In this research, a novel polarization reconfigurable fractal antenna with high gain is proposed for wideband applications. This antenna consists of a Koch curve based hexagonal ring patch, two Positive-Intrinsic-Negative (PIN) diodes, and partial ground. The patch is positioned on a Rogers RT/Duroid 5880 substrate (ϵr = 2.2) with overall dimensions 33 × 30 × 1.6 mm3. It has three frequency bands with three different cases i.e., case I, 3–7.91 (90%); case II, 3–7.73 (88.16%); and case III, 3.54–6.7 GHz (61.7%). As a result, the proposed antenna’s impedance bandwidth (IBW) offers constant wideband coverage ranging from 3–7.91 GHz (90%). The axial ratio bandwidth (ARBW) is below 3 dB over 3.6–6.9 (62.86%) and 3.33–7.14 GHz (72.78%) for LHCP (Case I) and RHCP modes (Case II), respectively. The value for LP mode (Case III) is 3.54–6.7 GHz (61.7%). A peak realized gains of 4.75, 5.07, and 3.8 dBi are achieved at 6.2, 6.3, and 6 GHz for Case I, Case II, and Case III, respectively. Both linear and circular polarization prototype was developed and the performance was verified through measurements. The design confirms good polarization-reconfigurable characteristics within the band of 3.91 – 7.91 GHz.

This paper proposes an air-filled substrate integrated waveguide (AFSIW) bandpass filter with a miniaturized non-resonant node (NRN). The NRN structure is introduced between the three resonators, and its size is smaller than the resonator size, which can realize the NRN structure’s miniaturization and reduce the model’s size. The NRN size of this filter is 41% of the NRN size of the existing AFSIW filter. This filter also introduces a transmission zero (TZ) above the passband. The measured results show that the filter’s center frequency is 20.73 GHz, and the bandwidth is 0.86 GHz. The insertion loss in the passband is 0.95 dB, and the return loss is better than 23 dB. Due to the TZ in the upper stopband, the AFSIW filter obtained good selectivity.

In this paper, a single-layer band-stop frequency selective surface (FSS) by combination of Mike Kastle unit and square ring unit is proposed to achieve wide angular stable shielding. Owing to the rotational symmetry of the structure, the designed FSS is insensitive to polarization. By the combination design, the wide angular stability can be achieved as the incident angle increases from 0° to 85°, with only a maximum frequency deviation of 0.012 GHz. Meanwhile, the mechanism of the proposed FSS is investigated by the parametric analysis of equivalent circuit model. The prototype was manufactured and measured to verify the design and simulation analysis, and the measurement results were in good agreement with the simulation results.

This contribution presents miniaturization techniques for folded circular substrate integrated waveguide (FCSIW) cavity filters. The cavities support dual-mode operation. Two of these cavities are combined to form a fourth-order filter. Two filter designs are implemented. The first one serves as a reference and exhibits good manufacturability. For the second one, the cavity is modified, which leads to $50\%$ more compactness. The designs are experimentally verified with 10 GHz bandpass filters. Even though the achieved level of compactness requires higher technological effort, the measurements validate the miniaturization concept. The out-of-band rejection exceeds 40 dB between 11.2 and 30 GHz for the reference filter and between 11.3 and 33 GHz for the miniaturized one. The implemented components are compared with state-of-the-art filters.

In this paper, a small ultra-wideband (UWB) antenna with two stop bands by a compact electromagnetic bandgap (EBG) cell loaded with two new open meander slots is presented. With the coupling of the EBG cell to the feedline, the stop bands are formed. The designed EBG cell is a mushroom type that has the advantages of being able to independently control the stop bands, high responsiveness selectivity of stop bands, easy switching, the need for fewer EBG cells, and low impact on the working characteristics of the antenna. To have a better understanding of the proposed EBG mechanism, characteristic mode analysis is used. The size reduction of the suggested antenna is obtained by halving the reference antenna relative to the axis of symmetry. The measurement results for −10 dB adaptation are from 2.73 to 13 GHz with stop bands at 3.51 GHz (12.9%) and 5.34 GHz (14.1%). The radiation behavior of the minimized antenna is similar to that of a reference antenna. Minimized UWB antenna with transmission function and group delay with small variations in the operating frequency range is suitable for small multiple-input and multiple-output (MIMO) and diversity systems.

