This article presents an ultrawide bandpass filter structure developed along a notch band using a small rectangular impedance resonator. The proposed filter structure consists of a coupled rectangular resonator (CRR), open stub, and composited split ring resonator (CSRR) at the bottom of the structure. In-band and out-of-band properties are improved by the CRR and open stub. The notch band is obtained by placing CSRR below the rectangular resonator. A filter with a compact size of 0.15 × 0.10 λg is obtained at a lowered cutoff frequency of 3.0 GHz, where λg is the corresponding guided wavelength. The proposed structure has been constructed on 5880 Rogers substrate with a thickness of 0.787 mm and a dielectric constant of 2.2. Additionally, equivalent lumped parameters were obtained, and a lumped equivalent circuit was created to explain how the suggested filter operated. The Electromagnetic (EM)-simulated results are in good agreement with the circuit-simulated and measured result. The various machine learning approaches such as artificial neural network, K-nearest neighbour, decision tree, random forest (RF), and extreme gradient boosting algorithms are applied to optimize the design, in which RF algorithms achieve more than 90% accuracy for predicting the S parameters of the ultrawideband filter.

A novel reconfigurable circular microstrip G-slotted antenna having a circularly defected ground structure (DGS) capable of switching its resonance frequency for several microwave applications is presented in this paper. Reconfigurability of the proposed G-slot antenna is obtained by incorporating three PIN diodes. One diode is embedded in the patch and two diodes are integrated into the DGS structure at appropriate places in the slot to achieve four different wireless applications such as aeronautical radio navigation (4.3 GHz with gain 3.6 dB), satellite communication (3.78 GHz with gain 3.7 dB), mobile communication (4.55 GHz with gain 4.0 dB), and WiMAX (3.35 GHz with gain 3.3 dB). These four bands are achieved depending on the different biasing conditions of the three PIN switches used. Antenna performance has been analyzed in ANSYS Electronics Desktop 2018.2 software. The equivalent circuit component of the switching element (PIN diode) has been considered and designed during the simulation. The creative structure lies in the way that it exhibits higher gain with compact size than the previously reported similar antenna. A prototype of the proposed patch antenna has been fabricated on a Roger substrate and its testing and measurement have been performed to demonstrate its desirable characteristics and features.

This article presents a compact rectangular impedance resonator (RIR)–based ultra-wideband bandpass filter with an improved reflection coefficient within the passband and controllable cut-off frequencies. The proposed filter consists of anti-parallel coupled RIR coupled with rectangular open-loop defected ground structure (ROL-DGS) etched on the ground plane. The ROL-DGS ensures better in-band and out-off-band characteristics with reduced size due to its high Q-factor. The short- and open-circuit stubs control the lower (fCL) and upper (fCU) 3-dB cut-off frequencies, respectively, by originating transmission zeros independently with the help of variations in design parameters. As a result, the filter having a compact size of 0.216λCL × 0.176λCL is achieved, where λCL is the corresponding guided wavelength at the lower cut-off frequency fCL of 2.95 GHz. Further, an equivalent circuit is also modeled to explain the working of the proposed filter, and equivalent lumped parameters were extracted. Simulated results reveal that the reported filter passes the frequencies effectively within 2.95–11.44 GHz with fractional bandwidth of 117.9%. The simulated insertion loss values within the passband are less than 1.17 dB, and the reflection coefficient is better than −19.6 dB. Further, the proposed filter is fabricated, and it was found that the measured and simulation results are in well agreement.

This article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18λ0 is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186° and 188° in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S11 ≤ −10 dB) of 2.6% (2.283–2.342 GHz), CP bandwidth of 0.9% (2.294–2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.

