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.     

Broadband simultaneously RHCP‐LHCP radiating microstrip fed rectangular slot antenna for polarization diversity applications

In this article, for the first time, an antenna that can radiate LHCP and RHCP waves simultaneously is presented. The antenna enables simultaneous transmission of both right‐handed (RH) and left‐handed (LH) circular polarized (CP) waves separately over an elevation range from ?45 ^° to ?5 ^° and 5 ^° to 45 ^° from the zenith. The simultaneous radiation of dual sense CP in the different spatial directions enables the antenna to act as polarization diversity transmitter. The mechanism of virtual sequential rotation of magnetic currents inside the different parts of the slot, excited with uniform phase fields results in dual CP generation. The uniform phase orthogonal fields are generated in the different parts of the slot essentially by exciting the full wavelength rectangular slot loaded with grounded stubs, symmetrically, with a shorted microstrip line. The final design of the slot antenna arrived with a rigorous parametric study on different dimensional parameters of slot and grounded stub. The measured impedance bandwidth of 22.5% centered around 7 GHz and axial ratio bandwidth of 19% is achieved. An overlapping bandwidth of 17% is achieved where both matching and AR are very good. The measured isolation between the RHCP and LHCP in the above‐mentioned elevation ranges is maintained above 10 dB. The simulated and experimental results are matching very well.     

Compact frequency reconfigurable triple band notched monopole antenna for ultrawideband applications

A compact ultra‐wideband (UWB) reconfigurable microstrip fed monopole antenna having size of 0.22 λ₀ × 0.28 λ₀ × 0.005 λ₀ with switchable frequency bands is presented. Triple band notched characteristics are achieved by inserting two stubs at top of radiator and one slot in between the radiator and microstrip feed line. Proposed antenna achieves reconfigurability with three PIN diodes at strategic positions to obtain eight different operational modes. In one of the operational modes, antenna operates in the entire UWB (3‐14 GHz) with fractional bandwidth of 127.5%. Two stubs are used to notch two frequency bands worldwide interoperability for microwave access (3.3‐3.6 GHz/WiMAX) and C‐band (3.7‐4.2 GHz). T‐shaped slot is also inserted to notch wireless local area network (5.725‐5.825 GHz/WLAN) frequency band. Proper biasing of PIN diodes is done by using suitable chip inductors and capacitors. Proposed antenna exhibits stable radiation patterns with average gain of around 3 dBi. Simulation and measurement results are in good agreement. Proposed antenna is suitable for on‐demand band rejection of parasitic bands coexisting in UWB.     

A wideband circularly polarized slot antenna with antipodal strips for WLAN and C‐band applications

A single‐fed circularly polarized square shaped wide slot antenna with modified ground plane and microstrip feed has been presented. The field in the slot is perturbed by introducing an antipodal strips section attached with a microstrip line to produce circular polarization in a wide band of frequencies. The antipodal strip section consists of a group of four strips of unequal length and separation. The presence of asymmetric perturbations in the slot is mainly responsible for exciting two orthogonal modes in the slot having equal magnitude and 90° phase difference which results in circular polarization. A wide bandwidth of 3.3 GHz (4.4 GHz‐7.7 GHz) has been achieved for an axial ratio value AR < 3 dB with the minimum axial ratio value being 0.3 dB. The impedance bandwidth for |S₁₁| < ?10 dB ranges from 4.3 GHz to 8 GHz, and therefore covers most of the C‐band communication systems. The antenna exhibits stable radiation patterns throughout the circular polarization bandwidth with a gain around 6 dBi in entire operational bandwidth. A prototype of antenna was fabricated and measured. The antenna has a planar size 0.40λ₀ × 0.40λ₀ and thickness of 0.02λ₀ where λ₀ is the wavelength in free space at the lowest frequency. With its compact size and low profile, the antenna is a favorable choice for WLAN (5.15‐5.85 GHz) and a wide variety of C‐band wireless applications.     