A miniaturized high-isolation quadplexer with wide upper-stopband based on open and short stub-loaded multimode-resonator is proposed in this paper. Based on the theory of multimode-resonator and stepped impedance resonator (SIR), the compact quadplexer is designed by using multimode-resonator and SIR. In order to further miniaturize the size of the circuit, the multimode resonator is employed as the common resonator to replace the common matching network of the quadplexer and the SIRs are curved. Equivalent topology circuit is given to analyze and design the quadplexer. Detailed analyses are given according to the equivalent circuits. The proposed compact quadplexer working at central frequencies of 1.8, 2.4, 2.8, and 3.5 GHz with over 40 dB isolation is finally simulated, fabricated, and measured. The measured results agree well with the simulated ones. The total size of the fabricated quadplexer is 0.36 λg × 0.42 λg.

A super-wideband (SWB) omnidirectional antenna is reported in Lau et al. in 2005 and 2008, but the antenna structure was complex and the radiation properties were unsatisfactory. In this paper, a SWB omnidirectional antenna with simple structure and improved radiation properties is presented. The antenna just consists of a two-stage inverted cone and two shorting pins. The proposed two-stage cone can improve the impedance matching in super-wide bandwidth, and the optimized shorting pins can reduce the cut-off frequency more than 50%. The calculated and measured results are investigated to confirm the antenna performances. The impedance bandwidth of the antenna for voltage standing wave ratio ≤ 2 achieves more than 1:22.1, covering 0.905 GHz to the above band. The smaller sizes than those referred by Lau et al. in 2008 are obtained. The profile of the antenna is 0.078λc, and the diameter of the radiation body is 0.217λc (λc is the wavelength of the cut-off frequency of the antenna). In addition, the radiation properties of the kind of SWB omnidirectional antenna are improved obviously. In the whole band, the ripple levels in horizontal radiation patterns are not more than 6.6 dB, and the cross-polarized levels are reduced by 9 dB.

A single-layer coaxial-fed compact rectangular microstrip antenna with very low voltage standing wave ratio (VSWR) is presented in this paper. The simulated VSWR of the proposed antenna 1.00374 is obtained near the center frequency of the operating band (3.5 GHz). Simulation and measurement results indicate that the bandwidth (simulated: 3.36–3.715 GHz, and measured: 3.295–3.645 GHz) of the antenna exceeds 10% below VSWR 2, when the size reduction of the antenna is about 81.6%. The realized peak gain is obtained about 2.15 dBi at 3.5 GHz. For the verification of the computational results, two designs were fabricated and measured. Good agreements between simulated and measured results were found.

This paper proposes a planar monopole antenna with a parabolic edge shape. This antenna, which has notch characteristics in the wireless local area network (WLAN) band, can be miniaturized. To obtain the notch characteristics in the WLAN band, a slot with a parabolic edge shape identical to that of the monopole structure was implemented. Because the planar monopole antenna with a parabolic edge shape possesses characteristics similar to those in self-complementary structure conditions, it can be miniaturized by reducing the antenna components at the same proportion. For the antenna fabrication, an FR4 dielectric substrate with a dielectric constant of 4.7 was used. The size of the miniaturized antenna that satisfies the ultra-wide band requirement was 15.6 × 18.6 mm2, and the 10-dB band was 3.013–12.515 GHz. At each frequency, the radiation pattern was similar to that of a dipole antenna.

