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Патент USA US3071739

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Jan. 1, 1963
B. M. SCHIFFMAN
3,071,729
MICROWAVE MIXER FOR MUTUALLY ORTHOGONAL WAVEGUIDE MODES
Filed Feb. 16, 1961
INVENTOR.
BERNARD M. SCHIFFMAN
BY
7/ ”“”
ATTORNEY
ire
31,071,729
tats
Patented Jan. 1, 1963
l
2
connecting waveguide con?guration in accordance with
the present invention,
3,il"7l,72;9
MICROWAVE MHXER FGR MUTUALILY GERTHSP
ONAL WAVI‘LGIEDE MGDES
FIG. 2 is an isometric view of a mixer constructed in
accordance with the principles illustrated in FIG. 1,
Bernard M. Schi?man, Mountain ‘View, Calif., assignor to
Varian Associates, Palo Alto, Calif., a corporation of
FIG. 3 is a front view, partially broken away, of the
mixer of FIG. 2 looking into the local oscillator wave
California
guide port, and
Filed Feb. 16, 11961, Ser. No. 89,803
6 Claims. (Cl. 325-446)
FIG. 4 is a rear view of the mixer of FIG. 2 looking
into the signal waveguide port.
7
The present invention relates in general to microwave
mixers of the type wherein the microwave frequency
Referring to FIG. 1, the mixer waveguide section 1
is energized in two orthogonal modes by a vertically
polarized signal wave propagated through a single mode
rectangular waveguide 2 connected at a step transition ad
jacent one end thereof, and a horizontally polarized local
oscillator wave propagated through a similar perpendic
ularly disposed waveguide 3 connected at a step transition
adjacent the opposite end thereof. Positioned inside the
waveguide section I is a pair of collinearly disposed
crystal diode recti?ers 4 and 5 contacted at the oppositely
poled inwardly extending terminals thereof by a hori
zontal output post 6. The electric ?eld of the signal wave
is unperturbed by the post 6 and couples into each of
waves are supported as mutually orthogonal modes in a
single waveguide, and more particularly to novel wave
guide structures for improving the energy coupling or
impedance match to the diodes of such mixers.
In the copending US. patent application of Richard
M. Whitehorn, Serial No. 862,356, ?led December 28,
1959, now US. Patent 3,066,290, issued November 27,
1962, there is disclosed and claimed an extremely com
pact and lightweight microwave mixer consisting of a
section of rectangular waveguide supporting two mutually
orthogonaldorninant electric modes respectively estab
lished by two microwave frequency waves, and having a
pair of diodes collinearly disposed therein. Means are
provided for perturbing the electric ?eld of one mode to
couple to each diode in an opposite direction whereas
the electric ?eld of the other mode is unperturbed and
couples to each diode in the same direction. Thus, the
the crystal recti?ers 4 and 5 in the same direction as in
dicated by the dotted arrows. The local oscillator wave,
however, is perturbed by the post 6 in such a manner
that the electric ?eld thereof couples into each crystal
recti?er in an opposite direction as indicated by the solid
arrows. The difference between the currents in the
signals of said diodes may be combined to obtain a bal
separate recti?ers ?ows along the conductor 6 through
anced beat frequency signal.
a low-pass insulating choke 6' in the side wall to the in
ner conductor of a balanced LF. beat frequency coaxial
output connector, the current components in the separate
In arrangements wherein the unperturbed wave is
coupled through a junction connection consisting of a
single mode rectangular Waveguide, it has heretofore
crystal recti?ers due to local oscillator noise cancelling
been the usual practice to make the dimension of the
each other at the junction of post 6.
orthogonal mode waveguide transverse to the polariza 35
Since the dielectric cartridges of crystal diodes 4 and
tion of the unperturbed wave the same as the width of
5 lie in the polarization direction of the signal Wave, they
the connecting waveguide. It has been discovered with re
tend to present a heavy capacitive loading thereto which
spect to such an arrangement that increasing the frequency
lowers the cut-o? frequency of higher order modes, there
of the unperturbed wave decreases its coupling to the
by degrading the coupling of signal energy to the diodes
diodes, thereby placing an undesirable limitation on the 40 at the high end of the band of frequencies which may be
operating frequency range. The apparent reason for this
propagated by the waveguide 2. In accordance with the
loss of coupling is that the dielectric diode cartridges pre~
present invention, this problem is overcome by making
sent a heavy capacitive loading to the unperturbed wave
the e?ective waveguide width a’ for signal waves in the
so that the cut-off frequency for undesired higher order
mixer section 1 substantially (approximately 25-30%)
modes is lower in the orthogonal mode waveguide sec 45 less than the waveguide width a of the connecting wave
tion than in the connecting waveguide.
guide 2. Under these conditions, the cut-off frequency
It is the principal object of the present invention to
for higher order signal modes in the mixer section 1
provide novel means for overcoming this and other limita
is comparable with that in the connecting waveguide 2,
tions of orthogonal mode mixers.
thereby enabling the useful frequency range to be eX
One feature of the present invention is the provision 50 tended. For example, making the dimensions at’ equal
of an orthogonal mode mixer waveguide section in which
to .650" as compared to the standard X-band dimension
the dimension transverse to the polarization of the un
of .909” enabled the high frequency end of the operating
perturbed mode is substantially smaller than the width
range to be raised from approximately 10.5 kmc. to
of the connecting waveguide through which said mode
greater than 12 kmc.
is, coupled.
