US1898180A

US1898180A - Coupling arrangement

Info

Publication number: US1898180A
Application number: US221091A
Authority: US
Inventors: Clarence W Hansell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1927-09-21
Filing date: 1927-09-21
Publication date: 1933-02-21
Anticipated expiration: 1950-02-21
Also published as: GB297434A; DE508899C; BE354357A

Description

Feb. 21, 1933. c. w. HANSELL COUPLING ARRANGEMENT Filed Sept; 21, 1927 4 m j/rI 0 n 0 H a N 2 2 00 w. w 9 $0YN QSQRwQ RA 7/0 0/-' INPUT 70 OUTPUT RfS/STAA/C! INVENTOR CLARENCE W. HRNSELL BY I I J22 /m AT RNEY Patented Feb. 21, 1933 UNITEDSTATES PATENT orricr.

CLARENCE w. rmnsnrr, or Ros n: 201m NEW YORK, ASSIGNOR ro arre CORPORATION or ensures, A corgronerron or DELAWARE COUPLING ARRANGEMENT Application filed September 21, 1927, Serial No. 221,091.

This invention relates to coupling arrangements. d e pa u ar y t su h. M'- rangements used to change impedance and phase relation.

It is frequently desired to couple circuits together with a change in impedance, as, for example, when matching theimpedance at the junctions in branched transmission With very high frequencies it is not feasible to obtain the desired impedance changes by the use of simple transformer circuits because insulation is so difiicult that reasonably close coupling between the primary and secondary is impossible. To use a parallel resonant circuit and couple the output at variable tapping points on the inductance of the circuit makes it impossible to obtain zero phase shift, and is relatively inefficient for it involves high losses owing to the circulating current in the resonant circuit.

Ithas been proposedto couple aseries circuit of inductive and capacitive reactances across one of the external circuits, and to couple the other external circuit across either the inductive or capacitive reactance. This arrangement is satisfactory but has the disadvantage that there is involved an inherent phase shift the direction of which is determined by that reactance across which the second external circuit is coupled, and the magnitude of which is fixed for any given impedance ratio. It is an object of my invention to provide a coupling arrangement which is efficient even at very high frequencies and which permits optional impedance change and phase shift.

To do this I change the impedance successively by means of cascade connected coupling circuits the impedance ratios of which are such that their product equals the desired ratio, and the phase shifts in which are such that their algebraic sum equals the desired phase shift. In the special case of zero phase shift the arrangement comprises two of the series circuits such as have been described, the impedance ratios of which are equal to the square root of the desired overall impedance ratio, and the phase shifts in which are equal but opposite in direction, a 50 result which is obtained by coupling the second coupling circuit to the first coupling circuit across either the inductive or capaci tive reactance, and coupling the second external circuit to the second coupling circuit across the capacitive or inductive reactance, respectively. in The invention is described more in detail in the following specification which is accompanied by a drawing in which it Figure 1 and Figure 2 represent known 60 coupling circuits; 8 i I Figure 3 is a combination of known cir cuits embodying my invention;

Fi ure 4 is a graph which is useful when selecting the circuit constants; and i i Figure 5 symbolically indicates an application of my invention.

Referring to Figure 1 there is shown a series circuit comprising the inductances 2 and the capacitance 4, which are connected 7o by means of the terminals 6 to an external circuit. The terminals 8, connected to condenser 4, lead to a second external circuit. The reactance values are so chosen that when the parallel circuit consisting of the resist: ance of the output circuit and the capacitance 4 is transposed to an equivalentseries circuit of capacitance and resistance the inductance 2 resonates with the fictitious series capacitance, and the fictitious series resist+ 8o ance is equal to the desired line impedance. In the direction from the terminals'fi to the terminals 8 the impedance is stepped up, but by connecting the circuit in the oppositeldirection the impedance may be stepped down. 8;; Figure 2 is similar to Figure 1 except that the terminals 18 have been connected to the inductive reactance 12 instead of to the capacitive reactance 14. In this case theparallel circuit consisting of the resistance of Q0 the second external circuit, that is, the circuit across the terminals 18, and the indlittance 12, may be transported into an equivalent series circuit of inductance andresistance, and the capacitance 14 resonates with 95, the fictitious inductance, while the fictitious resistance is the desired line impedance for the external circuit connected to the terminals 16. i In Figure 4 the curve 20 shows the degrees 199 of phase shift between the first and second external circuits as a function of the impedance ratio. It is clear that when employing circuits such as have been shown in Figures 1 and 2 the curve 20 is symmetrical, the phase shifts for either the capacitive or inductive couplings being equal for a given impedance ratio, but opposite in direction.

Adverting now to Figure 3 it will be seen that in accordance with my invention the coupling arrangement comprises a combination of the circuits shown in Figures 1 and 2. In this manner if the impedance ratios are equal the resultant phase shift is zero. .Thus, in the special case where zero phase shift is desired the two circuits are so designed that the impedance ratio of each is equal to the square root of the desired ratio, so that the overall ratio is that desired, and meanwhile the equal but opposite phase shifts in the two parts of the coupling arrangement neutralize one another so that the resultant phase shift is zero.

In the more general case the requirement for a desired impedance ratio accompanied by a desired phase shift is met by combining circuits the product of the impedance ratios of which is that desired while the algebraic sum of the phase shifts in which is that desired, which involves factoring the desired product into those factors, from among the many possible groups of factors, which give the correct phase shift. This selection may be readily accomplished by the use of a chart such as has been shown in Figure 4, the

curves

22, 24, 26 and 28 of which are plotted to the same scale of ordinates and abscissae as the curve 20, but which represent overall impedance ratio as a function of overall phase shift when using the combined circuit shown in Figure 3. The curve 22 is obtained by assuming that the impedance ratio of one of the circuits is 0.2 and taking various values from zero to one for the other circuit. The curve 24 is obtained by assuming that the impedance ratio of one of the circuits is 0.4 and taking various values for the other circuit. Similarly

c'urves

26 and 28 are obtained by assuming impedance ratios of 0.6 and 0.8 re spectively for one of the circuits.