In this paper, a miniaturized coaxial feed curved-slotted microstrip patch antenna over a fractalized uniplanar compact electromagnetic bandgap (F-UC-EBG) ground plane is proposed and investigated. Compact size is achieved by cutting the curved slots along the orthogonal directions of the patch radiator. The curved-slotted microstrip patch antenna is 38.30% miniaturized as compared with the conventional microstrip patch antenna resonating at 2.38 GHz. Furthermore, the ordinary ground plane of the curved slotted patch antenna is replaced by the F-UC-EBG ground plane. Due to the slow wave phenomenon created in the F-UC-EBG structure and the better impedance matching at the lower frequency further miniaturization and improved performance are obtained. The proposed antenna shows 74.76% miniaturization as compared with the conventional microstrip patch antenna resonating at 1.57 GHz and has 2.61% 10-dB fractional bandwidth, 1.49 dB gain, and 81.59% radiation efficiency. The proposed antenna is fabricated on a low-cost FR4 substrate having an overall volume of 0.184λ0 × 0.184λ0 × 0.0236λ0 at 1.57 GHz GPS band. The measured and simulated results are in good agreement and predicting appropriateness of the antenna in portable and handheld communication systems for GPS applications.

A new flexible and miniaturized power divider (PD), based on the Wilkinson PD topology, is carried out in this paper. Flexibility and size reduction are achieved simultaneously thanks to both an open-stub loading the input port and additional transmission lines (TLines) connecting the output ports to the isolation resistance. Design equations and rules are given. As a proof-of-concept, two PDs working at 2.45 GHz were fabricated and measured. Then, on the basis of the previous developments, a 1:4 power-dividing feeding network was realized. It highlights the high performance and flexibility of the proposed PD. Agreement between simulation and measurement results is very good, for PDs as well as for the feeding network, thus validating the proposed approach. This concept is straightforward to be applied at higher frequencies, in particular in the millimeter-wave range on CMOS technologies, where flexibility in the choice of the TLines characteristic impedances and size reduction are mandatory.

To enable mechanical milling of small (0.1–1.0 g) samples, a cylindrical grinding vessel machined from polypropylene and furnished with tungsten carbide rods has been designed and produced for use inside the conventional jar of a McCrone Micronizing Mill. The vessel is about one-seventh the volume of the conventional jar supplied by the manufacturer. The conditions of milling for both the conventional and the miniaturized-grinding assemblies were tested using quartz sand as a limiting case. The median grain sizes of the resultant powders were measured by an X-ray gravitational-sedimentation method, with contamination from the grinding media measured by Rietveld refinement and by instrumental neutron activation analysis. The use of tungsten carbide grinding elements permits rapid wet milling of a small sample to the same median grain size in about one-third of the time required by a regular sample ground in corundum. The relative contamination (by tungsten carbide on a weight basis) using the miniaturized-grinding assembly is about 6(1)% of the proportion of corundum contamination yielded by the conventional grinding assembly.

With a body length of only 0.3–0.4 mm, the parasitoid wasp Trichogramma evanescens (Westwood) is one of the smallest insects known. Yet, despite its diminutive size, it possesses compound eyes that are of oval shapes, measuring across their long axes in dorsoventral direction 63.39 and 71.11 μm in males and females, respectively. The corresponding facet diameters are 5.90 μm for males and 6.39 μm for females. Owing to the small radii of curvature of the eyes in males (34.59 μm) and females (42.82 μm), individual ommatidia are short with respective lengths of 24.29 and 34.97 μm. The eyes are of the apposition kind, and each ommatidium possesses four cone cells of the eucone type and a centrally fused rhabdom, which throughout its length is formed by no more than eight retinula cells. A ninth cell occupies the place of the eighth retinula cell in the distal third of the rhabdom. The cone is shielded by two primary and six secondary pigment cells, all with no apparent extensions to the basement membrane, unlike the case in larger hymenopterans. The regular and dense packing of the rhabdoms reflects an effective use of space. Calculations on the optics of the eyes of Trichogramma suggest that the eyes need not be diffraction limited, provided they use mostly shorter wavelengths, that is, UV light. Publications on the visual behavior of these wasps confirm Trichogramma’s sensitivity to UV radiation. On the basis of our findings, some general functional conclusions for very small compound eyes are formulated.