A wideband antenna with band notch function using electromagnetic bandgap (EBG) structure is proposed. The antenna is capable of reconfiguring up to three band notch operation. Three EBGs are aligned underneath the feed line of the wideband antenna. The transmission lines over EBGs unit cells perform as a band stop filter. A switch is placed on each of the EBG structure, which enables the reconfigurable band stop operation. The simulated and measured reflection coefficients, together with the radiation patterns, are shown to demonstrate the performance of the antenna.

A compact dual-band frequency reconfigurable microstrip-line fed open-end omnidirectional slot antenna is proposed in this paper suited for cognitive radio front end system. The antenna is capable of frequency switching at different frequency bands by changing the resonance length using two PIN diodes. The resonance frequency is tuned by a single varactor diode, placed at a certain location along the slot. The proposed antenna has a wide tuning range in the dual bands: 1.57 to 3.1 GHz and 3.8 to 5 GHz. The designed antenna has compact size of 40×40 mm². An approximate transmission line model of the proposed antenna is derived to calculate the proper positioning of the diodes, and the design has been verified through numerical simulations and measured results.

This paper presents the analytical design formulas for the bandpass filters which are built on the asymmetrically coupled-line conductor-backed coplanar transmission lines (CBCTLs) in multilayer configuration. The full-wave simulation is employed to characterize the far-field patterns of space-wave and surface-wave radiations as well as the frequency-dependent conductor, dielectric, and radiation losses. Good agreement among the results of full-wave simulation, transmission-line model, and measurement justifies the design procedure and validates the analytical design formulas. By properly placing the dielectric materials in multilayer configuration, a bandpass filter for minimizing the radiated power loss and improving the stopband characteristic can be achieved.

In some satellite navigation receiver systems, there is not enough space to settle several antennas for multi-port multi-band application generally. A triple-deck circularly polarized antenna with three ports for receiving and sending satellites signal is studied in this paper. The design idea in this paper is to place several single-feed microstrip antennas layer by layer for saving space. All patch antennas are probe-fed, and the probe connected to the upper patch goes through the clear hole in lower substrates. The structure of the multi-band antenna is investigated thoroughly. How to tune this kind of antenna is a big problem in application, and one special parameter is given to adjust the performance of the antenna. The designed triple-deck antenna works at the bands of GPS, BDS and 1.66 GHz independently. The formal two bands are RHCP, and the third band is LHCP, so it can receive and send signals at the same time. Both simulated and measured results show that all three working bands can cover the system use differently. Axial ratio less than 3 dB at center frequency is obtained, and absolute gain at center frequency is more than 4 dBic. The advantages of this antenna are compact in size for multi-port multi-band use and easy fabrication.

In this paper, a design of a dual-band series-fed dipole pair (SDP) antenna using proximity-coupled strip and split-ring resonator (SRR) directors is presented. Two different types of directors are placed close to the top element of the SDP antenna. First, a thick strip director is used to enhance the bandwidth and gain characteristics of the SDP antenna. Next, a pair of SRR directors is appended to both sides of the strip director to create a new resonance for dual-band operation. The performance of three different SDP antenna structures (with a strip director, with a pair of SRRs, and with both directors) are compared with the conventional SDP antenna without directors. When the strip and SRR directors are used together, the mutual coupling might affect the impedance matching of the original frequency band of the SDP antenna, and the distance between the two directors is an importance parameter to decide the performance of the antenna. The effects of the distance between the strip and the SRR directors on the input voltage standing wave ratio (VSWR) and realized gain characteristics are studied. A prototype of the proposed dual-band SDP antenna operating in the global positioning system L1 (1.563-1.587 GHz) and 1.7-2.8 GHz bands is designed and fabricated on an FR4 substrate. The experiment results show that the antenna has dual-band characteristics in the 1.56-1.63 GHz and 1.68-2.87 GHz frequency bands for a VSWR < 2. Measured gain is 5.9-7.5 dBi in the former frequency band, whereas it ranges from 6.2 dBi to 7.3 dBi in the latter.

