Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1998-04-01
2001-01-23
Hunter, Daniel S. (Department: 2749)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S078000, C455S080000, C455S081000, C455S082000, C333S012000, C333S204000, C333S246000
Reexamination Certificate
active
06178311
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to circuit boards and, more particularly, to methods of isolating stray high frequency signals in a circuit board.
BACKGROUND OF THE INVENTION
Despite the increased data transmission rates that are possible in landline and fiber optic networks, many communication systems employ radio frequency links to transmit and receive information. Such radio frequency links are used for point to point communication between telephone switches, between cellular telephone sites, or in satellite communication. For some high speed data communication applications some radio frequency links employ relatively high power transceivers, which may operate in the microwave frequency range.
A radio frequency (rf) transceiver typically includes a high power transmitter that broadcasts rf signals to a remote location and a receiver that detects weaker rf signals that are broadcast from the remote location. In a transceiver where the receiver is tuned to a frequency that is near the carrier frequency of the transmitter (or a multiple thereof), the transmitter may generate stray signals that could leak into the receiver and saturate it. When saturated, the receiver is generally unable to detect the rf signals that are transmitted from a remote location.
One prior art approach used to prevent the stray rf signals from leaking into a receiver is to physically separate the transmitter and the receiver. For example, a transmitter assembly may be placed in a separate cavity and shielded from the receiver assembly. While the physical separation of the transmitter assembly and the receiver assembly in two different cavities reduces the rf leakage problem, this approach typically increases the cost and overall dimensions of the radio transceiver.
Alternatively, attempts have been made to place the transmitter and receiver circuits on the same printed circuit board, while employing traditional shielding methods such as enclosing portions of the transmitter in a grounded metal shell or placing grounding holes or vias between the transmitter and receiver to isolate stray rf signals. However, such conventional isolation techniques generally do not prove effective in providing the desired level of isolation for satisfactory operation of a transceiver when operated at high power in certain applications.
Accordingly, there is a need for a better isolation technique for use in circuit boards to reduce the level of leakage signals from one portion of the board to another.
SUMMARY OF THE INVENTION
The present invention is a method of isolating portions of a circuit board in order to prevent signals from one part of the board from leaking into other parts of the board. In one embodiment of the invention, the isolating technique is used in a high power radio frequency transceiver having an integrated transmitter and receiver that are mounted on a single multilayer printed circuit board. The isolation technique involves placing a barrier strip between the transmitter and the receiver. The barrier strip is formed of an arrangement of grounding slots. The grounding slots may be oval in shape and staggered such that stray signals cannot pass through the barrier but signal traces on the board can be routed through the barrier strip.
According to another aspect of the invention, additional isolation is provided by placing a plurality of grounding holes or vias around those areas on the multilayer printed circuit board where a signal trace makes a transition from one layer to another layer on the printed circuit board.
According to yet another aspect of the present invention, microstrip filters are placed on the power or control lines at the point where such central lines pass from one area of the circuit board to another in order to further improve signal isolation. By placing microstrip filters on the power or control lines, the stray rf signals that may be induced onto the lines by the transmitter may be substantially prevented from reaching the receiver.
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Pance Gordana
Zoufonoun Amir H.
Christensen O'Connor Johnson & Kindness PLLC
Hunter Daniel S.
Western Multiplex Corporation
Zewdu Meless
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