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A&D Test & Measurement
Efficient Design and Analysis of Airborne Radomes
Accurate and efficient probing techniques play a vital role in the production process in order to guarantee the functionality for the customer. This is particularly true for today’s high speed, high data rate and wireless-everywhere generation where it is crucial to provide the industry with high performance testing solutions. That is precisely the market that INGUN has addressed when developing the HFS RF test probe series.
As a global specialist in the test and measurement business, the company has developed the series to complement its extensive range of highly precise mechanical products that constitutes the world’s largest selection of both general probes and spring-loaded RF probes as well as a wide variety of test fixtures. In the portfolio there are 10,000 general probe varieties and 475 different varieties of spring-loaded RF probes for either contacting a coaxial interface or directly contacting a pad on the surface of a PCB.
The HFS RF test probes have applications in virtually all sectors of the electronics industry, including the testing of automotive equipment (car stereos and GPS systems), telecommunications (cell phones), WiFi, ZigBee and UWB to name just a few. They feature a modular design approach where the probe body always stays the same (with regards to mechanical dimensions) and only the screw-in head has to be modified to meet the contacting needs of the customer.
In this product feature the focus is on the two latest tip-style additions for the HFS-860 6 GHz series, featuring R-SMA contacting for consumer-WLAN products and 6 GHz PCB pad contacting for contaminated surfaces. HFS-860 products are equipped with snap-in MCX input interfaces, which allows a secure and easy connection of a coaxial feed cable (e.g. SE-860-V-80 assembly or customer cable).
The two tip-style additions are the HFS 860 201 051 A 5306 S and the HFS 860 303 150 A 5343 ER. INGUN probes have an intelligent part number system, which is informative and descriptive as it includes spring forces, material, tip style and maximum operating range—all in one number. The whole part number is laser-engraved on the outer barrel to prevent mix-ups.
This probe is intended to be used for layouts where the ground ring is open on one side (see Figure 1). The ground ring is serrated, which means that the outer connector facilitates a secure ground connection even on highly contaminated boards. Another advantage of the serrated design is that it is much easier to penetrate through layers of flux and dust than is the case for a flattened style. For clean environments the usage of a flat outer-conductor design is recommended (e.g. the HFS 860 201 051 A 5302).
Figure 1 The HFS 860 201 051 A 5306 S probe for layouts where the ground ring is open on one side.
Whenever WLAN boards with reverse-SMA connectors have to be tested (this is the case for many routers, PCI-WLAN cards, etc.), the HFS 860 303 150 A 5343 ER is the right probe choice. Allowing signal transmission up to 6 GHz, this probe covers both the 2.4 and 5.8 GHz bands with ease.
The performance of the RF probes is constantly tested to ensure excellent electrical characteristics. The S-parameters are determined using either manual or semi-automatic test stations and a vector network analyzer. The test setups are calibrated using full-two-port short-open-load-reciprocal (SOLR) calibration. Also, whenever necessary, further steps are taken to compensate for losses through additional adaptors that have been inserted after the calibration has been done (such as contacting interfaces, PCB contacting pads, etc.).
Table 1, and Figures 2 and 3 show the typical S-parameter values of the probes. For the probe itself, the matching can be kept well above 15 dB/20 dB within the specified frequency range. Of course, the performance is highly dependent on the method of contact and the PCB pad or coaxial interface to-be-contacted. INGUN recommends using a complete testing solution consisting of fixture + probe to ensure good contact.
Table 1 Electrical Characteristics (Typical Values)
Figure 2 Typical return loss of probes.
Figure 3 Typical insertion loss of probes.
However, a probe without a good cable connection to the test system or interface is worthless. Users should not just select the test probe without considering the cable assembly it is to be used with, whether pre-configured or customized. For instance, the HFS RF test probes are highly compatible with the standard SE-860 series cable, which exhibits very low insertion loss and good impedance stability. Figure 4 shows the performance of SE-860 cable assemblies, which can easily be used in conjunction with the HFS RF test probes. The values are given for a cable length of 80 cm; losses for other lengths can be approximated using the formula:
Figure 4 Performance of SE-860 cable assemblies.
Engineers are currently working on a new probe solution for applications ranging up to 12 GHz and higher (the HFS-865 series); thus, not only will UWB signals be covered but virtually any high speed data applications up to the specified frequency. This model features an improved body design with MMPX™-input interface and is a joint venture between INGUN and Huber + Suhner.
The HFS RF test probe series is an easily configurable yet highly precise way for contacting PC boards and interfaces. Because they are spring-loaded probes there is no need to screw-in/plug-in some interfaces, with the result that time can be saved when carrying out high-volume pass/fail tests. With the latest tip-styles for the HFS-860 series and the upcoming HFS-865 probe, virtually all applications can be covered. For those that are not, the modular design approach allows customer-specified solutions to be developed quickly.
RS No. 301
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