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EXTERNALLY RESISTIVE SHIELDED TRANSMISSION LINE

IP.com Disclosure Number: IPCOM000198144D
Publication Date: 2010-Jul-27
Document File: 8 page(s) / 70K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique relating to an externally resistive shielded transmission line is disclosed. This technique proposes modifying the surface characteristics, either material or geometric, of an outer shield of a a transmission line in order to make it dissipative.

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RP13440

BRIEF ABSTRACT

    A technique relating to an externally resistive shielded transmission line is disclosed. This technique proposes modifying the surface characteristics, either material or geometric, of an outer shield of a a transmission line in order to make it dissipative.

KEYWORDS

    Shielded transmission line, current, outer shield surface, coating, coaxial cable, dissipative, sheathing, surface characteristics

DETAILED DESCRIPTION

    Coaxial cables generally include an inner conductor surrounded by a flexible, tubular insulating layer, which is further surrounded by a tubular conducting shield which transmits signals. Coaxial cable is commonly used as a transmission line for radio frequency signals. In numerous instances of signal measurement and transmission applications it is necessary to shield a signal. However, it is necessary to have currents flowing on the outer shield surface in certain applications. In such applications, external signals couple to the outer shield surface, propagate to one end of the transmission line and enter the signal path.

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EXTERNALLY RESISTIVE SHIELDED TRANSMISSION LINE

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RP13440

    Further, in some applications externally induced currents set up standing waves, causing potentially detrimental local heating or voltage break-down. In some instances, the outer shield surface provides a path to a ground state for a signal, thereby reducing the proportion of available signal reaching the receiver or detector. Additionally, the outer shield surface also reduces the signal to noise ratio.

    Conventionally, above mentioned problems are addressed by threading a shielded transmission line through ferrite cores or by using a balun, such as a cable trap or a bazooka balun. A balun is a type of electrical transformer that converts electrical signals that are balanced (differential) to signals that are unbalanced (single-ended) and vice versa. The use of ferrite cores is limited to applications where ferrites can be used. For instance, ferrite suppression is not used in areas with high magnetic fields, such as magnetic fields encountered in MRI.

    Generally, non-ferrite baluns are bulky, function only at specified operating frequencies, and add to the cost and complexity of the construction. Further, baluns only provide current suppression at specific points of the shield, thus requiring several baluns in applications where longer cables are required.

    Therefore there is a need in the art for a technique to effectively shield a signal in transmission applications without affecting the currents flowing on the outer shield surface.

    In numerous applications, signals in a shielded transmission line need to be on the shielded conductors and the inner side of the shield. According to the present technique, the outer surface of the shield is made glossy or resistive. Resistive outer surface provides a mechanism to suppress currents running through, while not affecting the desired signal flow path.

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