Design and Technology of Microwave and Millimeterwave LTCC Circuits and Systems

Transcription

1 Design and Technology of Microwave and Millimeterwave LTCC Circuits and Systems Ingo Wolff, Life-Fellow, IEEE IMST GmbH Carl-Friedrich-Gauss-Str. 2 D Kamp-Lintfort, Germany Abstract LTCC technology has large benefits in microwave and millimeterwave applications. In this presentation an overview is given on the design rules and the technological realization of components, circuits and systems for microwave and millimeter wave applications. The advantages and possible problems of the technology are described. Index Terns Low temperature cofired ceramics (LTCC), microwave and millimeterwave LTCC circuits, LTCC system packaging, LTCC antennas, LTCC design, LTCC technology. I. INTRODUCTION LTCC (low temperature co-fired ceramic) stands for a ceramic substrate system which is applicable in electronic circuits as a cost-effective and competitive substrate technology with nearly arbitrary number of layers. Printed gold and silver conductors or alloys with platinum or palladium will be used in general. Cupper conductors are available, too. The metallization pastes are screen printed layer by layer upon the un-fired or green ceramic foil, followed by stacking and lamination under pressure. The multilayer ceramic stack then is fired (sintered) in the final manufacturing step. The temperature of sintering is below 900 C for the LTCC glass-ceramic. This relative low temperature enables the co-firing of gold and silver conductors. The melting points of Au and Ag are 960 C and 1100 C respectively. The fabrication process principally is shown in Fig. 1. process on a field theoretical basis will be explained and sophisticated examples of microwave and millimeter wave circuits and systems will be demonstrated. II. WAVEGUIDES AND COMPONENTS IN LTCC A. Waveguides and Fundamental Structures Fig. 2 shows the fundamental technology processes for a microwave and millimeter wave circuit design which can be realized using LTCC technologies. Multiple layers (up to 30 or more) of dielectric materials allow to realize a real 3D circuit layout. Inner conductors (gold, silver, cupper) permit to fabricate ground meshes or ground planes, inner microstrip lines, inner strip lines and coplanar waveguides as well as passive lumped components like inductors and capacitors. Through connections (via s) allow to interconnect the different circuit layers effectively. Using resistive pastes, buried resistors can be realized. Finally, waveguide structures and passive components can be placed on the top and bottom side of the circuit, co-fired or even post-fired. Additionally cavities and windows allow to construct openings inside the circuit to realize resonators or even heat transfer constructions. With all these technology steps a very effective and flexible technology is available which, considering latest research results, is applicable for frequencies up to 60 GHz (and possibly higher). Standard screen printing technologies allow to realize line widths of 80 μm to 100 μm. With a high resolution screen printing technique also line widths below 50 μm can be fabricated. Fig. 1. Technology steps for fabricating a LTCC circuit. The low line losses as well as the competitive manufacturing costs are an advantage of LTCC also for microwave and even millimeter wave applications. LTCC for the first time offers the possibility to realize three-dimensional microwave and millimeter wave circuits in a cost effective production technique. In this paper the fundamentals of the technology at microwave and millimeter wave frequencies and the design Fig. 2. LTCC technologies. Figure 3 shows the measured results of microstrip line (MS) total line losses over a frequency range up to 40 GHz. This includes different kinds of losses resulting from conductivity, /07/$ IEEE 505

