Flat Group Delay Research Articles

A microstrip bandpass filter using coupled lines loaded by open stubs

A compact simple structure bandpass filter based on terminated three coupled line structures with high selectivity is introduced through odd and even-mode analysis. The proposed filter consists of three coupled lines loaded by open and short circuit stubs. The parallel-coupled lines structure is used to obtain high selectivity with transmission zeros near the passband. Meanwhile, simultaneously tuning on bandwidth and center frequency are introduced by coupled line. One type of bandpass filter based on terminated coupled line structure is theoretically analyzed, simulated, and measured. The stepped impedance structures at the input and output ports have been used to improve the attenuation level at the stopband region and create the multiple attenuation poles. The center frequency of 1.3 GHz, the fractional bandwidth (FBW) of about 65%, the low insertion loss of 0.25 dB, and the high return loss of 30 dB are obtained. Also, a flat group delay lower than 1.4 ns is achieved. Experimental and simulated results are presented, which are in good agreement.

Wideband Air‐Filled Coaxial Filter Line

ABSTRACTA design for manufacturing (DFM) of a well‐performing wideband coaxial filter line using direct metal laser sintering (DMLS) additive manufacturing is proposed. The demonstrated transmission line is an air‐filled coaxial line chosen for low loss and consistent group delay over the bandwidth. Transmission line theory is used first to account for the impact of the shorted stub needed to support the central conductor. Deviations due to parasitics are described to transition the design from an ideal model to a physical prototype. The constraints inherent in DMLS are discussed and accounted for throughout the DFM. This process is demonstrated with a prototype having return and insertion losses of greater than 10 dB and less than 1.64 dB, respectively, over a 5.3:1 bandwidth from 6.4 to 33.9 GHz with a flat group delay of 129 ps ± 7%.

Wideband Absorptive Bandpass Filter With Multiple Transmission Zeros and Flat Group Delay

Wideband Absorptive Bandpass Filter With Multiple Transmission Zeros and Flat Group Delay

Implementation of a Wideband Microwave Filter Design with Dual Electromagnetic Interference (EMI) Mitigation for Modern Wireless Communication Systems with Low Insertion Loss and High Selectivity.

By leveraging the advantages of the uniform transmission line, this manuscript presents a broadband high-selectivity filter range starting from 2.5 GHz to 16.8 GHz, utilizing a simple uniform transmission line structure loaded with three-quarter-wavelength stubs. The proposed UWB filter is studied using the ABCD network parameter method. After that, a shorted T-shaped stub-loaded resonator is coupled with the transmission line of the UWB filter to obtain dual-notch features at 4.4 GHz (for long distance wireless ISPs (WISPs), 4G/5G operator for LTE backhaul) and 7.5 GHz (for X-band downlink communication). The overall footprint is specified as 22.5 mm × 12 mm or 1.12 λg × 0.6 λg, where λg represents the wavelength at the central frequency. The operating principle of such a filter is explained, and its controllable broadband response, as well as controllable stopband frequencies, are optimized to show some of the attractive features of the new scheme, such as a super wideband response of about a 148.18% fractional bandwidth; an out-of-band performance up to 25 GHz; five single-resonator transmission poles filtering behaviour at different frequencies, with highly reduced radiation losses greater than 10 dB; a simple topology; a flat group delay; a low insertion loss of 0.4 dB; and high selectivity. Additionally, the filter is fabricated and evaluated, and the results show a good match for experimental validation purposes.

Cascaded Reflection-Type Group Delay Controller With a Wideband Flat Group Delay

This letter presents a wideband group delay controller (GDC) based on cascaded reflection-type phase shifters (RTPSs). Frequency tunable resonators are used as the reflective loads of each phase shifter so that the phase shifter has a variable group delay resulting in a reflection-type GDC (RTGDC). Two RTGDCs with different types of reflective loads are cascaded to compensate for their group delay variation over frequency. The first and the second stage of the cascaded RTGDC are respectively in charge of the delay in low and high-frequency bands and the cascaded delay is flat over a wide bandwidth. The proposed cascaded RTGDC operates at 3.7 GHz over 200-MHz bandwidth. The measured group delay varies from 0.67 to 2.18 ns, which is a 1.51-ns group delay variation under 9.1% normalized group delay variation over the bandwidth. The return loss is over 18 dB and the insertion loss is 2.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 1.3 dB at 3.7 GHz.

