Conventional Slot Antenna Research Articles

Design of compact slot antenna and octagonal blended shape antenna

ABSTRACT In this paper, two new compact halved-size single and UWB antennas are proposed for WiFi and UWB applications. The single-band compact halved size slot antenna is proposed for WiFi applications at 2.4 GHz. The resonant frequency of the conventional slot antenna can be reduced by cutting the antenna into two halves and without using any lumped elements inside the slot. Moreover, the impedance and radiation characteristics of the proposed halved-size antenna are suitable for WiFi applications at 2.4 GHz. The proposed WiFi antenna has a miniaturised size of 25 × 16.5 × 0.813 mm3. Then, an octagonal blended-shape antenna (OBSA) for UWB applications is proposed. The UWB band from 3.1 GHz to 10.6 GHz is encompassed by the halved-size OBSA using the same cutting concept. Furthermore, a grounded L-stub is added on the top side to improve the reflection coefficients. The proposed OBSA has a compact size of 28 × 13 × 0.813 mm3 with stable omnidirectional radiation patterns. Simulation and measured results are in good agreement.

Design of Dual-Stopband Rectangular Waveguide Slot Array Antennas

A dual-stopband rectangular waveguide slot array antenna is presented in this paper. Firstly, a rectangular filtering waveguide with dual stopbands is realized by periodically loading a row of T-type resonators and a row of Π-type resonators on the bottom broad wall of the rectangular waveguide, and its dual-stopband characteristic is verified by analyzing the equivalent circuit and dispersion curve. Secondly, a dual-stopband rectangular waveguide slot array antenna is obtained by etching radiation slots on the top broad wall of the filtering waveguide. To verify the proposed concept, a dual-stopband rectangular waveguide four-slot array antenna is designed, fabricated, and measured. The measured results are in good agreement with the simulation ones. The results show that, compared with the conventional waveguide slot antenna, the proposed waveguide slot antenna has almost the same radiation performance in the –10 dB impedance bandwidth of 5.51–5.95 GHz, and achieves additional suppressions of greater than 24.5 dB in 6.6–7.1 GHz and 34.6 dB in 8.4–9.3 GHz, respectively, without occupying extra space.

Miniature tri‐polarized MIMO slit‐postwall step impedance resonator slot antenna array

A miniaturized tri-polarized MIMO slot antenna loaded with slit-postwall-slot step impedance resonator (SIR) is proposed. The SIR, which shortens the length of radiation slot for the miniature purpose, consist of two slit-slot lines with high impedance and a slit-postwall-slot line with low impedance, because the postwall can decrease the characteristic impedance of slit-slot line. Meanwhile, the slits can improve the polarization purity and isolation of the antenna array effectively. Compared with the conventional slot antenna array, the measured results of proposed antenna array shows that the cross-polarization ratio has improved 2 dB on H plane and 3 dB on E plane at 2.45 GHz, while the lengths of ground plane and slot are shortened 77.8% and 77%, respectively. Furthermore, the proposed antenna array operates at dual band and the isolation are −22 dB at 2.45 GHz and -27 dB at 4 GHz. The performance and structure of the proposed antenna array can be applied for the condition of high polarization purity and demanding volume.

Broadband Circularly Polarized Rectenna With Wide Dynamic-Power-Range for Efficient Wireless Power Transfer

This paper presents a circularly polarized (CP) rectenna with the advantage of achieving high efficiency in both wide operating power and frequency ranges. The proposed rectenna is composed of a high-efficiency rectifier and broadband CP antenna. In the proposed rectifier, a novel wideband resistance compression technique is presented, highly improving the matching performance of the circuit in a wide range of input power and frequency. The technique is achieved by an impedance manipulation network and a coupled-lines-based resistance compression network (RCN). Theoretical analysis is carried out and closed-form equations are derived for the design of the rectifier. Simulated and measured results show that over 60% (up to 76%) conversion efficiency is achieved for the input power range of 5-17 dBm and frequency band of 1.7-2.9 GHz (mobile, Wi-Fi and ISM bands). Subsequently, unlike the conventional half-wavelength slot antenna, a compact CP antenna with a side length of quarter wavelength is designed by using a 1-wavelength loop slot and a coupled-line-based phase shifter. It has wide axial-ratio bandwidth and good radiation pattern. At last, by integrating the proposed rectifier together with the CP slot antenna, a broadband CP rectenna is completed with higher efficiency by about 18.6% than that without wideband RCN.

