Local optimization is a routine approach for fullwave optimization of microwave filters. For filter optimization problems with numerous local optima or where the initial design is not near to the optimal region, the success rate of the routine method may not be high. Traditional global optimization techniques have a high success rate for such problems, but are often prohibitively computationally expensive considering the cost of full-wave electromagnetic simulations. To address the above challenge, a new method, called surrogate model-assisted evolutionary algorithm for filter optimization (SMEAFO), is proposed. In SMEAFO, considering the characteristics of filter design landscapes, Gaussian process surrogate modeling, differential evolution operators, and Gaussian local search are organized in a particular way to balance the exploration ability and the surrogate model quality, so as to obtain high-quality results in an efficient manner. The performance of SMEAFO is demonstrated by two real-world design cases (a waveguide filter and a microstrip filter), which do not appear to be solvable by popular local optimization techniques. Experiments show that SMEAFO obtains high-quality designs comparable with global optimization techniques but within a reasonable amount of time. Moreover, SMEAFO is not restricted by certain types of filters or responses. The SMEAFO-based filter design optimization tool can be downloaded from http://fde.cadescenter.com.

This paper presents two WR-3 band (220-325 GHz) filters, one fabricated in metal using high precision computer numerically controlled milling and the other made with metallized SU-8 photoresist technology. Both are based on three coupled resonators, and are designed for a 287.3-295.9-GHz passband, and a 30-dB rejection between 317.7 and 325.9 GHz. The first filter is an extracted pole filter coupled by irises, and is precision milled using the split-block approach. The second filter is composed of three silver-coated SU-8 layers, each 432 µm thick. The filter structures are specially chosen to take advantage of the fabrication processes. When fabrication tolerances are accounted for, very good agreement between measurements and simulations are obtained, with median passband insertion losses of 0.41 and 0.45 dB for the metal and SU-8 devices, respectively. These two filters are potential replacements of frequency selective surface filters used in heterodyne radiometers for unwanted sideband rejection. Index Terms-Micromachining, SU-8, terahertz components, waveguide filter. I. INTRODUCTION M ULTICHANNEL air and spaceborne sounders are employed for spectroscopic characterization of the Earth's atmosphere [1]. These instruments perform molecular spectroscopy at millimeter and submillimeter wavelengths in relatively narrow frequency channels. Within the instrument, linearly polarized signals are frequency demultiplexed by a Manuscript

Diplexer coupling matrix synthesis often involves both analytical methods and optimization techniques. At present, general purpose optimization algorithms are used, but they need strong supporting information (e.g., high-quality starting points and very narrow search ranges) from analytical methods, which is not available or too complex to be obtained in many cases. Aiming to obtain the desired coupling matrix with highly reduced supporting information to relieve the pressure of analytical methods, a new optimization algorithm, called self-adaptive differential evolution for coupling matrix synthesis (SADEC), is proposed. Considering the landscape characteristics of diplexer coupling matrix synthesis problems, a new self-adaptive multipopulation search framework and a self-adaptive algorithm parameter control strategy are proposed and organized in a particular way. The performance of SADEC is demonstrated by two all-resonator-based narrowband diplexers using large search ranges only with the requirement of matching the diplexer topology and no ad hoc analysis is included. Experiments and comparisons show the high performance of SADEC and clear advantages compared with the state-of-the-art global optimization methods. SADEC is also applicable to filter coupling matrix synthesis and is downloadable.Index Terms-Coupling matrix, coupling matrix synthesis, differential evolution (DE), diplexer. 0018-9480

For terahertz systems, rectangular waveguide is an ideal low loss medium for interconnectivity and the construction of passive circuits. A drawback when manufacturing waveguides at submillimeter wavelengths is the demanding tolerances due to small dimensions. For example a WR-3 waveguide (operating between 220 and 325 GHz) has a cross-sectional dimension of just 864 by 432 µm, and higher frequency waveguides get proportionally smaller. An additional challenge is that if using waveguide for passive circuits such as filters, there are additional structures inside the waveguide which are significantly smaller than the waveguide itself. Traditionally, computer numerical control (CNC) milling has been used for waveguides, however at terahertz frequencies this is difficult to utilise. In this paper emerging technologies for terahertz waveguides are compared with conventional CNC solutions. The technologies include the photolithography based polymer etching of waveguides using SU-8 photoresist, and the laser machining of metal. Both have shown promise, and good quality terahertz passive components have been fabricated and measured.

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The Space Active Hydrogen-Maser (SAHM) can be used for the Space Very Long Baseline Interferometry Project to improve the resolution of the space astronomical telescope. The standard frequency signals provided by the SAHM have their stability dependent on the flux of effective H atoms. Therefore, a nickel (Ni) tube, one end closed, has been designed in this paper for the SAHM as a hydrogen (H2) purification and flux control device. Mechanisms of the H2 purification and flux control by a Ni tube were studied. H2 flux and ΔU, as a function of an input current, are given by experimental analyses. The diffusion activation energy of atomic H is much less than that of other atoms under the same conditions in Ni. The H atoms reversibly diffuse in Ni, and their diffusion speed has a high response to temperature. Experimental research shows that when the temperature of the tube was changed (from 27 to 700 °C), by an input heating electrical current (from 0 to 3.5 A), the H2 flux varied from 0 to 9.18 × 10−10 mol/s and no change in the phase structure of Ni. The data of flux should be useful for the frequency stability performance research of the SAHM. In addition, no phase change of the material indicates a stable performance of the tube for H-purifying and flux controlling. Finally, the above advantages make it a promising candidate for the reliability of the SAHM.

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