Showing papers on "Slot antenna published in 2013"
TL;DR: In this article, a metasurface (MS) is used to convert the linearly polarized (LP) signal from a source antenna into a circularly polarized (CP) signal.
Abstract: A metasurface (MS) used to convert the linearly polarized (LP) signal from a source antenna into a circularly polarized (CP) signal is proposed and studied. The MS consists of 16 unit cells arranged in a 4 × 4 layout. Each unit cell is a rectangular loop with a diagonal microstrip. By placing close to a source antenna, the MS converts the LP signal generated from the source antenna into a CP signal. Two source antennas (patch and slot antennas) are used for studies. The source antenna together with the MS is here called a MS antenna. A total of four low-profile MS antennas operating at the frequency of about 2.45 GHz are designed using computer simulation. For verification of simulation results, the MS antennas are fabricated and measured. Simulated and measured results show good agreements. Results show that the MS antennas have substantially better performances, in terms of gain, return-loss bandwidth (RLBW), axial-ratio bandwidth (ARBW) and radiation pattern, than the source antennas. Moreover, the ARBW of the MS antennas is mainly determined by the MS.
518 citations
Journal Article•
TL;DR: A review of the past and current technologies applicable to reconfigurable antennas, with several examples of implementations, can be found in this article, where both mechanically movable parts and arrays are discussed, as well as more recent semiconductor component and tunable material technologies.
Abstract: Reconfigurable antennas change polarization, operating frequency, or far-field pattern in order to cope with changing system parameters. This paper reviews some of the past and current technology applicable to reconfigurable antennas, with several examples of implementations. Mechanically movable parts and arrays are discussed, as well as more-recent semiconductor-component and tunable-material technologies applicable to reconfigurable antennas.
435 citations
TL;DR: Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas, which makes it a good candidate for the wearable telemedicine application.
Abstract: We present a flexible, compact antenna system intended for telemedicine applications. The design is based on an M-shaped printed monopole antenna operating in the Industrial, Scientific, and Medical (ISM) 2.45 GHz band integrated with a miniaturized slotted Jerusalem Cross (JC) Artificial Magnetic Conductor (AMC) ground plane. The AMC ground plane is utilized to isolate the user's body from undesired electromagnetic radiation in addition to minimizing the antenna's impedance mismatch caused by the proximity to human tissues. Specific Absorption Rate (SAR) is analyzed using a numerical human body model (HUGO) to assess the feasibility of the proposed design. The antenna expresses 18% impedance bandwidth; moreover, the inclusion of the AMC ground plane increases the front to back ratio by 8 dB, provides 3.7 dB increase in gain, in addition to 64% reduction in SAR. Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas. Furthermore, it offers a compact and flexible solution which makes it a good candidate for the wearable telemedicine application.
349 citations
TL;DR: In this article, a dual-band rectenna operating at 915 MHz and 2.45 GHz was proposed, which is optimized for low input power densities using harmonic balance (HB) simulation.
Abstract: A compact dual-band rectenna operating at 915 MHz and 2.45 GHz is presented. The rectenna consists of a slot-loaded dual-band folded dipole antenna and a dual-band rectifier. The length of the proposed antenna is only 36.6% of the half-wavelength $(\lambda_{0}/2)$ dipole antenna at 915 MHz while keeping dual-band property at 915 MHz and 2.45 GHz. The rectifier circuit is optimized for low input power densities using harmonic balance (HB) simulation. The efficiencies of the rectifier are evaluated with both single- and dual-frequency input signals. The measured results show an efficiency of 37% and 30% at 915 MHz and at 2.45 GHz when illuminated by a microwave signal of available power of $-$ 9 dBm for a load resistor of 2.2 k $\Omega$ .
207 citations
TL;DR: In this article, the authors investigated the application of metamaterial absorber (MA) to waveguide slot antenna to reduce its radar cross section (RCS) and demonstrated that the monostatic and bistatic RCS of the slot antenna are reduced significantly, and the performance of antenna is preserved simultaneously.
