Spiral Slot Research Articles

A low‐profile circularly polarized antenna based on a circularly symmetric high impedance surface

A circularly symmetric high impedance surface (HIS)-based low-profile circularly polarized antenna with stable phase center is investigated. The antenna consists of a series-fed eight-arm spiral slot antenna and a circularly symmetric HIS (CSHIS) used as the ground plane. As the use of CSHIS, the profile of antenna is decease to as low as 0.09λ (λ is the free space wavelength), while the phase center of the antenna maintains stable. Also, the gain of the presented antenna is enhanced compared with that utilizing HIS with rectangular unit cell. For verifying, a prototype of the antenna was fabricated and measured. The measured results show that the overlap bandwidth of 3-dB axial ratio and impedance matching covers 1.14–1.45 GHz (23.9%), and the gain can reach as high as 7.79 dBic. Over the operation band, stable phase center also can be observed.

Investigations on a circular UWB antenna with Archimedean spiral slot for WLAN/Wi-MAX and satellite X-band filtering feature

AbstractIn this article a compact circular monopole antenna is represented with dimensions of 38.87 × 24.00 × 1.60 mm3 applicable for WLAN/Wi-MAX and satellite band rejection characteristics. The impedance bandwidth is 9.42 GHz (3.12–12.54 GHz) for the final antenna with an equivalent fractional bandwidth of about 120.31%, producing triple notched bands centered at 3.95, 5.20 and 8.90 GHz with assistance of Archimedean spiral slot and incorporation of defected ground structure allowing WLAN (5.2 GHz), WiMAX (3.5 GHz) and higher satellite X-band (8.5 GHz) filtering abilities. Simulations of the antenna are performed to attain preferable return loss properties as well as gain and omni-directional radiation patterns. The suggested antenna yields a peak gain of about 7.46 dBi at 11.30 GHz and experimental values are in good obedience with simulated ones.

Twelfth mode on-demand band notch UWB antenna for underlay cognitive radio

A wide-slot ultra-wideband (UWB) antenna with on-demand band rejection characteristics that can serve underlay cognitive radio is presented in this paper. This antenna is designed to work in twelve operation modes; one to cover the whole UWB while each of the rest modes excludes one or more of the ranges that are allocated for Worldwide Interoperability for Microwave Access (WiMax), C-band, wireless local area network (WLAN), X-band and International Telecommunication Union (ITU) in a single, dual, triple, quad or penta band rejection state. A spiral shape slot in the patch and three slots mainly based on half-circular structures in the ground plane are the means to create the desired frequency notches. A positive-intrinsic-negative (PIN) diode across each of these slots is used to enable/disable band(s) rejection process. Configuration of the proposed antenna to the desired mode of operation is decided by the state of its four PIN diodes. This work is simulated by computer simulation technology (CST) v.10. It’s S11, voltage-standing-wave-ratio (VSWR) and realized gain results when combined with antenna's 25x25x0.8 mm3 compact size and the large number of modes and states, all ensure its capability to eliminate or reduce the interference within the targeted bands and hence being suitable for the applications of underlay cognitive radio.

Broadband circularly polarized compact MIMO slot antenna based on strip and stubs for UWB applications

ABSTRACT A small-size broadband circularly polarized (CP) two-element multiple-input–multiple-output (MIMO) slot antenna with a very low envelope correlation coefficient (ECC) is proposed for ultra-wideband (UWB) applications. Broadband circular polarization is attained by embedding the identical pair of spiral slots, rectangular slot, and grounded-L stub on the I-shaped slot antenna. Isolation is achieved through embedding two different slots between mirrored CP square slot antenna elements. The proposed MIMO antenna provides 58.82% (4.8–8.8 GHz) 3-dB axial ratio bandwidth (ARBW), 138.32% (3.17–17.39 GHz) impedance bandwidth (IBW), and more than 16 dB port isolation over the operating band. The MIMO slot antenna size is 40 × 20 mm2 with a measured peak gain of about 4.41 dBi and efficiency more than 70%. The diversity performance is computed and presented in detail.

