Title: Non-radiative dielectric waveguide mixer using a ring hybrid coupler
Abstract: Disclosed is a NRD waveguide mixer adopting a ring hybrid coupler applicable to a small-sized and high functional millimeter wave receiving/transmitting device. The NRD waveguide has a housing including two parallel conductive plates. The ring hybrid coupler is installed in the housing and has an annular ring formed with first to fourth ports which are radially extended about the annular ring. An oscillating device is connected to the first port so as to generate a local oscillating signal. A rod antenna is connected to the second port so as to receive/transmit a radio frequency signal. A first balanced mixer mount is connected to the third port and is provided with a first Schottky diode. A second balanced mixer mount is connected to the fourth port and is provided with a second Schottky diode. The radio frequency signal and the oscillating signal inputted from the first and second ports are mixed in the ring hybrid coupler to be transformed into an addition signal and a subtraction signal. The addition and subtraction signals are transmitted to the third and fourth ports to switch the Schottky diodes respectively so that an intermediate signal is generated.
Patent Number: 6,871,056 Issued on 03/22/2005 to Cho, et al.
| Inventors:
|
Cho; Dong Jin (Ulsan, KR);
Yoo; Young Geun (Ulsan, KR)
|
| Assignee:
|
NRD Co. Ltd. (KR)
|
| Appl. No.:
|
847668 |
| Filed:
|
May 2, 2001 |
Foreign Application Priority Data
| Feb 01, 2001[KR] | P.10-2001-4826 |
| Current U.S. Class: |
455/313; 455/318; 455/319; 455/326; 455/328 |
| Intern'l Class: |
H04B 001//26 |
| Field of Search: |
455/313,330,319,316,318,323,326,327,328
333/116,25
327/100
|
References Cited [Referenced By]
U.S. Patent Documents
| 3932815 | Jan., 1976 | Yuan et al. | 455/326.
|
| 4418429 | Nov., 1983 | Roberts | 455/328.
|
| 4480336 | Oct., 1984 | Wong et al. | 455/328.
|
| 4492960 | Jan., 1985 | Hislop | 455/323.
|
| 4697161 | Sep., 1987 | Buoli | 333/116.
|
| 5020148 | May., 1991 | Bonato | 455/319.
|
| 5428840 | Jun., 1995 | Sadhir | 455/327.
|
| 5678225 | Oct., 1997 | Kobayashi | 455/330.
|
| 5774801 | Jun., 1998 | Li et al. | 455/318.
|
| 5854974 | Dec., 1998 | Li | 455/326.
|
| 5977874 | Nov., 1999 | Konstandelos | 340/554.
|
| 6275689 | Aug., 2001 | Gill | 455/323.
|
Primary Examiner: Urban; Edward F.
Assistant Examiner: Le; Lana N.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
What is claimed is:
1. A NRD waveguide mixer comprising:
a housing including a pair of opposed parallel conductive plates;
a ring hybrid coupler installed in the housing, the ring hybrid coupler
having an annular ring and first to fourth ports radially extending about
the annular ring;
an oscillating means connected to the first port so as to generate a local
oscillating signal;
a rod antenna connected to the second port so as to receive/transmit a
radio frequency signal;
a first balanced mixer mount connected to the third port and provided with
a first Schottky diode; and
a second balanced mixer mount connected to the fourth port and provided
with a second Schottky diode,
wherein the radio frequency signal inputted from the first port and the
oscillating signal inputted from the second port are mixed in the ring
hybrid coupler to be transformed into an addition signal and a subtraction
signal, and the addition and subtraction signals are transmitted to the
third and fourth ports to switch the first and second Schottky diodes,
respectively, so that an intermediate signal is generated.
2. The NRD waveguide mixer as claimed in claim 1, wherein the first and
second ports make contact with the annular ring to form T-junctions, an
inductive iris made of a conductive thin plate is attached to each of the
T-junctions or a conductive post is accommodated in each of the
T-junctions for an impedance matching.
3. The NRD waveguide mixer as claimed in claim 1, wherein stubs are
provided at an inner side of the annular ring in directions opposite to
extending directions of the first and second ports for an impedance
matching.