2 dielectric losses, surface roughness and radiation. This evaluation shown here concentrates on the available low loss LTCC systems: Ferro A6, DuPont 943 and Samsung G6. Results of other materials are available. It is well known, that the losses depend on the line width of the conductors. With an increasing width the losses decrease. The goal here was to achieve a width of 390 μm for the MS waveguide. The tolerances of the fabricated lines can be read from the figure, too. A range from 385 μm to 445 μm is covered (average values) MS Line Losses [db/cm] Ferro A6M, Au Ferro A6S, Ag Samsung G6, Ag DuPont 943, Au DuPont 943, Ag w = 390μm w = 445μm w = 370μm w = 385μm w = 385μm MS Target Line Width = 390 μm Frequency / GHz Fig. 3. Measured losses of microstrip lines in LTCC technology. It is a big advantage of the LTCC technology that even rectangular waveguides can be realized using this technique. Fig. 4 shows how this can be realized. Using an arrangement of various through connections, a conducting wall on the left and right side of the waveguide can be simulated. It will be discussed in the oral presentation, how these rectangular waveguides can be designed correctly, i.e. how the distance and the position of the via connections (via s) influences the radiation properties of the walls. Using a 3D field simulation technique, it can be clearly shown that for a correct distance of the through connections the waveguide nearly works as a perfect rectangular waveguide (Fig. 4b). If the distance between the through connections is chosen too large (Fig. 4c), radiation occurs through the side walls into the neighbouring of the circuit. III. DESIGN AND TECHNOLOGY OF PASSIVE COMPONENTS A Passive Lumped Elements To demonstrate the possibilities to use lumped capacitances, inductances and resistances in LTCC technology, the design of a SMD filter for about 800 MHz shall be studied here. Arbitrary filter characteristics are frequently required for RF and microwave circuit design. At high GHz frequencies it is useful to build filters utilizing transmission line segments. The length of a line stub is related to the wavelength, thus filters are smaller in size for higher frequencies. In case of low GHz or hundreds of MHz frequencies it is useful to apply capacitors and inductors to achieve acceptable filter dimensions. With today s multilayer RF substrates it is possible to integrate C and L elements in standard sizes for surface mount technology, which are called Surface Mount Devices (SMD). A low pass filter for the frequency range up to 1 GHz shall be designed. A multilayer substrate environment shall be chosen, in this case the LTCC material system 951 from DuPont was selected, since it is a well known material with suitable properties. Fig. 5 shows the schematic of the filter. Term Term1 Num=1 Z=50 Ohm C C1 C=C1 C C4 C=C3 L L1 L=L1 R=0 C C2 C=C2 C C5 C=C3 L L2 L=L1 R=0 C C3 C=C1 Figure 5. Filter schematic Var Eqn VAR VAR3 C1=2.9 pf C2=5.8 pf C3=0.8 pf L1=10.8 nh Term Term2 Num=2 Z=50 Ohm The 3-dimensional multilayer inductors and capacitors of the filter are simulated and optimised with MultiLib TM [14]. This is a library with multilayer LTCC elements. It is an add-on to the design software ADS TM from Agilent. MultiLib TM allows an accurate 3D modelling of complex predefined and parameterised structures based on the Finite Differences Time Domain (FDTD) method. The desired inductance of the spiral inductor ( L 1 = 10.8 nh ) was found with a simple circuit optimisation in ADS. The multilayer capacitors have been found in a similar way as the inductor. Fig. 6 shows the layout of the multiplayer inductors and capacitors. Fig. 4. Realization of a rectangular waveguide in LTCC technique and simulated field distribution. Figure 6. Multilayer inductor and capacitor (layout). The lowpass filter finally consists of 2 inductors with an inductivity of 10.8 nh, 2 capacitors with 0.6 pf and 4 capacitors with 2.55 pf. The schematic circuit is shown in Fig

3 pf nh pf 0.6 pf nh 2.55 pf 2.55 pf 2.55 pf 1 2 Figure 7. Multilayer lowpass filter (equivalent circuit). In the next design step the multilayer L and C elements are transferred to a real 3D simulation software. Empire TM XCel [13] has been selected since this tool based on the FDTD method has proven to be very accurate. All conductors and via connections are implemented. Additionally two inner ground planes above and below the C1 and C2 capacitors are inserted for decoupling. Figure 8 delivers an insight into the filter structure. Conductors with real thickness and ohmic losses are analyzed as well as dielectric layers with a given tangent delta. The signal and ground terminations then are added in a final implementation step B Passive Waveguide Components in LTCC As examples for the design and the technology of sophisticated LTCC waveguide components, power dividers and waveguide filters for the millimetre wave range shall be shortly demonstrated. As a first example Fig. 10 shows the design and the simulated electric field of a LTCC Wilkinson power divider in stripline technology which finally is used as an element for a satellite antenna feeding network. A binary tree of this feeding structure is formed of