US3899756A

US3899756A - Microwave phase correcting network utilizing waveguide coupler having mismatched ports caused by laterally displaced end section

Info

Publication number: US3899756A
Application number: US459950A
Authority: US
Inventors: Janos Bodonyi
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1973-05-05
Filing date: 1974-04-11
Publication date: 1975-08-12
Anticipated expiration: 1992-08-12
Also published as: JPS5031760A; AU6830874A; DE2336175B2; GB1464543A; AU472641B2; FR2228307B1; DE2336175A1; FR2228307A1

Abstract

A phase correcting network is provided to reduce the nonlinearity of the phase/frequency characteristic of a delay line. The invention is applicable to delay lines which form part of a commutating hybrid. The phase correcting network includes a 3dB coupler which is terminated in a pair of susceptance loaded waveguide stubs.

Description

United States Patent Bodonyi h Aug. 12, 1975 MICROWAVE PHASE CORRECTING [56] References Cited NETWORK UTILIZING WAVEGUIDE UNITED STATES PATENTS COUPLER HAVING MlSMATCHED PORTS 3,277403 10/1966 Cohn 3. 333/10 x CAUSED BY LATERALLY DISPLACED END 3,493,898 2/1970 Ward 333 11 SECTION 3,727,!52 4/[973 Bodonyi 333/10 X [75] Inventor: Janos Bodonyi, Bicknacre,

England Primary ExaminerPaul L. Gensler Attorney, Agent, or FirmBaldwin, Wight & Brown [73] Asslgneez The Marconi Company Limited,

Ch I f e ms rd, England ABSTRACT [22] Flled: 1974 A phase correcting network is provided to reduce the [2]] Appl N 459,950 non-linearity of the phase/frequency characteristic of a delay line. The invention is applicable to delay lines which form part of a commutating hybrid. The phase [30] Forelgn Apphcuonrnorny Dam correcting network includes a 3dB coupler which is May 1973 Umted Kmgdom 2l4SO/73 terminated in a pair of susceptance loaded waveguide stubs. [52] US. Cl 333/; 333/28 R; 333/3] A; 333/98 R [51] Int. CIFM. HON H; H01? 5/18; H01P 9/00 [58] Field of Search 333/10, ll, 28 R, 31 A, 11 Claims, 6 Drawing Figures PATENTEU AUG I 2 I975 SHEET Q10 mIQ Eu QIQ E46 min 55 QIQ mIu .910 3 6 WNIQ 91m WIQ .010 Elm @Q. aaeaaww QWIQ 31o twin QNIQ 98:6 NNvIu QNIQ 3 UIQ PATENTEDAUG 1 2mm 3. 899 756 SHEET 2 PHASE fc FREQUENCY- FIG. 3.

f f2 LOAD 10,

PATENTED AUG I 2l975 SHEET mmqtm f2 FREOUENCY MICROWAVE PHASE CORRECTING NETWORK UTILIZING WAVEGUIDE COUPLER HAVING MISMATCI-IED PORTS CAUSED BY LATERALLY DISPLACED END SECTION This invention relates to a phase correcting network and has particular application in providing improved channel centre frequency distribution in commutating hybrid multiplexers at millimetric wave-lengths.

FIG. 1 of the accompanying drawings shows a known form of commutating hybrid formed of two 3dB couplers each having two inputs and two outputs. The first 3dB coupler 12 has one input connected to a load and the other input connected to receive a signal consisting of two frequencies fl and f2. A first output of the 3dB coupler 12 is directly connected to one input of the second 3dB coupler 14, the other output of the 3dB coupler l2 being connected to the other input of the 3dB coupler 14 by means of a length of waveguide 16 constituting a delay line. The action of the commutating hybrid is to separate the components fl and f2 of the input signal to the first 3dB coupler l2 and these appear as separate signals on the respective outputs of the second 3dB coupler 14.

