In this letter, a novel 3-D heterogeneous solenoid inductor with high inductance value is proposed. By adding planar spiral structure at the ends of through-silicon vias (TSVs) of typical 3-D solenoid inductor, the heterogeneous solenoid is formed. The total inductance is increased by more than 41% compared with that of typical solenoid inductor of the same size. Additionally, an accurate analytical model of the inductor is established considering all the factors including angle and offset. Q3D simulation results verified the accuracy of the model, and the percentage error is less than 5.38%. This work provides an important reference for inductor designers to quickly estimate inductance value, configuration, and layout area.

Linear Frequency Modulation (LFM) signals are widely used in radar and sonar technology. Many applications are interested in determining the source of an LFM signal. In recent years, the rapid development of machine learning has facilitated research in various fields, including signal recognition. The neural networks can extract the implicit features of the signals, which can help the system to sort and recognize the signal sources quickly and accurately. High performance of neural networks requires large amounts of high-quality labeled data. However, it is difficult and expensive to obtain a large amount of high-quality labeled data. Simultaneously, some features will be lost during data preprocessing, and feature extraction and classification tasks will be inefficient. The self supervised network is proposed in this paper for pre-training the signal waveform and fine-tuning the classification with a small amount of labeled data. The proposed method can extract more signal waveform features, save labeling costs, and has higher precision. This method can provide up to 99.7% recognition accuracy at 20 dB.

This paper presents the design and implementation of a C-Band Frequency Generator developed for Space-borne Synthetic Aperture Radar. This Frequency Generator subsystem generates stable and coherent reference signals for all the sub-systems of C-Band Synthetic Aperture Radar payload. Frequency Generator based on frequency multiplication technique generates various coherent signals namely 500 MHz signal for digital clock, local oscillator (LO) signals of 900 MHz and 4500 MHz needed for receivers and chirp signal of 5400±37.5 MHz. This chirp signal is generated by direct modulation of the full bandwidth baseband signal of DC-37.5 MHz at 4500 MHz and subsequently mixing with 900 MHz signal. Frequency generator unit is realized in a compact two-tier architecture, using novel concept of full chirp modulation, resulting in 6° rmsphase error in the transmit chirp signal along with in-band spurious rejection better than 20 dBc, whereas other coherent frequencies resulting in out of band spurious rejection better than 53 dBc against the specification of 40 dBc.

A metamaterial-inspired antenna is proposed that utilizes an artificial mu-negative (MNG) transmission line (TL) to incorporate the zeroth-order resonance (ZOR) into Wi-Fi 7 operation in the 2.4/5/6 GHz wireless local area network (WLAN) bands. The antenna comprises a meta-structured loop with periodically loaded series interdigital capacitors and a parasitic shorted strip, all formed on the same substrate layer in a coplanar structure. The 2.4 and 6 GHz bands are produced by the parasitic strip and the close-form loop strip, respectively, which are of typical right-handed antennas. The 5 GHz band caused by the ZOR mode, where the permeability is zero, can be adjusted by the series capacitance in the unit cell. The total antenna size is 5.4 mm × 19.6 mm only. In this work, the design applied to notebook computers for the upcoming Wi-Fi 7 operation is also demonstrated. Both numerical and experimental results validate our proof-of-concept design.

A 26 × 25 mm² arbitrary-shaped antenna is constructed in this article, and it was expanded to 2 x 2 Multiple Input Multiple Output (MIMO) antenna. It has a range of 3.1 to 8.2 GHz. A T-shaped stub is employed in this instance to reduce the mutual coupling between the two ports. The effectiveness of the MIMO aerial is demonstrated using envelope correlation coefficient and radiation pattern. Additionally, it has been shown that simulated and measured results generally agree.

This paper focuses on designing and manufacturing a compact microstrip diplexer, which operates at 3.5 GHz and 5 GHz for 5G and Wi-Fi applications, respectively. Indeed, two bandpass filters are combined to create the proposed diplexer. For making bandpass filters compact, a hairpin resonator is suggested and developed into an E-shaped resonator. To attain the central frequencies, a short microstrip stub loading the E-shaped resonator is proposed. The filters were combined by a coupling junction to form the final diplexer. The proposed diplexer exhibits good isolation that is better than 40 dB in the whole operational frequency band. Additionally, the passband insertion losses are about 1 dB, and the return losses are about 20 dB and 26 dB at the two channels, respectively. Moreover, the final size of the manufactured diplexer is 30 × 25 mm² (0.6λ_g x 0.52λ_g). These results confirm that the suggested diplexer is suitable for the demanded applications.

In this paper, we investigate the propagation behavior of electromagnetic waves through coaxial optical fiber bounded with DB-boundaries. For this purpose, an eigenvalue equation is derived by using suitable DB-boundary conditions to determine the allowed values of propagation constant β for each propagating mode. Moreover, we have analyzed the electric field and power distribution patterns through coaxial optical fiber for different propagating modes and dimensions, respectively. Our results show that small dimensional guide confinement remains maximum close to the lower interface of the guide, whereas, for larger dimensions, it shifts toward the upper interface. Investigations show that high power is confined by H₁₂ mode compared to H₁₁ mode, and, therefore, shows contrary behavior compared to commonly used fibers.