Compact 4 × 4 Proximity Coupled Microstrip Fed UWB Stepped Slot MIMO Antenna Having Triple Band Rejection

The presented antenna is a novel highly isolated compact four-element Multiple Input Multiple Output (MIMO) antenna with common ground, which can reject three undesired bands effectively for Ultra-Wideband (UWB) Communication. The overlapping of narrowband communication systems with the UWB spectrum makes radio signals interfere. Therefore, the proposed antenna is designed with triple-band rejection capability. The antenna consists of four feedlines and a common ground surface which acts as the main radiator. The four elements of the antenna are kept orthogonally to exploit polarisation diversity, resulting in high isolation. The presented antenna is having size = 44 × 44 mm2 and printed on FR4 substrate. A spiral slot was introduced in the ground surface which behaves similarly as a band-stop filter (BSF) and rejects the X- band for Uplink Satellite Communication. For rejecting WiMAX and WLAN band, the modified trident shape of the microstrip line is used. Also, Defected Ground Structure (DGS) is used for the isolation (> 23 dB) enhancement. Simulation and measurement results are quite similar. The proposed antenna is used for small handheld communication devices.

Bandwidth and gain enhancement of composite right left handed metamaterial transmission line planar antenna employing a non foster impedance matching circuit board

The paper demonstrates an effective technique to significantly enhance the bandwidth and radiation gain of an otherwise narrowband composite right/left-handed transmission-line (CRLH-TL) antenna using a non-Foster impedance matching circuit (NF-IMC) without affecting the antenna’s stability. This is achieved by using the negative reactance of the NF-IMC to counteract the input capacitance of the antenna. Series capacitance of the CRLH-TL unit-cell is created by etching a dielectric spiral slot inside a rectangular microstrip patch that is grounded through a spiraled microstrip inductance. The overall size of the antenna, including the NF-IMC at its lowest operating frequency is 0.335λ0 × 0.137λ0 × 0.003λ0, where λ0 is the free-space wavelength at 1.4 GHz. The performance of the antenna was verified through actual measurements. The stable bandwidth of the antenna for |S11|≤ − 18 dB is greater than 1 GHz (1.4–2.45 GHz), which is significantly wider than the CRLH-TL antenna without the proposed impedance matching circuit. In addition, with the proposed technique the measured radiation gain and efficiency of the antenna are increased on average by 3.2 dBi and 31.5% over the operating frequency band.

Broadband circularly polarized compact MIMO slot antenna based on strip and stubs for UWB applications

ABSTRACT A small size broadband circularly polarized (CP) two-element multiple-input-multiple-output (MIMO) slot antenna with a very low envelope correlation coefficient (ECC) is proposed for ultra-wideband (UWB) applications. Broadband circular polarization is attained by embedding the identical pair of spiral slots, rectangular slot and grounded-L stub on the I-shaped slot antenna. Isolation is achieved through embedding two different slots between mirrored CP square slot antenna elements. The proposed MIMO antenna provides 58.82% (4.8–8.8 GHz) 3-dB axial ratio bandwidth (ARBW), 138.32% (3.17–17.39 GHz) impedance bandwidth (IBW), and more than 16 dB port isolation over the operating band. The MIMO slot antenna size is 40 × 20 mm2 with a measured peak gain of about 4.41 dBi and efficiency more than 70%. The diversity performance is computed and presented in detail.