As is well known in the art, the commutating hybrid relies on the fact that the phase delay of the two frequencies fl and f2 will differ after passing through the delay line 16 and if the phase difference is an odd multiple of 11' for one frequency and an even multiple of 1r for the other frequency the two frequencies would be separated.

It is also known, (see for example our copending application Ser. No. 157,308, now US. Pat. No. 3,727,152) to connect a plurality of such commutating hybrids sequentially in the manner shown in FIG. 2 of the accompanying drawings so as to provide a multiplexer. The chain shown in FIG. 2 operates in what is believed to be a self-evident manner to separate l6 channels arriving at the input of the commutating hybrid 100. Of course, the operation of the arrangement in FIG. 2 is reversible and it is possible to feed in sixteen inputs over the respective channels CHI to CHI6 by feeding directly into the hybrids h to 10p and to obtain a single output consisting of the combination of these sixteen channels on the single waveguide connected to the commutating hybrid 10a.

FIG. 3 of the accompanying drawings shows the phase delay at the output of the delay line 16 as a function of frequency. Unlike a coaxial transmission line, a waveguide does not produce linear phase delay but instead follows the curve C in FIG. 3 which intersects the frequency axis at the point fc corresponding to the cutoff frequency of the waveguide. Because of the nonlinearity of the curve C it will be appreciated that the frequencies of the channels CH1 to CHI6 cannot follow an arithmetic progression but instead must follow the curve C. If a linear progression is desired, a phase characteristic corresponding to the line 1, shown in dotted line in FIG. 3, must be followed. It is believed that it may be necessary to modify the phase delay characteristic of the delay line in the commutating hybrids with a view to obtaining this linear relationship in order to allow standardization of the frequencies used in different countries and it is an object of the present invention to provide a phase correcting network which may be used in a delay line of a commutating hybrid in a multiplexer to improve the centre frequency distribution of the multiplexer.

In accordance with the present invention, a phase correcting network for improving the phase/frequency characteristic of a delay line includes a 3dB coupler adapted to be inserted in the said delay line and terminated in a pair of susceptance loaded waveguide stubs.

Conveniently, the susceptance loading of the waveguide stubs may be effected by providing one or more mismatches along the length of the stubs, the mismatches being achieved by laterally displacing sections of the waveguide relative to one another in the direction of the H-plane.

Each phase correcting network may correct for nonlinearity within a predetermined range of frequencies and if it is desired to provide linearity over a wide range more than one phase correcting network may be connected in series with one another. It will also be appreciated from the description that follows that phase correcting circuits in accordance with the invention can be used not only to provide linearity but generally to modify the phase/frequency characteristics of a waveguide so as to follow a desired configuration within a predetermined range of frequencies.

The invention will now be described further, by way of example, with reference to FIGS. 4, 5 and 6 of the accompanying drawings.

FIG. 1 shows a known form of commutating hybrid;

FIG. 2 shows the known connection of a plurality of such commutating hybrids to form a multiplexer;

FIG. 3 shows the phase delay at the output of the delay line as a function of frequency;

FIG. 4 is a block diagram of a modified commutating hybrid incorporating a phase correction circuit in accordance with the invention,

FIG. 5 is a graph generally similar to FIG. 3 showing variations in the phase characteristic of a delay line with variation of the mismatch in the stubs of the frequency correcting network, and

FIG. 6 is an exploded view of the phase correcting network shown in FIG. 4.

Referring now to FIG. 4, a modified commutating hybrid generally designated 10' includes two 3dB couplers l2 and 14 the interconnections between which include a delay line 16. To compensate for the nonlinearity of the phase characteristic in the delay line 16 there is inserted in the latter line a phase correcting network which is enclosed within the dotted line and is generally designated 15. The phase correcting network 15 includes a 3dB coupler 18 whose inputs are connected into the delay line 16 and whose outputs are connected to

stubs

20 and 22 which are lengths of waveguide terminated in a short-circuit represented by the symbols S/C in the drawing. Along the length of each waveguide there is a mismatch 24/26 and whilst only one mismatch is shown in each stub it is to be understood that more than one may be included if desired.

