A compact wideband circularly polarized square slot antenna for universal UHF RFID reader applications is proposed and tested. An L-shaped radiator at lower surface of the substrate is used to feed the proposed antenna. To achieve a broadband circular polarization (CP) and good performance, two rectangular stubs with different sizes are inserted at opposite corners of the square slot at the upper surface of the substrate. A small rectangular slit is used to improve the impedance matching of the proposed antenna. The antenna's measured <10-dB impedance bandwidth and measured 3-dB axial ratio bandwidth are 70.2% (660-1374 MHz) and 45.8% (796-1269 MHz), respectively. The proposed antenna has a dual circular polarization characteristic, wide impedance bandwidth, wide axial ratio, compact size, and maximum measured gain about 3.9 dBi. The total size of the proposed antenna is 120×120×1.6 mm3. Furthermore, the impedance bandwidth and axial ratio bandwidth of the proposed antenna cover the entire UHF RFID band easily. The proposed antenna is suitable for UHF RFID reader applications.
A new microstrip-to-microstrip vertical transition structure for ultra-wideband (UWB) applications is proposed in this paper. The transition consists of a low impedance microstrip ring stub and a couple of slotline square multiple-mode resonators (MMRs) on the common ground plane. The low impedance microstrip ring stubs are realized by the connection of three single stubs in parallel, and the high-impedance section of slotline SIR is realized by the connection of four single stubs in series. The simulated and measured results are in good agreement, showing good wideband filtering performance with ultra-wideband fractional bandwidth.
An approach to separate metallic and dielectric losses in ferroelectric capacitors in all range of tuning under control dc voltages (Udc) is considered. The procedure is based on measurements of the dc voltage dependencies of microwave losses (tanδt(Udc)) and capacitance (C(Udc)) for a set of capacitors with similar layout but with different nominals. Linear extrapolation of tanδt(C) dependencies at different control dc voltages to C = 0 allows to evaluate the dielectric losses tanδd as a function of the control dc voltage. The procedure of separation was performed for a set of sandwich metal/(Ba0:5Sr0:5)TiO3/metal capacitors. Capacitors parameters were measured at a frequency of 2 GHz in a range of electric field strength in ferroelectric of E = (0 - 30) V/μm. The intrinsic commutation quality factor of BSTO lm itself was estimated by the method proposed.
High frequency measurements at 50 MHz-10 GHz were performed for the first time using interdigitated electrodes on a low temperature co-fired ceramic substrate to analyze fungal spores. Wet and dry spore generation methods were evaluated and tested with two different fungal species. The dry generation method was found feasible for RF measurements, since the component capacitance increased 14-21% in the 2-6 GHz range, but for the wet generation method the capacitance decreased only slightly (<1%). Based on these initial results the RF measurements have the capacity to evaluate the quantity of fungal spores but not to identify their species.
A printed dual-port coplanar waveguide (CPW)-fed antenna is proposed for wideband communication systems. The antenna includes two identical hybrid trapezoidal-elliptical radiating elements that are printed perpendicular to each other. Also, two orthogonal CPW lines are used to feed the antenna. In order to achieve broadband dual-polarized operation with a compact size, the geometrical parameters of the antenna are optimized by using Ansoft HFSS. The antenna was fabricated and tested. Reasonable agreement between the simulation and experimental results is obtained. The fabricated prototype with a small size of 25×53 mm2 can cover the wide operating frequency band from 2.4 to 18 GHz (reflection coefficient less than -10 dB) for both ports. The measured isolation is better than 25 dB over the entire operating bandwidth. Moreover, the measured results show that the proposed antenna can provide omnidirectional radiation patterns with a good orthogonal polarization operation, reasonable gain, high radiation efficiency, and constant group delay.
In this paper, a broadband transition structure from microstrip line to slotline with band-notched characteristic is proposed. To match the 50 Ω microstrip line, 4 Chebyshev impedance transformations are used in the transition structure, and its bandwidth is widened. There is a fan-shaped radial line at the microstrip terminal. A U-shaped slot is etched on the microstrip line with stepped impedance matching to achieve band-notch characteristic. By changing the length of the slot, the band notch is realized at different frequencies. Simulation and optimization of the transition structure are made by using the high frequency simulation software HFSS in this paper to achieve the band-notch function at 3.37-3.84 GHz and 10.67-11.14 GHz. In the rest of the band, return loss S11 is less than -15 dB, and voltage standing wave ratio (VSWR) is less than 1.5.
To improve stability of time-domain integral equation, a stable implicit scheme is proposed to solve the transverse-magnetic (TM) electromagnetic scattering from 2D conducting objects. The time-domain electric-field integral equation (TD-EFIE) was adopted and expressed using second-order derivative of the magnetic vector potential. To reduce numerical error, the magnetic vector potential was approximated by second-order central finite difference. TM transient scattering from 2D conducting objects was calculated by an implicit marching-on-in-time (MOT) scheme. To obtain stable numerical results, the TD-EFIE MOT implicit scheme was firstly combined with the time-averaging technique. The accuracy and stability of the scheme were demonstrated by comparison with the results from inverse discrete Fourier transform technique.
