MIL-STD-220 Method Of Insertion Loss MeasurementThis standard covers a method of measuring, in a 50 ohm system, the insertion loss of feed-through suppression capacitors, and of single and multiple circuit radio frequency RF filters at frequencies up to 10 gigahertz GHz.

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MIL-STD-220C

APPENDIX A

FIGURE A-I.  Insertion loss good filter and shell ground.

Here are some things that can influence the result and some are easily correctable and there are some that will take time to correct.  The ground path of each circuit consists of the following elements in series:

The array electrode material, the ground plating, the array ground spring, the connector shell plating, and the attachment to the bulkhead.

Each one of these can decouple the filter from ground.  Since we are dealing with an RF signal, as frequency increases the capacitance reactance decreases.  Since it is in series to ground with the self inductance of each of the above items, the performance of the filter will be limited once the capacitance reactance equals and becomes less than the inductive reactance of these elements.

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