For the spaceborne synthetic aperture radar (SAR) system, in order to alleviate the complexity of the imaging algorithm and to improve the accuracy of the applications of SAR images, attitude steering is required to reduce the Doppler centroid to 0 Hz. In published literature, two-dimensional attitude steering, including yaw and pitch steering, is employed for elliptic orbiting SAR systems. This paper proposes a new steering approach involving only yaw steering to suppress the Doppler centroid of the mid-range to theoretically 0 Hz with a low residual Doppler centroid at the edge of the range extent. This may reduce the complexity of the attitude control system. The comparison of the performances of the current applied methods and the proposed approach is carried out with a simulation, and the effectiveness of the new approach is validated by the results.
In order to collect information for the manufacture and application of a designed dual left-handed material (LHM) structure, the influence of salt spray test on the two conductive composite coatings consisting of silver and copper is contrastively investigated. It is found that the salt spray corrosion test can influence the microstructure of the coated copper and silver layers, leading to the decrease of electrical conductivity of the coated copper and silver layers. As results, the transmission performance of the dual-LHM structure is reduced, while the bandwidth of the dual-LHM structure is broadened. Moreover, at the same conditions, the salt spray corrosion test has less influence on the transmission characteristics of the silver-plated dual-LHM structure than those of copper-plated dual-LHM structure.
A compact ultra-wideband (UWB) bandpass filter with high selectivity and deep notched band attenuation is presented in this letter. The main structure of this filter is a balun-based coplanar waveguide (CPW)-microstrip-CPW transition. This structure has UWB bandpass characteristic (2.85-11 GHz) and a transmission zero at its lower transition band. To achieve a transmission zero at its upper transition band, some complementary split ring resonators (CSRR) are added in the ground of microstrip. Therefore, this filter, whose skirt factor is 89%, presents high selectivity. Then, a notched band is created by short-ended stubs for 5.5 GHz WLAN. Owing to the stepped impedance characteristic of these stubs, this filter achieves -41 dB deep notch in its S21. Besides, the size of the whole filter is only 0.38λg*0.45λg. The simulated and measured results agree well with each other.
In this paper, a novel compact second-order quad-band bandpass filter (BPF) is applied based on a novel quintuple-mode stub-loaded trigonal ring resonator. Resonant characteristics are extracted by even- and odd-mode method. Designing procedure of resonant frequencies has also been presented. The last two resonant modes are utilized to cover a wide bandwidth for 5G WiFi application. The rest of other three resonant modes are used to form three passbands for GPS, WLAN and WiMAX applications. According to pseudo-interdigital structure four transmission zeros are generated among passbands to improve the band to band rejection and enhance the frequency selectivity. The measurement results agree well with the EM simulation ones.
In this paper, a printed split ring resonator (SRR) loaded log-periodic Koch dipole antenna (SLPKDA) is proposed. Koch-shaped dipoles when being loaded with split ring resonator (SRR) yielded a compact antenna, still preserving the radiation properties of log-periodic dipole antenna (LPDA). Measurement results show that the proposed antenna has a wide bandwidth, good impedance match and gain of 4 dBi over the band of frequencies from 0.9 GHz to 2.5 GHz. Both vertical and horizontal dimension reductions are achieved by loading Koch dipoles with SRR.
A dual-band two order filtering antenna is designed to cover both the GSM900 and GSM1900 bands. The resonator of the two order filter containsa half wavelength open-loop resonator and a T-shaped open stub. The antenna is composed of two parts. One is a printed monopole which covers lower frequency band, and the other is a strip with slot protruded from the ground plane, which covers higher frequency band. By substituting the antenna for the last resonator of the filter, the filtering antenna owns not only a good radiation function but also a good character of filter at the two working frequency bands.
The closed cavity method is proposed to measure the frequency temperature coefficient (τf) of a dielectric resonator. The τf polynomial, which is linear combination of the temperature coefficient of relative dielectric constant and the linear expansion coefficient of the dielectric and cavity, is given. The coefficients of τf polynomial are discussed in detail. The intrinsic temperature coefficient of resonant frequency (τf0) is introduced to improve the measurement precision. Resonators made of BaO-TiO2-Sm2O3 and (Zr0.8Ti0.2)TiO4 ceramics with Teflon and alumina as supports were measured. The results show that the τf values of the same resonator with above supports are different, and the measured variation between them is more than 3 ppm/˚C. Using the concept of τf0, the variation is less than 2 ppm/˚C.
