Microwave detector

A microwave detector includes a horn antenna and cavity formed by covering a metallic film of a printed substrate with an opened bottom microwave circuit component, and further includes a mixer diode which is positioned at the feeding point of the horn antenna and sandwiched between the microwave circuit component and the printed substrate, the mixer diode including a mixer diode substrate having a first protruding portion at a first end of the mixer diode substrate and a second protruding portion at a second end of the mixer diode substrate, separate anode and cathode electrode patterns formed on a surface of the substrate which includes the protruding portions, and a beam-lead-type or flip-chip-type diode which is mounted to a surface of the mixer diode substrate near the center thereof, the beam-lead-type or flip-chip-type diode having an anode and a cathode which are surface mounted to the anode and cathode electrode patterns to form electrically conducting pathways therewith, wherein the first and second protruding portions are directly or indirectly connected respectively to the microwave circuit component and the printed substrate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a microwave detector for detecting 
microwaves emitted from measuring devices and the like, and in particular 
relates to an improvement in the structure of the reception frequency 
conversion portion which carries out frequency mixing of the wave received 
by a horn antenna and the output of a local oscillator. 
2. Description of the Prior Art 
Microwave detectors which generate an alarm upon detecting microwaves 
having the specific microwave frequencies emitted by radar-type speed 
measurement devices are known in the prior art. In this connection, 
typical traffic monitoring radar-type speed measurement devices employ a 
plurality of microwave frequency bands, including the 10 GHz band (X 
band), 24 GHz band (K band) and 35 GHz band (Ka band). These kinds of 
speed measuring microwave detectors receive prescribed microwave bands 
with a super-heterodyne type circuit having a structure described below. 
In general, a horn antenna is used for the reception antenna. Arranged at 
the feeding point of the slot portion of such antenna is a mixer diode. 
Further, a microwave circuit composed of a local oscillator is provided in 
the interior of the slot portion of the horn antenna. In such arrangement, 
the signals received by the horn antenna and the output of the local 
oscillator undergo frequency mixing in the mixer diode. Further, a 
suitable filter is provided between the mixing step and the local 
oscillator to prevent the reception input by the horn antenna from having 
an adverse effect on the operation of the local oscillator. In this 
regard, two general types of microwave detectors are known: a first type 
constructed from a local oscillator and a mixer, in which a microwave 
circuit uses a waveguide; and a second type constructed from a local 
oscillator and a mixing portion, in which a microwave integrated circuit 
uses a microstrip line. 
In this connection, the present invention is directed toward the first type 
constructed from a microwave circuit which uses a waveguide, and an 
example of this type is disclosed in Japanese Laid-Open Patent Application 
No. HEI 5-308219. The invention disclosed in this publication is similar 
to that shown in FIG. 1. Namely, as shown in this drawing, a wide-area 
metallic film (e.g., copper foil) 11 having a prescribed pattern is formed 
on top of a printed substrate 10. Further, a microwave circuit component 
12 made of die-cast aluminum is secured to the printed substrate 10 by 
screws so as to cover the metallic film 11 portion of the printed 
substrate 10. The microwave circuit component 12 includes a horn antenna 
portion 12a and a cavity portion 12b which together form an open space in 
the entire underside surface of the microwave circuit component 12, and 
this open space in the underside of the microwave circuit component 12 is 
filled by the metallic film 11 when the microwave circuit component 12 is 
secured to the top of the printed substrate 10. In this way, a horn 
antenna and a cavity which communicates with the back of a slot portion of 
the horn antenna are constructed by securing the microwave circuit 
component 12 to the top of the printed substrate 10. Further, screw-type 
adjustment pins 20a, 20b are provided near the horn antenna slot portion 
of the microwave circuit component 12. 