Another feature of the present invention is the pro
vision of an orthogonal mixer waveguide section having
a rectangular cross-section which is oblong in the axial di
rection of the diodes collinearly disposed therein.
Another feature of the present invention is the provision
of a thin rectangular iris for coupling the unperturbed
mode of an orthogonal mode mixer to the connecting
55
It will be noted that the crystal diodes 4 and 5 are
positioned mid-way of the mixer dimension a’ in order
to insure maximum coupling to the signal ?eld, and that
the local oscillator connecting waveguide 3 is positioned
off~center so as to maximize the perturbing effect of the
post 6 for the local oscillator mode. In order to minimize
waveguide.
the space occupied by the entire waveguide assembly, the
signal waveguide 2 is also placed off-center to line up
with the local oscillator Waveguide 3.
Still another feature of the present invention is the pro
vision of a bifurcated iris for coupling the perturbed mode
of an orthogonal mode mixer to the connecting wave
In the usual situation where the same size of connecting
waveguide is used for both the local oscillator and signal
waves, the mixer waveguide section had heretofore been
guide.
These and other features and advantages of the pres
of _ a substantially square cross-sectional con?guration.
According to the present invention, however, the cross
ent invention will be more apparent after a perusal of
section is oblong in the axial direction of the diodes. In
the following speci?cation taken in connection with the 70 addition to the ability to eliminate higher order modes
accompanying drawings wherein,
as described above, such oblong con?gurations are found
FIG. 1 is a pictorial schematic view of a mixer and
to be generally advantageous in improving the coupling
shaman
3
(l
polarized dominant electric waveguide modes established
by ?rst and second waves propagating, respectively,
through a pair of junction connections adjoining said
of both the local oscillator and signal wave to the diodes
since the electrical distance from the signal waveguide port
to the diodes is relatively shorter for the signal wave, and
relatively longer for the local oscillator wave. Thus, the
diodes are placed in the regioni of strong signal ?eld
which is electrically close to the step transition between
the signal and mixer waveguides, and at the same time the
section, the junction connection for said ?rst wave con
sisting of a single mode waveguide coupled to one end
of said orthogonal mode waveguide section through a
step transition at which dimension of said waveguide sec—
tion transverse to the polarization direction of said ?rst
wave is substantially less than the width of said con
necting waveguide; 21 pair of collinearly disposed diodes
diodes are a substantial electrical distance from the short
ing plane presented by said transition to local oscillator
waves.
Further, this oblong con?guration allows a
greater insertion distance for the diodes.
Referring now to FIGS. 2, 3 and 4 there is shown, in
constructional detail, a mixer in accordance with the pres
ent invention, particularly useful in compact microwave
extending inwardly from opposed portions of the wall of
said Waveguide section in the polarization direction of *
said ?rst wave; and means for perturbing the mode estab
lished by said second wave so that the electric ?eld thereof
extends in an opposite direction along the axis of each
diode.
2. A microwave mixer comprising: a rectangular wave
receiver applications, which operates in the frequency
range of 10 to 12 krnc. with standard X-band connecting
waveguide. The oblong waveguide section 1 is recessed
in a rectangular metallic block 1’ provided with a ?ange
plate 10 for mating to a vertically polarizing signal
waveguide and a ?ange plate 11 for mating to a hori
guide section of oblong cross-section capable of suppoit
ing a pair of orthogonally polarized dominant electric
20 waveguide modes established by ?rst and second waves
zontally polarizing local oscillator waveguide. These two
propagating, respectively, through a pair of junction con
connecting waveguides are indicated in phantom as 10’
nections adjoining said section; a pair of collinearly dis
and 11', respectively. The crystal recti?ers 4 and 5 are
posed diodes extending inwardly from opposed portions
seated in removable caps 12 threaded through the top and
of the wall of said waveguide section in the polarization
bottom walls, and are held in contacting relation at 25 direction of said ?rst wave, the dimensions of said wave,
the inner terminals thereof by a connector 13. The
guide cross~section in said polarization direction being
output LF. post 6 is attached to the connector 13, and
substantially greater than that in the direction transverse
extends through the insulating low-pass choke 6' in the
thereto; and means for perturbing the mode established
waveguide wall to form the inner conductor of the out
by said second wave so that the electric ?eld thereof ex
put coaxial LF. connector 6". Each cap 12 is provided 30 tends in an opposite direction along the axis of each diode.
