Defected Ground Structure Unit Research Articles

A novel compact quad-band planar antenna using meander-line, multi-stubs, and slots for WiMAX, WLAN, LTE/5G sub-6 GHz applications

AbstractThis article concerns the design of a new quad-band monopole antenna with a specific configuration and reduced size. The antenna design is based on a single step meander-line parasitic structure, parasitic stubs, and double inverted L-shaped defected microstrip structure units on the top side of the substrate, and double rectangular-shaped defected ground structure units along with partial ground plane on the bottom side. This design procedure allows to achieve quad-band characteristics and improve the impedance matching. The fabricated antenna prototype with overall dimensions of (0.24λ0 × 0.17λ0 × 0.013λ0) is operating at 2.55, 3.65, 4.65, and 5.8 GHz with fractional bandwidth about 7.7, 12.84, 9.23, and 12.8%, respectively. The antenna exhibits an omnidirectional and a monopole like radiation patterns in the H- and E-planes, respectively, with suitable gains between 2.1 and 3.75 dBi. The measurement results are in good agreement with simulation values, which indicates that the proposed antenna design is suitable for WiMAX, LTE B7 (2.52–2.75 GHz), Sub-6 GHz 5G (n77) (3.39 – 3.87 GHz), Sub-6 GHz 5G (n78) (4.4–4.86 GHz), and WLAN, LTE B46 (5.1–5.82 GHz) wireless applications.

High-Performance Low-Pass Filter Using Stepped Impedance Resonator and Defected Ground Structure

A microstrip low-pass filter (LPF) using reformative stepped impedance resonator (SIR) and defected ground structure (DGS) is proposed in this paper. The proposed filter not only possesses the advantage of high frequency selectivity of SIR hairpin LPF with internal coupling, but also possesses the large stop-band (SB) bandwidth by adjusting the number and area of DGS units. The LPF proposed in this paper possesses the properties of miniaturization, wide SB, high selectivity, and low pass-band ripple (PBR) simultaneously. The characteristic parameters of the proposed LPF is that: the pass-band (PB) is 0~2 GHz, the PBR is 0.5 dB, the SB range is from 2.4 GHz to 9 GHz when the attenuation is under 20 dB, and the maximal attenuation could reach 45 dB in the SB. The size of this proposed LPF is 0.13 λ × 0.09 λ ; λ is the corresponding wavelength of the upper PB edge frequency of 2 GHz.

Study of compact microstrip lowpass filter with improved performance using defected ground structure

A compact lowpass filter (LPF) with wide stopband which uses four non-uniform cascaded defected ground structure (DGS) units along with a 50 Ω microstrip line is reported in this article. Each DGS unit, which consists of a combination of three isosceles U-shaped DGSs is analyzed in terms of an equivalent RLC circuit model. Every DGS of the DGS unit along with microstrip line provides one attenuation pole. It is found through performance comparison of the proposed U-shaped DGS with dumbbell- and fork-shaped DGSs that the proposed U-shaped DGS is compact and provides higher quality factor. Further, the modeling of the proposed LPF is carried out using equivalent RLC circuit model. The results obtained through numerical and circuit simulations are compared. The proposed LPF has size of 14.44 mm × 3.4 mm, 3-dB cut-off frequency of 14.2 GHz, and greater than 40 dB and 22 dB stopband rejection up to 21.8 GHz and 30 GHz respectively. The proposed LPF is fabricated and experimentally tested. The experimental results are nearly in agreement with corresponding numerical/circuit simulation results.

Super-compact ultra-wideband microstrip band-pass filter with improved performance using defected ground structure-based low-pass filter

A super-compact ultra-wideband (UWB) microstrip band-pass filter (BPF) with good selectivity and wide stopband is proposed in this paper. The super-compactness along with wide stopband of the proposed filter is achieved by integrating modified multimode resonator-based UWB BPF and defected ground structure (DGS)-based compact low-pass filter (LPF). The LPF structure is designed using four non-uniform configurations of DGS units along with a 50 Ω microstrip line. Each DGS unit is formed by cascading three isosceles U-shaped DGSs. Further, an equivalent RLC circuit model of the LPF is proposed to validate the numerical simulation and experimental results of LPF. The proposed filter has simulated passband frequency range 3–11 GHz with wide stopband: attenuation better than 40 dB and 25 dB over the frequency ranges 11.7–20.5 GHz and 11.2–30 GHz respectively. The experimental results for the proposed filter are nearly in agreement with corresponding numerical simulation results.

