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.     

High gain substrate integrated waveguide beam scanning antenna with sub‐array elements

A method to enhance the gain of substrate integrated waveguide (SIW) beam scanning antenna is proposed in this article. 2 × 2 SIW cavity‐backed sub‐arrays are employed in array design. The antenna is constructed on two layers. The top layer places four SIW cavity‐backed sub‐arrays as radiating elements and the bottom layer is an SIW transmission line to feed the sub‐arrays. Beam scanning feature can be obtained due to the frequency dispersion. Moreover, through separating radiators to the other layer and using 2 × 2 SIW cavity‐backed sub‐arrays as radiating parts, the antenna gain is improved significantly. For a linear array, 4.1 to 6.8 dB gain enhancement is achieved compared to a conventional SIW beam scanning antenna with the same length. Then, the linear array is expanded to form a planar array for further gain improvement. A 64‐element planar beam scanning array is designed, fabricated, and tested. Experimental results show that the proposed planar array has a bandwidth from 18.5 GHz to 21. 5 GHz with beam scanning angle from ?5° to 11.5° and gain in the range of 20.5 to 21.8 dBi. The proposed high gain beam scanning antennas have potential applications in radar detection and imaging.     

A high‐isolation dual‐polarized quad‐patch antenna fed by stacked substrate integrated waveguides for millimeter‐wave application

A high‐isolation dual‐polarized quad‐patch antenna fed by stacked substrate integrated waveguide (SIW) that is suitable for millimeter‐wave band is proposed in this paper. The antenna consists of a quad‐patch radiator, a two‐layer SIW feeding structure and two feeding ports for horizontal and vertical polarization. The two‐layer stacked SIW feeding structure achieves the high isolation between the two feeding ports (|S₂₁| ≤ ?45 dB). Based on the proposed element, a 1 × 4 antenna array with a simple series‐fed network is also designed and investigated. A prototype working at the frequency band from 38 to 40 GHz is fabricated and tested. The results indicate that the proposed antenna has good radiation performance at 38 GHz that covers future 5G applications.     

Quasi‐corrugated substrate integrated waveguide H‐plane horn antenna with wideband and low‐profile characteristics

A wideband H‐plane horn antenna based on quasi‐corrugated substrate integrated waveguide (SIW) technology with a very low profile is presented in this article. Open‐circuited microstrip stubs are applied to create electric sidewalls of the quasi‐corrugated SIW structure. The quasi‐corrugated SIW H‐plane horn antenna shows high performance and simple structure. A specify‐shaped horn aperture is utilized, so that the poor impedance matching owing to the structure restriction can be smoothened. The structure is simulated by ANSYS HFSS and a prototype is fabricated. The measured results match well with the simulated ones. An enhanced impedance bandwidth ranging from 5.3 GHz to 19 GHz (VSWR < 2.5) is achieved. The presented antenna also brings out stable radiation beam over the same frequency band.     

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).     

Compact bilayer substrate integrated waveguide leaky wave antenna with dumbbell‐shaped slot based on the TE20 mode

In this article, a compact dual layer leaky wave antenna array is simulated and constructed using the substrate integrated waveguide (SIW) based on the TE₂₀ mode at the X‐ and Ku‐bands. The proposed antenna is designed by creating dumbbell‐shaped slots on the upper layer of the SIW. These slots have increased the antenna bandwidth so that the proposed antenna has a bandwidth of 9.5 to 13.7 GHz and a fractional bandwidth of 36%. In addition, to excite the TE₂₀ mode, an SIW power divider is used in the feeding network of the antenna located in the bottom layer. Moreover, the gain and directivity are other advantages of the proposed antenna so that at 12.5 GHz the antenna peak gain reaches to 15.7 dB. Antenna beam scanning angle is from 5° to 81°. This antenna is simulated and analyzed by the CST Microwave Studio software. The obtained results from the antenna test lab confirm the simulation results.     

An SIW antenna utilizing odd‐mode spoof surface plasmon polaritons for broadside radiation

In this article, a substrate integrated waveguide (SIW) antenna utilizing odd‐mode spoof surface plasmon polariton (SSPP) for broadside radiation is proposed. Double gratings are etched on the top surface of SIW and the SSPP odd‐mode is excited on this hybrid SIW‐SSPP structure. The proposed SIW antenna has open‐circuit termination and can realize broadside radiation. A prototype of the SIW‐based odd‐mode antenna is fabricated. Reasonable accordance is achieved between measured results and simulated results. The antenna impedance bandwidth is about 5.5% (12.4~13.1 GHz) with |S₁₁| < ?10 dB. Stable broadside radiation is also realized within the operating band of 12.3~13.3 GHz and the measured gain varies from 5.66 to 6.34 dB in the frequency band. The proposed broadside radiation antenna is suitable for wireless communication systems due to its compact structure and good radiation performances.     