three Wilkinson dividers, Fig. 11. The resistors of the Wilkinson dividers are buried components to provide short connections without additional parasitics. Wider strip lines give lower ohmic losses. Thus the inner line impedance of the strip lines was decided to be 30 Ω. Therefore the resistor value of the Wilkinson divider is 60 Ω. The optimisation of the divider design was done with the IMST inhouse developed 3D FDTD field simulator EMPIRE TM [13]. Fig. 10 shows a Wilkinson divider in the software environment with visualised field distribution of the perpendicular electric field for two different field excitations at port 1 and port 2, respectively. Via chains around the structure suppress unwanted cross-talk with neighbouring components. Field excitation at Port 2 60 Ohmresistor Port 3 Field excitation at Port 1 Port 2 Port 1 Figure 8. Layout of the multilayer lowpass filter. The overall simulation is finally conducted for the SMD filter mounted on a PCB with a microstrip line environment S-Parameters (db) SMD: S11 SMD: S Frequency (GHz) Figure 9. S-parameter of the 3D lowpass filter. This ensures that simulation and measurement are comparable at the end. Fig. 9 shows return and insertion losses of the entire SMD filter. In comparison with the ideal filter response it is found, that in the final characteristic the slope between stop and pass-band is even steeper due to the parasitic capacitances of the terminations. Fig. 10. Wilkinson divider in LTCC with electric field. In the next step three dividers are combined to a 1 : 4 distribution network. Optimum chamfered bends and interconnecting lines lead to an overall satisfying electrical behaviour. The structure together with the field distribution of the perpendicular electric field is shown in Fig. 11. Field excitation at Port 2 Port 2 Port 3 Port 1 Port 4 Port 5 Fig : 4 distribution network with simulated electric field. The field excitation at port 2 gives a good imagination of the increasing isolation between the adjacent output ports. The 507

4 power is reduced by 3 db at every divider stage. This relationship is illustrated nicely by the fading amplitude of the electric field. The divider module has been fabricated in LTCC. DuPont 951 was chosen as material system for the substrate, the conductors, the vias and the resistors. Scattering Parameters (db) meas S 11 meas S 21 sim S 21 sim S Frequency f (GHz) Fig. 12: Measurement and simulation of divider module The simulated and measured S-Parameters in Fig.12 show very good results at the desired frequency of 19 GHz. The transmission loss is 1 to 2 db higher than predicted. The not well enough known ohmic losses and its frequency dependence of the conductor paste is a possible reason for this effect. The simulated ohmic losses are not frequency selective and have been calculated using a skin effect simulation at 19 GHz. Already the last example clearly demonstrates, that LTCC technology works well at very high frequencies. In the next example, the frequency again is doubled and a rectangular waveguide bandpass filter with good properties for a frequency of 40 GHz is described. The filter is made by a top and bottom screen-printed conductor on a 4 layer LTCC stack. The side walls have been build by stacked and later also staggered via fences on the left and right side of the ceramic strip. indicate the areas of high field magnitude. Filters from a first production run have been measured and show excellent performance. These results are plotted in Fig. 14. The S- parameters fit well with the given specifications S-Parameters (db) S 21 S 11 Specs Frequency (GHz) Fig. 14. Measured S-parameters of the bandpass filter. However, filters from later manufacturing runs using different material lots show significant shifts of the centre frequency. Such deviations can either result from the centre-via positions or the dielectric constant. Appropriate tolerance analyses have been carried out and are plotted in Fig. 15 and Fig. 16. Fig. 15 Filter simulation with different via positions. Fig. 13. Electrical field components in stop- and pass-band. The simulated electrical field components are plotted in Fig. 13 for the stop-band (38.5 GHz, S 21 = 33 db ) and the pass-band frequency (40.5 GHz, S 21 = 0.5 db ). Dark areas It is obvious that even typical manufacturing tolerances for via-processing can be responsible for a frequency shift of the pass-band at such high center frequencies as 40 GHz. However, the measured positions of centre-via s deviate in values from 20 µm to 30 µm, which cannot effect the observed frequency shift. That s why further investigations have concentrated on the dielectric constant of the ceramic material. Data sheets announce a value of

