This paper presents our research work on designing a dual-band dual-polarized (DBDP) series-fed S/X-band shared aperture antenna (SAA) for synthetic aperture radar (SAR) applications. The proposed SAA DBDP X-band antenna is designed with the concept of series-fed 4-group 2x2 planar arrays with high impedance microstrip line feeding in both vertical and horizontal polarizations. By etching out the inner edge elements from 2x2 X-band subarrays in all the four-groups, the S-band element could be accommodated. The design evolution stages have been presented. The S-band (3.2GHz) is best suited for volumetric soil moisture estimation using SAR and X-band (9.3 GHz) best suited for surveillance SAR applications and grain size estimation. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The antenna with reflection coefficient lS11l < -10 dB has an impedance bandwidth 3.12-3.42 GHz (9.3% BW) in S-band and 9.2-9.36 GHz (1.72% BW) in X-band. The measured isolation lS21l between two different bands in the same polarization is better than 25 dB, and the isolation between two different bands in two orthogonal ports is better than 30 dB. Measured gain of the antenna at S-band is better than 8.5 dBi at V-port and H-port, and X-band is better than 11 dBi at either port. Measured side-lobe level (SLL) at S-band is better than -17 dB at either port, and X-band is better than -20 dB at either port. The overall size of the S/X-DBDP SAA is 100 x 100 x 1.6 mm³. Measured results of the S/X-DBDP SAA show good agreement with the finite integration technique (FIT) based computer simulation technology (CST) microwave studio.
In this paper, a new flower-shaped microstrip line feed reconfigurable band-notched UWB monopole antenna using single varactor diode is introduced and fabricated. Different notch frequencies can be obtained using different capacitor values. The effect of changing the varactor position is also examined. The flower shape is first optimized to obtain UWB characteristics. Then, a slot is made in the microstrip line to be loaded later with a single varactor diode. A wide range of notch frequencies can be obtained using this simple configuration which cover most of the narrow band coexistence systems. The notch frequency can be lower by increasing the capacitance value. The notch frequency covers the WLAN band when C=0.8 PF and covers the WIMAX band when the capacitance is changed to 0.7 PF for the same antenna configuration and varactor position. Two prototypes of the proposed antenna using two different single capacitor elements with capacitances 0.6 PF and 1.5 PF are fabricated, and their reflection characteristics are measured and compared with the simulated ones. Notch frequencies at 6.1 GHz and 4.3 GHz are obtained respectively in both simulated and measured antenna structures. The proposed antenna a directive radiation pattern in E-plane and omnidirectional pattern in H-plane. Also the gain is suppressed in the notched frequencies. The group delay is nearly stable in the UWB frequency range with very little variations, but it is distorted sharply at the notch frequencies. So, the proposed antenna is a good candidate for the modern UWB systems.
Two novel compact 2.6/5.2 GHz diplexers with high common-mode suppression were designed and fabricated on the FR4 substrate. The diplexers were designed based on two open loop rectangle ring (OLRR) resonators and the two different resonant frequencies could be easily obtained by tuning the lengths of OLRRs. In the past, the traditional balun diplexer needed matching circuit to transfer signal to radio frequency (RF) transceiver with low loss because of the existence of unmatched impendences between the balun diplexer and RF transceiver. In order to improve their efficiency and low down the cost of the fabricated circuits, we would propose a method to tune the output impendence of the balun diplexer and the diplexer could have matching output impendence with the RF transceiver. The proposed balun diplexer had the structure of two stub-loaded microstrip lines, and the needed output impendence could be changed by tuning the widths of microstrip lines and stubs and by changing the length and position of stubs. For that, if the output impendence is well tuned, the designed balun diplexer will have the higher efficiency and low cost because the matching circuit is not necessary.
In this paper, a microstrip lowpass filter with -3 dB cutoff frequency of 1.8 GHz composed of two resonators with different polygon patches and six symmetric suppressing cells is presented. To design the proposed filter, the impact of each microstrip transmission line on the scattering parameters of the employed resonators is separately determined by extracting the equations of the insertion loss (S21) and return loss (S11) on the basis of their equivalent LC circuit. The designed filter is fabricated and measured, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss better than -0.35 dB and an acceptable suppression level of -22 dB from 1.87 to 19.75 GHz are achieved. Furthermore, a flat insertion loss in the passband and an acceptable return loss (-19.32 dB) in this band can verify desired in-band performance. The designed lowpass filter has a high figure of merit about 36969.34.
