US2686260A - Design for radar-automatic frequency control mixer - Google Patents

Description

H. H. ARNLD Filed Dec. 2.0, 1950 ,ya f r W M ,Z W Z A y u a l1 M m m .WW M. m im m f/J w E ,u ,431 i .llIl/L .l`ll V 7^ N. 2 ri Q IILJ w l a f WM 2 n m n n m vn u Aug. 10, 1954 DESIGN FOR RADAR-AUTOMATICFREQUENCY CONTROL MIXER Patented Aug. 10, 1954 UNITED STATES FTENT OFFICE DESIGN FOR RADAR-AUTOMATIC- FREQUENCY CONTROL MIXER Cl. Z50- 20) 4 Claims.

This invention relates to a device for preventing energy cross coupling between adjacent mixer stages in a hollow wave guide and more particularly to a unitary hollow wave guide mixer assembly having means for preventing energy cross coupling between a radar mixer and an AFC mixer.

In the design and construction of radar transmitter-receiver assemblies, it is often necessary to place both a radar mixer and an AFC mixer within a single hollow wave guide so that both mixers may be energized from a single local oscillator. However, the use of two mixers within a single section of wave guide is not too successful becausg the AFC mixer frequently becomes overloaded and consequently produces a large amount of voltage at a harmonic of the desired AFC frequency. Experimentation has determined that this overloading of the AFC crystal mixer is caused by extraneous coupling of the transmitted radar pulse from the radar mixer through the hollow wave guide to the AFC mixer. The presence of this large amount of harmonic frequency voltage limits the sensitivity which may be attained by the AFC unit since the harmonic voltage causes a high sensitivity AFC unit to lock in at the harmonic frequency and not at the desired fundamental frequency of the radar transmitter. Since the amount of harmonic frequency voltage present varies considerably among each of a plurality of radar transmitter-receiver units, it is impossible to design a standard AFC unit which will have maximum sensitivity and also be capable of use with all transmitter-re- -ceiver units. An attempt to overcome this limitation by providing a variable sensitivity control on each AFC unit was unsuccessful because of the difficulties of establishing a proper sensitivity adjustment under field service conditions.

Accordingly, an object of this invention is to prevent extraneous or cross coupling of oscillatory electrical energy between two adjacent mixers which are positioned within a single section of hollow wave guide.

Another object of this invention is to provide a unitary radarAFC mixer assembly having a single local oscillator for supplying oscillatory electrical energy to a radar mixer and an AFC mixer wherein cross coupling of the energy between the two mixers is prevented while permitting a free flow of oscillatory energy from the local oscillator to each of the mixers.

In view of these and other objects, one embodiment of the invention comprises a unitary radar- AFC mixer assembly having a wave guide stub projecting upwardly from a hollow wave guide adjacent a local oscillator and between a radar mixer crystal within the wave guide. and an AFC mixer crystal within the wave guide so as to prevent cross coupling of oscillatory energy between the crystals without attenuating the energy supplied to each of the crystals from the local oscillator.

Many other objects and advantages of this invention will be apparent from a consideration of the description in conjunction with the drawings wherein Fig. l is a plan view of a unitary radar-AFC mixer assembly embodying the invention;

Fig. 2 is an elevational View of the radar-AFC mixer assembly;

Fig. 3 is a partial sectional view, taken along line 3 3 in Fig. l, showing the relative positions of a radar mixer crystal and an AFC mixer crystal with respect to a wave guide stub;

Fig. 4 is a perspective View of a portion of the wave guide showing schematically the iiow of energy from a local oscillator to each of the mixer crystals; and

Fig. 5 is a perspective view of a portion of the wave guide illustrating the manner in which the terminated wave guide stub prevents a flow of energy between the mixer crystals.

Referring now to the several gures of the drawing wherein like reference numbers indicate the same elements throughout the several views, and more particularly tor Fig. 1 of the drawing, a straight hollow wave guide I0 is provided with a plurality of hollow wave guide sections or transmission branches II, I2, I3, and I4 which extend perpendicularly outward from the wave guide I0. One end of the wave guide l0 is apertured and is provided with an integral flange i5 which is used to interconnect the wave guide I0 with an external beacon cavity 3l,

The hollow wave guide section or transmission branch II has an integral flange I6 which serves to interconnect the branch I I with a local beacon oscillator 32 so that oscillatory energy from the local beacon oscillator 32 is supplied to the wave guide It. A connecting flange I'I on transmission branch I2 interconnects the signal voltage from a transmitting-receiving tube 33 to the interior of the hollow wave guide It.