5 synthesis of microstrip (MS) and stripline (SL) waveguides, followed by the optimisation of transitions and feedthroughs from one waveguide to an other. It could be demonstrated, that these RF structures fulfil the required specifications. In the next step MMIC circuits were mounted on top and into simple and stepped cavities of multilayer LTCC substrates. All these preceding tests have been performed as a preparation for the LMDS module development. Figure 17 shows a photo of the final circuit. 5 Layer LTCC-Substrate: FERRO A6-M DC f Tx = 25GHz, 28dBm Fig. 16. Filter simulation with different dielectric constants. An investigation of low loss LTCC materials in 2002 using ring resonator measurements determined a relative dielectric constant of ε r = 7.5, while a later survey made in 2005 results in ε r = 7.3 at 40 GHz for the DuPont 943 material. A lower dielectric constant will lead to a shift of the pass-band to a higher frequency. This is supported by filter simulations shown in Fig. 16. Additionally a modification in material composition or even a change of the material properties due to different firing conditions may be the reason for the measured frequency shift. IV. LTCC MICROWAVE AND MILLIMETER WAVE SYSTEMS Three different LTCC millimetre wave systems, a 26 GHz point-to-multipoint transceiver, a 24 GHz radar module and a 30 GHz digital beam forming antenna module will show the high potential of the LTCC 3D-circuit technology at high frequencies. A LTCC Point-to-Multipoint Transceiver The goal of the 26 GHz transceiver development was to demonstrate, that LTCC multilayer technology has great benefits in microwave applications: high level of integration, buried components, low losses, robustness, cavities for mounting MMICs, temperature coefficient close to that of GaAs, good thermal conductivity due to a thermal management and others. RF and microwave radio networks like point-topoint and point-to-multipoint applications are becoming a growing market even if optical links are in strong competition. This requires low cost components. Especially the costs of RF parts are driven by the high costs of integrated circuits and the commonly used thin film technology. Therefore it was decided to develop a transceiver module for LMDS (Land Mobile Digital Service) in a frequency band of 24.5GHz to 26.5GHz on the low cost LTCC technology with screen printed conductors. In early tests Ferro s A6M tape had shown the required microwave behaviour. The design started with the f IN =1.7 GHz f OUT =725 MHz TX IN MIXER MS SL ASL DC 55 mm LO DC Tx Rx f Rx = 26 GHz Fig. 17. The LTCC point-to-multipoint transceiver for 26 GHz MS SL AMP AMP Microstrip Line Stripline Asymmetric Stripline DC Line Bandpass-Filter ASL DC BP SL Ground GND-Via Thermal Via ASL ATT AMP TX OUT PA Fig. 18. Schematic top and cross view of the transmit path of the LMDS module. The complexity of the circuit is evident, when the schematic top and cross view of the transmit path, as an example, is considered in Fig. 18. The design starts with the transmit input port (TX IN ) which is connected to a microstrip line on top of the LTCC. The TX-signal is guided to a mixer in a stepped cavity. A wire bond connects the mixer with a microstrip (MS) line in the cavity. A feedthrough with a short stripline follows. This allows the crossing of a microstrip line. The output port of the amplifier (AMP), which is also mounted in a stepped cavity, is connected with a MS-ASL-SL transition, where ASL means asymmetric stripline, because only one substrate layer is above and three layers are below the conductor strip. SL Heat Dissipation PA ATT MS GPO f LO = 4.5 GHz 509

6 A bandpass filter has been designed in the SL level. L-shaped coupled segments are used. The filter is shielded by via fences on the left and right side of these segments. The vias are connected with the top and bottom ground plane. DC lines are crossing the filter on top of the substrate. Attenuator (ATT) and power amplifier (PA) are integrated in the same way like the other MMICs. Special micro-connectors (GPO from Gilbert) are utilized for the microwave ports. It is important to mention, that each inner ground layer is directly connected with the aluminium housing using dense arrays of filled vias. A similar filter is used in the receiver circuit. The bandpass filters have critical