Inductor devices – Coil forms protective casing
Reexamination Certificate
1998-02-20
2003-01-21
Donovan, Lincoln (Department: 2832)
Inductor devices
Coil forms protective casing
C336S200000, C336S221000, C336S231000, C336S233000
Reexamination Certificate
active
06509821
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lumped element inductors for use in very high frequency microwave applications, and more particularly to such inductors configured to operate over a wide bandwidth and to have a high low frequency Q.
2. Description of the Related Art
Lumped element inductors are commonly used in sub-microwave applications. Such inductors are typically used as elements in a filter, or as bias coils for injecting current into a transmission line of a circuit without disturbing the impedance of a transmission line. Such inductors generally include a coil of thin wire with either air, ceramic, or a ferrite material in the center of the coil.
Most lumped element inductors do not work adequately at microwave frequencies, especially over broad frequency ranges. The problem is intercoil capacitance which resonates with the coil inductance and produces a “glitch” at one or more frequencies where insertion loss through the coil will be significant. A glitch occurs at the Self Resonant Frequency (SRF) of the coil and is well recognized.
Generally, the larger the inductance of the coil, the higher the intercoil capacitance, and the lower the SRF for the coil. As the diameter of windings, diameter of the coil wire, and the number of turns of the coil are decreased, the coil will have a lower intercoil capacitance and a higher SRF, but the coil will also have a lower inductance. As the diameter of the turns get reduced to zero, the inductor becomes a distributed element and operates over a very limited frequency range. An example is a quarter wave shorted bond wire.
A well known technique for increasing the inductance of a coil is the use of a ferrite or other magnetic material core. A coil wrapped around a ferrite core will have much higher inductance than a coil without such a core, but generally intercoil capacitance will also increase and the SRF of the coil will be much lower. A coil with relatively thick wire and a ferrite material core may have a SRF of 25 MHZ, while a coil with thin wire, small diameter turns, and a limited number of turns may have a SRF as high as 10 GHz.
The two major applications of inductive coils, filter elements and bias lines have different requirements. Good filter structures require high Qs, necessitating near perfect inductive components, so inductors which are lossy due to a high resistance or high intercoil capacitance are undesirable. A bias coil merely has to look like a high impedance so that it does not cause mismatches on the transmission line, and the Q is unimportant.
A method of reducing resonant loss glitches is to put a resistor in parallel with the coil or use high resistance wire to make the coil. Unfortunately this also reduces the Q of the inductor making the inductor undesirable for filter structures.
For high frequency microwave applications, it is, thus, desirable to provide an inductor which does not experience significant resonant losses and which operates over a wide bandwidth while providing a high Q.
SUMMARY OF THE INVENTION
The present invention substantially eliminates resonant loss glitches from an inductive coil, while enabling the inductive coil to operate, over a wide bandwidth and provide a high Q at low frequencies.
The present invention is a microwave inductor including a coil with windings tapered from a first end of the coil to a second end of the coil. The diameters of the coil windings are tapered to reduce resonant loss found in typical inductors which have uniform diameter windings. With uniform diameter windings, each coil winding and its associated intercoil capacitance resonates at a common frequency. However, with a tapered coil, each winding and its associated intercoil capacitance is slightly different, and resonant losses are much less pronounced.
The coil further includes a core made up of a dielectric material containing a colloidal suspension of magnetic particles. Preferably, the magnetic material is iron powder, while the dielectric is an epoxy resin, making the core a poly-iron material. With the core made up of magnetic particles colloidally suspended in a dielectric, rather than a conventional core containing a solid mass of ferrite material, the core will have a low resistive loss at low frequencies enabling the coil to have a high Q. The resistive loss will increase at higher frequencies to reduce resonant loss glitches and enable the inductor to function through its SRF to higher frequencies well above its SRF. Further, because the suspended magnetic particles have magnetic permeability, the coil will have an increased inductance at higher microwave frequencies. As such, a single coil can be utilized in both a filter which requires a high Q at low frequencies, and as a bias line which requires a large resistance at high frequencies. By using a core composed of a mixture of magnetic particles and dielectric material, the percentage of magnetic particles relative to the dielectric material can be controlled to set the inductance value for a coil.
REFERENCES:
patent: 1727932 (1929-09-01), Medved
patent: 2255730 (1941-09-01), Frazier
patent: 2351604 (1944-06-01), Ferrill, Jr.
patent: 2442776 (1948-06-01), Newkirk
patent: 2547412 (1951-04-01), Salisbury
patent: 3812438 (1974-05-01), Hopfer
patent: 4087791 (1978-05-01), Lemberger
patent: 4236127 (1980-11-01), Scherba
patent: 4343029 (1982-08-01), Renga et al.
patent: 4429314 (1984-01-01), Albright
patent: 4543208 (1985-09-01), Horie et al.
patent: 4893105 (1990-01-01), Maeda et al.
patent: 4947065 (1990-08-01), Ward et al.
patent: 5321965 (1994-06-01), Baird
patent: 5679402 (1997-10-01), Lee
patent: 5715531 (1998-02-01), Liu et al.
patent: 5838215 (1998-11-01), Gu et al.
patent: 4-115507 (1992-04-01), None
Anritsu Company
Donovan Lincoln
Fliesler Dubb Meyer & Lovejoy LLP
Nguyen Tuyen
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