This paper presents a bidirectional coupler which is designed by combining nonuniform wiggly lines and the reflected power canceller (RPC) method. The combination not only brings about a high directivity but also makes a wideband structure with a compact size. Although, in the RPC method, an idle port is used to produce a reflected signal in order to achieve a high directivity, there are not any idle ports in the proposed coupler. The coupler was built on an FR4 substrate. The measurement results show that this structure is suitable to monitor forward and reflected signals in high power applications. The fabricated coupler has the directivity of more than 22 dB and the coupling flatness of ±0.12 dB in the forward and backward signals in a wide frequency range of 140 MHz-190 MHz.
In this paper, we discuss two well known definitions of electromagnetic momentum, ρA and \epsilon0[E x B]. We show that the former is preferable to the latter for several reasons which we will discuss. Primarily, we show in detail|and by example|that the usual manipulations used in deriving the expression \epsilon0[E x B] have a serious mathematical flaw. We follow this by presenting a succinct derivation for the former expression. We feel that the fundamental definition of electromagnetic momentum should rely upon the interaction of a single particle with the electromagnetic field. Thus, it contrasts with the definition of momentum as \epsilon0[E x B] which depends upon a (defective) integral over an entire region, usually all space.
Conventional dielectric lenses rely on the accumulation of phase delay during wave propagation to produce a desired wavefront. By considering the required phase delay at each lens position, an `equivalent' transmitarray antenna can be obtained. Despite a lack of curvature as in conventional lenses, the phase delay in the transmitarray antenna is achieved via a periodic arrangement of unit cell elements to bend the incident waves in the desired directions. This paper presents the design and characterization of a 4-layer transmitarray antenna consisting of double square ring elements. The gap between the double square rings is varied as a fixed proportion of their dimensions, while keeping the widths constant. The transmitarray element can achieve a transmission phase range of 2350 with a loss of less than 3 dB. The performance of the transmitarray antenna is explicitly compared to that of a convex dielectric lens, both of which are operating at 8 GHz.
An all-in-one UHF RFID tag antenna using nonuniform meandered lines for retail garments in the textile industry is presented. The all-in-one antenna offers relatively low cost, wide band, compactness, and good conjugate matching in the presence of its robust housing with good dipole-like read range. Results show an antenna with a wide bandwidth of 900MHz and a long read range of 10.2 m making the UHF RFID tag antenna using nonuniform meandered lines a potential candidate for retail garments in the textile industry. Simulations are corroborated by measurements and are in fair agreement.
A novel class of dual-mode filters with improved high frequency sideband suppression response making use of coplanar waveguide (CPW) square loop resonator is presented. The resonator is placed on the bottom plane and inside the defected area of the ground. The resonant property of the CPW square loop resonator as well as the coupling property between two degenerate modes with different patch perturbation is studied in the paper. Two T-shaped orthogonal feed lines are arranged on the top plane, which not only provide proper excitation to the resonator, but also introduce an additional source-load coupling, so the proposed filter is found to have two transmission zeros at high frequency sideband and takes on asymmetric frequency response. Such a compact dual-mode CPW square loop resonator filter operating at 2.68 GHz is designed and fabricated.
In this paper, a novel miniaturized frequency selective surface (MFSS) with capacitive loading is proposed; it has characteristics of low profile, second-order, wide-band, and remarkable wide stop-band properties. In a specific frequency band, the proposed MFSS has a second-order filter function characteristic. The proposed MFSS is composed of three metallic layers separated by two dielectric substrates, which offers the spatial form of the second order microwave filter. The band and operating frequency can be controlled by the thickness of dielectric substrates and the gaps between the capacitive loading structures. The element size is smaller than 0.05λ x 0.05λ. The element thickness is less than λ/30, where λ is the free space wavelength at the resonant frequency. The frequency response produced by the proposed MFSS had very good stability when the plane wave incidence angles varied from 0 to 60 degrees. The fundamental frequency f0 is 2.45 GHz; the relative bandwidth δ is 10%; and the stop-band is from 3 GHz to 39.6 GHz. The frequency response demonstrates the excellent filtering performance.
This paper presents a new saw-tooth shaped sequentially rotated fractal boundary (SRBF) square microstrip patch antenna (SMPA) for wireless application. The square shape is rotated by an angle `θ' and superimposed, realizing fractal like geometry at boundary. The rotation of square shaped patch is divided in equal number of scaling angles θn such that for every iteration of angle θ, fractal boundary geometry has been realized. The square shape is modified into a circular shape patch resonating at 2.5 GHz. A 450 tilted rectangular slot is cut inside the radiating element to achieve circular polarization at 2.45 GHz. The antenna is fabricated using an RT Duroid 5880 substrate, having size of 70 mm x 70 mm. The antenna offers measured impedance bandwidth (VSWR < 2) of 50 MHz (2%) with simulated peak gain about 7 dBi. The fabricated antenna is tested, and measured results are in close agreement with simulated ones.