We designed a dielectric resonator antenna (DRA) that carries orbital angular momentum and has dual-band ultra-wideband characteristics based on the advantage of minor rain decay in L-band and C-band of microwave bands. The cavity of the antenna adopts an inner and outer nested spiral structure, and the material of resonant cavity shell is photosensitive resin. The internal medium is distilled water with a dielectric constant of 81, and the outer filling is saline with a concentration of 0.035 g/ml at room temperature for the dielectric constant. At the bottom of the cavity, we applied 2 feeds with phase difference of 90° to produce a circularly polarized beam in the DRA. Adjusting the size of the DRA and the height of the helical step surface to excite the OAM waves in higher order modes. The designed DRA generates resonance in 0.82-1.63 GHz and 3.35-7.27 GHz, and achieves ultra-wideband in both operating bands, furthermore, the antenna can generate OAM waves in l=±1 and l=±3 modes when operating at 1.51 GHz and 5.28 GHz, respectively. The simulation results match the measured results. The results show that the vortex wave generated by our designed antenna also has advantages such as high mode purity. Therefore, it can be effective in near-field communication and also provides a new solution for OAM near-field communication in 6G which is of great importance, and also for satellite communication and downlink signal transmission of communication satellites.

In this paper, a planar wideband antenna array with wide scanning angle in both E- and H-planes is proposed. The dipole antenna is used as an essential element of the array. To enlarge the scanning angle of the array, two layers of frequency selective surface (FSS) superstrates are loaded on the top of the antenna elements. A conducting-patch with shorting pins is loaded under the unit patch to enlarge the bandwidth of the array. Both simulated and measured results have confirmed that the proposed antenna array can scan up to 85° and 70° in the E- and H-planes from 8 GHz to 11 GHz, respectively.

In this paper, a method of designing a SIW (Substrate Integrated Waveguide) bandpass filter with high selectivity is proposed. Four resonant cavities of the proposed filter are arranged in straight line. The microstrip gradient line is directly fed into the cavities. Two U-shaped slots are etched on the top face of each cavity which will result in the resonant modes reduced and the high modes of SIW cavity pushed far away from the dominant resonant mode. Thus the filter will have both the features of compact size and wide stopband. The center frequency of the filter is designed at 5.2 GHz. The measured results are highly matched with the simulated ones.

In order to meet the requirements for the suppression of mirror frequencies in the 5G RF front end, this paper proposes a novel miniaturized image rejection bandpass filter by loading Stepped-Impedance Resonators (SIR). By analyzing the relationship between the impedance ratio of a half-wavelength SIR and its electrical length, we have designed an improved second-order bandpass filter, which reduces the size by 34.3% compared to traditional five-order hairpin filters. In order to further enhance the performance of the filter, the use of a radial stub, as opposed to the traditional rectangular open stub, allows for the generation of a wider band transmission zero, which can be analyzed using lumped equivalent circuits. This integration improves the stopband rejection of the filter. The results show that the passband range is 5.35 GHz-6.64 GHz; the rejection in the stopband range 8.10 GHz-11.98 GHz is over 45 dB; and the size is only 0.385λ_g×0.295λ_g.

In this paper, a wide harmonic suppression filtering antenna with high selectivity is designed. The filtering antenna adopts dual-layer structures. By introducing four parasitic patches around the top driven patch, the impedance bandwidth is widened. Moreover, the current directions on the driven patch and the parasitic patches are opposite in some frequency, so that the radiation null is introduced. In addition, a rectangular split ring DGS is etched in the middle of the ground plane, the lower sideband radiation null is introduced. Two sets of dumbbell-shaped defected ground structures are etched on the ground plane of the intermediate layer. The high-order harmonics are suppressed, and another radiation null is introduced. The experimental results show that the antenna operates at 2.46-2.66 GHz; the relative bandwidth is 7.8%; the peak gain is 3.8 dBi; and the S₁₁ is more than -3 dB at 3-13 GHz.

A systematic technique for switching between horizontal and vertical polarizations is introduced. A fan-beam antenna array for base station applications employing a grounded reflector is implemented, and the proposed approach is implemented and validated on it. The antenna array is realized using planar monopole elementary elements against a non-parasitic reflector, which yields a desirable fan-beam pattern. The corresponding 3 dB H-plane beamwidth can be easily adjusted by changing the reflector height. Two versions of the antenna arrays are used to demonstrate suppression of unwanted asymmetrical modes in the current distribution yielding improved cross-polar isolation. The measured H-plane 3-dB beamwidth is approximately 127 degrees at 900 MHz and 124 degrees at 955 MHz. The corresponding side lobe level is almost -11.7 dB and -8.7 dB at 900 MHz, while the back lobe level of -9.3 dB and -11 dB at 955 MHz from measurements. The gain is within the acceptable level in both cases and compared with simulations that possess good agreement. By taking into account the antenna design and manufacturing aspects, such antennas will pave the way to be employed in OFDM reconfigurable antenna applications and Identification Friend or Foe (IFF).

