A folded slot with open end is introduced to achieve a dual-band coplanar waveguide (CPW)-fed monopole antenna for radio frequency identification (RFID) applications. The designed antenna, which, including the substrate, is only 32 mm in height and 20 mm in width, can operate simultaneously at the 2.45 and 5.8 GHz bands with −1.8 and 2.3 dBi gains, respectively. Its properties make the antenna suitable for RFID tags.
Abstract In this paper, a novel CPW-fed dual folded-strip monopole antenna with a pair of inverted L-shaped stubs is proposed for multiband applications. Reasonably large impedance matching bandwidth and good omni-directional radiation patterns have been observed. The measured impedance bandwidths reach about 27% for the lower band and 32% for the higher band, which meets the required bandwidth specifications of 2.4 GHz WLAN, 2.5 GHz WiMAX, DMB and 5.2/5.8 GHz WLAN standards. The proposed antenna with relatively low profile is suitable for multiband wireless communication systems.
A simple ultra-wideband planar rectangular printed monopole antenna with dual narrow band-notched characteristics is presented in this paper. Dual narrow band-notched frequencies at 3.4 GHz and 5.2 GHz are achieved by embedding a U-shaped slot in the radiation patch and a small pentagon patch on the ground, respectively. Moreover, input impedance, conceptual equivalent circuit models and surface current distributions are built for analysis and explanation of dual narrow band-notched characteristics. At the same time, an approximate expression of the notched frequency with the pentagon patch dimension is proposed in this paper. The designed antenna operates over the frequency band between 2.69 GHz and 12 GHz (126.8%), with one narrow notched band from 3.32 GHz to 3.55 GHz (6.7%) and the other from 5.04 GHz to 5.39 GHz (6.8%). The antenna is successfully simulated, fabricated and measured, showing broadband matched impedance, dual narrow band-notched characteristics, stable gain, high radiation efficiency and omni directional radiation patterns.
Abstract This paper presents a novel technique to change the impedance characteristics of patch antenna to achieve multi-band. The proposed structure is based on the metamaterial concept. By replacing the conventional substrate of patch antenna with metamaterial, the impedance characteristics can be effectively changed to produce multi-band property. The design is based on the dispersive characteristic of the substrate by using metamaterial structure. To validate the proposed approach, numerical and experimental results are presented; the results show the validity of our approach.
In this paper, a printed ultra-wideband (UWB) antenna with dual band-notched characteristics suitable for UWB applications is presented. The proposed antenna, by inserting a pair of line-shaped slots into the radiating patch and adding a pair of C-shaped strips coupled to the microstrip feed line, is designed to realize the dual band-notched characteristics at 3.5 GHz and 5.5 GHz, respectively. Good agreement between the simulated and measured results is obtained, which shows that the proposed antenna has a broad impedance bandwidth ranging from 2.3 to 12.5 GHz with VSWR less than 2.0, except the frequency bands of 3.2–3.8 GHz for WiMAX and 5.0–5.9 GHz for WLAN. Moreover, the nearly omnidirectional radiation patterns and stable gain over the operating frequency band have been obtained, which meet the UWB system requirements.
Climate change has intensified the frequency of extreme drought events in desert ecosystems, accompanied by uneven distribution of annual precipitation. Whether extreme precipitation events at different phenophases have equivalent impacts on desert plants is an unverified topic, yet it is crucial for understanding the mechanisms of vegetation adaptation to changes in precipitation. This study focuses on the typical desert plant Artemisia ordosica and employs in situ precipitation control experiments using rain shelters to simulate extreme drought events (30 consecutive days of precipitation removal) at three phenophases: the sprouting stage, vegetative growth stage, and flowering and fruiting stage. Against this backdrop, phenological differences in the leaf photosynthetic physiological regulatory mechanisms that affect the accumulation of Aboveground Net Primary Productivity (ANPP) in A. ordosica under extreme drought events were explored, including parameters such as photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant enzymes. The findings reveal that: (1) Extreme drought events at different phenophases markedly reduced the photosynthesis of A. ordosica leaves, subsequently leading to the significantly reduction in ANPP accumulation (p<0.05). With the impact degree ordered as follows: flowering and fruiting stage > sprouting stage > vegetative growth stage; (2) During extreme drought events, A. ordosica experiences a decrease in photosynthetic gas exchange capacity and an enhancement in water use efficiency, which are stomatal regulatory responses. Additionally, there is an increase in thermal dissipation, a decline in photochemical activity parameters (such as potential photosynthetic activity of PSII, initial light energy conversion efficiency, actual photochemical quantum yield, and photochemical quenching), and an augmentation of the antioxidant enzyme system, which are non-stomatal regulatory responses; (3) During extreme drought events at different phenophases, the dominant factor leading to a decline in the photosynthetic rate of A. ordosica leaves is stomatal regulation. However, there are phenological differences in the sensitivity of stomatal and non-stomatal regulation. The stomatal regulation of A. ordosica leaves during the sprouting stage is more sensitive compared to other phenophases. Non-stomatal regulation is most sensitive during the vegetative growth stage, with a heightened sensitivity in the modulation of chlorophyll fluorescence. The study reveals differences in the photosynthetic physiological regulation of desert vegetation in response to extreme drought events at different phenophases, offering an innovative perspective on the physiological and ecological regulatory mechanisms of desert ecosystems in the face of climate change.
