Band Rejection Research Articles

Performance improvements of a tunable bandpass microwave photonic filter based on a notch ring resonator using phase modulation with dual optical carriers.

A tunable bandpass microwave photonic filter can be achieved by using a notch ring resonator with optical phase modulation. However, the filter's out of band rejection ratio and shape factor are limited due to the ring resonator's residual phase, which can seriously degrade the filter's performance. By using dual optical carriers and setting their wavelengths oppositely detuned from two resonant frequencies of a notch ring resonator, the residual phase induced by the ring resonator at radio frequencies falling outside the region of the notch stopband is reduced, thus the out-of-band rejection ratio and shape factor of the microwave photonic filter are greatly improved. The proposed microwave photonic filter was both verified theoretically and experimentally. Compared with single optical carrier method, the out-of-band rejection ratio of the filter can be enhanced from 17.7dB to 31.5dB, and the filter's shape factor is improved from 3.05 to 1.78. Besides, the filter's frequency and bandwidth can be tuned by varying the wavelengths of the two optical carriers and the ring resonator's coupling coefficients. Finally, a tunable bandpass microwave photonic filter with frequency tuning range of 2~14GHz, 3dB bandwidth tuning range of 0.673~2.798GHz is demonstrated.

Microstrip Tunable Bandpass Filters with Combined Resonators

The paper presents a varicap-tunable fourth-order tunable microstrip bandpass filter with combined resonators: a U-shaped loop resonator and a resonator short-circuited at one end, which improved the symmetry of the frequency response while maintaining a wide rejection band inherent in comb filters with resonators short-circuited at one end. For the first time, the resonance equation for odd resonance frequencies of a U-shaped loop resonator with variable capacitance is obtained, which makes it possible to control the ratio of the first parasitic and the fundamental resonance frequencies of this resonator, f1/f0, on which the rejection band of the filter depends. An experimental sample of a filter, tunable in the frequency range of 225–400 MHz, is presented.

Planar UWB Antenna with Double Band Rejection Capability Using Double Inclined ESRRs

This paper deals with elliptical split ring resonator (ESRR) loaded CPW-fed ultra wideband (UWB) printed monopole antenna (PMA) with dual band-notching at 5.2 and 6.9 GHz to notch WLAN and C-band wireless applications, respectively. The antenna is fabricated on duroid dielectric substrate with thickness of 1.6 mm and e r = 2.2. The antenna uses two ESRR with different dimensions to create dual band-notched characteristics. Details of the proposed antenna are presented along with simulated results. The effect of ESRR dimensions and position is examined. The ESRR is also rotated and the effect of this rotation in the notch frequency is also examined. Radiation patterns are simulated by HFSS and omnidirectional radiation patterns in the H -plane could be observed. The group delay is nearly stable in the UWB frequency range, except at the notch frequencies, which is distorted sharply. So, the proposed antenna is a good candidate for the modern UWB systems. Finite element method (FEM) and finite integration technique (FIT) are used to simulate the proposed structures through the usage of HFSS and CST. A very good agreement between both results has been obtained.

Single-input multiple-output voltage-mode shadow filter based on VDDDAs

This paper presents a voltage-mode shadow filter with single-input multiple-output (SIMO) configuration using voltage differencing differential difference amplifiers (VDDDAs). In this design, the low-pass and high-pass output functions of the single-input three-output second order filter are feedback via the voltage amplifier. The proposed filter consists of three VDDDAs, one grounded resistor and two grounded passive elements. The proposed filter uses grounded elements which is attractive for integrated circuit (IC) fabrication. It can simultaneously provide low-pass (LP), high-pass (HP), band-pass (BP), band-reject (BR) and all-pass (AP) responses without matching condition. The proposed circuit has high input impedance. The natural frequency (ω0) and quality factor (Q) can be independently and electronically tuned by changing the external DC bias currents. The effect of the non-ideal and parasitic elements of the VDDDA is studied and investigated. The PSpice simulation and experimental results using CMOS technology and commercially available active devices are given to confirm the workability of the proposed filter.

