A broadband slant polarized cavity backed microstrip‐fed wide‐slot antenna array

This article deals with the design of a broadband cavity‐backed microstrip‐fed wide‐slot antenna array for L‐band applications. For verification purpose, a sample 1 × 4‐element antenna array has been designed, manufactured and tested. Experimental results have shown satisfactory agreement with the simulation. The proposed antenna array exhibits a measured impedance bandwidth of 1.4 GHz (90%) with frequency of 0.85 to 2.25 GHz and the gain is higher than 11 dBi. The designed antenna has small size and low weight and can be fabricated using a low‐cost fabrication process for easy integration with RF circuits and microwave components. This work is useful for some radar applications and radio frequency identification systems.     

Compact broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

Reconfigurable wide band circularly polarized antenna array for WiMAX,C‐Band,a and ITU‐R applications with enhanced sequentially rotated feed network

In this article, a wide‐band circularly polarized slot antenna array with reconfigurable feed‐network for WiMAX, C‐Band, and ITU‐R applications is proposed. Different novel methods are used in proposed array to improve antenna features such as impedance matching, 3 dB axial‐ratio bandwidth (ARBW), gain, and destructive coupling effects. Miniaturized dual‐feed square slot antenna, with one attached L‐shaped strip and a pair of T‐shaped strip at ground surface for improving impedance matching and circular polarization (CP) purity, is presented. For further enhancement of CP attributes, reconfigurable sequentially rotated feed network is utilized to obtain wider 3 dB ARBW. Furthermore reconfigurable property of network gives controlling Right and Left handed CPs, respectively. Finally, a special form of Electromagnetic Band gap structure is employed on top layer of substrate that provides high isolation between radiating elements and array feed network to enhance overall performance of antenna. The measured results depict 3 dB ARBW from 4.6 to 7.2 GHz, impedance bandwidth from 3.3 to 8.8 GHz for VWSR<2, and peak gain of 10 dBi at 6 GHz. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:825–833, 2015.     

Compact wide band directional antenna using cross‐slot artificial magnetic conductor (CSAMC)

In this article a novel wide‐band artificial magnetic conductor (AMC) based wideband directional antenna is presented for ultra‐wideband (UWB) applications. The proposed novel cross‐slot AMC (CSAMC) achieves wide ±90° reflection phase bandwidth of 4.07 GHz (44.69%) and is used as a reflector. The overall antenna structure is designed with 4 × 4 CSAMC unit cell array and has very compact size of (0.584λ₀ × 0.584λ₀). The proposed structure improves the radiation properties and exhibits 91.5% (3.13‐8.41 GHz) impedance bandwidth (VSWR ≤2). Additionally, it results in significant improvement in gain and front to back ratio. The proposed antenna is fabricated and its measured performance is in good agreement with simulation results.     

一种具有宽带双极化低散射特征的微带阵列天线

针对阵列天线宽带散射缩减设计进行研究,设计了一种基于无源对消技术的低散射阵列天线,该新型微带阵列天线在宽频带内具有双极化低雷达散射截面（RCS, Radar Cross Section）性能;对基于两种散射性能不同的单元组成阵列的RCS性能进行了理论研究,进行了单元的散射幅度和相位对阵列RCS的影响分析;提出了一种加载T型缝隙的新型微带天线结构,该单元结构的辐射性能与散射性能能够进行独立调控和综合优化,该单元与传统微带贴片单元具有相似的辐射特性,并可在宽频带（带内和带外）内与传统微带单元产生有效相位差;将传统微带单元和加载T型缝隙的新型微带单元组成4×4阵列天线,仿真结果表明,提出的阵列天线在3GHz～7GHz（相对带宽80%）频带内实现了同极化RCS缩减,在3.3GHz～7GHz（相对带宽71.8%）频带内实现了交叉极化RCS缩减,缩减峰值分别为16.3dB和36.3dB,带内RCS缩减均值分别为14.1dB 和17.6dB;与传统微带阵列天线相比,提出的阵列天线增益下降小于0.1dB;提出的微带阵列天线具有高效率辐射和宽频带双极化低散射性能,为低散射阵列天线设计提供了新的思路。     

Circularly polarized 1 × 4 square slot array antenna by utilizing compacted modified butler matrix and branch line coupler