Two compact differential bandpass filters (BPFs) based on coupled-line resonators and loaded capacitors are proposed in this work. By properly designing the coupled resonator and the loaded capacitance of original filter model, differential-mode (DM) passband responses and common-mode (CM) rejection can be obtained .For validation, two differential BPFs named Filter I and Filter II are discussed and experimentally characterized. One more DM transmission zero generated by out-of-phase cross-coupling is employed to control the DM bandwidth and sharpen the selectivity in Filter I while lumped capacitors are loaded in Filter II to replace capacitive coupled resonators for miniaturized size. Both filters are centered at 4.5 GHz with about 9% DM fractional bandwidth (FBW), less than 1.5 dB insertion loss, more than 15 dB return loss, and wideband CM suppression with more than 18 dB rejection. Furthermore, the size of Filter II is substantially smaller than Filter I and previously reported differential BPFs.

The number of composite insulators used in power transmission lines increases year by year. To detect and assess the aging status accurately concerns the security and stability of the power system. In order to achieve nondestructive testing of the sheds of composite insulators, a unilateral mini Nuclear Magnetic Resonance (NMR) sensor is proposed in this paper. The design of the magnet body and the optimization of the RF coil are presented. The Carr-Purcell-Meiboom-Gill (CPMG) sequence was employed to record the 1H relaxation curves of the sheds of three composite insulators from 110 kv lines with different service years. The curves were fitted to both single exponential function and inverse Laplace transformation functions. The results demonstrate that an increase of service year of the insulator results in a decrease of the effective transverse relaxation time (T_2eff). It is indicated that the sensor has a potential to assess the aging status of the composite insulators.

This paper discusses methods for expanding fields radiated by arbitrary sourcesenclosed by a certain minimum sphere in termsof Complex Source Point (CSP) beams. Two different approaches are reviewed; the first one is based on a spectral radiation integral, where the Fourier-spectrum is obtained by far field matching. The second approach consists of two steps: first, the equivalence principle is applied to a sphere enclosing the real sources, and a continuous equivalent electric current distribution is obtained in terms of spherical waves; then, the continuous current is extended to complex space and its SW components are properly filtered and sampled to generate the discrete set of CSPs. In both cases, the final resultis a compact finite series representation with a number of terms that matches the degrees of freedom of arbitrary radiated fields;it is particularly efficient when the fields are highly directional and the observation domain is limited to a given angular sector. The fact that the CSPs rigorously respect Maxwell's equations ensures the validity of the expansion from near to far zone and allows one to incorporate the CSP representation in a generalized admittance matrix formalism for the analysis of complex problems.

A new theory on designing electromagnetic/optical devices has been proposed, namely, a surface transformation (ST). Compared with Transformation Optics (TO), we do not need to consider any mathematics on how to make a coordinate transformation, and what we need to do is simple to design the shapes of the input and the output surfaces of the device with pre-designed functions. Unlike the devices designed by TO which are often inhomogeneous anisotropic media, all the devices designed by ST only need one homogeneous anisotropic medium (referred as the optic-null medium) to realize. Our method will lead a new way to device design without considering any coordinate transformations.

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.

A novel dumb-bell-shaped defected ground structure (DB-DGS) with embedded capacitor is presented in this paper. Compared with conventional DB-DB-DGS structure, the proposed DB-DGS exhibits many attractive characteristics including double resonance, high Q value and compact size. The equivalent lumped circuit model for the novel DGS is developed, and its parameters are extracted. Based on this new DB-DGS, a low-pass filter (LPF) using the novel DB-DGS has been constructed, which provides a more steep rejection property, a wider stopband and compact size. The proposed structure is experimentally verified through the demonstration of a low-pass filter design.

Here we present the design of a low loss top metal silicon (Si) hybrid dielectric-loaded plasmonic waveguide (TM-SiHDLW) and a compact, high performance optical resonator by numerical simulation based on finite element method. The waveguide adopted a thick (200 nm) top metal stripe structure to yield optimal performance due to reduced Ohmic loss in conductor around the stripe edge/corner. Moreover, a relatively thick (150 nm) dielectric spacer between the Si ridge and the metal stripe was employed to achieve both long propagation length and good field confinement. The effect of a thin (10 nm) silicon nitride (SiNx) layer covering the waveguide which was added for minimizing uncertainties on optical properties of SiHDLW resulting from high density of dangling bonds on Si surface was also investigated. Simulation results show that there is no significant degradation on the performance of the TM-SiHDLW. For the proposed plasmonic waveguide, a propagation length of 0.35 mm and a mode area around 0.029 μm² were demonstrated. The TM-SiHDLW waveguide was then used as the basis for anoptical resonator, which was designed to operate at the fundamental TE₀₁₁ mode for yielding high quality factor at a relatively small footprint size. A metal enclosure was also adopted to reduce the radiation loss, and a high quality factor of ~1900 was obtained, more than double the results in other disk or ring resonators of comparable size. Compared to the resonatorsbased on a rounded top metal Si hybrid dielectric-loaded plasmonic waveguide (RTM-SiHDLW) which has a much longer propagation length than the TM-SiHDLW, as reported in our previous work, the performance is essentially the same. This is simply because, for the resonators, the radiation loss is the dominate loss mechanism and the dissipation in the waveguide structure itself, thus, contribute little to the final quality factor of the plasmonic resonators.

