This paper investigates the effects on received mutual coupling of λ/2 dipole arrays placed near real-earth. As a rule of thumb, estimation of mutual coupling can be divided in two regions of antenna height that is very near ground 0 < h < λ and fairly freespace region h ≥ λ. The receiving antenna mutual coupling remains fairly unaffected from ground conductivity, when antenna height h ≥ λ. Both vertical and horizontal polarization cases showed the same trend. Investigation of effects of nearness of good-ground to the array on DOA estimation revealed that for azimuth DOA estimation, the proposed method of removing mutual coupling works well even for near ground.
A miniaturized trans-directional (TRD) coupled line coupler comprises series inductors and capacitor loaded coupled lines is proposed in the paper. Series inductors are added to the periodically loaded coupled lines for further miniaturization of volume. A novel equivalent circuit is presented and theoretically analyzed. Test circuits for the miniaturized and conventional 3-dB TRD couplers were designed to operate at 1.6 GHz and fabricated using printed circuit board (PCB) technology. Samples have been measured, and comparisons in terms of volume, schematic simulation results and measurement results between the miniaturized and conventional 3-dB TRD couplers have been made to validate the proposed structure. Results show that the proposed miniaturized TRD coupler achieves a size reduction of 47.6% compared to the conventional TRD coupler with similar performances.
In this article, a compact ultra-wideband (UWB) planar monopole antenna with the triple notched band is proposed. The antenna consists of a semicircular radiating patch and a modified ground plane with two bevels at upper edge. By etching two round shape slots in radiating patch the notch characteristics are achieved at WiMax band (3.3-3.7 GHz) and WLAN band (5.15-5.875 GHz). In order to realize notch band at X-band downlink satellite communication band (7.1-7.76 GHz) a pair of rotated V-shape slot are etched on the ground plane. The measured operating impedance bandwidth of proposed antenna ranges from 2.9 to 10.9 GHz having return loss less than 10 dB with triple notched bands. The proposed antenna exhibits a nearly omnidirectional radiation pattern in the H-plane, and a dipole-like radiation pattern in the E-plane for the ultra-wideband. The effects of each individual slot on band-notch characteristics are also investigated. The measured gain of the proposed triple band notched antenna is relatively stable across the operating frequency band except notched bands and thereby making the proposed antenna suitable for practical UWB applications. Proposed antenna has a compact size of 27x25 mm2.
In this paper, the design and analysis of a compact coplanar waveguide-fed ultra wideband pentagon antenna are presented. To achieve ultra wideband performance, two modifications are introduced. The first one is to remove a small fan angle on each side of the ground plan, and the second one is to modify the sharp of the patch in the width. The optimal dimensions can be achieved by a parametric analysis. The antenna design exhibits a very wide operating bandwidth of 16.7 GHz with a return loss better than 10 dB in the frequency range from 4.46 GHz to 21.14 GHz. The gain of the proposed antenna is 6.3 dBi. This antenna configuration will be useful for UWB indoor application as it is easy to fabricate and integrate with RF circuitry. All simulations in this work were carried out by using the electromagnetic software CST.
Optoelectronic devices triggered by a laser flash and operating in linear switching regime allow the generation of short pulses with small time jitters (2 ps typically). An Ultra Wide Band antenna array combining as many of this photoswitches as antennas has the advantage to increase the radiation power on one hand and to offer the agility of the radiation beam on the other hand obtained by time delay of laser illumination. During the step of antenna design, it becomes important to take into account the photoswitch integration in order to increase the peak power and the frequency band of the generated output signal. This paper presents an equivalent model of photoswitch obtained with the transient solver of CST Microwave Studio coupled within CST Design Studio. The second part of this article is dedicated to the integration of a photoswitch even within the antenna.