A ange I8 on transmission branch I4 interconnects an external AFC signal source 34- withy the branch I4 so that the control voltage from the AFC' signal source 311 is coupled to the interior of wave guide III. The transmission branch. I3 is connected to an external local. oscillator 30 by a connecting ange I9 so that oscillatory energy is supplied from oscillator 30 to a pair of crystal mixers 2i) and 2l.

Crystal mixer 20 is secured to and extends through the upper wall of wave guide I approximately midway along the transverse dimension of the wave guide l@ and in alignment with the transmission branch i2. Crystal mixer 2U serves as the radar mixer and is energized by oscillating voltage from the local oscillator 3G connected to branch i3 and from the signal input voltage supplied through branch I2.

Crystal mixer 2! is secured to and extends through the upper wall of Wave guide li! at a position midway along the transverse dimension of wave guide i@ and in alignment with transmission branch Eil. Crystal 2l is the AFC mixer and is supplied with oscillatory energy from the local oscillator 33 connected to branch i3 and from AFC unit 3c connected to wave guide section i4.

A hollow wave guide stub 22 which is terminated by an energy absorbing closure 'E3 extends perpendicularly upward from the upper wall of wave guide l in alignment with transmission branch l3- and at a position approximately midway between the mixers 2G and 2i. This position of stub 22 with respect to the mixers 2li and 2i is not critical. The terminated stub 22 is matched in impedance with the remainder of the Wave guide assembly to prevent signal distortion due to reflected waves from stub 22. One pair of side walls 25 of stub 22 is parallel to the side walls of transmission branch I3 and preferably is almost equal in length to the transverse dimension of the upper wall of wave guide iii. Another pair of side walls 2l of stub 22 is parallel to the side walls of wave guide l0 and preferably is shorter in length than the transverse dimension of the upper wall of transmission branch i3.

The schematic diagrams in Figs. 4 and 5 illustrate how wave guide stub 22 prevents the undesired cross coupling of energy past mixer 22 and through wave guide iii to mixer 2l while permitting a free flow of energy from the local oscillator 363 to each of the mixers 2S and 2|. In Fig. 4, local oscillator 3i) supplies energy to both of the mixers il@ and 2i through branch i3 and wave guide l@ in the manner shown by vectors 2li if a TEoi mode of propagation is assumed. Since the attenuating wave guide stub 22, shown in dotted outline, does not intercept the vectors 213 indicating the flow of energy to the mixers 2B' and 2i, there is no appreciable attenuation of the energy flowing to each of the mixers 28 and 2i from local oscillator 3E).

However, as shown in Fig. 5, vectors 25, which indicate the extraneously or cross coupled energy feeding from mixer 23 to mixer 2l, are almost completely intercepted by the stub 22, shown in dotted outline, so that most of the undesired cross coupled energy is absorbed in the stub due to attenuation. By thus preventing the transfer of energy from mixer 20 to mixer 2i, the overloading of the AFC crystal mixer 2i is positively prevented together with the attendant undesired production of harmonic frequency voltage.

It is to be understood that the above described embodiment is merely illustrative of the principles of this invention and that numerous other modifications may readily be devised by those 4 skilled in the art which will fall within the spirit and scope of these principles.

What is claimed is:

l. A hollow rectangular wave guide assembly comprising a main wave guide, first and second mixers longitudinally spaced and mounted on and extending through a top wall of the main wave guide, a rst wave guide branch extending from a first side wall of said main wave guide and between said first and second mixers to feed oscillator energy thereto, a second wave guide branch extending from a second side Wall of the main wave guide and in alignment with the first mixer to feed oscillatory energy thereto, a third wave guide branch extending from said second side wall in alignment with said second mixer to feed oscillatory energy thereto, a fourth wave guide branch extending from said first side wall adjacent said rst mixer to feed oscillatory energy thereto, and a terminated wave guide stub tending through said top wall of the main wave guide between said rst and second mixers to prevent energy coupling therebetween while permitting energy flow to said mixers from the first branch.

