Wave transmission lines and networks – Long line elements and components – Strip type
Patent
1997-12-23
1999-11-30
Pascal, Robert
Wave transmission lines and networks
Long line elements and components
Strip type
333260, 333 33, 174262, H01P 308, H05K 111
Patent
active
059949830
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention is related to a microwave circuit comprising a two-sided substrate having a lead-through structure for interconnecting a first microstrip conductor segment on the upperside of the substrate with a second microstrip conductor segment on the underside of the substrate. The invention further relates to a sealed design of such a microwave circuit, in which the sealing is obtained by means of a metal lid which is arranged on the substrate. Furthermore the invention is related to a use of such a microwave circuit as a function module unit in a circuit arrangement which is built by modules.
Microwave signals are the designation of electrical signals in the frequency range 0.5-50 GHz. Microwave circuits for handling such microwave signals generally consist of a substrate of an insulating material, commonly aluminum oxide. By sputtering followed by plating of a pattern on the substrate transmission conductors, resistors and optionally capacitors may be built. Remaining components are soldered or glued onto the substrate.
A general problem in microwave circuits of the type in question is that the high signal frequencies involved demand electrical matching at existing interfaces in the circuit, meaning that channels in which signals are transmitted and meeting each other at said interfaces shall have identical impedances, customarily 50 Ohm. For example, interfaces of this kind appear between inherent circuit elements and between different conductor sections. Impedance differences at said interfaces give rise to partial reflection of the signal and a consequent loss of power. The loss of power increases with an increasing frequency. The signal power is expensive at the high frequency levels involved, specifically in applications requiring a high output power level. From this it follows that the quality demands on matching are very high.
The provision of good matching at all interfaces in a microwave circuit means very often that difficult problems must be solved by the circuit design. Specifically, this problem is prominent when using a two-sided substrate in which the signal path for external connection of the circuit includes a metal plated hole, a so called through-hole, passing the substrate and interconnecting microwave components on the upperside of the substrate with an external connection terminal on the underside of the substrate. Said through-hole introduces discontinuities in the impedance level of the signal path. The through-hole shows an increased characteristic impedance due to the fact that an adjoining groundplane is missing. This part of the transmission line corresponds to an inductive series connected element. Furthermore, the conductors which are connected to said hole cross over a groundplane free area immediately adjoining the through-hole, said conductors introducing further inductive series elements.
Prior art in this field teaches the introduction of a compensating capacitive parallel element adequately positioned along the transmission line in the neighborhood of said hole by decreasing the distance between conductor and ground, widening of the microstrip conductor over a short distance, or a parallel connection of a distributed or a concentrated capacitive element of adequate design.
This compensation technology means a consequent introduction of a lowpass filter structure having an upper frequency limit restricting the usefulness of the lead-through.
One example of this prior art in a microwave circuit of the kind mentioned in the introduction has been disclosed in U.S. Pat. No. 4,626,805.
The disclosed microwave circuit (24) comprises a two-sided substrate (26), carrying on the upperside the microwave components of the microwave circuit and the transmission line for interconnecting the same and external connection of the microwave circuit, the underside being provided with a ground plane, coplanar conductors and external connection terminals. The external connection is provided by means of a through-hole (40) in said substrate which interconnec
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patent: 5428327 (1995-06-01), Bahl
patent: 5832598 (1998-11-01), Greenman et al.
Pascal Robert
Sivers Ima AB
Summons Barbara
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