Differential Dual-Band Filters With Flexible Frequency Ratio Using Asymmetrical Shunt Branches for Wideband CM Suppression

In this paper, a group of differential dual-band bandpass filters based on a single quad-mode stub-loaded twin-ring resonator (TRR) are presented, which utilize asymmetrical shunt branches for common-mode (CM) suppression. Under differential-mode (DM) operation, the stub-loaded TRR manifests quad-mode characteristic for dual-band design. The frequency ratio of the two passbands can be flexibly selected according to the form of the loaded stubs. Different from the inline topology, differential multimode structures inevitably suffer from the hardship in CM suppression, especially for dual-band designs. Despite previous work fulfilled moderate CM suppression via embedded defected ground structure units, but the CM noise in the DM lower band can just be shifted away rather than suppressed. Instead, a novel CM-suppression approach is devised attributing to the asymmetrical short-terminated branches along the bisection line of the TRR. The transmission of the CM noise near the DM passbands can be blocked effectively. Furthermore, multiple CM notches can be obtained by the cooperation of the asymmetrical branches and source–load coupling, leading to the favorable CM suppression in a wide frequency range. For verification, a prototype differential dual-band filter based on the open stub-loaded TRR has been realized with frequency ratio which is larger than two. Similarly, a differential dual-band filter using the short-circuited stub-loaded TRR is also presented as an extension for frequency ratio which is smaller than two. The simulation and experiment results of the two demonstrated filters are given, showcasing a good agreement.

Microstrip antenna array mutual coupling suppression using coupled polarisation transformer

This study presents a periodic defected ground structure (PDGS) to suppress the mutual coupling (MC) between coplanar antenna elements in a multiple-input and multiple-output (MIMO) communication system. The proposed PDGS consists of three defected ground structure units. They are etched away from the ground plane between antenna elements. The coupled polarisation transformer characteristic of the proposed PDGS is utilised to increase the antenna elements isolation. The increased coupled vertical linear polarisation component and decreased coupled horizontal linear polarisation component contribute to reduce the MC between antenna elements. By using this method, the authors achieve low MC level and better MIMO corresponding capacity. This method has little influence on the far-filed main radiation properties of the antenna elements.

Differential Dual-Band Bandpass Filter With Tunable Lower Band Using Embedded DGS Unit for Common-Mode Suppression

This paper presents a varactor- and stub-loaded dumbbell-shaped resonator (VSDSR) for application in differential dual-band bandpass filter, which possesses a tunable lower passband and a fixed upper passband. Under differential-mode (DM) bisection, the VSDSR behaves as a ring resonator with four resonant modes, which can be categorized into two independent groups for constructing two passbands. At the same time, the common-mode (CM) equivalent circuit of the VSDSR generates multiple CM resonant frequencies and some of them inevitably overlap with the DM ones. Accordingly, the traditional CM suppression methods such as adding shunt stub or lumped element are disabled. To suppress the CM signals in both DM passbands, the defected ground structure (DGS) units are embedded underneath the adjacent edges of the two rings directly to form a CM suppression filter without increasing the circuit size. Meanwhile, they have almost no effect on the DM responses. Benefitting from the bandstop and slow-wave effects of the employed DGS units, the CM noises in both DM bands can be rejected effectively. In particular, the level of the CM suppression in the DM lower passband can be improved by adjusting the location of the DGS units. Furthermore, the proposed CM suppression scheme is adaptive in the tunable lower DM passband.

S‐shaped periodic defected ground structures to reduce microstrip antenna array mutual coupling

A novel S-shaped periodic defected ground structure (PDGS) is proposed to reduce mutual coupling between antenna elements. Coplanar placed antenna elements work at the same frequency band with centre frequency 2.57 GHz. Centre-to-centre distance between the antenna elements is 50 mm which is ~0.43λ. The PDGS is three S-shaped defected ground structure units placed between microstrip antenna elements. By using the proposed PDGS, more than 40 dB mutual coupling reduction between microstrip antenna elements is achieved.

An improved parameter extraction scheme for dumbbell shaped defected ground structure

The present study proposes an improved scheme for parameter extraction of dumbbell shaped defected ground structure (DGS). A dumbbell DGS has similar kind of response like a single pole LC–Butterworth filter. There are L–C, R–L–C, π and quasi-static equivalent circuits available in literature for dumbbell DGS parameter extraction. In this article, the R–L–C equivalent of dumbbell DGS is re-formulated which provides better accuracy in parameter extraction and it is confirmed through simulation and experimental analysis. This improved model is finally used to extract R–L–C parameters against several structural variations of dumbbell DGS unit cell.