In order to explain the operation of the phase correcting network 15 in FIG. 4 let it first be assumed that the

mismatches

24 and 26 are absent. At the shortcircuited end of the

stubs

20 and 22 the electromagnetic wave travelling in the waveguide would be reflected and the effect of this would be that any signal arriving at the 3dB coupler 18 from the 3dB coupler 12 will be passed by the 3dB coupler 18 to the 3dB coupler 14 after a phase delay corresponding to twice the length of the stub 20. In effect, the wave arriving at one input of the 3dB coupler is split equally between the

stubs

20 and 22 and upon deflection from the shortcircuited ends of the

stubs

20 and 22 the waves combine again to provide constructive interference at the other input of the 3dB coupler 18. If now the effect of the mismatches is considered, it will be realized that standing waves are set up within the

stubs

20 and 22 and the effect of each mismatch will depend upon the intensity of the electric and magnetic waves at that point and this will in turn depend on the frequency. Thus, for certain frequencies where the electric and magnetic fields are a minimum at the location of the mismatch the mismatch will be of little effect whereas where the electric and magnetic fields are a maximum there will be partial reflection at the mismatch and this will shorten the phase delay of the signals received after reflection. The effect of various mismatches is shown in FIG. 5, in which the basic curve C has been modified to the curves C and C by including mismatches of different susceptance within the

stubs

20 and 22. It will be seen that where the mismatch has positive susceptance +jB the modified phase characteristic is more curved than the curve C but in the same sense whereas if the susceptance is negative the curvature is in the oppposite sense. It will be appreciated that by suitably choosing a negative susceptance it is possible to approach the ideal linear dotted line I within the range f1 and f2 in FIG. 5.

The physical construction of the phase correcting network will now be described with reference to FIG.

6. Two

grooves

30 and 32 are machined in

copper blocks

34 and 36 which upon mating together define two rectangular waveguides. The

blocks

34 and 36 are provided with holes 38 through which bolts are passed to keep the blocks together. Slots 40 are formed in the dividing wall 42 between the

grooves

30 and 32 and this provides for energy transfer between the waveguides and, as is known, such an arrangement can constitute a 3dB coupler. The ends of the

waveguides

30 and 32 to the right of the slots in the drawing constitute the inputs to the 3dB coupler and the other ends of these waveguides constitute the outputs. Secured to the end of the

blocks

34 and 36 is a further block 44 which is formed with blind rectangular bores 46 having the same dimensions as the waveguides. Elongate slots 48 are formed in the block 44 and bolts pass through these slots into the

blocks

34 and 36 to secure the block 44 in position. The stubs are thus constituted by the shortcircuited waveguides which terminate in the block 44 and the mismatch may be achieved by laterally moving the block 44 in an up and down direction as viewed relative to the

blocks

34 and 36 so as to provide a mismatch between the sections of the stubs inside and outside the block 44.

I claim:

1. A phase correcting network for improving the phase/frequency characteristic of a delay line including a 3dB coupler adapted to be inserted in the said delay line and terminated in a pair of short circuited waveguide stubs, each of said waveguide stubs being susceptance loaded by means of at least one mismatch achieved by laterally displacing sections of the waveguide relative to one another in the direction of the H- plane.

2. A phase correcting arrangement comprising a plurality of phase correcting networks as claimed in claim 1 connected in series with one another.