4. The NRD waveguide mixer as claimed in claim 1, wherein the first to
fourth ports have the same characteristic impedance Zo, the annular ring
has a characteristic impedance of Zo/√2, a circumference length of
the annular ring at a middle portion thereof is substantially .lambda.,
and the first to fourth ports are arranged spaced by .lambda./4 from each
other around the annular ring.
5. The NRD waveguide mixer as claimed in claim 1, wherein the first to
fourth ports have the same characteristic impedance Zo, the annular ring
has a characteristic impedance of Zo/√2, the first to fourth ports
are arranged around the annular ring in a clockwise direction in order of
first, third, second and fourth ports, and when a circumference length of
the annular ring is 6.lambda./4, the first port is spaced from the third
port by 3.lambda./4, the second port is spaced from the third port by
.lambda./4, the second port is spaced from the fourth port by .lambda./4,
and the first port is spaced from the fourth port by .lambda./4 in such a
manner that the first to fourth ports have phase differences with respect
to each other.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-radiative dielectric (NRD) waveguide
mixer adopting a ring hybrid coupler, and more particularly, to a NRD
waveguide mixer which employs a ring hybrid coupler with a simple
structure utilizing a NRD waveguide and is applicable to a millimeter wave
integrated circuits.
BACKGROUND OF THE PRESENT INVENTION
Recently, as a mobile telecommunication system and telecommunication
devices have been rapidly digitalized, it is commonly required to employ a
telecommunication system having a speedy and powerful data processing
capacity. Since the telecommunication system is required to process and
communicate a great deal of information, its frequency band has been
expanded from a microwave band to a millimeter wave band. In a wireless
telecommunication system using the millimeter wavelength, it was usually
manufactured as a hybrid type module. Recently, as semiconductor
technology makes great strides, the wireless telecommunication system has
been developed to employ a single chip of a monolithic microwave
integrated circuit (MMIC). Although the hybrid type, as a conventional
type, is less competitive than the MMIC in terms of price and mass
production, it may be advantageously adopted to manufacture the wireless
telecommunication system in small lots.
Nowadays, many attentions have been paid to a NRD waveguide since it can be
easily manufactured as compared with the hybrid type and can transmit
signals in a longitudinal-section magnetic (LSM) mode with a low
transmission loss.
FIGS. 1 and 2 show the structure of a conventional signal receiving device
adopting a NRD waveguide multi-layer type. The signal receiving device has
an upper conductive plate 1 and a lower conductive plate 2 which is
positioned in parallel to the upper conductive plate 1. Dielectric lines 3
and 4 are arranged between the upper and lower conductive plates 1 and 2.
A radio frequency signal and a local oscillating signal are inputted into
the signal receiving device through the dielectric lines 3 and 4. A horn
antenna (not shown) is attached to a rod antenna 10 for
receiving/transmitting the signals. When the radio frequency signal is
inputted into the rod antenna 10, a bias signal is applied to a Gunn diode
(not shown) mounted in a diode mount 7 so that the local oscillating
signal is generated. At this time, a longitudinal-section electric (LSE)
mode is created. However, the LSE mode is suppressed by a mode suppressor
8. Then, the radio frequency signal passes through a dielectric resonator
9 so that a transferring gain increases at a predetermined frequency band
and an intermediate frequency (IF) signal is outputted from two ports 16
and 17 through a 3-dB coupler having a bend shape. The signals outputted
from the two ports 16 and 18 are introduced into Schottky diodes of a pair
of balanced mixer mounts 5 and 6 and are inputted into an intermediate
frequency (IF) terminal 12. Each of the Schottky diodes receives a bias 13
having a predetermined voltage and is grounded by a ground 14 so that a
closed circuit is formed.
FIG. 1 represents the typical structure of the signal receiving device
using the NRD waveguide. The coupler is fabricated by bending the
dielectric lines based on the principle of a parallel dielectric line
coupler. In designing bending angles of the dielectric lines, an
established database with respect to proper widths and the bending angles
of the dielectric lines are used.
