Constant Group Delay Research Articles

Integrated bluetooth/LTE2600 superwideband monopole antenna with triple notched (WiMAX/WLAN/DSS) band characteristics for UWB/X/Ku band wireless network applications

In this manuscript, a compact superwideband monopole antenna with triple notched band characteristics is presented and is experimentally investigated. Proposed antenna is also suitable for lower band of applications including Bluetooth and LTE2600 bands. Superwideband bandwidth with bandwidth ratio ≥ 10:1 is obtained by using two identical ellipse which are placed at 70° with reference to major axis. A fractal stub is used to notch WiMAX interfering band while WLAN and DSS bands are notched by etching modified rectangular slots on the radiating patch. Antenna also constitutes slotted ground with chamfered corners for better matching of impedance. Proposed antenna is also investigated in terms of frequency, time and space domain. Antenna offers a wider superwideband bandwidth with VSWR ≤ 2 for 2.34 GHz to 20.00 GHz. In time domain, antenna offers constant group delay in entire operating bandwidth and acceptable impulse response for input signal. Also, antenna offers maximum gain of 4.98 dBi and radiation efficiency of 89%. Stable radiation pattern and above features of proposed antenna suggest antenna to be a good candidate for numerous applications in wireless system.

A 3–10-GHz CMOS Time-Domain Complex Dielectric Spectroscopy System Using a Contactless Sensor

This article presents an integrated time-domain (TD) microwave broadband dielectric spectroscopy (MBDS) system in the 3–10-GHz frequency span divided into nine subbands. The generated multitone input pulse with 1-GHz bandwidth is upconverted to RF frequencies in the transmitter using a broadband single-sideband (SSB) mixer to suppress the lower sideband of the excited signal and prevent the signal distortion at the configured dc-free direct conversion receiver with the center frequency of 500 MHz at the baseband. The upconverted pulse is passed through a contactless sensor in TD where the material under test (MUT) is placed in the middle of the two ultra-wideband (UWB) Vivaldi antennas coupled in their radiative near field. To identify both the real ( $\epsilon _{r}'$ ) and imaginary ( $\epsilon _{r}''$ ) parts of the MUT’s permittivity, the impact of the entire system on MUT characterization is alleviated by designing the system subblocks and the sensor with flat gain and constant group delay over the entire frequency range. The proposed MBDS system is fabricated in 65-nm CMOS and occupies an active area of 1.24 mm2 while consuming 64~69 mW from a 1-V supply. As a proof of concept, the complex dielectric permittivity of different pure organic chemical liquids has been detected within the desired frequency range with a customized quartz-glass cuvette with the MUT volume of ~ 5 mL by calibrating the sensor using the variations in the phase and the magnitude after FFT with respect to the reference material (air). The system results in an rms error of less than 0.2% and 0.4% for $\epsilon _{r}'$ and $\epsilon _{r}''$ , respectively, compared with theory. To the best of our knowledge, this is the first CMOS TD MBDS system with a homodyne RF transceiver architecture including an on-chip UWB excitation pulse generation and the contactless sensor.

Bandwidth Enhancement of a Wide Slot Antenna Using Fractal Geometry for UWB Application with Multiple Notched Bands

In this paper a combination of rectangular and elliptical fractal geometry is applied on a regular hexagonal wide slot antenna fabricated using a FR4 substrate to obtain ultra wide band (UWB) operation. The bandwidth enhancement of the wide slot antenna due to this fractal curve is studied in a step by step manner and the corresponding mathematical analysis is also presented. The comparison of the proposed fractal geometry with the existing fractal geometries is also exhibited. Multiple input multiple output performance of the proposed UWB antenna is also analysed. Two pairs of L-shaped slots are etched on the ground plane and a metallic ring is inserted inside the slot to produce triple band notch characteristics at 3.98 GHz, 5.56 GHz and 7.94 GHz. These three notch bands can avoid interference with existing WIMAX, downlink of C-band satellite communication, WLAN and uplink of X band satellite communication. The proposed band notched UWB antenna exhibits acceptable radiation characteristics with satisfactory gain, high radiation efficiency and constant group delay in the operation band.