3. A phase correcting network for improving the phase/frequency characteristic of a delay line comprising in combination a 3dB coupler having two input ports and two output ports, said two input ports being connected into the delay line for the purpose of transporting signals to and from said delay line; and

first and second waveguide means, each connected to one of said two output ports and each terminating in a common short circuit so that any signal arriving at one input port of said 3dB coupler is split equally between said two waveguide means and, upon deflection from the short circuit terminations of said waveguide means, the split signals recombine in said 3dB coupler so as to provide constructive interference at the second input port of said 3dB coupler, said waveguide means imposing on said recombined signal a phase delay which, without further modification to said waveguide means, is non-linear in relationship to the frequency;

wherein said first and second waveguide means are adapted to be subjected to at least one mismatch caused by the lateral displacement in each waveguide means of one section of said waveguide means with respect to the other section of said waveguide means in the direction of the plane of the magnetic field of the signal, said mismatches having susceptances of such polarity and magnitude as to cause the phase-frequency characteristic of the delay line to become linear in nature.

4. A phase correcting arrangement comprising a plurality of phase correcting networks as claimed in claim 3 connected in series with one another.

5. A phase correcting network as recited in claim 3 wherein said first and second waveguide means are rectangular in cross section and are formed by the mating of two copper blocks, into each of which there is machined a rectangular groove.

6. A phase correcting network as recited in claim 5 wherein the short circuiting termination of said waveguide means comprises a further copper block containing rectangular bores, one for each waveguide means and of the same dimension as said waveguide means, and so positioned at the opposite end of said waveguide means from said 3dB coupler that said waveguide means may be subjected to lateral mismatch by moving said further copper block in a direction perpendicular to said waveguide means.

7. [n a commutating hybrid network which includes a first 3dB coupler having two input ports, one connected to a load and the other connected to receive a multifrequency signal, and two output ports;

a second 3dB coupler having two input ports, a first input port connected directly to the first output port of said first coupler and a second input port connected indirectly to the second output port of said first coupler, and two output ports for transmitting two output signals;

and a delay line means in the connection between the second output port of said first coupler and the second input port of said second coupler to form the indirect connection therebetween so that a multifrequency signal transmitted by the second output port of said first coupler and passing through said delay line means undergoes separation into component signals so as to introduce a phase delay between said component signals, with the relationship between the phase delay and the fre uency being non-linear in nature;

the improvement wherein said delay line means comprises a phase correcting network which includes a third 3dB coupler having two input ports, a first input port connected to the second output of said first coupler, and a second input port connected to the second input port of said second coupler, and two output ports; and

first and second waveguide means, each connected to one of the output ports of said third 3dB coupler and terminated in a short circuit, and each adapted to be subjected to at least one mismatch caused by the lateral displacement in each waveguide means of at least one section of said waveguide means with respect to the other section of said waveguide means in the direction of the plane of the magnetic field of the signal, said mismatches having susceptances of such polarity and magnitude as to cause the phase-frequency characteristic of the delay line to become linear in nature.

8. Apparatus for combining and for separating a plurality of signals whose frequencies are distributed within a given range of frequencies, comprising in combination:

an array of commutating hybrids, each hybrid comprising first and second waveguide means for defining a pair of ports at one end of the hybrid and a further pair of ports at the other end of the hybrid in which one of said ports defines a load termination, a first 3dB coupler connected between said first and second waveguide means at said one end of the hybrid and a second 3dB coupler connected between said first and second waveguide means at said other end of the hybrid to define a predetermined waveguide length between said couplers within said first waveguide means. said second waveguide means defining a delay line between said couplers having a length greater than said predetermined length;

said second waveguide means comprising separate waveguide sections and a further 3dB coupler connecting such sections to provide a pair of waveguide stubs, and means terminating said waveguide stubs in short circuits whereby to provide susceptance loading of said stubs, at least one of said stubs having a mismatch along its length to provide susceptance loading which establishes a desired phase-frequency characteristic of the distribution of said frequencies within said range.

9. Apparatus as defined in claim 8 wherein said mismatch is effected by separating said one stub into two sections, one of which is displaced relatively to the other in the direction of the H-plane.

10. Apparatus as defined in claim 8 including a second mismatch along the length of the other waveguide stub, one mismatch establishing positive susceptance loading and the second mismatch establishing negative susceptance loading, the two loadings being related so as to provide a linear phase-frequency characteristic for said frequencies.

