Further slot antenna miniaturization and bandwidth enhancement

In this work, antenna miniaturization using slits and metallic strips fed by microstrip line has been demonstrated. It has been noticed that slot antenna fed by microstrip line provides more miniaturization and in some cases enhanced bandwidth in comparison with the slot antenna fed by other feeding mechanism, keeping the same length and width of the radiating slots, slits and metallic strips. We have achieved 51.67% reduction in resonant frequency and 74.72% improvement in ?10 dB bandwidth compared with 37.73% and no bandwidth improvement of either side slits loaded slot antenna topology. Further, it has been shown 63.52% reduction in resonant frequency and 2.23% improvement in ?10 dB bandwidth in comparison with 42.33% reduction in resonant frequency of only one side slits loaded slot antenna topology. The current work highlighted not only greater miniaturization and enhanced bandwidth but also almost unperturbed radiation pattern compared to reference antenna topology and low cross‐pol level even slot antenna loaded by only one side slits, which was not demonstrated in earlier works.     

Compact triband circularly polarized planar slot antenna loaded with split ring resonators

In this article, a coplanar waveguide (CPW) fed triband circularly polarized (CP) planar slot antenna loaded with split ring resonators (SRRs) is presented. The truncated slot antenna resonates at 4.15 GHz, which gives two orthogonal degenerate modes to produce circular polarization at the first band. The second and third band resonances are achieved at 4.77 GHz and 5.1 GHz respectively due to the loading of SRRs on the slot antenna. The electric fields produced by the single and multiple split gaps in each ring of SRR1 and SRR2 produce CP at the second and third band. All three bands are tuned independently to achieve optimized axial ratio bandwidth. The antenna is fabricated and verified experimentally. The measured results give impedance bandwidth of 64.54% and axial ratio bandwidths of 11.76%, 1.9%, and 3.87% at first, second, and third band, respectively.     

Triple band omnidirectional miniaturized metamaterial inspired antenna using flipped rectangular stub for LTE,WiMAX, and WLAN applications

In this article, a miniaturized metamaterial (MTM) inspired antenna with triple band characteristics is presented for LTE/WLAN/WiMAX applications. The antenna mainly consists of a square shaped split ring resonator (SRR) with rectangular stub connected in the outward direction. Due to inward flipping of the same rectangular stub leads to 20% antenna miniaturization without degrading the resonance behavior. The SRR produces first and second band, while the third band is enhanced due to flipping of inward stub and addition of rectangular type slot in the partial ground plane. The antenna exhibits tri‐band characteristics with each bands centered at 2.23, 3.65, and 5.13 GHz, having ?10 dB impedance bandwidth of 9.42%, 12.88% and 15.34% for the first, second, and third band, respectively. The antenna has a footprint size as low as 0.16 λ₀ × 0.18 λ₀ × 0.012 λ₀ corresponding to 2.23 GHz with a measured gain of 2.22, 2.31, and 1.98 dBi., and measured radiation efficiency of 70%, 72.75% and 82.57% in the three bands, respectively. The prototype of the antenna is fabricated and simulated results are verified through measurements.     

Miniaturized dual‐band metamaterial inspired antenna with modified SRR loading

A miniaturized dual‐band CPW‐fed Metamaterial antenna with modified split ring resonator (SRR) loading has been presented in this paper. Proposed antenna comprises a tapered rectangular patch with a slot in which an elliptically SRR has been loaded to achieve miniaturization. Proposed antenna shows dual band operations in the operating band 3.25‐3.42 and 3.83‐6.63 GHz, respectively. It has been observed that lower mode (at 3.36 GHz) is originated by means of modified SRR. SRR is being modified by small meandered line inductor which is placed instead of strip. This provides an extra inductance to SRR resulting miniaturization. Overall electrical size of the proposed antenna is 0.222 × 0.277 × 0.017 λ₀ at 3.36 GHz. Second band is due to coupling between feed and ground planes. The antenna offers an average peak gain of 1.72 and 3.41 dB throughout the first and second band respectively. In addition to that this antenna exhibits perfect omnidirectional and dipolar radiation patterns at xz‐ and yz‐ plane respectively. Due to consistent radiation pattern, ease of fabrication, and compact nature this antenna can be used for wireless applications such as worldwide interoperability for microwave access (WiMAX), industrial, scientific and medical (ISM) band, WLAN/Wi‐Fi bands.     