Abstract: This communication investigates the application of metamaterial absorber (MA) to waveguide slot antenna to reduce its radar cross section (RCS). A novel ultra-thin MA is presented, and its absorbing characteristics and mechanism are analyzed. The PEC ground plane of waveguide slot antenna is covered by this MA. As compared with the slot antenna with a PEC ground plane, the simulation and experiment results demonstrate that the monostatic and bistatic RCS of waveguide slot antenna are reduced significantly, and the performance of antenna is preserved simultaneously.
181 citations
TL;DR: Convex optimization is used to determine current distributions that provide upper bounds on the antenna performance and formulations for maximal gain Q-Factor quotient, minimal Q-factor for superdirectivity, and minimum Q for given far-fields are presented.
Abstract: The high Q-factor (low bandwidth) and low efficiency make the design of small antennas challenging. Here, convex optimization is used to determine current distributions that provide upper bounds on the antenna performance. Optimization formulations for maximal gain Q-factor quotient, minimal Q-factor for superdirectivity, and minimum Q for given far-fields are presented. The effects of antennas embedded in structures are also discussed. The results are illustrated for planar geometries.
173 citations
TL;DR: In this paper, a frequency reconfigurable microstrip patch switchable to slot antenna is proposed, which is capable of frequency switching at nine different frequency bands between 1.98 and 3.59 GHz.
Abstract: A frequency-reconfigurable microstrip patch switchable to slot antenna is proposed. The antenna is capable of frequency switching at nine different frequency bands between 1.98 and 3.59 GHz. The patch is resonating at 3.59 GHz, while the slot produces eight different operating frequencies between 1.98 and 3.41 GHz. Five RF p-i-n diode switches are positioned in the slot to achieve frequency reconfigurability. Simulated and measured results are used to demonstrate the performance of the antenna. The simulated and measured return losses, together with the radiation patterns, are presented.
159 citations
Proceedings Article•
08 Apr 2013TL;DR: This paper presents a unique review and survey of RF MEMS antennas, which can be categorized into (i) generic antennas and (ii) antenna circuits.
Abstract: RF MEMS technology can offer enhanced performance over the conventional solid-state devices. Along with other RF MEMS components, antennas have been investigated. This paper presents a unique review and survey of RF MEMS antennas. Here, antennas can be categorized into (i) generic antennas and (ii) antenna circuits. The former employs some forms of mechanical actuation for movements of the radiation elements. With the latter, individual radiation elements are physically stationary and integrated with RF MEMS switches and/or variable capacitors to alter their electrical length and diversity. In addition, (iii) antenna subsystems incorporating RF MEMS tuneable circuits and beam forming networks should not be overlooked. Examples of these antenna categories are described and conclusions drawn.
158 citations
Patent•
25 Jan 2013TL;DR: In this paper, a surface wave plasma source including an electromagnetic (EM) wave launcher comprising a slot antenna having a plurality of antenna slots configured to couple the EM energy from a first region above the slot antenna to a second region below the slot antennas, and a power coupling system is coupled to the EM wave launcher.
Abstract: The present invention provides a surface wave plasma source including an electromagnetic (EM) wave launcher comprising a slot antenna having a plurality of antenna slots configured to couple the EM energy from a first region above the slot antenna to a second region below the slot antenna, and a power coupling system is coupled to the EM wave launcher. A dielectric window is positioned in the second region and has a lower surface including the plasma surface. A slotted gate plate is arranged parallel with the slot antenna and is configured to be movable relative to the slot antenna between variable opacity positions including a first opaque position to prevent the EM energy from passing through the first arrangements of antenna slots, and a first transparent position to allow a full intensity of the EM energy to pass through the first arrangement of antenna slots.
