John Papapolymerou

Reconfigurable double-stub tuners using MEMS switches for intelligent RF front-ends

This paper presents novel planar dynamically reconfigurable double-stub tuners that utilize electrostatically activated microelectromechanical system (MEMS) switches. The tuners operate in the 10-20 GHz frequency range and have stubs that consist of a digital capacitor bank. Each bank has a predetermined number of capacitors that can be selected through the activation of appropriate MEMS switches. The value and number of capacitors is dictated by the range of loads that needs to be matched. Simulated and measured results from several designs are presented. A 4 bit /spl times/ 4 bit tuner that can match loads with 1.5 /spl Omega/<Re{Z/sub L/}<109 /spl Omega/ and -107 /spl Omega/<Im{Z/sub L/}<48 /spl Omega/ at 20 GHz equivalent to three quadrants of the Smith chart and loads with 3 /spl Omega/<Re{Z/sub L/}<94 /spl Omega/ and -260 /spl Omega/<Im{Z/sub L/}<91 /spl Omega/ at 10 GHz is demonstrated for the first time, as well as other designs. The demonstrated tuners provide real-time reconfiguration and matching for RF loads that change values during system operation. Applications include the development of several novel highly integrated microwave/millimeter-wave circuits such as ultra-wide-band high output power and increased power-added-efficiency amplifiers, ultra-wide-band multipliers, and very broad-band antenna arrays. It is expected that these circuits will be part of future low-cost and low-power intelligent RF front-end microsystems and systems-on-a-chip.

A high-Q reconfigurable planar EBG cavity resonator

A reconfigurable planar electromagnetic bandgap (EBG) cavity resonator has been designed, fabricated, and tested. The resonator, based on a microstrip-coupled cavity constructed with periodic metallic post side walls, resonates at 10.60 GHz or 8.63 GHz, depending on the state of two rows of switchable post elements. Fabricated on 0.031 inch 5880 Duroid, the resonator exhibits Qs of 348 and 274 for the 10.60 GHz and 8.63 GHz resonances, respectively. In addition to the reasonably high Qs achievable with this design, the circuit utilizes standard printed circuit board (PCB) fabrication techniques and is 100% compatible with commercial PCB processes, enabling low-cost mass production.

Microwave filters on a low resistivity Si substrate with a polyimide interface layer for wireless circuits

Novel low-pass and band-pass filter designs on low resistivity silicon substrate (1 /spl Omega/-cm) with a polyimide interface layer are presented for the first time. The filters utilize the finite ground coplanar (FGC) line technology, and operate from 10-30 GHz with very good insertion loss. The latter is possible by using a 20 /spl mu/m thick polyimide on top of the silicon wafer, and a line geometry that minimizes field interaction with the lossy Si substrate. The attenuation of the FGC lines is comparable with that of thin film microstrip lines on similar substrates. Experimental and full-wave analysis results are provided. These filters can be used as part of a wireless microwave interconnect system.

Coupling between microstrip lines embedded in polyimide layers for 3D-MMICs on Si

Three-dimensional circuits built upon multiple layers of polyimide are required for constructing Si-SiGe monolithic microwave/millimeter-wave integrated circuits on CMOS (low resistivity) Si wafers. However, the closely spaced transmission lines are susceptible to high levels of coupling, which degrades circuit performance. In this paper, Finite Difference Time Domain (FDTD) analysis and measured characteristics of novel shielding structures that significantly reduce coupling between embedded microstrip lines are presented.

A Hybrid Micromachined High -Q Cavity Resonator at 5.8 GHz

A novel hybrid micromachined resonator with high quality factor and small size at 5.8GHz is presented. The design of the resonator is based on a micromachined cavity filled with a high dielectric constant material. Energy is coupled into the cavity from input and output microstrip lines via slots. It is shown experimentally that the limiting factor in achieving a higher Q with the given dielectric materials is the dielectric loss. This resonator provides a low cost, minimum size and compact solution for the fabrication of planar, narrow-band filters and diplexers in modern wireless communication systems.

Multilayer Cost Effective Design of an Integrated Stripline Narrowband Filter for Wireless Applications

A stripline interdigital narrowband bandpass filter has been designed, fabricated, and tested. This filter has the advantages of minimal space utilization, low cost, excellent transfer characteristics, and ease of integration into a multilayer board scheme. Both numerical and electromagnetic wave simulation tools were used to perform the design and analysis, followed by fabrication and testing.

Electronically controlled microwave band gap filter structures

Microwave band gap structures (MBG) utilizing fixed defects have received much interest because of their ability to operate as narrow band filters. With the recent interest in reconfigurable wireless devices, the need for electronically controllable narrow band filters is on the rise. By altering the defects in an MBG crystal, the transmission properties of the crystal can be changed. Using this concept, two controllable defect structures have been studied. Microwave band gap crystals utilizing single and dual p–i–n diode defect structures have been simulated, fabricated, and tested. Through the control of the p–i–n diode bias current, the transmission effects caused by the crystal defects can be altered. Experiments demonstrating contrasts of more than 30 dB between the diode-on and diode-off states are presented along with the corresponding finite difference time domain simulation results.

A High Performance K-Band Diplexer using High-Q Micromachined Cavities

Microwave diplexers are often used on transmit / receive systems to isolate a power transmit stage from a sensitive receive stage sharing a common antenna. With the ever-increasing need for efficient bandwidth usage, diplexers exhibiting close channel spacing, low insertion loss and small channel bandwidths are increasingly necessary. Utilizing two high Q cavity resonators, a Duroid-based high performance diplexer has been designed, fabricated and measured. This diplexer shows transmit / receive bandwidths of 2.39% and 1.8% and insertion losses of 2.38dB and 2.89dB, respectively. Channel center frequencies of 18.8GHz and 20.7GHz provide a channel separation of approximately 9% and channel to channel isolation greater than 24dB. Utilizing machined aluminum cavities and a Duroid substrate the diplexer design provides insight into cavity based diplexer construction, allowing for the design of a silicon based micromachined cavity diplexer. Simulation results from this silicon-based diplexer are also presented.

Realization of an Active Narrow Band Filter with Electronically Controlled Defects in a Microwave Bandgap Structure

Microwave band gap structures (MBG) utilizing fixed defects have received much interest because of their ability to operate as narrow band filters. With the recent interest in reconfigurable wireless devices, the need for electronically controllable narrow band filters is on the rise. By altering the defects in a MBG crystal, the transmission properties of the crystal can be changed. Using this concept, a microwave band gap crystal utilizing PIN diode defect structures has been simulated, fabricated, and tested. Through the control of the PIN diode bias current, the transmission effects caused by the crystal defects can be altered. Experiments demonstrating contrasts of more than 30 dB between the diode-on and diode-off states are presented along with FDTD simulation results.

Coupling Between Finite Ground Coplanar Waveguides Embedded in Polyimide Layers for 3D-MMICs on Si

Three-dimensional circuits built upon multiple layers of polyimide are required for constructing Si/SiGe monolithic microwave/mm-wave integrated circuits on low resistivity Si wafers. However, the closely spaced transmission lines are susceptible to high levels of cross-coupling, which degrades the overall circuit performance. In this paper, theoretical and experimental results on coupling of Finite Ground Coplanar (FGC) waveguides embedded in polyimide layers are presented for the first time. These results show that FGC lines have approximately 8 dB lower coupling than coupled Coplanar Waveguides. Furthermore, it is shown that the forward and backward coupling characteristics for FGC lines do not resemble the coupling characteristics of other transmission lines such as microstrip.