and an active phased array antenna using the phase compensation circuit or the frequency converter device.
2. Description of the Related Art
In the radar system, the communication system, etc., the active phased array antenna consisting of a plurality of element antennas is employed as the antenna used therein from viewpoints such as reliability and a high speed operation, and also a transmitting module or a receiving module for amplifying or controlling the signal is employed in each element antenna.
Since the modules each has uniform phase including a temperature characteristic are requested particularly as these modules, normally the phase shifter for compensating variation in phase is incorporated in each module.
FIG. 15
is a view showing the phase shifter in the prior art, which is disclosed in the MICROWAVE JOURNAL, 1989, STATE OF ART REFERENCE, pp. 109, for example. In
FIG. 15
,
1
is a coupler;
2
, an input terminal;
3
, an output terminal;
4
, a coupling terminal;
5
, a passing terminal;
6
, a capacitor;
7
, a variable capacity element;
8
, a choke circuit; and
9
, a direct current power supply.
In this phase shifter, a series circuit of the capacitor
6
and the variable capacity element
7
is provided between the coupling terminal
4
of a coupler
1
having four terminals and ground and the passing terminal of the coupler
1
and ground respectively. Then, in order to apply a desired bias from the direct current power supply
9
to each variable capacity element
7
, the choke circuit
8
is connected to the variable capacity element
7
.
Also, a coupler such as a branch line coupler, an interdigital coupler, or the like, which can distribute the microwave signal to the coupling terminal
4
and the passing terminal
5
at the same amplitude to have phase difference of 90 degree between both terminals, is employed as the coupler
1
. Also, a varactor diode, an FET (Field Effect Transistor), or the like, whose capacitance is changed depending on its applied voltage, is employed as the variable capacity element
7
. Further, in order not to affect the microwave characteristic of the phase shifter as much as possible, the choke circuit
8
is designed to have a high impedance in a desired frequency band. Moreover, the capacitor
6
for preventing the direct current is selected to have a value which can yield as low impedance as possible in the microwave band.
Next, an operation of the phase shifter will be explained hereunder. The microwave signal which is input from the input terminal
2
is distributed to the coupling terminal
4
and the passing terminal
5
to have the same amplitude and the phase difference of 90 degree between both terminals respectively. The distributed microwave signal is supplied to the variable capacity element
7
via the capacitor
6
. Normally the impedance of the variable capacity element
7
substantially consists of a reactance component only since its resistance component is small, and therefore the microwave signal supplied to the variable capacity element
7
is totally reflected there toward the coupler
1
side. In addition, the reflected microwave signals are synthesized oppositely in phase at the input terminal
2
and also synthesized commonly in phase at the output terminal
3
, and as a result such microwave signal fully appears on the output terminal
3
.
In this case, the phase of the microwave signal being reflected by the variable capacity element
7
largely depends upon a capacitance of the variable capacity element
7
. Thus, the larger a degree of change in the capacitance is increased, the larger a degree of change in the phase is increased.
FIGS. 16A
to
16
C show an example of the microwave characteristic of the phase shifter shown in FIG.
15
. In general, the capacitance of the variable capacity element
7
is decreased smaller as the voltage VR of the direct current power supply
9
applied to the variable capacity element
7
is increased higher, so that the phase of the reflected microwave signal leads.
Therefore, as shown in
FIG. 16A
, the phase shifter shows the right-upward inclined phase characteristic if an angular frequency &ohgr; is kept constant. Also, as shown in
FIG. 16B
, VSWR at the input terminal
2
does not depend on the voltage VR and thus shows the good value since the reflected microwave signals are always synthesized oppositely in phase at the input terminal
2
. Further, as shown in
FIG. 16C
, the frequency characteristic of VSWR always shows the good value if the voltage VR is kept constant.
The phase of the microwave signal from the input terminal
2
to the output terminal
3
can be changed by varying the voltage VR of the direct current power supply
9
in this manner. For this reason, even though the phase characteristics of the amplifier, the mixer, etc. employed in the individual transmitting module or receiving module relative to the temperature are different, the phase compensation can be achieved by using this phase shifter. As a result, the transmitting modules or the receiving modules which can suppress the change in phase relative to the temperature and have the uniform phase characteristic can be implemented.
FIG. 17
is a block diagram showing one constituent element of an active phased array antenna to which the transmitting module having the phase shifter in the prior art shown in
FIG. 15
is applied. In
FIG. 17
, a reference
10
denotes a gain compensation circuit using a variable attenuator;
11
, a phase shifter in the prior art;
12
, a high-frequency amplifier using semiconductor;
13
, a transmitting module which consists of the gain compensation circuit
10
, the phase shifter
11
, and the high-frequency amplifier
12
; and
14
, an element antenna.
Therefore, the signal input from the input terminal
2
is passed through the gain compensation circuit
10
and the phase shifter
11
, then amplified by the high-frequency amplifier
12
, and then irradiated into a space from the element antenna
14
.
A large number of constituent elements, each consists of such transmitting module
13
and the element antenna
14
, are employed in the active phased array antenna. Thus, a very high output can be obtained by spatially synthesizing the signal which is transmitted from the element antenna
14
.
In this case, the active phased array antenna for transmission is disclosed herein. A large number of receiving modules and the element antennas
14
are also employed in the active phased array antenna for reception.
According to the phase shifter in the prior art shown in
FIG. 15
, since the interdigital coupler is normally employed as the coupler
1
, the wideband characteristic of about 1 octave can be derived.
However, such wideband is not necessary for the transmitting modules
13
or the receiving modules which are employed in the active phased array antenna. In many cases, the lower cost and the reduction in size of the module are requested rather than the wider bandwidth. In the phase shifter
11
in the prior art, there has been such a problem that, since two expensive variable capacity elements
7
are needed and also the coupler
1
having a length of ¼&lgr; in the predetermined frequency band is employed, the cost and the size of the transmitting modules
13
or the receiving modules are increased.
Further, there has been another problem that the cost and the weight of the active phased array antenna, to which the transmitting modules
13
or the receiving modules are applied, are increased.
SUMMARY OF THE INVENTION
The present invention has been made to overcome above subjects and it is an object of the present invention to provide a phase compensation circuit which is capable of compensating the pha
Burns Doane , Swecker, Mathis LLP
Glenn Kimberly E
Mitsubishi Denki & Kabushiki Kaisha
Pascal Robert J.
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