This paper proposes a novel planar beam tracking antenna and brings a new prototype antenna in wireless communication systems. The proposed antenna consists of a magic-T, two antenna elements and two phase shifters. The main idea for the antenna is to adjust the phase shifter using the difference of the signals received by the two antenna elements to tilt the beam in the direction of the arrival wave. Theoretical discussion is presented to explain the concept. Both-sided MIC technology is effectively used to integrate the magic-T and the phase shifters with the antenna elements in a simple structure. A prototype antenna of the new design for E-plane beam tracking is fabricated, and the radiation pattern and return loss are measured. Simulated and experimental results of the beam direction vs. applied voltage are successfully compared, and the proposed concept is experimentally demonstrated. An antenna structure for beam tracking in H-plane is also demonstrated in this paper.
A novel structure of a near-field communication (NFC) loop antenna for mobile phones with a metal back case is proposed. The proposed structure of the metal back case itself can operate as an NFC loop antenna through the design of a simple single turn loop antenna on the top portion of the metal back case, so that the simple structure of the proposed NFC loop antenna can reduce the overall thickness of the NFC antenna for slim mobile phones. Since a sintered ferrite sheet with generally higher relative permeability (μr ≈ 200) must be used to reduce the performance deterioration of the conventional NFC loop antennas due to the eddy current in the battery pack of a mobile handset, the cost of these conventional NFC antennas is high, and they are considerably fragile. In this paper, the proposed NFC antenna is designed without the ferrite sheet and in the optimal location to ensure minimum interference from the adjacent metallic components.
A novel method for further wideband RCS reduction on metasurface (MS) is proposed in this paper. By introducing a phasor interference element to the original MS composed of two elements, RCS of the proposed MS constructed by three elements can be further remarkably decreased in broadband. The measurement procedure on scattering performances of samples is conducted in an anechoic chamber, in which the experimental results indicate that the proposed MS can achieve further 3-dB RCS reduction from 6.94GHz to 15.35GHz compared to the original MS, and the maximum further reduction reaches 24.9dB. As a result, compared with a same-size metallic plate illuminated by a normal plane wave, RCS of the proposed MS can be reduced by more than 8.5-dB from 6.68GHz to 15.38GHz with the relative bandwidth of 78.9%.
As ultra high frequency (UHF) radio frequency identification (RFID) technology, a smart recognition technology, has been gradually spreading to various applications, and several sub-1 GHz wireless technologies are being standardized and developed. As such technologies operate at a specific frequency band (902-928 MHz industrial, scientific, and medical (ISM) bands), the impact of RF interference due to performance degradation of UHF RFID technology on the interference signal is emerging as a new obstacle. In this paper, we investigate the interference analysis and experimental results of passive UHF RFID systems in sub-1GHz wireless communications systems. By considering interference signal frequency and power, interference deployment, antenna polarization, RF system-level analysis, and experimental verification are conducted to evaluate the impact of performance degradation in the UHF RFID system on the interference signal.
This paper presents a wide-angle polarization independent triple-band absorber based on a metamaterial structure for microwave frequency applications. The designed absorber structure is the combination of two resonators (resonator-I and resonator-II). The proposed absorber is ultra-thin in thickness (0.012λo at lowest resonance frequency and 0.027λo at highest resonance frequency). The proposed absorber structure offers three absorption bands with peak absorptivities of 99.95%, 95.32% and 99.47% at 4.48, 5.34 and 10.43 GHz, respectively. Additionally, it also offers the full width at half maximum (FWHM) bandwidth of 167.2 MHz (4.40 - 4.56 GHz), 178.1 MHz (5.25 - 5.43 GHz) and 393.8 MHz (10.24 - 10.63 GHz), respectively. The metamaterial property of the designed absorber structure has been discussed by using dispersion diagram plot. The designed absorber structure exhibits wide-angle absorption at various oblique incidence angle for both TM and TE polarizations. The absorption mechanism of the designed absorber structure has been analyzed through electric field and surface current distribution plots. The input impedance of the designed absorber (375.67 Ω at 4.48 GHz and 346.73 Ω at 10.43 GHz), nearly matches the free space impedance. The proposed absorber structure is fabricated and measured. Simulated and measured results are in good agreement with each other.
