This paper presents the improved isolation property of the signals among transmitter and receiver antennas. The separation wall is laid at the center of the antennas to improve the isolation level between them. The introduced separation wall has serrated edges mounted on three sides i.e., top, left and right sides. These mounted serrated edges are implemented to reduce the diffraction which may occur due to the linear edge of the wall. The Fresnel diffraction problem has been solved using analytical method in order to get the optimized structure of the serration. The Fresnel diffraction patterns due to the different sizes of the serration are obtained, and their relative powers are compared to each other. The implemented antenna system with the serration wall is composed of corrugated feed horn, orthogonal mode transducer, and offset dual-reflector parabolic antennas. The effect of serration is well demonstrated by the measurement of isolation level of the antenna system. The measured results show that the serrated edges enhanced the isolation property among transmitter and receiver antennas.
This paper proposes a robust combination of digital predistortion (DPD) and crest factor reduction (CFR) for radio frequency (RF) power amplifiers (PAs). It is constructed using the architecture of CFR-DPD connected with a compensation module (CM). The compensation module is introduced to achieve mutual compensation between the output signals of CFR and DPD, and this can reduce the damage to the signal by CFR. The combination of CFR-DPD-CM provides the means to exploit margins in the transmitter performance, allowing the tradeoff among peak-to-average power ratio (PAPR), adjacent channel power ratio (ACPR) and error vector magnitude (EVM). The proposed combination of CFR-DPD-CM is assessed using a GaN Class-F PA driven by two modulated signals (a 4-carrier OFDM signal and a WCDMA 1001 signal with 20-MHz bandwidth), and a GaN Doherty PA driven by a 15-MHz long-term evolution (LTE) signal. The experimental results show that when the CFR reduces the PAPR about 4 dB, applying the proposed combination of CFR-DPD-CM, the average reduction of ACPR is 5.12 dB, and the average reduction of EVM is 1.26% compared with the conventional architecture of CFR-DPD.
A metamaterial inspired co-planar waveguide (CPW) fed compact low-pass filter is presented in this paper. The 3 dB cut off frequency of the filter is 1.4 GHz. The roll-off rate achieved for this filter is 47.4 dB/GHz. Sharp roll-off is obtained by introducing an additional resonance using an inductor in series with the shunt capacitor. The usage of chip inductor also results in a compact filter structure. The overall filter dimensions are 39 mm x 32 mm x 1.6 mm. The filter uses defected ground structure (DGS) for attaining stop band attenuation. The measured insertion loss of the filter in the pass band is less than 0.8 dB and average stop band attenuation is better than 23 dB. The equivalent circuit of the proposed filter is similar to that of a dual-CRLH (D-CRLH) transmission line.
A novel, compact asymmetric coplanar strip (ACS)-fed multi-band antenna for Bluetooth/WLAN/WiMAX applications is proposed and discussed in this paper. The proposed antenna is composed of a simple monopole structure with a mirror-L shaped branch and two rectangular radiating strips. It has a very small size of 13.75 x 26 mm2 including the ground plane. The mirror-L shaped branch excites a resonant mode at 2.5 GHz, and on the other side, ACS-fed monopole structure with two rectangular strips (one horizontal and one vertical) excite the resonant modes at 3.3 GHz and 5.75 GHz respectively. By properly selecting the lengths and positions of these radiating branches, multiband operation with wider impedance bandwidth can be achieved. The measured and simulated results show that the antenna has impedance bandwidth of 200 MHz (2.40-2.60 GHz), and 2800 MHz (3.2-6.0 GHz), and it can cover the 2.4 GHz Bluetooth, 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX bands. The resonances achieved with this technique can be tuned independently, and the equations governing the resonances are given and confirmed by parametric studies. The proposed technique is further validated by designing another antenna working at 1.8/1.9 GHz PCS, 3.5/5.5 GHz WiMAX, 5.2/5.8 GHz WLAN bands.