However, in fabricating the dielectric coupler having the above structure
in a small size, it is not a good choice to reduce lengths of the bend
dielectric lines. Accordingly, it is inevitable to bend the dielectric
lines much more, but this choice may cause a large error range in
fabricating them. A bend dielectric line may cause a transmission loss at
a bending portion if the width of the dielectric line is not adaptively
reduced with respect to respective bending angles corresponding
frequencies. In the fabrication, the reducing of the width without causing
a large error is very difficult. Furthermore, it is also difficult to
precisely design and fabricate the bending angles, the distance between
the dielectric lines and the isolation degree between ports. In addition,
if the dielectric coupler is fabricated in a small size with a light
weight, the width of the bending portion has to be reduced to enlarge the
bending angle. However, it is difficult to precisely reduce the width of
the dielectric line which is usually made of Teflon.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a NRD waveguide mixer
capable of enhancing the isolation degree between ports by adopting a ring
hybrid coupler which can be fabricated in a small size and can be easily
manufactured without bending dielectric lines.
To accomplish the object of the present invention, there is provided a NRD
waveguide mixer including a housing which has a pair of opposed parallel
conductive plates. The NRD waveguide mixer also includes a ring hybrid
coupler having an annular ring and first to fourth ports radially
extending from the annular ring, an oscillating device connected to the
first port so as to generate a local oscillating signal, a rod antenna
connected to the second port so as to receive/transmit a radio frequency
signal, a first balanced mixer mount connected to the third port and
provided with a first Schottky diode, and a second balanced mixer mount
connected to the fourth port and provided with a second Schottky diode.
Particularly, the radio frequency signal inputted from the first port and
the oscillating signal inputted from the second port are mixed in the ring
hybrid coupler to be transformed into an addition signal and a subtraction
signal, and the addition and subtraction signals are transmitted to the
third and fourth ports to switch the first and second Schottky diodes,
respectively, so that an intermediate signal is generated.
Preferably, the first and second ports make contact with the annular ring
to form T-junctions. For a good impedance matching, an inductive iris made
of a conductive thin plate is attached to each of the T-junctions or a
conductive post is accommodated in each of the T-junctions.
Preferably, for the good impedance matching, stubs are provided at an inner
side of the annular ring in directions opposite to the extending
directions of the first and second ports, respectively.
Preferably, the first to fourth ports have the same characteristic
impedance Zo. The annular ring has a characteristic impedance of
Zo/√2. A circumference length of the annular ring at a middle
portion thereof is substantially .lambda., and the first to fourth ports
are spaced by .lambda./4 from each other.
Preferably, the first to fourth ports are arranged around the annular ring
in a clockwise direction in order of the first, third, second and fourth
ports. When a diameter of the annular ring is 6.lambda./4, the first port
is spaced from the third port by 3.lambda./4, the second port is spaced
from the third port by .lambda./4, the second port is spaced from the
fourth ports by .lambda./4, and the first port is spaced from the fourth
port by .lambda./4 in such a manner that the first to fourth ports have
phase differences with respect to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
The above object and other advantages of the present invention will become
more apparent by describing in detail a preferred embodiment thereof with
reference to the attached drawings, in which:
FIG. 1 is a perspective view showing the whole structure of a signal
receiving device adopting the principle of a conventional parallel NRD
line coupler and a balanced mixer;
FIG. 2 is a plan view of the signal receiving device shown in FIG. 1;
FIG. 3 is an exploded perspective view showing a NRD waveguide mixer
adopting a ring hybrid coupler according to one embodiment of the present
invention;
FIG. 4 is a plan view of the NRD waveguide mixer shown in FIG. 3;
FIG. 5 is a front view of the NRD waveguide mixer shown in FIG. 3;
FIG. 6 is a bottom view of the NRD waveguide mixer shown in FIG. 3;
FIG. 7 is a right-side view of the NRD waveguide mixer shown in FIG. 3;
FIG. 8 is a left-side view of the NRD waveguide mixer shown in FIG. 3;
FIG. 9 is a perspective view showing the structure of a diode mount used in
a balanced mixer;
FIG. 10 is a perspective view showing the structure of the ring hybrid
coupler according to a first embodiment of the present invention;
FIG. 11 is a perspective view showing the structure of the ring hybrid
coupler according to a second embodiment of the present invention;
FIG. 12 is a view showing an equivalent circuit for analyzing a circuit
structure of the ring hybrid coupler shown in FIG. 11;
FIGS. 13a and 13b are views showing a T-junction of the ring hybrid coupler
formed with an inductive iris;
FIG. 14 is a schematic view showing an electromagnetic wave analyzing model
for the ring hybrid coupler; and
FIG. 15 is a view showing the size and direction of an electric field
obtained by analyzing the electromagnetic wave analyzing model.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, the present invention will be described in detail with
reference to the accompanying drawings.
