US2396708A - Impedance transformer - Google Patents

Description

March 19, 1946. L M. LET-:Ds 2,396,708

IMPEDANCE TRANSFORMER Filed Sept. 14. 1942 Fig. I. ff A/4/ v I i 3 f 6 Fig. 2.

Inventor:

Laur'ance M. Leeds,

b 8 His Attorneg.

Patented Mar. 19, 1946 UNITED'ISTATES PATENT OFFICE IMPEDANCE TRANSFORMER Laurance M. Leeds, Rotterdam Junction, N. Y.,

assignor to General Electric Company, a corporation of New York Applicationseptember 14, 1942, Serial No. 458,306 2 Claims. (Cl. 178-44) The present invention relates to an arrangement for improving the operation of a quarter wavelength transmission line used as an impedance matching transformer under conditions where there is unavoidable series or shunt reactance. The unavoidable reactance has the eifect of introducing an apparent reactance which has heretofore been compensated by changing the length of the transmission line with a resultant reduction in the transformer ratio.

The object of my invention is to 'provide an arrangement in which the effect of unavoidable -reactance is eliminated without changing the v series with a resistance 8 at the output. If the reactances X2 and X1 are related by the equation Zo =X2X1 I (1) where Z is the characteristic impedance of the transmission line, the transformer ratio between the input terminals 4 and the terminals '5 of the resistance. 3 is givenby the equation where Z1- is the terminating resistance 3 and Z. is the apparent value of this resistance measured at the input terminals 4.- This equation is identical with that which would be obtained if the reactances X2 and X1 were eliminated. The reactances X1, X2 accordingly provide perfect compensation without changing the impedance transformer ratio.

r The relations set forth above can be proved by considering the impedance at the input terminals 4 as equal-tothe reactance-Xa in parallel with from which it is apparent that the impedance ratio will be given by the equation- It will be noted that the reactances X1 and X: may be either inductances or capacitors and that either may be the unavoidable reactance. In the most'common case, the reactance & will be distributed capacity which will be compensated by a capacity X1 in series with the terminating resistance. p

In Fig. 2 the reactance X1'is in parallel with the terminating'resis'tance 3 and the reactance X2 is in series with the terminals 4 of the quarter wavelength transmission line I. The impedance connected across theterminals 5 consists of the terminating resistance Zr in parallel with the reactance X1 and is equal to ril r+j l where Xi may be eitherpositive (inductance) or negative (capacity).

The apparent'value at the terminals 4 or the impedance orthe transformer, is equal to the the rest of the. circuit. The inputimpedance Z; A

will be given by the equation or negative (capacity) The equation reduces to the form sum of the reactance X2 and the impedance at the terminals 4 is given by the equations As in Fig. 1, either of the reactances X1, X: may be lnductances or capacities and the effect of one is compensated by the other.

What I claim as new and desire to secure by Letters Patentot the'United States is:

transmission line and X is the reactance or the i0 unavoidable shunt capacity.

2. An impedance matching transformer comprising a quarter wavelength transmission line having a series reactance'at one end and a shunt reactanceat the other end, the reactances having values determined by the equation Zn'=X1Xzwhere Z0 is thecharacteristic impedance of the transmission line and X1 and x: are the respective reactances.

LAURANCE M. IEEDS.

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