A boss portion 12c is integrally formed in the slot portion of the horn 
antenna portion 12a of the microwave circuit component 12, and a through 
hole 13 which faces the boss portion 12c is formed in the printed 
substrate 10. Further, a pin-shaped leg 15a of a metallic pedestal 15 is 
fitted into the through hole 13 via a spring washer 16. The upper surface 
of the pedestal 15 includes a hole which is arranged coaxially with the 
hole of the boss portion 12c, and fitted into these holes of the boss 
portion 12c and pedestal 15 are the pin portions of both ends of a 
bill-type mixer diode 14. In this way, the mixer diode 14 is arranged at 
the slot portion feeding point of the horn antenna in a sandwiched state 
between the printed substrate 10 and the microwave circuit component 12. 
Further, a microwave substrate 17 is housed inside the cavity enclosed 
between the metallic film 11 of the printed substrate 10 and the cavity 
portion 12b of the microwave circuit component 12. A local oscillator is 
mounted in the microwave substrate 17. The oscillatory output of the local 
oscillator is emitted into the space inside the cavity and reaches the 
slot portion of the horn antenna, and as described above, because the 
mixer diode 14 is arranged at the slot portion, frequency mixing of the 
antenna input and the first local oscillator output are carried out in a 
microwave circuit mode. 
Further, although omitted from the drawings, an intermediate frequency 
processing circuit portion is horizontally mounted at a peripheral portion 
of the through hole on the underside of the printed substrate 10. This 
intermediate frequency processing portion includes a first intermediate 
frequency filter for inputting the output of the mixer diode 14, a second 
local oscillator, and a second mixer circuit for carrying out frequency 
mixing of the output of the second local oscillator and the output of the 
first intermediate frequency filter. Also, a sealed case is secured to the 
underside of the printed substrate 10 to cover this intermediate frequency 
processing circuit portion. 
As for the pattern of the metallic film 11 on top of the printed substrate 
10, it is designed not only to fill the space underneath the microwave 
circuit component 12, but to function as a shield for the intermediate 
frequency processing circuit portion as well. Further, low frequency 
circuits such as a wave detection circuit, a reception signal 
discrimination circuit and an alarm circuit are mounted on another region 
of the printed substrate 10. 
Now, as shown in FIG. 2, the mixer diode 14 is constructed from a 
cylindrical ceramic tube 14a which is open at both ends, and an anode 
electrode 14b and a cathode electrode 14c which are mounted to the ceramic 
tube 14a to plug both ends thereof. Further, a diode chip 14d is mounted 
to the upper end of the cathode electrode 14c (inside the ceramic tube 
14a), and this diode chip 14d is electrically connected to the anode 
electrode 14b by bonding wires 14e. 
Unfortunately, because there is no amplification circuit in the circuit 
design described above in which the reception signals and output of the 
local oscillator undergo frequency mixing in the mixer diode 14 and are 
directly converted to an intermediate frequency, the frequency conversion 
loss of the mixer circuit has a large effect on sensitivity. Accordingly, 
in order to improve the sensitivity, it is essential to make such 
conversion loss as small as possible. In this regard, the conversion loss 
is related to many factors, such as the characteristics of the mixer 
diode, the input voltage from the local oscillator, the impedance matching 
between the mixer diode and the antenna, and the impedance matching 
between the mixer diode and the local oscillator. 
In the bill-type structure described above, the main factors which 
determine the impedance of the mixer diode 14 are, in addition to the 
junction capacitance and series resistance inside the diode, the package 
capacitance and the inductance of the bonding wire 14e. Further, the 
higher the frequency of the microwave and milliwave, the larger the effect 
of such factors. 
Further, a Ga-As Schottky barrier-type diode is generally used for the 
microwave mixer diode 14. The junction capacitance inside the diode is 
semiconductor characteristic and is determined by the semiconductor 
material and the structure of the device. In the same way, the package 
capacitance and the bonding wire inductance are determined by the package 
material and structure. However, even though conversion loss can be 
lowered by lowering the impedance, it is difficult to remove the inherent 
impedance component of the circuit component described above. 