A bandwidth‐agile balanced filtering power divider

In this article, a balanced filtering power divider (FPD) that allows for operational agility of the bandwidth (BW) is presented. The differential‐mode power dividing and high common‐mode (CM) suppression can be realized by microstrip‐to‐slotline transition. Two slotline open stubs with different lengths are added in shunt to the main slotline for the transition, which can not only introduce transmission poles for extending and controlling transition BW, but also generate two extra transmission zeros (TZs) near to the passband edges, featuring good filtering response. The two transmission poles can be independently tunable by loading varactors to the open ends of slotline stubs and two TZs will be changed accordingly so that the filtering passband BW is electrically tunable. To verify the theoretical prediction, a prototype of tunable balanced FPD is fabricated and measured. The measured results show that the 3‐dB fractional bandwidth (FBW) of the passband varies from 5.6% to 12.6%, meaning more than a double tuning range for the FBW, and the CM suppression is better than 40 dB across the frequency band of interest.     

Design and development of enhanced bandwidth multi‐frequency slotted antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐band applications

A multi‐frequency rectangular slot antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐bands applications is presented. The proposed antenna is comprised of rectangular slot, a pair of E‐shaped stubs, and an inverted T‐shaped stub and excited using staircase feed line. These employed structures help to achieve multiband resonance at four different frequency bands. The proposed multiband slot antenna is simulated, fabricated and tested experimentally. The experimental results show that the antenna resonates at 2.24, 4.2, 5.25, and 9.3 GHz with impedance bandwidth of 640 MHz (2.17‐2.82 GHz) covering WiMAX (802.16e), Space to Earth communications, 4G‐LTE, IEEE 802.11b/g WLAN systems defined for S‐band applications. Also the proposed antenna exhibits bandwidth of 280 MHz (4.1‐4.38 GHz) for Aeronautical and Radio navigation applications, 80 MHz (4.2‐4.28 GHz) for uncoordinated indoor systems,1060 MHz (5.04‐6.1 GHz) for the IEEE 802.11a WLAN system defined for C‐band applications and 2380 MHz (7.9‐10.28 GHz) defined for X‐band applications. Further, the radiation patterns for the designed antenna are measured in anechoic chamber and are found to agree well with simulated results.     

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.     

Slot loading effect on impedance and radiation performance of high‐gain patch antenna under TM03‐mode operation

Based on antenna's impedance and radiation performance, the slot loading effect on the TM₀₃‐mode high‐gain square patch antenna is investigated in this paper. Three different slot configurations are loaded to the patch along the central line, which can reduce the sidelobe in the E‐plane. However, it is found that the H‐plane beamwidth, impedance bandwidth and radiation Q factor become significantly different in these cases. At first, broader H‐plane beamwidth, lower Q factor and wider impedance bandwidth can be obtained when only single slot is loaded in the center of the patch. In contrast, when two open slots are etched at two nonradiative edges of the patch, it will result in narrower H‐plane beamwidth, higher Q factor and narrower impedance bandwidth. Moreover, better balanced performance can be achieved by simultaneously loading the central and sided slots. For validation, three kinds of antenna prototypes are designed, fabricated, and measured. The measured and simulated results agree well with each other, which demonstrate that different impedance and radiation performance can be freely adjusted and achieved by using different slot configurations.     

A dual‐broadband circularly polarized halved falcate‐shape printed monopole antenna

A halved falcate‐shape dual‐broadband circularly polarized printed monopole antenna is proposed. To generate the equal amplitude orthogonal modes, two halved falcate‐shaped antenna are used. Also, to provide the 90° phase difference between the two modes, three stubs are used in the ground plane of the antenna. The proposed antenna provides 22.6 (1.36–1.72 GHz) and 44.4% (5.25–8.25 GHz) 3 dB axial ratio bandwidth over the lower and upper bands, respectively. By adjusting the parameters of the antenna, the lower and upper band center frequencies can be tuned individually. The proposed antenna is fabricated, and results are compared with those of the simulation. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Printed slot antennas for various wideband applications using shape blending

This article presents a novel design of wide slot antenna for various wideband applications created using a shape‐blending algorithm. The proposed printed antenna consists of a wide rectangular slot and a tuning stub, which is formed by blending the shapes of from a cross and a square. Various bandwidths can be obtained based on the structure with different blended shapes. The impact of the antenna geometry on the antenna performance has been investigated and analyzed in detail. To verify the proposed designs, six prototypes of slot antennas with various tuning stub shapes are designed, fabricated, and measured. The simulated results are compared with the measured performance and show good agreement. A bandwidth range from 38.5 to 126.4% for voltage standing wave ratio (VSWR) less than 2 is exhibited by selecting different blended shapes, which can be served as an antenna design guideline. Moreover, the proposed type of antenna has a compact size and a simple structure, which make it an excellent candidate for wideband applications. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:3–12, 2016.     