FIG. 3 shows the structure of a NRD waveguide mixer according to one
embodiment of the present invention in which an upper conductive plate 101
is separated from a lower conductive plate 102. In addition, FIG. 4 shows
a plan view of the NRD waveguide mixer shown in FIG. 3 in which the upper
conductive plate 101 is removed.
It is one of main features of the present invention that the NRD waveguide
mixer has a ring hybrid coupler 127. The ring hybrid coupler 127 includes
an annular ring having a predetermined width and first to fourth ports P1,
P2, P3 and P4 which radially and outwardly extend about the annular ring.
The first port P1 is connected to a dielectric line 108 accommodating a
mode suppressor 119 and the second port P2 is connected to a rod antenna
120 for receiving/transmitting signals. In addition, the third port P3 is
connected to a dielectric line 128 by interposing a first mixer mount 121,
and the fourth port P4 is connected to a dielectric line 129 by
interposing a second mixer mount 124. In practice, the first port P1 can
be integrally formed with the dielectric line 108 and the second port P2
can be integrally formed with the rod antenna 120.
A Gunn diode 105 is provided to generate a local oscillating signal. The
Gunn diode 105 is installed in a diode mount 107. The local oscillating
signal is introduced into the dielectric line 108 through a radio
frequency supplying line 118. The radio frequency supplying line 118 is
vertically arranged on the same plane of the mode suppressor 119.
The hybrid coupler 127 and elements connected thereto are installed in the
lower conductive plate 102. A plurality of coupling holes 104a, 104b, 104c
and 104d and a plurality of screw holes 104a', 104b', 104c' and 104d'
corresponding to the coupling holes 104a, 104b, 104c and 104d are
positioned at edge portions of the upper conductive plate 101 and the
lower conductive plate 102, respectively. Screws 103a, 103b, 103c and 103d
are coupled into the screw holes 104a', 104b', 104c' and 104d' through the
coupling holes 104a, 104b, 104c and 104d. The upper and lower conductive
plates 101 and 102 are assembled with each other, and thereby forming a
housing in which the ring hybrid coupler is accommodated. The size of the
housing can be varied depending on the frequency band of a signal
receiving device and a signal transmitting device. The upper and lower
conductive plates 101 and 102 are made of metals, such as aluminum, in
order to allow the upper and lower conductive plates 101 and 102 to have
high conductivity with a light weight. In addition, it is preferable that
the ring hybrid coupler 127, the dielectric lines 108, 128 and 129 and the
rod antenna 120 are made of one kind of dielectric material so that they
can have the same dielectric constant.
A first IF terminal inputting hole 122 and a direct current bias inputting
hole 123 are formed at both sides of the first mixer mount 121 of the
lower conductive plate 102 and a second IF terminal inputting hole 125 and
a mixer mount grounding hole 126 are formed at both sides of the second
mixer mount 124. In addition, first ends of lead wires 137a and 137b are
connected to both sides of the first mixer mount 121 and second ends of
the lead wires 137a and 137b are connected to an IF terminal connector 130
and a central terminal of an electromagnetic interference (EMI) filter 132
for supplying the bias via the first IF terminal inputting hole 122, the
direct current bias inputting hole 123, an IF circuit (not shown) and a
bias supplying circuit (not shown). In addition, first ends of lead wires
138a and 138b are connected to both sides of the second mixer mount 124
and second ends of the lead wires 138a and 138b are connected to the IF
terminal connector 130 and a grounding pin 131 via the second IF terminal
inputting hole 125, the mixer mount grounding hole, the IF circuit and the
bias supplying circuit.