Graphene-based high pass filter in terahertz band

In this paper, the design and simulation of graphene-based high pass filter in the terahertz band is proposed. This design is based on the transmission line model with short-circuit stubs. Optimum distributed high pass filter method is used for designing this filter with 0.1 dB band pass ripple and the characteristic impedance of each transmission line is obtained by power-current approach. The simulation results indicate insertion loss of less than 1.5 dB and constant group delay of 0.16 ps and these results make this graphene-based high pass filter a suitable choice in terahertz band.

Novel Ultrawideband and Multimode LTCC Common-Mode Filter Based on the Dual Vertical Coupling Paths

A novel ultrawideband and miniaturized common-mode filter (CMF) is proposed for suppressing the CM noise based on the dual vertical coupling paths. In the proposed CMF, a modified quarter-wavelength transmission line resonator and a modified half-wavelength transmission line resonator are utilized to introduce three CM transmission zeros. Moreover, another CM transmission zero is produced by the dual vertical path coupling. An ultrawide CM stopband is achieved by the four CM transmission zeros. Subsequently, equivalent circuit models have been established to give physical insight into the CMF operating mechanism, and the design procedures are also provided. By using the low-temperature cofired ceramic technology, a surface-mounted device prototype is fabricated and measured. The measured results show that the CM noise can be suppressed over 10 dB from 2.45 to 9.85 GHz with 120.3% fractional bandwidth. Meanwhile, the low insertion loss and the relatively constant group delay for differential mode ensure that the proposed CMF can maintain the signal integrity of differential signals below 10 GHz.

Multimode resonator‐assisted dual band notch UWB antenna with additional bluetooth resonance characteristics

A compact planar integrated ultra-wideband (UWB) and Bluetooth antenna are presented in this study. The basic radiator is circular in shape with a wide slit in it to accommodate a space optimised T-shaped stub for Bluetooth frequency band. The proposed antenna is CPW-fed with bevelled ground planes for the purpose of improvement in input impedance matching. A novel multimode resonator at the back of the substrate is responsible for the creation of two-notched band at 5.5 and 8.1 GHz. The antenna exhibits an operational bandwidth of 3.–12 GHz for UWB application. The proposed antenna also has Bluetooth resonance characteristics at 2.4 GHz. The overall size of the antenna is 14 × 32 × 1.59 mm 3 . The antenna has a peak realised gain of 4 dBi and a constant group delay. The radiation pattern is also stable throughout the operational bandwidth. A fabricated prototype is developed and tested. Results obtained from electromagnetic simulation, equivalent circuit model, and measurement are in good agreement.

Computationally Optimized MIMO Antenna with Improved Isolation and Extended Bandwidth for UWB Applications

Isolation and bandwidth are the two important performance parameters of the multiple-input-multiple-output (MIMO) antenna. A small footprint of an antenna with enhanced isolation and extended bandwidth is highly desirable for space-limited UWB applications. In this paper, we present a compact and computationally optimized MIMO antenna for UWB applications. The proposed antenna consists of two micro-strip-fed semicircular radiating elements. The inverted prism-shaped ground stub is used to enhance isolation. A truncated-shaped partial ground plane with two ground slots is used for impedance matching over the extended UWB. The circular monopole radiating elements of the reference antenna (RA) are converted into semicircular radiating elements for efficient utilization of the available space. The initial design parameters are obtained from the RA. In the next step, the initial design parameters are optimized by a fast and accurate surrogate-assisted optimization model. Using the optimized design parameters, the final design of the antenna is simulated using a computer simulation tool. The prototype of the antenna is fabricated on a Roger substrate (substrate height ‘h’ = 0.8 mm) with a dielectric constant of 3. The manufactured prototype with the size of 31 × 18 mm2 is experimentally evaluated and validated using vector network analyser and anechoic chamber. The proposed MIMO antenna provides extended ultra-wide impedance bandwidth of 3–25 GHz (fractional bandwidth 157%), enhanced isolation S21 ≤ − 27 dB envelope correlation coefficient (ECC = 0.002), good pattern diversity, and constant group delay. Finally, the obtained results are compared with the existing literature.