In this paper, three different compact circular-ring microstrip patch antenna structures have been proposed. These antennas have been analyzed, investigated and optimized using the CST-MW-simulator. The proposed designs are mainly based on the concept of patch shape reconfiguration while its overall dimensions are kept constant. The objective is to design dual and/or triple broadband antennas resonate within the fourth generation band (4G). The presented antennas are simulated and fabricated on cheaper and lossy FR-4 substrate, and their parameters are measured and compared. The obtained results show that the proposed antenna structures resonate within the 4G frequency band. The operating bandwidths have been varied between 270.0 MHz and 1000.0 MHz (about 4% up to 7% of center frequency). In addition, maximum VSWR value of less than 1.5 has been achieved. The obtained results verify the validity and the benefits of reconfiguring the patch shape. Finally, good agreement has been obtained between simulated and measured parameters.
A method for decreasing the loss in substrate integrated waveguide (SIW) structures is introduced. In this method, the dielectric substrate is partially removed. Accordingly, dielectric loss reduction has been explicated analytically. Its equivalence to the rectangular waveguide of solid walls which is partially filled with dielectric has been identified. A novel topology for demonstrating the idea is established and a low loss three port substrate integrated waveguide power divider is presented. This SIW power divider shows lower loss than conventional SIW power dividers. Proper TRL standards are realized for removing the effect of transition and/or matching sections in measurement process. For a low-loss three-port PSIW power divider, the return loss below 10 dB and transmission coefficients between -3 dB to -3.5 dB from 8.75 GHz to 10 GHz have been achieved. The measured amplitude imbalance is less than ±0.2 dB, and the measured phase difference between <S21 and <S31 is about 40 in the same frequency band.
In this paper, a novel concept for ultra-wideband simultaneous switching noise (SSN) mitigation in high-speed printed circuit boards (PCBs) is proposed. Using complementary spiral resonators (CSRs) etched on only a single layer of the power plane and cascaded co-centrically around the noise port, ultra-wideband SSN suppression by 30 dB is achieved in a frequency span ranging from 340 MHz to beyond 10 GHz. By placing a slit in the co-centric rings, lower cut-off frequency is reduced to 150 MHz, keeping the rest of the structure unaltered. Finally, the power plane structure with modified complementary spiral resonators (MCSRs) is designed, fabricated, and evaluated experimentally. Measurement and simulation results are in well-agreement.
A closely spaced dual-band notched UWB MIMO antenna is proposed in this paper. A traditional semi-circular monopole with ultra-wideband operation is chosen as an element of the proposed MIMO antenna. When two of the UWB monopoles are put together closely, the mutual coupling between them is apparently strong. To reduce the coupling between the antenna elements, a T-shaped branch is inserted between them, which reduces the mutual coupling obviously over the entire operating band. Also, the T-shaped branch can perform as a compensating radiator which can lower the operating frequencies of the proposed antenna. In order to achieve dual band-notched characteristics, meandering slots are cut in the patches, and symmetrical C-shape strips are nearly placed to the monopoles' feed-lines. The meandering slot is for lower band notch (WiMAX, 3.3-3.7 GHz) while the C-shape strips are for upper band (WLAN, 5.15-5.825 GHz). The measured radiation efficiencies, peak gains and radiation patterns are illustrated and show good agreement as anticipated.
In this paper, two types of reconfigurable Dielectric Resonator Antennas (DRAs) are presented. The designs are based on rotating a Dielectric Resonator (DR), placed on the patch of the antenna, using a DC stepper motor connected to the DR to reconfigure the notch frequency, in the first, and the resonance frequency in the second design. The attained results are a UWB DRA with a reconfigurable notch in the 3.2-5.1 GHz range that prevents interference to many narrowband systems in this range, and a DRA with a reconfigurable resonance frequency suitable for microwave and WiMAX applications. The characteristics of the designed antennas are investigated using HFSS and experimentally verified. The computed and measured results are in good agreement, and the antennas meet their design criteria.