FIGS. 5 to 8 show a front view, a bottom view, a right-side view and a left
side view of the NRD waveguide mixer shown in FIG. 3, respectively. The IF
circuit and the bias supplying circuit can be installed at a bottom of the
lower conductive plate 102. The position of the IF circuit and the bias
supplying circuit can be varied depending on the design requirement. An IF
circuit substrate and a lower lid of the conductive plate are omitted in
the figures. The upper conductive plate 101 is spaced from the lower
conductive plate 102 in FIG. 7. As shown in FIG. 8, the connector 130 is
connected to one side of the lower conductive plate 102 for allowing the
lower conductive plate 102 to be connected with other signal
receiving/transmitting devices.
FIG. 9 shows the structure of a diode mixer mount of the NRD waveguide
mixer. A sheet 133 of a high dielectric constant is attached to the third
port P3 or to the fourth port P4. Then, the mixer mount 121 or 124 and the
dielectric line 128 or 129 are added thereon. The dielectric line 128 or
129 is installed so as to protect a Schottky diode 134. In order to
fabricate the mixer mount 121 or 124, a patch antenna 139b having a
.lambda./4 choke circuit is manufactured by etching a copper film stacked
on a dielectric substrate 139a made of Teflon, and the Schottky diode 134
is coupled to the patch antenna 139b crossing a gap of the patch antenna
139b.
The NRD waveguide mixer having the above structure is used as a signal
receiver or as a signal transmitter of a wireless telecommunication
appliance.
When the NRD waveguide mixer is used as the signal receiver, the direct
current (DC) bias power supplied from the EMI filter 132 is transferred to
the Gunn diode 105 after removing the harmonic components contained in the
DC bias power by using a bias choke 106 so that an oscillating signal is
generated. A power and a frequency of the oscillating signal are tuned by
the length of the radio frequency signal supplying line 118. Then, the
oscillating signal is transferred to the dielectric line 108 so that an
LSM mode and an LSE mode are created. At this time, the LSE mode is
rejected by the mode suppressor 119 and the LSM mode with a low
transmission loss is transferred to the first port P1 of the ring hybrid
coupler 127.
In addition, the radio frequency signal is inputted into the rod antenna
through a horn antenna (not shown) and is transferred into the second port
P2 of the ring hybrid coupler 127 in opposite to the local oscillating
signal.
The local oscillating signal and the radio frequency signal transferred
into the first and second ports P1 and P2 are transferred into the third
and fourth ports P3 and P4 and are mixed therein. The third port P3 and
the fourth port P4 have phase differences of .lambda./4 or
(4n+1).lambda./4k, wherein n is an integer. Accordingly, an IF signal,
which is an addition signal of the local oscillating signal and the radio
frequency signal, and a baseband signal which is a subtraction signal
between the local oscillating signal and the radio frequency signal, are
created by mixing the local oscillating signal and the radio frequency
signal. For example, when the local oscillating signal of 59 GHz is
transmitted to the first port P1 and the radio frequency signal of 60-61
GHz is inputted into the second port P2, a subtraction signal having the
frequency of 1-2 GHz and an addition signal having the frequency of
119-120 GHz are generated from the third and fourth ports P3 and P4. At
this time, the signal having the high frequency band is disregarded and
the signal having the frequency of 1-2 GHz is utilized.
FIG. 10 shows the structure of the ring hybrid coupler 127. Characteristic
impedances of the first to fourth ports P1, P2, P3 and P4 are identically
predetermined as Zo and a characteristic impedance of an annular ring 135
is predetermined as Zo/√2 so as to obtain a desired coupling ratio.
Accordingly, the impedance matching is achieved at each port, and the
first and second ports P1 and P2 are separated to compensating the signals
therethrough. In addition, the input power of the wave incident into the
first and second ports P1 and P2 is uniformly distributed into the third
and fourth ports P3 and P4.
A circumference length of the annular ring 135 at a middle portion thereof
is substantially .lambda., and the first to fourth ports P1, P2, P3 and P4
are arranged around the annular ring 135 spaced by .lambda./4 from each
other. Accordingly, the first port P1 to which the local oscillating
signal is transmitted and the second port P2 into which the radio
frequency is inputted have the phase difference of 2.lambda./4, so the
signals introduced into the third and fourth ports P3 and P4 from the
first and second ports P1 and P2 have the phase difference of 180 degree.
