A Planar Magic-T Structure Using Substrate Integrated Circuits Concept and Its Mixer Applications
A Planar Magic-T Structure Using Substrate
Integrated Circuits Concept and
Its Mixer Applications
Fan Fan He,Ke Wu ,Fellow,IEEE ,Wei Hong ,Senior Member,IEEE ,
Liang Han ,Student Member,IEEE ,and Xiaoping Chen
Abstract—In this paper,a planar 180phase-reversal T-junc-tion and a modi?ed magic-T using substrate integrated waveguide (SIW)and slotline are proposed and developed for RF/microwave applications on the basis of the substrate integrated circuits con-cept.In this case,slotline is used to generate the odd-symmetric ?eld pattern of the SIW in the phase-reverse T-junction.Measured results indicate that 0.3-dB amplitude imbalance and 3phase imbalance can be achieved for the proposed 180phase-reversal T-junction over the
entire -band.The modi?ed narrowband and optimized wideband magic-T are developed and fabricated,respectively.Measured results of all those circuits agree well with their simulated ones.Finally,as an application demonstration of our proposed magic-T,a singly balanced mixer based on this structure is designed and measured with good performances.Index Terms—Magic-T,180phase-reverse T-junction,slotline,substrate integrated circuits (SICs),substrate integrated wave-guide (SIW).
I.I NTRODUCTION
A
SLOTINE presents advantages in the design of mi-crowave and millimeter-wave integrated circuits,espe-cially when solid-state active devices are involved.Recently,the substrate integrated circuits (SICs)concept,involving the substrate integrated waveguide (SIW)technique and other synthesized nonplanar structures in planar form with planar circuits,has been demonstrated as a very promising scheme for low-cost,small size,relatively high power,low radiation loss,and high-density integrated microwave and millimeter-wave
Manuscript received December 22,2009;revised May 21,2010;accepted September 08,2010.Date of publication December 03,2010;date of current version January 12,2011.This work was supported in part by the Natural Sci-ences and Engineering Research Council of Canada (NSERC),in part by the National 973Project of China under Grant 2010CB327400and in part by the National Nature Science Foundation of China (NSFC)under Grant 60921063.F.F.He is with the Poly-Grames Research Center,Department of Electrical Engineering,école Polytechnique de Montreal,Montreal,QC,Canada H3C 3A7,and also with the State Key Laboraotry of Millimeter Waves,College of Information Science and Engineering,Southeast University,Nanjing 210096,China (e-mail:fanfan.he@polymtl.ca).
K.Wu,L.Han,and X.Chen are with the Poly-Grames Research Center,De-partment of Electrical Engineering,école Polytechnique de Montreal,Montreal,QC,Canada H3C 3A7(e-mail:ke.wu@https://www.wendangku.net/doc/aa16548787.html,).
W.Hong is with the State Key Laboratory of Millimeter Waves,College of Information Science and Engineering,Southeast University,Nanjing 210096,China (e-mail:weihong@https://www.wendangku.net/doc/aa16548787.html,).
Color versions of one or more of the ?gures in this paper are available online at https://www.wendangku.net/doc/aa16548787.html,.
Digital Object Identi?er 10.1109/TMTT.2010.2091195
components and systems [1]–[6].Alternatively named inte-grated waveguide structures of the SIW,such as laminated waveguide or post-wall waveguide,can be found in [7]and [8].The transitions from the SIW to slotline [9]have already been investigated theoretically and experimentally,which provide a design base to integrate SIW circuits with slotline circuits.As a fundamental and important component,the magic-T has widely been used in microwave and millimeter-wave circuits such as balanced mixers,power combiners or dividers,balance ampli?ers,frequency discriminators,and feeding networks of antenna array [10],[11].Following intensive investigations of SIW components and systems in the past ten years,more and more attention is being paid to integrate the conventional magic-T based on SIW technology.Some SIW-based magic-T structures have been proposed and studied [9],[12],[13].In [12]and [13],magic-T techniques were developed using multilayer low-temperature co-?red ceramic (LTCC)or printed circuit board (PCB)processes.An SIW planar magic-T was successfully designed with relatively narrowband character-istics in [9].This magic-T consisting of an SIW T-junction,a slotline T-junction,and two phase-reverse slotline-to-SIW T-junctions,and it has an 8%bandwidth centered at 9GHz with 0.2-dB amplitude and 1.5phase imbalances.In this paper,a modi?ed version of a planar SIW magic-T,which only consists of a phase-reverse slotline-to-SIW T-junction and
an -plane SIW T-junction,is proposed and presented,as shown in Fig.1,which has smaller size and wider bandwidth than its previous version [9].