With appropriate geometry configurations, bistatic Synthetic Aperture Radar (SAR) can break through the limitations of monostatic SAR on forward-looking imaging. Thanks to such a capability, bistatic forward-looking SAR (BFSAR) has extensive potential applications. For the focusing problem of BFSAR, wavenumber-domain algorithm is accepted as the ideal solution. However, in practical application, the processing is limited because of its inability to combine the range-dependent motion compensation (MoCo). To cope with such a problem, an extended wavenumber-domain algorithm for BFSAR is derived in this paper. By modifying the reference function and mapping relationship in frequency interpolation, the extended wavenumber-domain algorithm of BFSAR integrates a two-step motion compensation. Simulation results verify the effectiveness of the proposed method.
In this letter, a new model of antenna with Jerusalem crosses (JC) as fractal slots for circular polarization applications is designed. The proposed slot antenna has a fractal cross formation with four Jerusalem crosses (JC) to achieve wide bandwidth and a compact size as well as circular polarization. A T-shaped feed line is implemented in the proposed antenna for improving the bandwidth while the interaction of the feed line with cross-shaped slots makes circular polarization. The proposed antenna shows bidirectional pattern and bandwidth at 2.42-3.0 GHz with VSWR<2, which can be used in Wi-Fi and Bluetooth applications with a gain of 3.5 dBi. The proposed fractal antenna size is 40×40 mm, and it is designed and fabricated on an FR-4 low-cost substrate with thickness of 1.6 mm. It is simulated by HFSS full wave software. In addition, the experimental results are presented and compared with the simulation for VSWR, radiation pattern and axial ratio.
This paper presents a design of wideband and low-profile linear array of H-plane horn antennas. In order to construct the linear array in H-plane, the aperture size of the horn antenna in the H-plane should be comparable with one wavelength in the free space, which leads to a poor impedance matching especially in the lower frequency range. The approach to the problem is removing the side walls of the flare part of the antennas. The array is fed by a wideband 4-way ridged SIW power divider. The designed array operates from 5.6 GHz to 18 GHz for VSWR 2.5 and exhibits stable radiation beam with a narrow beam-width in H plane over the same frequency rang while retaining the antenna array height of only 4 mm (0.17λ0 at the center frequency). The designed array is fabricated and tested. It is observed that measured results agree well with simulated ones.
In this paper, a band-notched UWB filtering antenna with defected ground structure (DGS) is presented. This defected ground structure as a lowpass filter (LPF) plays a role in filtering unwanted band. The DGS is applied to suppress the upper passband spectrum of the proposed antenna. A U-shaped slot line etched in the feeding line creates a single band-notched characteristic in 3.3-3.83 GHz for WIMAX to avoid potential interference with the existing system. The measured return loss has a wide fractional bandwidth up to 127.6%, which covers a range of 2.43-11 GHz, with the return loss higher than 10 dB except notch band and less than 2 dB up to 16 GHz. The measured and simulated results reveal that the antenna has good upper stopband performance and consistent quasi-omnidirectional radiation pattern within the UWB frequency range.
This letter presents a dual-wideband bandpass filter (BPF) by using open and shorted stubs loaded ring resonator. The resonator can excite multiple resonant modes. The transmission zeros (TZs) analyzed by the transversal signal interference concepts can divide the resonant modes into two groups that form dual-wide passband. The even-mode resonant frequencies can be controlled by the stubs parameters, and the TZs can be tuned by the port angle independently. So the center frequency (CF) and the bandwidth of each passband can be flexibly controlled. An experimental dual-wideband BPF with CF of 1.48/5.7 GHz and 3 dB FBW of 137.8%/49.3% is implemented, and the experimental results are presented for validation.
A novel microstrip coupled-line directional coupler is proposed in this paper. It is based on the introduction of a complementary split ring resonator and dumbbell-like defected ground structure on the coupled lines to strongly enhance the designed backward coupling. The designed frequency band is from 1.2 to 1.5 GHz. The coupler is fabricated and tested. The insertion loss is less than 3.5 dB. The simulated and measured return losses are better than -13.5 dB, and the isolation is higher than 20 dB across the operating band. The overall size of the coupler is 80 mm×70 mm, which is about 0.36λ×0.32λ at the central frequency 1.35 GHz.