The signals are transmitted to the third and fourth ports P3 and P4 in the
form of a compensated signal or a mixed signal.
The signals coupled in the annular ring 135 are transferred to the first
and second mixer mounts 121 and 124 through the third and fourth ports P3
and P4 and are transformed into the IF signals and the baseband signals.
For instance, the signals introduced into the third and fourth ports P3
and P4 pass the Schottky diode 134 mounted in the mixer mounts 121 and 124
through the dielectric lines 128 and 129. Then, the Schottky diode 134
performs the switching operation by receiving the bias signal through lead
wires 137b and 138b so that the signals are transformed into IF signals
through the lead wires 137a and 138a. The IF signals are amplified while
passing through the IF circuit and are outputted to the exterior through
the connector 130. The bias signal is applied to the Schottky diode 134
through the EMI filter 132.
On the other hand, the operation is reversely carried out when the NRD
waveguide mixer is used as the signal transmitter. That is, the IF signal
is transmitted to the annular ring 135 through the third and fourth ports
P3 and P4. In addition, the local oscillating signal is inputted into the
annular ring 135 through the first port P1. The addition signal of the
above two signals is radiated through the rod antenna 120.
FIG. 11 shows the structure of a ring hybrid coupler 127' according to
another embodiment of the present invention. In the figure, the first port
P1 receives the local oscillating signal and the second port P2 is
connected to the rod antenna 120 so as to receive the radio frequency
signal. It is possible to reversely arrange the first and second ports P1
and P2. The first to fourth ports P1, P2, P3 and P4 have the same
characteristic impedance Zo and the annular ring has a characteristic
impedance of Zo/√2. The first to fourth ports P1, P2, P3 and P4 are
arranged around the annular ring 135 in a clockwise direction in order of
the first, third, second and fourth ports P1, P3, P2 and P4. When a
circumference length of the annular ring 135 is 6.lambda./4, the first
port P1 is spaced from the third port P3 by 3.lambda./4, the second port
P2 is spaced from the third port P3 by .lambda./4, the second port P2 is
spaced from the fourth port P4 by .lambda./4, and the first port P1 is
spaced from the fourth port by .lambda./4 in such a manner that the first
to fourth ports P1, P2, P3 and P4 have phase differences with respect to
each other. Accordingly, the first port P1 has the phase differences of
2.lambda./4 and 4.lambda./4 with respect to the second port P2 so that the
first and second ports P1 and P2 have bidirectional phase differences of
180 degree and can be evaluated to have a good isolation with each other.
As shown in FIG. 12, when it is difficult to design the ports of the ring
hybrid coupler depending on a particular wave length, it can be
alternative to design the ports to have the distances therebetween
(4n+1).lambda./4 and (4n+3).lambda./4 rather than .lambda./4 and
3.lambda./4. The ring hybrid coupler can be analyzed by using a scattering
matrix with respect to the ports.
FIG. 12 shows the structure and an equivalent circuit for analyzing the
input impedance of the annular ring when output ports are terminated. When
the fourth port P4 is terminated, the impedance viewed from the first port
P1 is represented as the equivalent circuit shown in the right side of
FIG. 12. The impedance value viewed from the first port P1 is identical to
the sum of characteristic impedance values of third and fourth ports P3
and P4 and the annular ring 135. At this time, the characteristic
impedance value of the annular ring 135 is viewed as 2Zo which is the sum
of .lambda./4 and 3.lambda./4.
In addition, since the input power is uniformly distributed into the third
and fourth ports P3 and P4, the following equations are obtained.
b.sub.3 =ja.sub.1 /√2.
b.sub.4 =-ja.sub.1 /√2,
where a.sub.1 is an incident wave at the first port P1, b.sub.3 is a
reflected wave at the third port P3 and b.sub.4 is a reflected wave at the
fourth port P4. When a signal is applied to the third port P3, the first
and second ports P1 and P2 become the output port. At this time, b.sub.1
=0, b.sub.3 =ja.sub.2 /√2 and b.sub.4 =-ja.sub.2 /√2,and the
b.sub.3 and b.sub.4 have the same phase. Based on these relations, the
scattering matrix of the hybrid ring can be obtained as follows.
