Florian Ohnimus

Modeling, Quantification, and Reduction of the Impact of Uncontrolled Return Currents of Vias Transiting Multilayered Packages and Boards

The returning displacement currents of vias transiting multilayered stack-ups in electronic packages and boards excite parasitic transverse electromagnetic modes in power-ground plane pairs, causing them to behave as parallel-plate waveguides. These waves may cause significant coupling in the power-ground cavity, leading to electromagnetic reliability (EMR) issues such as simultaneous switching noise coupling, high insertion loss degradation of signal vias, and stray radiation from the periphery/edges of the package/board. In this contribution, we model and quantify EMR problems caused by uncontrolled return currents of signal vias in conventional multilayer stack-ups. Traditional methods used to minimize these problems, and their limitations are discussed. We propose a low-cost layer stack-up, which overcomes most of the limitations of conventional stack-ups by providing well-defined return-current paths for microstrip-to-microstrip via transitions. Test samples of the proposed configuration are designed, fabricated, and measured. Very good correlation is obtained between measurement and simulation. Finally, a circuit model for the microstrip-to-microstrip via transition, considering the return-current paths, is developed and the circuit parameters are analytically calculated. Conventional closed-form expressions used for the extraction of these parameters, particularly the via capacitance, are extended and modified.

Design and Analysis of a Bent Antenna-coil for a HF RFID Transponder

In this work, the design of a bent antenna-coil for a 13.56 MHz RFID transponder is presented. The tag is integrated into a plastic ballpoint pen, optimally making use of the marginal volume inside the cylindrical geometry of the casing. The coil is designed with a 50% higher inductance in its planar state, so that the required inductance of nearly 6 muH to ensure resonance is obtained when the bent tag is inside the pen. Quasi-static and full-wave methods for the electromagnetic simulation of the coil are compared and an analysis of the influence of the bend radius on the inductance of the coil is conducted. Furthermore, the designed tag was manufactured using two technologies comprising copper windings on a polyimide substrate and conductive polymer paste on a polyester foil for experimental verification. With a mid-range RFID reader configuration, read-ranges of up to 23 cm and 12 cm, respectively, were obtained with the bent tag inside the pen.

Modeling and analysis of return-current paths for microstrip-to-microstrip via transitions

In this contribution, the return-current paths for single-ended microstrip-to-microstrip via transitions in conventional layer stack-ups are modeled and analyzed. Electromagnetic reliability (EMR) problems which occur in these layer stack-ups, because the return-currents are not properly managed are discussed. Finally, a layer stack-up with well defined return-current paths, which overcomes the limitations of traditional layer stack-ups, is proposed.

An efficient and broadband slot antenna for 60 GHz wireless applications

In this work, a single-layered CPW-fed slot antenna element for low cost 60 GHz radio applications is designed, modeled and analyzed. The results show a -10 dB impedance bandwidth of over 7 GHz with a radiation efficiency of over 95% making it suitable for short-range WPAN/WLAN applications. It is shown that two of the slot antennas can be configured orthogonally to achieve polarization diversity when fed separately. An isolation of at least 18 dB is obtained with an element spacing of ¿/2. This can be advantageous for applications where the orientation of the terminal is not known.

Integration of Planar Antennas Considering Electromagnetic Interactions at Board Level

In compact wireless modules, electromagnetic (EM) interactions occurring between planar antennas and transmission lines (TML) sharing the same substrate may cause a high amount of undesired coupling and may also detune the antenna characteristics. In this paper, an approach for defining a block-out region around the planar antenna, where no components should be placed is developed, thereby ensuring that the antenna characteristics remain within tolerable limits when the antenna is integrated at board level. This region is comparable to the reactive near-field, but is determined by evaluating the reactive EM power density excited on the ground plane and deducing a threshold value. Its boundary will be termed the EM antenna boundary. Furthermore, a method for efficient estimation of EM coupling from the antenna to terminated TMLs routed outside the EM antenna boundary is developed. This method is based entirely on a postprocessing step to field simulations, i.e., the coupling is calculated based on the previously computed magnetic field distribution excited by the antenna on the ground plane. The coupling model uses the theory of field excited TMLs together with the Baum-Liu-Tesche integral equations for obtaining the terminal voltages of the TML and, hence, the coupling terms.

Minimizing electromagnetic interference in power-ground cavities

In this paper, electromagnetic interference (EMI) in power-ground cavities is quantified for conventional layer stack-ups used in low-cost electronic packaging. Traditional methods to minimize EMI and their limitations are discussed. Our novel approach to minimize EMI by minimizing/preventing the excitation of parallel-plate-modes in power ground cavities is then presented. Finally, the advantages of our approach in ensuring Electromagnetic Reliability (EMR) of microsystems are discussed.

Design and Comparison of 24 GHz Patch Antennas on Glass Substrates for Compact Wireless Sensor Nodes

Three patch antennas suitable for integration and operation in a compact 24 GHz wireless sensor node with radar and communication functions are designed, characterized, and compared. The antennas are manufactured on a low loss glass wafer using thin film (BCB/Cu) wafer level processing (WLP) technologies. This process is well suited for 3D stacking. The antennas are fed through a microstrip line underneath a ground plane coupling into the patch resonator through a slot aperture. Linear polarization (LP), dual mode (DM) operation, and circular polarization (CP) are achieved through the layout of the slot aperture and rectangular patch dimensions. Antenna gain values of ∼5.5 dBi are obtained in addition to the 10 dB impedance bandwidths of 900 MHz and 1.3 GHz as well as 500 MHz CP bandwidth with a 3 dB axial ratio for the LP, DM, and CP patch antennas, respectively.

Equivalent circuit modeling of signal vias considering their return current paths

A circuit model for signal vias, considering their return-current paths in five-layered stack-ups, is proposed. Closed-form expressions for the computation of via capacitance are derived and used together with conventional formulas for inductance and resistance computations to accurately account for the RF behaviour of the vias over a wide range of frequencies.