Polarizer superstrate and SRR‐loaded high‐gain dual band dual polarized waveguide slot array antenna

This article presents a high‐gain dual band dual polarized waveguide slot array antenna. Three split ring resonators (SRRs) are placed on the transverse plane of a slotted waveguide at uniform distance to achieve dual band response whereas a polarizer superstrate has been used to change the linear polarization of the lower band to circular polarization. Ansys HFSS 14.0 has been used for simulation and optimization purpose. Proposed antenna shows two 10 dB return loss bandwidth covering the frequency range 8.41‐8.88 and 9.31‐10.43 GHz, respectively. The lower band offers a circular polarization and upper band offers a linear polarization.     

CPW fed miniaturized dual‐band short‐ended metamaterial antenna using modified split‐ring resonator for wireless application

A miniaturized dual‐band metamaterial (MTM) antenna has been designed in this article. The designed coplanar waveguide fed antenna has composed of inner split‐ring resonator and an outer open ring resonator with rectangular stub. The series parameter of the antenna is used to determine the zeroth order resonance frequency due to short‐ended boundary condition. The whole size of proposed structure is 20 × 25.5 mm². This MTM antenna exhibits dual‐band operation at 3.17 GHz (3.1–3.22 GHz) and 5.39 GHz (5.27–5.47 GHz). The proposed MTM structure achieves measured peak gain of 0.71 and 1.89 dB at 3.17 and 5.39 GHz, respectively. The proposed antenna can be used for recent radio communication in form of S‐band application and Wi‐MAX.     

Miniaturization and dual‐banding of an elevated slotted patch antenna using the novel dual‐reverse‐arrow fractal

A novel fractal geometry called dual‐reverse‐arrow fractal (DRAF) is introduced and compared with various versions of Koch fractals for application to triangular patch antennas. It is shown that DRAF results in the reduction of antenna size and tends to maintain its bandwidth. The presented DRAF is applied for the reduction of size of an elevated triangular patch antenna for the dual band operation in WLAN. This DRAF antenna has achieved 40% size reduction compared to a simple triangular patch antenna. For the provision of required bandwidth in the second frequency band (4.9‐5.9 GHz), a stepped U‐shaped slot is cut in the triangular patch. This antenna is more compact than similar antennas reported in the literature but maintains its fractional bandwidth (%25). The optimized design of the proposed DRAF antenna with air gap and slot is fabricated and tested, which verifies its expected specifications.     

A compact asymmetric slot dual band antenna fed by CPW for PCS and UWB applications

A compact slot antenna with an overall dimension of 30 × 30 × 1.6 mm³ is proposed for dual band applications. The radiating element is a hexagonal shape patch which protrudes from a Co‐Planar Waveguide (CPW) feed into a step shape slot. The slot is basically rectangular in shape and is extended by inserting rectangular cuts of different sizes on the ground plane around it. The ultrawide impedance bandwidth is achieved using asymmetric feed line along with extended rectangular cuts around the slot. For realizing the second band for personal communication system applications (near 1.9 GHz), a metallic stub of quarter wave length is attached at the top of the slot. The measured impedance bandwidth (for S₁₁ < ?10 dB) is 110 MHz (1.86–1.97 GHz) for the first band and 9 GHz (3.0–12.0 GHz) for the second band. The antenna is further characterized by omnidirectional radiation patterns in the H‐plane, dumb‐bell shape radiation patterns in the E‐plane and a peak gain of 3–5 dBi over the ultrawideband. All the measured results are found to be in good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:243–254, 2015.     