In an effort to improve the bandwidth of the single layer reflectarray, this paper investigates the use of double concentric circular ring elements arranged in a range of sub-wavelength grids on a single layer of substrate. Compared to the traditional λ/2 grid arrangements, when the radiating elements are arranged in grids less than λ/2, the reflected phase is more uniform over a wider frequency bands when radiating elements' parameters are varied; albeit with a reduced reflected phase range. The double concentric circular ring elements used here also allow an additional degree-of-freedom to improve the bandwidth. A comprehensive investigation on reflectarrays' performance with various grid spacings is conducted and the trade-off between the reflectarray gain and bandwidth is also discussed. Based on the concentric ring element, four offset-fed 0.43 m×0.43 m reflectarrays centered at 10 GHz with various element periodicities, namely λ/2, λ/3, λ/4 and λ/5 grids, are designed and developed. The measured results show that among the four reflectarrays, the one with λ/4 grid spacing achieves the broadest 2-dB gain bandwidth of 33% with an aperture efficiency of 36.2%.
A new spiral antenna is proposed in this paper. The developed antenna has improved axial ratio (AR) and shorted arm length. The function of the new spiral is given. The developed spiral antenna combines the low frequency property of power spiral antenna and high frequency property of Archimedean spiral antenna. That is, the growth rate of radial distance at large winding angle is close to power spiral for improved AR in low frequencies, and the growth rate at small winding angle is close to Archimedean spiral for good AR in high frequencies. The results reveal that the developed spiral antenna has noticeable improved axial ratio at low frequencies compared with Archimedean spiral antenna, and the problem of axial ratio degradation of power spiral antenna was also solved. The arm length is shorted by 46.2% compared to conventional Archimedean spiral antenna, and 63.5% compared to power spiral antenna.
In this paper, a broadband class-F-1 power amplifier (PA) that can be integrated into compact-sized micro-radio units is introduced. This PA utilizes a multi-harmonic impedance merging technique at harmonic frequencies so that the circuit areas of matching networks can be minimized. As well, in order to maximize the bandwidth of high efficiency, circuit configuration was optimized by the first order differentiation of the fundamental-frequency impedance. For the sake of verification, a 10 W inverse class-F PA operating at 1.9 GHz was designed with a commercial GaN transistor. It exhibited a 39.2% size reduction as compared to conventional PAs of the similar power. In addition, it exhibited a bandwidth of 600 MHz (1.6 ~ 2.2 GHz) at an efficiency greater than 60%, a peak efficiency of 83.9%, and an output power of 42.2 dBm.
As an emerging technique with a promising application prospect, the device-free passive localization (DFPL) technique has drawn considerable research efforts due to its ability of realizing wireless localization without the need of carrying any device and participating actively in the localization process. Recent technological achievements of the DFPL technique have made it feasible to realize location estimation using the received signal strength (RSS) information of wireless links. However, one major disadvantage of the RSS-based DFPL technique is that the RSS measurement is too sensitive to noise and environmental variations, which incur the misjudgment of shadowed links and degradation of localization performance. Based on the natural sparsity of location finding in the spatial domain, this paper proposes an environmental-adaptive sparsity-based localization method for the DFPL problem in the existence of model mismatch. The novel feature of this method is to adjust both the overcomplete basis (a.k.a. dictionary) and the sparse solution using a dictionary learning (DL) technology based on the quadratic programming approach so that the location solution can better match the changes of the RSS measurements between the node pairs to the spatial location of the target. Moreover, we propose a modified re-weighting l1 norm minimization algorithm to improve reconstruction performance for sparse signals. The effectiveness of the proposed scheme is demonstrated by experimental results where the proposed algorithm yields substantial improvement for localization performance.
Based on the principle of discone antenna a new UWB monocone antenna is presented. Instead of using traditional cone geometry as a radiator for discone, planar vertical cross strips of aluminum are used as an antenna radiator. This results in wide impedance characteristic and miniaturization of antenna. The simulated model has broadband impedance bandwidth 18:11 form 550 MHz to 18 GHz with Omni directional radiation pattern. The two different antenna models are presented in this paper. Design software CST Microwave Studio, HFSS and Solid works are used for designing and parametric analysis of antenna. Size reduction up to 45 percent is achieved as compared to tradition discone antenna. The N type panel mount connector is used for antenna feeding. As a result of a low profile structure, antenna can be easily mounted for portable application. The antenna radiation pattern is measured in anechoic test chamber. The measured results of antenna are found to be in good agreement with simulation results. The features make the antenna highly suitable for UWB applications.