Circularly polarized (CP), beam steering antennas are preferred to reduce the disruptive effects such as multi‐path fading and co‐channel interference in wireless communications systems. Nowadays, intensive studies have been carried out not only on the specific antenna array design but also their feeding networks to achieve circular polarization and beam steering characteristics. A compact broadband CP antenna array with a low loss feed network design is aimed in this work. To improve impedance and CP bandwidth, a feed network with modified Butler matrix and a compact ultra‐wideband square slot antenna element are designed. With this novel design, more than 3 GHz axial ratio BW is achieved. In this study, a broadband meander line compact double box coupler with impedance bandwidth over 4.8‐7 GHz frequency and the phase error less than 3° is used. Also the measured impedance bandwidth of the proposed beam steering array antenna is 60% (from 4.2 to 7.8 GHz). The minimum 3 dB axial ratio bandwidth between ports, support 4.6–6.8 GHz frequency range. The measured peak gain of the proposed array antenna is 8.9 dBic that could scan solid angle about ～91 degree. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:146–153, 2016.     

Broadband T‐bar fed slot antenna array with stable horizontally polarized omnidirectional radiation

A broadband horizontally polarized omnidirectional antenna array is proposed, which consists of a circular array of four identical broadband T‐bar fed cavity‐backed slot antenna elements and a 1‐to‐4 power divider. The proposed omnidirectional antenna array has a compact diameter of only 0.44λ₀, a broad bandwidth of 75.9% (450‐1000 MHz) and a favorable omnidirectional radiation pattern in the azimuth plane with a gain variation below 3 dB in the operating band. Moreover, the cavity‐backed structure makes the proposed antenna array hardly affected by metal environment and the all metal construction allows for high‐power applications, and the reserved cable channel behind the cavities of the antenna elements ensures the extensionality and stability of the proposed array when longitudinal array expansion is needed. Design procedures of the proposed antenna array have been described in detail, simulations and measurements of the proposed antenna array have also been carried out to validate its performance in this article.     

Wideband slot antenna using a new feeding technique for wireless applications

This article presents a new wideband slot antenna for wireless applications at 5.8 GHz. To improve the antenna bandwidth, a new feeding mechanism based on a capacitively‐ and inductively‐coupled slot is proposed. To demonstrate this approach, an experimental antenna prototype operating at the 5.8‐GHz band was designed, fabricated, and measured. The obtained results indicate very good agreement between the numerical and experimental results. The proposed antenna achieves a 28.5% bandwidth, a 5.7‐dBi gain, and a ?15‐dB front‐to‐back ratio, which are very sufficient for broadband wireless applications. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Low‐cost and wideband circularly polarized slot antenna array

A slot antenna with wideband circular polarization (CP) array, which operates on millimeter waves band, is proposed. A four‐direction sequential rotation technique is used in the feed network to feed the 2 × 2 slot element based on waveguide. The shot element resonates at both the fundamental mode and the high‐order mode. The slot element is studied in high order mode, and the radiation lobe can be redirected by changing the size of the slot element, thus improving the multi‐lobe problem. A strong single lobe is formed in the +z‐direction by using the ground edge diffraction characteristics of the slot element in the waveguide. The designed broadband characteristics are obtained through the appropriate combination of the feed network and CP antenna. The prototype of the antenna with an overall size of 137 mm × 137 mm × 0.6 mm³ is processed and verified by experiments. The prototype of the slot array is processed and examined. The test results display that the device has good performance of |S₁₁| < ?10 dB bandwidth of 3.72 to 6.56 GHz (2.84 GHZ, 55.25%), a 3 dB axial ratio bandwidth of approximately 4.39 to 5.43 GHz (21.18%).     

Wideband cavity‐backed log‐periodic‐slot end‐fire antenna with vertical polarization for conformal application

A 6–18 GHz wideband cavity‐backed log‐periodic‐slot end‐fire antenna with vertical polarization for conformal application is presented. The log‐periodic folded slots and parasitic slots with 10 slot elements are applied to cover 6–18 GHz frequency band and the log‐periodic metallic cavity is placed under each slot element to keep wideband performance and prevent the effects of large metallic carrier on radiation patterns. The ground plane etched with log‐periodic slots is reversed and touched directly to the backed cavity and a dielectric cover is added to the antenna, to further improve the antenna performance. Meanwhile, a broadband microstrip‐coplanar waveguide transition is inserted in the antenna for measurements. With these designs, the proposed antenna shows good impedance matching (|S₁₁|<27 dB) and end‐fire gain (>4 dBi) performances in 6–18 GHz. The proposed antenna also keeps low‐profile and easy flush‐mounted characteristic which is suitable for conformal applications of high speed moving carriers.     

