Asymmetric Defected Ground Structure Research Articles

Optimisation of asymmetries in mm-wave single-element fractal antenna for gain-bandwidth enhancement

ABSTRACT In this study, a low-loss substrate was used to create an Asymmetric Irregular Hexagonal Fractal (AIHF) mm-wave antenna. The antenna consists of an Asymmetric Defected Ground Structure (ADGS) attached to the bottom of a 0.55λ0 ×0.40λ0 ×0.032λ0 mm3 substrate and an Irregular Hexagonal Fractal (IHF) patch on top of the substrate. The proposed fractal technique is unique and based on fractal-slot 3-stage iterations. The IHF patch is created by etching seven fractals arranged symmetrically about the y-axis, one of which has a central 1/3rd (scaling) iteration factor and six hexagonal fractals that are 1/9th of the parent 0th order iteration. On the patch, these fractal slots are evenly spaced out. By etching an Asymmetric Cascaded Double Dumbbell (ACDD) slot on the ground plane, an ADGS is created. With this etching in the patch and ground, a gain of > 5.0 dBi for a −10 dB S11 bandwidth of 4.655 GHz (32.84–37.215 GHz), a recorded peak gain of 13.4 dBi is at 33.55 GHz and an average radiation efficiency of 87.75% is achieved. Using the High-Frequency Structure Simulator (HFSS), the width of ADGS, the position of ACDD on ADGS, and the dimensions of etched fractals are optimised through a pattern search parametric iterative technique. These results are validated using the Vector Network Analyser (VNA), and the Anechoic Chamber and it is revealed that they agree well with the simulated results. The designed AIHF antenna’s RLC electrical equivalent circuit modelling is presented along with evaluated R, L, and C values.

Flexible and Small Textile Antenna for UWB Wireless Body Area Network

In this paper, a miniaturized textile microstrip antenna is proposed for wireless body area networks (WBAN). The ultra-wideband (UWB) antenna used a denim substrate to reduce the surface wave losses. The monopole antenna consists of a modified circular radiation patch and an asymmetric defected ground structure, which expands impedance bandwidth (BW) and improves the radiation patterns of the antenna with a small size of 20 × 30 × 1.4 mm3. An impedance BW of 110% (2.85–9.81 GHz) frequency boundaries was observed. Based on the measured results, a peak gain of 3.28 dBi was analyzed at 6 GHz. The SAR values were calculated to observe the radiation effects, and the SAR values obtained from the simulation at 4/6/8 GHz frequencies followed the FCC guideline. Compared to typical wearable miniaturized antennas, the antenna size is reduced by 62.5%. The proposed antenna has good performance and can be integrated on a peaked cap as a wearable antenna for indoor positioning systems.

Reduced Cross-Polarization and Backside Radiations for Rectangular Microstrip Antennas Using Defected Ground Structure Combined With Decoupling Structure

For cross-polarization (XP) reduction of microstrip antenna, it is proposed to use asymmetric defected ground structure (DGS) under the patch, which perturbs the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode. Unlike conventional DGS, the proposed DGS reduces the XP without increasing the back radiation. A method of higher order modes and surrounding electric fields is used to explain the DGS. The feasibility and superiority of the proposed scheme are further verified by constructing H-plane linear 4-element arrays. The XP reduction and decoupling are achieved simultaneously, as supported by simulation and measurement.

Pattern diversity and defected ground structure for decoupling planar Yagi MIMO antenna

In this paper, a novel decoupling technique both in pattern diversity (PD) and defected ground structure (DGS) is proposed for planar Yagi multiple-input multiple-output (MIMO) antenna arrays. The proposed planar Yagi antenna (PYA) is composed of two symmetrical printed dipoles and U-/V-shape directors. Based on the redirection effect of the directors, the desired pattern diversity and isolation improvement are achieved. DGS is added outside the excitation dipoles for closely packed elements, which achieves decoupling and better impedance matching. Through the whole frequency bandwidth (5.5–6.1 GHz), the mutual coupling between two-ports Yagi antenna elements is lower than −25 dB, and the stable gain is above 8 dBi with the variation of 1 dBi. Moreover, the validation of the proposed decoupling method is carried out on three and four-ports MIMO antenna arrays. By combining two kinds of directors and asymmetric DGS, the imbalance problem of the multi-port antennas is solved. The simulated and measured results validate the effectiveness of PD-DGS in MIMO directional antenna systems with high isolation and gain for 5.8 GHz WLAN application.

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.

An improved asymmetric defected ground structure cell and its application to lowpass filter

AbstractAn improved asymmetric defected ground structure cell is presented and analyzed. Based on this structure, a microstrip lowpass filter with low passband loss and high stopband suppression is designed and fabricated. Measured passband losses are below 1 dB, and a sharp slop is obtained at passband frequency fringe. The suppression is no &lt;30 dB in stopband from 2.98 to 10 GHz. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2933–2935, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24778

Quasi-elliptic filter characteristics of an asymmetric defected ground structure

An asymmetric defected ground structure (DGS) with respect to a microstrip line is proposed. Its unit cell consists of two square slots connected with a rectangular slot by meandered transverse slots. The simulated, measured and equivalent circuit responses have been presented. The unit DGS pattern under microstrip line produces wide rejection bandwidth and high sharpness factor. Its elliptic band-reject filter response is modelled by appropriate LC equivalent circuit. Two such DGS cells under a microstrip line produce 3-pole quasi-elliptic bandstop filter response, which shows deeper attenuation without appreciable change in pole frequencies in comparison to single cell structure. Unit DGS pattern under coupled gap microstrip lines produces band-accept filtering characteristics. The frequency characteristics show a quasi-elliptic highpass filtering characteristics with sharp lower transition knee. Accordingly, an LC equivalent circuit is proposed. A cascaded band-accept and band-reject filter is proposed for designing a wideband bandpass filter. The bandwidth and centre frequency of the bandpass filter can be varied by choosing different set of DGS dimensions.

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.

Suppression of harmonics in Wilkinson power divider using dual-band rejection by asymmetric DGS

In this paper, we present an effective technique of second and third harmonic suppression for a Wilkinson power divider by using an asymmetric spiral defected ground structure (DGS). With the proposed technique, a single asymmetric DGS provides two different resonance frequencies because of the different sizes of spiral-shaped defects on the ground plane. The transfer function of the asymmetric DGS shows signal rejection characteristics at two different resonance frequencies and the characteristics of asymmetric DGS is modeled by two parallel RLC resonance circuits in cascade. With the insertion of asymmetric spiral DGS into a quarter-wave line of the Wilkinson power divider, the second and third harmonics are suppressed simultaneously. In experimental results, 18-dB suppression for the second harmonic and 15-dB suppression for the third harmonic, respectively, are achieved. Using asymmetric DGS, the size of a quarter-wave line is reduced by 9.1% compared to that of the conventional divider without a DGS.