Eccentric annular slot patch antenna with frequency agility for UHF RFID reader applications

The design of a simple ultrahigh frequency RFID (radio frequency identification) reader antenna that can operate within the North America RFID band (902–928 MHz) is studied. To generate circular polarization (CP) radiation in this band, a novel method of loading two narrow open‐ended slots (slits) into an eccentric annular slot patch is proposed. To allow optimum impedance matching with enhanced CP bandwidth, the radiating patch is loaded to an L‐shaped ground plane. From the experimental results, the proposed antenna can yield an impedance bandwidth (10‐dB return loss) between 650 MHz to 1125 MHz, while good CP bandwidth (3‐dB axial ratio, AR) from 901 MHz to 930 MHz is also attained. Furthermore, gain level and efficiency of more than 7.8 dBic and 90%, respectively, were also measured. By simply removing one of the slits, this proposed antenna can also be modified to operate within the China (840–846 MHz) and European (865–868 MHz) RFID band.     

Circularly polarized planar monopole antenna for ultrawideband applications

A broadband circularly polarized (CP) planar monopole antenna is proposed here for ultrawideband (UWB) communication. The antenna is composed of a modified annular ring patch fed by a tapered microstrip line and a rectangular semiground plane on the opposite side of the substrate. Capability of generating wide axial ratio bandwidth (ARBW) is another feature of the proposed antenna. Wide ARBW is achieved by introducing a rectangular slot and a stub in the ground plane. The CP antenna has an impressive ARBW of 5.52 GHz (81.42%, 4.02‐9.54 GHz) within the UWB frequency range (3.1‐10.6 GHz). Measured 10‐dB return loss bandwidth of the proposed antenna is 120.86% centered at 7.48 GHz (2.96‐12 GHz). The proposed antenna is well used for wireless local area network (5.2 and 5.8 GHz), Worldwide Interoperability for Microwave Access (5.5 GHz), and other wireless systems in C band as well as CP‐UWB antenna communication.     

Fork‐shaped patch printed ultra‐wideband slot antenna with dual band‐notched characteristics using metamaterial unit cells

In this article, a miniaturized fork‐shaped patch ultra‐wideband (UWB) planar wide‐slot antenna with dual band‐notched characteristics is proposed. With fork‐shaped patch, ultra‐wideband impedance matching from 3.1 to 13.2 GHz is easily achieved. Then, two novel and simple methods are applied to solve the difficulty for UWB slot antennas with fork‐shaped patch to realize band‐notched characteristics. By etching one pair of I‐shaped resonators on both branches of the fork‐shaped structure and adding a rectangular single split‐ring resonator in the rectangular openings of fork‐shaped patch, the wireless local area network (WLAN) band from 5.5 to 6.1 GHz and the International Telecommunication Union (ITU) 8 GHz band from 7.9 to 8.7 GHz are rejected, respectively. The coplanar waveguide‐fed UWB antenna is successfully designed, fabricated, and measured. The measured and simulated results show a good agreement. The antenna provides nearly stable radiation patterns, high gains and high radiation efficiency.     

A modified split ring resonator based printed compact monopole UWB antenna with spiked elliptical radiator having five band rejection features

A coplanar waveguide (CPW) fed printed compact monopole antenna with five band rejection features is presented. Wide bandwidth was achieved by beveling the lower part and adding a modified ellipse on the upper portion of the patch. An inverted circular arc, single circular split ring resonator (SRR) with wide opening and two symmetrical circular single SRRs were embedded for obtaining three stop‐band characteristics. Two symmetrical slits were inculcated in the ground forming defected ground structure (DGS) to get another stop‐band characteristic. Two concentric rectangular modified SRRs were etched to obtain a higher frequency stop‐band feature. The proposed antenna was designed, fabricated, and experimentally tested for the validation of results. The overall dimensions of the proposed antenna were 29 mm × 24 mm × 1.6 mm. The measured impedance bandwidth of the antenna was 2.87 to 13.3 GHz at | S₁₁ |< ? 10 dB. The measured results show that the proposed antenna has five band notches centred at 3.96, 4.35, 5.7, 8.54, and 9.95 GHz to reject WiMAX band (3.65‐4.04 GHz), ARN band (4.29‐5.18 GHz), WLAN band (5.5‐6.9GHz), ITU‐8 band (7.37‐8.87), and amateur radio band (9.2‐10.3 GHz) respectively. The proposed antenna maintains omnidirectional radiation pattern in H‐Plane and dumbbell‐shape radiation pattern in E‐plane. Further, stable gain over the whole UWB except at notched frequency bands was reported.     

