In this paper, micromachined devices for millimeter-wave applications at U- and V-bands are presented. These structures are\ud designed using a rectangular coaxial line built of gold-coated SU-8 photoresist layers, where the coaxial center conductor is\ud suspended in air by stubs. The designs include a stepped coplanar waveguide (CPW)-to-coaxial transition at 63 GHz, with an\ud insertion loss of 0.39 dB at 67.75 GHz and a return loss better than 210 dB across the band of operation between 54.7 and\ud 70.3 GHz. Two filters have been designed; one centered at 42 GHz with a 10% bandwidth, and another at 63 GHz with a 5%\ud bandwidth. Measured insertion losses of 0.77 and 2.59 dB were obtained for these filters, respectively. Measured return loss\ud lower than 13.8 dB over the passband was achieved for both designs. The structures presented in this paper involve a low-cost\ud manufacturing process suitable to produce integrated subsystems at millimeter waves.Peer ReviewedPostprint (published version

Abstract-In this paper, two four-pole filters at X-band are presented, both designs use a coaxial quarter wavelength resonator suspended in air by short circuits between the coaxial center and outer conductor. Different couplings between suspended resonators have been used to obtain a Chebyshev and a quasi-elliptic response. The Chebyshev filter was designed to have a 9.2 GHz centre frequency with a 4% fractional bandwidth. The second design is a quasi-elliptic filter composed of two vertically stacked rectangular coaxial lines, where one pair of resonators is placed on the lower coaxial line and another pair is located on the upper line. Coupling between coaxial lines is achieved through an iris in the common coaxial ground plane. The quasi-elliptic filter has been designed to have a centre frequency of 9.1 GHz with a 4% fractional bandwidth. Two transmission zeros located at the sides of the passband have been successfully achieved with the proposed filter topology. Experimental results for both designs are presented, where a good agreement with simulations has been obtained.

This paper presents a micromachined filter for millimeter-wave applications operating at U-band. The structure was designed using a rectangular coaxial line with the center conductor suspended in air. The rectangular coaxial cables have been optimized to provide a low attenuation constant. The design includes a coplanar waveguide (CPW)-to-coaxial transition to interface the device with other components, or coplanar probes for measurements. The filter has been designed with a center frequency of 42 GHz and a 10% fractional bandwidth. A measured insertion loss of 0.77 dB has been obtained. This structure involves a low-cost micromachining manufacturing process using SU-8 photo resist which is very attractive for the implementation of integrated millimeter wave subsystems.

Several different fabrication techniques and materials have been proposed for the realization of low loss high-Q micromachined filters or tunable filters. In this paper a review of several filters that have been proposed over the last years is presented, including a discussion of topologies and the structures used to make microwave filters.

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