A quad-element reconfigurable radiation pattern Multiple Input Multiple Output (MIMO) antenna is designed for WLAN and 5G applications suitable for indoor wireless communications. Antenna system consists of four radiating elements that operate over triband frequencies 2.4, 3.5 and 5.5 GHz. Moreover, the pattern diversity is obtained by introducing two diagonally crossed slots in the radiator to steer the main beams of the antenna in eight different angular directions using eight PIN diodes. The overall physical dimension of the proposed antenna is about 0.55λ₀ × 0.55λ₀. In addition, an Acrylonitrile Butadiene Styrene (ABS) enclosure is designed, and the performance of the proposed antenna is evaluated. The measurement results show that the proposed antenna has an impedance bandwidth of 4.18%, 14.13%, and 28.5% at the said frequencies, respectively.

A hybrid-fed dual-polarized antenna with matesurface coverage is proposed in this paper, which can be used for 5G mobile communication base station antennas. By placing the two feeding ports on different layers of dielectric plates in an orthogonal manner, and using electromagnetic coupling and slit coupling for feeding respectively, the antenna can achieve inter-port isolation higher than 35 dB in the operating frequency band. In order to widen the bandwidth and obtain higher gain, the metasurface covering unit is loaded above the patch. The metasurface layer contains an array of 5 × 5 square patch units printed on the top surface of the dielectric plate. The measurement results show that the proposed antenna has an impedance bandwidth of 12% (3.24 to 3.66 GHz). In addition, the antenna obtains a stable gain of about 5.32 dBi at 3.5 GHz. The proposed antenna meets all the requirements of base station antennas and can be a promising candidate for application in 5G base station systems.

A novel wideband circularly polarized (CP) dipole antenna for RFID/WiMAX/WLAN applications is presented. A pair of crossed fan-shaped dipoles printed on both sides of the substrate are used as the primary radiating elements. The antenna achieves circular polarization by using a 90° phase shifted microstrip line between the dipoles. By changing the edge of fan dipoles into Minkowski fractal curve, miniaturization and wide bandwidth of the antenna can be realized. Besides, incorporating the U-slot into the fractal crossed dipoles can obtain a wider bandwidth. The test results show that the proposed antenna achieves a wide impedance bandwidth of 63.2% (1.9-3.7 GHz) for VSWR < 2 and a 3-dB axial ratio (AR) bandwidth of 42.9% (2.2-3.4 GHz). The maximum gain in the operating frequency band can reach 7 dBi. The proposed antenna has good radiation characteristics in both low and high frequencies, which makes it a candidate for applications of RFID, WLAN, WiMAX, and other communication systems.

This letter presents a compact constant absolute bandwidth (ABW) frequency tunable bandpass filter (BPF) with bandwidth and tuning range enhancement. The fundamental structure consists of two varactor-loaded step-impedance resonators (SIRs) and input/output feeding lines. By adjusting the position of varactors, the slope of coupling coefficient between the two resonators can bechanged easily, which is crucial to realizing constant ABW. The tuning range is improved due to the application of varactor-loaded SIR. To expand the bandwidth, interdigital coupling structures between varactor-loaded SIRs are adopted. Besides, source-load coupling is introduced, and two transmission zeroes (TZs) are generated on both sides of the passband to enhance the rejection level of stopband. The measured results show that the proposed BPF achieves a center frequency tuning range from 0.79 to 1.2 GHz (41.2%), and the 3-dB ABW remains 108 ± 5 MHz. The insertion loss (IL) is 1.8-2.2 dB, and the return loss is greater than 10 dB during the whole tuning range.

A low cost and compact chipless Radio Frequency Identification (RFID) humidity sensor with the size of 18 * 18 * 0.5 mm³ is designed for environmental humidity monitor. The sensor consists of a circular resonator and a rectangular substrate, which utilizes the polyvinyl alcohol (PVA) humidity sensitive material for relative humidity (RH) sensing. The PVA humidity sensitive material covers the sensor surface. The working principle of the sensor is that the change of environmental humidity results in the changing of dielectric constant of PVA and thus shifting of the resonant frequency of the sensor. The real-time humidity can be observed by monitoring the resonant frequency. The simulation results show that the humidity sensing range of the designed humidity sensor is 21.9% RH~52.5% RH, corresponding to the resonant frequency range of the sensor from 2.76 GHz to 2.51 GHz with the total offset 250 MHz. The maximum humidity sensitivity was 23.08 MHz/% RH within the monitoring range. The designed humidity sensor has the advantages of low cost, compact and simple structure, which is suitable for humidity monitoring in various complex environments.

This letter presents a compact ultra-wideband circularly polarized (CP) crossed-dipole antenna with enhanced axial-ratio beamwidth (ARBW) and half-power beamwidth (HPBW). It consists of four modified arms which are fed by vacant-quarter phase delay rings to excite CP radiation. Four parasitic elements are utilized rotationally between the dipoles and the reflector. Not only does inducing vertical currents on the parasitic patches excite additional impedance resonance to realize an ultra-wideband operating, but also reinforced radiation is obtained to improve the ARBW and HPBW. The experimental results show that the proposed antenna realizes a -10 dB impedance bandwidth of 134.3%, and a 3 dB axial-ratio (AR) bandwidth of 115.0%, while holding a compact volume of 0.25λ_L × 0.25λ_L × 0.09λ_L (λ_L: wavelength at the lowest operating frequency). Furthermore, an HPBW and ARBW of more than 110° and 160° are realized within a broad operating band of 67.5% and 55.0%, respectively.