Analysis of slot‐based radiators using TCM and its application in MIMO antennas

In this article, with the help of the theory of characteristic modes (TCM), it is found that the introduction of circular slots in a chassis modifies the chassis modes. Based on the location of the slot, different chassis modes will be affected. For a fixed location, the slot to chassis size ratio plays an important role in its effect on the radiating bandwidth (BW). For a small size ratio, a modified chassis mode will be created without affecting the radiating BW. The current concentration across the slot depends on the shape of the slot (circular, rectangular, triangular, or square) and its location on the chassis. Moreover, the effect of multiple circular slots on the chassis modes is investigated. For slots introduced in a symmetrical fashion, that is, four elements, the modes are not affected and are similar to the original chassis ones. We also investigate the principle behind frequency reconfigurability using TCM analysis. The varactors used for frequency reconfigurability do not alter the radiating BW (Modal Significance plots) but only help in the input impedance matching at different frequency bands of the same mode. If a mode is excited purely using a proper feeding arrangement, the same frequency reconfigurable antenna will behave as a wide band one. Based on the detailed analysis presented in this work, a compact multiple‐input‐multiple‐output annular slot frequency reconfigurable antenna operating between 1.8 and 2.45 GHz is presented. Frequency tuning is achieved using varactor diodes.     

Novel planar dual‐band balanced antipodal slot‐dipole composite antenna with reduced ground plane effect

A novel planar, dual‐band antenna composed of a symmetrical dipole and balanced antipodal slot radiator with low ground plane effect is proposed and investigated. Operation principle of the antenna is analyzed and design equations are drawn first. Then, the return loss, surface current distribution, radiation patterns, and gain are numerically and experimentally studied in detail. The impedance bandwidth of the antenna is from 2.36 to 2.56 and 5.13 to 12 GHz for return loss larger than 10 dB. The antenna has omnidirectional pattern at the lower band and quasi‐directional pattern at the higher band, and it has good immunity to a neighboring, large ground plane. The proposed antenna should be useful for dual‐band communication or identification systems. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

A compact UWB bandpass filter with a notched band using a multistubs loaded resonator

A novel multistubs loaded resonator (MSLR) is proposed in this article, which is constructed by several open‐ and short‐circuited stubs. The analysis shows that it is characterized by four resonant modes. Then, the MSLR is applied in the design of a compact ultra‐wideband (UWB) bandpass filter. The measured results show that its 3dB bandwidth can cover [3.0, 11.5] GHz, that is, 3 dB fractional bandwidth is 117%, and the return loss within the passband is greater than 15 dB. Especially, the roll‐off rate is higher than 33 dB/GHz and more than 40 dB harmonic suppression can be achieved up to 17 GHz. In order to suppress the interference of some undesired narrowband signal such as wireless local‐area network (WLAN) radio signal, a notched band is created for the UWB bandpass filter, which is realized by forming one stepped slot on each of the feedlines, respectively. The measured results show that a notched band with 2.01% fractional bandwidth at the center frequency of 5.85 GHz can be achieved and its suppression is about ?19 dB.     

A polarization reconfigurable CPW fed monopole antenna with L‐shaped parasitic element

A coplanar waveguide fed polarization reconfigurable monopole antenna is proposed in this letter. The proposed antenna consists of L‐shaped stubs placed on either side of a monopole, two p‐i‐n diodes and a slot in the ground plane. In the proposed antenna structure, the switching element is not directly connected to the feed line. Depending on the switching state of the p‐i‐n diodes, the antenna either radiates left/right circular polarization or linear polarization. To validate the proposed design, the antenna was fabricated and its performance was measured. Since the ground plane is electrically small, the effect of the cable and SMA connector on the performance of the antenna is also investigated. The measured impedance bandwidth is 66.78% (3.67 GHz to 7.35 GHz) and the axial ratio bandwidth is 13.62% (4.24‐4.86 GHz) for circular polarization and 23.61% (3.81‐4.83 GHz) impedance bandwidth for linear polarization.     