A compact ultra-wideband (UWB) top-loaded antenna for multiservice wireless applications is presented. It consists of a metal cone radiator, a small ground plane, four shorting poles and a top-cross plate, among which the top-cross plate with two slots shorted to the ground planet is important to broaden the low frequency bandwidth. The measured result shows that an improved impedance bandwidth of 185% from 1.17 to 30 GHz is achieved. The omnidirectional stable radiation pattern in the horizontal plane is also obtained. The volume of proposed design is approximately 0.0173λ3 at 1.17 GHz. With the small volume and UWB characteristic, the design of the proposed antenna is very suitable for many wireless standards such as Softbank (1427-1500 MHz), DCS1800, PCS1900, UMTS, IMT2000, Wi-Fi (2.4 GHz), WiMAX (2.2-5.5 GHz), UWB (3.1-10.6 GHz), and satellite communication (X band, Ku band and Ka band).
A 3-dB branch-line hybrid coupler with wide stopband responses is presented in this letter. An equivalent K-inverter with bandpass function is used instead of one quarter-wavelength transmission line, which will realize size reduction and wide stopband characteristic of the coupler. Prototype of a branch-line hybrid coupler, which divides the power equally with 90° phase difference between the output ports, is also fabricated and tested. Both the simulation and measurement results show that such a hybrid coupler exhibits an 83.2% size reduction and has transmission suppression of -20 dB or less within five-fold bandwidth.
This article presents the design, simulation and machining of a dual Orthomode Transducer for feeding antenna using waveguide technology. Linear orthogonal polarizations in common port are separated to single linear polarizations in other ports. This device is developed to work in K and Ka bands and could be exploited in satellite communications applications. Also, it is designed to provide good scattering parameters results experienced with simulation tools and real load laboratory measurement. The designed circuit exhibits important results with return losses less than 25 dB, insertion losses in theory of about 0.05 dB as well as a good isolation of 40 dB in both frequency bands of interest (19.4 GHz-21.8 GHz) and (27 GHz-32 GHz).
A compact size and wide stopband microstrip quadruplexer with a common crossed resonator is proposed in this paper. The resonator mentioned is theoretically analyzed and proved to be able to resonance at three different frequencies, which can be easily modified by changing the length of the corresponding stub of the resonator. This tri-mode resonator is proved to have the capacity of being shared by three different bandpass filters in a quadruplexer in this paper. Then an additional channel is designed to be coupled to the other side of the feed line of the common input port. Compared to conventional ones, the proposed quadruplexer has a more compact structure, cause no extra matching network is needed, and the number of resonators is reduced effectively. Moreover, a wide stopband is obtained by making the resonators work at the same fundamental frequencies but different higher order frequencies. Besides, open circuit stubs are also used to suppress the harmonic frequencies. To demonstrate the design procedure, a quadruplexer with a third order Chebyshev response in each channel is fabricated and measured. The measured result is in good agreement with the simulated one, showing an attenuation of 20 dB up to 10.16 times of the first channel frequency.
A new super compact ultra-wideband (UWB) bandpass filter (BPF) with triple-notched bands is presented in this paper. Firstly, a new square ring quad-mode resonator (SRQMR) is employed to obtain the initial UWB BPF. Then, a triple-mode stepped impedance resonator (SIR) is inserted into the initial UWB BPF to achieve three desired notched bands. The proposed triple-mode SIR is found to have the advantages of introducing triple-notched bands and provide a higher degree of freedom to adjust the resonant frequencies. To validate the design concept, a new super compact UWB BPF with triple-notched bands respectively centered at frequencies of 3.7 GHz, 5.2 GHz and 7.8 GHz is designed and measured. The predicted results are compared with measured data, and good agreement is reported.
This paper presents a study and analysis of a high performance microstrip branch-line 3dB hybrid coupler (BLHC) operating at 2.2 GHz for Long Term Evolution (LTE) application. High and low impedance meander lines are used to miniaturize the conventional Branch Line Hybrid Coupler. A prototype of the proposed coupler is fabricated and tested using a Rohde and Schwarz ZVB 20 vector network analyzer. The measured results agree well with the simulated ones.
A low-profile triple-band, dual-mode and dual-polarization antenna is proposed in this paper. An annular interdigital slot etched on the top conductor layer of the antenna is employed as a radiator. Through adjusting the location of coaxial probe, three operating modes TM11, TM02, and TM12 of the antenna are excited simultaneously. Two patch-like radiation patterns and one monopolar radiation pattern at three different frequencies are obtained. In addition, circularly polarized (CP) property for TM11 and TM12 modes is achieved by employing a 45° inclined rectangular slot at the center of the antenna. To validate the properties, a prototype is fabricated and measured. The results illustrate that this antenna is attractive in wireless communication systems for its simple structure and multifunction.