The chart may be used as follows. A point representing the desired impedance ratio and phase shift is located on the chart, such as the point 30, located at an impedance ratio of 0.4 and a phase shift of 30 degrees lagging. The point 30 is followed out on a line 32, approximated from the nearest adjacent curve, until it intersects the curve 20, which indicates the phase shift and the impedance ratio for one of the coupling circuits to be 48 and 0.45. The impedance ratio of the other of the circuits may be obtained by dividing the desired ratio by the ratio found for the first circuit, which comes out 0.89, or by subtracting the desired phase shift from the phase shift in the first circuit to obtain the phase shift in the second circuit, namely, 18 leading, and locating the impedance ratio for that phase shift on the curve 20, giving slightly less than 0.9, which is as it should be.

So, in Figure 4, the lines 34-and 36 represent the impedance ratio and phase shift for one of the circuits, while the

lines

38 and 40 represent the impedance ratio and phase shift for the other of the circuits. It will be seen that the phase shifts differ by 30 degrees, and that the product of the impedance ratios equals 0.4, as was desired.

The chart as drawn serves only for values of ratio and shift which lie within the boundaries of Y the curve 20, for it has been assumed that the circuits have phase shifts of opposite sense and impedance ratios of like sense, which is the more usual case. It is clear, however, that the chart may be extended to include more general cases by continuing the

curves

22, 24, 26 and 28, which is done by taking impedance ratios for the second circuit which are greater than unity. One such curve is shown in Figure 4, curve 22. To obtain ratios greater than unity one of the coupling circuits in Figure 3 is re versed.

An application of my invention is indicated in Figure 5, in which there are

broadside antennae

102 and 104, with

energized reflectors

106 and 108, fed by

transmission lines

110 and 112, which in turn are fed by a transmission line 114. Such antennae are described in a copending application of Nils E. Lindenblad, Serial No. 229,407, filed October 28, 1927. If the

transmission lines

110 and 112 are similar to the transmission line 114 their combined impedance is half of that of line 114, and therefore impedances must be matched at the junction point 116. At this junction a phase shift is not injurious, and therefore the older type of coupling arrangements may be employed. But at the

points

118 and 120, where the line impedances also must be matched, the relative phase of the energies supplied to the

antennae

102 and 106 is of great importance, for their phase displacement should equal the natural phase displacement of the wave in space at points spaced at the distance between the antenna 102 and the reflector 106. To meet this requirement my coupling arrangement may be applied at the

points

118 and 120, and similarly at the

points

122 and 124 for the other antenna.

I claim 1. The method of obtaining a desired impedance ratio and a desired phase shift which includes changing the impedance successively by ratios the product of which equals the desired ratio, and accompanying the impedance changes with phase shifts the algebraic sum of which equals the desired phase shift.

2. The method of obtaining a desired impedance ratio with no phase shift which includes changing the impedance by a ratio which is the square root of the desired ratio accompanied by a phase shift in one direction, and again changing the impedance by the square root of the desired ratio accompanied by an equal phase shift in the opposite direction.

3. A coupling arrangement for obtaining a desired impedance ratio and a desired phase shift comprising a plurality of cascade connected impedance changing devices the procluct of the ratios of which equals the desired ratio and the algebraic sum of the phase shifts in which equals the desired phase shift.

4. A coupling arrangement for obtaining a desired impedance ratio with no phase shift comprising a plurality of cascade connected impedance changing devices having impedance ratios the product of which equals the ratio desired, and the algebraic sum of the phase shifts in which equals zero.

5. A coupling arrangement for obtaining a desired impedance ratio with no phase shift comprising two impedance changing devices having equal impedance ratios, and equal but opposite phase shifts, connected in cascade.

6. An arrangement for changing impedance and phase by desired amounts comprising an external circuit, a coupling circuit connected thereto and having inductive and capacitive reactances in series, a second coupling circuit having inductive and capacitive reactances in series coupled across a reactance of one sign of the first coupling circuit, and a second external circuit coupled across a reactance of another sign of the second coupling circuit.

7. An arrangement for changing impedance and phase by desired amounts comprising an external circuit, a coupling circuit connected thereto and having inductive and capacitive reactances in series, a second coupling circuit having inductive and capacitive reactances in series coupled across a reactance of one sign of the first coupling circuit, and a second external circuit coupled across a reactance of another sign of the second coupling circuit, the coupling circuits having impedance ratios the product of which equals the desired ratio, and phase shifts the algebraic sum of which equals the desired phase shift.

8. An arrangement or changing impedance and phase by desired amounts comprising an external circuit, a coupling circuit connected thereto and having inductive and capacitive reactances in series, a second coupling circuit having inductive and capacitive reactances in series coupled across the inductive reactance of the first coupling circuit, and a second external circuit coupled across a capacitive reactance of the second coupling circuit.

9. An arrangement for changing impedance and phase by desired amounts comprising an external circuit, a coupling circuit connected thereto and having inductive and capacitive reactances in series, a second coupling circuit having inductive and capacitive reactances in series coupled across the inductive reactance of the first coupling circuit, and a second external circuit coupled across the capacitive reactance of the second coupling circuit, the coupling circuits having impedance ratios the product of which equals the desired ratio, and phase shifts the algebraic sum of which equals the desired phase shift.

CLARENCE W. HANSELL.