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.

As we know, a moving target's azimuth shift in SAR image is proportional to the projected velocity of its across-track velocity in the slant-range plane. Therefore, we can relocate the moving target in SAR image after estimating its velocity. However, when Doppler ambiguity occurs due to the limitation of the SAR system's pulse repetition frequency (PRF), this relationship will not hold any more, in this case, we cannot relocate the moving target to the right position. The Doppler spectrum of a moving target with arbitrary velocity may entirely situate in a PRF band or spans in two neighboring PRF bands. In this paper, we conduct a detailed theoretical analysis on the moving target's azimuth shift for these two scenarios. According to the derived formulas, one can relocate a moving target with arbitrary velocity to the right position no matter Doppler ambiguity occurs or not. Simulated data are processed to validate the analysis.

A matrix method which takes into account the probe positioning errors in cylindrical and spherical near-field (NF) measurement techniques is proposed. The near-field irregularities made impossible the determination of the cylindrical or spherical wave expansion from the measured data using classical techniques based on 2D Discrete Fourier Transformation (2D-DFT) in cylindrical case (CC) and orthogonality properties in spherical case (SC). The irregularities can be randomly distributed but known and the matrix method expresses the linear relation between the measured near-field and the corresponding cylindrical or spherical modal expansion coefficients. Once the coefficients of the cylindrical and the spherical wave expansions are known the far-field of the antenna under test (AUT) is easily determined. Accuracy of the matrix method is numerically studied as a function of the irregularities magnitude and for different noise levels (data Signal to Noise Ratio). Also, experimental results have shown the efficiency of the proposed technique.

A dual-band and ±45° dual-polarized antenna is proposed for 2G/3G mobile communications in this paper. The proposed antenna consists of five elements for the lower band and ten elements for the upper band. Results for a single element and antenna array are presented. The front-to-back ratio is from 25 dB to 30 dB, and the axial cross polarization ratio is from 19 dB to 22 dB in a single low band unit. The dual-band array achieves a bandwidth of 15.7% (820-960 MHz) for the lower band and a bandwidth of 23.7% (1710-2170 MHz) for the upper band, covering the frequency bands required by 2G/3G systems. Simulation results show that the gains for antenna array are 15.7 dBi for the lower band and 19.1 dBi for the upper band, which is suitable for base stations applications.

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.

Satellites are the most important link in today's battle field, and with the advancement of anti-satellite technologies like anti-satellite missiles and directed energy weapons, satellites are becoming vulnerable to attack. The vulnerability of satellite depends highly on its probability of being detected and tracked, and optics or radars are the two major means of detection. To avoid detection, several suggestions have been made in the past to deflect ambient light and decrease the RCS (radar cross section) to avoid detection. The most notable RF stealth suggestion among them is the proposal of using an inflatable polymer cone to change its shape and reduce satellite's RCS. In this study we examine the RCS of this so-called stealth satellite in S-band with FDTD simulations, and analyze its frequency and radar incident angle dependence. Results indicate this shape is advantageous in bore sight monostatic backscatter RCS reduction, but in other directions the RCS increases due to sheer size effect, which makes it even more vulnerable to bi-static radar tracking. When it is slant illuminated, the RCS of the stealth satellite shows no RCS reduction effects. Such inflated device is susceptible to space debris damage and cumbersome to operate, and may interfere with the original mission of the satellite. Best strategy for satellite self-defense is orbit change.

A high selectivity wideband balun bandpass filter based on substrate integrated waveguide (SIW) and complementary split rings resonators (CSRRs) is proposed. 180° reverse phase characteristic between the two output ports can be easily realized by the multi-layer SIW power divider. Eight complementary split rings resonators are used to achieve the sharp rejection upper stopband. The proposed wideband balun filter exhibits a fractional bandwidth of 37% centered at 9.45 GHz and amplitude and phase imbalance less than 0.5 dB and 1°.