A broadband end-fire antenna loaded with magneto-electro-dielectric metamaterial (MED-MTM) is presented in this paper. Based on a planar printed structure, many periodic structures are investigated in antenna design. The metal patch is embedded with a C-shaped complementary split-ring resonator (CSRR) array, and many cross slots are etched on the ground plane. The zeroth-order resonance (ZOR) and first-order resonance (FOR) can be excited. As a result of electromagnetic coupling effect, the C-shaped patch and ground plane compose metamaterial transmission line (MTL). For potential applications, the broadband and end-fire antenna can work with a 53.5% (3.81-6.59 GHz) impedance bandwidth. The proposed antenna achieves size reduction, gain improvement and bandwidth enhancement.
A passband filter where the central frequency can be one of seven selectable frequencies is presented. Its operation region ranges from 325 to 455 MHz, and each bandwidth is about 20 MHz. The filter is based on a highly miniaturized ring resonator with a size reduction from about 77% to 83% compared to a conventional closed ring. The reconfiguration of its resonant frequency is implemented by shifting a short location, thus changing its effective inductance. This is opposed to the conventional capacitance change of other reconfigurable filters. Simulated and experimental results are in good agreement. Reflections are below -10 dB at central bandpass frequencies for all selectable bands.
In this paper, a broadband planar modified quasi-Yagi antenna using a two-element log-periodic dipole array as a driven element is proposed. To feed the two-element log-periodic dipole array, a simple microstrip to stripline transition as a balun is designed, which converts the unbalanced input to balanced output. The antenna is fabricated on a low cost glass epoxy FR4 substrate with dielectric constant = 4.4, substrate thickness = 1.6 mm, and loss tangent = 0.02. The overall size of the antenna is 84 mm×111 mm, which is 0.41λo×0.54λo at the center frequency of 1.45 GHz. Measured results show a bandwidth of 41.4% for VSWR≤2. A gain of 6.5 dBi±0.5 dB and front to back ratio (F/B) of better than 20 dB are achieved over the bandwidth. Measured results are in good agreement with the simulated ones. This antenna is useful for RFID, portable direction finding, spectrum monitoring systems, etc.
A novel W-band WR 10 waveguide to microstrip line transition is designed, simulated in a 3D full-wave EM simulation software, fabricated, and evaluated by measurements. The main advantages of this transition are frequency-flat transmission, low reflection, and uncomplicated fabrication. Simulation shows a reflection coefficient of better than -23 dB from 75 to 90 GHz for one hollow waveguide to microstrip line transition. The port reflections increase for a fabricted prototype with two transitions and a connecting microstrip line to a level of about -14 dB. This is mainly caused by fabrication tolerances. The overall transmission of the dual transition prototype is found at a very satisfactory level of about -4.8 dB at 90 GHz for a connecting microstrip line with a length of 45 mm corresponding to an estimated loss of approximately 0.6 dB for a single transition.
In this paper, measurement, modeling and validation of existing models on the effect of nonhomogeneous vegetation on UHF radio-wave propagation through a long forested channel at frequency of 1835 MHz are reported. The paper focuses on vegetation attenuation measurement through a long forested channel of about 8 km long with mixed vegetation of different density. The measured data were fitted using exponential decay function, and a new model was proposed from the fitted curve. The new proposed model will take care of the limitation in vegetation depth posted by some existing models. Generic models, mainly modified exponential decay and analytical models were also fitted to the data and validated, while RMSE was used to determine the best model that describes the data. The evaluated data results show that all the models tested give significant errors which show that they are not suitable for long forested channel scenario. Though COST 235 has the least error (17.05 dB), the error is still significant because COST 235 could only account for vegetation attenuation of short distance scenario. Attenuation shows corresponding increase with increase in leaves thickness in the forested channel considered, which was due to complex permittivity of the leaves moisture content and the dielectric properties of the leaves saline water. The developed model and other results obtained in this study will help to improve prediction accuracy of the effects of vegetation attenuation in nonhomogeneous vegetation along forested channels and also help in establishing efficient UHF radio link budget for long forested channel scenario.
A novel compact wideband printed loop antenna is presented for wireless applications. The wideband characteristic is achieved by combining three dierent loop resonant modes of the antenna. The antenna geometry is simple and consists of a rectangular meandering loop, a coplanar waveguide (CPW) structure, and a monopole feed. This proposed antenna has a dimension of only 27×20×1 mm3 while operates at a wideband from 2.4 GHz to 5.9 GHz (84.3%) with stable gain, radiation pattern and vertical linear polarization. This antenna is suitable for WLAN and future 5G sub-6 GHz spectrum communications. Good agreement between the simulation and measurement is obtained.