7

Figure 13. Soldering details of connector fingers to upper ground plane.

Figure 14. Soldering details of connector fingers to lower ground plane.

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 diameters in length. Subse-

quently, the connector fingers were soldered to the upper

ground plane (Figure 18). 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 19).

Test Results

Measurements of the reference line’s return and insertion

losses were used to gauge the effectiveness of the VSWR

mitigating steps. In our prototype, the worst case return

loss of the reference line was 20 dB at 5 GHz (Figure 20).

Figure 15. Swept Return Loss of Reference

Line.

FREQUENCY (GHz)

1

6

2

4

5

3

-18

-22

-26

-30

-34

-38

Figure 12. Demo-board DEMO-HMPP-389T.

test line

reference line

Agilent

SK063A

HMPP-389T

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 evaluate 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 inductance, 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.

Figure 15. Swept return loss of reference line.