Microsemi

Page 7

Copyright

 2005

Rev. 0, 2005-09-15

UM9401 / UM9402 / UM9415

COMMERCIAL TWO-WAY RADIO

ANTENNA SWITCH DIODES

diode antenna switch can handle depends on the

expression is as follows:

Characteristic curves are shown in the data section

which gives both the maximum and typical diode

maximum power dissipation rating of the PIN diode

depends both on the length of the diode leads and the

temperature of the contacts to which the leads are

connected. A graph defining the maximum power

dissipation at various combinations of overall lead

data section. From these curves and the above

equation, the power handling capability of the PIN

diode may be computed for a specific application.

Curves are also presented which show the

maximum transmitter power that an antenna

switch using UM9401s and UM9415s can safely

handle for various forward currents and lead

temperatures. These curves are based on a typical

design condition of a ½ in. total overall lead length,

50 Ω line impedance, and a totally mismatched

antenna (σ = ∞). For the case of a perfectly matched

antenna, the maximum transmitter power can be

increased by a factor of 4.

Design Information

A circuit configuration for a two-way radio antenna

switch using PIN diodes consists of a diode placed in

series with the transmitter and a shunt diode placed a

quarter wavelength from the antenna in the direction

of the receiver as shown. For low frequency

operation, the quarter wave line may be simulated by

lumped elements. Typical performance of antenna

switches using PIN diodes forward biased at 100 mA

is less than 0.2 dB insertion loss and 30 dB isolation

during transmit; at zero bias the receive insertion loss

is less than 0.3 dB. This performance is achievable

across a ±20 % bandwidth at center frequencies

ranging from 10 to 500 MHz.

ANTENNA

ANTENNA

DC SUPPLY

D1

D2

L

D1

D2

DC SUPPLY

/4

TRANSMITTER

TRANSMITTER

RECEIVER

RECEIVER

(H)

C = 1/2

L

CC