Page 358 - Maxwell House

338 Chapter 6

Looking back at Figure 6.1.1c and 6.1.1d, we see that the EM field pattern in coaxial line and
microstrip is someway similar but not completely matched. If so, we can expect more or less
reactive energy concentration in the transition area even in the case of equal impedances. This
phenomenon is plainly seen in Figure 6.7.7c illustrating the E- and H-field energy distribution.
Evidently, > in the longitudinal gap between the strip and connector body that is

equivalent to small series inductance. Adjusting the length and size of this gap we can tune the
transition reaching the broadband performance such way that at the frequency band between 0
and 10GHz the reflection coefficient does not exceed 0.003.

6.7.5 Coax-to-Coplanar
Waveguide Inline Adapter

Figure 6.7.8 illustrates such transition
that looks like the same as in Figure
6.7.7. The main differences are: CPW
does not require the ground metal
layer (lamination) on the bottom of
the substrate, the dielectric substrate
in CPW is much thicker (0.381mm
instead of 0.127mm) and have the
higher dielectric constant (10 instead
of 3) to diminish the EM energy Figure 6.7.8 Coax-to-coplanar waveguide inline
outside infiltration. Besides, the trace adapter: a) and c) Schematic, b) E- and H-field
in CPW is wide (0.432mm instead of di ib i
0.254mm) to get the same 50 Ohms characteristic impedance. The protruded coaxial center
conductor or probe is soldered to the strip as before. There are no vias. Looking back at Figure
6.1.1d and 6.6.21, we see that the EM field pattern in coaxial line and CPW is similar but not
completely matched. If so, we can expect some reactive energy concentration in the transition
area even in the case of equal impedances. This phenomenon is plainly seen in Figure 6.7.8b
illustrating the E- and H-field energy distribution in the connection area. Evidently, E-field
energy is accumulated nearby the coaxial connector while H-field energy spreads along the
probe. Therefore, the equivalent circuit must be close to depicted in Figure 6.7.5d with 2 ≪
. At the frequency band between 0 and 10 GHz, the reflection coefficient is not exceed 0.01
1
as shown on Smith
chart of Figure
6.7.8c.

6.7.6 Vertically
Mounted (Right-
Angle) Coaxial
Transitions

The inline
transitions like
Figure 6.7.9 Vertically mounted coaxial transitions: a) Trough-hole, depicted in Figure
b) Surface-mount 6.7.7 are cheap in
production and

installation. On the other hand, they are connected straight to thin and quite fragile PCB (printed