Aperture‐coupled microstrip antennas loaded with very high permittivity ceramics

The use of very high permittivity ceramic materials (εr = 38, 80) to miniaturize an aperture‐coupled microstrip patch antenna is reported in this article. A loss of the antenna gain in such a technique is observed, and then a novel substrate‐superstrate structure is developed to enhance the gain. The whole process of gain enhancement is analyzed by using the finite‐difference time‐domain (FDTD) method. The simulations are excellently correlated with the experiments. They validate that the loss of the antenna gain can be recovered up to that of conventional microstrip antennas loaded with low permittivity materials (εr < 3). In addition, the performance comparison of the aperture‐coupled microstrip antenna of very high permittivity with the probe‐fed microstrip antenna of very high permittivity is presented. It is shown that the aperture‐coupled antenna has wider impedance and radiation bandwidths than the probe‐fed one while keeping the antenna gain at about the same level. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 154–160, 2003.     

Probe‐fed microstrip antennas loaded with very high‐permittivity ceramics

This article reports the feasibility study of miniaturizing probe‐fed microstrip patch antennas by dielectric loading. The loading materials are barium tetratitanate ceramics of very high dielectric constant (ε_r = 38, 80). It is shown that, simply through loading, the antenna sizes are greatly reduced; however, the antenna performances are deteriorated. For instance, the antenna gain becomes lower. Then enhancement of the antenna performances follows. A substrate–superstrate structure is used to recover the gain. Both the experiments and the finite‐difference time‐domain (FDTD) simulations demonstrate that the gain and impedance bandwidth can be retrieved such that they are comparable to those of conventional microstrip antennas loaded with low permittivity materials (ε_r < 3). © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Design and fabrication of a new high gain multilayer negative refractive index metamaterial antenna for X‐band applications

This article presents the design of a planar high gain and wideband antenna using a negative refractive index multilayer superstrate in the X‐band. This meta‐antenna is composed of a four‐layer superstrate placed on a conventional patch antenna. The structure resonates at a frequency of 9.4 GHz. Each layer of the metamaterial superstrate consists of a 7 × 7 array of electric‐field‐coupled resonators, with a negative refractive index of 8.66 to 11.83 GHz. The number of layers and the separation of superstrate layers are simulated and optimized. This metamaterial lens has significantly increased the gain of the patch antenna to 17.1 dBi. Measurements and simulation results proved about 10 dB improvement of the gain.     

A novel dual‐wideband inscribed hexagonal fractal slotted microstrip antenna for C‐ and X‐band applications

This paper presents a novel geometry of inscribed hexagonal slotted microstrip antenna for dual‐band performance where the fractal iteration has been made by introducing concentric slots in the patch geometry. Using the equivalence principle and cavity model, the basic geometry of the hexagonal slotted patch is analyzed, and the resonant frequencies of different modes of the patch are computed. Higher‐order modes of the patch antenna are used to obtain dual band. Good performance in terms of the reflection coefficient is proved with the help of parametric analysis. The antenna geometry is simulated using electromagnetic simulation software based on the finite‐element method. The prototype of this antenna is fabricated and tested. The practical results match with the simulated results. The proposed antenna provides improved average gain. The peak values of measured gain are found to be 5.238 and 7.023 dBi—in the two bands 5.85 to 6.48 GHz and 7.28 to 8.63 GHz, respectively. Stable radiation patterns with good average gain make the proposed antenna appropriate for long‐range transmission. Furthermore, low profile and low cost make this antenna suitable for the future point‐to‐point high‐speed wireless communication applications.     

Dual‐polarized high gain resonant cavity antenna for radio frequency energy harvesting

A Fabry pérot antenna with a multilayer superstrate having nonuniform unit cells has been investigated as a receiving antenna for radio frequency (RF) energy harvesting applications. Here, the primary radiator is selected as a dual‐polarized aperture coupled microstrip antenna with a double‐layer superstrate. This antenna excites orthogonal polarizations, vertical (V) and horizontal (H) in the frequency band of 6.2 and 5.8 GHz, respectively, due to the presence of two orthogonal H‐shaped slots in its ground plane. The proposed antenna provides a gain enhancement of 9.8 and 10.1 dBi at the respective frequencies. The rectifying circuit is designed for a frequency of 5.8 GHz using a voltage doubler topology. The circuit provides a power conversion efficiency of 41% at 0 dBm input power.     

