POSSIBILITY TO THE REMOTE SENSING APPLICATION OF
THE SIX-PORT TECHNOLOGY
Toshiyuki Yakabe
University of Electro-Communications
1-5-1 Chofugaoka Chofu-Shi, Tokyo, 182-8585, Japan
Keywords: remote sensing, six-port based wave-correlator (SPC), vector network analyzer (VNA).
Abstract: The six-port technology and its many useful applications are now being recognized once again in modern
society. Since the six-port based wave-correlator (SPC) technology is well known for its unique ability to
accurately measure the complex wave ratio (amplitude and phase difference between two waves), many
applications of the SPC have been extensively investigated including a SPC based vector network analyzer
(SPC-VNA).
In this paper, we start with the basic concepts and fundamentals on both the six-port based reflectometer and
the six-port based wave-correlator. Next, we introduce one of the best microwave applications of the six-
port technology, i.e. a prototype SPC-VNA using a developed MMIC of the SPC. Finally, we will discuss
about possibility to the remote sensing technology as an alternative application of the developed MMIC
SPC.
1 INTRODUCTION
The six-port technology and its many useful
applications are now being recognized once again in
modern society, and are published in book form. The
six-port based wave correlator (SPC) technology is
well known for its unique ability to accurately
measure the complex wave ratio (amplitude and
phase difference between two waves), besides many
applications including a SPC based vector network
analyzer (SPC-VNA). The SPC-VNA is very
interesting for us, however, it is important to
understand a basic theory firmly first of all.
In this paper, we start with the basic concepts
and fundamentals on both the six-port based
reflectometer and the six-port based wave-correlator.
Next, we introduce one of the best microwave
applications of the six-port technology, i.e. a
prototype SPC-VNA using a developed MMIC of
the SPC. Finally, we will discuss about possibility to
the remote sensing technology as an alternative
application of the developed MMIC SPC.
2 SIX-PORT FUNDAMENTALS
2.1 Six-Port Refrectometer
As an alternative measurement technique for the
complex reflection coefficient of a device under
test (DUT), the six-port reflectometer was proposed
by Engen and Hoer in the 1970s.The six-port
reflectometer comprises a signal source port, a
measurement port, and four sidearm ports to which
power detectors are connected as shown in Fig. 1.
Γ
Figure 1. Six-port reflectometer
72
Yakabe T.
POSSIBILITY TO THE REMOTE SENSING APPLICATION OF THE SIX-PORT TECHNOLOGY.
DOI: 10.5220/0005414100720075
In Proceedings of the First International Conference on Telecommunications and Remote Sensing (ICTRS 2012), pages 72-75
ISBN: 978-989-8565-28-0
Copyright
c
 2012 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

The incident and emergent scattering variables at the
measurement port are denoted by a
2
and b
2
respectively. When the DUT of reflection coefficient
Г = a
2
/ b
2
is connected to the port, the four sidearm
port power readings P
h
, (h=3, 4, 5, 6) may be written
as
,
22
2
2
22
hhh
hhihh
BAb
bBaAP
+Γ=
=+=
α
α
(1)
where A
h
and BB
h
are complex constants depending
on the six-port reflectometer and α are the power
conversion parameters of the power meter connected
to the sidearm ports. If we denote an arbitrary
sidearm port by subscript h, and one of the other
four ports by i,
i=3, 4, 5, 6,
,hi ≠
then the power ratio with port h as
reference port can be expressed as
hiih
PPP /≡
,
1
1
22
Γ+
Γ+
=
+Γ
+Γ
=≡
h
i
ih
hh
ii
h
i
ih
k
k
K
BA
BA
P
P
P
= b + c
(2)
where
h
K
i
, k
i
, and k
h
are calibration parameters of
the six-port reflectometer which should be
determined in advance.
.
2.2 Six-port Wave Correlator
A six-port wave-correlator is shown in Fig. 2. In this
case, the six-port wave correlator is operated as a
two-channel wave receiver. Two ports incident
waves are denoted by a
2
and a
1
, and defined their
complex wave ratio W= a2/a2, then the four sidearm
port power readings P
h
, (h=3, 4, 5, 6) may be written
as same formulas as (1) and (2),
.Figure. 2. Six-port wave correlator
,
22
1
2
12
hhh
hhhh
DWCa
aDaCP
+=
=+=
β
β
(3)
,
1
1
22
Wt
Wt
T
DC
DC
P
P
P
h
i
ih
hh
ii
h
i
ih
+
+
=
+Γ
+Γ
=≡
(4)
where β are the power conversion parameters. C
h
and D
h
are complex constants, and
h
T
i
, t
i
, and t
h
are
calibration parameters f the six-port wave-correlator
which should be determined in advance. Although
the choice of h is wholly arbitrary, we set h=4
(i=3,5,6) in harmony with Engen’s notation.
Then, (4) can be rewrite,
,
1
1
2
4
44
Wt
Wt
TP
i
ii
+
+
=
(5)
where real
4
T
3
,
4
T
5
,
4
T
6
and complex t
3
, t
4
, t
5
, t
6
are
the system parameters of the wave correlator, and W
is the correlation ratio of the two incident waves a
2
and a
1
. By expanding (5) into quadratic form, we
have three circles in the complex W plane with the
centers zi and radii Li described as
.
,
44
44
4
2
44
444
ii
ii
i
i
ii
iii
i
PT
TP
tt
L
TP
TtPt
z
−
−
=
−
−
−=
(6)
Since the locus of each circle represents the possible
values for W, the complex W is the intersection of
three circles as shown in Fig. 3.
Figure. 3. Complex W plane
Possibility to the Remote Sensing Application of the Six-Port Technology
73

3 ALTERNATIVE VNA BASED
ON MMIC SPC
A Prototype MMIC six-port correlator based VNA
to measure the scattering parameters of a two-port
DUT is shown in Fig. 4. This configuration is
composed of directional couplers, switches,
isolators, circulators, and matching loads.
Figure. 4. Scheme of the MMIC six-port correlator based vector network analyzer
First International Conference on Telecommunications and Remote Sensing
74

For determining the system parameters of the six-
port correlator, three lines of different length are
used as standards for measuring the transmission S-
parameters, and three shorts with different length are
used as standards for measuring the reflection S-
parameters. The system performance was evaluated
by measuring various two-port passive components.
Figure 5 illustrates the measured S-parameters of a
UWB filter. The measurement is conducted from 9
to 12 GHz with 151 points. For comparison, the
measured results using a commercial VNA (Agilent
N5230C) are also shown in the same figure. One can
see the agreement between the two measured data is
very good up to the dynamic range of 60 dB for S21.
The measurement results of S11 are also in very
good agreement.
Figure. 5. S-parameters of a UWB filter measured
by the developed six-port VNA and a commercial
VNA
4 CONCLUSIONS AND A
POSSIBILITY TO THE
REMOTE SENSING OF MMIC
6PC
In this time, we introduce the six-port based wave-
correlator (SPC) technology. With our improved its
calibration theory, our developed MMIC SPC has a
good ability to accurately measure the complex
wave ratio (amplitude and phase difference between
two waves). That is why we are studying and
developing an alternative VNA using the SPC. Now,
we are developing a compact and MMIC PSC-VNA
for high frequency student experimental equipment
with reasonable price as education support. In near
future, we will pursue possibility of the application
to the remote sensing.
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