SUMMARY OF THE INVENTION 
With a view toward overcoming the problems of the prior art described 
above, it is an object of the present invention to provide a highly 
sensitive microwave detector, in which the frequency conversion loss of 
the mixer circuit is lowered by forming a prepared circuit component 
having a lower inherent impedance. 
In order to achieve the object stated above, the present inventor 
considered the use of beam-lead-type or flip-chip-type diode. In the case 
of the flip-chip-type diode, because the bare chip is surface mounted 
directly in the circuit without the use of a package, there is no need for 
bonding wire, and this makes it possible to eliminate the element which 
generated the impedance component described above, and because the 
impedance of the chip itself is also lowered, it is possible to lower the 
frequency conversion loss of the mixer circuit. However, because the 
mechanical strength of such a flip-chip-type diode is extremely low, it is 
not possible to directly mount the flip-chip-type diode in the requisite 
microwave circuit component of the present invention. 
In response to this, a structure was developed to achieve impedance 
matching and lower the frequency conversion loss of the mixer circuit 
while using a flip-chip-type diode. In this connection, a first structure 
of a microwave detector according to the present invention comprises: 
a printed substrate; 
an electrically conductive microwave circuit component provided on top of 
the printed substrate so as to integrally form a horn antenna having a 
slot portion and a cavity which communicates with the rear of the slot 
portion of the horn antenna; 
a microwave circuit substrate; 
a local oscillator mounted on the microwave circuit substrate and housed 
inside the cavity; 
a horn antenna slot portion feeding point formed in the upper surface of 
the microwave circuit component; 
a through hole formed in the lower surface of the microwave circuit 
component so as to face the feeding point of the horn antenna; and 
a mixer diode positioned at the feeding point of the horn antenna, the 
mixer diode including a first end which is directly or indirectly 
connected to the feeding point of the horn antenna, a second end which is 
directly or indirectly connected to the printed substrate with the through 
hole preventing a short circuit from forming between the second end of the 
mixer diode and the microwave circuit component, a mixer diode substrate 
having a first protruding portion at a first end of the mixer diode 
substrate and a second protruding portion at a second end of the mixer 
diode substrate, separate anode and cathode electrode patterns formed on a 
surface of the substrate which includes the protruding portions, and a 
beam-lead-type or flip-chip-type diode which is mounted to a surface of 
the mixer diode substrate near the center thereof, the beam-lead-type or 
flip-chip-type diode having an anode and a cathode which are surface 
mounted to the anode and cathode electrode patterns to form electrically 
conducting pathways therewith, wherein the first and second protruding 
portions are directly or indirectly connected respectively to the 
microwave circuit component and the printed substrate. 
The structure described above is suitable for the type of microwave 
detector in which an entire microwave circuit component made of die-cast 
aluminum or the like forms the horn antenna and cavity. However, the 
present invention is not limited to this structure, and it is possible to 
apply the present invention to the type of microwave detector in which the 
horn antenna and cavity are formed in a portion of the microwave circuit 
component. Namely, for this type, a second structure of the microwave 
detector according to the present invention comprises: 
a printed substrate; 
an electrically conductive microwave circuit component which is provided on 
top of the printed substrate, the microwave circuit component having an 
open underside portion which covers the metallic foil, whereby the 
microwave circuit component and the metallic foil integrally form a horn 
antenna having a slot portion and a cavity which communicates with the 
rear of the slot portion of the horn antenna; 
a microwave circuit substrate; 
a local oscillator mounted on the microwave circuit substrate and housed 
inside the cavity; 
a horn antenna slot portion feeding point formed in the upper surface of 
the microwave circuit component; and 
a mixer diode positioned at the feeding point of the horn antenna and 
sandwiched between the microwave circuit component and the printed 
substrate, the mixer diode including a mixer diode substrate having a 
first protruding portion at a first end of the mixer diode substrate and a 
second protruding portion at a second end of the mixer diode substrate, 
separate anode and cathode electrode patterns formed on a surface of the 
substrate which includes the protruding portions, and a beam-lead-type or 
flip-chip-type diode which is mounted to a surface of the mixer diode 
substrate near the center thereof, the beam-lead-type or flip-chip-type 
diode having an anode and a cathode which are surface mounted to the anode 
and cathode electrode patterns to form electrically conducting pathways 
therewith, wherein the first and second protruding portions are directly 
or indirectly connected respectively to the microwave circuit component 
and the printed substrate. 