In this paper, a compact super wideband annular ring antenna using 45° clock-wise square patch inclusions for super high frequency and polarization diversity applications is proposed. The inclusions consist of a combination of squares and circles into one another in the inner area of a main annular ring radiator. The antenna uses a partial ground plane having a stair-type defected ground structure, is designed on an FR-4 substrate, and has a total size of 25 × 26 × 1.6 mm3 (0.17λ × 0.18λ). The design was fabricated and experimental results fairly agreed with simulations and resulted in an antenna with an operating frequency from 2.07 to 30 GHz; that is, a large fractional bandwidth of 174.2$\%$ with a bandwidth (BW) ratio of 14.5:1 and a high BW dimension ratio, BW per unit electrical length of 5693, and a measured peak gain of 8 dBi with an average gain of 5 dBi for the overall operating frequency. For the polarization diversity, a 4 × 4 multiple input-multiple output configuration is additionally presented, offering an effective isolation of ≥ 22.5 dB between ports and corroborated by measurements.

In this paper, miniaturization of fractal geometry with defected ground structure (DGC) concept has been experimentally verified at S-band (2–4) GHz. The design starts with a self-symmetry structure using conventional Vicsek snowflake-box fractal antenna. The same has been used in third iteration to achieve miniaturization. This proposed microstrip patch antenna (MPA) is resonating at 2.12 GHz with acceptable gain and broadside radiation. The miniaturization of about 87.26% when compared to conventional fractal MPA is achieved. The fractal unit cell is optimized for miniaturization and bandwidth by carrying out parametric study and applying the DGS shapes like rectangular and U-shaped slot etched in the ground plane of Vicsek snowflake-box fractal microstrip antenna. A fractal microstrip antenna is designed for wireless applications at 3.95 GHz. The fractal microstrip antenna is simulated using HFSS-V15 simulator. It is observed that the maximum size reduction of 87.26% is achieved in the third iteration of the Vicsek snowflake-box fractal radiating patch. The proposed fractal patch antenna is designed and fabricated using epoxy substrate of FR-4 with dielectric constant of 4.4 and thickness of 1.6 mm. The simulated results are compared with the measured results.

In this paper, a low profile 4 × 4 multiple input and multiple output (MIMO) antenna is proposed and designed for wireless local area network (WLAN) application using a square split-ring resonator. Initially, a single square-patch antenna is designed with square-shaped split-ring slot. Subsequently, the two-element MIMO antenna is designed and it is extended to four-element MIMO antenna. Finally, the defected ground structure (DGS) is implemented in order to enhance antenna performance. The antenna elements are placed opposite to each other. The mutual coupling between the antennas elements is reduced by DGS. The proposed single, two and four-element antennas operate at 5.8 GHz for WLAN. The overall performance is measured in terms of S parameter, radiation pattern, and envelope correlation coefficient. The simulated results are verified through measurements. The simulated and measured results demonstrate that the proposed 4 × 4 MIMO antenna is the most suitable for WLAN applications.

Design of single-feed circularly polarized (CP) microstrip antenna is proposed in this article. The design employs the concept of E-shape patch with inclined fractal defected ground structure (IFDGS), which can improve the impedance bandwidth, gain, and axial ratio (AR) bandwidth. The excellent enhanced impedance bandwidth, axial ratio bandwidth, and gain are achieved by an inclined E-shaped fractal etched on the ground plane. The parameter studies of the E-shaped IFDGS are given to illustrate the way to obtain CP radiation. The third iterative IFDGS is fabricated on easily available FR4 substrate with a size of 0.494 λ0 × 0.494 λ0 × 0.019 λ0 (λ0 is the wavelength in free space at 3.624 GHz). The measured results verify the simulated results and show good agreement. The proposed antenna shows an impedance bandwidth of 12.7% at a centre frequency of 3.47 GHz and 3-dB AR bandwidth for this band is 2.39% at a centre frequency of 3.626 GHz. The measured peak gain for the proposed antenna is found as 8.1 dBi. The proposed antenna can be suitable for mobile WIMAX operation (IEEE 802.16e-2005 standard), wireless communication in CA-band and FCC.

The spectral congestion in existing Industrial, Scientific, and Medical (ISM) Wireless Local Area Network (WLAN) bands has led to the emergence of new ISM bands (Unlicensed National Information Infrastructure (UNII)) from 5.150 to 5.710 GHz. In this paper, a simple uniplanar, high gain, microstrip antenna is designed, fabricated, and tested for existing WLAN and new UNII standards. The proposed antenna provides dualband operation by joining two rectangular rings and cutting Defected Ground Structure in the Coplanar Wave Guide (CPW) feed. The experimental and simulation results show good return loss characteristics and stable radiation pattern over the desired frequency bands ranging from 2.20 to 2.65 GHz (WLAN band) at a lower frequency and from 5.0 to 5.45 GHz (UNII-1/UNII-2 bands). The measured peak gains are 5.5 and 4.9 dBi at 2.45 GHz (WLAN band) and 5.15 GHz (UNII band), respectively.