Circuit Modeling and EM Simulation Verification of DGS based Low-Pass Filter Employing Transmission Line Model along with Microstrip-Slotline Transitions

In this paper, an equivalent circuit model (ECM) for a defected ground structure (DGS) pattern is proposed and evaluated for designing a compact low-pass filter (LPF). The proposed ECM is based on microstrip lines and microstrip-slotline transitions. Every slotlines of the DGS unit are modeled by ideals transmission lines of characteristic impedance and electrical length. Comparison between full-wave EM and circuit simulations illustrates the validity of the proposed ECM.

Miniaturized Dual-Mode Star-Shaped Bandpass Filter with Spurious Suppression

A compact dual-mode resonator bandpass filter with harmonic suppression is presented. The filter is composed of a perturbed star-shaped resonator and defected ground structure units. The spurious suppression of the bandpass filter could be realized by controlling the dimension of the defected ground structure, which provides a low-pass characteristic. The star-shaped resonator offers a 37% size reduction compared to a conventional ring resonator operating at 2.5 GHz. Measured results agree well with the simulation ones.

Comparative Study of Three DGS Unit Shapes and Compact Microstrip Low-Pass and Band-Pass Filters Designs

In this paper, three types of defected ground structure (DGS) units which are triangularhead (TH), rectang ularhead (RH) and Ushape (US) are investigated. They are further used to lowpass and bandpass filters designs (LPF and BPF) and the obtained performances are examined. The LPF employing RHDGS geometry presents the advantages of compact size, lowinsert ion loss and wide stopband compared to the other filters. It provides cutoff frequency of 2.5 GHz, largest rejection band width of 20 dB from 2.98 to 8.76 GHz, smallest transition region and smallest sharpness of the cutoff frequency. The BPF based on RHDGS has the highest bandwidth (BW) of about 0.74 GHz and the lowest center frequency of 3.24 GHz, whereas the other BPFs have BWs less than 0.7 GHz. Keywords—Defected ground structure (DGS), triangularhead (TH) DGS, rectangularhead (RH) DGS, Ushape (US) D GS, low� In this paper, we present three DGS unit shapes which are triangularhead (TH), rectangularhead (RH) and Us hape (US) and their characteristics are compared. Further, these units are employed in lowpass and bandpass filter s designs and the obtained performances are examined. The simulations are carried out using the fullwave EM IE3D simulat or and all prototypes are designed on substrate material with thickness of 0.25 mm, conductor layer of 35 Em and a relative permittivity of 3.63. The following section of this paper describes the comparison of three DGS units. In Section III, LPFs based on the above DGS units are designed and their characteristics are investigated to determine which one offers the best filter specifications. In Section IV, BPFs based on the DGSs with a discontinuity in the 50 G (characteristic impedance) microstrip line are designed and analyzed. Finally, conclusions are drawn in Section V.

Design and Development of Lowpass Filter and Harmonics Reduction

The shape of a popular split-ring defected ground structure (DGS) is modified by etching two concentric split-ring defective pattern which have different size and inverse split direction in the ground plane underneath a microstrip line. The frequency characteristics of proposed DGS unit show an attenuation zero close to the attenuation pole frequency. As a result, better transition sharpness is observed. An equivalent lumped L-C network is proposed to model the introduced DGS unit and corresponding L-C parameters are extracted. A 3 rd order quasi-elliptic lowpass filter is designed by cascading the three investing DGS units under High-Low impedance microstrip line and the generated first harmonic has been removed with the help of defected microstrip structure (DMS) underneath the cascading DGS unit.

Design of a Quasi- elliptic Lowpass Filter using A New Defected Ground Structure and Capacitively Loaded Microstrip Line

The modern microwave and millimeter wave communication system demands good filtering characteristics with compact sizes. In this paper the attention has been given towards the design of a good elliptical lowpass filter with sharp transition between passband and stopband, negligible passband insertion loss and wide stop band. A new defected ground structure (DGS) consisting of two square slots connects with a rectangular slot by two thin transverse slots underneath a microstrip line is proposed. In the frequency characteristics of proposed unit pattern provides an attenuation zero close to an attenuation pole. As a result, better transition sharpness, lower passband insertion loss and broader stopband are observed compares to dumbbell DGS. An equivalent lumped L-C network is proposed to model the introduced DGS unit and corresponding L-C parameters are extracted. A 3rd order quasi-elliptic lowpass filter with 1.4 GHz cut- off frequency, 1.7 GHz attenuation pole frequency, negligible passband insertion loss, almost 100 dB/GHz sharpness factor and 1.56GHz passband bandwidth (at -15 dB) is designed by cascading three investigated DGS units of different dimensions under capacitively loaded microstrip line.

