This paper presents two W-band waveguide bandpass filters, one fabricated using laser micromachining and the other 3-D printing. Both filters are based on coupled resonators and are designed to have a Chebyshev response. The first filter is for laser micromachining and it is designed to have a compact structure allowing the whole filter to be made from a single metal workpiece. This eliminates the need to split the filter into several layers and therefore yields an enhanced performance in terms of low insertion loss and good durability. The second filter is produced from polymer resin using a stereolithography 3-D printing technique and the whole filter is plated with copper. To facilitate the plating process, the waveguide filter consists of slots on both the broadside and narrow side walls. Such slots also reduce the weight of the filter while still retaining the filter’s performance in terms of insertion loss. Both filters are fabricated and tested and have good agreement between measurements and simulations.

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$W$ -Band Waveguide Filters Fabricated by Laser Micromachining and 3-D Printing

A micromachined 385 GHz rectangular waveguide cavity bandpass filter is presented. The proposed filter is fabricated using deep reactive ion etching on silicon substrate, with sputtered gold inner surface metallization. The vector network analyzer measured results show the lowest insertion loss is about 2.7 dB with a 15 GHz bandwidth. Effects of micro-electro-mechanical systems process on the filter's performance are discussed in detail.

Micromachined Terahertz Rectangular Waveguide Bandpass Filter on Silicon-Substrate

This paper presents a novel way of constructing waveguiding structures by stacking several thin metal plates for millimeter-wave and terahertz applications. The metallic layers do not require any electrical contacts among them. An air-filled multilayer waveguide (MLW) transmission line is successfully designed and manufactured at $D$ -band. Five vertically stacked thin metal layers are used to form an air-filled rectangular waveguide line. The layers are simply assembled by allowing a small air gap among them, without the need of using advanced manufacturing methods such as adhesive bonding techniques. The possible field leakage due to the air gaps is prevented by using an electromagnetic bandgap structure, consisting of glide-symmetric holes. A straight MLW line and a line with double 90 $^\circ$ bends are fabricated by using chemical metal etching, as a proof of concept. The measurement results of the straight line show that the reflection coefficient is better than $-$ 18 dB with an average insertion loss of 0.02 dB/mm over the frequency band 110–170 GHz. For the double 90 $^\circ$ bend line, the reflection coefficient is better than $-$ 18 dB with a similar average insertion loss of 0.02 dB/mm over the frequency band 110–150 GHz. The proposed concept could be an excellent candidate for designing compact and thin passive waveguide components and active components packaging, with a great potential for low-cost, light weight, and mass producible at millimeter-wave frequencies.

Novel Air-Filled Waveguide Transmission Line Based on Multilayer Thin Metal Plates

In this paper, a 400-GHz silicon micromachined elliptic cavity waveguide filter with two transmission zeros on both sides of the passband is presented. The filter is cascaded by two elliptic cavities which are operating at quasi- ${\rm TM}_{110}$ mode. Each elliptic cavity can introduce a transmission zero near the passband of the filter. By adjusting the axial-ratio (AR) of the elliptic cavity, the position of the introduced transmission zero could be moved to the upper side or the lower side of the passband. The micromachining process of deep reactive ion etching (DRIE) is used for the fabrication. The measured 3-dB bandwidth of the filter is 7.52%, from 380.2 to 409.9 GHz, and the measured insertion loss is 2.84 dB, including extra waveguide of about 4.5 mm at the input and output ports. In addition, the insertion loss of straight waveguide is also measured and analyzed. Then, an analysis method for the loss property is summarized. According to the measurement, the unit length loss of the waveguide is about 0.144 dB/mm at 400 GHz.

Silicon Micromachined Terahertz Bandpass Filter With Elliptic Cavities

Millimeter-wave (mmW) bandpass filter using substrate integrated waveguide (SIW) is proposed in this paper The propagation constants of three different types of electromagnetic bandgap (EBG) units are discussed and compared with their passbands and stopbands performance The slotted-SIW unit shows a very good lower stopband and upper stopband performance The mmW bandpass filter with three cascaded uniform slotted-SIW-based EBG units is constructed and designed at 40 GHz The extracted coupling coefficient ( ${K}$ ) and quality factor ( ${Q}$ ) are used to determine the filter circuit dimensions To prove the validity, the previous proposed structure is fabricated in a single circuit layer using low-temperature co-fired ceramic technology and measured at 40 GHz, respectively The measured results are in good agreement with simulated results in such frequency and the measured insertion losses at 40 GHz is 142 dB, respectively

U-Shape Slots Structure on Substrate Integrated Waveguide for 40-GHz Bandpass Filter Using LTCC Technology

The 140 GHz silicon micromachined bandpass rectangular waveguide filters are firstly fabricated by the deep reactive ion etching (DRIE) processes for submillimeter wave applications. The filter circuit structure is once-formed using the ICP reactive ion etcher to etch through the full thickness of the silicon wafer, and then bonded together with the two metallized glass covers to form the waveguide cavity. The measured lowest insertion losses are lower than 0.5 dB. The unloaded quality factor can reach 160. It demonstrates a successful and practical way to fabricate these types of waveguide filters.

C. H. Shek

Papers

D-Band Micromachined Silicon Rectangular Waveguide Filter