Ignacio Llamas-Garro

SU-8 Ka-band filter and its microfabrication

This paper presents the design and microfabrication of a coaxial dual model filter for applications in LMDS systems. The coaxial structure is formed by five conductive layers, each of which is of 700 µm thickness. The filter uses an air filled coaxial transmission line. It is compact with low dispersion and low loss. The design has been extensively tested using a prototype filter micromachined using laser drilling on a copper sheet and the results show a good agreement with the theoretical calculations. The laser fabrication has exposed weakness in suitability to volume production, uneven edges and oxide residuals on the edges, which affects the filter performance. A process for fabrication of such a filter in SU-8 has been developed which is based on a UV lithographical process. In order to fabricate such thick SU-8 layers, the SU-8 process has been optimized in terms of UV radiation and post exposure baking. During the test fabrication, the optimized SU-8 process has produced microstructures with an aspect ratio of 40:1 and a sidewall of 90 ± 0.1 ◦ . The high quality SU-8 structures can be then either coated with a conductive metal or used as moulds for producing copper structures using an electroforming process. The microfabrication process presented in this paper suits the proposed filter well. It also reveals a good potential for volume production of high quality RF devices. (Some figures in this article are in colour only in the electronic version)

Microstrip Switchable Bandstop Filter using PIN Diodes with Precise Frequency and Bandwidth Control

In this paper a switchable bandstop filter able to switch between two different central frequency states while precisely maintaining a fixed bandwidth is presented. The filter topology allows precise control over the design parameters frequency and bandwidth, achieved by choosing adequate resonator sections which are switched by PIN diodes to obtain two discreet states. The central frequency control was obtained by modifying resonator length. Bandwidth control was achieved by choosing a resonator width and controlling the normalized reactance slope parameter of a decoupling resonator by means of a switchable resonator extension. The filter was designed to have center frequencies of 2 and 1.5 GHz both having an 8% fractional bandwidth. The comparison between simulations and measurements showed a central frequency deviation of 4 MHz for the 2 GHz frequency response, and a deviation of 2 MHz for the 1.5 GHz frequency response. The fractional bandwidth deviation for the 2 GHz filter response was 0.67%, while at 1.5 GHz a 0.4% deviation was observed. The simulation and measured responses are in very good agreement.

Halved Vivaldi Antenna With Reconfigurable Band Rejection

This letter presents a Vivaldi antenna having the capability of dynamically rejecting interferers, mainly aiming at multistandard communication with dynamic frequencies allocation. Only half of the Vivaldi is used and placed over a ground plane, which is suitable to vehicular communication. The rejection Alter is integrated to the antenna real estate and consists of two microstrip resonators and two varactor diodes coupled to the slot of the Vivaldi. It is simply biased by applying the control voltage at the antenna RF port. Good matching is achieved from 2.5 to 8 GHz while rejecting a band whose central frequency can be tuned from 1.8 to 5.8 GHz. Simulated and measured return loss, gain, and radiation patterns are presented. The measured gain rejection in the direction of the radiation maximum is about 20 dB or better in the entire tuning range.

Micromachined Transmission Lines for Millimeter-Wave Applications

Several different fabrication techniques and materials have been proposed for making low loss high performance micromachined transmission lines. In this paper a review of several micromachined transmission lines that have been proposed over the last years are classified into four types according to their physical structure and their power losses addressed.

