In microwave systems coaxial microwave links often have to be regularly connected and disconnected, which means threading and unthreading, torquing and untorquing. As a result, it is not possible to densely pack regular connectors as room is needed for threading and for the use of a torque wrench. Also, in helicopters, airplanes and vehicles, connectors usually have to be safely secured, normally using safety wire through the wire holes in the coupling nuts of the connectors, which is time-consuming.

An alternative is to use multipin connectors to connect microwave signals between two parts of a system. Standard circular blind mate series MIL-DTL-38999 connectors are designed and approved by the military and aerospace industry to meet the most stringent requirements in severe environments and are used for cable-to-panel applications in military, aerospace and other demanding situations.

Originally these connectors were designed to connect up to 128 wires for electronic equipment, but the necessity arose to incorporate coaxial cable contacts for high frequency or microwave applications and the requirement to combine simple electronic wire contacts and microwave coaxial contacts. The disadvantage is the dependence on the contact layouts offered for size 8, size 12 or other coaxial contacts. There is often the need to package numerous microwave links in a connector and to use different coaxial cables, e.g. a fairly thin and flexible cable for higher frequency applications or shorter leads, or a thicker cable for low loss applications and longer assemblies. Size 8, size 12 or other contacts are only available for some coaxial cables and might not be ideal for the application it is intended for. In addition, most standard coaxial contacts are not designed for higher frequency applications.

Figure 1 SQ-8 multipin connectors can be fitted in compact areas.

To address this issue, Spectrum Elektrotechnik has introduced multipin connectors beginning with the SQ-8 (shown in Figure 1), which uses a 4.3 mm high performance low loss coaxial cable and is supplied with eight coaxial inserts for applications up to 24 GHz, using the size 21 MIL-DTL-38999 series III shell. For applications in harsh environments the assemblies are supplied armored and water protected.

The need for circular connectors using more coaxial assemblies in a connector and different cables has resulted in Spectrum designing a whole family of multipin connectors that are fully compliant with the MIL-DTL-38999 standard, Series I with a bayonet coupling and Series III with a threaded coupling. Both series are rugged, designed to operate in harsh environments and are available in five different keyed versions, ensuring proper and fool-proof connection.

Figure 2 The SQ-8 has eight RF contacts.

Figure 3 The TQ-12 has 12 coaxial inserts.

The original SQ-series uses eight RF contacts (an example is shown in Figure 2) in a size 21 shell; the cable assemblies terminated with spring loaded bayonet catch connector inserts. The TQ-Series and IQ-Series offer size 21 and size 25 shells, with threaded coupling and 4, 7, 8 or 12 (shown in Figure 3) coaxial inserts, and are available for four different cables: spring loaded, limited spring loaded, fixed and pressurized. They are available for DC to 24 GHz and DC to 40 GHz frequency ranges, although the cable used may limit the frequency range. For example, if Spectrumís Type 141 cable is favored, a low loss high performance cable with a jacket diameter of 7.8 mm and an insertion loss of 0.64 dB/m, the frequency range is limited to 18 GHz.

The outer conductors of the cable assemblies in the TQ-Series use the common ground of the MIL-DTL-38999-shell, while the assemblies of the IQ-Series are isolated from each other and also from the ground of the MIL-DTL-38999-shell. Both the BQ-Series and the CQ-Series are identical to the TQ-Series with the exception that they employ the MIL-DTL-38999 standard, Series I with bayonet coupling. They differ from each other because the assemblies of the CQ-Series do not use the same ground, but are isolated from each other and from the ground of the MIL-DTL-38999-shell.

Also, all circular designs, the SQ, TQ, IQ, BQ and CQ-Series are available in pressurized versions, meeting the EIA364_02C test specifications, replacing MIL-STD 1344 and with the capacity to withstand 0.6 bar (8 PSIG) for 35 minutes. These connectors, which are usually bulkhead feed-through or are four-hole flanged versions, are required in airplanes where cable assemblies are installed in walls separating pressurized and unpressurized areas.

Figure 4 Drawing of the 8TQB-Z2ID-29 multipin adapter.

Alternatively, multipin adapters (shown in Figure 4) are designed for applications where bulkhead multipin connectors cannot be installed in the wall separating pressurized and unpressurized areas, as male multipin connections need to be used on both sides for disconnection purposes. These adapters are also available in pressurized versions to meet the EIA364_02C test specifications. In addition, hermetically sealed connectors and adapters are designed to be installed in the walls of vacuum test chambers.

The RQ-Series has been developed to address the need for even more cable assemblies to be packaged into one shell, taking up as little room as possible. They are designed for those applications where many more microwave coaxial connections are needed than circular designs can accommodate (where limited space is available) and where many DC and driver signals using AWG wire also have to be connected.

Figure 5 The RQ23-DC26 connector.

Figure 6 Drawing of the RQ80-DC120 connector.

For example, the RQ23-DC26 (shown in Figure 5) connects and disconnects 23 coaxial RF lines and 26 signal and supply lines at once and in seconds, while being as small as possible for such a complex design. When connecting such a high number of assemblies the insertion and withdrawal force is particularly significant. For the RQ23-DC26 a maximum of 150 N is specified for the insertion and withdrawal of all 23 coaxial lines plus the 26 signal and supply lines. The 23 coax inserts use the standard Type 11 or Type 43 high performance cable and are grouped in four to eight assemblies, secured by mounting bolts for easy replacement in the shortest time. Its maximum operating frequency is specified as 25 GHz, but higher frequency designs are available on request.

For applications where even more connections are needed, the newest design, the RQ80-DC120 (see Figure 6), features 80 coaxial connectors operating to 40 GHz and 120 signal lines, all in a unit measuring 107 x 304 mm. Designs are also available that operate up to 65 GHz.

Modern systems also require accurate phase matching of the cable assemblies in multipin harnesses and Spectrum achieves phase matching through the latest cable manufacturing processes, interface cutting techniques and advanced adjustable connector designs. Also, the adjustable matching mechanism can meet the most serious shock and vibration requirements.

Selecting the proper materials and aging techniques is important as well as ensuring that the cable assemblies and harnesses operate effectively in the standard temperature range of -54° to +115°C or the extended temperature range of -72° to +200°C. All the Spectrum connectors are RoHS compliant and meet the conditions and corrosion requirements of MIL-STD- 202, method 101, condition B. The multipin connectors are compliant with thermal shock to MIL-STD-202, method 107, condition B, vibration to MIL-STD-202, method 204, condition D, and shock to MIL-STD-202, method 213.

Spectrum Elektrotechnik GmbH,
Munich, Germany,
Tel: +49 89 3548 040,,
RS No. 304