Two‐dimensional synthesis and optimization of a broadband shaped beam reflector antenna using IWO and PSO algorithms

A new technique for broadband shaped beam reflector antennas synthesis is presented. The surface of the shaped reflector is represented by a set of orthogonal Jacobi–Fourier expansion functions. To achieve a cosecant squared pattern in the elevation plane and a pencil beam in the azimuth plane, the expansion coefficients are optimized using invasive weed optimization and particle swarm optimization algorithms. High accuracy is achieved by combining optimization tools and analysis methods such as physical optics and integral equation. Besides, in the optimization procedures, a complex object function is used to achieve the desired performance over the entire 26–40 GHz operating bandwidth. The simulation results via FEKO and CST Microwave Studio software packages prove the validity and versatility of this technique for solving shaped reflector synthesis problems. There are several features that distinguish this technique from the previous methods. First of all is the wide bandwidth. The second is its ability to shape the radiation patterns in the elevation and azimuth planes simultaneously (two‐dimensional synthesis). Moreover, compared with other techniques, the proposed method allows achieving extra desired features such as high directivity, low sidelobe levels, and small ripples in the shaped beam region. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:129–140, 2015.     

A wideband circularly polarized antenna using mutual coupling method

A novel wideband circularly polarized (CP) antenna is presented in this article. The proposed antenna consists of a four‐leaf clover patch, four L‐probes, and wideband networks. Based on the tightly coupled mechanism, the four L‐probes are formed as a ring with the adjacent ones kept close for strong mutual coupling. Consequently, the proposed antenna realizes a wideband impedance matching. Meanwhile, the four‐leaf clover patch is put closely inside of the ring for further improving the impedance bandwidth, which is proximity‐coupled fed by the four sequential‐rotation L‐probes with phase of 0°, 90°, 180°, and 270°. The four L‐probes are connected to the respective ports of a wideband feeding network by a two‐stage impedance transforming network. The measured results indicate that the proposed design has an impedance bandwidth of 66.7% from 1.0 to 2.0 GHz for VSWR ≤ 2 and a 3‐dB axial ratio bandwidth of 56.5% from 1.08 to 1.93 GHz. Furthermore, in the operating bandwidth, stable and symmetry radiation patterns and high gain are obtained. The design has a 3‐dB gain bandwidth of 38% from 1.3 to 1.9 GHz with a peak gain of 8.5 dBic.     

A multi to wideband frequency reconfigurable antenna

A frequency reconfigurable antenna with a simple design structure and biasing circuit is presented. The antenna is able to configure its frequencies to operate either in multiband or wideband modes. The antenna is fed by a coplanar waveguide transmission line. The reconfiguration characteristics of the antenna is achieved by using PIN diode switches. The operating frequencies of the multiband mode are designed within the wideband mode operating range, from 2 to 6 GHz. Both simulated and measured results of S₁₁, radiation pattern and realized gains are verified. The antenna allows a degree of freedom in providing the frequency reconfiguration from multiband to wideband mode and vice versa.     

A wideband omnidirectional filtering patch antenna with high selectivity

A wideband omnidirectional filtering patch antenna with high selectivity is proposed in this article. The annular ring is surrounded by the hexagonal patch with inner circle, whereas a series of shorting vias are regularly distributed among them and a copper top hat is suspended right on the top of the radiator, respectively. And, omnidirectional pattern is mainly performed on account of the symmetry and center‐fed structure. In addition, broadband performance is achieved by merging three resonant modes, which include the TM₀₁ and TM₀₂ modes of the annular ring and the TM₀₂ mode of the hexagonal patch with inner circle. Taking advantages of the hexagonal patch and six shorting vias in it, two radiation nulls are provided in the upper band. Besides, another radiation null is generated in the lower band by reason of the top hat and other shorting vias. As a result, an ideal quasi‐elliptic bandpass response, high selectivity, and good out‐of‐band rejection are obtained simultaneously. The proposed filtering patch antenna, with a profile of 0.056 λ ₀, shows a wide impedance bandwidth of 30.2% from 2.05 to 2.78 GHz. The average gain in the passband is about 6.5 dBi, and the out‐of‐band suppression level is greater than 15 dB in the wide stopband.     