In both of the structures of the present invention described above, 
"surface mounting" is carried out directly by placing the anode and 
cathode of the diode in contact with the anode and cathode electrode 
patterns and then applying an adhesive or solder to fix them in place, or 
indirectly by forming an electrically conducting pathway by means of an 
electrically conducting adhesive or solder arranged therebetween. In the 
latter case, the connection can be made my means of a metallic bump or the 
like to minimize surface contact. 
Further, even though the electrically conducting microwave circuit 
component is described in the embodiments of the present invention as 
being formed from a metal (in particular, die-cast aluminum, but other 
metals of course being usable), the present invention is in no way limited 
to the use of metal for forming the microwave circuit component, and it is 
also possible to use either an electrically conducting non-metallic 
material such as electrically conducting resin or a non-conducting resin 
or plastic which is formed into shape and platted on the top and/or 
underside surface with an electrically conducting material. In other 
words, it is possible to use any material having the necessary properties 
for an antenna. 
In the first structure described above, the horn antenna and cavity are 
formed by the microwave circuit component, and in the second structure 
described above, the horn antenna and cavity are constructed by the 
microwave circuit component and the metallic foil of the printed 
substrate. In both of these structures, a local oscillator is housed 
inside the cavity, with the output of the local oscillator and the antenna 
input undergo frequency mixing by the mixer diode in a microwave circuit 
mode. Further, the output of the mixer diode is guided from the point 
where the output terminal is mounted to the printed substrate to a 
prescribed intermediate frequency processing circuit portion of the 
printed substrate. 
In this connection, in accordance with the structures described above, the 
impedance of the flip-chip-type diode is low and the frequency conversion 
loss is small. Further, the problems mentioned above in relation to the 
low mechanical strength of the diode are eliminated by surface mounting 
the diode to the mixer diode substrate. Furthermore, because the anode and 
cathode of the diode are mounted to anode and cathode electrode patterns 
on the mixer diode substrate, there is no need for bonding wires and the 
like, and this makes it possible eliminate or greatly suppress the 
generation of the unwanted impedance component. 
Furthermore, by changing dimensions such as the length and/or width of at 
least one of the anode and cathode electrode patterns, it is possible to 
introduce inductance and capacitance components between the microwave 
circuit component and the mixer diode, and this makes it easy to adjust 
the impedance for optimum performance. Of course, minor adjustments can be 
carried after manufacture or at a prescribed time by removing a portion of 
such pattern. 
Preferably, an elastic body is provided to bias the mixer diode substrate 
toward either the microwave circuit component or the printed substrate. In 
this way, it is possible to prevent poor contact between the mixer diode 
and the microwave circuit component and/or the printed substrate. Further, 
by forming the elastic body from an electrically conducting material, it 
is possible to form an electrically conducting pathway between the mixer 
diode and the microwave circuit component or the printed substrate via the 
elastic body. 
Further, at least one of the anode and cathode electrode patterns can be 
formed to extend over both side surfaces of the respective protruding 
portion of the mixer diode substrate. In this connection, the front 
surface electrode patterns can be easily formed by using a printed mixer 
diode substrate, and the side surface electrode pattern can be easily 
formed by applying an electrically conducting material such as plating or 
the like. Further, at least one of the anode and cathode electrode 
patterns can also be formed on the rear surface of the mixer diode 
substrate, and at least one through hole can be formed through the mixer 
diode substrate t connect such rear surface electrode pattern to the 
respective front surface electrode pattern. In this connection, the 
connection made via the through hole formed in the mixer diode substrate 
can be achieved by applying an electrically conducting film to the inside 
surface of the through hole or by plugging the through hole with an 
electrically conducting material to form a so-called closed bare hole. 