SIW cavity‐backed 24° inclined‐slots antenna for ISM band application

In this article, a novel resonant series slot linearly polarized antenna is realized using substrate integrated waveguide (SIW) technology for industrial scientific medical radio band (ISM) at 5.8 GHz. The proposed antenna consists of two 24° inclined slots and two metallic vias to produce alternate inductive and capacitive loads. The rectangular slots are introduced at the top metallic surface at an angle of 24° from the Y‐axis to excite a hybrid mode (TE₁₁₀ + TE₁₂₀) near to the modified cavity mode TE₁₂₀. The resonant slots are excited with the help of an inset microstrip feedline which retain its planar integrability. The slots are excited to resonate in the TE₁₂₀ mode at 5.8 GHz. To enhance the bandwidth, the location of two shorting vias are optimized in proximity to the slots. These vias help to couple the hybrid mode and the cavity modes in the desired frequency band, which leads to enhancement in the bandwidth significantly. The proposed geometry is fabricated and experimentally verified. The measured and simulated results depict a good co‐relation which show measured ?10 dB fractional bandwidth of 5.2% with a maximum gain of 7.15 dBi and the front to back ratio better than 15 dB at 5.8 GHz.     

An SRR based miniature implantable antenna with a slit loaded ground at MedRadio and ISM bands for biotelemetry applications

A miniaturized implantable microstrip split‐ring antenna (IMSRA) is proposed for wireless biotelemetry. The IMSRA takes up a miniaturized volume of 153.35 mm³ (10.5 × 11.5 × 1.27) and provides a dual‐band operation in 360 to 620 MHz and 2.32 to 2.54 GHz that covers The Medical Device Radiocommunications Service (MedRadio) (401‐406 MHz) and Industrial, Scientific, and Medical (ISM) (433‐434 MHz and 2.4‐2.48 GHz) bands. The principal part of the radiator consists of three homocentric split‐ring elements. In addition, three conductor paths located between the split rings are used for precise adjustment of the frequency. In order to reduce the antenna size, a shorting pin is appropriately inserted between one of the metallic rings and the ground plane. The impedance matching of the antenna is improved by the use of a hook‐shaped slit placed on the ground plane. For verification of the in vivo operation, the proposed IMSRA was measured in two separate skin‐mimicking gels for MedRadio and ISM bands. A prototype was also tested in the skin tissue sample of a donor rat. The proposed antenna offers 53% (360 ~ 620 MHz) bandwidth at 490 MHz and 9% (2.32 ~ 2.54 GHz) bandwidth at 2.43 GHz. The IMSRA exhibits well‐behaved radiation patterns and SAR values at the respective bands.     

Planar integrated substrate integrated waveguide circularly polarized filtering antenna

A new design of substrate integrated waveguide (SIW) circularly‐polarized (CP) filtering antenna is presented, which is based on dual‐mode (TE₁₀₂ and TE₂₀₁) cavities. The satisfying filtering performance of the antenna is realized by a coupled‐resonator circuit of two dual‐mode SIW cavities. And the radiating element of the antenna is a cavity‐backed CP slot antenna which is formed by a nonuniform ring slot integrated with the back cavity. To demonstrate the idea, a prototype antenna operating at X band is designed, fabricated, and measured. Measured results show that the 10‐dB impedance bandwidth is 4.2% (from 11.6 to 12.1 GHz), the 3‐dB axial‐ratio (AR) bandwidth is 4%, and the gain is 5.6 dBi at the center frequency of 11.8 GHz.     