Reconfigurable antenna arrays play a major role in the current and future wireless communication systems due to their multifunctional capabilities and many other advantages. Conventionally, the array pattern reconfigurations were usually achieved by controlling the excitation amplitudes and phases of all or most of the array elements which are generally costly and complex methods. In this paper, a simple method for controlling the reconfigurability of beam-patterns of the linear and planar arrays is presented. It can be easily switched between narrow and wide beams using thinned-elements strategy. First, the array elements are divided into three groups based on their locations namely central, middle, and outer elements. Their amplitude weights are chosen to be unity, adaptive, and zero respectively. To add some desired constraints on the array beam-patterns such as limited sidelobe level and specified nulls placement, the excitation weights of the middle elements are optimized such that an abrupt change in the array taper is avoided. This also avoids an undesired change in the sidelobe pattern. A genetic algorithm is used to perform such optimization so that the produced beam-patterns are best matched to the desired ones. Moreover, the size of the thinned region controls the resulting beam width.

The problem of defeating a swarm of unmanned aerial vehicles (UAVs) is of considerable importance to the modern warfighter. In recent studies high power radio frequency (HPRF) directed energy weapons (DEWs) have been shown to be suitable for this purpose. Hence there is a need to develop mathematical modelling frameworks to quantify HPRF DEW performance, especially when they are operating in a wideband or ultrawideband mode. Consequently this paper introduces a novel mathematical model, based upon a new interpretation of UAV vulnerabilities to HPRF DEW, which permits performance assessment to be undertaken. The key to this is to view each UAV through its vulnerabilities to HPRF DEW energy at given frequencies and analyse its impact on the lifetime of each of the UAVs. This results in the definition of an appropriate stochastic process to count the number of UAVs still active in the swarm over a given time interval. Consequently this permits the determination of minimum HPRF DEW power levels at given frequencies in order to guarantee likelihood of defeat of the swarm before it reaches the HPRF DEW source. Hence the results in this paper will provide a novel framework for determining the specifications of an HPRF DEW's required power distribution over target vulnerabilities to ensure a desired level of system performance.

In this paper, a novel dual-band series-fed array (SFA) has been proposed. By introducing a new dual-band series-fed network (SFN) consisting of uniform transmission lines (TLs) and C-sections, independent beam direction can be realized. The design procedure for the proposed dual-band SFA has also been presented in this paper. To validate the design method, a prototype antenna has been fabricated and measured. The experimental results verify the performance of the proposed dual-band SFA.

A highly packaged coupler using vertically placed inductors and capacitors (LC)-elements is proposed for 1 and 1.5 Tesla (T) magnetic resonance imaging (MRI) applications. The coupler is made on a 24-layer thickness low temperature co-fired ceramic (LTCC) substrate, and the full integration is reached by heaping up LC-elements in the vertical dimension. The coupler has a smallest reported size of only 0.0035 × 0.0021 × 0.001λg and a wide fractional bandwidth (FBW) of 44%. The measured in-band phase difference between the coupled and through ports and the amplitude imbalance are less than 91°±0.5° and 0.75 dB, respectively. Comparisons and discussions are also implemented.

This paper presents a coplanar waveguide (CPW)-fed tri-mode hybrid antenna that is suitable for quad-band applications. The antenna design is compact, measuring only 30×30 mm², and consists of a zeroth-order resonator (ZOR) antenna, a torch-shaped monopole antenna, and a T-shaped slot antenna. The most significant feature of this design is its ability to provide three independent working modes, making it a hybrid antenna. By incorporating a Composite Right/Left-Handed Transmission Line (CRLH-TL) unit cell, the first mode is excited as a ZOR antenna, corresponding to the lowest resonance at around 1.57 GHz. The second mode relies on the torch-shaped monopole antenna with two resonances at about 2.5 GHz and 3.5 GHz. The third mode employs the T-shaped slot antenna with a resonance at around 5.5 GHz. Experimental results demonstrate that the proposed antenna exhibits a wide and multi-band behavior with impedance bandwidths of 60 MHz (1.56-1.62 GHz), 210 MHz (2.30-2.51 GHz), 370 MHz (3.40-3.77 GHz), and 1100 MHz (5.05-6.15 GHz). This antenna can not only support the current GPS/WLAN/WiMAX systems but can also be considered as one element of a multiple-input-multiple-output (MIMO) antenna array for the fifth-generation (5G) mobile communication in the sub-6 GHz frequency range.

A frequency selective absorber for harmonic absorption (HA-FSR) is proposed in this paper. It consists of a miniaturized frequency selective surface (FSS) for harmonic suppression and a circuit analog absorber (CAA) for harmonic absorption. The frequency selective rasorber (FSR) unit is 6.7 mm × 6.7 mm (0.129λ × 0.129λ, where λ is the free space wavelength of 5.8 GHz). The simulation and measurement show that the HA-FSR can generate a transmission band from 4.51 GHz to 7.47 GHz and a -10 dB absorption band from 11.96 GHz to 22.31 GHz, which covers more than 3 times of the main passband harmonic band. In addition, the FSR has good polarization stability and angle stability within 30˚ of oblique incidences under both TE and TM polarizations, which can be applied to electromagnetic interference shielding field and low-observable platforms.

