Microsemi

Page 11

Copyright

 2005

Rev. 0, 2006-01-17

UM9601 – UM9608

FOR MICROSTRIP 900 MHz ANTENNNA SWITCHES

CO S

OS

AND MICROWAVE APPLICATIONS

10

100

1000

DIODE CURRENT (mA)

6

8

10

12

14

16

18

20

22

24

26

28

ISOLATION vs FREQUENCY AND DIODE CURRENT

0.025" (0.635mm) ALUMINA MICROSTRIP SPST SWITCH

TYPICAL

UM9601 - UM9604

UM9605 - UM9608

UM9601 - UM9604

UM9605 - UM9608

1 GHz

3 GHz

Installation in Microstrip

The cup type flange on the UM9601, UM9602, UM9605, and

UM9606 is designed to be affixed to the ground plane surface

of a microstrip board. The UM9603, UM9604, UM9607, and

UM9608 were designed to be affixed to a backing plate as

shown. It was experimentally determined that at frequencies

greater than 2 GHz the anode of the diode should be

approximately 0.010” (.254mm) above the top surface of the

microstrip for lowest insertion loss.

Figure: UM9601/UM9602 Microstrip Mount

Design Example – 900 MHz Antenna Switch

An example of a practical circuit design using a UM9601

diode is a quarter-wave antenna switch covering the frequency

of 800-900 MHz. The circuit design for this switch is shown

and was constructed using 0.025” (0.645mm) alumina

microstrip.

This antenna switch uses a series mounted diode and a shunt

mounted diode. The UM9601 was selected for shunt mounted

device (SPST performance at 1 GHz: 0.2dB insertion loss and

25dB isolation) and because it is the lowest cost diode in the

UM9601-UM9608 series. A UM9401 axial lead diode was

chosen for the series mounted device.

The performance of this switch is displayed in the graphs

and in the following table. It should be noted that the loss

values are actual measured numbers including losses due to the

capacitors, bias networks, connectors, as well as the board. In a

typical radio application where the antenna switch circuit board

is integrated in the same microstrip board that contains

transmitter and receiver elements the connector loss is

eliminated. This will result in lower overall insertion loss values

than indicated here.

For solder adhesion the microstrip may be heated to solder

diode. Conductive epoxy may also be employed. The thermal

resistance of solder mounted UM9601-UM9604 in their test