Reconfigurable method of smart antenna beam shaping in indoor fading environment using adaptive algorithms: An exhaustive experimental study

Adaptive algorithms for beam shaping of a phased array antenna and multiple‐input multiple‐output (MIMO) system gaining importance in today's advanced wireless networks to mitigate interference effects and distortion in the receiving signal due to multipath, small scale, and large scale fading effects. This article deals with the development of reconfigurable field programmable gate array (FPGA)‐based hardware for smart antenna system to explore parameter dependencies, drawbacks, and relative performance comparison of popular adaptive beamforming and interference suppression algorithms. These are least mean square, recursive least squares (RLS), and sample matrix inversion (SMI) used in real‐time under laboratory environment where the existing wireless channel between transmitters and receivers is linear time‐varying in nature due to presence of secondary sources giving rise to small‐scale fading. For this at first, we propose a novel received signal strength indicator‐based procedure to measure the radiation pattern of the antenna under an echoic indoor environment on a reconfigurable and portable FPGA system named wireless open‐access research platform (WARP), controllable by generic programming codes over a user‐friendly MATLAB interface. For better performance, the SMI algorithm was modified to increase block size rather than block shifting in general SMI. Later a comparative study was performed under varying conditions to observe the best utilization of three adaptive algorithms in beam shaping. In all cases, SMI performs the best with less beam shaping error and faster convergence, validating its use in a real‐time fading environment.     

Design of high gain/directional ultra‐wideband antenna for radar imaging systems

A compact size of 40 × 40 mm² ( λ₀ × λ₀ ) semi‐elliptical slotted ground structure (SESGS) directional ultra‐wideband (UWB) antenna is proposed for radar imaging applications. A vertical semi‐elliptical slot is inserted into ground and subsequently, an axis of semi‐ellipse is rotated diagonally (with 45°) in direction of the substrate. Axes of semi‐ellipse are optimized symmetrically around the circular patch to work antenna as a reflector. Furthermore, semi‐elliptical slot is rotated horizontally (with 90°) again to improve the impedance bandwidth. Proposed antenna achieves fractional bandwidth around 83% covering the UWB frequency range from 4.40 to 10.60 GHz (S₁₁ < ?10 dB) having 4.5/6/7/8/9.3/10.2 GHz resonant frequencies. Also, antenna is capable to send low‐distortion Gaussian pulses with fidelity factor more than 95% in time‐domain. Measured gain and half power beam width (HPBW) are 6.1‐9.1 dBi and 44°‐29° in 4.40‐10.60 GHz band, respectively, which show an improvement of 1‐3 dBi in gain and half power beam‐width is reduced by 5°‐10° when compared with previously designed antennas. Experimental results show good agreement with CST simulation.     

Effects of reflector antenna panel installation errors on average power pattern

A large reflector antenna generally consists of several rings of panels and panel installation errors (PIEs) are inevitable during the panel installation process. In this paper, a mathematical model is developed to analyze the effects of PIEs on reflector's average power pattern. Whether for the PIEs of each ring of panels or for the PIEs of all the panels for the whole reflector, the proposed model can be used to calculate the average power pattern with the root‐mean‐square value of the PIEs, and its correctness is demonstrated by the results calculated by Monte Carlo simulation. For a given paneled reflector, the peak gain losses and the first side lobe level increments caused by different PIEs for the whole reflector are presented. Then, through an analysis for each ring of panels, including the effects of different amplitude aperture distribution functions and different ratios of focal length to diameter (F/D ratios), the results clearly show that the PIEs of the panels for different rings have different effects on the reflector's average power pattern, and valuable results are obtained. The derived results will greatly benefit the panel installation and adjustment of large reflector antennas.     

A wideband circularly polarized antenna array with sequential rotation feed

A novel wideband circularly polarized (CP) antenna array is designed, which consists of a horizontally placed wideband phase shifting feed network and four vertically placed linearly polarized dipole antenna elements, and the circular polarization is realized based on sequential rotation feeding technology. By placing two parasitic strips and two grounding strips on the top and side of each T‐shaped dipole antenna element, the impedance bandwidth and circular polarization performance of the antenna can be further improved. The simulation results show that the 10‐dB impedance bandwidth of the antenna is 93% (1.56‐4.27 GHz) and the 3‐dB AR bandwidth is 80.7% (1.7‐4.0 GHz). The measured results are in good agreement with the simulation results. Due to the use of orthogonally placed wideband feed network and wideband array elements, the proposed antenna array has a wider circular polarization bandwidth than the similar antenna arrays reported.     

Analysis of wideband circularly polarized ring slot antenna using characteristics mode for bandwidth enhancement

In this article, a coplanar waveguide fed ring slot antenna is proposed for the generation of circular polarization. It is shown that the bandwidth can be improved by adding a stub. Characteristics mode analysis is used to understand the wideband behavior and generation of circular polarization in different antenna configurations. Parametric analysis is used to optimize the performance of the antenna. The proposed antenna is fabricated and the measured results are compared with the simulated performance. The measured impedance bandwidth (|S₁₁| ≤ －10 dB) is 64.6% (2.25 GHz–4.4 GHz) and a 3 dB axial ratio bandwidth is 64.6% (2.25 GHz–4.4 GHz).     