A miniaturized filter design approach using GMDH neural networks

AbstractA miniaturized microstrip low‐pass filter (LPF) has been designed and fabricated using semicircular‐shaped resonators. The designing procedures as well as the LC equivalent circuit of each step have been reported. Due to the small size of the presented filter, flat group delay in the pass‐band, low insertion loss (IL), and high return loss (RL) in operational frequency. By producing adjusted transmission zeros (TZs), the second to fourth unwanted harmonics were attenuated using the proposed LPF. The machine learning approach has been utilized to adjustment of the filter parameters. The 3 dB cut‐off frequency (Fc), TZs, IL, and RL were predicted using the group method of data handling neural network (GMDHNN). Ninety simulations were performed with different inductor and capacitor values. The collected data were used for neural network training. The GMDHNN can diagnose the efficient inputs, so this feature was applied to determine the efficient L and C elements on TZs, Fc, IL, and RL. Finally, the fabricated filter results are well‐matched with the simulation ones. IL and RL of the suggested filter in operational frequency are −0.09 and −17.26 dB, respectively. The total filter size is only 14.65 mm × 3.5 mm.

Digital Finite Impulse Response Equalizer for Nonlinear Frequency Response Compensation in Wireless Communication

Signal distortion can occur when the gain or attenuation of a component changes non-linearly with frequency, which is referred to as nonlinear frequency response. Common communications components such as filters, amplifiers, and mixers can lead to nonlinear frequency responses, which can cause errors in transmitting and receiving. This article outlines the design and demonstration of a static and dynamic finite impulse response (FIR) digital equalizer circuit. Using predistortion topology with a coupled feedback loop, the adaptive Least-Mean Square (LMS) algorithm was implemented. The FIR filter was simulated in MATLAB and Vivado and then implemented onto an Eclypse Z7 Field Programmable Gate Array (FPGA) evaluation board. Simulations showed that the custom RTL module gave the same frequency response that was produced in MATLAB calculations. The filter was able to dynamically equalize the frequency responses of different nonlinear boards that were used as the devices under test (DUT). Measurements showed that the equalizer was able to compensate for system distortion from 0.2 to 0.8 Nyquist frequency. The phase response remained relatively linear across the band of interest, with a group delay flatness less than 10 ns.

Four Subbands from Dual Mismatched Wideband Bandpass Filter for 5G/WAS/Wi-Fi/WiMAX/WLAN Applications

Based on the simplicity of the design method, this paper presents a new approach for developing matched subbands when splitting two mismatched dual-wideband bandpass filters (BPFs) for the fifth generation (5G), wireless access systems (WAS), wireless fidelity (Wi-Fi), worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN), radar, and other communication devices. The method’s novelty involves using identical quarter-wavelength resonators terminated by alternated short-and-open stub configurations. Both configurations alternate and describe a perfect symmetry by their location from each other to make the subbands possible in the low-frequency and its harmonic (high-frequency) bandwidths (BW). A stub admittance Y 1 is defined and associated with the mainline section characteristic impedance Z 0 and an operating frequency f 0 . A quality factor Q a p is connected to Y 1 and f 0 to approach the BPF global quality factor Q g initially fixed. The stub characteristic impedance and the mainline one differ, while electric lengths (stub and mainline section) are identical. Using the operating frequency determines physical dimensions, creates harmonic frequencies and the rejected BW, mismatches the main frequency BW, matches the subbands, and creates transmission zero (TZ). Hence, a 28.118-dB stopband that separates the two bandpasses at 9.373 GHz is made. At the same time, the unmatched dual ultrawideband (UWB) covers a large panel of communication systems. The lowest (3.146–5.431) and highest (11.891–14.749) GHz BW exhibit a minimum insertion loss (IL) of 0.656 dB and 3.027 dB. The subbands return losses (RL) are better than 28 dB and 19 dB, respectively, and a flat group delay of 0.205 ns is obtained in the upper band. All subbands adaptation methodology is read from 10 dB of the RL. In that case, the four matched subbands in its lower wideband are 3.327–3.709 GHz and 4.442–5.048 GHz, and in its higher wideband are 11.922–12.486 GHz and 14.281–14.653 GHz. The 2275/2858 MHz is the dual-wideband with a fractional BW 53.282/21.456%. The fabricated prototype has validated the EM-simulations, and Anritsu MS4642B 20 GHz vector network analyzer (VNA) has been used for experimental results by scanning the frequency range 3 GHz–15 GHz. The tested prototype is made with a 1 mm FR4 HTG-175 thickness by considering a dielectric constant of 4.4, and its overall size occupies 22.45 × 5.72 m m 2 ( 0.32 λ 0 × 0.082 λ 0 mm 2 ).