Compact Ultra-Wideband Slot Antenna with Dual Band Rejection by Using H-Shape Notch

The main objective is to design a dual band rejection micro strip patch antenna. In this antenna, H-shaped slots are made in the patch to achieve notched characteristics at two licensed band employed for Wimax and WLAN band. The above mentioned frequency ranges are licensed for WLAN and satellite communication applications. These antennas maintain the Omni-directional radiation patterns and are mostly suited for ultra wide band applications. For wide band operation, the shape of patch has been altered to octagonal just by chamfering the corners of the rectangular patch. The antenna parameters like radiation patterns, VSWR, reflection loss have been described clearly in this section. Radar applications, terrestrial networking and communication, space communications are some of the applications in this ultra wide band frequency range.

Solar blind Schottky photodiode based on an MOCVD-grown homoepitaxial β-Ga2O3 thin film

We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 Å thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.

Enhanced bandwidth reconfigurable single and dual band-notch antenna by using DGS for UWB and KU applications

In this article, a dual band notch reconfigurable antenna for ultra-wide band applications by switchable band notch characteristics is reported. The antenna includes rectangular patch with two L-shaped strips, rectangular and L-shaped slits on the ground sheet. To create much wider impedance bandwidth, slits on the ground sheet have been added. To create dual band notch characteristics, the L shaped strips on the radiating patch are connected using two PIN diodes in order to control the band rejection range. The reconfigurable antenna includes single and dual band notch 4.5–6.5 and 9–10.5 GHz. The presented antenna with final size of 12×18×1.6 mm3 is manufactured on an affordable FR-4 substrate and tested. The measured and simulated results are in good agreement.

Compact multiband planar monopole antenna for Bluetooth, LTE, and reconfigurable UWB applications including X‐band and Ku‐band wireless communications

In this article, a small-printed Bluetooth/LTE/UWB/X-band/Ku-band monopole antenna with high rejection triple band-notch is presented. Notched bands include WiMAX (IEEE802.16 3.30-3.80 GHz), WLAN IEEE802.11a/h/j/n (5.15-5.35 GHz, 5.25-5.35 GHz, 5.47-5.725 GHz, and 5.725-5.825 GHz), and downlink satellite system (7.1-7.9 GHz). By including inverted T-shaped stub and etching two C-shaped slots on the radiating patch, triple band-notch function is obtained with measured high band rejection (VSWR = 14.59 at 3.69 GHz, VSWR = 39.40 at 5.42 GHz, and VSWR = 6.43 at 7.57 GHz) and covers a UWB useable fractional bandwidth of 157.75% (2.285-19.35 GHz = 17.065 GHz). Reconfigurable characteristics are obtained using PIN diodes, which control the individual notched bands. Proposed antenna is printed on Rogers RT/duroid5880 substrate with compact dimensions of 20 × 22 mm2. Proposed antenna finds its applications for Bluetooth, LTE, UWB, other multiple wireless applications for close range radar (8-12 GHz) in X-band, and satellite communication in Ku-Band with omnidirectional pattern in H-plane.

A novel compact fractal UWB antenna with triple reconfigurable notch reject bands applications

A compact, circular UWB fractal antenna with triple reconfigurable notch rejection bands is proposed. It rejects the crowded frequency bands WiMAX, WLAN and X band interferences produced in UWB communication systems. The proposed fractal structure consists of a basic circular patch with circular fractal iterations. By employing this new structure of fractals, the overall size of antenna is reduced 53% to 21 × 25 mm, in comparison with traditional circular monopole antenna. The implemented antenna operates at 3.1–10 GHz. Re-configurability is realized by designing slots and split ring resonators in desired frequencies with the attached PIN diodes. WLAN band rejection was realized by creating a pair of optimized L-shaped slots in the ground plane. By etching a split ring resonator and a U-shaped slot, X and WiMAX bands were also rejected. Furthermore, by attaching diodes to aforementioned slots and designating the diodes on/off, different bands can be included or rejected. In time domain, the antenna properties are evaluated by a figure of merit called fidelity factor. Finally, the antenna properties are measured in anechoic chamber and the results agrees with simulation findings.