A novel wideband Minkowski fractal antenna with assistance of triangular dielectric resonator elements

This article concentrates on the design and analysis of a novel Minkowski fractal‐based antenna design with the aid of triangular dielectric resonator (TDR) elements for wideband wireless applications. mode is excited inside equilateral TDR antenna with the help of coaxial probe feed. Wide impedance bandwidth has been achieved by reducing the quality factor with the help of increasing surface area‐to‐volume ratio of radiating structure. Another important feature of this article is that recurrence formulas are derived to calculate the fraction of surface area to volume of proposed fractal antenna up to nth iteration. The proposed antenna design is fabricated and measured up to third iteration to verify its simulated outcomes. Practically measured outcome confirms that the proposed antenna design operates over the frequency range, that is, 2.23‐3.1 GHz with the maximum gain of 3.62 dBi. These features make it appropriate for wireless LAN (2.4 GHz) and WiMAX (2.5 GHz) applications.     

Wideband high gain conical dielectric resonator antenna: An experimental study of superstrate and reflector

A physically feasible new hybrid geometry for gain improvement with wideband characteristics is designed and validated experimentally in a conical shaped dielectric resonator antenna (DRA). It comprises of one superstrate and one reflector, with simple slot coupling technique for excitation. The reflector beneath the ground plane mainly accountable for significant gain improvement (～109%) by reducing the back radiation, whereas the superstrate dedicates for maintaining wideband (12.65%). The demonstrated result shows S ₁₁ < ?10 dB band between 7.4 GHz and 8.4 GHz, with 11.25 dBi peak gain, which are well matched with their simulated counter parts. It also gives high co‐pol to cross‐pol difference (～40 dB) in broadside direction. This new geometry can be eligible for X‐band applications as well can usher the DRA researchers for further innovations.     

A compact wideband circularly polarized antenna with two pairs of driven patch arrays

In this article, a new wideband circularly polarized (CP) antenna is presented. The antenna is composed of a circular‐loop feeding structure which provides sequential phase (SP), four primary‐parasitic crown patches and four secondary‐parasitic crown patches. The circular‐loop SP structure is used to feed the two pairs of crown patches by a capacitively coupled way. The presented antenna features a wide 10‐dB impedance bandwidth (IBW) of 23% (6 GHz, 5.31‐6.69 GHz), and a wide 3‐dB axial ratio bandwidth (ARBW) of 11.1% (5.875 GHz, 5.55‐6.2 GHz). The proposed antenna features compact structure and broad 3 dB‐ARBW, which could include the WLAN (5.725‐5.85 GHz), ITS (5.8 GHz), and WIFI (5.85‐5.925 GHz) band.     

A novel wideband circularly polarized modified square‐slot antenna with loaded strips

In this article, a novel inverted L‐shaped microstrip‐fed wideband circularly polarized (CP) modified square‐slot antenna is designed. By cutting a pair of triangle chamfers and introducing a pair of triangle patches at the square‐slot, the antenna achieves a wideband CP radiation. Moreover, CP performance of the antenna can also be remarkably enhanced by protruding an L‐shaped strip and embedding a tuning rectangle slot into the slot ground. The measured results demonstrate that the axial‐ratio bandwidth for AR < 3 is 75.1% (from 4.45 to 9.8 GHz) and the impedance bandwidth (|S₁₁| < ?10 dB) reaches 65.8% (from 4.95 to 9.8 GHz). In addition, surface current studies are performed to illustrate the operating mechanism of CP operation, and the antenna has bidirectional radiation characteristics with an average gain of ~4 dBic within the CP band.     

A wideband stacked dielectric resonator antenna for 5G applications

A wideband stacked dielectric resonator antenna with stable patterns is proposed for fifth‐generation of mobile technology in this paper. With the help of inserted air gaps to reduce the radiation Q factor, the stacked structure with two thin high permittivity sheets and two hollow low permittivity slabs can provide four adjacent resonant modes to form a wide bandwidth. Measured results demonstrate that the antenna obtains an impedance bandwidth of 54% for |S₁₁| < ?10 dB and a peak gain of 9.2 dBi. The radiation patterns remain stable and symmetrical over the entire operating band.     

A high gain wideband circularly polarized antenna with asymmetric metasurface

An asymmetric‐metasurface based wideband circularly polarized (CP) microstrip antenna using a coaxial probe is proposed for L‐band applications. The antenna involves a stacked asymmetric‐metasurface, a radiating rectangular‐patch and a coaxial feed. An asymmetric‐metasurface is designed using rectangular unit cells and smaller size unit cells along one of the diagonal lines. The asymmetric‐metasurface is placed above a radiating rectangular‐patch with support of foam layer to achieve a wideband CP radiation. The measured performance of the prototype antenna achieves an impedance bandwidth (?10 dB return loss bandwidth) of 15.7% (1.58‐1.85 GHz) with CP bandwidth (3‐dB axial ratio) of 13% (1.58‐1.80 GHz) and gain of ≥9 dBic.     

