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In this paper, a half mode substrate integrated waveguide (HMSIW) and microstrip rectangular patch (MRP) hybrid integrated coupler with two HMSIW ports and two microstrip ports is presented. The HMSIW ports are compatible with HMSIW components (e.g. HMSIW antennas), while the microstrip ports are compatible with active devices (e.g. power amplifiers). Due to the compact geometry and great compatibility with various topologies, the proposed hybrid integrated coupler is attractive for the design of active antennas, balanced amplifiers, six-port receivers, etc. To verify the proposed scheme, a 3-dB prototype coupler is designed, fabricated and measured, which achieves a fractional bandwidth (FBW) of 21 % with 1 dB amplitude imbalance and 4° phase imbalance.

A low-sidelobe series-fed microstrip patch antenna array operating at 78 GHz is proposed for millimeter-wave automotive radar applications. The proposed array is mainly composed of 10 patch elements and an impedance transformer. A hybrid HFSS-MATLAB optimization method is adopted to quickly achieve the design goals. The simulated results show that the proposed antenna array achieves a -10 dB impedance bandwidth of 2.5 GHz from 76.9 to 79.4 GHz and a stable peak gain of 15-16.2 dBi. By optimizing the widths of the patches and the spacing between the elements simultaneously, the proposed antenna array achieves a low sidelobe level of -23.5 dB in the E-plane.

A wideband SIW Yagi antenna array is proposed for 5G millimeter-wave applications. The array is composed of 4 antenna elements, a power divider and a CPW to SIW transfer structure. The element is designed based on the planar dipole antenna with two directors in radiation direction. To further increase the gain, a 1×4 Yagi antenna array is proposed. The measured result shows that the array has an −10 dB impedance bandwidth of 25.0% (35.0–45.0 GHz) and a gain of about 11.2 dBi.

A three-dimensional microwave absorber based on a lossy notch-slot resonator is proposed in this paper. Utilizing the resistor-loaded microstrip line coupling to the notch-slot, dualresonance can be obtained with a wide absorption band. The two resonances can be independently tuned by varying the length of the notch slot and the microstrip line. The proposed absorber exhibits an absorption band $(\vert \mathrm{S}_{11}\vert \leq-10\text{dB})$ from 3.7 GHz to 5.9 GHz, which is 46% FBW.

This paper proposes a novel dual-polarized absorptive/transmissive frequency selective structure (ATFSS) utilizing slotted magnetic material. It has a transmission band at high frequencies and a wide absorption band at low frequencies. The absorption is produced by the magnetic material, while the transmission is produced by the square slot channel in the magnetic material and a band-pass FSS. A cross-shaped metallic plate is placed above the magnetic material to improve the absorption performance. Compared to the conventional ATFSSs, the proposed one has a simple structure and is with no lumped elements. Simulation results a shows a pass-band around 14.1 GHz, with a minimum insertion loss of 1.34 dB and a bandwidth (|S 21 |≥-3dB) of 0.9 GHz. It also achieves a fractional bandwidth of 116.5% of the absorption band (|S 21 | ≤ -10dB). The operating principle and analysis are also discussed in the paper. This proposed ATFSS has potential for military applications to improve the stealth performance.

A switchable absorber/absorptive frequency selective reflector (AFSR) is proposed in this paper. This structure is switchable by enabling an ideal PIN diode or not. When the PIN diode is enabled, the structure works as an absorber with an ultra-wide absorption band. And the structure works as an AFSR when the PIN diode is disenabled. Simulated results show that the achieved absorber has a wide absorption band $(\vert \mathrm{S}_{11}\vert \leq-10\text{dB})$ with a fractional bandwidth of 150.3%, which is from 1.92 GHz to 13.42 GHz. The realized AFSR has two absorption bands, and one reflection band $(\vert \mathrm{S}_{11} \geq-1\text{dB})$ . The lower absorption band is from 1.98 GHz to 4.86 GHz (84.2%) and the upper absorption band is from 8.37 GHz to 13.37 GHz (50%). The simulated reflection band is from 4.86 GHz to 8.37 GHz (46%). The relative thickness of the proposed structure is 0.128.

A wideband differential-fed patch antenna with high isolation and high selectivity is presented. The differential-fed method is used to provide the antenna with high polarization isolation characteristic. A parasitic patch is adopted in the design not only to improve the impedance bandwidth, but also to generate a radiation null at the upper band-edge. Filtering response is improved by etching slots and loading resonant stubs on the feeding lines. Simulated results show that the proposed DFDP filtering antenna has an operation band of 34.16% (from 3.86 to 5.45 GHz) for |S dd11 | < -10 dB and a maximum gain of 9.64 dBi, and the cross-polarizaiton level is below -27 dB. Moreover, a high out-of-band gain-suppression level which reaches 21.9 dB is also obtained.

