Double Mode X-band T/R Module Based on LTCC

Dai Yuefei, Lv Chunming, Xie Qilin, HAN junEast China Research Institute of Electronic Engineering, Hefei 230031, China

Email: daiyuefeigecriee.ac.cn

Abstract-LTCC is usually applied as basic PCB for high-density and high-reliability integrating in MCM. Thestructure and operating principle of a double mode X-bandT/R module based on LTCC are discussed in this paper, andthe performance analysis in theory is performed. Finally, thetest results and conclusion are given.

Key words: T/R module, LTCC

I. INTRODUCTION

The T/R modules based on GaAs is employed from1970's, and it is developed due to micro-electronicstechnology in 1980's. With the grown up of monolithicmicrowave integrated circuit(MMIC) in 1990's, the T/Rmodules have been developed towards the direction ofbecoming an independent apparatus and single patch on itsstructure, performance, consistence and reliability. Thenthe designers of phased array radar system have a moreopportunity to design new radar system.

However, based on the existing semiconductortechnology level, considering to avoid the risk ofdesigning MMIC and making MMIC, the microwavemultichip module (MCM) technique is often adopted toproduce high performance and high consistence T/Rmodules whose performance may compare favourablywith MMIC modules, meanwhile, the advantage instructure would not lose too more. Just owing to thissuperiority, MCN has been developed into a microwaveapplication industry which has the independent designcompany , sell entity and large market.

On the other hand, as the vital MCM substrate ofLTCC technology is gradually grown up, the designingand making problems about multilayer substrate inmicrowave are solved gradually. The X-band microminiature T/R modules that can be used in active phasearray are made with GaAs MMIC technology and LTCCmultilayer structure (surface layer is for microwave circuitand underlayer is for control circuit) by MitsubishiElectric Corporation in 1992 In 1997, K. Lkuina and hispartners succeeded to produce a new type LTCC whichcontained a great deal of integrated circuit in millimetermicrowave band. This new type of LTCC can greatlydecrease the size of T/R modules used in satellitecommunications system or local area microwave andmillimeter microwave network. It is reported that LTCCwas successfully applied in 30 GHz-40GHz frequencyband in USA in 1996. By 2000, MMIC at 76GHzfrequency was produced, based on thick film, via holes,wire bonding package technology, its inserting loss is nomore than 1dB.

It is just the development of LTCC that promotingthe hybrid printed circuit technology, especially promotingthe design and manufacture technology, so as to put thebase for integration in more great scope (the hybridprinted circuit technology stated above means thatmultiple signal, such as microwave signal, low frequencysignal, digital signal, analog signal, high power signal,small power signal, linearity signal, non-linearity signal,are integrated in a common substrate.).

A novel type T/R module based on MCM designmethod and LTCC substrate is introduced in this paper.On the "single transmit double receive"telecommunication structure, this T/R module can workwith two modes, i.e. the horizontal polarization andvertical polarization, and these two modes have thecharacteristics of good performance and simple interface.

II. LTCC DESIGNIt is well known that layering and grounding are the

very important problems for microwave application ofmulti-layer LTCC. These problems usually determinewhere the unexpected resonance in the frequency bandwill occur. On the other hand, these problems also partlydetermine the electro magnetic compatibility (EMC)performance of T/R module which employed LTCC.

A layering principle[1]In general, LTCC used in the microwave T/R

module usually is composed of four parts: microwavelayers, power supply layers, control signal layers andgrounding layers. The grounding layers perhaps includethe microwave grounding layers, power supply groundinglayers and control signal grounding layers.

Considering EMC, signal integrality (SI) and powerintegrality (PI), the microwave layers usually occupy thetop layers of LTCC, at the same time, those controllingsignals which are rapidly changed or greatly rippledshould be put far apart from the microwave layers. Inaddition, grounding layers are inserted into those layers soas to increase isolation performance to the greatest extent.

Sometimes, a grounding layer, for example, thegrounding layer for signal, is isolated from modules boxand connected to far ground by the pins of low frequencyconnector.

B Grounding method[1][2]Considering the particularity of microwave signal,

the microwave grounding layers should be directlyconnected to box body via perpendicular connection holesinstead through other middle grounding layers.Furthermore, the width of these grounding holes should be

0-7803-9582-4/06/$20.00 c2006 IEEE

twice as much as that of microwave signal routes, in orderto avoid margin effective. Enough routing space should beleft for control signal and power supply signal whengrounding holes along transmission direction are arranged.

- LTCC surface layers* > Microwave layers

microwave grounding layers* s signal layers

- signal grounding layers

* signal layers

__________ -_-k signal grounding layers

power supply layers

- LTCC substrateFigure 1. LTCC layers

Though the two grounding modes shown in Fig. 2and Fig.3 can sufficiently ensure good microwavegrounding performance (simulation results showed thatthe grounding performance of Fig.3 is somehow betterthan that of Fig.2.), it is obviously that these two modesbring great limit to routing of control signal and powersupply signal. So, we proposed a "honeycomb" groundingmethod shown in Fig.4. The grounding performance ofhoneycomb grounding method is close to that of Fig.3.The advantage of honeycomb grounding method is thatrouting is realized among the honeycomb. Moreover, theintrinsic resonance frequency of LTCC can be eliminated,or the resonance intensity can be decreased by adjustingthe intervals among honeycombs. That is beneficial tomodule stabilization.