11. Apparatus as defined in claim 10 wherein said stubs are parallel and said mismatches are effected by separating said stubs into two sections which are displaced relatively to each other in the direction of the H-plane.

* a it

Claims

1. A phase correcting network for improving the phase/frequency characteristic of a delay line including a 3dB coupler adapted to be inserted in the said delay line and terminated in a pair of short circuited waveguide stubs, each of said waveguide stubs being susceptance loaded by means of at least one mismatch achieved by laterally displacing sections of the waveguide relative to one another in the direction of the H-plane.

3. A phase correcting network for improving the phase/frequency characteristic of a delay line comprising in combination a 3dB coupler having two input ports and two output ports, said two input ports being connected into the delay line for the purpose of transporting signals to and from said delay line; and first and second waveguide means, each connected to one of said two output ports and each terminating in a common short circuit so that any signal arriving at one input port of said 3dB coupler is split equally between said two waveguide means and, upon deflection from the short circuit terminations of said waveguide means, the split signals recombine in said 3dB coupler so as to provide constructive interference at the second input port of said 3dB coupler, said waveguide means imposing on said recombined signal a phase delay which, without further modification to said waveguide means, is non-linear in relationship to the frequency; wherein said first and second waveguide means are adapted to be subjected to at least one mismatch caused by the lateral displacement in each waveguide means of one section of said waveguide means with respect to the other section of said waveguide means in the direction of the plane of the magnetic field of the signal, said mismatches having susceptances of such polarity and magnitude as to cause the phase-frequency characteristic of the delay line to become linear in nature.

7. In a commutating hybrid network which includes a first 3dB coupler having two input ports, one connected to a load and the other connected to receive a multifrequency signal, and two output ports; a second 3dB coupler having two input ports, a first input port connected directly to the first output port of said first coupler and a second input port connected indirectly to the second output port of said first coupler, and two output ports for transmitting two output signals; and a delay line means in the connection between the second output port of said first coupler and the second input port of said second coupler to form the indirect connection therebetween so that a multifrequency signal transmitted by the second output port of said first coupler and passing through said delay line means undergoes separation into component signals so as to introduce a phase delay between said component signals, with the relationship between the phase delay and the frequency being non-linear in nature; the improvement wherein said delay line means comprises a phase correcting network which includes a third 3dB coupler having two input ports, a first input port connected to the second output of said first coupler, and a second input port connected to the second input port of said second coupler, and two output ports; and first and second waveguide means, each connected to one of the output ports of said third 3dB coupler and terminated in a short circuit, and each adapted to be subjected to at least one mismatch caused by the lateral displacement in each waveguide means of at least one section of said waveguide means with respect to the other section of said waveguide means in the direction of the plane of the magnetic field of the signal, said mismatches having susceptances of such polarity and magnitude as to cause the phase-frequency characteristic of the delay line to become linear in nature.

8. Apparatus for combining and for separating a plurality of signals whose frequencies are distributed within a given range of frequencies, comprising in combination: an array of commutating hybrids, each hybrid comprising first and second waveguide means for defining a pair of ports at one end of the hybrid and a further pair of ports at the other end of the hybrid in which one of said ports defines a load termination, a first 3dB coupler connected between said first and second waveguide means at said one end of the hybrid and a second 3dB coupler connected between sAid first and second waveguide means at said other end of the hybrid to define a predetermined waveguide length between said couplers within said first waveguide means, said second waveguide means defining a delay line between said couplers having a length greater than said predetermined length; said second waveguide means comprising separate waveguide sections and a further 3dB coupler connecting such sections to provide a pair of waveguide stubs, and means terminating said waveguide stubs in short circuits whereby to provide susceptance loading of said stubs, at least one of said stubs having a mismatch along its length to provide susceptance loading which establishes a desired phase-frequency characteristic of the distribution of said frequencies within said range.