Browse Prior Art Database

Broadband Miniature Balun

IP.com Disclosure Number: IPCOM000039688D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Coveyou, DJ: AUTHOR [+2]

Abstract

The balun (balanced/unbalanced line) has design and operation similar to prior full-size baluns but is miniature in size and is effective at high frequencies, such as 300-1000 MHz, to be unaffected by resonances caused by stray capacitances and inductances. Therefore, the balun has a broadband frequency response. A conceptual drawing of the balun is shown in Fig. 1. The two legs of the coax loop form what is essentially a one-turn transformer. The shield of the coax makes up the primary winding, and the center conductor is the secondary. The result is that the secondary has the same impedance as the primary (1:1 turns ratio), but it is isolated from the system ground (the shield of the input cable). In this way, the transformation is made from an unbalanced line to balanced. The length of each leg of the balun is important.

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Broadband Miniature Balun

The balun (balanced/unbalanced line) has design and operation similar to prior full-size baluns but is miniature in size and is effective at high frequencies, such as 300-1000 MHz, to be unaffected by resonances caused by stray capacitances and inductances. Therefore, the balun has a broadband frequency response. A conceptual drawing of the balun is shown in Fig. 1. The two legs of the coax loop form what is essentially a one-turn transformer. The shield of the coax makes up the primary winding, and the center conductor is the secondary. The result is that the secondary has the same impedance as the primary (1:1 turns ratio), but it is isolated from the system ground (the shield of the input cable). In this way, the transformation is made from an unbalanced line to balanced. The length of each leg of the balun is important. It was arrived at through experimentation with various lengths to find the best combination of frequency response, loss and balanced-to-unbalanced transition. Fig. 2 shows the preparation of the cable.

(Image Omitted)

The construction of the balun is shown in Fig. 3. The cable is prepared as shown, and the input line is connected; then the cable is formed into a loop. The shape of the loop is that which the cable assumes naturally. Connections are covered with heat-shrinkable tubing. It may be impractical to physically place the balun right where it is needed, because of its size. If this is the case, a balanced trans...