A Wideband Substrate Integrated Waveguide-Fed Open Slot Antenna

In this article, we introduce a new structure of an open slot antenna excited by a substrate-integrated-waveguide (SIW) feed to obtain a wide bandwidth of about 60%. Different from conventional slot antennas, two short sides of the slot are open which do not connect to any metal. To excite the open slot, an SIW section is used as the feed. In this way, the antenna is constructed on a single laminate which includes the feeding structure and the radiator. The open slot structure serves as a single-mode resonator with a low Q-factor and, thus, contributes a much wider bandwidth than that of conventional slot antennas and simultaneously maintains stable radiation performance. Intensive parametric studies were implemented to provide a design guideline. To verify our design, antenna prototypes were fabricated and measured. The measured results validate that the antenna achieves a wide impedance bandwidth of 59.3% from 50.8 to 93.6 GHz. Meanwhile, the radiation patterns keep stable over the entire operating frequency band. This new type of slot antenna with wide bandwidth and planar structure is a good candidate for mmW applications.

Resonator-Loaded Multi-Band Microstrip Slot Antennas With Bidirectional Radiation Patterns

In this communication, an approach for designing multi-band microstrip slot antennas is proposed. Multiple resonators are loaded on a conventional microstrip slot antenna to introduce multiple resonances. The number of the operational bands of the antenna can be easily controlled by varying the number of the loading resonators. The locations of each resonance can be adjusted by varying the positions and lengths of the loading resonators together with the geometry of the slot if necessary. For validation, prototypes with dual-, tri-, and quad-band operations are designed, fabricated, and measured. Since no modified slot is used in this design method, all the operating bands show good bidirectional radiation patterns. The measured and simulated results agree well. The proposed antenna features low profile, small radiating slot, and easy fabrication, showing promising application prospect for modern communication system.

Microstrip slot antenna as an indoor wireless RFID with multiband attributes based on composite right‐hand/left‐hand load

AbstractThe goal of the present work is to present a slot antenna for wireless application based on a stack layer and composite right‐hand/left‐hand technique to achieve a multiband characteristic together with miniaturization and gain enhancement. This antenna covers 1.825 to 1.975 GHz for global system for mobile communications 1800, 2.9 to 4.3 GHz for long‐term evolution (LTE) and Worldwide Interoperability in Microwave Access, and 5.2 to 5.8 GHz for Wi‐Fi networks with the return loss of less than −6 dB (VSWR<3). We used a slit ring resonator structure with four vias and strip as the left‐hand circuit. We have also utilized a disk at the center of the top layer to improve the bandwidth and matching. We present the equivalent RLC circuit model for the final antenna which can help us realize the role of capacitance and inductances based on parametric studies. Both layers are fabricated over the FR4 substrate, and experimental results confirm the simulation results obtained by the HFSS. Moreover, the stack layer provides higher directivity and gain in comparison with the conventional slot antenna.

Design of a Microwave Global Endometrial Ablation Device

Endometrial ablation is a minimally invasive treatment employed for thermal coagulation of the endometrial lining of the uterus for treatment of menstrual heavy bleeding. Here, we present an applicator employing a microwave loop antenna for global endometrial ablation enabling conformal ablation of uterine cavities of varying size in the range 4–6.5 cm in length and 2.5–4.5 cm in width, with a single positioning of the device. For treating large cavities, conformal microwave radiation is achieved by coupling the loop antenna with a passive element. A 3-D-coupled finite element method electromagnetic and heat transfer simulator was employed to optimize the antenna geometry with the goal of maximizing return loss at the 915 MHz operating frequency, and achieving adequate ablation depths for a range of uterine cavity sizes. Proof-of-concept devices were fabricated and experimentally evaluated in ex vivo tissue. The simulated and measured return loss of the optimized design was 20 dB at 915 MHz. Experiments in ex vivo tissue demonstrated the ability of the presented device to achieve mean ablation depths of 7.3 mm. We demonstrated a technique for creating planar ablation patterns suitable for global endometrial ablation of different uterine cavity sizes by employing a loop antenna with a passive element. Our design provides a planar ablation pattern by using a loop antenna with a passive element that will allow for ablation applications not realizable with conventional coaxial monopole, dipole, and slot antennas.