A novel substrate integrated waveguide cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic

This article presented a substrate integrated waveguide (SIW) cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic. The proposed array consists of 16 SIW cavity‐backed slot antennas. The SIW cavity‐backed slot antenna can be fed by two separate ports to resonate at two different frequencies and achieve high isolation better than 20 dB between two input ports. The proposed element is a typical self‐diplexing antenna. These cavity‐backed slot antennas are shunt‐fed by a compact 1 to 16 SIW power divider and series‐fed by a set of microstrip lines, respectively. As a result, this array achieves an unidirectional radiation pattern at 10.2 GHz with high gain of 15.10 dBi, and a frequency beam scanning characteristic from 7.0 to 9.0 GHz ranging from ?50° to 46°.     

CPW‐fed C‐shaped slot antenna for broadband circularly polarized radiation

A novel broadband circularly polarized (CP) C‐shaped slot antenna fed by a coplanar waveguide is presented. The broadband CP operation can be achieved simply using a C‐shaped slot in the ground to produce orthogonal surface currents for left‐hand circular polarization. Using the semicircle‐shaped radiator patch, wide impedance bandwidth and broad axial‐ratio (AR) bandwidth can be obtained simultaneously. The measured results show that the proposed antenna can provide a 10‐dB impedance bandwidth of 105% from 2.78 to 8.92 GHz, and a 3‐dB AR bandwidth of 70.4% from 2.9 to 6.05 GHz. Finally, an antenna prototype with a reflector for unidirectional pattern applications is also developed. The proposed antenna has broader impedance and CP bandwidths but with a more compact size compared with the previous designs. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:739–746, 2015.     

Gain and bandwidth enhancements of sequential‐fed circularly polarized patch antenna array using multiple parasitic elements

This paper presents a circularly polarized (CP) antenna array with wideband operation and high gain characteristics. The single array element is composed of a slotted CP patch and parasitic elements. It has been found that besides improving the operating bandwidth (BW), properly choosing a number of parasitic elements can also contribute to a significant increase in the antenna gain over the entire operating band. For further boost in the performance, multiple array elements are arranged in 2 × 2 configuration and fed by a sequential‐phase feeding network. In comparison with the related works in the literature, the proposed design shows approximately 3‐dB higher gain. The design concept has been validated by experiments. The fabricated array has a measured operating BW of 28% (4.6‐6.1 GHz) and a peak broadside gain of 15.8 dBic.     

Compact four‐element MIMO SIW cavity backed slot antenna with high front‐to‐back ratio

In this article, a novel design of single layer, compact, multiple input multiple output (MIMO) half‐mode substrate integrated waveguide (HMSIW) cavity backed quad element slot antenna with high front‐to‐back ratio (FTBR) is proposed. The proposed antenna consists of four rectangular SIW cavities with semi‐taper radiating slots. The antenna elements are placed in a fashion to achieve high isolation. This antenna is designed for WLAN vehicular communication system to cover the frequency range of 5.84 GHz to 5.96 GHz. It has high front to back ratio (FTBR) of more than 25 dB without using any external metallic reflector. It has more than 37 dB isolation in between orthogonal elements and more than 24 dB in between parallel elements. The envelop correlation coefficient (ECC) and diversity gain are 0.003 and 9.99 dB respectively in between all the elements. Moreover, the antenna has high gain and efficiency of more than 8 dB and 94%, respectively, in 10 dB impedance bandwidth. It can be tuned in a wide range of frequency.     

A new broadband circularly polarized square‐slot antenna with low axial ratios

A new broadband circularly polarized (CP) square‐slot antenna with low axial ratios is proposed in this article. The antenna is comprised of an L‐shaped microstrip line with tapered section and a square‐slot ground plane with some stubs and slots, which are utilized as perturbations for the desirable antenna performance. By loading stubs and slots in the square‐slot ground plane, the 2‐dB axial ratio bandwidth (ARBW) and 10‐dB return loss bandwidth for the presented antenna can be markedly improved. The measured results show that its 2‐dB ARBW is 4.2 GHz (54.2% from 5.65 GHz to 9.85 GHz) and its 10‐dB return loss bandwidth is about 8.9 GHz (92.7% from 5.15 GHz to 14.05 GHz). The proposed antenna features compact structure and broad 2‐AR bandwidth which could completely cover the WLAN (5.725‐5.85 GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band.     