The present work describes a new wideband circularly polarized MIMO rectangular antenna in cube form for X-band application (8 to 11.8 GHz). Proposed antenna structure shows pattern diversity in whole 360° angle with polarization diversity. The isolation between the antennas is more than -14.5 dB. The impedance matching bandwidth (IMBW) is 3.8 GHz, and 3 dB axial ratio bandwidth is 2.91 GHz. The envelope correlation coefficient is less than 0.035, and its diversity gain is 10 dB. A copper metallic cylinder is placed inside the cube antenna to reduce the mutual coupling between the antennas.
This research work introduces a compact dual composite right/left handed (D-CRLH) unit cell structure for filtering power divider (FPD) application. The D-CRLH unit-cell consists of an interdigital capacitor with two shorted fingers in series. It contains a meander line, a rectangular stub, and a via in shunt, both series and shunt elements provide filtering response as a bandpass filter. This design has been developed on dielectric material of thickness 1.6 mm, usually called as Epoxy glass substrate (FR-4). The transmission line of length λg/4 of a Wilkinson power divider has been replaced with a D-CRLH unit cell to reduce the size of proposed structure more than 60%. Another advantage of using a D-CRLH structure is the position of resonance frequency independently controlled by series parameter only because of shorted structure. The series chip resistor has been utilized to improve the isolation at resonance in between output ports. It offers miniaturization with electrical footprint area of 0.15λg x 0.27λg (11.4 mm x 20.4 mm), here λg represents the guided wavelength at resonance frequency of 2.5 GHz.
A dual-band antenna operating in dual bands is presented. The antenna is composed of two substrate layers covered with three printed patch layers. The top layer is an electrically small ring; the middle consists of four spiral resonators (SRs); and the bottom is a split-ring resonator (SRR). Inductive couplings between layers change the radiation Q factor of the original ring antenna and promote resonating modes in UHF and S bands. Besides, the input matching property is also improved. The measured return loss agrees well with the calculated results, and the radiation patterns are also presented. From experiments it is found that the proposed antenna is electrically small at operation dual-bands.
For a radiating structure such as dipole/patch array mounted on an aerospace platform, the radiation mode radar cross section (RCS) plays a significant role compared to the structural mode RCS. Thus the estimation and control of array RCS without degrading its radiating characteristics poses a challenge for an antenna engineer. In this paper, a novel design of a low profile 4-element patch array with hybrid HIS-based ground plane is presented to demonstrate both in-band and out-of-band structural RCS reductions. A significant broadband reduction in structural RCS has been achieved from 1 GHz to 80 GHz. The radiation mode RCS of the patch array is computed and controlled through optimized design parameters without degrading the radiation characteristics. The computed array RCS shows that even radiation mode RCS can be reduced except in operating frequency range.
A triple-section arm structure is proposed for designing a planar spiral antenna. All three sections are designed by combining logarithmic, rooted, and sine equations. The slowly outstretched and contractive structure is innovatively realized. According to the radiation characteristics of the spiral antenna, each section corresponds to different in-band enhancement effects. Numerical simulation in the frequency domain and experiments using two different baluns are carried out. The results show that the novel spiral topology could simultaneously achieve improved axial ratio, low cross-polarized gain, and excellent impedance matching throughout the whole band. The axial ratio is reduced by 1.5 dB at mid frequencies and more at low frequencies, comparing the proposed arm with a sinusoid-added equiangular spiral arm. Without applying the resistive loading method, a lower cut-off frequency of 750 MHz is still realized both in impedance bandwidth and axial ratio bandwidth. The low cut-off frequency of the proposed arm is 30.2% lower than the conventional Equiangular spiral arm. Besides, the polarization isolation is significantly improved, especially at low frequencies. Therefore, the proposed miniaturized spiral arm structure could be a competitive form for designing spiral antennas.
The design of a compact stubbed microstrip balun with very wide range higher order harmonic suppression, is presented based on multiple open stub units, for which advantages are twofold, compared to single and double open-stub based designs. First, the high degree of size and harmonic reduction is achieved within the realizable impedance values. Second, the achieved bandwidths are fairly large (close to those of conventional balun) for a given set of electrical lengths. Unlike other methods, here, predetermined bandwidth analysis is provided for various levels of size and harmonic reduction. A prototype balun, having 75% size reduction and simultaneous wide higher order harmonic suppression extended up to 12f0, while maintaining good input matching, amplitude and phase balance bandwidths, is fabricated for validation.