Compact substrate integrated waveguide mono‐pulse antenna array

A compact monopulse antenna array based on substrate integrated waveguide technology is presented through this article. The design is fabricated on Printed Circuit Board (PCB) technology consisting of a double‐layered 8‐cell array antenna with a slot in the middle‐ground metal used for aperture‐coupling excitation and reducing unwanted spurious emissions from feed network. The Impedance bandwidth and AR bandwidth are enhanced due to optimal feed network, including Rat‐Race coupler to generate sum and difference patterns for mono‐pulse applications operating at 10 GHz. The prototype of the proposed antenna with the size of 124*25 mm² is fabricated and tested. Measured results compared very well to simulation results obtained by CST microwave studio and show ?10‐dB impedance bandwidth of 4% and ?22 dB null‐depth in difference mode.     

Dual‐band circularly polarized aperture‐coupled stack antenna with fractal patch for WLAN and WiMAX applications

This article presents a novel circular polarized (CP) aperture coupled stack antenna for wireless local area network and worldwide interoperability for microwave access dual‐band systems. The compact stack antenna consisted of square fractal patch, aperture couple, feed line and the perturbation. The square patch is constructed with the complementary Minkowski‐island‐based fractal geometry. By way of adjusting the relevant parameters, we can obtain the dual‐band responses at 3.5 and 5.25 GHz respectively. The CP of each band are presented. The measured 10 dB return loss impedance bandwidth are 270 MHz (7.5%) for 3.5 GHz band and 450 MHz (8.6%) for 5.25 GHz band. The 3 dB axial ratio bandwidths for each bands are 1.4 and 0.76%, the polarization of radiation patterns are both left‐hand CP, and the antenna power gain are 2.84–3.1 and 0.16–2.2, dBic respectively. The proposed antenna is successfully simulated and measured with frequency responses, radiation patterns and current distributions. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:130–138, 2014.     

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.     

A coplanar‐waveguide‐fed planar integrated cavity backed slotted antenna array using TE33 mode

This short communication presents a substrate integrated waveguide planar cavity slotted antenna array. The proposed antenna array, excited in its TE₃₃ higher mode, incorporates a grounded coplanar‐waveguide (CPW) CPW‐feeding excitation mechanism. The electromagnetic energy is coupled to the air through 3 × 3 slot array etched on top metallic layer. The proposed antenna operates in the X‐band for the frequency range around the 10 to 11 GHz with resonances at 10.4 and 10.8 GHz frequencies. The proposed antenna array was fabricated and tested. Experimental results show good impedance matching with enhanced radiation characteristics, in terms of peak gain, cross‐polarization level, and low back‐radiation. The proposed antenna has the advantages of low‐footprints, lightweight, high gain, low‐cost, and ease of integration with other electronic circuits. With these characteristics, the proposed antenna array can find its applications in compact wireless digital transceivers.     

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.     

Low‐profile omnidirectional circularly polarized antenna based on substrate integrated waveguide technology

A substrate integrated waveguide (SIW) circularly polarized (CP) antenna with omnidirectional radiation in the azimuthal plane is proposed. The antenna consists of five identical end‐fire CP antenna elements in a pentagonal array configuration, which is loaded on a circular substrate. Each element contains an H‐plane horn antenna in SIW structure and a printed dipole antenna. Five parasitic curve elements are introduced to improve the omnidirectional property of the antenna. Combined with complementary dipoles theory and SIW technology, prototype antenna is designed, fabricated and measured. With a low profile of 0.024λ₀, the antenna has a 10‐dB return‐loss impedance bandwidth of 4.08% (2.4～2.5 GHz) and a 3‐dB axial‐ratio (AR) bandwidth of 5.76% (2.36～2.50 GHz). The antenna works well in the 2.45 GHz ISM band, with good cross‐polarization and excellent omnidirectional property.     

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.     

Dielectric resonator array antenna for triple band WLAN applications with enhanced gain

An H‐shaped dielectric resonator array antenna is presented for wideband applications. The proposed antenna is excited by slot feed mechanism and investigated experimentally. The antenna covers the frequency ranges from 1.41 to 2.59 GHz, and 4.73 to 6.06 GHz with the corresponding impedance bandwidth of 59% and 24.65%, respectively. The simulation results fulfill the bandwidth requirements of IEEE 802.11a/b/g (2.4‐2.484 GHz/5.15‐5.35 GHz/5.725‐5.825 GHz) for Wireless local area network (WLAN) applications. The proposed antenna has simple structure, easy to fabricate and its measured radiation pattern shows a reliable performance in the desired operating bands.     