151 citations
TL;DR: In this paper, two novel preprocessing techniques are applied to reinforce the detection performance and image quality in microwave imaging systems designed for brain stroke detection, which are validated on a realistic head phantom that is fabricated to emulate the electrical properties of real human head.
Abstract: Two novel preprocessing techniques are applied to reinforce the detection performance and the image quality in microwave imaging systems designed for brain stroke detection. The image of energy distribution is obtained by applying a delay-and-sum beamforming to the backscattered signals measured using a hemielliptical array of 16 corrugated tapered slot antenna elements surrounding the head. The beamformer forms a spatially filtered combination of time-delayed response of scattering points in the head exposed to microwave radiation over the band from 1 to 4 GHz. The proposed techniques are validated on a realistic head phantom that is fabricated to emulate the electrical properties of real human head. The results show how the proposed techniques enable the detection and localization of hemorrhagic stroke accurately.
146 citations
TL;DR: In this article, the authors proposed a U-slot patch antenna design for single-layer and single-single-patch communication with U-slotted U-Slots in a broadband U-beam antenna.
Abstract: Recently, it was shown that a dual- or triple-band patch antenna can be designed by cutting U-slots in the patch of a broadband antenna, and the method was applied to the L-probe fed patch, the M-probe fed patch, coax-fed stacked patches, and aperture coupled stacked patches. All these cases involve either a rather complicated feed, or more than one patch, or more than one layer. In this communication, this method is applied to a broadband U-slot patch antenna. When one additional U-slot patch is cut in the patch, a dual-band antenna results. When two additional U-slot patches are cut in the patch, a triple-band antenna results. The advantages of the resultant configurations are (1) the feed is simple and (2) the structures remain single-layer and single-patch. Both simulation and measurement results are presented to demonstrate the feasibility of this design.
TL;DR: In this article, a novel antipodal Vivaldi antenna (AVA) is proposed, which improves the low-end operating frequency by 9% with the dimension unaltered, while the radiation patterns at higher frequencies are improved due to the loaded lens and the choke slot edges (CSE) configuration at the termination of the flares.
Abstract: A novel antipodal Vivaldi antenna (AVA) is proposed in this letter. The addition of regular slot edges (RSE) helps the antenna lower the low-end operating frequency by 9% with the dimension unaltered, while the radiation patterns at higher frequencies are improved due to the loaded lens and the choke slot edges (CSE) configuration at the termination of the flares, which also contribute to the enhancement of antenna gain. The improved antenna is fabricated and verified experimentally. The measured results coincide with the simulated ones perfectly, which proves the feasibility of the novel design.
TL;DR: In this paper, a compact asymmetric-cross slotted square patch antenna is proposed for circularly polarized (CP) radiation with a small antenna volume of 0.292λo × 0.0308λo on a low cost FR4 substrate.
Abstract: Compact, asymmetric\symmetric-slotted\slit-microstrip patch antennas on reactive impedance surface (RIS) are proposed and studied for circularly polarized (CP) radiation. The antennas consist of a slotted-slit-microstrip patch on a RIS substrate. The CP radiation with compact size is achieved by asymmetric\symmetric-slot-slit cut along the orthogonal\diagonal directions of the patch radiator. The asymmetric\symmetric-slotted\slit microstrip patches on the RIS structure are used for further miniaturization of the antenna with improvement in CP radiation. The measured results of the compact asymmetric-cross slotted square patch antenna are 1.6% (2.51-2.55 GHz) for 3-dB axial ratio bandwidth, 5.2% (2.47-2.60 GHz) for 10-dB return loss bandwidth, and 3.41 dBic for gain over 3-dB axial ratio bandwidth. The overall antenna volume is 0.292λo × 0.292λo × 0.0308λo on a low cost FR4 substrate at 2.5 GHz.
TL;DR: In this paper, the authors examined the structure needed to achieve high output power in resonant tunneling diode (RTD) oscillators in the terahertz range.