A three-dimensional (3-D) bandstop frequency selective structure (FSS) with an ultra-wide stop-band is presented in this paper. It is comprised of two stepped-impedance parallel-plate waveguide (PPW) channels, which are stacked along the E-field direction. Simulated results show that the proposed FSS achieves a wide stop band (|S 11 |≥–1dB) with a fractional bandwidth of 138.8%, ranging from 3.17 GHz to 17.55 GHz. Moreover, the stop-band is quite flat, across which the fluctuation is less than 0.4 dB. The simulated reflection coefficients of the FSS under the oblique incidence up to 60° are also given, which indicate good stability of the frequency response. The proposed band-stop FSS has potential in radomes of radars to suppress the higher order harmonics of certain communication systems.

In this paper, the integration design of a millimeter-wave filtering patch antenna array fed by a substrate integrated waveguide (SIW) four-way anti-phase filtering power divider is proposed. The multilayer four-way anti-phase filtering power divider handily implemented using the intrinsic field distribution of TE20-mode in SIW is proposed for miniaturization. The signal of the lower substrate integrated waveguide cavity (SIWC) bandpass filter is directly coupled to the upper TE20-mode SIW through a coupling slot. The intrinsic field distribution of TE20-mode SIW is used to generate anti-phase signals. This filtering power divider can be utilized as the feeding structure of a millimeter-wave filtering antenna array. To verify the design concept, a 28-GHz SIW-fed 1 × 4 filtering patch antenna array with three-layer substrates is designed and fabricated. The measured results show a fractional bandwidth of 5.03% ranging from 27.15 to 28.55 GHz, a peak gain of 11.1 dBi, cross-polarization levels lower than -20 dB, symmetric radiation patterns in both E-plane and H-plane, and high selectivity.

A low-profile wideband metasurface antenna with quad-polarization reconfiguration ability is presented in this paper. The proposed metasurface antenna is composed of a square patch, a metasurface formed by a lattice of $4 \times 4$ periodic metal plates, and four switchable feeding probes connected with two designed single-pole double-throws switches. By properly selecting the feeding probes, the polarization of the metasurface antenna can be dynamically reconfigured among four polarization states, i.e., $x$ -direction linear polarization, $y$ -direction linear polarization, left-hand circular polarization, and right-hand circular polarization. To validate the proposed concept, a prototype operating at 5.6 GHz with a relatively height of $0.067~\lambda _{0}$ ( $\lambda _{0}$ is the operating wavelength in free space) is designed, fabricated, and measured. The measured results show that both the 10-dB impedance bandwidths and the 3-dB axial ratio bandwidths are wider than 5.1–6.0 GHz for the linear and circular polarization states. The measured maximum gains are 9.39 dBic and 9.85 dBi for the circular polarization states and the linear polarization states, respectively. The simulation and experimentation verify that the proposed antenna can achieve quad-polarization reconfigurable features in a wide frequency band, which indicate the good performance of the proposed polarization reconfigurable metasurface antenna.

A dual-polarized antenna with omnidirectional radiation and high isolation performance is proposed in this paper. The proposed antenna consists of courtyard-shaped metal frame, feeding network, and metal background. Working mechanism of the proposed antenna is analyzed by the theory of characteristic modes. Two orthogonal polarizations can be achieved by utilizing the orthogonal current distributions on the courtyard-shaped metal frame. In order to obtain the horizontal-polarized mode, eight slots etched on the walls of the courtyard-shaped metal frame are excited. A feeding network is placed at the inner part of courtyard-shaped metal frame for a compact design. Measured results show that the proposed antenna can cover the impedance bandwidth of 1.80–2.81 GHz for both polarizations with their corresponding isolations better than 35 dB. A peak gain of 7 dBi and a gain ripple less than 3 dB in the horizontal radiation plane are achieved. The proposed antenna can be applied in the indoor wireless communication.

Spoof surface plasmon polaritons are mimicing surface plasmon polaritons (SPPs) modes at microwave or terahertz frequencies based on periodic metamaterial. The SPP mode has been widely used in novel transmission waveguides and functional devices, due to its unique properties of great confinement, shorter operating wavelength, low loss, and ability in flexible transmission. A frequency-sweep radiation based on complementary SSPP transmission line is proposed, in which the frequency-scanning on both sides of the transmission line is achieved. Additional array of circular patches is introduced to overcome the disadvantage of low-radiation-efficiency in the normal direction. Leaky-wave radiation within wide-range from backward direction to forward direction is achieved.