Broadband circularly polarized printed falcate‐shaped monopole antenna

In this study, a simple broadband circularly polarized (CP) printed monopole antenna for S/C‐band applications is proposed. The CP antenna is composed of a falcate‐shaped monopole with a right‐angle trapezoid stub, then wide impedance and axial ratio (AR) bandwidths are achieved. By placing one rectangular split‐ring resonator above the stub for generating upper CP mode, both of impedance and CP performances are further improved. The proposed antenna is fabricated on a FR4 substrate and measured. The measured ?10‐dB impedance bandwidth is 107%, ranging from 2.4‐7.9 GHz, and the measured 3‐dB AR bandwidth is 94% (2.4‐6.6 GHz), covering the entire wireless local area network (WLAN) and WiMAX bands.     

Reconfigurable ultra‐wideband monopole antenna with single‐, dual‐, and triple‐band notched functions

A miniaturized ultra‐wideband (UWB) monopole antenna with reconfigurable multiple‐band notched performance is demonstrated. By modifying the shape of the patch and the ground plane, the UWB operation is achieved. The first and second band‐notches are respectively generated by etching a rectangular slot with open ends and a U‐shaped slot in the patch, and the third band‐notch is produced by loading a C‐shaped parasitic element beneath the patch. To realize the reconfigurable band‐notched functions, four PIN diodes are inserted in three band‐rejected structures. The antenna has a compact dimension of 30 mm × 26 mm. It can switch between a UWB state and several band‐notch states by alternating the states of the diodes. Also, good radiation patterns are obtained.     

A dual‐band half‐mode substrate integrated waveguide‐based antenna for WLAN/WBAN applications

A dual‐band half‐mode substrate integrated waveguide (HMSIW) based cavity‐backed antenna is proposed for WLAN/WBAN applications at 5/5.8 GHz, respectively. A semi‐hexagonal slot is introduced on the top plane of the cavity primarily for radiation. This slot offers miniaturization for both the TM₂₁₀ and TM₀₂₀ modes. Later on, two rectangular slits are loaded on the open edge of the patch, to provide miniaturization and tuning mainly for the higher frequency band. The performance of the proposed antenna is investigated in free space and in proximity of the pork tissues. In free space conditions, the measured ?10 dB fractional bandwidths are 3% and 3.1% along with peak gains of 6.25 and 6 dBi for the frequency bands at 5 and 5.8 GHz, respectively. In proximity of the pork tissues, the measured fractional bandwidth is 3.2% along with the efficiency of 81.5% at 5.8 GHz. The specific absorption rate (SAR) is 0.48 mW/g averaged over 1 g of tissues with 100 mW input power.     

A dual‐band dual‐polarized end‐loaded quasi‐open‐sleeve dipole antenna with stable pattern for wireless local area network applications

This article presents a dual‐band dual‐polarized end‐loaded quasi‐open‐sleeve dipole antenna (ELQOSDA) with stable radiation patterns for WLAN applications. The ELQOSDA consists of an end‐loaded planar dipole and two parasitic strips. Dual polarization is obtained by two ELQOSDAs perpendicularly crossing, with some parts overlapped. The unidirectional stable radiation patterns are achieved by adding a square resonance ring between the ground plane and antenna. The ring has little influence on antenna performance at the lower frequency, but improves the coupling currents between the ground and antenna at the upper frequency. As a result, satisfactory dual band and broadside radiation performance is obtained. For demonstration, the proposed antenna is implemented. Measured dual‐band 10‐dB impedance bandwidths are 9.4% (2.33‐2.56 GHz) and 33.5% (4.23‐5.93 GHz) in the lower and upper bands, covering the entire WLAN 2.4/5.2/5.8‐GHz bands. Moreover, the measured antenna has a 6.7‐8.1 dBi broadside gain and stable radiation patterns over the whole operating band.