This paper presents a novel test platform for passive intermodulation measurement on planar microwave circuits using a filter design strategy. A finger planar band-pass filter is proposed and optimized to have an evenly distributed stimulation field on the surface. The layout is optimized with symmetrical coupling lines from two directions, and the feed line is with a tapered transformer. A pair of T-type resonators is adopted to improve the flatness of the field distribution. In the application of this test platform, print circuit boards with different layouts are tested, and the passive intermodulation difference of different layouts can be differentiated. As this platform is with open space, the device under test can be easily changed without suspending the passive intermodulation test system, which can be applied in the production line to speed up the production quality inspection.

An ultra-compact band-pass filter is presented in this paper. The filter is designed to operate in the medical implants communication service (MICS) band ranging from 401 MHz to 406 MHz. The filter is designed on a Rogers RT/duroid substrate with ε_r = 2.94 and tanδ = 0.0012. The overall size of the proposed filter is only 30.6 mm x 18.5 mm (0.058λ_g x 0.035λ_g), making it suitable for compact, portable devices. An equivalent circuit model is also proposed for the analysis of the filter geometry. From the circuit model, it can be concluded that the filter exhibits the characteristics of a dual-composite right left-handed (D-CRLH) transmission line. This is also confirmed from the dispersion characteristics. The salient features of the proposed filter include ultra-compactness at low operating frequency, harmonic suppression of 3.7 times of the passband frequency, fractional bandwidth of 4.45%, and good roll-off rate of 297.6 dB/GHz in the lower stopband and 116.4 dB/GHz in the upper stopband.

A new miniaturized patch antenna based on a metal strip is proposed in this paper. The antenna is designed by adding a middle metal strip layer to the substrate of a traditional rectangular patch antenna. By increasing the length of the metal strip, the working frequency of the patch antenna can be continuously reduced without significantly impacting the radiation pattern. The simulation results indicate that as the metal strip length increases from 5 mm to 25 mm, the working frequency of the patch antenna decreases from 2.39 GHz to 1.84 GHz, and its gain decreases from 6.72 dBi to 5.4 dBi. Two antenna samples with metal strip lengths of 5 mm and 20 mm are fabricated. The experimental results indicate that their working frequencies are 2.64 GHz and 2.43 GHz, respectively. And the radiation patterns of two antennas are consistent with the simulated results. All results confirm the effectiveness of the proposed miniaturization method.

The quality of a honey can be affected by adulteration through the addition of often unauthorized substances such as sugar syrups or water. The water content in honeys is restricted to 20% according to CODEX ALIMENTARIUS. This research proposes a method which will allow to detect the water content in the honey directly in the jar. The method uses electromagnetic probing with several antennas around the jar. This method is based on the knowledge of the dielectric contrast between a pure honey and a honey containing different water contents. To validate this contrast, a campaign of dielectric measurements has been investigated on two different commercial honeys (H1 and H2) with arbitrary and controlled added water. The added water content in the honey has been varied from 0% to 15%. The experimental setup uses a coaxial transmission line with a sample holder. The frequency range extends from 100 MHz to 5000 MHz. The mixtures of honeys with water have been measured at an ambient temperature (25˚C).

This letter presents the fabrication and measurement of a novel loaded line phase shifter design providing four different phase shifts using only two RF MEMS switches. The flexibility of choosing DC or capacitive load depending upon the phase shift required in a single RF MEMS switch makes the phase shifter compact and requires less no. of proposed switches. The RF MEMS Switch has been designed to provide isolation better than 10 dB in both DC and capacitive states from 16 to 45 GHz. Due to the designed RF MEMS beam switching between DC and capacitive loading, the proposed phase shifter provides a 2-bit phase shift using only two switches. The measured phase shifter has the maximum insertion loss of 0.8 dB with a bandwidth of 8 GHz from 16 to 24 GHz. The return loss is better than 10 dB for all four states. The maximum Root-Mean-Square (RMS) insertion loss error is 0.28 dB, and the phase shift error is 0.98º. The proposed phase shifter is fabricated using the surface micromachining on the sapphire substrate and occupies an area of 3.931 mm².

In this article, a 15 × 20 mm² arbitrary-shaped antenna is built. The same is extended to a 2 × 2 MIMO antenna with size 32 × 20 mm². It covers two bands. Band-1 covers 3-4.44 GHz, and band-2 covers 5.32-11.1 GHz. In this case, a circular neutralization structure is used to lessen the mutual coupling between the two ports. The ECC, DG, CCL, and radiation pattern are used to demonstrate how well the MIMO antenna performs. Also, it has been noted that there is good agreement between simulated and measured outcomes.

Frequency diversity array (FDA) can generate distance and angle dependent ``S'' beam patterns, but there is a problem of distance and angle coupling, which can be well solved by using nonlinear frequency offset in recent years' research. The rotational symmetry of the arc-shaped structure brings the beam scanning capability of the array antenna within a range of 360°, which can realize the all-round monitoring of the target position, and provides a more flexible method for radar communication. In this paper, a nonlinear frequency offset based frequency diversity arc array (FDAA) beam scanning method is proposed, which activates the selection matrix according to the target direction. In order to form equal phase plane beam scanning, phase compensation between array elements is carried out, and three kinds of nonlinear frequency bias are introduced to simulate beampattern synthesis. Compared with the traditional linear frequency offset FDAA, the numerical simulation results verify the feasibility and effectiveness of the scheme.