Direct and electromagnetically coupled compact microstrip antenna design with modified fractal DGS

This article proposes ultra‐miniature microstrip patches with direct and electromagnetically coupled feeding mechanism for wireless communications at 10 GHz. Antenna size reduction is achieved here by loading a modified Minkowski fractal (type‐2) defected ground structure (MFDGS‐II) exactly beneath the radiating patch. The proposed method involves the selection of best DGS configuration through sensitivity analysis of the antenna structure. From different applications point of view, three different designs: a single layer direct fed patch and two electromagnetically coupled fed multi‐layered microstrip patch antennas are proposed here and designed with MFDGS‐II. The resonant frequencies of the antenna designs are reduced in a significant manner incorporating MFDGS‐II without any change in the physical size of the antenna. The prototypes of the proposed antennas are fabricated, and the performance parameters are measured. Compared with other existing structures, with a lower patch size of 0.20 λ₀ × 0.15 λ₀, the proposed single layered antenna with microstrip feed achieves a patch size reduction up to 67% and an overall volumetric reduction of 84%, respectively. Similarly, the proposed multi‐layered patch with proximity feed exhibits a maximum impedance bandwidth of 600 MHz and the aperture coupled fed patch has a realized gain of 6.2 dBi with radiation efficiency of 91% centered at 10 GHz. All three proposed compact antenna structures are best in three different aspects and have the potential to meet the practical requirements for X‐band portable wireless applications.     

Design of a linear array of fractal antennas with high directivity and low cross‐polarization for dedicated short range communication application

In this article, the authors proposed an eight‐element linear array of fractal antennas for dedicated short range communication (DSRC; 5.9 GHz) service band. The single element of the array is a newly proposed fractal antenna whose radiating patch is derived from the Fibonacci series with the incorporation of Koch snowflake, and it poses a 2D quadrantal symmetry. The gain of the structure is improved by down shifting the radiating patch with respect to its ground plane. The feed network of the array is designed in such a manner to make the structure compact as well as to use the advantage of array mutual coupling for improving the array radiation pattern. The fabricated single element gives 7.54 dB gain and 128 MHz bandwidth with a radiation efficiency of η = 85.11%. The prototype array gives 15.18 dB gain with 105 MHz bandwidth and radiation efficiency of η = 72.12%. The measured cross‐polarization of single element and the array along the direction of the main beam are less than ?80 dB and ?60 dB, respectively, in both the xz‐ and yz‐plane. Both single element and the array are capable of satisfying the bandwidth requirements for DSRC applications.     

A 2 × 2 array antenna with circular polarization and conical beam radiation

A circular disk patch antenna loaded with a hemi‐circular slot is initially proposed for achieving circular polarization (CP). To exhibit broad CP bandwidth that can cover the WLAN 2.4 GHz operating band, the patch antenna is fed by an L‐shaped probe. To further attain conical beam radiation with peak gain of ～8 dBic at ±30 degrees theta angle (θ), a 2 × 2 array type is proposed in this study, in which four circular disk patch array elements are arranged in a sequentially rotated fashion via a corporate feed network. Here, desirable 3‐dB axial ratio (AR) bandwidth and 10‐dB impedance bandwidth of ～5% and 21% were measured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:223–228, 2014.     

A dual‐feed microstrip grid array antenna for balanced or unbalanced operation

The development of a dual‐feed microstrip grid array antenna for either balanced or unbalanced operation to radiate pencil‐beam patterns has been described. As an example, the dual‐feed microstrip grid array antenna on RT/duroid 5880 substrate with a size of 60 × 60 × 0.787 mm³ or 4.8λ × 4.8λ × 0.063λ at 24 GHz were designed and fabricated. The measured results show that the dual‐feed microstrip grid array antenna has achieved excellent performances: 4.85% impedance bandwidth, 9.03% gain bandwidth, and 20.6‐dBi gain at 24.15 GHz as a balanced antenna and 6.05% impedance bandwidth, 7.74% gain bandwidth, and 17.8‐dBi gain at 24.15 GHz as an unbalanced antenna. The dual‐feed microstrip grid array antenna is a suitable antenna candidate for radar and sensor applications.     

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.