In this paper, a compact wideband planar monopole antenna suitable for slim mobile handsets applications is presented. The proposed antenna operates over LTE700/GSM800/900 (0.742 GHz-1.36 GHz), GPS L1/GSM1800/1900/UMTS/IMT2100/Wi-Fi/LTE2300/2500 (1.475 GHz-2.7 GHz), and WiMAX (3.4 GHz-3.72 GHz) based on reflection coefficient better than -6 dB. It consists of coupling strip, shorted radiating strip, and parasitic meandered lines. The wider impedance bandwidth is achieved by placing the meandered line as parasitic element on the back side of the coupling and shorted radiating elements. With this configuration, the antenna gives extremely wide impedance bandwidth which covers all the required frequency bands of the smart mobile phones. To investigate the proposed antenna, S-parameters, surface current distributions, and radiation performances are studied. To check the robustness of the proposed antenna, investigation is also carried out in the vicinity of the mobile environment. Further, specific absorption rate (SAR) is calculated on the human head and found to be below 0.535 W/kg. The simulated and measured results are found in close agreement.
In this paper, a compact dielectric resonator antenna (DRA) with bandnotched characteristics for ultra-wideband applications is presented. A comprehensive parametric study was carried out using CST Microwave Studio suite TM 2011 to analyze and optimize the characteristics of the proposed antenna. Three shapes for the coupling slot were investigated. Simulation results show that the proposed DRA had a -10 dB impedance bandwidth of 23% from 9.97 GHz to 12.558 GHz, and a maximum gain of 7.23 dBi. The antenna had a notched band centered at 10.57 GHz, which increased the reflection coefficient by 23.5 dB, and reduced the gain by 6.12 dB. The optimized designs were verified by experimental tests on fabricated samples.
A novel multi-band band-reject filter based on multi-ring complementary split-ring resonators (multi-ring CSRRs) is presented. The proposed filter is realized by etching the multi-ring CSRRs in the ground plane beneath a microstrip line. The multi-ring CSRR offers the possibility of designing multi-band filters with a small size and simple structure. To validate the proposed prototype of the multi-band filter, a dual-band and tri-band filters were fabricated and tested. The proposed filters show a good multi-band property to satisfy the requirement of WLAN in the 2.4/5.8 GHz bands and WiMAX in the 2.5/3.4 GHz bands. A good agreement between experimental and simulated results is obtained.
In this paper, a novel printed microstrip-fed monopole ultra-wideband (UWB) antenna with triple-notched bands using triple-mode stepped impedance resonator (SIR) is presented. The proposed triple-mode SIR is found to have the advantages of introducing triple-notched bands and providing higher degree of freedom to adjust the resonant frequencies. By coupling the triple-mode SIR beside the microstrip feedline, band-rejected filtering properties around the 5.2 GHz WLAN band, the 6.8 GHz RFID band, and the X-band satellite communication band, are generated. To validate the design concept, a novel compact UWB antenna with three notched bands is designed and measured. Results indicate that the proposed compact antenna not only retains triple band-rejections capability but also owns omni directional radiation patterns across nearly whole operating bandwidth for UWB communications.
For the first time, the higher-ordered modes of a stepped-impedance slotline resonator are closely combined for designing the broadband in-phase andout-of-phase power dividers. It was found that the output phases of the two modes can be easily reversed at the same time by changing the direction of their feeding currents. For this configuration, interestingly, a multifunctional power divider which is reconfigurable to produce either in-phase or out-of-phase signals can be easily designed from its passive counterparts by incorporating multiple RF diodes into the output feedlines, leading to significant cost saving and high compactness. The design procedure and equations of the power-dividing structures are discussed.
A novel direction of arrival (DOA) and polarization estimation method with sparse conical conformal array consisting of concentred loop and dipole (CLD) pairs along the z-axis direction is proposed in this paper. In the algorithm, the DOA and polarization information of incident signals are decoupled through transformation to array steering vectors. According to the array manifold vector relationship between electric dipoles and magnetic loops, the signal polarization parameters are given. The phase differences between reference element and elements on upper circular ring are acquired from the steering vectors of upper circular ring, it can be used to give rough but unambiguous estimates of DOA. The phase differences are also used as coarse references to disambiguate the cyclic phase ambiguities in phase differences between two array elements on lower circular ring. Without spectral peak searching and parameter matching, this method has the advantage of small amount of calculation. Finally, simulation results verify the effectiveness of the algorithm.