We present an ultra-compact modular division (de) multiplexer [(de) MUX] based on the tilted lithium niobate waveguide, an asymmetric directional coupler (ADC) composed of silica-lithium niobate waveguide (SLNW) and lithium niobate waveguide (LNW) for the modular division multiplexer. The TE0 and TE1 modes were optimized by using the finite element method (FEM). By rationally designing the size of SLNW waveguide and LNW waveguide, TE0 mode light is injected into the In1 port of LNW waveguide, TE0 mode light is converted to TE1 mode in the coupling zone, and transmitted in the SLNW waveguide, output from the Out2 port. It show that the coupling length of this MUX is only 6 μm. At a working wavelength of 1.55 um, when TE0 enters the coupling area from port In1, the mode is coupled and converted to TE1; the TE1 mode is output from Out2; the value of IL is 0.87 dB; and the value of MCE is 99.5%. When TE0 enters from port In2, the TE0 mode is output from Out2, with 0.1 dB for IL, 99.7% for MCE, and -25 dB for CT.

In this paper, a compact planar dual-band circular-shaped polarization-dependent electromagnetic band gap (DCS-PDEBG) structure operates at 2.97 GHz and 7.77 GHz in y-direction and 3.14 GHz and 10.90 GHz in the x-direction. A proposed DCS-PDEBG structure consists of a circular patch inside a square patch with a slot at the center, and the established arrangement gives additional capacitance and compact size. The simulation of the DCS-PDEBG is carried out using the Finite Element Method (FEM) of Ansys High-Frequency Simulator (HFSS) and experimentally validated. A truncated microstrip line (TML) method is used to measure the band gap of the proposed planar DCS-PDEBG structure. Experimental results agree well with simulation one. The periodic size of proposed DCS-PDEBG structure is 0.13λ_{2.97 GHz} × 0.13λ_{2.97 GHz}, which is a good candidate where compact size is highly desired.

This paper aims to classify oil samples using the Metamaterial (MTM) unit cell as a sensor. The S-shaped broadside coupled Split-Ring Resonator (SRR) acts as an MTM and is designed to operate at X-band (8-12.4 GHz). The proposed MTM unit cell was simulated through the High Frequency EM simulation tool, and then the MTM properties were extracted using the standard equations. The MTM behavior was studied through its negative permittivity and permeability characteristics in the X-Band. The simulated and extracted properties exhibit that the proposed MTM unit cell is suitable for the analysis at X-band. A sample container was designed to hold the different oil samples. The experimental analysis was carried out by filling the container with different oils without/with an MTM sensor. Mainly, the variations in S-parameters magnitude were studied for classification applications. This paper proposes the study of transmission coefficients phase response in addition to magnitude as an easy way to classify different oils. Further, the phase transition results were compared with the kinematic viscosity and refractive index properties of the oil sample. The comparison results proved that the classification of oil samples using the phase transition approach agrees well with the existing oil properties.

An aperture-coupled full polarization reconfigurable MIMO antenna is proposed in this letter. A cross-shaped slot loaded with PIN diodes is embedded on the ground plane, and ±45° linear polarization is realized by controlling the states of the diodes. Four slots integrated with PIN diodes are etched at the corners of the radiating patch, and then the left- and right-handed circular polarization modes are achieved by changing the ON/OFF states of the diodes. Experimental results show that the antenna can achieve good impedance matching in the range of 2.4-2.46 GHz in four modes with an isolation greater than 15 dB and an axial ratio less than -3 dB in the circular polarization modes.

This letter addresses a new approach to improve the gain and isolation of a multiple input multiple output (MIMO) antenna. A C-shaped printed antenna with both ends terminated by a small rectangular section is designed as the basic antenna element for a 2 element MIMO antenna of size 0.8λ×0.67λ×0.04λ (λ, corresponding to lowest operating frequency) which operates over the X band with peak gain of 3 dBi. By introducing a double layered frequency selective surface (FSS) of unit cell dimension 0.2λ×0.2λ×0.0375λ between the two antenna elements as an isolation wall and additionally by placing a 5×3 array of FSS geometry as a reflector below the antenna, the isolation and gain of the two element MIMO antenna are improved by 37 dB and 3 dBi, respectively. The proposed FSS loaded MIMO antenna provides very high isolation about -51 dB (measured) and a very low envelope correlation coefficient (ECC) of 0.000177282 (simulated) using far field approach and 0.000000033414 (calculated measured) using scattering (S) parameter approach. Further MIMO parameters like diversity gain (DG), total active reflection coefficient (TARC), mean effective gain (MEG) and channel capacity loss (CCL) have been evaluated. The radiation pattern is unidirectional in nature with a peak gain about 6 dBi. The letter also presents detailed design guidelines for the proposed FSS loaded MIMO antenna along with their verifications for Ku and K bands. The proposed structure can also be scaled up to a 4 element MIMO antenna.