Novel miniaturized design of complementary spoof surface plasmon polaritons transmission line (CSSPP-TL) is proposed in microwave frequency. It is composed of complementary corrugated metallic strip and interdigital structures (ISs). The proposed CSSPP-TL features small linewidth, flexible dispersion control, and highly selective filtering performance. Simulated results show that the proposed CSSPP-TL has low insertion loss and high transmission efficiency. The dispersion properties of CSSPP with interdigital structures are studied. The cutoff frequency of the design is decreased by 50%, compared to that of conventional CSSPP transmission line, which indicate that, by introducing extra ISs, a smaller propagating wavelength and a tighter electric field confinement is realized, ensuring reliable applications in miniaturized plasmonic devices and low-interference SPPs circuits.

This paper presents a hexagonal piezoelectric micromachined ultrasonic transducer (PMUT) array that can avoid spurious modes known to occur by mode coupling with adjacent elements. By designing an optimal hexagonal PMUT array with 10 µm spacing resulting in high fill-factor, we were able to experimentally demonstrate well-matched spurious mode free resonances operating around 10 MHz. Furthermore, the effects of the center PMUT in arrays were investigated through various array designs based on finite element method (FEM) simulations and experimental measurements.

A key metric of micromachined ultrasonic transducer (MUT) performance is the volume velocity, which determines the transmitting output pressure. Here, we present a study to demonstrate corrugated-diaphragm piezoelectric MUTs (PMUTs) which have up to 3.2X higher volume velocity than conventional PMUTs of the same area. The PMUTs are manufactured by a surface-micromachining process forming a high fill-factor (80%) array, and corrugations can be added without any additional masks or process steps. The PMUTs with corrugations are implemented to have the increased displacement and resonant frequency. The corrugations and released holes are etched and formed by the same fabrication step, and their opening-area ratios determines the corrugation depth which is critical to PMUT efficiency. By corrugating PMUT diaphragm, it provides a simple method to tune resonant frequency. The study includes design, fabrication, and characterization for the various approaches to corrugated PMUTs.

This paper presents a 3D frequency selective structure (FSS) with low transmission loss in the low frequency band and an upper absorption band. The proposed structure uses band-stop parallel strip line (PSL) arrays, instead of conventional metallic plate, as the reflector of a single-layer circuit analog (CA) absorber by using resistive single-square-loop. Results show that the proposed FSS exhibits an absorption band from 8.64 GHz to 13.58 GHz, while maintain a low insertion loss (lower than 0.5 dB) below 2 GHz.

A right-angle broadband transition between air-filled rectangular waveguide (RWG) and the differential substrate integrated waveguide (SIW) is proposed at Ka-band. By utilizing two SIW cavities with two H-shaped slots in the proposed transition, a simulated impedance bandwidth wider than 45.9% ranging from 25.5 to 40.7 GHz for return loss less than -15 dB can be achieved. The insertion loss of a single transition is less than 0.1 dB within the operating band. Meanwhile, the phase difference and amplitude imbalance between the two differential output ports are less than 180°±0.15° and 0.02 dB, respectively.

A 3-D band-absorptive frequency selective rasorber based on stepped-impedance hybrid transmission/absorption channels is proposed in this paper. These two channels act as a 3D absorber within its absorption band, while it is like two stacked parallel-plate waveguides (PPWs) below the absorption band. Therefore, the proposed FSR exhibits an absorption band from 3.78 GHz to 7.14 GHz, with a fractional bandwidth of 61.53%, and the cut-off frequency of the passband is 931MHz ( $\vert S_{21}\vert \geq-1\text{dB}$ ).

Magnetic localized surface plasmons modes are supported on metallic spiral structures. Coupling mechanisms for these metamaterial resonators are studied, which are the joint action of magnetic and electric coupling.

Cloud resource management research and techniques have received relevant attention in the last years. In particular, recently numerous studies have focused on determining the relationship between server-side system information and performance experience for reducing resource wastage. However, the genuine experiences of clients cannot be readily understood only by using the collected server-side information. In this paper, a cloud resource management framework with two novel turnaround time driven auto-scaling mechanisms is proposed for ensuring the stability of service performance. In the first mechanism, turnaround time monitors are deployed in the client-side instead of the more traditional server-side, and the information collected outside the server is used for driving a dynamic auto-scaling operation. In the second mechanism, a schedule-based auto scaling preconfiguration maker is designed to test and identify the amount of resources required in the cloud. The reported experimental results demonstrate that using our original framework for cloud resource management, stable service quality can be ensured and, moreover, a certain amount of quality variation can be handled in order to allow the stability of the service performance to be increased.

