Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
2002-02-08
2004-09-21
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Long line elements and components
Strip type
C333S02400C
Reexamination Certificate
active
06794961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high frequency circuit module and, more specifically, to a high frequency circuit module in which a high frequency circuit part such as a monolithic microwave integrated circuit (hereinbelow, called an MMIC) and an antenna are provided on the surface and the rear face, respectively, of a multilayer dielectric substrate. More particularly, the invention relates to a high frequency circuit module suitable for an automotive radar module using millimeter waves.
2. Description of the Related Arts
As the most effective system of an intelligent transport system (ITS) solving a traffic accident, traffic jam, environmental problems of exhaust gas, noise, and so one, resource problems due to large consumption of oil energy, and the like caused by “vehicles”, a millimeter wave radar has been developed. In order to equip vehicles as many as possible with millimeter wave radars, realization of an automotive radar module having improved flexibility of a vehicle mounting layout by reducing the size and thickness of the millimeter wave radar, reliability, and low cost is demanded.
As a high frequency circuit module adapted to the automotive radar, a high frequency circuit module in which an antenna and an MMIC are provided on the surface and rear face, respectively, of a multilayer dielectric substrate having therein metallic layers is known
For example, as shown in
FIG. 10
(conventional technique
1
), on the surface and rear face of a ceramic multilayer substrate
38
in which a plurality of metallic layers
30
to
33
are provided, an antenna
28
and an MMIC
29
are provided, respectively. As high frequency transmission lines between the antenna
28
and the MMIC
29
, microstrip lines
34
and
35
and electro-magnetic coupling slots
36
and
37
are used. Techniques using electro-magnetic coupling slots of this kind are disclosed in Japanese Unexamined Patent Application Nos. 9-237867 and 8-250913. In this example of mounting, when a slot having the same structure is formed over a slot to make the transmission line length shortest, a microstrip line having a length of around &lgr;/2 remains between the slots and works as a resonator. However, when electro-magnetic coupling slots are provided above and below the microstrip line, a potential difference occurs between the upper and lower slot metallic layers. Consequently, an electromagnetic wave which propagates in parallel between the slot metallic layers is generated. An amount corresponding to the energy of the electromagnetic wave becomes a loss, so that it difficult to realize the transmission line of a low loss. Therefore, by setting the distance between the electro-magnetic coupling slots to &lgr;/2 or longer, interference between the slots is prevented and a loss in the transfer line is minimized. Due to such a structure, the mounting method using the electro-magnetic coupling slots needs a mounting area having the distance of 2 &lgr; or longer between the slots, and layout of the upper and lower electronic parts has to be considered so as not to cause interference with the transfer mode of the slot coupling part.
As shown in
FIG. 11A
(conventional technique
2
), there is a known technique in which connection between a plurality of conductive layers
31
and
33
in the multilayer dielectric substrate
38
having the plurality of conductive layers
30
to
33
and
39
is realized by a via satisfying the condition of (R·r)/(2·h)≦L≦(5·R·r)/h (where R, r, and L denote sizes shown in
FIG. 11C and h
denotes the distance between the conductive layers). When a signal to be transmitted is in a millimeter wave band, the connection between conductive layers in the multilayer substrate formed by the via satisfying the condition can be made by a connecting method of a low loss only in the case where there is one grounding layer connected to the via. However, occurrence of an electromagnetic wave propagating between a plurality of grounding layers cannot be suppressed. Consequently, the method cannot be used to connect the conductors to realize a low loss in the millimeter wave band.
Further, as a technique which does not use a dielectric multilayer substrate, as shown in
FIG. 12
(conventional technique
3
), there is a technique in which an MMIC
43
and an antenna
44
are provided on the surface and rear face, respectively, of a metal base plate
42
, and a coaxial structure
45
formed in the base plate
42
is used to connection the MMIC
43
and antenna
44
. In the structure, the RF circuit substrate including the MMIC
43
and the antenna are connected to each other via the coaxial structure, so that a thin, small millimeter wave radar can be relatively easily produced. In the diagram, reference numerals
46
,
47
,
48
,
49
,
50
and
51
denote a circuit substrate, an insulating material, an outer terminal, an insulating material, a bonding wire, and a transmission/reception circuit cover, respectively.
As described above, the conventional techniques have problems with respect to easiness in manufacture, manufacturing cost, and circuit characteristics. Particularly, to use the modules for an automotive millimeter wave radar, since the millimeter wave radar is a device mounted outside of a vehicle and use environments of temperature, moisture, vibration, and the like are hostile, generally, an RF circuit has a hermetic structure of interrupting the outside air. Since the transmission loss in the millimeter wave band is much larger as compared with that in a microwave band, the transmission line has to be designed to be as short as possible. Although the line length can be shortened by mounting the RF circuit part on the same face of the substrate as the antenna, it is difficult to mount the RF circuit part and the antenna on the same face due to the limited size of the RF circuit part and the hermetic structure.
In order to mount the RF circuit part and the antenna of the millimeter wave radar as close as possible, the RF circuit part and the antenna are mounted on both sides of the mounting substrate so as to be overlapped, and an oscillator and an amplifier of the RF circuit parts have to be disposed so that the transmission line length becomes the shortest. However, as the mounting substrate of the millimeter wave band, a thin substrate having a dielectric thickness of 0.2 mm or less is used to suppress a transmission line radiation loss. Therefore, the base plate
42
for assuring the mechanical strength is needed as shown in
FIG. 12
for the millimeter wave radar. Consequently, the structure whose assembling and processing cost is high has to be employed.
A both-sided two-layer substrate is generally used to assure the characteristics of the millimeter wave transmission line for an RF circuit. A transmission line for a millimeter signal, a power providing line, and a transmission line for a low frequency signal are formed on the same face. Since the high/low frequency signal transmission lines and the power providing line cannot cross each other, aerial wiring such as a bonding wire is required. The higher the frequency of a signal is, the more the signal easily radiates, and it causes a crosstalk in another line. It makes the millimeter waver radar unstable. In addition, since the flexibility of designing of layout of the RF circuit is regulated in the two-layer substrate, reduction in cost by reducing the substrate area of the expensive RF circuit part is limited.
SUMMARY OF THE INVENTION
An object of the invention is therefore to realize a high frequency circuit module in which high frequency circuit parts such as MMICs for millimeter waves and microwave and a plane antenna are mounted on a multilayer dielectric substrate and a loss of energy of electromagnetic waves is reduced, and which can be realized at low cost and, further, to provide a small, thin, and light automotive radar module with high design flexibility.
To achieve the object, there is provided a high frequency circuit (hereinbelow, called an RF circuit
Kondoh Hiroshi
Nagaishi Hideyuki
A. Marquez, Esq. Juan Carlos
Fisher Esq. Stanley P.
Glenn Kimberly
Hitachi , Ltd.
Pascal Robert
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