A quasi-equal inductor filter and its corresponding multilayer realization are proposed in this paper. The circuit transformation is performed using the Norton transformation. In the proposed filter, ratio between the largest and smallest component values is reduced, which makes the design of components much easier. Meanwhile, by carefully selecting the transformation ratio, all grounding inductors are equal in value. As a result, the multilayer filter design is simplified because only one instance of grounding inductors needs to be designed instead of three. An experimental prototype is fabricated and measured. The measurement result agrees well with the desired one, which shows the effectiveness of proposed filter.

Directed energy weapons (DEWs) have been identified as valuable assets in future land and joint combat. High-power radio frequency (HPRF) is a form of DEW which can neutralise robotic systems by discharging electromagnetic (EM) radiation over a region to couple system electronics. Its widespread effect enables the simultaneous disruption of groups of electronic systems, such as swarms of unmanned aerial systems (UASs). Since EM radiation is a distance-based effect, the arrangement of defensive HPRF systems with respect to their target is critical to understanding their utility and viability. Consequently, a mathematical model to assess the effectiveness of HPRF DEW positioned at a given location is formulated. Towards this, a combat scenario specialised to land operations is defined. The assumptions required to formulate the scenario geometrically and mathematically are also outlined. Provided with the position of an effector, it is then possible to quantify the vulnerability of a UAS swarm in terms of a disruption probability. This accounts for uncertainty stemming from UAS and swarm behaviour and assumes that UASs are independent and identically distributed. The model also draws upon work previously conducted at Defence Science Technology Group (DSTG) which derived an HPRF disruption probability function. An optimisation of the disruption probability is undertaken in terms of the position of a single narrowband HPRF effector. Under a hypothesised set of HPRF and threat parameters, maximal swarm defeat probabilities are examined in different swarm deployment regions and HPRF beam widths. This led to the discovery of various tradeoffs between aforementioned features. In particular, under a fixed beam width, proximity to the swam provided an increased defeat probability but reduced the beam's coverage of the swarm. Hence, numerous UASs might not be affected by EM radiation throughout the engagement, reflected in a reduction to the swarm defeat probability.

This paper presents the design of dual-band spatial filter for shielding S band and X band wireless signals. The proposed Frequency Selective Surface (FSS) geometry consisting of a square loop convoluted with four strips positioned along the conducting loop. The FSS is aimed to reject WLAN/S-band (2.64 GHz) and X-band (8.3 GHz) wireless signals. The proposed FSS is tested for its angular stability by considering the wave incidence at various angles between 0˚ and 60˚. It is also tested for its polarization insensitive feature via TE mode and TM mode. The prototype FSS is printed on an FR-4 substrate with 1.6 mm thickness and the unit cell footprint of 14.8 mm and tested in an anechoic chamber. The working principle is explained through surface current distribution and the equivalent circuit model of the FSS. Measured results have better similarity with the simulated results.

This paper presents a terahertz high gain beam steering transmitarray antenna (BSTA) working at 340 GHz. Substrateless double hexagon ring slots unit-cells which present low loss characteristics at THz band are used to constitute the layout of THz BSTA. To improve the beam steering performance, bifocal technique is used to design the layout of BSTA. Because the fabrication risk of the THz BSTA prototype increases a lot as the aperture dimension is enlarged, four inch silicon wafer is chosen after weighting the risk and gain of the BSTA. Micromachining process is used to fabricate the large aperture THz BSTA to ensure the machining accuracy of the unit-cells. The measured results of the prototype show that the THz BSTA could realize -15°~15° range beam scanning with gain > 38.3 dB, scanning loss < 1.2 dB and side lobe level < -17.8 dB, by moving the feed along the focal plane of the BSTA.

A low-cost and mechanical reconfigurable substrate integrate waveguide (SIW) equalizer is presented and studied in this work. Different from the previous SIW equalizers using Tantalum Nitride (TaN) or absorbing material as the resistive element, the indium tin oxides (ITO) are introduced into SIW equalizer. The absorbing material will deform under uneven pressure due to the structural softness of material, resulting in instable equalizing values. Compared with the absorbing material, ITO provides more structural stability, excellent high frequency characteristic, and can be easily integrated with traditional printed circuit board (PCB). Furthermore, an equalizer with reconfigurable equalizing values can be realized by adjusting ITO materials with different impedances. A SIW equalizer based on the ITO Conductive Film, operating from 26 to 40 GHz, has been designed, fabricated and experimentally verified. For measurement results, the return losses are better than -17.4 dB with 3, 6, and 10 dB equalizing values respectively over the entire Ka-band, and the insertion losses at the frequency point of 40 GHz are -2.89 dB, -4.80 dB, and -7.37 dB, respectively. The proposed equalizer presents the advantages of mechanical reconfigurable, low cost, and high stability. In addition, ITO Conductive Film is a good candidate for the design of high millimeter-wave band equalizer.

In this paper, a compact reconfigurable bandstop filter suitable for multistandard and multiband mobile terminals is reported. The proposed dual bandstop filter consists of a microstrip line coupled to two switchable Capacitively Loaded Loops (CLLs). We achieve tuning of individual notched frequency bands by using open circuits as switches and incorporated in each CLL element. The performance characteristics in terms of S-parameters and surface currents distribution show that the proposed filter is able to adjust two stopbands independently in a wide tuning range. A corresponding prototype of tunable dual-stopband filter is manufactured, and practical measurement agree well with the simulation results.