Performance analysis of the longitudinal-torsional ultrasonic milling of Ti-6Al-4V

Titanium alloy is a typical difficult-to-cut material due to its high strength and high stiffness. To solve the problem of the low efficiency and poor surface quality in the milling of titanium alloy, this paper proposes a novel longitudinal-torsional ultrasonic vibration milling (LTUVM) process. An ultrasonic horn with spiral slots was designed to convert the longitudinal vibration into longitudinal-torsional vibration. The tooltip trajectory was modeled, and the finite elements analysis was used to analyze the cutting mechanism of LTUVM. The simulation results indicate a kind of separation cutting characteristics in every vibration cycle, which is beneficial to reduce the cutting force and improve the surface finish compared with the single longitudinal ultrasonic vibration milling (SLUVM). Then, cutting tests were conducted on Ti-6Al-4V to evaluate the performance of LTUVM. Experimental results demonstrated that the LTUVM could reduce the cutting force by 46–86% compared with the conventional milling (CM) and the SLUVM due to its separation cutting characteristics. Moreover, the surface morphology was analyzed, and a fractal dimension (FD) method was proposed to characterize the regularity and fragmental property of the machined surfaces. The surface morphology analysis results showed that the LTUVM can be used as a novel high-efficiency and high-quality surface texturing method for Ti-6Al-4V. The textured surface of the LTUVM has the superiority of high integrity and periodicity, which could be applied to effectively tune the tribological property of surface.

Research on 90° corrugated-horn antenna with spiral slots

In order to meet the requirement of the broadband communication system, a novel broadband 90° corrugated-horn antenna is proposed. The corrugations of the horn expand outward in the shape of Archimedes spiral.Simulated and measured results indicate that the optimal bandwidth of the new corrugated horn can reach 2∶1. Over the frequencies from 10 GHz to 20 GHz, the proposed antenna can produce the relatively-the-same phase center with low cross-polarization levels in 45° plane below −25 dB. In the wide frequency band, the beamwidth is relative constant and the −10 dB beamwidth of E-plane and H-plane is very close. The proposed design of corrugated slots can make the radiation pattern of the horn more symmetrical in a wide frequency band, which is a new idea to improve the performance of corrugated horn.

A Travelling-Wave-Fed Slot Spiral Antenna With Wide Axial-Ratio Bandwidth and Beamwidth for GNSS Applications

A travelling-wave-fed slot spiral antenna with wide axial-ratio (AR) bandwidth and beamwidth for GNSS applications is proposed in this paper. The evolution procedure of the proposed antenna can be classified into three steps. Firstly, 12 identical spiral slots are arranged concentrically in a compact area, and AR roundness in low elevation plane is improved by virtue of good rotational symmetry of slot radiators. Secondly, a two-turn travelling-wave feed line is sequentially coupled to the slots, and wideband response of desired magnitude ratio and phase difference of $E_{\theta }$ and $E_{\varphi }$ is obtained by optimizing the number and growth rate of microstrip turns. Thirdly, by supporting the antenna with a modified metallic cavity, the CP radiation performance in low elevation plane is well improved, and thus a widened AR beamwidth is obtained. Finally, the proposed antenna with satisfactory performance is realized in a diameter of $0.56\lambda _{0}$ and height of $0.12\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at center frequency 1.4 GHz. Measured bandwidth of $|S_{11}|$ fully covers the entire GNSS bands, and the 3-dB AR bandwidth ranges from 1.14 to 1.67 GHz (37.7%). Moreover, the 3-dB AR beamwidth exceeds 140° at 1.4 GHz.

A CPW‐fed compact square slot antenna with wideband circularly polarized for C‐band application

AbstractThis paper presents a compact wideband circularly‐polarized square slot antenna (CPSSA). The antenna is a coplanar waveguide feed structure with three T‐stubs toward the slot center and one semi‐circle tuning stub was etched to the feed line and modified inverted L‐shaped strips around the corners of the ground. Moreover, two spiral slots were loaded in the ground plane for exciting currents in a different direction. A prototype of the designed antenna is fabricated and measured to confirm the simulation results. A reasonably good agreement between the measured and simulated results in terms of the reflection coefficient <−10 dB and axial ratio are achieved. The 3‐dB axial ratio bandwidth achieved by the combination is from 4.35 to 8.15 GHz (60%, measured). The designed CPSSA has a compact size of 0.57λₒ × 0.57λₒ × 0.0116λₒ at the center frequency and fabricated on the FR4 substrate.

