Similarly, a portion of the side trace 534 on the membrane overlaps a portion of the side trace 504 on the surface of the interface board 500 and a portion of the membrane side trace 532 overlaps a portion of the interface board waveguide side trace 506. On the side (ground) traces, the pair 546 of raised pads 540 nearest the center trace 502 are located as close to the inner edge of the trace as is permitted by the tolerance to misalignment and the second pair 548 of raised pads are preferably located nearer the center line of the membrane trace than the second edge of the trace. The electro-magnetic field is carried in the region between the traces of the waveguide and locating the pads of interconnecting structure closer to the region in which the electro-magnetic field is confined reduces the inductance of the connection.The accuracy of measurements performed with the membrane probing apparatus, particularly at frequencies in the radio and microwave frequency ranges, is improved by optimizing the impedance of the interface between co-axial cables, interconnecting the test instrumentation and the probing apparatus, and the co-planar waveguide that extends the signal path to the contact tips. A longer service life and lower operating cost for a membrane probing apparatus is achievable by including the contact tips on an elastic coupon that is attachable to a membrane that includes a plurality of traces over which signals, data and power can be transmitted. Replacing the probe needles of a needle type probing apparatus with a coupon attachable to a space transformer and including elastically supported contact tips can also improve the performance of a needle-type probing apparatus by substantially lower the inductance of the apparatus.The detailed description, above, sets forth numerous specific details to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid obscuring the present invention.All the references cited herein are incorporated by reference.The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.