Spectral degradation of Type II π-phase-shifted fiber Bragg gratings due to femtosecond laser induced loss.

Narrowband high-temperature stable fiber Bragg gratings (FBGs) can be made by introducing a π-phase shift in the middle of a Type II periodic grating structure. This creates a passband inside the wavelength rejection band. During the inscription of Type II Bragg gratings broadband, optical loss is induced in the fiber core as a result of interaction between the inscription beam and the silica host. The amount of broadband loss will determine the passband's spectral characteristics (bandwidth and loss).

A compact printed ultra‐wideband multiple‐input multiple‐output prototype with band‐notch ability for WiMAX, LTEband43, and WLAN systems

A compact ultra-wideband multiple-input multiple-output (UWB-MIMO) antenna with good isolation and multiple band-notch abilities is developed in this work. It consists of two quadrant shaped monopole antennas backed by ground stubs. A good isolation is achieved due to the two proposed extended curved ground stubs. The frequency rejection for the WLAN system is realized by loading a capacitive loaded loop resonator adjacent to the feed line. The band rejection for the WiMAX and LTE band43 system is achieved by embedding a quadrant shaped CSRR on each radiator's surface. The measured bandwidth of the antenna is 3.06 GHz-11 GHz (|S11| < −10 dB and |S21| < −18 dB) with a band rejection from 3.5 GHz-4 GHz to 5.1 GHz-5.85 GHz, respectively. Time domain performances are investigated in terms of group and phase delay characteristics. Diversity characteristics are evaluated in terms of the envelope correlation coefficient, mean effective gain, and channel capacity loss.

Programmable Controls of Multiple Modes of Spoof Surface Plasmon Polaritons to Reach Reconfigurable Plasmonic Devices

AbstractSpoof surface plasmon polaritons (SSPPs) can be supported and propagated on metal surfaces decorated with periodic subwavelength structures, whose dispersion properties are determined by geometrical dimensions of unit structures. However, the functions of plasmonic devices made of the conventional passive SSPPs will be fixed once the devices are fabricated. Here, an electronically controlled programmable SSPP waveguide is presented, whose dispersions can be manipulated in real time at fast speed by programing the bias voltage instead of changing the dimensions of the unit structures. There are three different modes at different frequency bands, with a forbidden band existing between the first‐order (fundamental) mode and the third‐order mode, where the second‐order mode cannot be propagated. By loading varactor diodes in the unit structure, the dispersions of SSPPs can be controlled by changing the capacitance of the loaded varactor diode. The proposed programmable SSPPs have a unique advantage of designing smart plasmonic devices with reconfigurable functions. As an example, a compact plasmonic waveguide with reconfigurable rejection bands is designed, simulated, and measured, showing that the central frequency, the number, and bandwidth of the rejection bands can be freely reconfigured in real time by programming the bias voltages.

CPW-Fed Planar Ultra-Wideband Notched Antenna at Wimax Frequency

Abstract This paper presents a new design of compact CoPlanar Waveguide (CPW)-fed patch antenna for Ultra Wide Band (UWB) operation with a radiating element presented of size 20mm x 20mm x 1.6 mm using FR4 lossy substrate with a band rejection (Voltage Standing Wave Ratio VSWR > 2) achieved at 3.38–3.85 GHz to reject WiMAX band. This antenna consists of a radiating patch with partial ground above the substrate to increase the band width. A C-shaped slot is etched on the patch to provide frequency notch to avoid interference of UWB band with the existing systems. This antenna has an operating frequency from 3.5 to 18 GHz. In this paper, the variations of frequency notches characteristics are discussed by varying the length and width of the slot. The performance of the suggested antenna is investigated by using CST microwave studio.

