This paper presents a zeroth order metamaterial substrate integrated waveguide antenna. The antenna is designed to have a compact size based on employing only one composite right/left-handed cell. The antenna resonates at 6.1 GHz with overall radiator size of 14.4 mm × 8 mm2 which represents 50% size reduction compared to conventional microstrip antenna operates at the same frequency. The zeroth order mode of the antenna has been verified using both analytical explanation and full wave simulations. Moreover, the full wave simulations in addition to experimental measurements have been employed to demonstrate the antenna resonance and radiation characteristics.
In this paper, an improved broadband substrate integrated waveguide (SIW) phase shifter with embedded air strips is presented. Phase shifter can be generated based on the variable widths of SIW, variable lengths of microstrip line and a row of embedded air strips. The simulated and measured results both show that this kind of SIW phase shifter has excellent performance for a wider bandwidth. Measured results indicate that the proposed SIW phase shifters for the 45° and 90° versions have achieved the fractional bandwidths of 59.6% from 10.2 to 18.85 GHz with the accuracy of 2.5°, and of 62.3% from 9.5 to 18.1 GHz with the accuracy of 5°, respectively. The return losses are better than 15.8 dB and 14.5 dB for 45° and 90° modules, respectively. In addition, the insertion losses are both found to be better than 1.6 dB in the considered band.
In this paper, a novel approach is attained to the design of low profile antenna structures with wire dipoles and multiband operation. The aim is achieved by utilization of non-uniform Electromagnetic Band Gap (EBG) lattices as reflectors, and this potential comes to be added to the total of special capabilities of this type of Artificial Magnetic Conductors (AMC). It is proved that a properly designed EBG of this type can resonate at more than one frequency and is capable to drive, inside these bands, the dipole to higher order modes of operation besides its basic one. The resulting hybrid radiator apart from its multiband operation exhibits high gain that reaches the value of 9.6 dB, satisfactory Mean Effective Gain (MEG) and very low correlation coefficients, much less than 0.1, between the signals at the input of the dipoles in the case that the radiator is configured as an antenna array. The study of these quantities was performed using the signal parameters of a real mobile communication environment along with the hybrid antenna properties of operation. The presented analytical results show that the designed radiators are competitive to the classical microstrip ones and can be effectively used in modern wireless communication networks, incorporated either into stationary or into mobile units.
A magneto-electric dipole antenna with high front to back ratio (FBR) for femtocell base station is proposed. By using circular defects in the ground plane, the back radiation of the antenna is reduced. The prototype antenna achieves high FBR without affecting the bandwidth and gain. At S11 = -10 dB, the simulated and measured impedance bandwidths of the proposed antenna are 58.06% (1.54-2.8 GHz) and 60.9% (1.55-2.91 GHz), respectively. The measured FBR value ranges from 21 to 29 dB. Stable unidirectional radiation pattern at both planes and average gain of 7 dBi are also obtained.
MIMO systems have become an essential part in many communications networks and Long Term Evolution (4G) mobile communication systems. Mobile handsets using lower band of LTE (LTE-700 band) require antennas of reduced size that can be adapted to the limited space in the handset. This paper presents the design, optimization and implementation of two meandered-line PIFA antennas working as an MIMO system with high isolation for LTE-700 band mobile applications. To solve the problem of mutual coupling, a combination of decoupling arrangements was used to improve the isolation between the two antennas. The influences of various design parameters are investigated using the CST Microwave Studio Suite. A prototype of the proposed Meandered-line PIFA Antenna was fabricated and tested using vector network analyzer. Good agreement was found between the simulated and measured results. The fabricated MIMO antenna shows an isolation better than 12 dB and a -6 dB bandwidth of (75 MHz) in the frequency range from (720 MHz) to (795MHz). The antenna has 1.94 dB gain, total efficiency of 85%, and volume of 110 x 65 x 1.6 mm3, that is (0.275 x 0.1625 x 0.004) in wavelengths.