Abstract: We report the theoretical and experimental results of an examination of the structure needed to achieve high output power in resonant tunneling diode (RTD) oscillators in the terahertz range. An offset-fed slot antenna and antenna width adjustments were employed in a single oscillator to increase the output power by increasing the radiation conductance and impedance matching. A high output power oscillation (~400 μW) at 530-590 GHz was obtained by RTDs with a large negative deferential conductance (NDC) region and offset-fed slot antennas. The maximization of the output power that was obtained by adjusting the antenna width was attributed to the impedance matching between the RTD and antenna. An output power of >;1 mW is theoretically expected in an oscillator that combines an RTD with a large NDC region, offset-fed slot antenna, and antenna width adjustment. In an array configuration, oscillators with an offset structure were employed for array elements and connected together with the metal-insulator-metal stub structure. A single peak was observed in the oscillation spectrum, and combined output powers of 610, 270, and 180 μW at 620, 770, and 810 GHz were obtained in a two-element array.
TL;DR: In this paper, a zero-index metamaterial (ZIM) structure is proposed for the gain enhancement of an antipodal tapered slot antenna (ATSA) at 60 GHz bands.
Abstract: A zero-index metamaterial (ZIM) structure is proposed for the gain enhancement of an antipodal tapered slot antenna (ATSA) at 60-GHz bands. The single ATSA loaded with the proposed ZIM cells exhibits a gain enhancement of up to 2.6 dB in the frequency band of 57–66 GHz. A prototype of a two-element ATSA array loaded with the ZIM cells measures a $\vert {\rm S}_{11} \vert$ of less than $-10~{\rm dB}$ and gain of 12–13.2 dBi over 57–66 GHz. The measurement results agree with the simulated ones and the gain enhancement of the ZIM cells is confirmed.
TL;DR: In this article, the authors proposed a reduced-size single-feed circularly-polarized (CP) patch antennas based on the strategy of combining meta-surfaces and meta-resonators owning strong space-filling capability.
Abstract: Reduced-size single-feed circularly-polarized (CP) patch antennas are proposed and investigated based on the strategy of combining meta-surfaces and meta-resonators owning strong space-filling capability. They all comprise a slot-loaded square patch printed over a well designed reactive impedance surface (artificial meta-surface with magnetic response at the resonant frequency) for improved antenna performances and size reduction. The complementary crossbar fractal tree (CCFT) slot and three-turn complementary spiral resonators (TCSRs) with asymmetric gap orientation are employed as meta-resonators to render the antennas to radiate CP waves in single-band or dual-band operation and to facilitate further miniaturization. Numerical and experimental results indicate that these antennas owning a maximum size of 0.262λ0 × 0.262λ0 around 3 GHz exhibit a comparable impedance and axial ratio (AR) bandwidth over 1.05% and high gain of more than 4.15 dBic, predicting promising applications in portable and handheld communication systems.
TL;DR: In this article, four band-notched antennas suitable for ultra-wideband (UWB) applications are proposed, and the results of both simulation and measurement confirm that the gain suppression of the single and multiple band notched antennas in each desired notched band are over 15 dB and 10 dB, respectively.
Abstract: To mitigate potential interferences with coexisting wireless systems operating over 3.3-3.6 GHz, 5.15-5.35 GHz, or 5.725-5.825 GHz bands, four novel band-notched antennas suitable for ultra-wideband (UWB) applications are proposed. These include UWB antennas with a single wide notched band, a single narrow notched band, dual notched bands, and triple notched bands. Each antenna comprises a half-circle shaped patch with an open rectangular slot and a half-circle shaped ground plane. Good band-notched performance is achieved by using high permittivity and low dielectric loss substrate, and inserting quarter-wavelength horizontal/vertical stubs or alternatively embedding quarter-wavelength open-ended slots within the feed line. The results of both simulation and measurement confirm that the gain suppression of the single and multiple band-notched antennas in each desired notched band are over 15 dB and 10 dB , respectively. The radiation pattern of the proposed triple band-notched design is relatively stable across the operating frequency band.