In this letter, two different types of band-notch UWB-MIMO antennas are presented. the filtering effect can be achieved by integrating slot resonators to a UWB antenna. Both of the proposed antennas have very compact size and are smaller than most of the other band-notch UWB-MIMO antennas. The ultra-wideband is achieved by etching stepped slots on the ground. The band-notch characteristic can greatly reduce the potential interference between the UWB and WIMAX/WLAN system. Our proposed antennas can also possess a wide bandwidth from 3.3 GHz to 11 GHz with |S11| < -10 dB. Some effective measures have been taken and illustrated to reduce the isolation. Measurements demonstrate that the mutual coupling between the antenna elements is good enough for a MIMO system. Their stable radiation patterns are simulated, designed and measured successfully. The good performance and compact size make the antennas good candidates for UWB applications.
A Ku-band bandpass frequency selective surface (FSS) with high selectivity and miniaturization is proposed in this paper. We use two metallic strips and one slot to design the frequency selective surface structure which contains both electrical and magnetic couplings. A metallic via is introduced in the FSS element for miniaturization. With the via inserted at the end of the metallic strip, the FSS unit size is reduced to half compared to that without via inserted. To investigate the operating principle of the slot-coupled FSS, an equivalent-circuit model is given and analysed using the odd- and even-mode method. The constructed out-of-phase signal path causes two transmission zeros (TZs) near the skirts of the narrow pass band, thereby enhancing the selectivity. A prototype of the proposed FSS operating at 16GHz is fabricated and measured. The measured results agree well with the full-wave and circuit simulation results, thus verifying the FSS design.
In this paper, a compact MIMO antenna with improved isolation is proposed. Elliptical slots and an SRR like structure are employed to improve the isolation. The proposed MIMO antenna structure consists of two semi-circular radiators attached to a rectangular monopole which are mirror images of each other with edge to edge spacing of 0.125 λ0, where λ0 is the free space wavelength corresponding to the lowest operating frequency of the structure. Two square steps are added to the above semi-circular monopole to increase the effective path length to cover the lower frequencies. Thereafter, a semi-annular ring slot is introduced, and square steps above the semi-circular monopole are modified to curved steps to further improve the impedance bandwidth of the antenna. The mutual coupling over the wideband is reduced by placing elliptical slots and SRR like structure in the ground plane. The proposed antenna has impedance bandwidth of 2.1- 12 GHz with |S21| < -20 dB over the entire frequency range. The antenna is designed and fabricated on an FR-4 substrate having overall dimensions of 38 mm × 33.4 mm× 1.6 mm. The measured results show a good correlation with the simulated ones. The envelope correlation coefficient (ECC) of the antenna is less than 0.02 over the entire band. The proposed MIMO antenna is an appropriate candidate for 3G, 4G, Wi-Fi, Bluetooth and UWB applications.
The mutual coupling between very low frequency (VLF) antenna elements is an important factor affecting the radiation performance of umbrella antenna arrays. This study evaluates the factors influencing the mutual coupling between the elements of an umbrella antenna array. We develop a mutual coupling analysis method for calculating the input impedances of a VLF antenna based on the impedance effect of mutual coupling. The radiation resistance of the VLF umbrella antenna can be obtained using numeric integral from Method of Moments (MoM) solution. Using the FEKO simulation software, a model of a trideco-tower umbrella antenna array is established. The electrical parameters of the VLF umbrella antenna array on inhomogeneous ground are calculated for both single and dual feeding modes. The impedance characteristics of the umbrella antenna arrays are also simulated for different array inter-element spacings on homogeneous ground. Representative numerical results are reported and discussed to assess the mutual coupling effect of the proposed method in comparison with full-wave simulations.
An integer-N quadrature frequency synthesizer for single-band UWB application was designed in 0.18 μm CMOS technology. A modified bottom-series quadrature voltage-controlled oscillator (QVCO) based on reconfigurable LC tank is employed to provide quadrature signals and cover a range from 6.48 GHz to 7.07 GHz. In order to suppress the reference spur levels, an improved charge-averaging charge pump and a highly linear phase-frequency detector (PFD) are used. From the carrier of 6.6 GHz, the measured reference spur is -78.2 dBc, and the measured phase noise is -115.4 dBc/Hz at 1MHz offset. The frequency synthesizer including buffers consumes a total power of 99 mW from a 1.8 V power supply. Chip size is 1.6 mm×0.9 mm.
