Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With waveguide or long line
Reexamination Certificate
2000-01-11
2003-02-11
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With waveguide or long line
C324S106000
Reexamination Certificate
active
06518743
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power detecting element for detecting the power of a wide-band RF signal and a power detecting device using the same and, more particularly, to a wide-band RF signal power detecting element which has an improved frequency characteristic and can be easily manufactured, and a power detecting device using the same.
BACKGROUND ART
As is well known, to detect the power of a RF signal over a wide band, it is possible to use a diode detecting system which detects a signal by using a diode and a thermocouple system which allows a resistor to absorb a signal and detects heat generated by the resistor by using a thermocouple.
The diode detecting system has the advantage that a response is obtained with almost no delay when an input signal is supplied to the diode.
This diode detecting system, however, has the problem that the detection accuracy is low because the system is readily influenced by the signal waveform and the signal level.
Additionally, the junction capacitance of the diode makes it difficult for the diode detecting system to detect the power of a RF signal of millimeter waves or more.
On the other hand, the thermocouple system cannot achieve such high-speed responses as in the diode detecting system, because heat is generated by supplying a signal to the resistor.
This thermocouple system, however, has the advantage that the system can accurately detect the power of a signal without being influenced by the signal waveform.
The present applicant has disclosed a power detector (element) and a power detecting device using this thermocouple system in International Publication No. WO88/03319 (Japanese Patent Application No. 62-506672).
As shown in
FIG. 20
, this power detector includes a first thermocouple
4
A and a second thermocouple
4
B formed on an insulating substrate
1
. The first thermocouple
4
A is formed by connecting a metal thin-film conductor
3
A to a silicon germanium mixed-crystal thin film
2
A. The second thermocouple
4
B is formed by connecting a metal thin-film conductor
3
B to a silicon germanium mixed-crystal thin film
2
B.
In this structure, the silicon germanium mixed-crystal thin film of the first thermocouple
4
A and the metal thin-film conductor
3
B of the second thermocouple
4
B are formed parallel to oppose each other.
End portions of the silicon germanium mixed-crystal thin film
2
A of the first thermocouple
4
A and the metal thin-film conductor
3
B of the second thermocouple
4
B are connected by a first electrode
5
.
A second electrode
6
is connected to the metal thin-film conductor
3
A of the first thermocouple
4
A.
A third electrode
7
is connected to the silicon germanium mixed-crystal thin film
2
B of the second thermocouple
4
B.
The electromotive forces of the first and second thermocouples
4
A and
4
B are added and output to between the second and third electrodes
6
and
7
.
Beam lead electrodes
8
,
9
, and
10
for decreasing the thermal resistance in a cold junction between the first and second thermocouples
4
A and
4
B are connected to the first, second, and third electrodes
5
,
6
, and
7
, respectively.
This power detector is mounted on a dielectric substrate
11
of a power detecting device shown in FIG.
21
.
This dielectric substrate
11
has a transmission line composed of a central conductor
12
having a predetermined width and external conductors
13
A and
13
B formed parallel with a predetermined spacing between them on the two sides of the central conductor
12
.
The beam lead electrode
8
of this power detector
14
constructed as shown in
FIG. 20
is connected to the central conductor
12
on the dielectric substrate
11
.
The beam lead electrode
9
of the power detector
14
is connected to ground (GND) which communicates with the external conductor
13
B on the dielectric substrate
11
.
The beam lead electrode
10
of the power detector
14
is connected to an output conductor
15
on the dielectric substrate
11
.
The central conductor
12
on the dielectric substrate
11
is connected to a connecting portion
17
via a coupling capacitor
16
.
The output conductor
15
on the dielectric substrate
11
is connected to ground (GND) which communicates with the external conductor
13
A via a bypass capacitor
18
.
A lead line
19
A for central conductor output is connected to the output conductor
15
.
A lead line
19
B for GND output is connected to the ground (GND) which communicates with the external conductor
13
B.
FIG. 22
shows an equivalent circuit of this power detecting device.
That is, a signal S to be measured input from the connecting portion
17
is supplied to the two thermocouples
4
A and
4
B via the coupling capacitor
16
, and these two thermocouples
4
A and
4
B generate heat.
The electromotive forces generated in the two thermocouples
4
A and
4
B by the heat generated by these two thermocouples
4
A and
4
B are added and output from the lead lines
19
A and
19
B.
In the power detecting device constructed as above, the upper-limit value of a band in which the sensitivity lowers by 1 dB extends to 32 GHz.
In addition to the above system (so-called direct heating type), a so-called indirect heating system is also proposed as the thermocouple system. In this indirect heating system, a resistor for converting a power signal to be measured into heat, i.e., an input resistor, and a thermocouple for detecting a temperature rise resulting from the heat generated by this resistor, are separated from each other.
This indirect heating type thermocouple has a longer response time than that of the direct heating type thermocouple. However, the number of thermocouples can be arbitrarily increased independently of the resistor, and a signal having magnitude directly proportional to the number of these thermocouples can be output.
Accordingly, this indirect heating type thermocouple has the advantage that high detectivity is obtained. Thermocouples having frequency characteristics of about 20-odd GHz have been realized.
In the power detector and the power detecting device using the direct heating type thermocouples described above, a signal is supplied to the thermocouples themselves to cause these thermocouples to output DC electromotive forces. Hence, the power of a DC signal cannot be detected. Also, since the capacitance of a capacitor formable on a substrate is limited, the power of a low-frequency signal cannot be accurately detected.
Additionally, in the power detector and the power detecting device using the direct heating type thermocouples described above, the two thermocouples split the load on an input signal, and impedance matching is difficult owing to the influence of the capacitor. Therefore, it is difficult to further extend the upper-limit detection frequency.
Furthermore, in the power detector and the power detecting device using the direct heating type thermocouples described above, a larger number of thermocouples must be provided in the power detecting element in order to detect micro watt power at high sensitivity.
Unfortunately, in the power detector and the power detecting device using the direct heating type thermocouples described above, if the number of thermocouples is increased, the number of necessary capacitors increases accordingly. This makes impedance matching more difficult. As a consequence, the frequency characteristic must be sacrificed.
Especially in recent years, RF communication apparatuses using millimeter waves and microwaves are extensively developed.
To measure these communication apparatuses, it is increasingly demanded to accurately detect the power of signals with higher frequencies. However, the conventional power detecting elements and power detecting devices described above cannot satisfactorily meet this demand.
Also, in the power detector and the power detecting device using the direct heating type thermocouples described above, electronic materials forming the input resistor and the thermocouple are different. This complicates the manufacturing method. Additionally, no knowl
Anritsu Corporation
Karlsen Ernest
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