This work presents a novel efficient and compact size coupled resonator system for wireless power transfer (WPT) based on compact half-ring resonators defected ground structure (HRRs-DGS). The proposed design is capable of supplying low power electronic devices. The suggested system is based on coupled resonators of DGS. An HRR-DGS band-stop filter is designed and proposed, and when two HRRs-DGS are coupled back-to-back, it transfers to a band-pass filter leading to a compact and highly efficient WPT system working at 3.4 GHz. The measured efficiency of the proposed coupled HRRs-DGS system is around 94% at a transmission distance of 12 mm which is filled with foam for stable measurements. The proposed design is suitable for charging electronic devices such as wireless sensor nodes at 3.4 GHz. Simulation and experimental results have shown acceptable agreement.

A novel planar printed phase shifter design is proposed in this paper. The design is developed with microstrip–conductor-backed coplanar waveguide– microstrip (MP–CBCPW–MP) transition line with different defected ground structures (DGS). The differential phase shift can be controlled by altering the DGS dimensions. Three prototypes with DGS dimensions 5 × 10, 10 × 20, and 10 × 30 mm2, are employed at the finite ground plane to achieve 5°, 20°, and 30° shift in phase respectively and are validated with the phase delay relation. The prominent effect of the transition region is to confine the field area. The resonance is at 700 MHz with a bandwidth of 400 MHz (0.4–0.8 GHz). The proposed phase shifter can be used for broadcasting applications. The proposed MP–CBCPW–MP transition phase shifter design with DGS is simulated, fabricated, and measured to analyze its performance.

In this paper, a compact, dual-band patch antenna is proposed over Minkowski fractal defected ground structure (DGS) for bandwidth enhancement of global positioning system (GPS) applications. The proposed design combines the truncated dual L-shaped slits cut on diagonal corners of radiating patch and fractal defect on the metallic ground plane. This concept shifts the frequencies to lower bands with improvement in antenna radiation properties. By deploying symmetrical and asymmetrical boundaries to the structure for the fractal DGS on metallic ground plane, improvement in bandwidth and gain are obtained. Compact antenna size is achieved for dual-band GPS frequencies of L1 (1.575 GHz) and L2 (1.227 GHz). The measured results for antenna prototype are (1.2–1.245 GHz): L2 band and (1.51–1.59 GHz): L1 band for 10 dB return loss bandwidth with better pattern radiation. Gain value with and without DGS is observed for compact antenna overall volume of 0.32λ0 × 0.32λ0 × 0.024λ0.

Asymmetric slits loaded irregular shaped microstrip patch antenna with three different ground structures is proposed. All three antennas show triple band characteristics. First antenna with regular ground plane resonates at 1.95, 2.4, and 4.90 GHz with good radiation characteristics and shows right-hand circular polarization at 1.95 GHz. 18.75% of compactness is achieved with triple band characteristics. Further, same patch is used with different defected ground structures. Second antenna resonates at 1.85, 2.4, and 4.85 GHz with suppressed cross-polarization level and antenna shows right-hand circular polarization at 1.85 and 4.85 GHz. Compactness is further improved to the value of 22.91%. The third antenna resonates at 1.95, 2.4, and 4.85 GHz with better gain and radiation characteristics and antenna shows right-hand circular polarization at 1.95 and 2.4 GHz. The small frequency ratio f2/f1 is achieved and the value of f2/f1 is 1.29 and 1.23 for second and third configuration, respectively. Proposed structures show right-hand circularly polarized with suppressed left-hand circularly polarized radiations and suitable for fixed mobile wireless communication applications. All structures are analyzed using Ansoft HFSS v.14 based on finite element method and measured results satisfy the simulated results.