Based on two orthogonal linear sparse arrays (LSA) which consist of the coupled-sensors (CSs), a high resolution and no ambiguity (HRNA) method is proposed to estimate the two-dimensional (2D) angles of single source. The HRNA method first constructs a new covariance matrix to achieve no ambiguity independent angles estimation by using the covariance matrix generated by each LSA, and then computes joint elevation and azimuth angles by utilizing both the estimated independent angles and triangular relationship. For large array aperture of the LSA, the HRNA method earns a high angle resolution; however, its independent angles estimation accuracy is slightly lower than the multiple signal classification (MUSIC) with a uniform linear array (ULA). In order to enhance the independent angle estimation performance, first improved HRNA (FI-HRNA) method is developed based on the HRNA and MUSIC methods. Further, in order to decrease the computational cost, second improved HRNA (SI-HRNA) method is presented based on FI-HRNA and MUSIC methods. The proposed SI-HRNA method obtains high angle resolution, high angle estimation accuracy and low computational load. In addition, the spacing between two adjacent CSs is not limited, and thus the angle resolution and estimation accuracy can be set according to practical demand. Numerical experiment and comparison with the other existing algorithms verify the effectiveness and superior performance of the method proposed in this paper.
A compact, low profile, dual polarized, ultra wideband, frequency selective surface is proposed. It is designed by using two similar metallic array structures separated by dielectric material FR4. The simulated reflection bandwidth (with transmission < -20 dB) for TE incident wave is 8 GHz from 2.87 GHz to 10.87 GHz corresponds to 116%. The unit cell dimension and periodicity are of the order of 0.37λ at the centre frequency. The overall thickness of the proposed FSS is 1.8 mm. The proposed FSS has higher order of band-stop response and good angular stability. The measured transmission response of FSS is very close to simulated response. Design expressions for the resonance frequencies are proposed, and the calculated results are found to be in good agreement with the simulated ones. Finally, a parametric analysis of the proposed FSS is presented.
In this paper, a printed wideband Yagi-Uda antenna with a novel folded dipole driver is proposed. The folded dipole driver is comprised of a folded dipole and a microstrip feedline which functions as an internal balun to mainly determine its wide impedance bandwidth. With the optimized parameters, an operating band of 1.69 GHz~2.72 GHz can be obtained. Besides the folded dipole driver, the broadband printed Yagi-Uda antenna also consists of three directors and a reflector. Its wideband performance is mainly determined by the folded dipole driver, while the reflector and directors improve its performance slightly. By optimizing the geometrical parameters of the folded dipole driver, a bandwidth of 61.8% (1.53 GHz~2.93 GHz) for return loss being higher than 10 dB is achieved. The proposed printed Yagi-Uda antenna is realized on FR4 substrate with a measured operating bandwidth of 62% (1.51 GHz~2.94 GHz), a flat gain (5.6 dB~7.3 dB), more than 10dB front-to-back ratio and lower than -15 dB cross-polarization level.
In this paper, we propose a novel UHF RFID coupled slot metallic tag antenna with a radome. The proposed tag antenna consists of a frequency tuning slot, imaginary part tuning slot, real part tuning stub, micro-chip, and radome. All simulations were carried out using an Ansys HFSS simulator. The RFID tag antenna was designed and fabricated for use in the Korean and Japanese UHF band of 916.7 to 923.5 MHz. The measured 3 dB frequency bandwidth is 914 to 926 MHz. The measured read range is 12 m on a metallic surface. Details of the proposed tag antenna design, as well as simulated and measured results are presented and discussed.
Cuckoo optimization Algorithm (COA) is employed for the optimization of linear and non-uniform circular antenna arrays. COA is a novel nature inspired computing algorithm which is motivated by the life of Cuckoo. Like other nature-inspired algorithms, COA is also a population-based method and uses a population of solutions to proceed to the global solution. The method of COA is used to determine a set of parameters of antenna elements that provide the required radiation pattern. The effectiveness of COA for the design of antenna arrays is shown by means of numerical results. Comparison of results obtained with COA is made with that obtained using other popular methods. The results reveal the superior performance of COA as compared to other techniques both for design of linear and circular antenna arrays.