Wideband terahertz imaging pixel with a small on-chip antenna in 180 nm CMOS

We propose a Si-CMOS terahertz image sensor to resolve paucity of low-cost and small-size detectors. The imaging pixel consists of an on-chip antenna and an amplifier acting as envelope detector. The pixel uses a microstrip patch antenna for receiving THz waves. However, the antenna’s narrow bandwidth and large ground plane size causes major problems. A low-resistivity Si substrate degrades the gain of planar antennas besides the microstrip patch antenna. We introduce an on-chip folded-slot antenna to reduce the pixel size and prevent gain degradation due to the Si substrate. The antenna has a broader bandwidth and higher gain than conventional on-chip slot antenna. We fabricated the patch/folded-slot types of the pixel circuits by using 0.18 μm CMOS process. Measurement results show that the folded-slot antenna has a broader bandwidth from 850 GHz to 1.05 THz.

A Substrate Integrated Cavity Backed Filtering Slot Antenna Stacked With a Patch for Frequency Selectivity Enhancement

A patch is proposed to stack above a substrate integrated cavity (SIC) backed filtering slot antenna to enhance antenna frequency selectivity. The antenna is composed of a slot radiator backed by an SIC, a stacked patch, and a microstrip feed line. Two parallel slots are cut onto the top broad wall of the SIC, which is excited by a microstrip line through a nonresonant short slot on the center of the bottom broad wall. The stacked patch is positioned right above the SIC supported by a piece of substrate slab for gain enhancement. Compared with the traditional SIC-backed slot antenna, the proposed antenna achieves higher frequency selectivity as well as enhanced bandwidth and gain. The field distribution and parametric study are conducted to exhibit the operating mechanism of the antenna more clearly. Compared with the conventional SIC-backed slot antenna, the antenna prototype operating at 10 GHz, as example, achieves wider 10 dB impedance matching bandwidth of 8.67%, higher gain of 7.2 dBi, better frequency selectivity of 0.9/0.45 at the lower and upper edges of the operation band, and lower maximum cross-polarization levels of -23/-22 dB in E- and H-planes within the 3 dB beam range, respectively.

Dual-Patch Polarization Conversion Metasurface-Based Wideband Circular Polarization Slot Antenna

In this paper, a novel polarization conversion (PC) structure is introduced, and its use with a wideband, wide 3-dB axial-ratio (AR) beam, low-radar-cross-section (RCS) circular polarization (CP) slot antenna is suggested. The unit cell of the proposed PC metasurface (PCM) consists of square and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -shaped patches separated by an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -shaped slot printed on an FR4 substrate. The mechanisms for linear to circular polarization and bandwidth improvement of a conventional antenna are analyzed theoretically. Through numerical optimizations and parametric studies, a simulated 10-dB impedance bandwidth of 42.7% (4.15–6.4 GHz) and a 3-dB AR bandwidth of 26.2% (4.8–6.25 GHz) are achieved by the proposed antenna. As the simulation demonstrates, the proposed antenna achieves an average 20-dB RCS reduction in a wide band from 5.25 to 6.8 GHz compared with a conventional slot antenna covered by the PC band. In addition, compared with the previously reported work, the PCM-based CP antenna exhibits a larger 3-dB AR beam width of 200° in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xoz</i> plane and 120° in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">yoz</i> plane, and a wider CP bandwidth within the operational bandwidth. Finally, an overall volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.55\lambda _{0}\times 0.55\lambda _{0}\times 0.05\lambda _{0}$ </tex-math></inline-formula> centered at 5.275 GHz is fabricated and measured, demonstrating good agreement with the simulation results.

Efficient design of electrically small antenna using metamaterials for wireless applications

In this paper, a simple and efficient approach is presented for the design of a compact CPW fed slot antenna loaded with complementary split ring resonators (CSRRs) and metamaterial (MTM) slab. It has been shown that the fundamental resonant frequency of the conventional slot antenna can be lowered considerably by loading CSRRs and an MTM slab. The MTM slab consists of an array of 1 × 3 single-sided periodic structure of split ring resonator unit cells. The CSRRs are incorporated on both sides of the rectangular slot and the MTM slab is placed below the dielectric substrate of the antenna to achieve miniaturization. About 56.7% miniaturization is attained for the proposed CSRRs and MTM slab loaded antenna in comparison to the conventional antenna. It is also observed that the minimal effect on the co-polarization and cross-polarization is obtained in the case of proposed antenna. The overall antenna size is 0.23 λ0 × 0.23 λ0 × 0.009 λ0, where λ0 is the free space wavelength. In this proposed antenna a high radiation efficiency of about 84.2% is obtained. Owing to the high efficiency and compact size, the proposed antenna will find broad applications in the field of wireless communication.

