Biblio

The achievable bandwidth in ladder acoustic filters is strictly limited by the electromechanical coupling coefficient (k;) in conventional ladder-acoustic filters. Furthermore, their out-of-band rejection is inherently weak due to the frequency responses of the shunt or series-connected acoustic resonators. This work proposes a coupling-matrix-based solution for both issues by employing acoustic and electromagnetic resonators within the same filter prototype using prescribed Chebyshev responses. It has been shown that significantly much wider bandwidths, that cannot be achieved with acoustic-only filters, can be obtained. An important strength of the proposed method is that a filter with a particular FBW can be designed with a wide range of acoustic resonators with different k; values. An 14 % third-order asymmetrical-response filter is designed and fabricated using electromagnetic resonators and an acoustic resonator with a k; of 3.5 %.

This paper presents the synthesis and circuit transformations of acoustic wave filters based on a transversal arrangement of the individual resonators. This configuration allows for the synthesis of any filter response without detrimental of the limited value of the electro-acoustic coupling coefficient. The synthesis can be performed in the low-pass domain to be latter transformed into the band-pass domain. This latter step results in significant differences between the low-pass and the band-pass responses in wideband stringent filters. This work, after an initial synthesis in the low-pass domain, directly applies the pass-band circuit transformation achieving a more accurate synthesized network even for wideband filters.

This paper proposes a method to synthesis acoustic wave (AW) filters with Chebyshev response automatically. Meanwhile, each AW resonator used to design the filter can be easily fabricated on the same piezoelectric substrate. The method is based on an optimization algorithm with constraints for constant electromechanical coupling coefficient ( kt2) to minimize the defined cost function. Finally, the experimental result for a surface acoustic wave (SAW) filter of global positioning system (GPS) frequency band based on the 42° lithium tantalate (LiTaO3) substrate validates the simulation results. The designed filter shows insertion loss (IL) and return loss (RL) better than 2.5dB and 18dB respectively in the pass-band, and out-band reflection larger than 30dB.

Compressive sensing (CS) is a novel technology for sparse signal acquisition with sub-Nyquist sampling rate but with relative high resolution. Photonics-assisted CS has attracted much attention recently due the benefit of wide bandwidth provided by photonics. This paper discusses the approaches to realizing photonics-assisted CS.