Design of single‐fed spiral‐shaped slotted planar antenna for GPS L2 and L5 applications

An innovative design of a right hand circularly polarised (RHCP) antenna at two different resonant frequencies that is GPS (global positioning system) L2 and L5 has been proposed in this study. The proposed design comprised the concept of slotted radiator excited with a coaxial probe. Two asymmetric spiral slots were incorporated in a rectangular radiator to realise size miniaturisation, the axial ratio bandwidth and beamwidth at L2 (1.22760 GHz) and L5 (1.17645 GHz) frequencies of GPS applications. The proposed design has accomplished an excellent axial ratio bandwidth and beamwidth at both GPS L2 and L5 bands. The size of the designed antenna has been , which makes it attractive for the consumer market. Measured and simulated results achieved that the antenna conquered RHCP radiation at two separate operating bands, i.e. GPS L2 and L5.

UWB aperture coupled circular fractal MIMO antenna with a complementary rectangular spiral defected ground structure (DGS) for 4G/WLAN/radar/satellite/international space station (ISS) communication systems

In this article, a dual-port aperture-coupled circular fractal antenna array is designed, developed and tested for its usage in 4G, WLAN, radar, satellite and ISS communication systems, covering C-band, X-band and Ku-band of frequencies. The proposed array is designed on two FR-4 substrates (with overall dimensions of 34 × 68.7 × 3.245 mm3) where the upper and lower substrate consists of circular fractal radiators (2nd order of iteration) and a feed network respectively. The aperture slots in the ground are transformed into complementary rectangular spiral slots with a tree-shaped DGS, to achieve the desired operational band (4.6–16.8 GHz) with improved matching performance. It provides a maximum gain of 4.57 dB (at 6.6 GHz) and high port-to-port isolation (S21 ≤ −19 dB) performance. The implementation of the proposed array in MIMO systems is validated by various diversity parameters like low ECC, high DG, high MEG, low CCL and stable TARC attributes. An acceptable agreement is achieved between the simulated and experimental results.

A complementary Sierpinski gasket fractal antenna array integrated with a complementary Archimedean defected ground structure for portable 4G/5G UWB MIMO communication devices

AbstractThis article presents the design, development, and experimental validation of an aperture coupled complementary Sierpinski gasket equilateral triangular fractal antenna array for portable 4G/5G UWB communication devices. The proposed antenna array is printed on two FR‐4 substrate layers (ε r = 4.4, height = 1.57 mm, and tan δ = 0.024) with two fractal triangular patches on the top layer (separated by a distance of 3λ/2) and feed network on the bottom layer of FR‐4. The fractal patches (optimized up to second order of iteration) are fed using an aperture‐coupled feeding mechanism, where the aperture slots in the ground layer are modified to complementary Archimedean spiral slots which are interconnected by a modified “X” shaped slot to improve the impedance matching at the operational bands. The proposed array has overall volumetric dimensions of 41 × 99.4 × 3.245 mm3 and provides a size reduction of 46% for the metallic area using the fractal geometry. The proposed array shows a simulated UWB response from 4.3 to 11.6 GHz (fractional bandwidth of 91.8% at 7.95 GHz) with a simulated peak gain of 4.7 dB (at 9.2 GHz) and port‐to‐port isolation of ≤−15.8 dB for the entire band. For validation of simulated responses, the proposed array is fabricated and tested for S‐parameters (S11, S22, S12, and S21). A measured impedance bandwidth of 6.3 GHz is observed for a frequency band from 5.7 to 12 GHz. Two additional frequency bands are also exhibited by the array from 4.1 to 4.25 GHz and 4.7 to 5.3 GHz. The array diversity parameters such as envelope correlation coefficient (≤0.007 [simulated], ≤0.0057 [measured]), diversity gain (≥9.999 [simulated], ≥9.971 [measured]), mean effective gain (≥−3.9 dB [simulated], ≥−5.1 dB [measured]), and channel capacity loss, (≤0.37 bits/s/Hz [simulated], ≤0.4 bits/s/Hz [measured]) which are calculated using the simulated and measured S‐parameters of the array are also observed. These parameters allow the proposed fractal array to be implemented in a diversity combining technique to improve the overall SNR and hence support a high data rate for 4G/5G multimedia services.