Figure 4. The honeycomb microwave grounding mode

III. DOUBL MODE MODULE DESIGN

A PrincipleThe module principle is shown in Fig.5. In order to

realize double-mode working, a polarization switch and atransmit channel are added in common single channelmodule. The double-mode working is switched betweentwo transmit channels. Of course, corresponding to theadditive transmit channel, a separated receive channel isalso added.

A switch is inserted between attenuator and phaseshifter in additive receive channel to obtain betterconsistence of its gains and phases.

ratmce

power ndrdwmplifer WmphLfe

ratraelim= LNA1 kferoto

wich

ph.e shifter

LNA2

Figure 2. The run-in microwave grounding mode

Figure 5. Module principle

B Analysis ofprimaryperformance1) Transmitting output powerThe output of final power amplifier in transmitting

channel is sent out through the circulator. The insertingloss values of the circulator, the SMA connector and themicrostrip after the final power amplifier is about 0.6dB,0.2dB and 39 dB respectively.

Pout (39-0.6-0.2-0.4) dBm=6.03 W2) Receiving gain and noise coefficientNoise coefficient and gain of each stage in receiving

channel are listed in Tabale 1.

TABLE I. THE NOISE AND GAIN IN RECEIVING CHANNEL

stage12345Figure 3. The cater-corner microwave grounding mode

Gain-1.8dB19dB-0.5dB25dB

-17.1dB

NF1.8dB1.4dB0.5dB2.5dB17.1dB

remarkInput attenuation

LNA1Level's attenuation

LNA2Output attenuation

The input attenuation of first stage is the lossproduced primarily by circulator, isolator, amplitudelimiter and transmission line. The third stage's attenuationis mainly the loss of transmission line. The fifth stageoutput attenuation includes zero state attenuation ofattenuator, connection losses of switch and phase shifter.

The total noise coefficient of a cascade system iscomputed as follows

F -i

F=Fl+ 2GI

+ ...... +

Fn - 1

G G2G Gn-

IV. PRIMARY TEST RESULTSThe primary test results are showed from Fig.7 to

Fig. 12, From which we can find, (1) the output power oftwo transmitting channels is over 6W, (2) the gaindifference of two transmitting channels is obvious,because the chip gain is dispersed, which had beendiscovered when the chips were tested alone, (3) thereceiving channel attenuation fluctuation in highattenuation state of digital attenuator is acute, it is theinherence characteristics of the apparatus used.

In fact, the connection loss on module receivinginput port is far more than 1.8dB due to the instability ofmanufacture technology. The module's receiving channelnoise coefficient is close to 4.2dB or more because thegreater connection losses between SMA tie-in andconduction strip, circulator and conduction strip are bigger.

3). Implementation of inside wave beam controlIn order to realize wave beam control function while

ensure a simple module structure, wave beam controlsignal is fed in module in series code. Depending on a

fixed clock pulse, a conversion from series to parallel isimplemented by using shift register in module.

4) StructureThree aspects have to be noticed when module

structure is designed. The first is to ensure better heatexchange ability. The second is to make an effort to avoidcavity resonance effect in its work frequency band. Thethird is to pledge EMC inside module. Therefore, thedesign of module is not only associated with structuredesigner but also associated with telecommunicationdesigner. The dimension of module is 75x22x 1Omm3 ifthe connectors are not considered.

C PackageA lot of micro-electronics assembling technology

such as solder, eutectic bonding, ultrasonic electron beampackage and so on are used. In order to ensure betterconnection performance inside module, preventing split ofLTCC and adapting the different demand for differentapparatus, four temperature grades are employed to isolateand to distinguish the jointing infection in package process.

4, 5

4, 03, 5

alS~~~~~~~~----9,409' 4 95 955 9GO 96 9,T 9 98

Figure 7. Receiving noise of module

Figure 8. Receiving gain of module

10 _9

54 Ma, i

2~~~~~~~~~~~~~d ..a_1

Figure 9. Receiving phase accuration of module

3.0

.0.D9nt4D 9, S 9.950 9.55 9)60 9.63 9.io 9. 9.0

Figure 6. Photograph of module practicalityFigure 10. Receiving attenuation accuration of module

4- v

Il 0

89

.5 -

0I9 i40 %y 45 9i 50 9HX5 9 0 9 5 % %7

Figure 11. Transmitting phase accuration of module

'0 -

381

41

34)34

31

9.'to 9.'45 9, 50 9. i 9 ,.5 9. so

V. CONCLUSIONThe module design method proposed in this paper

gives better consideration to both the demands of phasedarray radar and synthetic aperture radar (SAR), whichimplements the double-mode working in very small spaceand possesses the feature of high output power and lownoise.

REFERENCES[1] [1] YAN Wei, HONGWei, XUE Yu. LTCC Microwave Multichip

Modules[J]. Acta Electronic Sinica,2002,30(5):711-714.[2] [2] Jiang wui zhuo,yan wei xie lian zgong. The Placement Routing

Design And Manufacture technology of Multilayer MicrowaveJoining Substrate.ElectronicsProcess Technology, 2000, 21(2):81-83.

Figure 12. Transmitting power of module