A Multifeed Antenna for High-Efficiency On-Antenna Power Combining

This paper presents a multifeed antenna structure that synthesizes the desired far-field radiation characteristics with on-antenna power combining and increases the total radiated power of a wireless transmitter. The driving signals at the multiple antenna feeds are scaled properly in amplitude and phase, so that they collectively synthesize the desired on-antenna current/voltage distribution and achieve the resulting desired far-field radiation pattern. The proposed multifeed antenna offers flexibility to optimize the antenna driving impedances based on the locations of the feeds. It also simplifies the passive impedance matching and power-combining networks between the antenna feeds and the transmitter outputs, substantially increasing the total transmitter power efficiency. Most importantly, the proposed multifeed antenna achieves on-antenna low-loss power combining, which, compared with antenna array-based spatial power combining, does not suffer from narrowed beamwidth or enlarged antenna panel size. As proof of concept, multifeed slot antennas and a multifeed square loop antenna are designed and characterized at 10.3 GHz. Conventional single-feed slot antennas and a single-feed square loop antenna are also implemented as reference designs. Well matched antenna gains and radiation patterns between the proposed multifeed antennas and the conventional single-feed antennas are achieved in the measurements, demonstrating the on-antenna power combining of the proposed multifeed antennas without distorting the far-field radiation patterns.

High-gain waveguide slot antenna using simple parasitic patch's cover

In this article, a way based on using miniature patch cells has been proposed to increase gain and bandwidth of the waveguide slot antenna. In the presented approach, an array of 3 × 3 metal patches has been used as superstrate to create Fabry Perot theorem resonance cavity. The proposed high-gain and simple antenna is composed of a conventional waveguide slot antenna with an extended broad wall, and an array of parasitic patches which are symmetrically placed over slot at a distance of about free-space half wavelength. The slot has been created on a rectangular waveguide WR90 with 22.86 mm × 10.16 mm × 52.5 mm dimension, also extended wall dimension is 2λ0 (67.5 mm) × 3λ0 (107 mm). It has been shown that the proposed structure compared with the conventional waveguide slot antenna improves antenna peak gain from 6.5 to 16.5 dBi and, in the same time, antenna bandwidth from 11% to around 16.2%. More important advantage of the proposed antenna is that unlike to other Fabry Perot antenna with the same gain, there is not any dielectric material in the proposed structure. A prototype antenna was simulated, fabricated, and measured for verification.

Compact Omnidirectional Circularly Polarized Antenna

In certain radar and wireless communication applications, omnidirectional circularly polarized (CP) antennas are desired but existing solutions have complex 3-D structures and are large in size. In this paper, a compact and low profile CP antenna having omnidirectional pattern on azimuthal plane is demonstrated. The CP waveform is synthesized by combining two linearly polarized and omnidirectional antennas with 90° phase difference on their terminals. The most challenging part of the design is the realization of the horizontally polarized antenna with omnidirectional radiation pattern. This antenna is designed using a novel two-faced slot antenna structure capable of emitting in-phase radiation of equal magnitude on both sides of the antenna. The two faces of the low-profile slot antenna are connected by a thin meander parallel plate waveguide to provide antiparallel field distributions over the two faces of the slot radiators. This special design removes radiation nulls on E-plane that exists on conventional slot antennas, the mechanism of which has been carefully discussed in this paper. The other antenna is a compatible pair of planar inverted-F antennas constructed on the sides of the finite-ground plane two-faced slot antenna for the provision of vertically polarized omnidirectional radiation. A feed network with power splitter and phase shifter is also accommodated on the compact CP antenna. The antenna is designed and fabricated, and its performance is measured against numerical simulations. It is shown that the fabricated antenna at 2.4 GHz can provide measured axial ratio of lower than 1.8 and gain variations of less than ±1.5 dB over all azimuth angles.

