Wave transmission lines and networks – Long lines
Patent
1985-01-02
1987-01-20
Gensler, Paul
Wave transmission lines and networks
Long lines
178 45, 333 22R, H01P 304
Patent
active
046382720
DESCRIPTION:
BRIEF SUMMARY
This invention relates to transmission lines particularly lossy transmission lines, which are defined as cables or lines having high attenuation per unit length.
The characteristic impedance (Zo) of a transmission line is normally characterized in terms of the distributed series resistance (R) and inductance (L) elements, and the distributed shunt conductance (G) and capacitance (C) elements, by the following expression: ##EQU1##
The attenuation constant (.alpha.) is given by the expression
For open wire lines G approaches zero, and for low loss lines R<<wL, hence ##EQU2##
For conventional lossy lines where the series resistance is the significant loss element, ##EQU3## which can be rearranged into the form ##EQU4## and
The capacitive reactance (-b) component of Zo will cause a mismatch between the lossy line and the normally purely resistive source.
The resulting mismatch, which is commonly specified in terms of the voltage standing wave ratio (VSWR), will typically govern the acceptability of the match and hence the ratio of R/wL has an upper limit determined by the highest acceptable VSWR.
Hence, for a given frequency range the value of resistance per unit length (R) has an upper limit which in turn determines the upper limit of attenuation (.alpha.).
In conventional lossy lines used as terminating units it is very desirable that they provide a minimum of 20 dB attenuation. Under this condition the termination at the far end of the line is of little or no importance in terms of matching at the input end of the line.
The minimum line length required to achieve 20 dB attenuation (.alpha.) for a specified line impedance (Zo), "match" (VSWR), and frequency range can therefore be determined.
The power capability of such a line is a function of the wire diameter and/or allowable temperature rise at the input end of the line.
By way of example, a typical conventional 600 .OMEGA. lossy transmission line exhibiting a VSWR of <1.5 and capable of dissipating 1 kW over the HF frequency range would need to be approximately 140 meters long to satisfy the VSWR requirement, but would need to be approximately 600 meters long to satisfy the power rating. (Assumes a maximum temperature rise of approximately 200.degree. C.-higher temperatures would require the use of impractically small wire diameters.)
Thus a disadvantage with conventional lossy lines is the long length required. This makes them unsuitable as terminating units for applications such as portable travelling wave antenna and may even make them unsuitable for fixed travelling wave antenna where space is at a premium.
Typically, terminating units for portable (and some fixed) travelling wave antenna consist of a "lumped" resistive element which may be required at the top of the antenna mast.
This is a distinct disadvantage, especially for high power transmitting antenna because of the significant wind loading on the terminating unit. This necessitates a more rugged mast and guy arrangement which consequently increases the weight and volume of the antenna and makes is less portable.
This invention describes an improved lossy transmission line which overcomes the disadvantages of:
It is an object of this invention to provide a short well matched lossy transmission line to replace long conventional lossy transmission lines or lumped resistive element terminating units.
To this end this invention provides a lossy line which exhibits approximately constant loss per unit length (watts/m) characterized in that a conventional low loss transmission line is modified by securing ferrite beads to the wire.
Ferrite beads have previously been proposed for use as absorbers of electromagnetic energy as detailed in German Pat. No. 2,524,300.
Ferrite beads have also previously been proposed for use as a means of artificially loading antenna elements to reduce their physical length as detailed in U.S. Pat. Nos. 2,748,386 and 3,303,208. However the fundamental and unique difference between the use of ferrite material as disclosed in these patent specifications, and the lo
REFERENCES:
patent: 1900962 (1933-03-01), Vezey
patent: 2228797 (1941-01-01), Wassermann
patent: 2748386 (1956-05-01), Polydoroff
patent: 3560889 (1971-02-01), Suetake et al.
patent: 4104600 (1978-08-01), Mayer
patent: 4233577 (1980-11-01), Raveglia et al.
Gensler Paul
The Commonwealth of Australia
LandOfFree
Lossy transmission line using spaced ferrite beads does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lossy transmission line using spaced ferrite beads, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lossy transmission line using spaced ferrite beads will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2137136