TL;DR: In this paper, a novel broadband CPW-fed circularly-polarized slot antenna with an open slot is presented, which can reach as large as 1000 MHz (27% relative to the center frequency of 3700 MHz) for the 3.3-3.8 GHz WiMAX band.
Abstract: A novel broadband CPW-fed circularly-polarized slot antenna with an open slot is presented. The broadband circular polarization can be achieved simply by opening the radiation slot at the lower left of slot. From the experimental results, the 3-dB axial-ratio bandwidth can reach as large as 1000 MHz (27% relative to the center frequency of 3700 MHz) which can cover the 3.3-3.8 GHz WiMAX band. In addition, the proposed design has the VSWR ≤ 2 impedance bandwidth of 5330 MHz (111% relative to the center frequency of 4795 MHz) which can cover the 2-6 GHz WiMAX band. The proposed antenna also has a peak antenna gain of about 5.3 dBic and gain variations can be less than 1 dBic for frequencies within the CP bandwidth.
TL;DR: In this article, a CPW slot loop fed Minkowski shaped fractal dielectric resonator antenna is proposed to bring higher order modes close together to realize a wide impedance bandwidth.
Abstract: A CPW slot loop fed Minkowski shaped fractal dielectric resonator antenna is proposed. Self similar property of fractal geometry is utilized to bring higher order modes close together to realize a wide impedance bandwidth. A comparative study of the resonant frequency behavior between the well established fractal electrical boundary antennas and fractal magnetic boundary antennas is presented to provide insight into the functionality of the proposed antenna. The comparison highlights the fact that electrical boundary lowers resonance frequency, whereas fractal magnetic boundary increases the resonant frequency. Minkowski fractal is also compared with Koch fractal and Sierpinski curve geometries. It is observed that the Minkowski fractal DRA yields the widest impedance bandwidth along with stable gain amongst the three proposed geometries. The proposed antenna exhibits a fractional bandwidth of 64% (5.52 -10.72 GHz) and a maximum gain of 4.9 dBi.
TL;DR: In this paper, a novel pattern reconfigurable antenna is proposed to achieve two different radiation patterns by controlling the bias voltage of switches, where the maximum radiation intensity occurs at the normal to the aperture surface defined as the boresight direction.
Abstract: A novel pattern reconfigurable antenna is proposed to achieve two different radiation patterns by controlling the bias voltage of switches. Initially, the proposed antenna operates as a top-loaded monopole antenna fed by a co-planar waveguide (CPW). When the slot from the CPW is disturbed by switching on PIN diodes, it operates as a slot antenna. Therefore, when the switch turns on, the maximum radiation intensity occurs at the normal to the aperture surface defined as the boresight direction, which is similar to a slot antenna. When the switch turns off, the maximum radiation intensity occurs at right angles to the boresight direction, which is similar to a monopole antenna. The pattern reconfigurable capability is successfully demonstrated at 2.3 GHz by full-wave simulation and measurement.
TL;DR: In this paper, an F-shaped microstrip slot antenna for WLAN and WiMAX multiple-input-multiple-output (MIMO) systems is presented, which consists of both open-ended and short-ended slots connected by a metal "via" to a microstrip line.
Abstract: A novel F-shaped microstrip slot antenna for WLAN and WiMAX multiple-input-multiple-output (MIMO) systems is presented. The proposed antenna structure consists of both open-ended and short-ended slots connected by a metal “via” to a microstrip line. The open-ended slot is exploited to obtain resonant mode at 2.4 GHz, and three short-ended slots are aimed to obtain resonant modes at 3.5, 5.2, and 5.8 GHz, whose center frequencies can be adjust by the slot lengths. The parametric studies show that the center frequencies are independent of each other. A four-element array configuration of the proposed antenna for MIMO applications is also studied. The simulation and measurement results of reflection coefficient, mutual coupling, and radiation pattern are presented, which attest to the applicability of antenna.