This paper presents the design, simulation, fabrication and measurement of a wideband bandpass filter with wide stopband performance operating at 3.5 GHz. The proposed filter consists of two parallel coupled lines (T-PCL) centered by T-inverted shape. The location of transmission zeros can be adjusted by varying the physical lengths of T-inverted shape to improve the filter selectivity. The wide bandwidth is achieved through enhanced coupling between the input and the parallel coupled lines. Due to the transmission zeros in the lower and upper stopbands, the filter exhibits good performance including an extremely wide stopband and sharp attenuations near the passband together with low insertion and good return losses in the passband. The filter performance is investigated numerically by using CST-MWS. Finally, the microstrip wideband BPF with minimum insertion losses 0.3 dB, centered at 3.5 GHz with a 3-dB fraction bandwidth of 70 % and four transmission zeros is implemented and verified experimentally. In addition, good agreement between the simulated and measured results is achieved.
Many traditional sparse signal recovery based ISAR imaging methods did not utilize the block scatterers information of targets. Some block Bayesian learning based ISAR imaging algorithms are computational expensive. In this paper, a 2D block l1l0 norms homotopy sparse signal recovery algorithm (the BL1L0 algorithm) is proposed and utilized to form the ISAR image. Compared with Bayesian-based algorithms, this algorithm can obtain ISAR images with similar image quality, but the computation speed is faster. Real data experiments verify the merits of our algorithm.
A wide-beamwidth circularly polarized (CP) asymmetric microstrip antenna is proposed by etching four novel unequal fan-shaped notches at the vertexes of the square radiator. A bandwidth of 1.5% and beamwidth of 156° are well achieved for an axial-ratio ≤ 3 dB (3-dB AR) at the central frequency of 1.575 GHz. To widen the bandwidth, the asymmetric microstrip antenna is further expanded with the construction of a 2×2 antenna array using sequentially rotated feeding technique. Moreover, by properly optimizing the distance between each two neighboring elements and the radii of the fan-shaped notches, the 3-dB AR bandwidth of the sequential-rotation array (SRA) is approximately extended to 7.8% with a wide-beamwidth at the central frequency of 1.6 GHz. In addition, the gain variation within the bandwidth is less than 1 dB. Finally, a laboratory model of the SRA has been fabricated, and acceptable agreement of the simulated and measured results makes it a good candidate for applications where wide-bandwidth, wide-beamwidth and small gain variation are needed.
A compact printed ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with embedded structure is proposed. The proposed MIMO antenna consists of two coplanar waveguide-fed (CPW) antenna elements, and the element with smaller size is built in the radiator of the other element. Thus, the compact size, 30 × 22 mm2, is completely determined by the larger one, which makes the MIMO antenna have similar size to the conventional single UWB antennas. The antenna elements are fed perpendicularly to achieve superior isolation. A T-shaped parasitic stub, a pair of C shaped slots, an extended Z-shaped stub and a rectangular slot are employed and each two structures filter the interference for one antenna element. The achieved rejection bands remain relatively stable over the stop-band frequencies and decline rapidly at cut-off frequencies. Thus the proposed MIMO antenna obtains superior filtering performance. The proposed antenna is fabricated and measured. The measured results indicate that two antenna elements can operate in the impedance bandwidth larger than 3.1-10.6 GHz with notched bands of 5-6 GHz, and the mutual coupling is below -15 dB over the entire UWB frequency spectrum. The proposed MIMO antenna is a competitive candidate for UWB MIMO communication systems.
A miniaturized microstrip rat-race coupler with harmonics suppression is proposed by using shorted trans-directional (TRD) coupled lines. The shorted TRD coupled lines consist of a set of capacitor-loaded λ/4 coupled microstrip lines with two shorts, which are used to replace the 3λ/4 uniform transmission-line section (UTLS) in the traditional 3λ/2 ring coupler for miniaturization. To attain perfect matching for any coupling factor of the TRD coupled lines, shorted TRD coupled lines are synthesized and the design equations are derived. To further reduce the ring size, T-type transmission-line equivalent circuits are also adopted to replace the λ/4 UTLS and associated with a transmission zero for harmonic attenuation. Using the proposed method, a microstrip ring coupler with 26.7% circuit size of a traditional one is fabricated and tested. The measured results show that the bandwidth for the return loss of better than 10 dB is 43.9% and that for isolation of better than 20 dB is 18.7% with a maximum isolation of 40.6 dB. There is no spurious passband up to the sixth harmonic of the design center frequency with more than 20 dB suppression from the third to fifth harmonics.