with a ?lter network bypassing the AC. crystal current
3. A microwave mixer comprising: a section of rec
components to the grounded waveguide block 1' so
tangular waveguide capable of respectively supporting
that the DC. current levels in the crystal recti?er may
in two orthogonally polarized dominant electric modes,
be monitored at the lugs 14 without producing undesir
able leakage ?elds.
a ?rst wave received through a ?rst single mode con
necting Waveguide adjoining one end thereof at a ?rst
A thin, horizontally extending, rectangular iris 21 in
step transition, and a' second wave received through a
the signal‘ waveguide ?ange Ill, centered with respect to
perpendicularly disposed second single mode connecting
the diode recti?ers, is found to improve the signal VSWR
and hence the noise ?gure. A thin, vertically extend
ing, bifurcated iris 22 in the local oscillator ?ange 1.1,
centered with respect to the local oscillator waveguide
11', also aids in improving the noise ?gure, especially at
waveguide adjoining the opposite end thereof at a second
step transition, the dimension of said waveguide section in
the polarization direction of said second wave being sub~
stantially smaller than the width of said ?rst connecting
waveguide; a pair of collinearly disposed diodes extend
higher frequencies, by reducing the protrusion of the
ing inwardly from opposed portions of the wall of said
signal ?eld into the local oscillator waveguide and hence
waveguidesection in the polarization direction of said
moving in the effective shorting plane for signal waves, 45 ?rst Wave, the inwardly extending terminals of the sep
without any substantial degradation in the coupling of
arate diodes being of opposite polarity; and a conducting
local oscillator energy therethrough.
post contacting said inwardly extending terminals and
Certain possible modi?cations of the present invention
insulatedly extending through an adjacent wall portion of
should be particularly noted. Since the mixers of the
said waveguide section along the perpendicular bisector of
present invention are reciprocal hybrid devices, the roles
the axis of said crystal recti?ers to provide a balanced
beat frequency terminal.
of the various terminals can, under suitable conditions,
be reversed. For example, the signal and local oscillator
4. The mixer of claim 3 wherein said ?rst step transi
inputs could be reversed; or the mixer operated as a
tion includes a thin coupling iris extending transverse to
side-band modulator by using the perturbing post as the
the polarization direction of said second wave.
input terminal for the modulating signal and the opposite 55 5. The mixer of claim 3 wherein said second step
waveguide connections for the carrier input and modu
transition includes a thin bifurcated coupling iris extend
lated output, respectively. Further, the mixer may be
ing transverse to the polarization direction of said sec
operated as a parametric ampli?er by using voltage-con
trolled diode capacitors instead of dissipative diode recti
ond wave.
6. The mixer of claim 3 wherein said diodes are cen
?ers. Still further, it may be desirable in some instances 60 tered with respect to’ said waveguide section dimension
to establish a waveguide mode of desired polarization by
and said second connecting waveguide is oil-set in the
means of a junction connection consisting of a coaxial
direction of said conducting post.
probe rather than a single mode waveguide.
References Cited in the ?le of this patent
UNITED STATES PATENTS
Since many changes could’be made in the above con
struction any many apparently widely diiferent embodi
ments of this invention could be made without depart
ing from the scope thereof, it is intended that all matter
contained in the above construction or shown in the
accompanying drawings shall be interpreted as illus
trative and not in a limiting sense.
What is claimed is:
1. A microwave mixer comprising: a rectangular wave
guide section capable of supporting a pair of orthogonally
70
2,514,679
2,761,061
2,806,138
2,813,972
Southworth ___________ __ July 11, 1950
Mattern ______________ __ Aug. 28, 1956
Hopper ______________ __ Sept. 20, 1957
Anderson et al _________ __ Nov. 19, 1957
OTHER REFERENCES
Corbell: “Microwave Mixer for Airborne Radar,” Elec
tronics, February 5, 1960, pages 70 and 71.
UNITED STATES PATENT OFFICE
CERTIFICATE OF CQRRECTION
Patent No. 3,071 IT29
January 1 Y 1963
Bernard M. Schiffman
It is hereby certified that error appears in the above numbered pat
ent requiring correction and that the said Letters Patent should read as
corrected below.
Column 4Y line 25,’ for "dimensions" read —— dimension —-;
line 54,
for "second" read —— first --.,
Signed and sealed this 20th day of August 1963.,
(SEAL)
Attest:
ERNEST w. SWIDER
DAVID L- LADD
Attesting Officer
Commissioner of Patents
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