Testing the HMPP-389T on the
Demo-board
Introduction
The HMPP-389T PIN diode is a
high frequency shunt switch. It
has been designed as a smaller
and higher performance version of
the HSMP-389T (SC-70 package).
The DEMO-HMPP-389T demo-
board allows customers to evalu-
ate the performance of the
HMPP-389T without having to
fabricate their own PCB. Since a
shunt switch’s isolation is limited
primarily by its parasitic induc-
tance, the product’s true potential
cannot be shown if a conventional
microstrip pcb is used. In order to
overcome this problem, a coplanar
waveguide over ground-plane
structure is used for the demo-
board. The bottom ground-plane is
connected to the upper ground
traces using multiple via-holes.
A 50Ω reference line is provided at
the top to calibrate the board loss.
The bottom line allows the
HMPP-389T diode to be tested as
a shunt switch.
reference line
Demo-board Preparation
Since the performance of the
shunt switch is ultimately limited
by the demo-board, a short
discussion of the constructional
aspects will be beneficial. Edge-
mounted SMA connectors
(Johnson #142-0701-881) were
mounted on both the reference
and test lines. A special mounting
technique has been used to
minimize reflection at the pcb to
connector interface. Prior to
mounting, the connector pins
were cut down to two pin diam-
eters in length. Subsequently, the
connector fingers were soldered
to the upper ground plane (Figure
13). Solder was filled between the
connector body and fingers on the
lower ground plane until the small
crescent of exposed teflon was
completely covered (Figure 14).
Test Results
Measurements of the reference
line’s return and insertion losses
were used to gauge the effective-
ness of the VSWR mitigating steps.
In our prototype, the worst case
return loss of the reference line
was 20 dB at 5 GHz (Figure 15).
-18
-22
RETURN LOSS (dB)
-26
-30
-34
-38
1
2
3
4
5
6
FREQUENCY (GHz)
Figure 15. Swept return loss of reference line.
Figure 13. Soldering details of connector
fingers to upper ground plane.
Insertion loss of the reference was
very low and generally, increased
with frequency (Figure 16). If the
demo-board has been constructed
carefully, there should not be any
evidence of resonance. The
reference line’s insertion loss
trace can be stored in the VNA’s
display memory and used to
correct for the insertion loss of
the test line in the subsequent
measurements.
Agilent
SK063A
test line
HMPP-389T
Figure 14. Soldering details of connector
fingers to lower ground plane.
Figure 12. Demo-board DEMO-HMPP-389T.
6
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