This paper presents air-coupled piezoelectric micromachined ultrasonic transducers (PMUTs) fabricated from single-crystal PZT, enabling very high sound pressure level (SPL) output of 100.3 dB at 33 cm distance. The single-crystal PZT deposited via PVD has low permittivity, enabling the highest figure of merit (FOM, $e_{31}j^{2}/\varepsilon_{r}\varepsilon_{0}$ ) PMUTs to date. The PMUTs operate at a low resonant frequency of 40 kHz, which results in lower acoustic absorption loss and therefore longer operating distance, and have 10X greater mechanical displacement and SPL output compared to prior-art AlN PMUTs. Comparing to prior PZT PMUTs, the single-crystal PZT used here has low permittivity ( $\varepsilon_{r}=308$ ) and high piezoelectric coefficients ( $\boldsymbol{e}_{31,\ \boldsymbol{f}}\sim 24.5$ ), resulting in low insertion loss. Acoustic experiments conducted with commercial ultrasonic transducers and reference microphones show that a 2×2 array PMUTs has 1.91mV/Pa (−74.3dB) receive sensitivity, demonstrating much higher efficiency per unit transducer volume compared to conventional transducers.

With continuously increasing of signal bandwidth, the transmitter leakage issue in frequency division duplexer (FDD) transceivers becomes severer. In this letter, an enhanced behavioral model is proposed to suppress FDD transmitter leakage at a low-sampling rate. The theoretical analysis is provided to explain the operation principle of the proposed model. The experimental results show that the proposed model can effectively increase the accuracy of generating sideband replica and thus improve the suppression performance. Science Foundation Ireland Natural Science Foundation of China

Piezoelectric micromachined ultrasonic transducers (PMUTs)using 36% Scandium-doped aluminum nitride (ScAIN)thin-film are presented in this work. ScAIN is known to exhibit higher piezoelectric properties compared to pure AIN leading to significant improvements in various MEMS applications including PMUTs. Here, the concentration of Sc in the actual sputtered 1 um thick ScA1N film was 36% that is slightly below the phase boundary. The piezoelectric coefficient is close to maximum at this high concentration leading to significant improvement in the PMUT performance. The ScA1N film quality was verified via X-Ray Diffraction (XRD), electron probe microanalysis (EPMA), and d33 meter. The operation frequency was designed to around 80 kHz to achieve long range detection, where the air absorption loss is low. The displacement sensitivity of 1 mm diameter ScA1N PMUT was 806 nm/V at 84 kHz resonant frequency. A large displacement of 4.8 um was achieved at 20 V pp input at the fixed frequency of 84 kHz. This represents a factor of 9 increase in transmit amplitude compared to prior art air-coupled A1N PMUTs.

Analytical models for micro machined ultrasonic transducers (MUTs)show that the transmit voltage sensitivity (Pa/V)has an inverse dependence on thickness. However, the ability to scale capacitive MUTs (CMUTs)to submicron thickness is limited by electrostatic pull-in instability. PMUTs are not subject to pull-in instability, making them an ideal vehicle to explore the benefits of thickness scaling. Using analytical model and experiment measurements, we demonstrated individual PMUT's transmit voltage sensitivity at a given frequency is inversely proportional to the device thickness, while the quality factor dominated by the acoustic radiation loss linearly scales with the device thickness. AIN PMUTs with 500 nm and 1 μm thick piezoelectric layer were fabricated to demonstrate an improved transmit voltage sensitivity via sub-micro thickness scaling.

This study presents encapsulated piezoelectric micromachined ultrasonic transducers (PMUTs)fabricated by surface micromachining, forming high fill-factor arrays for high transmitting pressure output. The structures were made by the low-temperature processes, and in-situ sealed by SiO2 PECVD reactor in vacuum, and coated by a PDMS layer to have good protection and acoustic impedance matching, resulting in a high mechanical displacement and wide bandwidth for immersion applications. The displacement-frequency measurement shows the bandwidth improvement by a quarter wavelength thickness PDMS coating, which agrees with the simulations. By pulse-echo measurements, a 6⨯6 PMUT array of 0.81 mm2is characterized by 20Vp-p continuous-wave excitation, resulting in 1.3kPa echo receiving and 60% fractional bandwidth with 0.7 mm fluid depth. This study achieves 5X greater transmission efficiency and 2X better receiving bandwidth than the previous work.