Dual‐band dual‐polarized leaky‐wave structure with forward and backward beam scanning for circular polarization‐flexible antenna application

AbstractIn this paper, a novel dual‐band dual‐polarized leaky‐wave antenna (LWA) with polarization diversity is proposed using half mode substrate‐integrated waveguide (HMSIW)‐based technology. HMSIW LWAs are generally single band. In this work, by etching simple spiral type slots on the HMSIW cavity, a novel dual‐band dual‐polarized LWA is designed. The proposed antenna resonates at 5.6 and 8.5 GHz. Moreover, the antenna radiates the linearly polarized wave in the lower band and circularly polarized (CP) wave in the higher operating band. Also, in the higher operating band between 8.7 and 9.3 GHz, the proposed overall antenna exhibits both right‐hand circular polarization as well as the left‐hand circular polarization in the near main beam direction. The −10 dB impedance bandwidth of the proposed antenna at the lower and the higher operating bands are 27% (4.86‐6.4 GHz) and 25% (7.4‐9.6 GHz), respectively. In the higher band, the 3‐dB axial ratio bandwidth of 6.6% (8.7‐9.3 GHz) is achieved. The main beam of the antenna can be steered from 19° to 69° in the forward direction in the lower operating band. In the higher operating band, the antenna can steer the CP beam between −17° and −32°. In both the lower bands, the realized peak gain is observed around 13.3 dBi, whereas in the higher band, the realized peak gain is observed around 14 dBi.

Frequency coupling design of ultrasonic horn with spiral slots and performance analysis of longitudinal-torsional machining characteristics

Longitudinal-torsional (L-T) vibration in rotary ultrasonic machining (RUM) can further reduce the cutting force and improve the machining efficiency compared with the single longitudinal vibration in RUM. In this study, an ultrasonic step horn with spiral slots using the principle of mode conversion was designed to realize L-T vibration. The torsional amplitude to longitudinal amplitude (AT/AL) ratio is proposed to quantify the efficiency of mode conversion. Moreover, a simulation method was used to carry out the frequency coupling design of the ultrasonic horn with spiral slots. The influence of the step position and slot position with a spiral angle of 52° on the resonant frequency and amplitude of the ultrasonic horn were analyzed, respectively. Based on the simulation results, ultrasonic horns with different AT/AL were designed and fabricated. Finally, the results obtained through experiments with milling glass plane revealed that the cutting force was reduced by 48–73%, while the surface quality improved compared with single longitudinal vibration when the torsional vibration is coupled with the longitudinal vibration in RUM. The reasonable AT/AL ratio could effectively reduce the cutting force when the synthetic amplitude was the same. This indicates that the L-T vibration changes the trajectories of the diamond abrasives, which improves the machining performance.

Estimating the mixture friction factor for the dense-phase transport of particulates in horizontal pipes with inner longitudinal spiral slots