specifications, because they cover the transmit and receive bands, which are very close together. Fig. 19 shows the filter response of the 25 GHz filter split into specifications, simulated and measured return and insertion losses. The simulated and measured data agree very well and match the specifications. A figure of the test circuit is placed at the bottom of the diagram. The top ground plane, the vias (small dots) and the cavities with the RF ports inside are visible. The optimisation of the filter has been performed with the 3D FDTD full-wave simulation tool EMPIRE TM [13], which is a software tool of IMST. Insertion S-Parameters Losses (db) / db S11_sim S21_sim S11_meas S21_meas Specs Frequency Frequency / (GHz) GHz Fig. 19. Specifications, simulations and measurements for the S-parameters at 25 GHz and a picture of the bandpass filter. Figure 20 shows a visualization of the current distribution in the inner filter segments. Top and button ground as well as the substrate layers are faded out to allow a view into the stripline area. The shielding via fence is still visible. The field shot has been taken in the passband at 25 GHz. The peaks especially at the conductor edges indicate a high current level due to skin effects. A special heat management system for the PA has been introduced: An array of 21 silver filled via holes was placed under the amplifier chip to increase the thermal conductivity of the LTCC substrate. The thermal resistance of the Ferro A6 tape is 2W/mK, which is better in comparison with PTFE Fig. 20. Simulated current distribution of the bandpass filter at 25 GHz in the passband. boards (around 0.15 to 0.35W/mK) but worse compared to Alumina substrates (16 to 20W/mK). The thermal resistance of the silver vias is around 150W/mk, which results in a common thermal resistance of about 20 to 30W/mK depending on the density of the vias in the array. Marconi s (today Bookham) PA has a RF output power of 28 dbm generating a thermal energy of 2.4 W, which has to be dissipated from the transistors through the substrate and the aluminium housing. Ireland s ICT Research Centre NMRC has simulated and optimised the heat dissipation for the LMDS application. B LTCC Short Range Radar Sensor for Automotive Applications at 24 GHz The RADAR-sensor presented here is designed for use as driver assistance system in vehicles. FMCW method is utilized to measure distances up to 30 m and velocity of obstacles around the car. Especially safety enhancement systems like collision warning and mitigation but also comfort features can be realized. Moreover, the sensor is capable to be integrated in manifold industrial applications where distance and velocity have to be determined with high precision. Another interesting field of application is the monitoring of buildings and real estates, because the module concept is qualified for the free 24 GHz ISM band, too. The main focus of the development is directed towards the reduction of costs in comparison with conventional sensors. Hybrid circuit technology using a 5-layer LTCC substrate from DuPont Microcircuit Materials has been realized. The module is assembled with cost-effective discrete semiconductor devices, avoiding the use of expensive monolithic integrated circuits (MMICs). A patch-antenna is printed on one side of the multilayer ceramic, while the RF front-end has been integrated on the opposite side. The microwave front-end with the integrated patch antenna measures only 34 mm x 21 mm. Signal conversion and signal processing are executed on an external board, which is connected via USB interface to a PC. Fig. 21 shows the RF circuit on the bottom of the radar module. Considering wireless or radar applications, the idea of integrating the antenna within the module is quite appealing: the integration of the antenna on the top side of the module as shown in Fig. 22 makes the antenna connector obsolete and minimizes the feeding line length, thus reducing feeding losses. Yet, due to the high dielectric constant of the LTCC material, the design of a broadband planar antenna array is quite 510

