Coaxial radio frequency test probe

Details Coaxial radio frequency test probe Coaxial radio frequency test probe

1996-07-19

2001-08-28

Elms, Richard (Department: 2824)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S761010

Reexamination Certificate

active

06281690

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved coaxial RF probe for testing or trouble-shooting microstrip circuits while avoiding the need for adding conventional coupled test ports or resistive network test ports, which test ports degrade the performance of microstrip circuits, require space and increase the cost and weight of the circuit board.
2. Discussion of the State of the Art
Manufacture and maintenance of a microstrip circuit require that functionality of various stages of the circuit be measurable. In RF circuitry it is conventional to incorporate coupled test ports on resistive network test ports at predetermined critical locations along the microstrip circuit in order to test, measure or trouble-shoot the performance of the circuit at these specific locations.
Such test ports have several disadvantages including being localized, expensive, requiring space and adding weight to the circuit board. More importantly, such test ports degrade the operation or performance of the circuit even when no tests are being performed.
It is also known to test the operation or performance of a microstrip circuit by means of a coaxial RF probe or sniffer probe having a central circuit contact and an outer coaxial jacket contact having a flexible ground wire designed to be clipped to a ground plane area spaced from the microstrip circuit. A DC-blocking device is associated with the central contact in order to provide a contact which protects the sensitive measurement device, such as a spectrum analyzer, power meter or other similar instrument against direct current damage.
While such conventional coaxial RF probes enable testing at any point along a microstrip circuit and avoid the need for test ports on the microstrip circuit, they do not have a reliable grounding system or provide a fixed-distance ground point and therefore their performance is erratic and unreliable. Any coaxial RF probe exhibits high electrical losses, and such losses are unpredictable and variable when the spacing between the microstrip contact and the ground contact is varied.
SUMMARY OF THE INVENTION
The present invention provides a novel, fixed-contact coaxial RF probe which avoids the problems of prior coaxial RF probes by fixing the distance between the circuit contact and the ground plane contact in order to provide reliable and repeatable measurements. The need for test ports, which degrade the performance of the microstrip circuit, is avoided. Also variation in the electrical losses normally encountered with the use of conventional coaxial RF probes having a flexible ground wire, depending upon the arbitrary distance between the ground contact and the microstrip contact, are eliminated so that the losses are predictable and balance each other with repeated measurements. Moreover, the present test probes are easier to use than the prior-known test probes having a flexible wire ground lead which must be clipped or otherwise grounded to a ground plane, in a first operation, prior to the steps of pressing the central test contact against the area of the microstrip circuit being evaluated.


REFERENCES:
patent: 4116523 (1978-09-01), Coberly et al.
patent: 4593243 (1986-06-01), Lao et al.
patent: 4829242 (1989-05-01), Carey et al.
patent: 4871964 (1989-10-01), Boll et al.
patent: 5041782 (1991-08-01), Marzan
patent: 5594358 (1997-01-01), Ishikawa et al.

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