Performance characterization of wideband,wide‐angle scan arrays of cavity‐backed U‐slot microstrip patch antennas

This work looks at the use of wideband cavity‐backed U‐slot microstrip antennas in finite phased arrays. This configuration retains the single‐patch and single‐layer characteristics of conventional microstrip antenna arrays and provides a good impedance matching over wider scan angles when electrically thick substrates are used to improve the frequency bandwidth. The characteristics of finite phased arrays of U‐slot rectangular microstrip patches enclosed in cylindrical cavities are analyzed from a validated hybrid methodology based on the finite element method, the modal analysis, and the properties of spherical waves. The results are compared with those obtained using an infinite array model. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A low profile dual band resonant cavity antenna

A low profile dual band resonant cavity antenna that incorporates double sided partially reflective surface (PRS) with complementary layers is presented here. The PRS is formed by printing periodic array of complementary metallic square loops on the opposite sides of the dielectric material. The PRS has been used as a superstrate, placed above the radiating microstrip patch. This PRS acts as a dual band matching section between the microstrip patch and free space, hence resulting in dual resonance. The proposed structure has been analyzed using equivalent circuit model. Parametric analysis of the sensitive structural parameters has also been discussed. To validate the design, the simulation analysis and experimental results obtained from a prototype operating at 8.9 and 9.4 GHz are presented. The measured gain at the two frequencies is 10.2 and 8.5 dBi, respectively. The overall size of the antenna is 1.78λ × 1.78λ × 0.09 λ with λ corresponding to 8.9 GHz.     

Design of circular patch antenna with a high gain by using a novel artificial planar dual‐layer metamaterial superstrate

This study presents a new dual‐layer metasurface structure proposed to enhance the performance of a circular patch antenna. A novel unit cell planar metasurface is characterized by nearly equal enhanced effective permeability and permittivity ε_r ? μ_r > 1 at the resonant frequency. In addition, a 5*5 array of these unit cells are used as a superstrate over a circular patch antenna which is fed by 50 Ω microstrip line and operating at 2.45 GHz for improving the antenna performance. The patch antenna gain is increased by creating an in‐phase electric field area on the top surface of the metasurface. The obtained results showed that the maximum gain of the antenna increased from 2.31 dBi to 7.5 dBi. A 30% increase in the bandwidth is also remarked. The proposed antenna with metasurface occupies an overall volume of 1.01λ_g ×1.01λ_g ×0.025λ_g . The simulation analysis and measured results were performed using the microwave studio, high frequency structure simulator software, and vector network analyzer. The proposed antenna prototype has been fabricated. The measured results indicate that the antenna has a good impedance matching in the desired operating band (2.37‐2.49 GHz) with the resonant frequency of 2.44 GHz which make the proposed antenna appropriate for microwave applications.     

High performance microstrip monopole antenna with loaded metamaterial wire medium superstrate

A novel design of printed monopole antenna loaded with wire medium is developed for radar applications. The advocated design aims to simultaneously enhance the gain and bandwidth of the proposed geometry. The proposed antenna is composed of a circular patch etched with double C‐shaped slots and the ground is defected to achieve wide bandwidth. Wire medium superstrate and a metal reflector are implemented to provide high gain. The promising tunable wire medium superstrate consists of a periodic array of parallel metallic wires arranged in a rectangular pattern that mimic the behavior of epsilon‐near‐to‐zero (ENZ) metamaterial. This medium is suspended at a distance of a quarter‐wavelength in air above the antenna to provide the optimum gain and reduce the side lobes level. Prototype of the optimized antenna is fabricated using Rogers's substrate to offer ?10 dB bandwidth over the entire frequency range (900 MHz to 2.85 GHz). Details of the design process are investigated through full wave electromagnetic simulations performed by CST software. Experimental results of the fabricated prototype are presented and also compared with simulation results where an appreciable agreement between them is demonstrated.     

A wideband frequency agile fork‐shaped microstrip patch antenna with nearly invariant radiation patterns

A wideband frequency agile fork‐shaped microstrip patch antenna is presented. Its operating frequency is tuned by incorporating four varactor diodes, which are placed symmetrically on the patch. The operating mechanism of this antenna is also briefly discussed. The full wave analysis simulated results show that the operating frequency can be tuned from 1.47GHz to 1.84GHz (frequency agility of 26.50%) with nearly invariant radiation patterns while achieving acceptable gain throughout the operating frequency range. Finally, the proposed fork‐shaped antenna was fabricated and measured for its impedance matching and gain radiation patterns. Measurement results show reasonable agreement with the simulated data. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:623–632, 2016.     

