23cm Hybrid Combiner
by
N2UO

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The 90 degree hybrid used to combine the output of a pair of GI-7B cavity PAs was homebrewed using standard, easily found tools. The stripline was cut out of 40 mil copper sheet using a jigsaw. The performance graphs are simulations, not actual measurements. Because a jigsaw was used to cut the stripline, actual performance is not quite as good as the simulation. Those wanting isolation and balance between the ports identical to calculations may want to use tuning screws to optimize the performance. It works well as shown, just the same.

The stripline is cut out of 40 mil thick copper plate. The enclosure is made of 1/8" copper plate. The walls are strips of 1/8" copper either 1" or 3/4" wide (see "side view" drawing below). The covers are made of 1/8 thick copper plate, and fitted to the walls to create exactly 0.750" spacing between them. The inside dimensions of the enclosure are 137mm x 145mm x 0.750". The 0.759" (750 mil) dimension is critical. The stripline fits in it with some extra room on the sides; it is soldered to N connectors mounted on the long (145mm inside dimension) sides of the enclosure. The solder cups of the connectors are slotted such that the stripline is mounted exactly in the middle of the 750 mil dimension of the enclosure. The edges of the stripline must be as close as possible to the connectors; it almost touches the teflon insulator of each connector.

The ports are as follows (see "top view" drawing, below): if the hybrid is used to split a signal (input hybrid), port B is input, C and D are the outputs, and A is the dump (which must be terminated with a 50 ohm dummy load). When used as a combiner (output hybrid), ports A and B are the inputs (corresponding to D and C outputs, respectively). C is the dump port and must be terminated with a 50 ohm dummy load, and D is the output. You will notice that the dummy load is reversed comparing splitter to combiner.

See figures below showing details of this written description.

Click on graphs to enlarge

 

Calculated results showing that power is equally divided (-3 dB), and that the dump port gets very little power.


Calculation of how well the ports match to 50 resistive ohms


The actual performance of this hybrid is 3.2/2.8 dB split (rather than the 3/3 split shown by modelling). This is acceptable for this application.

Click on drawings for zoom

   

The stripline; cut this from 40 mil copper sheet


TOP VIEW showing stripline installed in the enclosure. Note that it is centered both top to bottom and left to right.


Side view of the hybrid assembly. Note there are two approaches to cutting side strips and cover material.


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Last Updated: 20 February 2003
Feedback: Paul S. Goble, III, ND2X
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