This paper presents a miniaturized tunable bandpass filter, consisting of two coaxial dielectric resonators and a pair of parallel-coupled lines. A coaxial dielectric resonators and a microstrip line form a new step-impedance resonator (SIR), which is different from a conventional SIR. Varactor diodes are connected to SIRs to tune the center frequency. The gap between parallel-coupled lines controls the inter-stage coupling coefficient. Lumped inductors used for coupling to I/O ports can reduce design complexity. The variations of coupling coefficient and external quality factor with tuning frequency are analyzed using HFSS software. A appropriate coupling coefficient which satisfies with constant fractional bandwidth within the tuning range is available. A tunable filter has been made of dielectric ceramics with dielectric constant of 38, fabricated on dielectric substrate and measured using Networks analyzer. Center frequencies vary from 0.43 GHz to 0.78 GHz, 3 dB fractional bandwidth from 6.4% to 6.8% when bias voltages are applied from 0 V to 10 V. The measured results validate the approach and agree with the simulation.
An internal dual-band flexible antenna is described. The antenna employs a rectangular patch to improve the interrogation range (above 100 mm) for near-field communications (NFC), as well as the passive average gain performance (above -20 dBi) for FM radio. A preliminary prototype antenna exhibits an interrogation range of 110 mm at 13.56 MHz and a passive average gain performance from -15.6 to -13.5 dBi in the range 86-108 MHz, while demonstrating an omnidirectional radiation pattern for FM radio applications.
Nowadays the mobile personal communication systems and wireless networks are commonly used. Experience has revealed that the antennas suitable for these applications should have small size and operate in assigned different frequency bands. For this purpose, circularly polarized (CP) multi-band square microstrip antenna with three N-slots and a pair of truncated corners is proposed, designed and simulated. To reduce the losses and improve the antenna efficiency in addition to the bandwidth, an efficient electromagnetic band gap (EBG) structure is introduced. The proposed antenna has produced a higher efficiency, an improved operational bandwidth, and a higher gain relative to the conventional microstrip antenna.
A new miniaturization methodology suitable for printed linear antennas is presented. Miniaturization is accomplished by replacing a linear radiator element of a conventional antenna with a compact continuously varying-impedance profile governed by a truncated Fourier series. A design example of a printed half-wavelength dipole antenna is designed and realized in microstrip technology. The performance of the proposed antenna is compared with its equivalent uniform dipole to highlight the performance equivalency. With a 25% reduction in the dipole arm length, both antennas show a measured peak gain and a fractional bandwidth of 5.4 dBi and 16%, respectively at 2.5 GHz; hence, the overall electrical performance is preserved. It will be shown that the design procedure is systematic and accurate. The proposed approach has potential for achieving advanced frequency characteristics, such as broad- and multi-band antenna responses.
In this paper, three commonly used on-ground antenna types (loop, monopole and planar inverted-F antenna) are compared in the scope of wireless body area networks (WBAN) for on-body communications at 2.45 GHz. The bandwidth of the antennas can be enhanced by placing them towards the edge or the corner of the small ground plane (25 × 35 mm2) which has, as a consequence, detrimental effects on radiation characteristics that motivates the examination of the impact of feeding location for on-body propagation in detail. The present study quantifies the trade-off between on-body efficiency, the gain in the direction tangential to the surface, applicability to launch creeping waves and bandwidth potential of the different antenna types with various feeding locations. The simulated channel gain |S11| around tissue-equivalent numerical phantoms is compared to an analytical WBAN path loss model.
This work addresses the low-pass equivalent behavioral modeling of radio frequency (RF) power amplifiers (PAs) for modern wireless communication systems. Similar to a previous approach, here the PA behavioral modeling is based on two independent real-valued feed-forward artificial neural networks (ANNs). A careful analysis is first presented to show that the nonlinear training algorithm for the previous ANN-based approach can be easily trapped into local minima, especially for the ANN that estimates the polar angle component of a complex-valued signal. Then, a modified ANNbased model is proposed to eliminate the local minimum problem, in this way significantly improving the modeling accuracy. Indeed, in the proposed model the two real-valued ANNs are responsible for estimating the in-phase and quadrature components of a complex-valued base-band signal. When applied to the behavioral modeling of a GaN HEMT class AB PA, the proposed ANN-based model reduces normalized mean-square error (NMSE) by up to 2.2 dB, in comparison with the previous ANN-based model having an equal number of network parameters.