2. A hollow wave guide transmission system for protecting an automatic frequency control (AFC) mixer against overload comprising a radar mixer and the automatic frequency control mixer spaced from each other within a hollow wave guide, a nrst transmission branch extending outwardly from the wave guide between the two nixers for feeding local oscillatory electrical energy thereto, a second transmission branch of the wave guide in alignment with the radar mixer for feeding electrical energy of a first frequency thereto, a third transmission branch of the wave guide in alignment with the AFC mixer for feeding electrical energy of a second frequency thereto, a fourth transmission branch of the wave guide adjacent the radar mixer for feeding electrical energy of a third frequency to the radar mixer, a fth transmission branch at one end of the wave guide and adjacent the radar mixer and connected to a beacon cavity, and a hollow wave guide stub connected to the wave guide between the two mixers and in alignment with the rst transmission branch to prevent the transmission of electrical energy between the two mixers, said stub being matched in impedance with the remainder of the wave guide assembly.

3. in a radar system, a hollow main wave guide, a radar mixer, an automatic frequency control mixer, said mixers mounted in spaced relation in the upper surface of said main wave guide and centrally located with respect to the lateral dimension of the upper surface of the main wave guide, a rst hollow wave guide branch perpendicularly secured to said main wave guide, said first branch being in alignment with the automatic frequency control mixer, an automatic frequency control signal source connected to said first branch to energize the automatic frequency control mixer, a second hollow Wave guide branch perpendicularly secured to said main wave guide, said second branch being in alignment with the radar mixer, a transmitting-receiving tube connected to said second wave guide branch to connect a received signal to the radar mixer, a third hollow wave guide branch perpendicular-ly secured to said main wave guide, said third branch secured to a side of the main wave guide opposite that of the irst and second branches and the axis of the third branch being centrally located between the axes of the first and second branches,

a source of oscillatory energy connected to the third branch for energizing both the radar mixer and the automatic frequency control mixer, and a hollow wave guide stub connected to the upper surface of the main Wave guide between the two mixers and in alignment with the third wave guide branch to prevent the transfer of electrical energy between the two mixers, said stub being matched in impedance with the remainder of the wave guide assembly and terminated by an energy absorbing closure.

4. 1n a radar system, a wave guide assembly comprising a hollow rectangular main wave guide having two horizontal sides and two vertical sides, an automatic frequency control mixer mounted on the upper horizontal side of the main wave guide and extending therethrough, a radar mixer mounted similarly to and spaced from said automatic frequency control mixer, a first transmission branch connected perpendicularly to the main wave guide and in alignment with the automatic frequency control mixer to guide energy from an automatic frequency control signal source to the automatic frequency control mixer, a second transmission branch connected perpendicularly to the main wave guide and in alignment with the radar mixer to guide a received signal from a transmitting-receiving tube to the radar mixer, a third transmission branch connected perpendicularly to the main wave guide and centrally disposed between the mixers to guide energy from a local oscillator to both of said mixers, a fourth transmission branch connected perpendicularly to the main Wave guide and adjacent the radar mixer to guide energy from a beacon oscillator to the radar mixer, said rst and second transmission branches extending from an opposite vertical side of the main wave guide than said third and fourth transmission branches, a fth transmission branch extending from an end of the main wave guide and adjacent the radar mixer to guide energy from the radar mixer to a beacon cavity, and a hollow wave guide stub having four sides mounted on the upper horizontal side of the main wave guide and in alignment with the third transmission branch, two of the sides of the stub being parallel to and slightly less in length than the horizontal sides of the main wave guide and the other two sides of the stub being parallel to and slightly less in length than the lateral dimension of the third transmission branch, said stub being matched in impedance with the remainder of the Wave guide assembly and terminated with an energy absorbing material to prevent the cross-coupling of energy from the radar mixer to the automatic frequency control mixer.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,413,939 Benware Jan. 7, 1947 2,496,521 Dicke Feb. 7, 1950 2,514,678 Southworth July 11, 1950 2,545,994 Gabler et al Mar. 20, 1951 2,577,540 Pound Dec. 4, 1951 2,593,120 Dicke Apr. 15, 1952

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