A planar I-shaped folded-patch antenna with a footprint of 21 mm x 21 mm x 1.6 mm is designed for compact UHF RFID tags to cohere on metal. The antenna consists of three parts: a square ground plane, an I-shaped patch and a ring resonator. The I-shaped patch is interconnected to the ground plane through a narrow shorting stub, and the microstrip feed line is inserted into the patch to reduce the input impedance of the patch. Extra capacitance and inductance introduced by the ring resonator can lower the tag's resonant frequency down to the expected UHF RFID band. The proposed antenna is manufactured, and there is excellent consistency between simulation and measurement results. The proposed tag antenna achieves a far read distance up to 6.3 m on metal (with 4 W equivalent isotropic radiated power) at resonant frequency of 920 MHz.
Compressed sensing (CS) imaging radar can obtain higher resolution than the traditional synthetic aperture radar (SAR) with less data, which makes it important for military and civilian applications. However, noise, especially active noise jamming will degrade its performance. This paper describes the signal model of the CS imaging radar under noise jamming. Through theoretical analysis and simulation experiments, the influences of different jamming patterns, jamming parameters and reconstruction algorithms on the performance of CS imaging are compared. It can provide reference for the research of anti-jamming technology of CS imaging radar.
A novel dual-band frequency selective surface (FSS) operating at Ku- and Ka- bands is presented in this paper. The proposed FSS is an aperture element constituted by a square loop loaded with four symmetrical umbrella-shaped stubs on the front side of the dielectric substrate. A good angular stability up to 60° angle of incidence for both TE and TM polarizations is provided by the FSS. Moreover, the two passbands of FSS can be controlled independently and flexibly by changing corresponding structural parameters. A prototype of the FSS is fabricated and measured. The good agreement between simulation and measurement results further proves the performance of the FSS.
A CPW (coplanar waveguide) bandpass filter based on spiral-shaped DGSs (defected ground structures) which can be used in the 5G band is proposed. Two pairs of face-to-face symmetrical spiral-shaped DGSs are added to the ground planes of a CPW main transmission line. A cross-shaped notch is adopted in the central strip of the CPW main transmission line to generate the passband, while two m-shaped DGSs are brought in to improve the passband performance of the filter. The measured results show that the central frequency is 3.54 GHz, and the 3-dB bandwidth is from 3.29 GHz to 3.79 GHz. The filter has a 10.1% bandwidth with a return loss better than 10 dB from 3.35 GHz to 3.71 GHz, and the insertion loss is less than 2.0 dB in the passband. Besides, there are two transmission zeros near the passband at 2.45 GHz and 4.81 GHz, which can improve the stopband rejection.
A method is proposed to calibrate a planar phased array by reconstructing its aperture distribution, in which the aperture distribution is superposed within the physical range of radiating element. Consequently, the calibration coefficients are solved for the linear relationship between the superposed aperture distribution and elements' excitations. The calibration accuracy that is influenced by resolution of aperture distribution is also discussed in this paper. In practice, the reconstruction procedure of aperture distribution is based on the plane wave spectrum (PWS) theory, utilizing FFT and IFFT techniques. This method turns out to be valid by experiment.
A novel hybrid resonant structure is proposed to decouple a dual-band microstrip antenna array. The decoupling structure is composed of two H-shaped strips, and the lower and upper ones respectively collaborate with an X-shaped slot to reduce mutual coupling at 4.5 GHz and 5.5 GHz. Two sub-patches of different sizes share a connection feeding line to construct the dual-band array element, which is arranged along H-plane with the edge-to-edge spacing 0.15 λl and 0.24λh (λl and λh are the free-space wavelengths of 4.5 GHz and 5.5 GHz, respectively). Simulated and measured results indicate that through loading the hybrid resonant structure, 31.6dB and 24.0dB reductions of mutual coupling at two frequencies are obtained, while the levels of coupling coefficients are both below -30 dB in two operating bands. Moreover, the modified radiation patterns, improved diversity metrics and weakened coupled current distributions further verify its superior decoupling capability. The proposed decoupling structure reveals its promise in being employed in communication system and multielement linearly antenna arrays.
In this letter, a multiband compact low-profile planar antenna based on multiple resonant stubs is proposed and studied. By utilizing two pairs of stubs embedded on a defected ground, the reflection coefficient less than -10 dB can be achieved with broadband characteristic for applications of wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX). Meanwhile, a pair of inserted slots on both sides of a curve slot is applied to the antenna design, which decreases the cross polarization. A multiband antenna is fabricated and measured to verify the design. The antenna is compact with operation frequencies for WLAN (2.45/5.2/5.8 GHz) and WiMAX (2.8/3.8/5.5 GHz) applications. The measured peak gains are 5.5, 4.4, 0.0, and 5.6 dBi at 2.45, 2.8, 3.8, and 5.5 GHz, respectively.