7 Connector to DC-board Transition to Antenna IF-amplifier stacked patches buried microstrip antenna feeding line buried patches Mixer Coupler VCO Buffer Amplifier RF frontend circuit & components aperture coupled RF to antenna interface ground plane Fig. 21. Frontend on the bottom of a multilayer LTCC module. challenging because the bandwidth decreases with the dielectric constant. However, LTCC materials are ideally suited for multilayer structures; this characteristic can be exploited by using stacked patch elements, thus considerably enhancing the bandwidth. The antenna design presented here is based on this principle. Fig. 22. Layout of the FM-CW radar module with integrated stacked patch antenna array on the top and the frontend on the bottom. The antenna has to comply with the following specifications: The operation frequency range is defined by a centre frequency of 24 GHz, with a bandwidth of at least 2 GHz. This broadband behaviour is important, since the range of the frequency modulation ramp of the radar module defines its resolution. The polarisation of the antenna has to be linear, with a high suppression of the cross polar components. The antenna pattern should meet the 3dB beam width requirement of ±15 in the E-plane and ±30 in the H-plane. The radar module consists of five LTCC layers, each with a 200 μm layer thickness. Fig. 22 depicts the layout of the complete FMCW radar module, Fig. 23 shows this module in a cross sectional view. The bottom side of the ceramic block carries the RF front-end circuits and components. An aperture in the buried ground plane between the first and second ceramic layer (counted from the bottom), is used to interconnect RF and antenna circuitry. The antenna array and its feeding lines are located between the third and fourth layer. Stacked patches on the topside of the ceramic are used to enhance the bandwidth of the antenna. The ceramic material consists of DuPont 951-AT Fig. 23. Cross section of the radar module with integrated stacked patch antenna. green tape, with a dielectric constant of 7.8, and a loss tangent of This material has been favoured for reasons of economy, since it is cheaper than the similar low loss material, DuPont 943-A5, with an indicated loss tangent of The complete antenna has been calculated including the RF-to-antenna interface using the FDTD simulator EMPIRE TM [13]. The 10 db bandwidth of the antenna is about 2.5 GHz, giving a relative bandwidth of over 10 %. Considering the high dielectric constant of the material used, this is a remarkably good result. The directivity of the antenna is calculated to be 12 dbi, with a 3 db beam width of ±15 in E-plane, and ±30 in H-plane, respectively. C Digital Beam-Forming Antenna Module in LTCC Multilayer Technique The increasing demand for mobile access to fast data services is one of the drivers for future broadband satellite systems in Ka-Band. antenna 20 / 30 GHz airplane GEO satellite Fig. 24. Airplane-satellite antenna in LTCC technique. Steerable antennas e.g. for an airplane-satellite connection (Fig. 24) employing Digital Beam-Forming (DBF) provide fast and flexible reconfiguration capabilities required for such systems without any moving parts. DBF means that phase and amplitude shifts are applied at baseband level using a direct upor down-conversion of the signal transmitted/received by each element, being a patch here. Therefore, each antenna element is equipped with a complete RF front-end, IF circuits, DA- and AD-converters respectively, and dedicated digital logic. In conjunction with fast algorithms for beam forming and beam 511

8 steering this defines a very flexible and versatile system for broadband mobile communication. LTCC multilayer technology has been selected to build up such antenna arrays because it provides the necessary degree of vertical integration for the high-density microwave circuit presented here. The area defined by the cell size of one antenna element which is half a wavelength in x- and y-direction accommodates a transmit hybrid coupler feed and the complete RF-circuitry thereof. In further layers a complex calibration network is located. The array building block, consisting of 16 antenna elements, features a calibration network to enable an automatic array calibration of each building block. The area of one calibration network is limited to the size of the 4 4 element array building block, which is two wavelengths. Terraced cavities for the antenna patches with conductive walls (via fences) improve the accuracy of the calibration (off-line as well as on-line), and the radiation pattern by reducing unwanted mutual coupling between adjacent patches. A lossy line termination for the hybrid coupler provides a good match without trimming the buried resistors. Furthermore, it is essential to have a low loss material with good microwave performance for this application. Low permittivity is certainly an advantage for microwave antennas. LTCC cavity patch field probes