A simple printed slot antenna for WWAN metal-rimmed mobile phone application is presented in the paper. The antenna is mainly composed of two slots, and fed with an L-shaped coupled feedline. By etching a slit on the metal frame, a good excitation of the monopole slot resonant mode can be achieved. Then combining with fundamental (half-wavelength) modes of two slot, the GSM850/900 (824∼960 MHz) and DCS/PCS/UMTS2100 (1710∼2170 MHz) operating bands can be covered. Detailed operating principle of the proposed antenna is discussed in the article.

In this paper, a dual-polarized broadband band-absorptive frequency selective rasorber (FSR) is proposed. The band-absorptive FSR exhibits a wide absorption band; meanwhile it is almost transparent to the incident electromagnetic (EM) waves at the frequencies below the absorption band. The FSR is comprised of a lossy layer and an absorptive transmission/reflection surface (ATRS). The lossy layer is realized by a square loop loaded with lumped inductors and resistors. The ATRS is different from the conventional reflective surface - it is comprised of two lossless square loops and one lossy square loop. Those loops are all achieved by loading lumped elements. Simulated results of the FSR is shown in the paper. It exhibits a broad absorption band from 4.02 GHz to 9.34 GHz (79.64% fractional bandwidth), while the cut-off frequency of the passband is 905 MHz ( $\vert S_{21}\vert \ge {-1}$ dB)

A novel tri-band monopole antenna for multi input multi output (MIMO) application is presented. The MIMO antenna is designed on FR4 substrate, whose triband performance is generated by two orthogonally placed E-type monopoles. The compact triband MIMO antenna can work at 2.45/3.5/5.2GHz frequencies. I-type branches on the ground act as a reflector to isolate the radiation beams of the two monopole elements. Thus mutual coupling is reduced and isolation is improved to less than −15 dB within its working frequency range.

Evaluating radar performance under complex electromagnetic environment is important for modern warfare. Traditional experimental method is expensive due to large number of experimental parameters. This paper presents a new machine learning based method via a case study. In this case, only a small number of experimental samples are required. After the data preprocessing and feature selection, the model for predicting the radar performance is learned by the machine learning algorithm. We compare six machine learning algorithms via cross-validation and find the multiple layers perceptron (MLP) possesses the highest prediction accuracy with a satisfied root-mean-square error (RMSE) of 1.77. The results of the paper exhibit the effectiveness of the machine learning based radar performance evaluation method.

This article describes a new H-slot coupled microstrip filter-antenna. In the antenna design, these microstrip lines are used to feed H-shaped coupling slots on the grounded metal plane. The H-shaped coupling slots feed top radiating patches, which can realize the radiation function of the antenna. The bilateral power divider is connected with the microstrip line, and realize the filtering function. The antenna has a bandwidth of 0.78 GHz from 3.02 to 3.8 GHz. In the frequency band of 3.4 to 3.6 GHz, the average gain in the direction perpendicular to the antenna plane has exceeded 11 dBi.

This paper presents a 3D frequency selective rasorber with low transmission loss and a wide lower absorption band. The pass-band is produced by an open-ended lossless resonator, while the absorption band is attributed to a wideband absorber realized by a periodic stack printed circuit boards (PCB). Simulated results show that the proposed FSR exhibits a pass-band around 6.2 GHz, and a lower absorption band from 1.57 GHz to 4.50 GHz. Moreover, the thickness of the FSR is only 0.1 wavelength at 1.57 GHz.

A broadband and high isolation MIMO antenna using the theory of characteristic modes (TCM) is proposed in this paper. A ground plate with slots, expanding the operating bandwidth, is printed in the bottom of dielectric substrate. And the feeding structure was located in the top of dielectric structure, which connected with the ground plate by a metal via. After studying performance of the structure by using eigenvalue, characteristic angle (CA), characteristic current and modal significance (MS), we used the feeding structure in the suitable location to achieve the wide operating band. Antenna has an operating band of 4.62 GHz from 2.53 GHz to 7.15 GHz, a relative band of 95.5%. In order to increase the isolation of the MIMO antenna, we have made slits in the ground plate combined two antenna units. It has the good isolation achieved −18 dB in the operating band.