Compact, silicon-on-insulator, series-cascaded, contradirectional-coupling-based filters with >50 dB adjacent channel isolation.

In this work, we present optical add/drop multiplexer (OADM) filters for coarse wavelength-division-multiplexing (CWDM) systems with high sidelobe suppressions that result in high adjacent channel isolations (Ai). The filters are realized by using a compact, series-cascaded configuration of apodized, contradirectional-coupling-based filters. We experimentally demonstrate a device with a measured Ai of 53dB (these devices hold the promise of achieving even higher Ais). While having large Ais, our devices have the wide bandwidths and low insertion losses required for CWDM applications. In addition, our demonstrated OADM has a nearly constant group delay, which results in low dispersion in the passband.

Butterworth transfer function with the equalised group delay response in the maximally flat sense

An effective method for the design of the continuous-time all-pass network for the low-pass filter group delay response equalisation is presented in this Letter. Since the method is derived from the maximally flat conditions at the origin of the group delay response's rational function, the cascade connection of the designed all-pass network and low-pass filter exhibits a constant group delay response at the origin in the flat sense. Illustrative examples regarding group delay equalisation of the Butterworth filters are given.

Planar tunable graphene based low-pass filter in the terahertz band.

In this paper, design and analysis of planar graphene-based low-pass filters in the terahertz band are proposed. Using the proposed approach, it is possible to design plasmonic low-pass filters with the desired properties in the form of open stubs. The transfer matrix method is used based on the transmission line model for analyzing filters. The propagation constant and characteristic impedance required for this method are obtained according to the electrostatic scaling law and power-current approach, respectively. A typical fifth-degree low-pass filter is designed and analyzed according to the mentioned process. The frequency response of the low-pass filter indicates insertion loss of less than 2dB, roll-off rate of 17dB/THz, return loss higher than 10dB, and constant group delay of 0.3ps. The results of the full-wave simulation confirm the analytical ones. Also, the theory of graphene equivalent circuit variation to the different chemical potentials is expressed so the filter frequency response can be explicitly predicted for any bias value. These filters, due to their compact structure and integrated electrical and physical shape, are the suitable choice for use in full-integrated planar circuits of terahertz systems.

A CPW - Fed Octagonal Ring Shaped Wide Band Antenna for Wireless Applications

A CPW – Fed octagonal ring shaped antenna for wideband operation is presented. The radiating patch of proposed octagonal ring antenna consists of symmetrical slot in place of conventional annular ring microstrip antenna. The ground plane consists of two rectangular slots, while the radiator and the ground plane are on same plane that utilizes the space available around the radiator. The proposed antenna is simulated through Ansoft’s High Frequency Structure Simulator (HFSS). Measured result shows balanced agreement with the simulated results. The prototype is taken with dimensions 47 mm × 47 mm × 1.6 mm that achieves good return loss, constant group delay and good radiation patterns over the entire operating bandwidth of 2.0 to 9.5 GHz (7.5 GHz). The proposed antenna achieves high impedance bandwidth of 130%. Thus, the proposed antenna is applicable for S and C band applications.

Capacitive Emulation Using Predictive Current Control in LCL-Filtered Grid-Connected Converters to Mitigate Grid Current Distortion

This paper presents an improvement of the capacitive emulation (CE) method to reduce the line current distortion caused by grid-tied LCL-filtered converters. In these cases, the grid voltage is applied to the LCL’s capacitor, which generates a distorted capacitor current that pollutes the line. The CE method consists in controlling the converter currents instead of the grid currents, while the converter generates a copy of the distorted capacitor current, so that both the copy and the distorted currents cancel each other in the grid. Therefore, we can say that the converter emulates a negative capacitance connected to the grid, while at the same time delivers its active and reactive powers at the fundamental frequency. The CE method is achieved by adding an estimation of the distorted capacitor current to the converter current reference. However, an effective capacitive emulation requires a current control capable of accurately tracking all harmonics added to the current reference. In this sense, this paper proposes the use of a new integral predictive current control (IPCC), a dead-beat type of control that ensures a constant closed-loop group delay in a wide bandwidth. Unlike a PI control where the closed-loop delay varies with the frequency of the tracked harmonic, the constant control delay of the IPCC can be effectively compensated with a buffer-based advanced current reference. The effectiveness of the proposed CE method with IPCC control to reduce the total harmonic distortion (THD) of the line currents has been proved experimentally on a 10 kVA transformerless grid-connected three-phase inverter.