TL;DR: In this paper, the authors presented the synthesis of one-dimensional (line-source) leaky-wave antennas (LWAs) in substrate integrated waveguide (SIW) technology with modulated geometry, demonstrating the capability to flexibly tailor the radiated fields pattern, both in near and far field regimes.
Abstract: We present the synthesis of one-dimensional (line-source) leaky-wave antennas (LWAs) in substrate integrated waveguide (SIW) technology with modulated geometry, demonstrating the capability to flexibly tailor the radiated fields pattern, both in nearand far-field regimes. The synthesis technique is inspired in holographic concepts, which are related to the existence of modulated leaky waves. A systematic design algorithm to obtain the requested modulation of the SIW width and distance between posts to synthesize the desired radiation pattern is described. Several design examples operating at 15 GHz are reported and experimentally validated, showing the power and versatility of the proposed holographic SIW technology.
TL;DR: In this paper, a triple-band H-shaped slot antenna fed by microstrip coupling is proposed, and four resonant modes are excited, including a monopole mode, a slot mode, and their higher-order modes, to cover GPS (1.575 GHz) and Wi-Fi (2.4-2.485 GHz) respectively.
Abstract: A compact triple-band H-shaped slot antenna fed by microstrip coupling is proposed. Four resonant modes are excited, including a monopole mode, a slot mode, and their higher-order modes, to cover GPS (1.575 GHz) and Wi-Fi (2.4-2.485 GHz and 5.15-5.85 GHz), respectively. Sensitivity study of the slot geometry upon the resonant modes have been conducted. The measured gains at these four resonant frequencies are 0.2 dBi, 3.5 dBi, 2.37 dBi, and 3.7 dBi, respectively, and the total efficiencies are -2.5 dB, -1.07 dB, -3.06 dB, and -2.7 dB, respectively. The size of this slot antenna is only 0.24λ0×0.034λ0, where λ0 is the free-space wavelength at 1.575 GHz, hence is suitable to install on notebook PC's and handheld devices.
TL;DR: In this paper, a uniplanar slot antenna for ultrawideband (UWB) polarization-diversity applications is presented, which consists of an annular slot and orthogonal feeding mechanisms to achieve polarization diversity performance across the UWB from 2.8-11 GHz.
Abstract: A uniplanar slot antenna for ultrawideband (UWB) polarization-diversity applications is presented. The antenna consists of an annular slot and orthogonal feeding mechanisms to achieve polarization diversity performance across the UWB from 2.8–11 GHz. By introducing a cross-shaped strip diagonally between the two U-shaped stubs, an interport isolation better than 14 dB is accomplished except at the lower and higher frequency end. The notch band from 5.0–6.3 GHz is realized by embedding arc-shaped slot resonators on the feeding structures. The proposed antenna facilitates nearly omnidirectional radiation pattern, low envelope correction coefficient, moderate gain, and efficiency. Moreover, the time-domain analysis displays minimum dispersion to the radiated pulse. All these features make the proposed antenna a good candidate for future wireless communication systems with polarization-diversity operation, where the challenge such as multipath fading is a major concern.
TL;DR: In this paper, a novel wide-slot ultrawideband (UWB) antenna with dual band-notched characteristics is presented, which consists of an inverted U-shaped slot on the ground plane and a radiation patch similar to the slot that is fed by a 50-Ω microstrip line.
Abstract: A novel compact wide-slot ultrawideband (UWB) antenna with dual band-notched characteristics is presented. The antenna consists of an inverted U-shaped slot on the ground plane and a radiation patch similar to the slot that is fed by a 50-Ω microstrip line. By etching a C-shaped slot on the radiation patch and extruding an L-shaped stub from the ground plane, dual band-notched properties in the WiMAX (3.4-3.69 GHz) and WLAN (5.15-5.825 GHz) are achieved. The proposed antenna has a compact size of 20×27 mm2 and operates from 2.89 to 11.52 GHz. Furthermore, nearly omnidirectional radiation patterns and constant gain are obtained in the working band.