Described in Section II are the analysis and discussions of the proposed 180phase-reversal slotline-to-SIW T-junction with its simulated and measured results.In Section III,the modi?ed planar magic-T structures with direct design and with further optimization are discussed with their transmission line models.Measured results agree with simulated results very well.Ad-ditional wideband slotline-to-microstrip and SIW-to-microstrip transitions are designed for port-to-port measurements of mi-crostrip line in support of experimental characterization of the proposed structures.In the end,a singly balanced mixer based on our modi?ed wideband magic-T is developed.All the struc-tures in this paper are simulated with means of the full-wave simulation tool Ansoft HFSS,designed and fabricated on an RT/Duroid 6010substrate with a dielectric constant of 10.2and a thickness of 0.635mm.
0018-9480/$26.00?2010IEEE
Fig.1.Physical 3-D con?gurations of the modi?ed magic-T.
II.P HASE -R EVERSAL S LOTLINE -TO -SIW T-J UNCTION Here,the slotline-to-SIW T-junction acts as a mode converter between the slotline and SIW.Fig.2(a)depicts the physical 3-D
con?guration of the slotline-to-SIW T-junction,
where
is the width of metallic
slot,
is the SIW width,
and is the slotline width.The yellow (in online version)and dark layers are the top metal cover and bottom metal cover.The light gray area means substrate.The slotline and SIW structures in-tersect with each other in which the slotline extends
length into the metallic cover of the SIW with a short-circuited termina-tion.Two via-posts with the diameter
of are used to optimize the return loss of the T-junction.Fig.2(b)shows the cross sec-tion at the A–A plane,where the orientation of electric ?elds is sketched.When the signal is coupled from the slotline into the SIW at the A–A plane,the electric ?elds of the slotline mode are converted to those of the half-mode SIW (or HMSIW)mode [14]because of overlapped metallic covers on the top and bottom of the SIW.As such,two phase-reverse waves come out of ports P2and P3.
Fig.2(c)shows the equivalent circuit model of the T-junction.The model is similar to that of an -plane waveguide T-junc-tion due to their similar electric ?eld
conversion.
and are the characteristic admittances of the slotline and HMSIW,re-spectively.In the equivalent
circuit,
is used instead of the SIW characteristic admittance because both of them have al-most the same value.Based on the above principle,
parameters
,,
and are mainly dependent on slotline’s
length ,
width ,
and at the slotline port (port 1),
and mainly depends on the SIW
width .Therefore,the rela-tionship between parameters of the equivalent circuit and return loss at port 1is replaced by that between parameters of phys-ical con?guration and return loss at port 1.In order to minimize any potential radiation loss while transmitting signal from the slotline to the SIW,a possible minimum width of the slot line is
chosen
as
mm.Fig.2.(a)Physical description and parameters of the slotline-to-SIW T-junc-tion.
W
=0:2mm,
W =7:3mm,D =0:6mm,
L =4:6mm,L =4mm,and
W =8mm.(b)Electric ?eld distribution at cross section A–A plane.(c)Equivalent circuit for the slotline-to-SIW T-junction.
Fig.3shows simulated and measured frequency responses of power dividing and return loss of the 180phase-reversal slot-line-to-SIW T-junction.The imbalance in amplitude and phase are,respectively,0.3dB and 3,as shown in Fig.4.These results suggest that the junction has broadband characteristics.Fig.5presents a photograph of the T-junction.
III.M ODIFIED P LANAR S LOTLINE -TO -SIW M AGIC -T A.Magic-T Circuit Con?guration and Operating Principle Fig.1describes the physical 3-D con?guration of the pro-posed magic-T.The yellow (in online version)and dark layers are the top metal cover and bottom metal cover.The light gray area means substrate.The orange areas (in online version)are metallic slots for the SIW.This magic-T consists of an
SIW -plane T-junction and a slotline-to-SIW T-junction.Two such T-junctions share the two common arms with 45rotation.Metallic vias V1and V2with
diameter are used to construct the
SIW -plane T-junction.Ports 1
(port)and 4
(port)are sum and difference ports,respectively,while ports 2and 3are the power dividing arms.Without the microstrip line-to-SIW and slotline-to-microstrip line transitions,the size of the magic-T is about 20
mm 20mm.A signal applied to
Fig.3.Simulated and measured frequency responses of power dividing and return loss for the 180slotline-to-SIW
T-junction.