Constant In-Band Group-Delay Acoustic-Wave-Lumped-Element-Resonator-Based Bandpass Filters and Diplexers

The RF design of acoustic-wave (AW)-resonator-based bandpass filters (BPFs) with constant in-band group delay ( $\tau _{g}$ ) and analog transfer-function reconfigurability is presented. The proposed filter concept is based on $N$ identical acoustic-wave-lumped-element resonators (AWLRs) that are electromagnetically coupled through impedance inverters and result in quasi-elliptic-type transfer functions shaped by $N$ poles and $2N$ transmission zeros (TZs). Unlike conventional ladder- or lattice-type AW-resonator filter configurations, they facilitate: 1) flat in-band $\tau _{g}$ that does not depend on the electromechanical coupling coefficient ( $k_{t}^{2}$ ) of its constituent AW resonators and does not require the incorporation of lossy elements; 2) passbands with fractional bandwidths (FBWs) that can exceed $k_{t}^{2}$ ; and 3) continuous analog-type FBW tuning. The operating principles of the devised concept are presented through two different filter architectures that, respectively, present advantages in terms of size and FBW tuning and are subsequently extended to the design of RF diplexers. They are experimentally verified through the following prototypes: 1) a three-pole/six-TZ BPF that is centered at 418 MHz and exhibits bandwidth (BW) of 0.3 MHz, minimum in-band insertion loss of 2.1 dB (i.e., effective quality factor $Q_{\mathrm {eff}}$ of 9000), and in-band $\tau _{g}$ between $1.78 \pm 0.02~ \mu \text{s}$ ; 2) a two-pole/four-TZ BPF with 2.4:1 BW tuning ratio, flat $\tau _{g}$ , and $Q_{\mathrm {eff}}> 9000$ ; and 3) a flat $\tau _{g}$ diplexer with two transmission bands centered at 418 and 433.9 MHz.

Asymmetrically CPW-fed ladder-shaped fractal antenna for UWB applications

A compact asymmetrically CPW-fed ladder- shaped UWB fractal antenna is presented. An impedance bandwidth of 4.56---13.1 GHz is achieved by using four iterations of H-shaped radiating element, modified feed line, asymmetrical feeding and slot loaded ground plane. Omnidirectional radiation patterns are achieved in H-plane at all frequency points in the operating frequency band. The bidirectional nature of E-plane patterns at lower frequencies is observed to be shifted to directional nature at higher frequencies. The designed antenna structure has an average gain of 2.84 dB with a constant group delay. The designed antenna structure is analyzed for three different substrate materials i.e. CNT, Ni0.2Co0.2Zn0.6Fe2O4 and FR-4 epoxy. A good agreement is achieved between the simulated and measured results. This antenna structure has advantages of wider bandwidth and smaller dimensions over already reported ones.

A CPW-Fed Structure Shaped Substrate Wideband Microstrip Antenna for Wireless Applications

A structure shaped substrate wideband microstrip patch antenna fed by coplanar waveguide (CPW) is proposed for wireless applications. Structure shaped substrate is produced by cutting the rectangle shape substrate in the form of a semicircular disc. The radiating patch of proposed antenna is taken in the form of U-shape. The ground plane is extended towards both sides of radiator for reducing the size of the antenna. The proposed antenna is simulated by Ansoft's High Frequency Structure Simulator (HFSS). A good agreement is observed between simulated and measured results. The prototype is taken with dimensions 24 mm × 24 mm ×1.6 mm that achieves wide bandwidth, constant group delay and good radiation patterns over the entire operating bandwidth from 3.4 to 9.4 GHz (6.0 GHz) with 93.7% impedance bandwidth at 6.4 GHz center frequency. Thus, the proposed antenna is applicable for C band applications.