TL;DR: In this article, a new broadband circularly polarized (CP) printed-slot antenna fed by a coplanar waveguide (CPW) is designed and fabricated and good agreement is achieved between the simulation and measurement, which shows that the presented antenna covers an impedance bandwidth (S11 <; -10 dB) of 104% from 1.78 to 5.64 GHz, and a 3-dB axial-ratio bandwidth (ARBW) of 58.6% from 2.85 to5.21 GHz.
Abstract: In this letter, a new broadband circularly polarized (CP) printed-slot antenna fed by a coplanar waveguide (CPW) is designed and fabricated. To achieve a broadband CP wave, an S-shaped slot is employed in the ground to produce orthogonal surface currents for right-hand circular polarization (RHCP). Furthermore, an L-shaped radiator is introduced to obtain a broad impedance bandwidth that can cover the whole CP bandwidth completely. Good agreement is achieved between the simulation and measurement, which shows that the presented antenna covers an impedance bandwidth (S11 <; -10 dB) of 104% from 1.78 to 5.64 GHz, and a 3-dB axial-ratio bandwidth (ARBW) of 58.6% from 2.85 to 5.21 GHz. The surface current analysis and a parametric study of the design are also carried out to explain the mechanism of circular polarization.
TL;DR: The proposed antenna could be a suitable candidate for advanced and smart radio applications such as cognitive radio (CR) as it can enhance the radio front-end flexibility and performance by adding the benefits of pattern diversity, specifically in multipath environments.
Abstract: A novel pattern-reconfigurable compact planar ultra-wideband monopole antenna is presented. By the incorporation of four p-i-n diode switches and two parasitic elements, the antenna's radiation patterns can be shaped to concentrate energy in specific directions while minimising the gain in other unwanted directions without significantly affecting the impedance bandwidth of the antenna. A fully functional prototype has been developed and tested. The measured results of the return loss, radiation patterns, and realised gain verify the effectiveness of the proposed antenna configuration. The antenna switches its radiation patterns between an omni-directional mode and two directional modes with opposite directions in the operating range from 3 to 6 GHz. The proposed antenna could be a suitable candidate for advanced and smart radio applications such as cognitive radio (CR) as it can enhance the radio front-end flexibility and performance by adding the benefits of pattern diversity, specifically in multipath environments.
TL;DR: In this article, the authors presented the investigation results on a novel circularly polarized square-slot antenna (CPSSA) array designed to operate at a frequency of 5.5 GHz.
Abstract: This letter presents the investigation results on a novel circularly polarized square-slot antenna (CPSSA) array designed to operate at a frequency of 5.5 GHz. In order to realize the proposed antenna array, four miniature circular polarized square-slot antennas are used with L-shape grounded strips located at the slots' opposite corners to reduce cross polarization. The antenna is fed by symmetric coplanar waveguide. The CPSSA element achieves a bandwidth of 16.6% for an axial ratio $\leq 3~$ dB. The CPSSA's performance is further enhanced with the construction of a novel 2 $\,\times\,$ 2 antenna array that is designed using sequentially rotated feed technique. The 3-dB axial ratio of the array extends to approximately 2 GHz with an impedance bandwidth of 31%. The CPSSA array was designed to operate over the frequency range between 4 and 6.825 GHz corresponding to an impedance bandwidth of 52% for ${\rm VSWR} (1.71:1). Acceptable agreement between the simulation and measured results validates the proposed design.
TL;DR: In this article, a complete mathematical model of microwave ablation using the porous media approach is proposed, which uses transient momentum equations (Brinkman model extended Darcy model) and energy equation coupled with electromagnetic wave propagation equation to describe the specific absorption rate (SAR) profile, temperature profile and blood velocity profile within the porous liver.