A Ku-band RF-MEMS frequency-reconfigurable multimodal bandpass filter

Abstract

In this paper, a uniplanar RF-MEMS second-order bandpass filter with reconfigurable center frequency is presented. It is based on quarter-wavelength slotline resonators and coplanar waveguide (CPW)-to-slotline multimodal immitance inverters (MIIs), which are reconfigured using RF-MEMS switchable CPW air-bridges (SABs). The filter can be adequately explained and designed using multimodal theory and circuit models. A surface micromachining process on high-resistivity silicon substrate was used to fabricate the filter. Experimental results show frequency reconfiguration from 12 to 13 GHz, maintaining the same relative bandwidth, and insertion losses of 4.6 and 4.7 dB, respectively.

RF-MEMS switches for a full control of the propagating modes in uniplanar microwave circuits and their application to reconfigurable multimodal microwave filters

“…The switch DC behavior (V pull_in and V pull_out ) is derived from measurement of its transmission coefficient (S 21 parameter) as a function of the applied voltage. This approach has proved to be an adequate and straightforward characterization technique (Contreras et al 2012). Since the RF-MEMS switches are embedded in CPW transmission structures for characterization and integration purposes, their equivalent circuits take into account the propagating modes which are extracted from the measured S parameters.…”

“…The presence of two fundamental modes in the same CPW section allows the design of innovative compact reconfigurable microwave circuits since more circuit functionality can be assembled in less area. This multimodal approach has already been applied by the authors to the design of 90º-hybrids (Llamas et al 2009) compact bandpass filters ) and also RF-MEMS enabled reconfigurable devices, such as phase switches (Llamas et al 2010; and bandpass filters with reconfiguration of centerfrequency (Contreras et al 2014) or bandwidth . RF-MEMS switches offer a simple yet effective solution to provide reconfiguration in multimodal circuits since these require a selective control of each CPW mode (even (Llamas et al 2010; and odd , which can be accomplished only in particular cases using semiconductor switches (Contreras et al 2011).…”

“…2008;Entesari et al 2005;Scarbrough et al 2009). Concerning the RF-MEMS mechanical topologies required in microwave reconfigurable circuits they typically include clamped-clamped bridges or cantilever switches (either ohmic or capacitive), with different type of suspensions such as straight-beam Fedder 1994;Persano et al 2016) and folded-beam (Contreras et al 2012;Fedder 1994;Peroulis et al 2003, Kim et al 2014Kim et al 2009;Lakshmi et al 2016). The type of suspension influences the fabrication residual stress of the MEMS membrane, a critical parameter to meet the desired ON/OFF capacitance ratio in capacitive switches, the contact resistance in ohmic switches, and the actuation voltages (Peroulis et al 2003;Mahameed et al 2010;Philippine et al 2013;Persano et al 2016;Kim et al 2009;Lakshmi et al 2016), which in turn determine the microwave behavior (central frequency, bandwidth) of frequencyreconfigurable filters.…”

“…The latter was first introduced in (Contreras et al 2012) and consists of a bridge with two ohmic contacts (one at each end of the membrane) which behaves as a switchable short-circuit for the CPW odd mode (switchable air bridge) that does not affect the propagation of the even mode. Using two ohmic contacts keeps the switch structure symmetric (which is required in order not to affect the propagating CPW even mode) with the additional advantage of introducing redundancy in case one contact fails.…”

“…Using two ohmic contacts keeps the switch structure symmetric (which is required in order not to affect the propagating CPW even mode) with the additional advantage of introducing redundancy in case one contact fails. Furthermore, a combination of optimized-shape suspensions (folded beam as in (Contreras et al 2012), and diagonal beam) and a reinforced membrane is used, resulting in a robust structure against either positive or negative stress gradients. To perform the mechanical evaluation of the different devices, a finite-element analysis has been developed and the simulated pull-in voltage and residual stress have been validated through experimental measurements.…”