In this paper, an ultra-wideband (UWB) bandpass filter (BPF) with dual notched bands using a T-shaped resonator and L-shaped defected microstrip structure (DMS) is proposed and fabricated. First, the principle of generating notched bands by using a T-shaped resonator and L-shaped defected microstrip structure to determine the size parameters of the structure is analyzed. High frequency structure simulator (HFSS) software is used to analyze the performance of the filter, and advanced design system (ADS) is used to extract the equivalent circuit model parameters. The two simulation results are consistent, which further verifies the correctness of the circuit model. Finally, the filter is fabricated and measured. The measured results are in good agreement with simulated results, demonstrating good insertion loss and return loss. The proposed filter has dual independently controllable notched bands which are implemented by coupling the T-shaped resonator to the transmission line and by etching the L-shaped defected microstrip structure respectively. The proposed filter can suppress dispensable bands at 3.5 GHz and 7.5 GHz in WiMAX band and X-band to improve the performance of the ultra-wideband communication system. By adjusting the parameters of the T-shaped resonator and L-shaped defected microstrip structure, the UWB bandpass filter with dual notched bands working at WiMAX band and X-band can be designed and applied to the wireless communication system.

With the development of artificial electromagnetic structures, defective grounding structures (DGS), defective microstrip structures (DMS), and electromagnetic bandgap (EBG) have been widely used in the design of microstrip filters. In this paper, a triple notches ultra wideband bandstop microstrip filter based on Archimedean spiral electromagnetic bandgap structure (ASEBG) structure is proposed. Firstly, the equivalent circuit of ASEBG is analyzed, and L and C values are extracted by using Advanced Design System (ADS). Secondly, the correctness of the lumped parameter model is verified by comparing the High Frequency Structure Simulator (HFSS) simulation results with the measured results. Finally, the influence of ASEBG structure parameters on resonant performance is analyzed by HFSS simulation, and the filter parameters are further optimized. By coupling ASEBG structure to existing double notch microstrip filters, a triple notches ultra wideband bandstop microstrip filter is realized. This method can also be used in the design of other microstrip devices with stopband characteristics. The three bandgap center frequencies of the proposed triple notches ultra wideband bandstop microstrip filter are 3.5, 5.2, and 7.4 GHz, respectively. The corresponding maximum attenuation of the three stopbands is 33.6, 24.8, and 21.7 dB, respectively.

In response to the demand for broadband antennas in 5G mobile communications, this paper proposes a compact broadband multiple-input multiple-output (MIMO) antenna array. By chamfering a radiation patch and adding parasitic patches, the antenna is miniaturized while also expanding its bandwidth. The mutual coupling between the two antenna elements is reduced by loading a double-layer metamaterial decoupling structure above the elements which consists of an open resonating ring and a square ring. The antenna is simulated and measured using the three-dimensional electromagnetic simulation software HFSS and a vector network analyzer. The results show that the proposed antenna has a good radiation performance of S11 < -10 dB in the operating band of 12.11–13.99 GHz (relative bandwidth of 14.41%). Furthermore, the isolation of the proposed MIMO antenna array in the operating band is improved by more than -18.8 dB on loading the metameterial structure, indicating that the array antenna is suitable for use in the Ku-band.

In this letter, we report high-speed photoconductive switches based on low-temperature (LT) grown GaAs on Si substrate. Epitaxially grown LT GaAs was separated from its substrate, transferred on an SiO/sub 2/-coated Si substrate and integrated with a transmission line. The 10/spl times/20-/spl mu/m/sup 2/ switches exhibit high breakdown voltage and low dark currents (<10/sup -7/ A at 100 V). The photoresponse at 810 nm shows electrical transients with /spl sim/0.55-ps full-width at half-maximum and /spl sim/0.37-ps decay time, both independent on the bias voltage up to the tested limit of 120 V. The photoresponse amplitude increases up to /spl sim/0.7 V with increased bias and the signal bandwith is /spl sim/500 GHz. The freestanding LT GaAs switches are best suited for ultrafast optoelectronic testing since they can be placed at virtually any point on the test circuit.

A new microstrip ultra-wideband (UWB) bandpass filter (BPF) with dual notched bands based on E-shaped resonator is proposed in this paper. The basic UWB BPF is composed of microstrip lines and rectangular patch mutiple-mode resonator (MMR). To achieve dual notched bands, the proposed UWB BPF used E-shaped resonator coupled to the main transmission line of the basic UWB BPF. The filter has passband from 2.9 GHz to 10.6 GHz, the first notched band is designed from 3.5 to 3.9GHz and the second notched band is designed from 6.7 to 7.3GHz, both of which have less than 0.8 dB magnitude of insertion loss and greater than 20dB return loss. The simulation results show that the proposed filter has good wideband filtering performance with sharp rejection skirts outside the passband.

The electromagnetic band gap structure (EBGs) is widely used in microwave engineering, such as amplifiers, waveguides, microstrip filters, due to the fact of its excellent band stop characteristics. In this paper, three kinds of microstrip band stop filters were proposed which were etched with a hexagonal ring EBGs, octagonal ring EBGs and elliptical ring EBGs. Firstly, the etching coefficient of a band stop filter is proposed, and the performance of filters with different etching coefficient was analyzed. Secondly, the equivalent circuit of an EBGs band stop filter is proposed. By comparing the simulation results using advanced design system (ADS) and high frequency structure simulator (HFSS), it was found that the simulation results had the same −10 dB stopband width which verifies the correctness of the equivalent circuit model. Finally, three kinds of microstrip stopband filters were fabricated and measured. The experimental results of the −10 dB stopband width and resonant frequency were in good agreement with the simulation results. The −10 dB stopband fractional bandwidth of the three kinds of microstrip stopband filters was more than 63%. The proposed microstrip band stop filters can be widely used in microwave devices with a wide stopband.