As a very powerful optimisation approach, differential evolution algorithm for continuous optimisation problems has been applied to electromagnetic (EM) design problems. However, the optimisation of a thinned array can be formulated as a discrete-variable optimisation problem with solutions encoded as binary strings. Here, a Boolean differential evolution (BDE) algorithm for 0–1 integer programming problems is proposed to design planar thinned arrays with minimum sidelobe levels. The BDE algorithm with only one control parameter is easily implemented. Meanwhile, a fast Fourier transform is employed to speed up the calculation of the pattern. Numerical experiments show that the BDE algorithm is an effective technique.
In this paper, a novel UWB (Ultra-wide Band) antenna is proposed. This design mainly consists of a wide slot square ground plane and a frequency independent feed line-a 0.5 turn equiangular spiral, which are etched on each side of a substrate separately. Additionally, a circular patch connected with the slotted ground is introduced to tune the working bandwidth of this antenna. Prototypes are instructed and tested to know the performance of the proposal. From the results, it can be seen that the proposed antenna has enough impedance bandwidth for UWB applications with VSWR (Voltage Standing Wave Ratio) less than 2, acceptable radiation patterns, as well as relatively high gains.
A novel feeding mechanism for realizing circular polarization characteristic is presented in this paper. Detailed theoretical analysis proves that a circular microstrip antenna, which is excited by three centrosymmetric feeds with equal amplitudes and relative 120° phase shifts, can obtain good circular polarization. This circular microstrip antenna is designed to work on TM11 mode. Good equal input powers with relative 120° phase shift for three feeds are provided by a Wilkinson power divider with three phase-adjusting transmission lines. Probe feeding for the radiating patch is accomplished by vertical via holes through the substrate material. The measured results show that the proposed antenna obtains a 10 dB return-loss impedance bandwidth of 22.3% and a 3 dB axial-ratio CP bandwidth of 18.9%, with the peak gain of 7.0 dBi. Additionally, the measured symmetrical radiation patterns are in good agreement with the simulated ones.
Climate change has intensified the frequency of extreme drought events in desert ecosystems, accompanied by uneven distribution of annual precipitation. Whether extreme precipitation events at different phenophases have equivalent impacts on desert plants is an unverified topic, yet it is crucial for understanding the mechanisms of vegetation adaptation to changes in precipitation. This study focuses on the typical desert plant Artemisia ordosica and employs in situ precipitation control experiments using rain shelters to simulate extreme drought events (30 consecutive days of precipitation removal) at three phenophases: the sprouting stage, vegetative growth stage, and flowering and fruiting stage. Against this backdrop, phenological differences in the leaf photosynthetic physiological regulatory mechanisms that affect the accumulation of Aboveground Net Primary Productivity (ANPP) in A. ordosica under extreme drought events were explored, including parameters such as photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant enzymes. The findings reveal that: (1) Extreme drought events at different phenophases markedly reduced the photosynthesis of A. ordosica leaves, subsequently leading to the significantly reduction in ANPP accumulation (p<0.05). With the impact degree ordered as follows: flowering and fruiting stage > sprouting stage > vegetative growth stage; (2) During extreme drought events, A. ordosica experiences a decrease in photosynthetic gas exchange capacity and an enhancement in water use efficiency, which are stomatal regulatory responses. Additionally, there is an increase in thermal dissipation, a decline in photochemical activity parameters (such as potential photosynthetic activity of PSII, initial light energy conversion efficiency, actual photochemical quantum yield, and photochemical quenching), and an augmentation of the antioxidant enzyme system, which are non-stomatal regulatory responses; (3) During extreme drought events at different phenophases, the dominant factor leading to a decline in the photosynthetic rate of A. ordosica leaves is stomatal regulation. However, there are phenological differences in the sensitivity of stomatal and non-stomatal regulation. The stomatal regulation of A. ordosica leaves during the sprouting stage is more sensitive compared to other phenophases. Non-stomatal regulation is most sensitive during the vegetative growth stage, with a heightened sensitivity in the modulation of chlorophyll fluorescence. The study reveals differences in the photosynthetic physiological regulation of desert vegetation in response to extreme drought events at different phenophases, offering an innovative perspective on the physiological and ecological regulatory mechanisms of desert ecosystems in the face of climate change.
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