In this article, a dual-polarized hybrid cylindrical dielectric resonator antenna (CDRA) is studied. A ring-shaped patch along with an inverted L-strip is used to excite two different hybrid modes (HE11δ and HE12δ-like mode) in CDRA. HE12δ mode in CDRA is very advantageous in terms of gain and radiation characteristics. The proposed antenna design shows triple-band characteristics i.e. 1.88-2.06 GHz, 2.29-2.58 GHz and 2.9-3.93 GHz with the fractional bandwidth of 9.13%, 11.9% and 30.16%, respectively. Due to inverted L-strip, it shows circular polarization characteristics within the frequency range 3.3-3.55 GHz (AR<3 dB). The simulated results are practically verified by using archetype of proposed antenna structure. The proposed antenna design is applicable to WLAN (2.4 GHz) and WiMAX (2.5/3.5 GHz) applications.
In this paper, a compact wideband planar balun is studied and investigated. The proposed balun comprises a broadband Wilkinson divider followed by non-coupled lines to attain wideband 180° phase shift. Due to the inherent broadband characteristics of the proposed structure, good performance is accomplished in terms of phase and amplitude balance. The balun is optimally designed and validated by experiments. Both measured and computed results have shown a return loss better than -10 dB, an insertion loss around of -3.15 dB with a maximum absolute phase and amplitude imbalance around 2.5° and 0.2 dB over frequency range from 700 to 3200 MHz. Practical and computed results of the present balun are in good agreement.
This paper presents a novel compact Koch snowflake fractal ring based Dielectric Resonator Antenna (DRA) for ultra wideband application. Firstly, Koch snowflake fractal geometry is implemented on the conventional Cylindrical Dielectric Resonator Antenna (CDRA). Further, the performance of the DRA is enhanced by fractal ring created on the snowflake geometry. With the application of the fractal and the fractal ring geometry, the Q-factor of DRA is reduced, thus the bandwidth of DRA is increased. The proposed antenna offers a wide impedance bandwidth of 90% ranging from 4.7 GHz-12.4 GHz. The effect of the fractal geometry enhances the gain of DRA. The proposed antenna achieves radiation efficiency more than 78%, throughout the bandwidth. Interestingly, the proposed configuration reduces the DRA volume by 76.63% with reduced volume of 7.91 cm3. The experimental verification of the proposed structure shows good agreement between simulated and measured results.
A novel approach to design Tunable Dual Band Band-Stop filters will be presented in this paper. These filters have a new configuration which have a coplanar microstrip line loaded with Stepped-Impedance Resonators (SIRs). These can be tuned by using tuning elements such as a tuning diode and ferroelectric capacitor. The Dual-Band Band-Stop Filter (DBBSF) and Band-Pass Filter (DBBPF) have become the most attractive circuit components in modern communication devices. Several studies have been done in this area but without tuning. Tuning is important in these circuits because the same circuit could be used in multiple band frequencies by applying a voltage, without needing to design new circuits. Thus, this approach leads the circuits to become smaller, increases the efficiency of the circuits, and reduces the costs. The filters were designed with notch frequencies at 1.5 GHz and 3.5 GHz, and then loaded respectively with Tuning Diode or BST capacitors, to compare their performance. The filter circuits were simulated with an Agilent ADS and Matlab program and were fabricated on FR-4 substrates. By loading the resonators with BST capacitors or tuning diodes, with no DC applied voltage, the first and second notch frequency shifts significantly. The application of DC bias to these varactors changes the center frequencies of the dual band filter.
Digital beamforming (DBF) on receive in elevation with a large receiving antenna will be widely adopted in future spaceborne synthetic aperture radar (SAR) missions to improve system performances. Furthermore, DBF can be used to separate echoes corresponding to different sub-pulses in some novel spaceborne SAR imaging modes. This paper proposes an improved DBF processor with a large receiving antenna for separating echoes. The proposed DBF processor includes three important parts: multiples sharp receiving beam generation, range compression and null steering. Compared with the conventional DBF processor in spaceborne SAR, the proposed DBF processor can separate echoes with better performances. Simulation results on point targets demonstrate the validity of the proposed DBF processor.