Fig.4.Measured amplitude and phase imbalances of the slotline-to-SIW
T-junction.
Fig.5Photograph of the slotline-to-SIW T-junction.Left and right ?gures are the top view and bottom view,respectively.
port 1is split into two in-phase components by metallic via V1.The two components cancel each other at the slotline,while port 4is isolated.In this case,the four-port junction works as an
SIW -plane T-junction and the symmetrical plane A–B becomes a virtual open plane.Otherwise,the four-port junction works as a slotline-to-SIW T-junction and the plane A–B becomes a virtual ground plane when a signal is applied to port 4.The input signal is naturally split into two equal and out-of-phase signals at ports 2and 3,and port 1is isolated in this
case.
Fig.6.Corresponding equivalent circuit of the
magic-T.
Fig.7.Simpli?ed equivalent circuits of the magic-T.(a)In-phase.(b)Out-of-phase.
The operating principle of the modi?ed magic-T can also be well explained by its corresponding equivalent cir-cuit at the working frequency shown in Fig.6,where the slot-to-SIW T-junction can be seen as an ideal transformer and the
SIW -plane T-junction as a divider.
Parameters
,
,,
and stand for the characteristic impedances,slotline,ground slotline,HMSIW,and SIW,re-spectively.In the in-phase case,the equivalent circuit model will further be simpli?ed as depicted in Fig.7(a),
when
at the working frequency.In
the out-of-phase case,the simpli?ed equivalent is shown in
Fig.7(b),
where
.On the basis of the above dis-cussion,
distances
and should depend on the positions of the three metallic vias in the magic-T circuit.B.Implementation and Results
Based on the above-stated principle,two magic-T struc-tures are designed and fabricated on an RT/Duroid 6010LM
Fig.8.Photograph of the modi?ed magic-T.Left and right ?gures are the top view and bottom view,respectively.
TABLE I
D IMENSIONS OF TH
E M ODIFIED N ARROWBAND M AGIC
-T
substrate,respectively,with narrowband and wideband char-acteristics.Thus,the narrowband and wideband cases of the magic-T will be discussed separately.Fig.8shows the top view and bottom views of the modi?ed magic-T’s photograph.From this photograph,we can estimate that the size of the magic-T is reduced by near 50%with reference to [9].
1)Narrowband Case:The two out-of-phase signals cancel each other at port 1as described in Section II-A,and simulta-neously the
distance is equal to a quarter of the guide wave-length of the SIW at the working frequency.Thus,the working bandwidth of the return loss at port 4should be narrow in a sim-ilar manner to the previous design [9].However,the working bandwidth judging from the return loss at port 1should be wider because the two in-phase signals cancel each other in the slotline at port 4.In this demonstration,the magic-T was designed at 9GHz.All design parameters of the magic-T are listed in Table I.Fig.9shows the return loss and insertion loss of the fabri-cated narrowband
magic-T.
is lower than 15dB from 8.7to 9.4GHz with a 7.8%bandwidth,which has validated the above discussion.Within the frequency range of interest,the minimum insertion loss is 0.7dB and it is less than 0.8dB in both in-phase and out-of-phase cases.Simulated and measured isolation characteristics are described in Fig.10.The isolation is better than 30dB between ports 1and 4,and better than 20dB between ports 2and 3over the entire frequency range.As shown in Fig.11(a)and (b),the maximum phase and amplitude imbal-ances for both in-phase and out-of-phase cases are less than 1.5and 0.5dB,respectively.
2)Wideband Case:The narrowband characteristics of this magic-T have well been con?rmed in the above discussion.However,an interesting outcome can be observed in that the re-turn-loss de?ned bandwidth can be broadened by optimizing the
parameter values
of
,
,,
and .When the signal ?ows into the SIW from the slotline in this slotline-to-SIW structure,it would be split into two components and each of
them will propagate along
line
at the working frequency,
as Fig.9.Simulated and measured frequency responses of the magic-T.(a)Return
loss.(b)Insertion
loss.