Now, by forming the electrode pattern on the sides of the mixer diode 
substrate, the electrode pattern is given a solid formation, and this 
lowers the inductance. Further, by forming a through hole in the mixer 
diode substrate, a strong electrical connection is established between the 
electrode patterns formed on the front and rear surfaces of the protruding 
portion, and because the through hole is equivalent to forming a thick 
electrode portion, the inductance is lowered. As a result, the impedance 
of the electrode pattern is lowered. 
Further, by forming a first connecting hole in the microwave circuit 
component to connect the first protruding portion of the mixer diode to 
the microwave circuit component and a second connection hole in the 
printed substrate to connect the second protruding portion of the mixer 
diode to the printed substrate, and by making the dimensions of the 
contacting surfaces inside at least one of the connection holes match the 
dimensions of the respective protruding portion, it becomes possible to 
set the angular position of the mixer diode at a desired angle with 
respect to the microwave circuit component by inserting the respective 
protruding portion into the connecting hole formed with matching 
dimensions. 
Further, by forming the mixer diode substrate to have a length which is 
shorter than the distance between the microwave circuit component and the 
printed substrate, it is possible to provide a metallic connecting member 
between the microwave circuit component and the printed substrate to form 
a series connection with the mixer diode substrate. In this connection, 
even though the metallic connecting member is described in the embodiments 
as being arranged between the mixer diode substrate and the printed 
substrate, the present invention is not limited to this structure, and it 
is possible to arrange the metallic connecting member between the mixer 
diode substrate and the microwave circuit component. Of course, it is also 
possible to arrange a metallic connecting member between the mixer diode 
substrate and the printed substrate and between the mixer diode substrate 
and the microwave circuit component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Except for a modification of the mixer diode which forms the mixer circuit, 
the basic structure of the microwave detector is similar to the prior art 
microwave detector shown in FIG. 1. Accordingly, a detailed description of 
such modification will be given below. 
FIGS. 3(A), (B) are enlarged views of a mixer circuit portion which forms 
the essential portion of the present invention. In the structure shown in 
FIG. 3 (A), the elements that are the same as those shown in FIG. 1 are 
designated by the same reference numbers. As shown in FIG. 3(B), a mixer 
diode 32 is constructed from a substrate 30 and a flip-chip-type diode 31 
which is mounted on a surface of the substrate 30. Of course, it is 
possible to use a beam-lead-type diode in place of the flip-chip-type 
diode 31. 
In addition to forming a mounting board for mounting the diode 31, the 
substrate 30 also serves to electrically and mechanically connect the 
anode and cathode of the diode 31 respectively to the printed substrate 10 
and the microwave circuit component 12 (horn antenna 12a). The specific 
structure is described below. 
Namely, the substrate 30 is constructed from a printed substrate formed 
from a dielectric base material such as glass epoxy, Teflon (registered 
trademark), ceramics or the like. Further, the substrate 30 is shaped as a 
rectangle with the four corners thereof removed so as form protruding 
portions 30a, 30b at both ends in the lengthwise direction. The width W of 
both protruding portions 30a, 30b taken with respect to the surface of the 
substrate 30 are tapered toward the ends thereof. In this way, the 
surfaces 30a=92, 30b=92 of the sides of the protruding portions 30a, 30b 
have at least one curved portion. 
Further, an anode electrode pattern 33a and a cathode electrode pattern 33b 
are formed on prescribed regions of the substrate 30 which include the 
periphery of both protruding portions 30a, 30b. The anode electrode 
pattern 33a is formed from the four side surfaces of the protruding 
portion 30a up to the vicinity of the center of the surface of the 
substrate 30 to enable surface mounting with the anode of the diode 31. 
