Dominique Cros

Low-loss 2-bit tunable bandpass filters using MEMS DC contact switches

This paper presents the development of tunable filters using ohmic contact microelectromechanical system switches. It is shown that this type of switch is very well suited for the fabrication of low-loss high tuning-range microwave filters. Two sets of tunable Ku-band microstrip filters and resonators have been fabricated, with measured tuning ranges of 20% and 44%, and unloaded quality factors better than 75 in all cases. The 2-bit 5.7% fractional bandwidth, tunable bandpass filters exhibit insertion losses lower than 3.2 dB in all states.

Low-loss micromachined filters for millimeter-wave communication systems

This paper describes the design and the realization of two membrane supported microstrip millimeter-wave planar bandpass filters. Both filters exhibit transmission zeros and a 2.3 dB port-to-port insertion loss for the 37 GHz 3.5% bandwidth 2-pole filter and a 1.5 dB insertion loss for a 60 GHz 8% bandwidth 4-pole filter. The use of membrane technology allows a significant reduction of insertion loss, combined with a reproducible, low cost fabrication process.

Study of whispering gallery modes in anisotropic single-crystal dielectric resonators

The Rayleigh-Ritz method and the finite element method nongenerating spurious solutions are employed for analysis of whispering gallery modes (WGMs) in cylindrical single-crystal anisotropic dielectric resonators. These methods allow accurate computation of the resonant frequencies, the Q-factors (depending on the dielectric and on the conductor losses), and the electromagnetic field distributions for all WGMs in the presence of additional elements like metal shields, MIC substrate, or supports. Different families of modes are studied both theoretically and experimentally. The mode coupling phenomenon is investigated. A WGM single-crystal quartz resonator is presented having an unloaded Q-factor greater than 30000 at about 100 GHz, including radiation and dielectric losses. >

Millimeter-wave tune-all bandpass filters

Distributed microelectromechanical varactors on a coplanar waveguide have been used to design a two- and four-pole bandpass tune-all filters. The two-pole initial bandwidth is 6.4% at 44.05 GHz with a mid-band insertion loss of 3.2 dB and with matching better than 15 dB. The four-pole initial bandwidth is 6.1% at 43.25 GHz with a mid-band insertion loss of 6.5 dB and with matching better than 10 dB. The use of microelectromechanical system bridges allows a continuous tuning for both center frequency and bandwidth. The varactors biasing network has been designed so that the center frequency and bandwidth can be tuned separately. The two-pole filter center frequency can be changed from 44.05 to 41.55 GHz (5.6% tuning range), while the bandwidth can be independently changed from 2.8 to 2.05 GHz. The four-pole filter center frequency can be changed from 43.25 to 40.95 GHz (5.3% tuning range) and the bandwidth can be changed from 2.65 to 1.9 GHz.

An electromechanical model for MEMS switches

This paper presents a new dynamic and parametric model of a capacitive micro-electromechanical switch electro-statically actuated. It is built of elementary electrical equivalent-circuit blocks constructed of voltage-controlled current sources. The model describes the nonlinear mechanical behavior of the membrane movement, which allows the computation or the bridge capacitance. It can be inserted as a model to perform simulations at microwave frequencies. All the switch parameters such as dimensions and materials properties are adjustable.

Dielectric resonators suitable for use in planar integrated circuits at short millimeter wavelengths

Experimental results are presented of planar whispering-gallery-mode dielectric resonators. The three-dimensional field pattern obtained by using finite-element techniques as well as measured resonant frequencies and quality factors carried out in the Ka (26.5-40 GHz) and 90-100-GHz bands is presented. The application to millimeter-wave components is discussed. >

InAs quantum wires in InP-based microdisks: Mode identification and continuous wave room temperature laser operation

We present the design, fabrication, and characterization of an optical microsource, which comprises InAs/InP quantum wires embedded in a suspended microdisk. Comparison between photoluminescence measurements and theoretical analysis allows for a clear identification of the whispering gallery modes. cw room temperature lasing operation is demonstrated.

High-Q whispering gallery traveling wave resonators for oscillator frequency stabilization

Usually a frequency-stabilized standing wave resonator-oscillator incorporating a resonator as a frequency discriminator requires a circulator to separate the injected and reflected wave, A ferrite circulator is a noisy device and can limit the phase noise or frequency stability. Moreover, we show that the noise in a circulator varies, and detailed low noise measurements are necessary to choose an appropriate quiet circulator. Thus, by realizing a configuration that does not require a circulator, an improvement in performance and reliability can be obtained. A solution to this problem is to design a high-Q whispering gallery traveling wave (WGTW) resonator. This device naturally separates the injected and reflected wave in the same way as a ring cavity at optical frequencies, without degrading the frequency discrimination. Q-factor measurements of a WGTW sapphire resonator are presented, along with a derivation of critical parameters to maximize the frequency discrimination. New measurements of noise in ferrite circulators and isolators have also been made, which is followed with a discussion on oscillator design.

Ferroelectric Thin Films for Applications in High Frequency Range

Abstract SrBi 2 Nb 2 O 9 and KTa 1− x Nb x O 3 thin films were grown by pulsed laser deposition on various substrates. Structural investigations evidenced that single phase polycrystalline randomly oriented films were grown on sintered alumina whereas epitaxial films were grown on (100)MgO. The microstructure was strongly controlled by the structural characteristics. Interdigited capacitors patterned on SrBi 2 Nb 2 O 9 films on both substrates as well as permittivity and losses measurements performed at 12.5 GHz showed a strong effect of the structural characteristics on the dielectric behavior.

Spherical Bragg reflector resonators

In this paper we introduce the concept of the spherical Bragg reflector (SBR) resonator. The resonator is made from multiple layers of spherical dielectric, loaded within a spherical cavity. The resonator is designed to concentrate the energy within the central region of the resonator and away from the cavity walls to minimize conductor losses. A set of simultaneous equations is derived, which allows the accurate calculation of the dimensions of the layers as well as the frequency. The solution is confirmed using finite-element analysis. A Teflon-free space resonator was constructed to prove the concept. The Teflon SBR was designed at 13.86 GHz and exhibited a Q-factor of 22,000, which agreed well with the design values. This represents a factor of 3.5 enhancement over a resonator limited by the loss-tangent of Teflon. Similarly, SBR resonators constructed with low-loss materials could achieve Q-factors of the order of 300,000.