Polarization conversion of metasurface for the application of wide band low-profile circular polarization slot antenna

In this letter, based on a corner-cut square metasurface, a planar polarization conversion structure is presented and the application for wide band low-profile circular polarization (CP) slot antenna is proposed. The mechanisms for achieving the CP state from a linearly polarized incident wave and for broadening the working bandwidth of conventional slot antenna are analyzed theoretically. The wide band low-profile CP slot antenna is achieved with numerical optimizations and parameter studies. Both simulations and measurements are performed to demonstrate the proposed antenna, and good agreements are obtained. Such results will open the path for polarization conversion metasurfaces used in the CP antenna area.

Investigation on the performance of low‐profile insensitive antenna with improved radiation characteristics for the future 5G applications

ABSTRACTA new method to design an insensitive antenna with improved performance for fifth generation (5G) systems is proposed in this letter. In order to improve the antenna performance and also eliminate the effect of high‐loss FR‐4 substrate, the resonator of the conventional slot antenna has been converted to the air‐filled slot‐loop structure with a thickness of hsub. Since the main substrate of the resonator is the air, the antenna is insensitive for different values of permittivity, loss tangent characteristics of the substrate. So, for different kinds of substrates, the antenna has a same performance in terms of maximum gain, radiation and total efficiencies. The antenna is designed and fabricated on a low‐cost FR4 substrate and has more than 90% (−0.5 dB) radiation and total efficiencies at 22.25 GHz (center frequency). It has the reflection coefficient (S11) less than −10 dB in the frequency range of 21–23.5 GHz (more than11% fractional bandwidth) which is one of the candidate bands for future 5G communications. The antenna has a very compact size and could be used in mm‐wave phased arrays. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2148–2151, 2016

A CPW-FED DUAL-BAND SLOT ANTENNA WITH CIRCULAR POLARIZATION

In this paper, a coplanar waveguide (CPW)-fed dual-band slot antenna with circular polarization (CP) is presented. In order to achieve CP characteristic, an asymmetric slot and F-shaped end patch are introduced to a conventional rectangular slot antenna. Moreover, by cutting a T-shaped notch on the ground plane, the axial ratio (AR) bandwidth (ARBW) can be extended. The antenna shows left-hand CP (LHCP) radiation in the boresight direction (i.e., +Z direction) at both ARBWs. The proposed antenna is fabricated and measured. The measured results have a good agreement with the simulated ones. The measured impedance bandwidths (|S11| < �10 dB) are 1.08 GHz (2.02 to 3.10 GHz, 40% at 2.70 GHz) and 2.31 GHz (4.57 to 6.88 GHz, 39.8% at 5.8 GHz). The two measured ARBWs are 600 MHz (2.60 to 3.20 GHz, 22.2% at 2.70 GHz) and at least 1.15 GHz (4.85 to 6.0 GHz, 19.8% at 5.8 GHz) at the lower and upper bands, respectively.

Design of Wideband Cavity-Backed Slot Antenna With Multilayer Dielectric Cover

A novel wideband cavity-backed slot antenna operating at X-band is proposed. Compared to conventional cavity-backed slot antennas, both the bandwidth and gain of the proposed antenna are significantly increased by adding a multilayer dielectric cover. This antenna offers a 40% (|S 11 | <; -10 dB) impedance bandwidth. Meanwhile, the gain of a single antenna within this band is 6-9.5 dBi, 2-3 dB higher than those without that multilayer dielectric cover at most of the bandwidth. To further validate the capability of the proposed antenna, a 4 ×4 antenna array is designed, fabricated, and tested. The measurement results corroborate with simulations well. Taking advantage of its wider bandwidth and higher gain compared to the counterparts, this antenna could find great potential application in the future.

Compact Frequency-Reconfigurable Slot Antenna for Wireless Applications

A compact frequency-reconfigurable slot antenna for LTE (2.3 GHz), AMT-fixed service (4.5 GHz), and WLAN (5.8 GHz) applications is proposed in this letter. A U-shaped slot with short ends and an L-shaped slot with open ends are etched in the ground plane to realize dual-band operation. By inserting two p-i-n diodes inside the slots, easy reconfigurability of three frequency bands over a frequency ratio of 2.62:1 can be achieved. In order to reduce the cross polarization of the antenna, another L-shaped slot is introduced symmetrically. Compared to the conventional reconfigurable slot antenna, the size of the antenna is reduced by 32.5%. Simulated and measured results show that the antenna can switch between two single-band modes (2.3 and 5.8 GHz) and two dual-band modes (2.3/4.5 and 4.5/5.8 GHz). Also, stable radiation patterns are obtained.