Excellent Frequency Selectivity Research Articles

Plasmonic dual-band waveguide with independently controllable band-notched characteristics

Abstract In this present paper, an investigation is conducted on a dual-band waveguide with independently controllable band-notched characteristics. The proposed slot structure, featuring a loaded gap, facilitates the operation of the plasmonic waveguide at two distinct frequency bands. Moreover, the working bandwidth of the waveguide can be flexibly adjusted through the use of varactors loaded across the gap. Notably, the dual band can be adjusted independently and flexibly by regulating the varactors. The measurement results demonstrate that the plasmonic filtering waveguide possesses excellent frequency selectivity and compact physical size, particularly concerning its real-time controllable notched-band response with the varactor voltages.

Independently controllable dual band filtering characteristics of a spoof surface plasmonic waveguide employing compound slot structure

The dual band filtering characteristics of a spoof surface plasmonic waveguide (WG) loaded with a composite slot structure are studied in the present paper. The proposed composite slot structure enables the plasmonic WG to work at dual bands in the microwave region, where the working bandwidth can be flexibly adjusted with a broad isolation band between them. In particular, the second bandwidth can be adjusted independently without affecting the first passband by controlling the special parameter of the composite slot. As a demonstration, the measurement results of the proposed prototype filter illustrate that the plasmonic filtering WG has a dual bandpass performance with excellent frequency selectivity, where the insertion loss of the dual-band filter is less than −3 dB in the frequency from 2.7 GHz to 6.7 GHz and 7.7 GHz to 9.1 GHz, and the stopband rejection level is lower than −10 dB from 6.9 GHz to 7.5 GHz. Compared with the traditional dual band plasmonic filtering WG, the proposed filter has compact physical size, lower insertion loss in the passband and stronger isolation ability between the two passbands.

A novel dual‐band highly efficient power amplifier for 5G applications

This paper presents a novel dual-band highly efficient power amplifier (PA) design for 5G applications. The presented dual-band matching network consists of an impedance tuning network and a dual-band impedance transformer. This structure can not only achieve the precise fundamental and second harmonic control at two 5G bands, but also the excellent dual-band filtering response. Compared with other dual-band PAs, it shows better frequency selectivity and wider bandwidth. For demonstration, a dual-band PA is designed, fabricated, and measured. The measured results display the power added efficiencies of 60% and 47% at 2.5 GHz and 3.5 GHz (bandwidth >150 MHz) under the saturated output power of above 40 dBm, and excellent frequency selectivity with return loss (> 14.7 dB) and stopband rejection (> 25.2 dB).

Tri-Band Band-Pass Filter Based on Multi-Mode Spoof Surface Plasmon Polaritons

This paper presents a novel tri-band bandpass filter based on multi-mode spoof surface plasmon polaritons (SSPPs) in microwave frequencies. The combination of multi-mode resonance and cutoff characteristic of SSPPs contributes to a tri-band bandpass response. The proposed SSPPs-based filter consists of two coplanar waveguides, two conversion parts and a SSPPs transmission structure made of five unit-cells. Each unit cell is a multi-mode resonator, which is constructed by a pair of oppositely oriented double-side folded strips, and the ends of folded strips are placed closely to form coupled-stubs. Two distinct passbands divided by a sharp stopband are produced under the cutoff frequency of SSPPs transmission structure. The third passband above the cutoff frequency is introduced by the resonant tunneling effect due to the self-resonant mode of proposed SSPPs unit cell. Dispersion relations, electric field distributions and proposed equivalent transmission line model give a physical insight into the filter operating mechanism. As a demonstration, a prototype of the proposed filter has been fabricated and measured. The measurement results demonstrate that the proposed filter has a tri-band bandpass performance with excellent frequency selectivity, which may be very useful in many applications, such as multi-band wireless systems.

Normal-mode splitting in coupled high-Q microwave cavities

Three-dimensional radio frequency cavities demonstrate excellent frequency selectivity and, as such, are known for their use in RF filters. These cavities have potential applications in quantum information science, precision displacement metrology, and quantum electrodynamics. Additionally, coupled cavities that form a spectral doublet allow for parametric gain when incorporating mechanical elements. Here, we investigate normal-mode splitting in a pair of quarter-wave stub microwave cavities at room temperature and cryogenic environments in order to identify coupling mechanics for normal and superconducting systems. Superconducting quarter-wave stub cavities with a resonant frequency of 10 GHz are made from reactor-grade niobium and exhibit Q ranging from 105 to 109. We varied cavity-to-cavity coupling to observe several normal-mode splittings of increasing peak separation until we observed a mode crossing. The minimum observed peak separation was 7 MHz for room temperature tests and 200 kHz for cryogenic tests. We also report on values of an intrinsic quality factor for the tuning cavity as a dielectric rod is translated along its symmetry axis. The realization of coupled superconducting radio frequency (SRF) cavities of this type is a necessary step toward implementation of parametric SRF-mechanical gain.

Overlapped complex-modulated transmultiplexer filters with simplified design and superior stopbands

A simple method for the design of the finite-impulse-response prototype filter for maximally decimated overlapped complex-modulated transmultiplexers with near perfect reconstruction property is presented. The procedure is unified for all values of overlap factor and leads to a prototype filter with excellent frequency selectivity and fast sidelobe fall-off rate. The high stopband attenuation and fast sidelobe fall-off rate, which is justified analytically, make the proposed filters suitable candidates for high-speed data communication applications employing multicarrier modulation.

A new design algorithm for two-band orthonormal rational filter banks and orthonormal rational wavelets

We present a new algorithm for the design of orthonormal two-band rational filter banks. Owing to the connection between iterated rational filter banks and rational wavelets, this is also a design algorithm for orthonormal rational wavelets. It is basically a simple iterative procedure, which explains its exponential convergence and adaptability under various linear constraints (e,g., regularity). Although the filters obtained from this algorithm are suboptimally designed, they show excellent frequency selectivity. After an in-depth account of the algorithm, we discuss the properties of the rational wavelets generated by some designed filters. In particular, we stress the possibility to design "almost" shift error-free wavelets, which allows the implementation of a rational wavelet transform.

On processing of Doppler returns from the foetal heart: an electronic processing method for extraction of valvular timing information.

An electronic processing scheme intended for use in conjunction with a multicrystal ultrasonic array to measure cardiac intervals in the human foetus is described. This new processing method possesses sufficient signal extraction capability to allow the time of opening of the aortic valve to be determined and tracked. Application of this method to a pulsed Doppler and continuous wave Doppler system is discussed. Features include amplitude independent detection, rapid response time and excellent frequency selectivity. Laboratory and clinical test results are presented that demonstrate the viability of an instrument based on this principle.