Very small planar broadband monopole antenna with hybrid trapezoidal–elliptical radiator

A compact and broadband printed monopole antenna (PMA) with a hybrid trapezoidal–elliptical radiator is proposed. An overlap region between the trapezoidal and elliptical patches is introduced to enhance the impedance bandwidth. Meanwhile, by etching two symmetrical quarter-elliptical slots on the ground plane and optimising the ellipticity ratio, further improvement in the impedance bandwidth is achieved. Measured results show that the antenna can cover the frequency range of 2.4–18.6 GHz (|S 11| < −10 dB) while its total size is only 25 × 25 × 1.2 mm3. In addition, omnidirectional radiation patterns, desirable gain, high radiation efficiency and nearly constant group delay are obtained. Compared with recent PMAs, the proposed antenna has a smaller size and wider bandwidth, simultaneously.

Measurement Analysis of Ultra-Wideband Monopole Antenna With Defected Ground Structure

This article describes how a compact, low profile Ultra-wideband (UWB) monopole antenna with a defected ground structure is designed and demonstrated experimentally. The design and experimentation activities have been carried out with the help of a CST Microwave studio tool. The UWB characteristics of the proposed antenna are achieved with a modification of the ground structure of the referenced antenna with novel L shaped defected ground structure (DGS). Both antennas are fabricated on the same substrate with the dimensions of 28.3 x 24 mm2. The comparative analysis of the results for both antennas clearly indicate that the proposed UWB monopole antenna enhanced the impedance bandwidth from 3.7 GHz – 14.9 GHz without DGS and to 3.4 GHz – 20 GHz with DGS. The enhanced bandwidth, constant group delay and good radiation characteristics of the proposed antenna have identified it as a good candidate for portable UWB applications.

A Compact Fractal-Shaped Antenna for Ultrawideband and Bluetooth Wireless Systems With WLAN Rejection Functionality

A compact planar quasi-self-complementary antenna is presented for ultrawideband applications. The antenna also radiates at Bluetooth frequency band centered at 2.4 GHz and exhibits band rejection at 5.5 GHz. A Koch fractal boundary is embedded over the hexagonal-shaped radiator to improve the input impedance matching of the antenna at higher frequencies. An arc-shaped protruded ground plane is incorporated to match the input impedance of the antenna at lower frequencies. A modified meandered-shaped stub is introduced to resonate at Bluetooth frequency band. The property of band rejection is achieved by etching a quadratic fractal slot on the radiator. Overall size of the antenna is 18.5 × 39 mm2. The antenna shows almost a constant group delay with a deviation of 1 ns throughout the operational bandwidth and also has a stable radiation pattern. An equivalent circuit is also developed for the proposed antenna. The results obtained from circuit model, electromagnetic simulation, and measurement are in good agreement.

Investigation on microwave photonic filter group delay performance

Investigation on the group delay performance of microwave photonic filters is presented. Analysis and simulation results show symmetrical distribution on the delayed optical signals in the impulse response is required to obtain a constant group delay performance. Experimental results for both symmetrical and asymmetrical tap distribution microwave photonic notch filters are presented showing the group delay response with <±25 ps and around 1 ns ripples, respectively.

Design and Analysis of Super-Formula-Based UWB Monopole Antenna and its MIMO Configuration

In this paper, the design and analysis of a nature inspired UWB antenna is carried out. The contour profile of the antenna is obtained by setting the six different parameters of the super-formula. The antenna is microstrip-fed and mounted on compact size FR4 substrate of dimensions of 25 × 35 × 1.6 mm3. To improve the impedance bandwidth, a notch is cut from the ground plane and the edges are chamfered with specific dimensions. The antenna is simulated using a full-wave simulator and then fabricated and tested. Results showed that simulation and measurements are in a good agreement, and the antenna works in the UWB range (3.1---10.6 GHz) with VSWR less than 2. Also, it exhibits good advantages of being compact and having almost constant gain and group delay. To further increase the capacity and improve the reliability, two similar antennas are placed beside each other to have a MIMO configuration. The proposed MIMO antenna is also fabricated and tested.