A wideband compact antenna with quad‐circular polarized bands in its operating regions

This article presents the design of an offset CPW‐fed slot antenna which exhibits a narrow impedance bandwidth (IBW; |S₁₁| ≤ ?10 dB) extending from 1.20 GHz to 1.45 GHz and another wide impedance bandwidth from 1.86 GHz to 8.4 GHz thus covering almost all the conventional operating frequencies. The antenna is loaded with semicircular and rectangular stubs and meandered microstrip lines to realize circular polarization at 1.35 GHz, 3.3 GHz, 4.9 GHz, and 7.5 GHz with axial ratio bandwidth (axial ratio ≤ 3 dB) of 19.25% (1.2‐1.46 GHz), 4.24% (3.24‐3.38 GHz), 4.1%(4.8‐5 GHz), and 5.2% (7.3‐7.69 GHz) respectively thus covering the GPS, WiMAX, WLAN, and X‐band downlink satellite communication application bands. The mechanism of generation of CP is discussed using vector analysis of surface current density distribution. The gain is fairly constant in the wide IBW region with maximum fluctuation of 1.2 dB. The structure is compact with an overall layout area of 0.27λ × 0.27λ, where λ is the free‐space wavelength corresponding to the lowest circular polarized (CP) frequency. A comparison of the proposed antenna with previously reported structures is performed with respect to impedance bandwidth, compactness, number of CP bands, LHCP to RHCP isolation and gain to comprehend the novelty of the proposed design. A prototype of the proposed antenna is fabricated and the measured results are in accord with the simulated results.     

Design of a low‐profile broadband antenna with E‐shaped patch cells

This article presents a low‐profile broadband antenna. The E‐shaped metal cells are utilized on the top layer, which is excited by the microstrip line through the coupling slot in the ground plane. The characteristics of the E‐shaped patch cell and antenna are extensively investigated and presented. Dual resonances with close proximity are obtained to realize wideband impedance matching. An attractive feature is found that the bandwidth of the antenna exhibits good correlation with the inductance. The interesting analysis is presented by directly loading inductors to the antenna, and the bandwidth shrinks quickly with larger inductance loaded. Therefore, the antenna proposed in this article has good potential in bandwidth tuning applications. A typical bandwidth from 5.1 to 6.7 GHz is achieved by the fabricated antenna with a maximum measured gain of 10.4 dBi. Meanwhile, the antenna remains a low profile of 0.09 λ _g.     

Circular microstrip antenna with off‐centered Y‐slot

A novel dual‐frequency broadband design of a single‐layer single‐feed circular microstrip antenna with an off‐centered Y‐slot is demonstrated in this communication. By selecting a suitable location of the Y‐slot in the circle, the proposed antenna on glass epoxy FR‐4 substrate not only resonates efficiently at two closely spaced frequencies (2.736 and 2.868 GHz) but also offers improved bandwidth (210 MHz or 7.5%) in comparison with a conventional circular microstrip patch antenna (～2%). From the measured results, almost identical broadside radiation patterns are obtained at two resonant frequencies, and the variation of less than 1 dBi in gain values is achieved in the frequency range where broadband behavior is observed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure

In this article, a wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure is presented. By means of the differential microstrip‐slot‐line‐microstrip transition, the proposed filter has a wideband bandpass filtering response. Simultaneously, the utilization of the strip‐loaded slot‐line extends its upper stop‐band. The proposed bandpass filter has wider upper‐stopband, wideband bandpass response, and intrinsic high common‐mode (CM) suppression. To verify the design concept, one filter example has been designed, fabricated, and measured. It has a differential‐mode (DM) 3‐dB fractional bandwidth of 157% with a low 0.82 dB minimum insertion loss. What's more, it shows a very wide 20 dB DM stop‐band bandwidth of 6.5 f_0d. The experienced results are in good agreement with the theoretical and simulated results.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

A wideband reflectarray antenna using single‐layer dipole element attached with T‐shaped stubs

A wideband reflectarray antenna consisting of single‐layer dipole element attached with T‐shaped stubs is proposed. By varying the lengths of the T‐shaped stubs, the unit cell can provide a linear phase curve covering about 420°. Critical design parameters are analyzed to understand its wideband operating mechanism. Using this novel type of unit cells, a 441 element 25° offset‐fed reflectarray with grid spacing of λ/3 at 10 GHz is designed, fabricated, and measured. The experimental results show that the proposed reflectarray can achieve 1‐dB gain bandwidth of 24% and 1.5‐dB gain bandwidth of 37%. In addition, aperture efficiency of 66.6% and cross polarization level of 29 dB are obtained at 10 GHz, respectively.