A Wideband High-Gain Dielectric Horn-Lens Antenna for Wireless Communications and UWB Applications

A wideband high-gain dielectric horn-lens antenna (DHLA) for wireless communications and ultra-wideband (UWB) applications, featuring 122% fractional bandwidth, is presented. The antenna, consisting of a dielectric horn equipped with a spherical-axicon dielectric lens that increases and equalizes the gain within the operating band, is placed on a PCB featuring a wideband eight-shaped slot fed by a tapered microstrip line employed to excite the radiating system. The lens, integrated within the body of the dielectric horn, has the property of focusing the RF energy near its vertex on an extended frequency band, thus ensuring compact size, excellent field coupling with the antenna excitation system, and a significant increase of antenna gain. The antenna operates in the 3–12.4 GHz frequency range with relatively flat group delay, making it suitable for operating with narrowband, broadband, and impulsive UWB signals. The antenna can work properly without or with a metal reflector useful to enhance gain (up to 19 dBi), improve the front-to-back ratio, and reduce the impact of the antenna characteristics from the installation site. CST Studio Suite, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated numerically were found to be in good agreement with the experimental results performed on an antenna prototype.

A SUPER-WIDEBAND QUADRATIC BEZIER OUTLINE ANTENNA FOR THZ APPLICATIONS

This paper describes a novel Super-Wideband monopole antenna for THz applications. It has a Super-Wideband performance (3-16 THz) and up, which presents a fractional bandwidth greater than 135&amp;#37;. It has 2:1 VSWR with 10 dBi peak realized gain and flat group delay. These results satisfy the frequency and time-domain characteristics of the antenna. The radiator and ground plan of the antenna are based on quadratic Bezier outlines, which can be optimized with few control points. The proposed antenna is designed on Rogers RT5880 substrate (&amp;epsilon;r &amp;#61; 2.2) with a very compact size (42 &amp;times; 32 &amp;times; 1.6 &amp;mu;m&lt;sup&gt;3&lt;/sup&gt;). Therefore, this antenna can be used in THz wireless communication systems such as T-WPAN, T-WBAN, and T-WLAN. It can be employed as an elementary antenna on MIMO systems

Wideband Flat Negative Group Delay Circuit With Improved Signal Attenuation

A novel wideband flat negative group delay (NGD) circuit with improved signal attenuation is proposed. The proposed negative group delay circuit (NGDC) is composed of three transmission lines and two parallel branches, which are consisted of two series transmission lines with a resistor linking to a T-type stub. The complete closed-form design equations are presented. For verification, an NGDC is designed, fabricated, and measured at the center frequency of 2.14 GHz. From the measured results, NGD time of −1.11 ns at the center frequency is obtained with an insertion loss of 9.75 dB and return loss of 22.3 dB. The flat-NGD bandwidth reaches 6.1% from 2.072 to 2.202 GHz with ±11.5% group-delay fluctuation.

A new compact ultra-wideband frequency selective surface with angular stability and polarization independence for antenna radiation enhancement in microwave imaging application