Similarly, the cathode electrode pattern 33b is formed from the four side 
surfaces of the protruding portion 30b up to the vicinity of the center of 
the surface of the substrate 30 to enable surface mounting with the 
cathode of the diode 31. 
In this way, when the diode 31 is mounted to the center of the substrate 
30, the anode and cathode of the diode 31 are respectively surface mounted 
to the anode electrode pattern 33a and the cathode electrode pattern 33b. 
As described above, the microwave circuit component 12 is made from 
die-cast aluminum and is integrally formed into a horn antenna portion 12a 
and a cavity portion 12b for holding a local oscillator. Further, a boss 
portion 12c is integrally formed at the slot portion of the horn antenna 
portion 12a, and a through hole 13 which faces the boss portion 12c is 
formed in the printed substrate 10. With this structure, the mixer diode 
32 is mounted between the microwave circuit component 12 and the printed 
substrate 10 by inserting the protruding portions 30a, 30b respectively 
into the hole formed in the boss portion 12c and the through hole 13 of 
the printed substrate 10. In this way, because the protruding portions 
30a, 30b are respectively in contact with the boss portion 12c and the 
through hole 13, the anode and cathode electrode patterns 33a, 33b formed 
on the surfaces of the protruding portions 30a, 30b form electrically 
conducting pathways with the boss portion 12c and the through hole 13. 
Consequently, because the anode of the diode 31 is electrically connected 
to the horn antenna 12a and the cavity 12b via the anode electrode pattern 
33a and the boss portion 12c, the reception signals and the output of the 
local oscillator undergo frequency mixing in the diode 31. Further, the 
related mixed frequency signal is sent from the cathode of the diode 31 to 
an intermediate frequency processing circuit portion formed in the printed 
substrate 10 via the cathode electrode pattern 33b and the through hole 
13, and a prescribed signal process such as a process to detect whether 
the target microwave is present or absent is carried out. In this way, a 
mixer circuit is constructed by arranging the mixer diode 32 at the slot 
portion feeding point of the horn antenna in a sandwiched state between 
the printed substrate 10 and the microwave circuit component 12. Of 
course, the anode and cathode may be arranged at reversed positions with 
respect to those described above. 
Further, in the present embodiment, the protruding portions 30a, 30b have 
quadrilateral shaped outlines. Accordingly, by forming the hole portion of 
the boss portion 12c and the through hole 13 to have a prescribed size 
quadrilateral shaped plane cross section which matches the shape of the 
protruding portions 30a, 30b, it is possible to easily set the direction 
of the substrate 30 (mixer diode 32) at a prescribed angle with respect to 
the microwave circuit merely by inserting the protruding portions 30a, 30b 
into the boss portion 12c and the through hole 13. 
Namely, because the electrode patterns 33a, 33b are plate shaped, the 
impedance of the microwave circuit is changed in accordance with the 
direction of the substrate 30 at the time of insertion into the microwave 
circuit. Accordingly, by setting the shape of the hole portion of the boss 
portion 12c to establish the optimum impedance in advance, it becomes 
possible to automatically obtain the optimum impedance and lower the 
frequency conversion loss merely by inserting the protruding portion 30a 
into the boss portion 12c without having to think about angular 
adjustments at the time of assembly. Now, in order to carry out angular 
alignment, at least one of the boss portion 12 and the through hole 13 may 
be formed with internal dimensions which match the outer dimensions of the 
protruding portions 30a, 30b. 
Next, FIGS. 4(A), (B) show a second embodiment of the present invention. As 
shown in FIG. 4(B), the second embodiment uses a plate spring 35, with the 
elastic restoring force of the plate spring 35 being utilized to force the 
anode electrode pattern 33a of the mixer diode 32 into firm contact with 
the boss portion 12c. In this way, it is possible to avoid problems such 
as bad circuit conductivity and large resistance loss due to poor contact. 