A compact unidirectional slot antenna with front to back ratio (FBR) enhancement is proposed. The antenna consists of a novel compact slot driven antenna, a stepped reflector and a vertical balun from a microstrip to a parallel strip line. Better FBRs are obtained by optimizing the stepped reflector. Impedance bandwidths are enhanced by applying the balun and a pair of microstrip stub etched on the opposite side of the slot. Then, the antenna is manufactured and measured. Measured results show that the proposed antenna has a bandwidth of 76% (1.53-3.41 GHz) for VSWR ≤ 1.5. In addition, from 1.7 to 3.2 GHz, the antenna gains are higher than 8.6 dBi, and the FBRs are greater than 22 dB. Good agreement between the simulated and measured results is obtained. All above indicates that the proposed antenna can be widely used in wireless communications.
This paper presents an independently tunable dual-band bandpass filter based on center shorting-stub-loaded resonators. The center shorting-stub-loaded resonator is a dual-mode resonator that generates odd-even modes approximately equal and coupled when the shorting stub is very short. Two different sizes of center shorting-stub-loaded resonators produce two separated resonant frequencies, which are mutually independent. The coupling between the source and load is introduced in the circuit by designing an appropriate coupling structure, and the skirt selectivity of the filter is greatly improved. Four varactor diodes are placed at the two open-circuit ends of the center shorting-stub-loaded resonator to control the two separated resonant frequencies. A prototype of a tunable dual-band filter with Chebyshev response is designed and fabricated. The measured results are in good agreement with the full-wave simulated results. Results show that the first passband varies in a frequency range from 0.81 GHz to 0.95 GHz with a 3 dB fractional bandwidth of 4.2% to 5%, whereas the second passband can be tuned from 1.51 GHz to 1.79 GHz with a 3 dB fractional bandwidth of 6.8% to 8%.
A new design of a circularly polarized planar magneto-electric dipole antenna is proposed and presented. This antenna consists of dual horizontal T-shaped electric dipole and an inverted U-shaped feed line. The antenna possesses 21.1% impedance bandwidth, from 8.9 GHz-11.0 GHz, provides 3-dB axial ratio bandwidth of 9.52% ranging 10.0 GHz-11.0 GHz, exhibits stable omnidirectional radiation pattern with almost equal E-plane and H-plane radiation patterns and provides a peak gain of 6.2 dBi. Due to its good electrical characteristics and radiation parameters, the antenna is suitable for satellite and RADAR communication in X-band.
A novel hybrid antenna capable of both spectrum sensing and frequency reconfigurability is proposed in this paper. The proposed hybrid antenna senses spectrum over a wide frequency range from 1 GHz-12 GHz and accordingly reconfigures its operating frequency in any of the four different frequencies i.e., 2.1 GHz, 2.96 GHz, 3.5 GHz and 5 GHz. Since wideband response for spectrum sensing and each frequency state works independently, there is no interference among various signals. The wideband response for spectrum sensing is obtained by exciting semicircular arc having staircase-shaped slot in the ground plane. Frequency reconfiguration is achieved by electronic switching among various matching stubs. Both simulated and experimental results for the return loss, gain and radiation patterns are presented. The proposed hybrid antenna shows a measured return loss better than -20 dB in all the operating bands, a bidirectional radiation pattern and 4.8 dB gain in θ = 20˚ and 120˚ in E plane.
In this paper we provide new recommendations for a type of antenna design in applications where a human is present in the vicinity of a wireless power transfer (WPT) system by means of power transfer efficiency (PTE) and specific absorption rate (SAR). The interaction between a homogenous human model and different WPT systems is investigated at 13.56 MHz using spherical mode theory antenna model (SMT-AM) and full-wave numerical analysis. The human model exposure and the performance of the proposed WPT system are analyzed further for some typical scenarios. It is shown that the position in which the human model is closer to the receiver is favorable over the position closer to the transmitter, concerning both PTE and SAR. Also, the consideration of variable receiver load indicates that different levels of SAR coupled by degraded PTE can be expected. The proposed antennas are designed and proof of concept WPT measurements are carried out.