Fig.10.Simulated and measured isolation characteristics of the magic-T.
shown in Fig.1.Nevertheless,the propagating directions being different slightly at different frequencies provide a possibility of broadening the bandwidth of the magic-T.In other words,
it is possible for the magic-T to simultaneously
realize
,
and
,at two
different frequencies.In our proposed broadband design,these two frequencies are set at 8.7and 9.8GHz.Through optimiza-tion,some geometrical parameters of magic-T are changed
Fig.11.Measured results of amplitude and phase imbalance characteristics of the magic-T.(a)Amplitude.(b)Phase.
such
that
mm,
mm,mm,
and mm.
Fig.12(a)shows the newly designed magic-T’s simulated and
measured return losses at each port.Among the results,simu-
lated indicates that the above two geometrical conditions
for achieving broadband performances are readily satis?ed at
8.7and9.8GHz.Measured return loss is better than15dB from
8.4to10.6GHz with23.2%bandwidth.In this broadband fre-
quency range,the insertion loss is less than0.9dB and the min-
imum insertion loss is0.7dB in both in-phase and out-of-phase
cases,as shown in Fig.12(b).Measured and simulated isola-
tion curves between port1and port4or port2and port3are
plotted in Fig.13.In addition,the amplitude and phase imbal-
ances of the magic-T are2and0.5dB,respectively,as shown
in Fig.14(a)and(b).Measured results of all circuits agree well
with their simulated counterparts.
IV.M ODIFIED M AGIC-T’s A PPLICATION IN M IXER D ESIGN
As a practical and straightforward demonstration of our
modi?ed magic-T applications,a singly balanced mixer is
designed,as shown in Fig.15.Fig.16shows the photograph
of the practical mixer.An antiparallel pair of series
connected
Fig.12Simulated and measured frequency responses of the magic-T.(a)Re-
turn loss.(b)Insertion
loss.
Fig.13.Simulated and measured isolation characteristics of the magic-T.
diodes(SMS7630-006LF from Skyworks Inc.,Woburn,MA)
is adopted.Generally,a quarter-wavelength short stub in the
matching circuit is need for providing a dc return and good
IF-to-RF and IF-to-local oscillator(LO)isolations.However,
a matching circuit is designed between the diode and SIW
without using a quarter-wavelength short stub because the SIW
is grounded inherently.
Two open-circuited stubs on
Fig.14.Measured results of amplitude and phase imbalance characteristics of the magic-T.(a)Amplitude.(b)
Phase.
Fig.15.Circuit topology of the proposed mixer.
the right side of the diodes pair are used to provide a terminal virtual grounding point for LO frequency and RF frequency simultaneously.In addition,a low-pass ?lter is designed to suppress LO and RF signals at IF port.The mixer designed and simulated by the harmonic balance (HB)method in Agilent ADS software combined with
measured -parameters of the wideband magic-T structure.
Fig.17depicts the measured conversion loss versus LO input power level when the IF signal is ?xed at 1GHz with an input power level of 30dBm and LO frequency is ?xed at 10.2GHz.When the LO input power level is larger than 13dBm,the con-version loss almost is about 7.4dB.Fig.18shows the measured conversion loss versus IF frequency when the IF signal is
swept Fig.16.Photograph of the
mixer.
Fig.17.Measured conversion loss versus LO input
power.
Fig.18.Measured conversion loss versus IF frequency.
from 0.1to 4GHz (RF is from 10.1to 6.2GHz)with a constant input power level of 30dBm,and the LO signal is ?xed at the frequency of 10.2GHz with a 13-dBm power level.The mea-sured conversion loss is about
80.6dB over the IF frequency range of 0.1–3GHz (RF is from 7.2to 10.1GHz).Fig.19plots the measured conversion loss versus input RF power level,where RF frequency is set at 9.2GHz and LO frequency is at 10.2GHz with a power level of 13dBm,input RF power level is swept from 30to 5dBm.The output IF power almost in-creases with the RF power linearly when the RF power level is less than 3dBm.On the other hand,when the RF power level is larger than 0dBm,the mixer is driven into the nonlinearity region.From this ?gure,it can also be seen that the input 1-dB