Novel Compact Microstrip Lowpass Filters with Wide Stopband Using Defected Ground Structure

In this paper, a novel defected ground structure (DGS) is proposed for lowpass filter (LPF) applications. The proposed structure exhibits wideband attenuation without increasing the circuit size, as compared with the conventional DGS. An equivalent circuit for the proposed DGS is described, and its equivalent-circuit parameters are analyzed and extracted. Benefitting from the quasi-elliptic function of the DGS, a demonstration LPF using one DGS unit and a compensated microstrip line is designed, and an attenuation pole near to the passband edge is realized to enhance roll-off of the stopband. To improve rejection level of the stopband, three cascaded DGS units are utilized for the LPF design. The fabricated LPF shows more than 20 dB attenuation from 2.1 GHz to over 8.0 GHz, as well as sharp rolloff. The simulated and measured results are presented, showing good agreement.

Design of Novel 4-GHz Bandpass Filter Using a Combination of Defected Ground Structure Resonators and Admittance J-Inverter

A wideband quasi-elliptical bandpass filter with enhanced reject-band performance is presented. The proposed bandpass filter utilizes a new asymmetric defected ground structure (DGS) under a pair of end-coupled microstrip line. The DGS consists of two square headed slots connected transversely with a rectangular slot. The DGS-microstrip resonator provides band-accept filtering characteristics. To be equivalent to the circuit DGS is demonstrated. The presented equivalent circuit shows both resonant and anti-resonant properties. The equivalent circuit parameters are extracted using the modeling method of proposed DGS. A better selectivity in lower transition band in comparison to upper transition band is observed in the frequency response. To improve the roll-off in upper transition band, a pole is created by putting an additional DGS unit under the same microstrip line. The combined structure shows bandpass characteristics with deep and wide stopband on both sides of the passband. The bandwidth and centre frequency of the filter is controlled by the dimensions of both DGS cells. The article presents some promising patents on Defected Ground Structure Resonators and Admittance J-Inverter.

Application of a defected ground structure and alternative transmission line for designing a quasi-elliptic lowpass filter and reduction of insertion loss

A new defected ground structure (DGS) consisting of two square ring slots connects with a rectangular ring slot by two thin transverse slots under a microstrip line is proposed. In the frequency characteristics of proposed unit pattern, an attenuation zero is observed close to the attenuation pole. As a result, better transition sharpness, lower passband insertion loss and broader stopband are observed compares to dumbbell DGS. An equivalent lumped L-C network is proposed to model the introduced DGS unit and corresponding L-C parameters are extracted. Insertion loss is reduced by alternative transmission line on the top plane of the DGS unit. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.

Novel complementary split ring resonantor DGS for low‐pass filter design

AbstractThis article has investigated a novel complementary split‐ring resonator (CSRR) defected ground structure (DGS) theoretically and experimentally. The proposed CSRR DGS provides excellent performances including double resonant property, ripple in the passband, sharp selectivity at the cut‐off frequency, and spurious free wide stopband. The equivalent circuit model of the CSRR is also presented. Low‐pass filters using DGS units are fabricated to obtain wide reject band. The measured results show a good agreement with the theoretical analysis. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1748–1751, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24405

An asymmetric defected ground structure with elliptical response and its application as a lowpass filter

A new asymmetric defected ground structure (DGS) consisting of two square headed slots connected with a rectangular slot transversely under a microstrip line is proposed. In the frequency characteristics of its unit cell, an attenuation zero is observed close to the attenuation pole. The DGS unit is represented by Cauer's T-network, modeled by a third order elliptical lowpass filter and finally equivalent L-C parameters are extracted. Several studies have been accomplished on the influence of the geometric modification of the filter on its characteristics. Better transition sharpness, lower passband insertion loss and broader stopband are observed, compared to popular dumbbell DGSs due to its additional attenuation zero. The two-cell configuration of this DGS produces a three-pole lowpass filter having wide and deep stopband at low cutoff frequency. This is applied under the input and output feed lines of a parallel-coupled bandpass filter for suppressing harmonic frequencies. A lowpass filter is realized using cascaded investigated DGS and dumbbell DGS under a microstrip line.

Design of novel microstrip low‐pass filter using defected ground structure

AbstractA novel microstrip low‐pass filter utilizing defected ground structure (DGS) units is presented in this article. A DGS unit is simulated with different physical dimensions in order to show variation of attenuation pole and cut‐off frequency. Next, a low‐pass filter using proposed DGS unit is designed. A method for determining dimensions of microstrip structure and DGS units is proposed. Influence of dimensions of the microstrip structure on filter characteristics is investigated and simulated. Filters of various orders are simulated as well. Selected filter is simulated and experimentally verified. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 10–13, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22982