Compact slot‐loaded ultra‐wideband multiple‐input multiple‐output antenna with fractal‐inspired isolator

In this paper, a compact multielement ultra‐wideband (UWB) multiple‐input multiple‐output (MIMO) antenna is presented. The proposed antenna is designed by integrating novel technique of stub‐loaded slot, split square ring (SSR), and fractal‐inspired isolator. The antenna size is effectively miniaturized by implementing three‐sided symmetrical stub‐loaded Koch slot and square split ring. The impedance bandwidth is broadened by using small notched partial ground plane. The mutual coupling between the element is impressively reduced by isolating the structure with a Sierpinski fractal. As a result, the proposed antenna achieves a UWB response with a very broad impedance bandwidth of 3.1 to 19 GHz. Moreover, the proposed antenna obtains high peak stable gain and diversity gain of up to 10 dBi, lower group delay (<1 ns), and lower envelop correlation coefficient of <.01. The proposed antenna has electrically small dimensions of 35 × 53 × 0.8 mm. With this low‐profile configuration, the proposed antenna is especially a good candidate for portable UWB‐MIMO wireless communication system.     

Antipodal tapered slot antenna array using broadband decoupling structure for mutual coupling reduction

In this article, an effective method to reduce the mutual coupling between the antipodal tapered slot antenna (ATSA) array is proposed. This method is mainly implemented by loading a set of decoupling structures (DS) perpendicular to the dielectric substrate between two antenna elements. The proposed DS can provide transmission forbidden band which can effectively prevent leaked electromagnetic waves. DS can operate in most frequency bands within 4 to 17.5 GHz. It can enhance about 23 dB isolation between the ATSA array without affecting bandwidth and radiation characteristics. The proposed ATSA arrays are fabricated and tested. The measured results can verify its excellent properties. The proposed broadband decoupling method is a suitable candidate for restrain mutual coupling of ultra‐wideband planar end‐fire antennas. This design sheds new light on broadband decoupling.     

Gain enhancement of the ultra‐wideband tapered slot antenna using broadband gradient refractive index metamaterial

In this article, a broadband gradient refractive index (GRIN) metamaterial is designed and used to enhance the gain of the tapered slot antenna (TSA). The proposed GRIN is implemented using nonresonant parallel‐line unit cell with different refractive index values. GRIN lens are placed in front of the tapered slot direction in the direction of x‐axis. The designed GRIN metamaterials have broad bandwidth (2‐12 GHz) characteristics due to the nonresonant parallel‐line elements which is suitable for the ultra‐wideband frequency band. The measurement results indicates that the radiated beam becomes more directive with narrow beam width. The measured reflection coefficient is below ?10 dB over the frequency bandwidth of 3‐11 GHz. The peak gain of TSA is obtained up to 14 dB at 10 GHz using GRIN lens.     

Planar circularly polarized X‐band array antenna with low sidelobe and high aperture efficiency for small satellites

A planar broadband circularly polarized (CP) X‐band array antenna with low sidelobe and high aperture efficiency is presented for small satellite applications. The array design is composed of 4 × 4 broadband CP stacked patch elements, which are fed by a feeding network consisted of unequal series‐parallel power dividers to achieve the low sidelobe and high aperture efficiency. The final prototype with overall size of 100 mm × 100 mm × 3 mm (2.73λ₀ × 2.73λ₀ × 0.082λ₀ at 8.2 GHz) was fabricated and measured. The antenna has a broadband characteristic with |S₁₁| < ?10 dB bandwidth of 15.9% (7.52‐8.82 GHz) and 3‐dB axial ratio bandwidth of 11.95% (7.63‐8.60 GHz). Also, it achieves an excellent broadside CP radiation with a gain of 17.2‐20.03 dBic, a sidelobe level of <?20 dB, and aperture efficiency of 65% to 97.5%. With these features, the proposed antenna is a good candidate for high‐speed data downlink onboard small satellites (MiniSat, MicroSat, NanoSat, and CubeSat).     

Mutual coupling reduction by SIW ZOR elements on broadside high gain CP beam steering array

In this article, a new circularly polarized (CP) beam steering array antenna based on substrate‐integrated‐waveguide (SIW) is proposed for mm‐wave applications. To generate a wider half power beamwidth (HPBW) and reduce mutual coupling effect a radiation element relying on zeroth order resonance (ZOR) technique has been used which has a treatment such as electromagnetic band gap (EBG) structure to have a specific structure. The antenna element can operate in a bandwidth from 33.82 to 36.37 GHz and AR bandwidth from 34.32 to 35.94 GHz. Besides, the propose element has a HPBW wider than 103°, and a maximum gain of antenna is of 9.2 dBic. A 4 × 4 Butler matrix feed network based on SIW feeding technique is then designed. This feed network includes novel techniques in designing cross‐over and broadband phase shifter. The synthesis of proposed Butler matrix and ZOR elements lead to a four‐beam array antenna with circular polarization can cover a beam switching angles range more than 44° with a gain of 17.6 dBic.