Metal fusion bonding – Process – Applying or distributing fused filler
Reexamination Certificate
2001-11-15
2003-07-15
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process
Applying or distributing fused filler
C228S123100, C228S124100, C228S040000, C156S321000
Reexamination Certificate
active
06592021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high frequency (HF) circuit in a communication device and more specifically to a technique for bonding a circuit board to a metal chassis or case, a waveguide-microstrip line transition, a branch circuit, and a high frequency circuit incorporating these elements.
2. Description of the Prior Art
Recently, as frequency resources in communications technology are running dry, frequency bands available for building a new communications system have been and are shifting to higher bands. In this situation, the government and the people are jointly promoting a development to milliwave and microwave communication systems domestically and internationally. For example, it has been decided that extremely high frequency bands ranging from some GHz to hundreds GHz are assigned as available frequency bands to various communication systems under development for wireless LAN (local area network) and ITS (Intelligent Transport System).
Since available frequencies are rising as described above, antennas and HF (high frequency) circuits are desired which satisfactorily work in milliwave and microwave bands. However, design and manufacturing techniques that have been believed to be available may not work satisfactorily with an increase in frequency. For this reason, there is a need for novel design and manufacturing techniques.
FIG. 1
is a diagram showing an arrangement of a prior art array antenna assembly
1
. In
FIG. 1
, the antenna assembly
1
comprises an dielectric substrate
10
, a circuit pattern
20
, a chassis
30
that holds the dielectric substrate
10
and serves as the ground, and a waveguide-microstrip line transition
40
. The circuit pattern
20
, which constitutes an array antenna, includes a T branch circuit
50
. A signal transmitted through a waveguide (not shown) is passed by the transition
40
to a microstrip line of the circuit pattern
20
, and further passed by the T branch circuit
50
to the right and the left portions of the array antenna.
FIG. 2
is a schematic diagram showing an arrangement of the transition
40
of FIG.
1
. In
FIG. 2
, the transition
40
comprises a ridge waveguide
42
, a ridge
41
formed inside the ridge waveguide
42
, and a microstrip line
21
which is formed on the dielectric substrate
10
and which is extending to (or a part of) the circuit pattern
20
. As described above, the signal transmitted through the not-shown waveguide is converted into a transmission mode of the microstrip line
21
by the ridge
41
provided inside the waveguide
42
and transmitted to the array antenna
20
.
Problems exist in conjunction with working if an antenna with the just-described arrangements are to be implemented for milliwave or microwave. With an increase in frequency, dielectric materials available for the dielectric layer
10
is limited to substances lack of a mechanical strength, e.g., ceramics, quartz, silicon, etc. Further, if an antenna that radiates a beam of two degrees in mesial width in a 76 GHz band is to be fabricated, the dielectric substrate
10
for the antenna will be approximately 100 to 300 &mgr;m thick and 15 cm long in one side. Bonding such a thin and wide substrate
10
to the chassis
30
often results in a breakage of the dielectric substrate
10
. Also, as the frequency increases, the characteristics of the antenna
20
depends strongly on the grounding state of the dielectric substrate
10
. For this reason, a sufficient electrical contact is indispensable for the junction of the dielectric substrate
10
and the circuit pattern
20
. However, this is hard to be achieved by conventional techniques.
Since the degree of freedom is very low in designing a waveguide-microstrip line transition, i.e., the design parameters are limited only to the width, the length and the height of the ridge
41
, this sometimes causes the width of ridge for a milliwave band to be extremely narrow. Accordingly, the height of the ridge
41
of the transition
40
, which is manufactured through machining of a brass material, becomes higher as compared with the ridge
41
width, making the work difficult. The lack of freedom in the design makes transition with a microstrip line having a lower characteristic impedance difficult and cause the problem that too large a difference between the widths of the designed ridge
41
and the microstrip line
21
leads to an unexpected deterioration in the impedance matching characteristics.
As is not limited to a high frequency (HF) antenna, an array antenna
20
as a whole generally exhibits a narrower frequency band characteristic with an increase in the number of array elements. Taking for example an antenna used in a front monitoring radar being put to practical use in 60 GHz, the antenna needs a beam width of about 2 degrees and accordingly a very large size. If a structure incorporating a conventional branch circuit were used as it is for such antenna, the resultant antenna would exhibit a very narrow frequency band characteristic, causing the band width of the antenna to be narrower than that of the radar. This is because conventional branch circuits mainly use stubs for impedance matching.
FIG. 3
is a diagram showing an exemplary pattern of a conventional T branch circuit comprising a matching circuit that uses stubs
51
(the T branch circuit is shown as a dark area). Using stubs for impedance matching generally tends to narrow the frequency characteristics of the circuit. Specifically, the larger the distances (D
1
and D
2
) between the matching circuit and circuits (
22
) that need matching, the narrower the frequency band of the whole circuit. However, if stubs are to close to the antenna (or the circuits that need matching) so as to broaden the frequency band of the antenna, the antenna will fail to provide the desired characteristic. Thus, matching by stubs while providing a desired characteristic to the antenna or the circuits having their impedance matched inevitably narrows the frequency band of the resultant circuit such as an antenna.
SUMMARY OF THE INVENTION
The invention is directed to solving these and other problems and disadvantages of the prior art.
It is an object of the invention to provide a technique of bonding a thin and large-area circuit substrate to a metal layer with a sure and uniform contact but no fear of substrate breakage; a waveguide-microstrip transition that has a high degree of freedom in design and easy to work; and a branch circuit that permits the frequency band of circuit to be wide.
It is another object of the invention to provide a high frequency circuit and an antenna that incorporate an circuit substrate implemented by such a bonding technique, such a waveguide-microstrip transition and such a branch circuit, and to provide a communication system using such a high frequency circuit and such an antenna.
According to an aspect of the invention, a method of bonding a circuit board with a metal plate is provided. The method includes the steps of working the metal plate so as to have a shape that permits a fluid to form a bath in an area including a part where the circuit board is to be bonded; heating the worked metal plate to such a temperature as melt a conductive bonding material; forming a bath of the conductive bonding material in the area of the metal plate; floating the circuit board on the bath; and absorbing excessive portion of the conductive material without applying a force to the dielectric substrate.
A circuit assembly according to just-described aspect of the invention is provided with a thin and large-area dielectric substrate with an improved grounding condition. A bonding agent with a low melting point, a low melting point solder, etc. may be used as conductive material.
According to another aspect of the invention, a branch circuit for branching a first path into at least two second paths in a high frequency circuit is provided. The impedance matching between the first path and each of the branch paths is achieved by mainly using impedance transforme
Fujita Suguru
Sangawa Ushio
Connolly Bove & Lodge & Hutz LLP
Elve M. Alexandra
Matsushita Electric Industrial Co. Ltd
McHenry Kevin
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