In this article, a low-profile microstrip patch antenna using an FR-4 substrate with relative permittivity of 4.4 and thickness of 1.6 mm is designed. On the top of a substrate, it consists of one metallic hexagonal patch and a metallic-fed hexagonal ringtone, and the ground part of the structure is covered with orthogonal rectangular slots. The designed structure operates in the ISM band of 434 MHz, and the overall size of the antenna is 124x124x1.6 mm³. The antenna provides a valid SAR input profile.

This work aims to evaluate the contribution of cascaded optical amplifiers in improving the performance of optical communication systems in optical access networks. This study is thus carried out by a system simulation software which presents results concerning the characteristic parameters of two optical amplifiers, EYDWA (Erbium Ytterbium Doped Waveguide Amplifier) and SOA (Semiconductor Optical Amplifier) used in cascade, namely their gains, the length of the guide and the concentration of ions.

As wireless devices become increasingly compact, portable, and accessible anywhere, there is a need to increase isolation between them and reduce frequency interference. The purpose of this paper is to suppress interference by using pixelated patterns on a single layer in a miniaturized unit cell. To miniaturize of unitcell, the surface was pixelated into 50 × 50 pixels with a resolution of 0.2 mm × 0.2 mm. The proposed unitcell occupies a small area of 0.06λ₀ × 0.06λ₀ at GSM frequency (f = 1.8 GHz). The pixelation of the surface allows the surface current to follow a long path. Therefore, unlike the previous works, the miniaturized structure is obtained using a 1D layer without any vias and lumped elements. A significant advantage of this structure is that it is significantly more miniaturized than the current state-of-the-art unitcells and allows for a wider range of applications. Full-wave simulation and measurement results are in good agreement with each other and show stopband at operation frequency. As a result, both simulation and measurement results show that the proposed structure has a dual-polarized characteristic with good angular stability under a variety of incidence angles.

A narrowband, high selectivity Substrate Integrated Waveguide (SIW) bandpass filter with perturbing vias and CSRR is proposed for Sub-6 GHz applications. Firstly, the perturbing vias are positioned at the symmetrical axis of the SIW cavity which produces distinct electric field distribution for the first two modes. Next, the ground plane is engraved with the CSRR placed at an offset distance on either side of the perturbing vias, forming the coupling arrangement that combines mixed and magnetic, electric coupling. The presence of CSRRs resulted in a narrowband filter. The filter's center frequency is 4.947 GHz with a fractional bandwidth of 1.16%. By comparing the fabricated filter to an existing SIW conventional multi-cavity or cascaded resonator, a size reduction of 117% is achieved. The simulated and measured results agree with each other.

A W-band dual-circular-polarization (dual-CP) monopulse Cassegrain antenna for polarization detection of radar target is presented in this letter. The proposed antenna consists of a main reflector, a sub reflector, a dual-CP feed source based on the septum polarizer, and a comparator. Two orthogonal circular-polarized signals [left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP)] electromagnetic wave can be transmitted and received simultaneously by this antenna. The principle of the antenna is introduced and analyzed, and then a prototype of the antenna is simulated, fabricated, and measured. Measured results are in good agreement with the simulated ones. At 94 GHz, the gains of the LHCP and the RHCP sum beam (SUM beam) are 38.6 dBi and 38.8 dBi counting the insertion loss of the comparator, which indicates that the radiation efficiency is better than 44.2%. The 3-dB beamwidth is about 1.5° with a sidelobe level (SLL) of -16.6 dB, and the axial ratio is lower than 1.43. A null depth of -26 dB for the difference beam (DIFF beam) is observed, and the gain ratio between the LHCP monopulse beams is 5.9 dB. Measured results demonstrate that the proposed antenna is very applicable in the polarization detection of radar target at W-band.

In this paper, a high front-to-back ratio (FTBR), broad bandwidth planar printing structure, and electromagnetic dipole complementary antenna that generates end-fire radiation pattern is investigated. The antenna consists of a segmented loop, planar electric dipole, and microstrip coupling feed structure, which are printed on the top and bottom surfaces of a dielectric substrate. The segmented loop is equivalent to a magnetic dipole. A high front-to-back ratio is achieved by combining the electric dipole and equivalent magnetic dipole with the same radiation intensity and antiphase. The proposed antenna is fabricated and measured. The measured results show that the proposed antenna achieves an impedance bandwidth of 48.05% (1.66 GHz-2.71 GHz). The largest gain can get to 3.89 dBi, and the maximum front-to-back ratio is 25.4 dB in the frequency band. The measured results are well consistent with simulated ones.

This paper presents a new design of a compact microstrip ultra-wideband (UWB) single notch-band bandpass filter (BPF) along with its equivalent circuit model. The basic structure of the proposed filter consists of dual symmetrical multiple-mode resonator (MMR), four stub-loaded stepped impedance resonators (SLSIRs), two defected ground structure (DGS) units and a coupled folded arm resonator (CFAR) with feeding line. The presented filter is tested using R&S® ZNB20 vector network analyzer (VNA) to validate the simulated results. A good agreement between the measured and simulated (EM and circuit model) results is achieved.