Small-Sized UWB MIMO Antenna With Band Rejection Capability

A very compact and small sized 2-element planar Ultra Wide band (UWB) antenna having high isolation with band rejection characteristics designed on a FR4 substrate (23 × 26 × 0.8 mm 3 ) is presented in this paper. Each antenna element have a rectangular stepped-slot and a z-shaped slot, both etched in ground plane. The rectangular slot, proximity fed by a 50 Ω micro-strip transmission line, acts as a main radiator while z-shaped slot acts as a filter for rejecting the full WLAN band (5.15-5.85 GHz). Use of an inverted T-shaped slot near top end of ground plane improves isolation more than 24.5 dB in lower UWB band i.e. 3-5 GHz, while the rectangular vertical slot etched at center of the ground plane near the bottom edge reduces the mutual coupling at lower as well as at higher UWB band i.e. 5 - 10.6 GHz. Both measured and simulated results are presented which are found generally in good agreement.

Superimposed long period gratings based mode converter in few-mode fiber

Mode-division multiplexing (MDM), as one of the promising techniques for overcoming current limitation of transmission capacity in single-mode fibers (SMFs), has attracted considerable attention. A key component in the MDM system is a mode converter, which makes conversion between the fundamental mode and the higher-order mode. Many mode converters have been demonstrated, such as spatial light modulators, phase plates, silicon-based asymmetrical directional couplers, fiber-based photonic lantern, and long period fiber grating (LPFG). Compared with other methods, mode converter used LPFG is a very feasible technique, which has the advantages of small size, low loss, low backward noise, high coupling efficiency and easy fabrication. However, the limitation of the mode converter is relatively narrow bandwidth. In this paper, a novel broadband all-fiber mode converter is proposed, in which two long period fiber gratings (LPFGs) with different periods are fabricated in the same spatial domain of few-mode fiber to achieve coupling from LP&lt;sub&gt;01&lt;/sub&gt; to LP&lt;sub&gt;11&lt;/sub&gt;, thus forming superimposed long period fiber gratings (SLPFGs). The influences of grating parameters, such as the interval between two periods, the length of grating and the coupling coefficient on the mode converter, are analyzed by numerical simulation. It is found that the gap between the two resonant wavelengths becomes smaller with the periodic interval decreasing, which can form one rejection band when the gap is small enough, thus a broadband mode converter can be realized. The corresponding bandwidth at a conversion efficiency of 10 dB is about twice that of traditional LPFG. Moreover, with the increase of grating length, the conversion efficiency first increases and then decreases, because coupling efficiency experiences deficient coupling, full coupling and over coupling. The effect of coupling coefficient on converter is similar to that of grating length. According to the numerical results, grating I is fabricated with &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}${\varLambda _1} = 673\;{\text{μ}}{\rm m} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181674_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181674_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, 35-period. After that, the platform is rotated 180° and grating II is fabricated with &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}${\varLambda _2} = 688\; {\text{μ}}{\rm m}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181674_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181674_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, 35-period by CO&lt;sub&gt;2&lt;/sub&gt; laser in tow mode fiber (TMF steped-index fiber). The bandwidths of both LPFGs at a conversion efficiency of 10 dB are about 57 nm and 67 nm respectively, while the bandwidth of SLPFG is about 153 nm. The experimental results are in pretty good agreement with the theoretical analyses. In addition, the proposed superimposed structure can also be extended to the conversion of fundamental mode into other high-order core modes. By designing the period of two sub-gratings reasonably, a wide band rejection filter with arbitrary wavelength can be realized. Compared with the traditional mode converter, the converter has the advantages of broad bandwidth, high conversion efficiency and small size, which can be widely used in the mode division multiplexing system and optical communication.