##EQU1##
The ring hybrid coupler is an E-plane T-junction having a ring shape. The
characteristic impedance at the annular ring for satisfying the matching
condition is Zo/√2.
On the other hand, a coupling area at which that the ports are connected to
the annular ring has a structure the same with the T-junction. However, it
is difficult for a device having three ports to obtain a preferred
impedance feature since the impedance matching of the ports is difficult.
For this reason, as shown in FIG. 13a, an inductive iris made of a thin
conductive plate is attached to the T-junction areas of the annular ring
135, at which the electromagnetic wave signal inputted through the first
and second ports P1 and P2 is distributed into the third and fourth ports
P3 and P4, so as to reduce a reflection loss thereby increasing a transfer
gain. Alternatively, post members 140A and 140B made of conductive
material are accommodated in the T-junction areas for the same reason.
Besides the inductive iris, a stub can be provided at the T-junction areas
of the first and second ports P1 and P2 so as to improve the signal
isolation degree between the first and second ports P1 and P2 and so as to
allow the signal to be stably distributed from the first and second ports
P1 and P2 to the third and fourth ports P3 and P4. As shown in FIG. 13b,
it is preferred to terminate first and second ports P1 and P2 by using
stubs 142A and 142B. Preferably, the stubs 142A and 142B are made of
dielectric material identical to material of the annular ring 135.
FIG. 14 shows an electromagnetic wave analyzing model for the ring hybrid
coupler. The first to fourth ports P1, P2, P3 and P4 are symmetrically
arranged and the ring hybrid coupler is surrounded by an air space 141.
The remaining space is regarded as a perfect conductor. The signals
inputted into the first and second ports P1 and P2 are coupled in the
annular ring 135. The wave can be transmitted or attenuated by adjusting
the phase of it in proportional to the wavelength.
FIG. 15 is a view showing the intensity of the electric field obtained by
analyzing the model shown in FIG. 14. When each port is symmetrically
arranged and the wave having the same intensity is incident into the first
and second ports P1 and P2, the wave is transmitted into the third and
fourth ports P3 and P4. At this time, a desired signal isolation degree is
obtained between the first and second ports P1 and P2. In addition, the
LSM mode created in the first and second ports P1 and P2 is maintained in
the third and fourth ports P3 and P4. It means that the ring hybrid
coupler can be applicable to the NRD waveguide coupler and a divider as
well as the balanced mixer.
As described above, it is difficult to fabricate the conventional NRD line
coupler in a small size. However, the present invention employs the ring
hybrid coupler which occupies a small space as compared with a bend type
coupler so that the mixer can be fabricated in a small size with a light
weight.
In addition, in the fabrication of the conventional NRD line coupler, it is
required to precisely maintain the distance between two bends. However, it
is difficult to precisely arrange the two bends. Furthermore, it is
difficult to bend the two bends in a precise bending angle. On the
contrary, the ring hybrid coupler of the present invention is integrally
formed without forming the bends therein so that the ring hybrid coupler
can be mass-produced by using an injection molding process.
In addition, the conventional parallel dielectric line coupler has not any
particular device for obtaining the precise impedance matching, and the
isolation degree between ports is poor. However, the ring hybrid coupler
of the present invention can improve the impedance matching by using the
inductive iris and the post member. In addition, the isolation degree and
the transmitting feature between two ports can be improved by adding the
stubs to the ring hybrid coupler. Furthermore, the ports can be designed
to have various phase differences and the number of the ports can be
increased.
In addition, the ring hybrid coupler of the present invention can adjust
the wave mode of the signal from the LSM mode to the LSE mode or vise
versa by using the T-junctions. Accordingly, the ring hybrid coupler can
be applicable to the mode converter and the power divider as well as the
mixer.
Although the preferred embodiments of the invention have been described, it
will be understood by those skilled in the art that the present invention
should not be limited to the described preferred embodiments, but various
changes and modifications can be made within the spirit and scope of the
invention as defined by the appended claims.
*
