LF-to-2.5GHz Dual Logarithmic Detector/

Controller for Power, Gain, and VSWR Measurements

12

______________________________________________________________________________________

Measuring VSWR and Return Loss

In Figure 2, the two logarithmic amplifiers measure the

incident and the reflected power levels to produce two

proportional output voltages at OUTA and OUTB. Since

OUTD is a DC voltage proportional to the difference of

OUTA and OUTB, return loss (RL) and VSWR can be

easily calculated within a microprocessor using the

following relationships:

where return loss (RL) is expressed in decibels,

25mV/dB (for R3 = 0

Ω).

RL

P

P

VV

SLOPE

RFINA

RFINB

OUTD

CENTER

=−

=

−

()

MAX2016

CSETL

COUTL

LOGARITHMIC

DETECTOR

LOGARITHMIC

DETECTOR

COUTL

OUTD

SETD

20k

Ω

RFINB

RFINA

OUTD

TRANSMITTER

COUPLER

CIRCULATOR

ATTENUATOR

GND

Figure 1. VSWR Monitoring Configuation

MAX2016

RFINA

RFINB

GND

ADC

µP

IN

LOAD

4-PORT DIRECTIONAL

COUPLER

LOGARITHMIC

DETECTOR

LOGARITHMIC

DETECTOR

OUTD

SETD

20k

Ω

Figure 2. Measuring Return Loss and VSWR of a Given Load