A Monolithic Surface Micromachined Half-Coaxial Transmission Line Filter

In this paper, a novel monolithic surface micromachined half-coaxial transmission line filter was designed, fabricated and measured. The band pass filter presented here has a unique ground structure compared to the other research groups -the suspended ground plane is 100 ptm over the center conductor. The high Q0results from this large gap and an additional reduction of loss is obtained by using quartz substrates. The filter is a 3-pole, 500 fractional bandwidth, bandpass filter centered at 31.75 GHz, consisting of three capacitively coupled resonators composed of half coaxial transmission lines, which are connected to input and output transitions designed to interface with external CPW probes for measurement. The spacing between resonators and the input and output coupling to the filter were calculated from a low pass filter prototype. The fabricated filter has a length of 13 mm and width of 1 mm. A 100-ptm-thick sacrificial layer was made by JSR THB-15IN photoresist. Suspended Au ground plane was supported at the substrate by electroplating process. The pass band return and insertion loss were -10.07 dB at 31.1 GHz and -2.83 dB at 32.0 GHz, respectively. In order to extract total losses of the proposed half coaxial transmission line, we fabricated and measured single resonators. A maximum Q0value of 153 was obtained and these Q values showed the potential of this filter structure, because much higher air gap can be obtained with the same process, resulting in further increase of Q0. Measured loss from the transition was around -0.

A Planar High-

In this paper, a surface micromachined high-Q planar transmission line is presented. The proposed structure is a half-coaxial transmission line on a quartz substrate. The half-coaxial transmission line has a 100-mum air gap between the half-coaxial center conductor and ground plane. The unloaded quality factor extracted from an experimental resonator was 153 at 32 GHz. The proposed structure can be easily integrated with other components on a chip and can be used to partially isolate components, e.g., a microwave filter. A three-pole 5% fractional bandwidth filter centered at 31.75 GHz with a Chebyshev response has been designed with the proposed half-coaxial transmission line, where a measured insertion loss of 2.83 dB has been obtained. Variations in filter response due to different etch hole positions on the suspended ground plane is discussed

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In this paper a reconfigurable bandstop filter able to reconfigure central frequency, bandwidth and selectivity for fine tuning applications is presented. The reconfigurable filter topology has four poles and a quasi-elliptic bandstop filter response. The filter is tuned by varactor diodes placed at different locations on the filter topology. The varactors are voltage controlled in pairs due to filter symmetry for central frequency and bandwidth control. An additional varactor is placed on a crossing line to move a pair of transmission zeros, closer or farther to the filter central frequency, which tunes filter selectivity. The filter has a tuneable fractional bandwidth range from 11.51 to 15.46%, a tuneable central frequency range from 1.346 to 1.420 GHz and a selectivity tuning range from 0.37 to 0.40 dB/MHz.

Micromachined Monolithic Half-Coaxial Transmission-Line Filter

A reconfigurable frequency measurement (RFM) device operating from 1 to 4 GHz has been designed, simulated, fabricated and tested. The RFM device can identify an unknown signal by assigning it to one of the four sub-bands defined by a switched circuit. The 2-bit design is formed by switching between two branches, where each branch corresponds to one bit. The RFM device is made using PIN diodes and other surface mounted components, integrated on the same dielectric substrate in microstrip technology. Simulated and measured results are shown with a very good agreement.

Characterizing a Tune All Bandstop Filter

This paper presents a new release technique for efficient and complete removal of the thick sacrificial layer applicable to surface-micromachined devices and compares this with other conventional release methods. A fully surface-micromachined half-coaxial transmission line filter having a large air-filled gap of 100 µm in thickness is successfully demonstrated using the proposed release technique. The effects of the sacrificial layer residue on the RF responses of the filters, completed by a conventional oxygen plasma ashing process, are analyzed with the aid of x-ray photoelectron spectroscopy (XPS). Experiments show that the proposed new release technique makes it possible to completely remove the thick sacrificial layer, shorten the process time, increase the after-fabrication yield and improve the process reproducibility of the large air-filled gap filters compared to the conventional oxygen plasma ashing method.

2-Bit, 1–4 GHz Reconfigurable Frequency Measurement Device

Surface plasmon resonance (SPR) based sensors are usually designed using the Kretschmann prism coupling configuration in which an input beam couples with a surface plasmon through a thin metal film. This is generally preferred by sensor developers for building planar devices instead of the Otto prism coupling configuration, which, for efficient coupling, requires the metal surface to be maintained at a distance on the order of the wavelength from the input prism surface. In this paper, we report on the microfabrication and characterization of an Otto chip device, which is suitable for applications of the SPR effect in gas sensing and biosensing.