Now, because this structure may make it possible for spaces to form 
between the cathode electrode pattern 33b and the through hole 13, a more 
secure electrical and mechanical connection can be achieved by carrying 
out soldering or the like at the through hole 13. Further, in the case 
where the plate spring 35 is formed from an electrically conducting 
material such as a metal plate, the conducting pathway with the 
intermediate frequency circuit can be designed through the plate spring 
35. Further, in the present embodiment, the protruding portion 30b of the 
substrate 30 is inserted through a through hole 35a formed in the plate 
spring 35, and by shaping the through hole 35a to match the external shape 
of the protruding portion 30b, the through hole 35a can function as a 
means of carrying out the angular alignment described above. 
Now, even though the plate spring 35 in the embodiment shown in the 
drawings was described as being provided on the printed substrate 10, the 
present invention is not limited to this structure, and the plate spring 
may of course be provided on the microwave circuit component 12. Further, 
the present invention is not limited to the use of a plate spring, and it 
is possible to use a variety of other spring members such as coil springs 
and the like. Further, the present invention is not limited to the use of 
springs, and it is possible to use other elastic members including 
spring-like washers such as C-rings and elastic packing. 
Next, FIG. 5 shows a third embodiment of the present invention. In this 
embodiment a spring 36 (spring washer) is used in the same manner as that 
shown in the embodiment of FIG. 4 to prevent poor contact as much as 
possible. Further, in this third embodiment, and metallic connecting 
member 38 is interposed between the mixer diode 32 and the through hole 13 
of the printed substrate 10. 
The electrode patterns 33a, 33b formed in the substrate 30 are made of 
metallic foil and include an inductance component. Accordingly, as the 
electrode pattern is made longer, the inductance component becomes larger, 
and even though the use of the flip-type diode 31 is designed to lower the 
impedance component, the large inductance generated by the electrode 
patterns 33a, 33b make it impossible to sufficiently lower the impedance 
of the entire mixer circuit. 
Thus, the length of the entire substrate 30 is shortened in order to 
shorten the length of the electrode patterns 33a, 33b which cause the 
increase in the impedance component. However, this makes the substrate 30 
shorter than the spacing between the microwave circuit component 12 and 
the printed substrate 10, and therefore the substrate 30 can not be 
mounted by itself. In response to such situation, the connecting member 38 
is interposed as described above to make up such shortage. Further, 
because the connecting member 38 is electrically conductive, the cathode 
of the diode 32 forms a conductive pathway with the through hole 13 via 
the connecting member 38. 
Now, in order to suppress the generation of inductance, the plane 
cross-sectional area of the connecting member 38 can be made relatively 
high and dense. Further, a protruding portion 38a adapted for insertion 
into the through hole 13 is formed on the bottom end of the connecting 
member 38, and a concave portion 38b adapted to receive the protruding 
portion 30b of the mixer diode 32 is formed in the top of the connecting 
member 38. 
Next, FIGS. 6 and 7 show a fourth embodiment of the present invention. In 
this connection, while the embodiments described above were suitable for 
use in the type of microwave detector shown in FIG. 1 in which the horn 
antenna and the like is constructed from the microwave circuit component 
12 and the metallic film 11 form on the printed substrate 10, the present 
embodiment is suitable for use in the type of microwave which has a horn 
antenna and the like formed from only a microwave circuit component. 
Namely, a microwave circuit component 40 is formed by joining two halves 
comprised of an upper component (cover) 41 and a lower component (base) 42 
made of, for example, die-cast aluminum or the like. Further, a horn 
antenna portion 40a and cavity portion 40b for holding a local oscillator 
are integrally formed by the metallic microwave circuit component 40. In 
this way, a horn antenna and a local oscillator housing cavity which 
communicates with the rear of the slot portion of the horn antenna are the 
general structures formed by constructing the whole metallic microwave 
component. Further, the microwave circuit component 40 is mounted on top 
of a printed substrate 10. 