The electromagnetic characteristics of two-dimensional composite right/left-handed transmission lines (2D CRLH TLs) were investigated for the normal incidence of plane waves. The measured characteristic impedance and reflection phases exhibited resonant high impedance properties (equivalent to zero reflection phase) at a frequency within the left-handed mode for one-dimensional CRLH TL. An equivalent circuit was proposed to explain the measured characteristics. The relationship between the resonant frequency and the circuit parameters for 2D CRLH TLs was clarified by deriving an approximate equation for the resonant frequency. The surface-wave transmission characteristics for the 2D CRLH TLs were compared with those for a mushroom structure.
In this paper, Gysel type Unbalanced-to-Balanced (UTB) Power Divider (PD) with arbitrary power division is proposed. UTB PD is a five-port device, and a standard scattering matrix for a five-port PD with arbitrary power division isderived. Design equations are obtained analytically. Using design equations, a UTB PD is designed at 2 GHz for power division ratio of 1:2, and simulation is carried out using HFSS. A prototype is fabricated, and measurement is performed to verify the simulation results of PD. Measured results are in good agreement with the simulated ones. The proposed PD shows in-phase characteristic within ±5◦. Measurement results show that isolation between two output ports is greater than 20 dB. Greater than 20 dB common-mode suppression from input port to output balanced ports is achieved. Differential-mode power is divided in power division ratio of 1:2 from unbalanced port to balanced ports. Measured fractional bandwidth of the proposed PD is 21%.
Sparse reconstruction technique can be used to provide high-resolution imaging result for through-the-wall radar (TWR) system. Since conventional sparse imaging reconstruction algorithms usually require a tremendous amount of computer memory and computational complexity, it is very difficult to apply in the practical large-scale TWR imaging applications. To solve the above problem, an efficient sparse imaging reconstruction algorithm is proposed in this paper. The proposed imaging method combines the spectral projection gradient L1-norm (SFGL1) algorithm with nonuniform fast Fourier transform (NUFFT) technique to achieve imaging reconstruction. Benefiting from the function handle operation of SPGL1 and computational efficiency of NUFFT, the proposed imaging algorithm can significantly reduce the memory requirement and computation complexity. The simulated and experimental results have shown that the proposed imaging method can significantly reduce the required computer memory and computational cost while providing the similar recovered image quality as the conventional sparse imaging method.
A novel high-gain and high-power cavity slot antenna is presented in this paper. The antenna consists of a slotted cavity cover, a driven antenna and a polarization twist reflector. The driven antenna is a balanced-fed dipole. And a 2×4 slots array is etched on the top surface of the cavity cover. To excite the cavity slots with uniform amplitude and phase, the polarization twist reflector is used here. Compared with the antenna without the twister, the gain is improved by almost 4.0 dB across the operating band. In addition, the field distributions of the proposed antenna are analyzed through simulation, which proves a high power-handling capacity of 3.94 MW. To verify the design, a prototype operating at 5.8 GHz bands has been fabricated and measured. The measured maximum gain and radiation efficiency are 13.6 dBi and 95%, respectively.
We introduce a novel two-stage approach for rapid design of massive metamaterials (MTMs), where performances of thousands of microstructures require evaluation. In Stage I, an equivalent circuit model is synthesized via rational function modeling to represent the frequency response of MTMs microstructures. In Stage II, Gaussian process (GP) regression models are unitized to build the relation between the physical setting of the microstructure, including geometric design variables and incident angles of electromagnetic (EM) waves and the representing parameters of the equivalent circuit model. As a consequence, the mapping from the microstructure physical parameters to the frequency response is easy to achieve and with high accuracy. We offer two metamaterial prototypes to illustrate that the proposed approach allows high efficiency in facilitating the design of massive MTMs. The experimental results demonstrate that our method is no longer limited by the complexity of microstructures and the spatial dispersion, induced by the variation of incident angle. We compare the accuracy of predicted responses against the reference data, and both examples yield average RMSE less than 0.05, which meets the requirements for many MTMS engineering applications.
We present the design of an infrared metasurface harvester based on the full absorption concept. The metasurface unit cells consist of an H-shaped resonator with the load placed across the gap of the resonator. Different from infrared metamaterial absorber designs, the resonator is capable of not only full absorption but also maximum energy channeling across the load resistance. Numerical simulation demonstrates that 96% of the absorbed energy is dissipated across the load resistance. In addition, cross-polarized H-resonators design is presented, which is capable of harvesting infrared energy using dual polarizations within three frequency bands.
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