A compact double‐layer wideband circularly polarized microstrip antenna with parasitic elements

In this article, a new broadband circularly polarized (CP) microstrip patch antenna (MPA) with a sequential phase (SP) square‐loop feeding structure is proposed. The presented antenna is composed of a square‐loop feeding structure, four L‐shaped parasitic patches with L‐shaped slots, four parasitic square patches, and a corner‐truncated square patch. At first, a SP square‐loop is designed as a feeding structure. Then, four L‐shaped parasitic patches with L‐shaped slots are utilized to generate one CP mode by a capacitive coupled way. At last, four parasitic square patches and a corner‐truncated square patch are together placed above the SP feeding structure to broaden the circularly polarized bandwidth (CPBW). The presented antenna has a wide 3‐dB axial ratio bandwidth (ARBW) of 16.7% (5.4 GHz, 4.95‐5.85 GHz), and a wide 10‐dB return loss bandwidth of 25.5% (5.5 GHz, 4.8‐6.2 GHz). The proposed antenna features compact structure and broad 3‐AR bandwidth which could completely cover the WLAN (5.725‐5.85GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band.     

Switched beam dielectric resonator antenna array with six reconfigurable radiation patterns

A single feed, four element rectangular Dielectric Resonator Antenna (DRA) array, with beam switching capability is proposed. A wide impedance bandwidth of more than 25% at the center frequency of 1.95 GHz is achieved. Each DRA has two excitation strips and four parasitic patches. The six cases are discussed; each case corresponds to a diverse radiation pattern. The antenna beam is switched in azimuth (θ = 45°) at Φ = 0°, 60°, 120°, 180°, 240°, and 300°. The antenna gain is found to be more than 7 dB in most of the frequency band of interest. A passive prototype is developed and tested to validate simulation results. The comparison between the simulated and measured reflection coefficients and the radiation patterns for the six cases is presented. A good agreement between the measured and simulated results is observed. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:519–530, 2016.     

A coaxial probe fed wideband circularly polarized antenna using unequal and adjacent‐slided rectangular dielectric resonators for WLAN applications

In this article, a coaxial probe fed wideband circularly polarized antenna has been designed and investigated using unequal and adjacent‐slided rectangular dielectric resonators radiating in broadside direction (Φ = 0°, θ = 0°). Wi‐Fi wireless network use radio signal either in 2.4 or 5 GHz band. Owing to high rush in 2.4 GHz band, the proposed antenna is designed for 5 GHz (5.15‐5.825 GHz) WLAN band. The proposed design uses fundamental orthogonal modes and excited in two individual rectangular dielectric resonators to achieve wide axial‐ratio bandwidth (below 3 dB). Measured input reflection coefficient (below ?10 dB) and axial ratio bandwidth (below 3 dB) of 26.07% (5.27‐6.85 GHz) and 26.85% (5.32‐6.97 GHz) has been attained, respectively, in this proposed antenna. The measured far‐field patterns such as gain and radiation patterns are showing consistent performance throughout the working band.     

A multi‐mode wideband omnidirectional monopolar patch antenna for indoor wireless communication systems

A wideband omnidirectional monopolar patch antenna merged multi‐mode with a simple structure is proposed in this article. The antenna consists of a circular patch and a concentric annular ring, which is coupled‐fed by a T‐shape monopole at its center. A wideband performance is achieved by converging multi‐mode: TM₀₂ mode of the circular patch, TM₀₂ mode of the annular ring and monopole mode of the T‐shape monopole. The measured results show that the proposed antenna has an impedance bandwidth of 55.3% from 4.45GHz to 7.85GHz. All of the three resonant modes lead to conical radiation patterns in the elevation plane and omnidirectional radiation patterns in the azimuth plane, and the measured peak gain varies from 6.1 to 10 dBi within the operating band, which verifies it can be a good choice for indoor wireless communication systems.     

A coplanar waveguide‐fed flexible antenna for ultra‐wideband applications

This paper presents a novel ultra‐wideband (UWB) antenna printed on a 70 μm thick flexible substrate. The proposed antenna consists of a hybrid‐shaped patch fed by coplanar waveguide (CPW). The ground planes on opposite sides of the feeding line have different height to improve antenna bandwidth. Simulation shows that the proposed antenna maintain wide bandwidth when changing its substrate's thickness and dielectric constant, as well as bending the antenna on a cylindrical foam. The proposed antenna is fabricated in laboratory with a simple and low‐cost wet printed circuit board (PCB) etching technique. Measured bandwidths cover 3.06 to 13.58, 2.8 to 13.55, and 3.1 to 12.8 GHz in cases of flat state and bent with radii of 20 and 10 mm, respectively. Measured radiation patterns show the antenna is omnidirectional in flat and bent cases.