A new compact, rudimental, uni layered frequency selective surface (FSS) is proposed to work in the commercial ultra-wideband (UWB) spectrum with its application in enhancing broadside radiation of an UWB antenna. The overall unit cell dimension (length × width × thickness) of the proposed UWB FSS is 0.15λL × 0.15λL × 0.016λL only where λL represents the wavelength corresponding to lowest band edge in the 3.04 to 10.88 GHz (∼112.6 %) spectrum with transmission coefficient less than −10 dB. Moreover, the proposed FSS provides certain degree of angular stability of 45° in both TE and TM planes of polarization. The proposed FSS is well suited for antenna gain augmentation as it offers linearly decreasing reflection phase profile. A compact ultra-wideband U-shaped CPW fed antenna with the dimension of 32 × 26 × 0.8 mm3 is designed that covers a bandwidth from 2.7 to 12.76 GHz (130 %). The proposed FSS is integrated with the U-shaped antenna to exhibit an improved and steady gain profile of 5.1–6.8dBi in the 2.82–12.92 GHz (128.34 %) impedance band. Maximum gain augmentation of 3.62 dBi is achieved at 9.5 GHz along with steady gain profile in the entire operating band of “antenna-FSS”, linear S21 response and flat group delay variations which implies the applicability of proposed antenna-FSS in various UWB communication purposes that comprise impulse radar, through wall imaging, microwave imaging, short range indoor communication etc. The applicability of UWB ‘antenna-FSS’ is established by ground coupling microwave imaging test in proximity of soil test bed where the fundamental characteristics of ‘antenna-FSS’ is found to be unaltered.

Theory of Optimum Taper for Distortionless Pulse Transmission

A theory of nonuniform transmission line taper with almost linear transmission phase characteristics has been proposed in this article. The proposed taper provides a preferably flat group delay with optimum time domain characteristics compared to the conventional tapers. Closed-form expressions for the impedance profile of the optimum taper has been discussed here. A stripline and dispersive microstrip line implementation of the taper has been measured to validate the proposed theory.

Reconfigurable negative group delay circuit with tunable group delay flatness

A reconfigurable negative group delay circuit (NGDC) with tunable group delay flatness is presented. The proposed NGDC is composed of an amplifier, three series resistors connecting with two transmission lines, two varactors, and a diode. By shorting different resistors through the diode, different negative group delay (NGD) times can be obtained. Two varactors are utilized to tune the flatness of the group delay. For verification, an NGDC is designed, fabricated, and measured at the center frequency of 1.0 GHz. The measured NGD time is tuned from −2.0 to −5.8 ns. The flat-NGD bandwidth varies from 2.2% to 8.8% with ±8% group-delay fluctuation. And the insertion loss varies from 6.5 to 13.8 dB.

Three-line coupled-line narrowband bandstop filter with wide upper bandpass bandwidth

A three-line coupled-line narrowband bandstop filter is proposed to obtain wide upper bandpass bandwidth and avoid the tightly-coupled limitation. This structure of the proposed bandstop filter has two three-line coupled-line sections, four open-circuit stubs and one through transmission line. The main advantages of this filter include very narrow band rejection, wide upper bandpass bandwidth, high selectivity with sharp roll-off skirt, small and flat group delay performances. The measured results indicate that the stop bandwidth with 10-dB suppression at the center operating frequency of 0.97 GHz is about 4.12% and the highest frequency of the upper passband with 15-dB return loss is 6.44 GHz (the frequency ratio h is almost 6.64). The circuit size is 0.027 λg2. In addition, this proposed bandstop filter is very suitable for low-cost single-layer microstrip implementations with small size.

Investigation and Improvements of UWB Microstrip Delay Lines

Microstrip ultra-wide band (UWB) delay lines consisting of a novel periodically loaded transmission line (PLTL) are presented, along with discontinuous structured guard lines (DSGLs). The distinctive advantage of the proposed approach is that the far-end crosstalk (FEXT) between the adjacent lines is effectively suppressed comparing to the conventional circuits. Afterward, the crosstalk of connected adjacent lines is effectively suppressed by modifying the DSGLs, since the current distributions are different from the separated adjacent lines. Subsequently, the strong reflection points are eliminated, which seriously deteriorate the performances in amplitude and group delay. Moreover, the serpentine delay line (SDL) and serpentine meandered delay line (SMDL) are studied, respectively, using the conventional microstrip (CMS) and the proposed PLTL with DSGLs. As a result, the SMDL pattern is also demonstrated useful to suppress the near-end crosstalk (NEXT) between the adjacent second-level curves, which in turn reduce the fluctuations in the group delay. In addition, the PLTL SMDL with DSGLs consequently have the superiority of suppressing the NEXT and FEXT simultaneously. Further simulations and measurements indicate that the performances of the PLTL SMDL with DSGLs lines are superior to the conventional method in a UWB range of dc to 25 GHz, including amplitude and group delay flatness, along with high time delay efficiency due to the slow wave property.