hybrid ring Fig. 25. Exploded view of the 11 layer antenna structure. } antenna block } hybrid ring coupler } calibration network RF } interface Fig. 25 shows the complete architecture of such an antenna element. The structure consists of eleven layers of FERRO A6 LTCC substrates. Four different functional blocks can be identified: The antenna block (first 6 layers from the top), the hybrid ring coupler block with 2 layers, the calibration network (2 layers) and finally the RF-to-antenna interface (1 layer). The different functional blocks of the antenna element and their specific design issues are described in detail in [7] and will be discussed in the oral presentation. SUMMARY An overview of LTCC microwave and millimeterwave circuit design and realization has been given. It shows that LTCC technologies are applicable up to high frequencies with advantage. The high density of interconnects in LTCC substrates facilitates the integration of passive and active microwave circuits, antenna structures, IF electronic, and optional digital parts on one multilayer substrate. Utilization of multilayer ceramic for microwave and millimetre wave circuits allows the use of bare semiconductor dies and the abandonment of microwave monolithic integrated circuits (MMIC) which lowers the cost, increases the availability of components and expands second source capabilities. Inherent housing properties like hermetic tightness, thermal conductivity and good temperature coefficient match to semiconductors make LTCC an ideal candidate for compact and environmentally rugged modules. Despite the high dielectric constant of the LTCC material, antenna concepts can exhibit broadband behaviour by exploiting the LTCC multilayer characteristics. All these advantages result in compact microwave and millimetre wave modules with outstanding properties like small dimensions, proper performance and, last but not least, low cost. REFERENCES [1] I. Wolff, R. Kulke, P. Uhlig, "LTCC for micro- and millimeter-wave applications", Short Course, IEEE-IMS, International Microwave Symposium, Honolulu, Hawaii, June 3-8, [2] R. Kulke, G. Möllenbeck, P. Uhlig, K. Maulwurf, M. Rittweger, "Designing SMD lowpass filters in multilayer LTCC technology", EMPC, European Microelectronics and Packaging Conference, Oulu, Finland, June 17-20, [3] R. Kulke, O. Kersten, J. Winkler, C. Günner, M. Rittweger, "Packaged microwave components for multimedia satellite communication", IMAPS Symposium (Wireless/RF Session), San Diego, USA, Oct. 8-12, [4] P. Uhlig, S. Holzwarth, O. Litschke, A. Serwa, D.T. Tran, "On the influence of layer-to-layer misalignment on the microwave performance of LTCC antenna modules", IMAPS Symposium, San Diego, USA, Oct. 8-12, [5] I. Wolff, R. Kulke: "LTCC-Technologie zur Systemintegration im Mikrowellen- und Millimeterwellenbereich", EEEfCOM Conference, Ulm, Germany, Juni [6] R. Kulke, O. Kersten, G. Möllenbeck, M. Rittweger, B.-S. Kim, K.-S. Kim, W. Byun, M.-S. Song: "Frontend components for 40 GHz FWA applications in multilayer LTCC", IMAPS (Wireless/RF Session), San Diego, USA, Oct. 8-12, 2006 [7] P. Uhlig, S. Holzwarth, O. Litschke, W. Simon, R. Baggen: " A digital beam forming antenna module for a mobile multimedia terminal in LTCC-multilayer technique ", 15 th European Microelectronics and Packaging Conference (IMAPS), Brugge, pp , June 12-15, [8] R. Kulke, C. Günner, S. Holzwarth, J. Kassner, A. Lauer, M. Rittweger, P. Uhlig, P. Weigand: ". 24 GHz radar sensor integrates patch antenna and frontend module in single multiplayer LTCC substrate, 15 th European Microelectronics and Packaging Conference (IMAPS), Brugge, pp , June 12-15, [9] S. Holzwarth, R. Kulke, J. Kassner: " Integrated stacked patch antenna array on LTCC material operating at 24 GHz ", IEEE AP-S International Symposium on Antenna and Propagation, Monterey, California, June 20-26, [10] J. Kassner, R. Kulke, P. Uhlig, M., Rittweger, P. Waldow, R., Münnich, H. Thust: " Higly integrated power distribution networks on multiplayer LTCC for Ka-band multiple-beam phased array antennas, IMAPS Nordic Conference, Proceedings pp , September 2003, Espoo, Finland. [11] R. Kulke, G. Möllenbeck, W. Simon, A. Lauer, M. Rittweger: " Point-tomultipoint transceiver in LTCC for 26 GHz ", IMAPS-Nordic, Proceedings pp , 29. Sept.-2. Oct. 2002, Stockholm. [12] [13] IMST GmbH, User and reference manual for the 3D EM time domain simulator EMPIRE XCEL, 2006, [14] IMST GmbH, User and reference manual for MULTILIB, 512

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