A beam scanning Fabry–Pérot cavity antenna for millimeter‐wave applications

A beam scanning Fabry‐Pérot cavity antenna (FPCA) for 28 GHz‐band is presented in this article. The proposed antenna consists of a slot‐fed patch antenna and several layers of perforated superstrates with different dielectric constant. The beam of the antenna can be controlled by moving the superstrate over the antenna. By increasing the offset between the feeding antenna and the superstrate, a larger tilt angle can be obtained. The size of the antenna is 0.95λ₀ × 0.95λ₀ × 0.48λ₀ at 28.5 GHz. The results show the proposed antenna achieves an impedance bandwidth (S₁₁ < ‐10 dB) of 10.5% (27.2‐30.2 GHz), and the beam can be scanned from 0° to 14° in the yoz‐plane with the offset changed from 0 mm to 2 mm. The gain of the antenna is enhanced by 5 dBi in comparison with the feeding antenna without the superstrate, which ranges from 10.91 to 11.53 dBi with the different offset. The proposed antenna is fabricated and shows a good agreement with simulated result.     

Very small aperture terminal broadband shared‐aperture planar antennas

The design and development of a shared‐aperture dual‐band, dual‐polarized, dual‐aperture coupled rectangular microstrip patch antenna element is presented, which is suitable for portable very small aperture terminals. Detailed parametric studies of the locations of orthogonal coupling slots and their influences on the isolation and impedance bandwidth of the antenna element are performed. The experimental results are presented. The prototype dual‐band dual‐polarized antenna element achieves a 21% input impedance bandwidth at the S‐ and C‐bands. The design and development of a four‐element array with such an antenna element is also presented. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 180–193, 2003.     

High gain microstrip antenna design for broadband wireless applications

This article presents a new broadband microstrip antenna for personal communications systems (PCS) applications. Using multilayer substrate structure with aperture‐coupled feed, a rectangular microstrip patch antenna operating at 1.9‐GHz band is designed and experimentally validated. This antenna configuration uses a quarter‐wave transformer to enhance the matching between the feed transmission line and the antenna patch. To demonstrate the design procedure, a first experimental broadband microstrip antenna prototype is designed and implemented. To analyse its performance, measurements are carried out and good performances are achieved. However, this prototype has a low front‐to‐back ratio. To overcome this drawback, an optimization process is proposed, and a second prototype is designed and successfully realized. To examine the effect of the optimization, experimental investigations are carried out on the second prototype. Very good agreement is obtained between numerical and measured results. Experimental results indicate that the proposed antenna achieves a bandwidth of 21%, a gain of 9.5 dB, and a front‐to‐back ratio of 20 dB, which are very sufficient for broadband wireless applications. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 511–517, 2003.     

Metasurface cavity antenna for broadband high‐gain circularly polarized radiation

The article presents a microstrip patch (MSA) fed high gain circularly polarized metasurface cavity (CP‐MSC) antenna using a planar progressively‐phased‐reflector and a transmissive linear to circular polarization conversion metascreen. The bottom metasurface reflector consists of a remodeled Jerusalem cross to obtain 2π reflection phase variation. Linear to circular polarization conversion is achieved by a hexagonal ring based meta‐element with high transmission and bellow 3 dB axial ratio from 9.5 to 10.5 GHz. Simulated and measured results of assembled CP‐MSC antenna with MSA are in good agreement. The gain of the proposed cavity antenna with 10 and 10.5 GHz MSA are 14.9 and 16.3 dBi, respectively. Below 3 dB AR throughout the operating band denotes significant circular polarization performance of the proposed antenna.     

Gain enhancement of slot antenna using zero‐index metamaterial superstrate

This article presents a technique to enhance the broadside gain of a CPW fed slot antenna using a single layer metamaterial (MTM) superstrate. A finite array of 3 3 ring unit cell has been designed on both sides of a dielectric substrate to form the MTM superstrate. The gain enhancement is obtained using the zero‐index property of the metamaterial. The broadside gain enhancement for the proposed antenna is 7.4 dB more in comparison to that of the reference slot antenna. The proposed MTM superstrate loaded antenna provides a minimum overall thickness in the context of using ZIM superstrate for gain enhancement of antennas reported in earlier literatures. The overall thickness of the MTM loaded antenna is 0.13λ₀, where λ₀ is the free‐space wavelength at the resonance frequency of the antenna. Also, a high efficiency of about 93.2% is obtained in this case. The loading of the MTM superstrate produces a minimal effect on the cross polarization performance of the proposed slot antenna.     

