Fabrication of Receiver Components

The micro NC machine described above has been used to fabricate several state-of-the-art receiver components. We have successfully fabricated several blocks of a 810 GHz tripler. The electromagnetic design for the tripler is outlined in [16]. Figure 3a shows a photograph of the split block of the fabricated tripler. Five different tools were used in the fabrication: two endmills of diameter 8 mils and 4 mils respectively, two saws of thickness 5 mils and 2 mils respectively, and the horn broach described above. Figure 3b shows a magnified view of the features in one half of the tripler block. The smallest feature of the tripler block is a 2 mil wide, 6 mil deep waveguide section. This section, that is part of the output waveguide, was cut using the 2 mil saw. The fabrication proceeded with the preliminary roughing operations with the endmills, followed by broaching with the horn broach and the saws. Subsequently, final deburring passes were required to remove chips generated by the broaching operations. After a few trial runs with dummy blocks, several fully functional units were fabricated. Careful inspection of the resultant metal blocks revealed a maximum error of $\sim 7~\mu$m. Including setup time, both halves of the tripler block were fabricated in under three hours. The performance of the tripler fabricated with the micro NC machine was found to be comparable to a previous tripler fabricated with conventional machining. One of the finished tripler blocks now forms part of the LO system for a 810 GHz SIS receiver system being used currently at the South Pole AST/RO facility.

 

Figure 3: (a) Photograph of split blocks of a 810 GHz tripler fabricated using the micro NC machine. (b) Magnified view of one half of the tripler block showing details of the waveguide features. For details of the electrical design see [16].

With this low cost precision machining technique, it is now possible to consider the construction of large format arrays of high performance heterodyne waveguide receivers. The first test SIS mixer block of a seven element 345 GHz focal plane array [17] for the HHT was fabricated with the micro NC machine. Figure 4(a) shows the fabricated split blocks and Figure 4(b) shows the magnified details of one half of the split block. The mixer employs a diagonal feed horn to half-height rectangular waveguide transition. A suspended stripline substrate channel orthogonal to the waveguide houses the SIS junction. The 345 mixer block was machined with the horn broach described above and a 6 mil endmill. The maximum error in the machined mixer blocks is $\sim 8~\mu$m.

 

Figure 4: (a) Photograph of split blocks of a 345 GHz SIS mixer block fabricated using the micro NC machine. (b) Magnified view of one half of the mixer block showing details of the transition from diagonal feedhorn to half-height waveguide. For details of the electrical design see [17].

The micro NC machine has also been used as a precision lathe to turn coaxial pins to be used in multiplier circuits. The pin is held in the high speed spindle and one tooth of a saw blade held in the XYZ positioners was used as the turning tool. Preliminary results of this procedure indicates that the remaining problems to overcome in making precision, micro diode pins are mostly related to software issues.