This research was devoted to establishing a dimensionless model for estimating mixture friction factor based on the Buckingham Theorem. An experimental test-rig with conveying pipeline of 40 mm I.D was designed, assembled and used to collect the data needed to model the mixture friction factor. Experiments were carried out in four levels of slot depths (0, 0.35, 0.55 and 0.9 mm), three levels of air pressure (100, 200 and 300 kPa) and three pipeline lengths (3, 6 and 9 m). Conveying tests with three particulate materials of mung bean, corn, and polyethylene pellets were completed using three replications. Static air pressure across the conveyor, mass flow rate of discharge solids and inlet air mass flow rate were measured during the tests. The model developed can estimate the mixture friction factor within the range of variables studied. The comparison between predicted and measured mixture friction factor showed no significant difference. According to values of R 2 , RMSE, reduced chi-square and MRD parameters, mixture friction factor modelling of the pneumatic conveyor had good accuracy. Other results showed that the mixture friction factor was 65% less than that of pipelines with inner trapezoidal slots studied earlier, therefore lower upstream pressure was required for dense-phase pneumatic conveying of particulate materials in the new conveyor. The developed model showed acceptable error in predicting pressure drop from the experimental data.

A Compact EBG Structure With Etching Spiral Slots for Ultrawideband Simultaneous Switching Noise Mitigation in Mixed Signal Systems

In this paper, a compact electromagnetic bandgap (EBG) structure for mitigating simultaneous switching noise (SSN) in high-speed mixed signal systems is proposed. Only one spiral slot is etched on the square patch, which constitutes the unit cell of the presented EBG pattern. The equivalent circuit model is developed to interpret the mechanism of the proposed power distribution network structure. By etching slot in the square patch of the EBG pattern, a high impedance is provided for prohibiting the SSN propagation. Furthermore, the capacitance is increased correspondingly, which can enlarge the bandwidth of the SSN suppression performance. An ultrawideband SSN suppression property is achieved from 0.35 to 20 GHz under the suppression level of −40 dB. In comparison with the traditional multiturns spiral EBG structure, not only the bandwidth but also the rejection level can be improved significantly with the presented design. Moreover, the SI performance is investigated, and the corresponding improvement measure is presented. Good agreements are observed between the simulation and measured results.

Dual wideband circular polarized CPW-fed strip and slots loaded compact square slot antenna for wireless and satellite applications

A small size coplanar waveguide-fed dual wideband circularly polarized square slot antenna (CPSSA) is presented. It composed of an inverted C-shaped patch, grounded-L strip, a pair of grounded spiral slots and a horizontal rectangular grounded slot. The circular polarization (CP) is achieved by embedding grounded-L strip and a pair of grounded spiral slots. By engraving rectangular slot in left corner of CPW ground plane, the 3-dB axial ratio bandwidth (ARBW) of lower band is enhanced and it also generates another CP band at about 12 GHz and a notched band. From the experimental results, it is observed that the 3-dB ARBWs of the proposed antenna are 74.62% (5.01 GHz, 4.21–9.22 GHz) and 12% (1.37 GHz, 11.26–12.62 GHz) while the impedance bandwidths are 92.70% (6.48 GHz, 3.75–10.23 GHz) and 13.70% (1.63 GHz, 11.12–12.75 GHz) in lower and upper bands, respectively. The antenna has peak gain about 3.67 and 6.36 dBic in lower and upper CP bands, respectively, with good LHCP radiations. The overall size of antenna is 20 × 20 × 1 mm3.

Mutual Coupling Reduction of DRA for MIMO Applications

In this paper, A multiple input Multiple Output (MIMO) antenna using two Square Dielectric Resonators (SDRs) is introduced. The mutual coupling between the two SDRAs is reduced using two different methods; the first method is based on splitting a spiral slot in the ground plane, then filling the slot with dielectric material, "E.=2.2". The second method is based on inserting a copper parasitic element, having the same shape of the splitted Spiral, between the two SDRAs. The effect of replacing the copper parasitic element with Carbon nanotubes (CNTs) parasitic element "SOC12 doped long-MWCNT BP" is also studied. The antenna system is designed to operate at 6 GHz. The analysis and simulations are carried out using finite element method (FEM). The defected ground plane method gives a maximum isolation of l8dB at element spacing of 30mm (0.6λo), whereas the parasitic element method gives a maximum isolation of 42.5dB at the same element spacing.