Reflective coupled microring resonators for reconfigurable photonic systems: Performance analysis

We propose reflective type triple coupled microring resonators (TCMMRs) for reconfigurable photonic based systems. We have developed an analytical model and analyzed its useful performance characteristics. The TCMMRs based device exhibits a wide range of performance characteristics such as multi-band filtering, optical logical operations, and optical true-time delay lines. Reconfigurable multiple resonances and their splitting features associated with the device provide useful filtering performance characteristics such as high out-of-band rejection, flat-top bandwidth, and near to ideal shape factor. The device can perform multiple functions such as bandpass, bandstop, and notch filtering with a good performance. Unlike two input narrowband logical operations demonstrated in the literature, our proposed device can perform as three-input optical logical operator, and it can switch wideband microwave frequency signals optically. Moreover, the device exhibits wideband flat top group delay response. It carries out delay tuning using a single variable coupling coefficient which simplifies the complexity of the tuning encountered in binary tree-structured optical beamforming networks based on conventional microring resonators.

Manipulating multipole resonances in spoof localized surface plasmons for wideband filtering

The spoof localized surface plasmon (LSP) has been widely investigated but mostly with fixed multipole resonances. This Letter proposes a method to generate multipole resonances by adding a slit on the metallic ring of a complementary LSP. This slit theoretically introduces two new boundary conditions and new modes. To validate this approach, complementary LSPs with and without slits at three different angular positions are theoretically analyzed and numerically simulated. To validate and demonstrate the potential application of the proposed LSP structure, a bandpass filter (BPF) in a single-layer substrate is designed and measured by exciting the LSP with a slit on the metallic ring. The measured results show that by simply adding a slit, the BPF achieves a fractional bandwidth of 42.7% (2.5 GHz), for both |S11|<-10dB and |S21| within 1 dB variation. In the passband, a flat group delay between 0.57 ns and 0.75 ns is obtained. Moreover, the proposed structure features a low profile and a compact radius of 0.136 wavelength. By dynamically controlling slit/slits with varactors or diodes, the proposed structure is theoretically promising to be reconfigurable at microwave and even terahertz frequencies.

Design of Dualband Bandpass High-Temperature Superconducting Filter With Group Delay Equalization

A novel dualband high-temperature superconducting (HTS) bandpass filter is proposed with group delay equalization for 5G emergency communication receivers with N41 and N79 bands in this paper. The dual-folded stub-loaded stepped impedance resonator (DSLSIR) is applied to realize dualband performance. The proposed DSLSIR has miniaturized circuit size and more design freedom to independently adjust the two designed center frequencies, comparing with other reported DSLSIRs. Two cross-coupling transmission lines are added at the top and bottom parts of the cascaded sixth-order filter with DSLSIRs to flatten the group delay of the passband at both bands. A dualband bandpass HTS filter etched on the YBCO superconducting material is fabricated to verify the proposed design method. The measurement is actualized at the temperature of 77 K to make YBCO microstrip lines perform superconducting features. The results show that the first center frequency is 2.595 GHz with 6.2% bandwidth for N41 band and 0.3 dB insertion loss while the second center frequency is 4.85 GHz with 2% bandwidth for N79 band and 0.4 dB insertion loss. Meanwhile, the group delays at the N41 and N79 bands keep 2 ns fluctuations in the 60% passband. The agreement between the measured and simulated results indicates that the proposed dualband bandpass HTS filter with low insertion loss, sharp roll-off skirt and flat group delay is a promising candidate for emergency communication receiver.

A compact fractal dual high frequency band notched UWB antenna with a novel SC-DGS

A compact and novel fractal dual band notched UWB antenna with time domain characteristics is presented. A tapered microstrip fed circular fractal radiating patch along with a novel semi circular defected ground structure produce − 10 dB bandwidth from 3.73 to 16.7 GHz. The proposed antenna is a miniature size of 16 × 21 mm2 and is printed on FR-4 substrate with two high frequency notched bands from 7.29–7.76 GHz to 9.53–11.17 GHz to notch X-band satellite communications link by incorporating L and C-shaped parasitic elements respectively. The proposed antenna exhibits a uniform gain of 2–4.26 dBi, flat group delay around 1.2 ns, and peak radiation efficiency about 96% in operating frequencies makes it suitable for wireless UWB portable devices.