This study presents a high fill-factor array of aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducers (PMUTs) fabricated on a transparent substrate. PMUTs with diameters ranging from 40 microns to 100 microns were fabricated, resulting in resonant frequencies from 3 MHz to 18 MHz in air. A high fill factor of 62% was achieved. Immersed pulse-echo experiments were conducted at 2.5 MHz.

A novel compact Ultra-wideband (UWB) microstrip patch antenna using planar metamaterial structures is proposed. The metamaterial microstrip antenna has two layers consists of a meshed top patch and a patterned ground plane. The inductances and capacitances coupled due to the ground plane and patterned radiating patch leads to the left handed behavior of the metamaterial. The proposed antenna which designed on the low cost FR4 substrate has compact size 28×32 mm2 with height 0.794mm. The impedance bandwidth operates from 3.3 to 12 GHz for S-parameter of less than −10 dB level. The results obtained from the simulation studies shows that the antenna has good radiation characteristics for the UWB applications.

This paper presents design methods of tri-beam antenna systems. To produce a forward beam along antenna normal axis, 3×3 Butler matrix network with three directional couplers and four −90 degree phase shifters is proposed. When different input ports are excited, the proposed structure can produce three output signals with equal amplitude and the phase differences of −120 degree, 120 degree and 0 degree, respectively. For verifying the design concept, a tri-beam antenna system based on microstrip structure at 2GHz is proposed. The results indicate that the antenna array can produce −30 degree, 30 degree and 0 degree beam when different input ports are excited. A tri-beam slot antenna array based on substrate integrated waveguide (SIW) operating at 10GHz is designed and realized. The antenna array can produce tri-beam radiation performance with peak directions of −45 degree, 45 degree and 0 degree respectively.

Based on substrate integrated waveguide (SIW) technology and the standard single layer printed circuit board (PCB) process, a slot antenna array with three beams at X-band is designed and realized. A slot antenna unit based on SIW technology is analyzed and designed at 10GHz. S parameters and radiation patterns are given. Finally, a 3×1 antenna array is connected with the Butler matrix as a beam-forming network. The antenna array can produce −45 degree, 45 degree and 0 degree beam when different input ports are excited. The antenna array has a peak isolation between input ports better than 30dB, and a peak gain of 10.5dBi.

A 60GHz patch monopole Antenna-on-chip (AoC) with a cross-shape Artificial Magnetic Conductor (AMC) is presented based on standard 0.18um CMOS process. The novel cross-shape AMC acts as a shield between the radiating element and the lossy silicon substrate. Both AMC and the patch antenna are optimized to achieve a wideband operating performance covering 57–66 GHz. The optimized AoC has a compact size of 0.9×2.1mm2 and provide a high gain of 1.53 dBi.

A wideband 60GHz monopole on-chip antenna based on 0.18μm CMOS process with an artificial magnetic conductor (AMC) is presented. The structure of the proposed on-chip antenna consists of a circular ring-shaped monopole antenna fed by a 50Ω coplanar waveguide (CPW). Results show that the proposed circular ring-shaped monopole antenna mounted on AMC plane can offer higher gain, higher radiation efficiency and wider impedance bandwidth, while has a smaller antenna size.

In this paper, a novel linear polarized cavity-backed antenna based on normal InP HBT technology is proposed and simulated. In this design, half-mode substrate integrated waveguide (HMSIW) technique is used to create a radiating aperture, which helps minify the InP substrate and reduce the cost. The proposed antenna is numerically investigated using HFSS. The simulated results show that the proposed antenna has an impedance bandwidth about 3 GHz at the center frequency of 60 GHz, in which the gain and radiation efficiency of the proposed cavity-backed antennas is beyond 3.8 dBi and 89%, respectively. Compared with the conventional on chip antenna based on CMOS technology, this novel antenna's gain and radiation efficiency has been largely increased.

An improved compact ultra-wideband (UWB) patch antenna with metamaterials is proposed. The total size is reduced and the simulated impedance bandwidth operates from 3.8 to 19.4 GHz for S-parameter of less than −10 dB level. The bandwidth of this antenna is 15.6GHz. Both strong radiation in the horizontal direction and practical characteristics are observed. Thus, this antenna would have some specific applications for UWB wireless communications in the future.

The design of circularly polarized microstrip patch antenna (MPA) with wide axial ratio beamwidth working at 2.4GHz band is proposed. The wide axial ratio beamwidth is achieved by a 45° rotated slot cut in the center of the square MPA. By placing two back-to-back MPAs on intelligent door lock, the function of indoor-outdoor recognition has been successfully realized.