A UWB antenna with reconfigurable rejection band using split ring resonator for radio cognitive technology

Abstract In this article, we propose the study of an ultra-wide band antenna with the possibility of reconfigurable band rejection. The stopped bands are obtained by the incorporation of periodic structures SSR. Inserting an equivalent switch model (ON or OFF) in these rings that we have placed near the feed line causes the rejection of different frequencies in the UWB band. The use of this technique can reduce interference between the UWB band defined by the FCC in 2002 and operate technologies in the same band. The suggested antenna is compact in size (36mm * 18mm * 1.6mm), printed on a substrate of relative permittivity 4.4 and loss tangent 0.02. The study of the antenna was made by the electromagnetic simulation software CST.

On-chip Bragg grating waveguides and Fabry-Perot resonators for long-wave infrared operation up to 8.4 µm.

Taking advantage of unique molecular absorption lines in the mid-infrared fingerprint region and of the atmosphere transparency window (3-5 µm and 8-14 µm), mid-infrared silicon photonics has attracted more research activities with a great potential for applications in different areas, including spectroscopy, remote sensing, free-space communication and many others. However, the demonstration of resonant structures operating at long-wave infrared wavelengths still remains challenging. Here, we demonstrate Bragg grating-based Fabry-Perot resonators based on Ge-rich SiGe waveguides with broadband operation in the mid-infrared. Bragg grating waveguides are investigated first at different wavelengths from 5.4 µm up to 8.4 µm, showing a rejection band up to 21 dB. Integrated Fabry-Perot resonators are then demonstrated for the first time in the 8 µm-wavelength range, showing Q-factors as high as 2200. This first demonstration of integrated mid-infrared Fabry-Perot resonators paves the way towards resonance-enhanced sensing circuits and non-linear based devices at these wavelengths.

Transmission and radar cross-section reduction by combining binary coding metasurface and frequency selective surface.

A modified reflective metasurface, which is constructed by replacing the metal ground of the reflective coding metasurface with a bandpass frequency-selective surface, is proposed. The metasurface has transmission and reduction of radar cross-section characteristics. This allows the metasurface to overcome the drawbacks of conventional realizations, which use lossy materials. The modified metasurface provides high-efficiency transmission in the passband of a frequency-selective surface and broadband reduction of the radar cross section in the rejection band of the frequency-selective surface. Transmission of -0.24 dB was achieved at 4.6 GHz, as well as a -15 dB reduction of radar cross section from 8.5 to 13.5 GHz. This work provides advancements in metasurface applications.

Monolithically integrated CdTe/InSb visible/midwave-infrared two-color photodetectors

This paper reports on the demonstration of two-terminal, two-color (visible/midwave-infrared, MWIR) photodetectors (2CPDs) consisting of monolithically-integrated CdTe nBn and InSb PN sub-detectors connected by an n-CdTe/p-InSb heterovalent tunnel junction grown on lattice-matched InSb substrates. The 2CPD can be switched between MWIR (1.5–5.5 μm with a peak responsivity of 0.75 A/W at 77 K) and visible (350–780 nm with a peak responsivity of 0.3 A/W) detection bands by applying different optical and electrical biases. Band rejection ratios of 18 dB and 52 dB, and spectral cross-talks of 40 dB and 31 dB are achieved for the visible and the MWIR bands, respectively. This 2CPD can be potentially used for visible/MWIR two-color focal plane arrays with optimal fill-factors and zero spatial offset between the visible and MWIR imaging channels.

A novel compact dual‐mode SIW filter with wide rejection band and selective response

AbstractA compact dual‐mode substrate‐integrated waveguide (SIW) bandpass filter with wide upper stopband is presented. A cross shaped slot is etched on the top plane of SIW cavity to alter the second mode (TE201) current distribution and move it closer to the first mode (TE101), to enhance the bandwidth flatness. Removing few via near the excitation ports, provides longer path for the current to resonance and give us the transmission zeros (TZ1) in a simple way. Another 2 TZs are used to improve the stopband by suppressing higher order modes resonances. The designed filter is fabricated and tested and a very good result is achieved to confirm the design idea. There is also a good agreement between the measured and Full Wave simulated results. The fabricated sample realizes a fractional bandwidth of 9.1% at 7.5 GHz center frequency and 2 zeros at 12.5 GHz and 15 GHz.