The upper component 41 has a short height and is shaped roughly the same as 
the shape of the lower opened microwave circuit component 12 of the 
embodiments described above. Further, the lower component 42 has roughly 
the same shape as the upper component 41, but they differ with regards to 
the points described below. Namely, a boss portion 40c is integrally 
formed at the slot portion of the horn antenna portion 40a in the bottom 
of the upper component 41 of the microwave circuit 40, and a through hole 
44 which faces the boss portion 40c is formed in the lower component 42. 
Further, in the same manner as was described above, a through hole 13 is 
formed in the printed substrate 10 so that the boss portion 40c, the 
through hole 44 and the through hole 13 are arranged on a single straight 
line in the vertical direction. 
Also, in the same manner as was described above, the protruding portion 30a 
formed with the anode electrode pattern 33a of the mixer diode 32 is 
adapted to be mounted to the boss portion 40c. Further, the protruding 
portion 30b formed with the cathode electrode pattern 33b of the mixer 
diode 32 is adapted form a conducting pathway with the through hole 13 of 
the printed substrate 10 via the connecting member 38. In this connection, 
the inner diameter of the through hole 44 is made sufficiently larger than 
the outer shape of the connecting member 38 to prevent the connecting 
member 38 from coming into contact with the lower component 41 of the 
microwave circuit component 40. Now, because this embodiment is different 
from the third embodiment only in regards to the structure of the 
microwave circuit component which forms the horn antenna and the like, a 
description of the other essential elements of the present invention which 
are the same as those described for the third embodiment will be omitted. 
In this connection, it is of course possible to adapt the embodiment shown 
in FIGS. 6 and 7 in to enable the mixer diode 32 to be directly connected 
to the printed substrate 10 without the provision of the connecting member 
38 in the same manner as described above for the first embodiment shown in 
FIG. 2. Furthermore, in the same manner as was described for the second 
embodiment, it is of course possible to provide the structure of the 
fourth embodiment with an elastic body such as a plate spring or spring 
body arranged at a suitable position to bias the mixer diode in a 
prescribed direction. 
Next, FIG. 8 shows a fifth embodiment of the present invention which is 
related to an improvement of the mixer diode 32. In this regard, in the 
embodiments described above, the electrode patterns were formed on the 
four peripheral surfaces of the protruding portions 30a, 30b. Accordingly, 
the electrode patterns are formed on both the front surface of the 
substrate 30, where the diode 31 is mounted, and on the rear surface 
thereof. In addition to this, in the present embodiment the substrate 30 
is also provided with through holes 46 which pass through the substrate 
30. In this way, electrically conducting pathways are established between 
the electrode patterns on the front and back of the substrate 30 not only 
through the side peripheral portions, but also through the inside of the 
substrate 30 via the through holes 46. 
Furthermore, even though electrode patterns were formed on all four 
peripheral surfaces of the protruding portions 30a, 30b in the embodiments 
described above, the present invention is not limited to such structure, 
and it is possible, for example, to form an electrically conducting film 
on only the front and rear surfaces of the protruding portions 30a, 30b 
and not on the side surfaces 30a=92, 30b=92 thereof. In such case, where 
no electrically conducting film is formed on the side surfaces, through 
holes may or may not be provided. Further, it is also possible to omit the 
electrode pattern from the rear surface as well and form an electrode 
pattern on only the front surface of the substrate 30. 
Now, in the microwave detector according to the present invention, because 
the mixer diode structure includes a diode which is surface mounted to a 
substrate, with the substrate used to form connections with a microwave 
circuit component and a printed substrate, it becomes possible to lower 
the impedance of the diode itself and eliminate or largely suppress the 
cause of the generation of unwanted inductance. As a result, by forming a 
structure which lowers the inherent impedance of a prepared circuit 
component, the present invention makes it possible to lower the frequency 
conversion loss of the mixer circuit and thereby construct a highly 
sensitive microwave detector.