Design of 4-element microstrip array of wideband reflector antenna with stable high gain characteristics

In this paper, three microstrip antennas with and without reflector are proposed with stable and high gain characteristics. The proposed antennas are simple to design and do not involve loading of any active elements on the patch or ground plane. The designed antennas cover the total frequency range of 10.5–44.5 GHz and operate well within the 5G communication frequency band of 27–30 GHz; consequently, making proposed antennas suitable for upcoming wireless technology. Furthermore, a 2 × 2 antenna array with phase diversity is proposed which offers an almost stable gain of about 14 dBi within the operating band. The proposed antennas are analyzed by finite element method based Ansys HFSS simulator. The fabricated prototypes of the optimized designs are made and simulated results are found in good agreement with the measured results.

     

Path loss compensated millimeter wave antenna module integrated with 3D‐printed radome

Millimeter wave antennas designed at 28 GHz is essential for future 5G base stations or access points and mobile terminals. In this paper, a compact pattern diversity module for millimeter wave 5G base stations is proposed by using 3D‐printing for radome design. In order to achieve path loss compensation in an indoor base station context, the gains of the antennas radiating at ±45° must be 3 dB higher than the antenna radiating in the boresight axis. First, an inset fed patch antenna integrated with a low‐cost industry standard 3D‐printed superstrate with Polylactic acid (PLA) is investigated to study its radiation characteristics. The radome is designed in such a way for optimal gain enhancement with minimal physical footprint. The height of the 2 mm thick superstrate is optimized for a boresight gain of 8 dBi. Second, the 3D‐printed superstrate is optimized for a boresight gain of 11 dBi, which satisfies the criterion of path loss compensation, in this case the antenna achieves an aperture efficiency of close to 72% at 28 GHz. A compact pattern diversity module with customized 3D‐printed radome is also presented to achieve path loss compensation and wide angular coverage of ±70° with associated isolation of less than 35 dB across the ports and the band. Detailed simulation and measurement results are presented.     

A novel microstrip Yagi antenna with an improved end‐fire radiation pattern under operation of the TM20 mode

In this article, a novel microstrip Yagi antenna under operation of the TM₂₀ mode is proposed to obtain an enhanced end‐fire radiation pattern. First, a two‐element microstrip Yagi antenna is theoretically analyzed under different dimensions of the parasitic element. The results demonstrate that the parasitic element can act as either a reflector or director when its size is smaller or larger than the size of the driven patch, respectively. After that, the equivalent magnetic currents and electric fields of the two‐element antenna are formed to provide physical insight into the working principle and radiation performance of the antenna. With these arrangements, an array of four patch elements including one driver, one director, and two reflectors are selected for the antenna design. Unlike the traditional microstrip Yagi operating with the TM₁₀ mode, all the patch elements involved in this design resonate with the TM₂₀ mode, thus effectively enhancing the tilted beam angle toward the desired end‐fire direction on an infinite ground. Finally, the proposed antenna is designed, fabricated and tested. The measured results show that its impedance bandwidth is maintained at approximately 3.3%, ranging from 4.76 to 4.92 GHz. Most importantly, the maximum deviation angle of the antenna is significantly improved to approximately 58° from the broadside direction at the center frequency (4.84 GHz), while maintaining a low profile and compact size.     

Wideband linear microstrip array antenna with high efficiency and low side lobe level

In this letter, the design and fabrication of the linear microstrip array antenna by series fed are presented. The array antenna consists of 16 reflector slot‐strip‐foam‐inverted patch (RSSFIP) antennas. The gain and efficiency of the linear array antenna is 16.6 dBi and 61% at 10 GHz, respectively. The antenna has a bandwidth (BW) of 45% from 8.1 to 12.8 GHz (S₁₁ < ?10 dB) and side lobe level (SLL) of ?25.6 dB across the BW of 19.2% from 9.4 to 10.4 GHz. These are achieved by using a microstrip series fed with defected ground structure (DGS) to feed the patch array antenna. Good agreement is achieved between measurement and simulation results.     

Dual segment rectangular dielectric resonator antenna with metamaterial for improvement of bandwidth and gain

The simulation and experimental studies of an aperture‐coupled wideband dual segment rectangular dielectric resonator antenna with metamaterial for C‐band applications are presented in this paper. The antenna consists of Alumina (Al₂O₃) ceramic as upper segment and Teflon as lower segment. The combination of circular‐shaped coplanar split‐ring resonator and conducting strip has been used as metamaterial superstrate. With the use of metamaterial superstrate, the bandwidth of the antenna is increased by 48% through simulation and 22% experimentally. The broadside radiation pattern of the antenna is converted into directive radiation pattern with reduced beamwidth when metamaterial superstrate is used. The peak gain of the antenna is also enhanced by 33% through simulation and 31% experimentally with the use of metamaterial superstrate. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:646–655, 2014.