In this paper a compact planar dual-mode metamaterial (MTM) antenna using rectangular type complementary split ring resonator (CSRR) is proposed. It is observed that an increase in series capacitance tends to decrease resonant frequency at which n = 1 mode is obtained in the proposed antenna. Zeroth order mode (ZOR) is obtained by means of rectangular type CSRR, tends to provide the miniaturized area. Dispersion relations are shown in order to characterize the metamaterial behavior by extracting the equivalent circuit parameters. The resonant frequency of the antenna is 2.14 GHz with input reflection coefficient up to -45 dB. The electrical size of the proposed MTM antenna is 0.321λ0 × 0.285λ0 × 0.011λ0. ZOR mode is observed at 1.15 GHz although the proposed antenna is operated at 2.14 GHz. Furthermore, it achieves simulated antenna gain of 2.60 dB with 70% radiation efficiency. In order to verify the simulation results of antenna, a prototype is fabricated and measured.
The present paper analyses and documents the merits of incorporating fractal design in microstrip antenna intended to be mounted on and integrated into the design of smart vehicles. A novel design is proposed for a compact tri-band hexagonal microstrip antenna to be integrated with the body of a smart vehicle for short range communication purpose in an Intelligent Transport System (ITS). This antenna can be used at 1.575 GHz of GPS L1 band for vehicle to roadside communication, at 3.71 GHz of mobile WiMAX band (IEEE 802.16e-2005) for blind spot detection and at 5.9 GHz of DSRC band (IEEE 802.11p) for vehicle to vehicle communication. At 3.71 GHz, the two major lobes of the antenna radiation beam, tilted by 35° on both sides from its broadside direction, help the vehicle to detect blind spots efficiently. The largest dimension of the proposed antenna corresponds to the lowest resonating frequency, 1.575 GHz. Compared to the conventional hexagonal patch, the modified Sierpinski fractal proposed herein reduces the overall area, at 1.575 GHz, by 75%, with 5.2 dBi gain. In comparison with other popular fractals, the proposed fractal structure achieves demonstrably better antenna miniaturization. When the antenna is mounted on the vehicle, considered an electromagnetically larger object, the simulated and on-vehicle experimental results show antenna gains of more than 5.5 dBi at 1.575 GHz, 8 dBi at 3.71 GHz and 9 dBi at 5.9 GHz in the desired direction with negligible amount of electromagnetic interference inside the car.
We have studied dynamics of a periodic X-band Gunn oscillator (GO) forced by microwave chaotic signals through numerical simulation and by hardware experiment. The chaos used as forcing signal is generated in a periodically driven non-oscillatory GO. Numerical simulation results indicate that the forced periodic GO becomes chaotic for a moderate strength of forcing chaos. The generated chaos in driven GO is found to become phase or general synchronized to the forcing chaos depending on strength of the latter one. Hardware experiments are performed in X-band of microwave frequency. It shows generation of chaos in driven GO due to forcing. Moreover, synchronization between forcing and generated chaos is indirectly verified.
In this paper, a dual-band Substrate Integrated Waveguide (SIW) resonator with Sierpinski fractal geometry is proposed. The space-filling property of the employed fractal shape allows to reduce the resonator size. The bandwidth, the minimum insertion loss, the maximum return loss and the stop band rejection are considered for evaluating the effect of the fractal geometry on the resonator characteristics. An accurate electromagnetic investigation is made using a full wave finite element method solver (Ansoft HFSS). Simulated and measured results are in good agreement. The second iteration fractal resonator exhibits two simulated bands centered at the frequencies f1=11.57 GHz and f2=25.7 GHz, while the measured frequencies are f1=11.33 GHz, f2=23.67 GHz. The measured bandwidths are BW=1.15 GHz and BW=2 GHz and the minimum insertion losses are close to -1.36 dB and -1.97 dB, respectively. The prototypes of the square resonator without, with first and with second iteration fractal geometry are fabricated via standard printed circuit board process (PCB). A Rogers Duroid 5880 substrate with thickness t=0.381 mm is employed.