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FEED LINE BASICS 339

circuit board). If so, PCB must have a metal flange or other fixed structure providing strong
mechanical bond and rising above the top substrate surface. The latter blocks access to the
mounted on PCB elements thereby complicating their test and tuning. There are two ways out.
The first one is the so-called through-hole transition where the coaxial connector is attached to
the bottom ground plate of the printed circuit as shown in Figure 6.7.9a and connected to the
strip through the hole drilled into the substrate. The second one is the surface-mount transition
mounted on the top side of PCB and depicted in Figure 6.7.9b. Such design allows picking up
or injecting signals from any sport of PC board other than at its edge. Besides, both types offer
greater PCB mechanical strength and reliability than edge mountings.

23
Figure 6.7.10 illustrates the surface-mount transition to CPWG and its matching performance.
It is worthwhile to point out that this transitions are enough broadband and only slightly inferior
in their performance to the inline variants.

Figure 6.7.10 Surface-mount transition to CPEG: a) Schematic, b) Top view, c) E-field
distribution, d) Smith chart showing matching performance between 0 and 10GHz

6.7.7 Rotary Joint

One of the possible design of this joint is illustrated in Figure 6.7.11. E- and H-field pattern in
TE10 →TM01 transition and speaks for itself. Note only that bottom section of WC plays the role
of the coaxial line section. Therefore, this joint includes the modes conversion
TE10 →TEM →TM01. The CST model behind this pictures was developed to prove the concept
only and not optimized to get a good match.

We stop here because the number of
different types of transitions is in the
hundreds. We hope that the reader has
gotten the general idea how the
transitions work. Without a doubt, the
main guide is the field patterns in lines
supposedly to be connected and the
distribution of electric and magnetic
energy in the transition area. The reader
may be surprised how to get all this
Figure 6.7.11 E- and H-field pattern in information if the structure of transition
TE10 →TM01 transition was not developed yet and there is no

23 The authors are grateful to HUBER+SUHNER Astrolab for the simulation data and CST model.