Abstract
This paper presents several freestanding bandpass mesh filters fabricated using an SU-8-based micromachining technique. The important geometric feature of the filters, which SU8 is able to increase, is the thickness of the cross-shaped micromachined slots. This is five times its width. This thickness offers an extra degree of control over the resonance characteristics. The large thickness not only strengthens the structures, but also enhances the resonance quality factor ( Q-factor). A 0.3-mm-thick, single-layer, mesh filter resonant at 300 GHz has been designed and fabricated and its performance verified. The measured Q-factor is 16.3 and the insertion loss is 0.98 dB. Two multi-layer filter structures have also been demonstrated. The first one is a stacked structure of two single mesh filters producing a double thickness, which achieved a further increased Q-factor of 27. This is over six times higher than a thin mesh filter. The second multilayer filter is an electromagnetically coupled structure forming a two-pole filter. The coupling characteristics are discussed based on experimental and simulation results. These thick mesh filters can potentially be used for sensing and material characterization at millimeter-wave and terahertz frequencies.
Highlights
A MESH filter is an important frequency-selective component in many millimeter-wave and terahertz (THz) systems
The mesh filters were measured in a free space quasi-optical (QO) system driven by a vector network analyzer
When the two mesh filters are in very close proximity, e.g., 0.05 mm, a third matching condition can be met as shown in Fig. 9(a).Now is comparable to the slot width, so the coupling should be attributed to evanescent modes of the mesh filter
Summary
A MESH filter is an important frequency-selective component in many millimeter-wave (mm-wave) and terahertz (THz) systems. An even thicker THz mesh filter of 2 mm in depth, 25 times the slot-width, was fabricated using X-ray LIGA [17]. In both cases, the purpose for introducing the thickness was to enhance mechanical strength. The thick mesh filter is fabricated using a micromachining technique based on thick photoresist SU-8 This is a simple and potentially low-cost fabrication method and yet provides better surface quality of the structure than laser or DRIE based methods. The technique has been successfully used to produce mm-wave 3-D air-filled devices of more complicated structures [18]
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