A simple dual-wideband magneto-electric (ME) dipole directional antenna is proposed in this letter. The antenna is composed of a ground plane, four Γ-shaped parasitic strips and an ME dipole fed by a Γ-shaped feed strip. Simulated results show that the ME dipole can only work in the higher frequency band from 1.7 to 2.7 GHz. By adding four Γ-shaped parasitic strips at each corner of the ground plane, the lower frequency band (0.788~1.17 GHz) impedance matching is improved. The antenna is prototyped and measured. Measured results show that the antenna obtains -10 dB impedance bandwidths of 39% (0.788~1.17 GHz) and 51.7% (1.62~2.75 GHz) for the lower and higher bands. The achieved gains are 5.5±0.5 dBi in the lower frequency band and 7±1 dBi in the higher frequency band. The proposed antenna has good impedance and directional radiation characteristics in the whole frequency band. It can be widely used for 2G, 3G, LTE, WLAN, etc. communication systems.
A planar power divider with unequal power division and out-of-phase feature is presented. Firstly, the principle of the proposed power divider containing transmission lines with the same characteristic impedance is analyzed. The power dividing ratio can be adjusted by only the elctrical lengths of the transmission lines. Design equations of the proposed circuit are derived. Secondly, the method to reduce the size of the power divider is discussed. For illustration, a 2:1 prototype operating at 1.5 GHz is designed, fabricated and measured. The measured results show that S21, S31, and S11 are about -1.84, -4.96 and -28.4 dB at 1.5 GHz, respectively, that the isolation S23 is better than -20 dB from 1.44 to 1.56 GHz and that the phase difference between two output ports is about 180.54˚ at the center frenquency.
A frequency reconfigurable antenna suitable for handset is proposed in this research. The antenna structure includes an inverted-L shaped monopole and two meandered shorting strips. A wide high frequency band is excited from the inverted-L shaped strip monopole by direct feeding, and then the low and middle frequency bands are excited from two meandered shorting strips. Furthermore, a PIN switch diode is added at the end of shorting strip1 to implement the frequency reconfigurable property. The antenna was fabricated on an FR4 substrate and with a volume of only 9×50×5 mm3. It can cover the operation bands of LTE700/2300/2500, GSM850/900/1800/1900, UMTS2100, and WLAN2400. The detailed considerations and analyses of the design are studied in this paper.
This paper proposes a wideband dual-polarized magneto-electric dipole antenna composed of two pairs of vertical shorted patches and two pairs of horizontal double-layered planar dipoles. To achieve dual-polarization radiation, two orthogonal Γ-shaped stepped-impedance strip feed lines are designed to excite the antenna. The regions between the vertical shorted patches are loaded by dielectric materials to reduce the antenna profile. In addition, the antenna is backed with a rectangular cavity-shaped reflector to improve radiation pattern stability and diminish back radiation. Experimental results demonstrate that the proposed antenna has obtained a wide impedance bandwidth of 57.1% from 1.5 to 2.7 GHz and high port isolation of better than 30 dB within the bandwidth. The average antenna gain is about 9.7 dBi with a variation of below ±1.5 dB and the radiation patterns are unidirectional, symmetric with low back radiation, and low cross-polarization radiation across the entire operating band.
This paper presents a design of a compact triple-band bandstop filter (BSF) using embedded capacitors. The presented BSF is useful to suppress the signal frequencies 2.2 GHz, 5.53 GHz and 4.15 GHz from the WLAN and UWB band with attenuation level 33.5 dB, 27.6 dB and 24.9 dB, respectively. The quality factors of the three bands are 5.21, 31.92 and 79.0, respectively. The simulated and measured results are presented to validate the concept. Such BSFs could find application in modern communication systems to suppress the potential interference of the unwanted frequencies from the WLAN and UWB band.
In this paper, a broadband power amplifier with high efficiency and output power based on GaN HEMT is presented. The design of broadband matching network and transistor package modeling is presented, and a simulation strategy is proposed to increase the simulation accuracy. According to measured results, the PA module shows a linear gain of 10~13 dB during 1.9-4 GHz. The efficiency can reach 74.5%, and the maximum output power reaches 33.2 Watt. For a 5-MHz WCDMA signal, the designed power amplifier achieves an average output power above 20 W when ACLR = -30 dBc over the entire working band.
A fast design technique for lumped-element multilayered bandpass filters is proposed. With this technique, the difference between multilayered component values and theoretical component values can be quickly estimated and tuned. The design procedure for filters can be obviously simplified, and the efficiency can be improved. This technique is discussed in detail, and mathematic explanation is given. An example is used to show the entire design procedure. The measurement result agrees well with the desired result, which shows the effectiveness of proposed technique.