A wideband high-gain microstrip patch/Fabry-Perot (FP) resonator cavity antenna with low radar cross section (RCS) is proposed, which consists of a microstrip patch, a ground plane, a double-layer partially reflective surface (PRS), a resonant complementary metasurface (RCM), and a checkerboard metasurface (CBM). A PRS is designed as circular patches and rectangular slot patches corresponding to the top and bottom, for achieving high-gain with wideband. RCM consists of three rectangular patch arrays of varied sizes for bandwidth enhancement and compensation using characteristic mode analysis (CMA). CBM adopts a fusion of two 4 × 4 metasurface modes to achieve low RCS. The three types of metasurfaces collaboratively enable frequency band resonance in the proposed antenna, resulting in enhanced gain, wide bandwidth, and reduced RCS. The measured results agree well with the simulated ones, showing that the antenna has an impedance bandwidth of 37.3%, a peak gain of 14.9 dBi at 7.0 GHz, and its cross-polarization greater than 20 dB. Monostatic RCS reduction of 10 dB is achieved across the frequency range from 5.0 GHz to 17.6 GHz (111.5%).

A broadband super surface antenna is proposed and simulated with the unmanned aerial vehicle (UAV) for 5G at emerging bands in FR3 and FR1 (sub-7 GHz). The antenna is composed of 4x4 circular patch metasurface, rectangular transmission line patch, ground with rectangular slot and two layers of substrate. The circular unit cells-based metasurface is analyzed by the characteristic mode (CM) to find the resonant bandwidth. Then, the proposed antenna is simulated with the UAV designed with different dielectric constants to simulate the scene. The results indicate that the -10 dB impedance bandwidth, gain, and radiation pattern exhibit notable effects. After analysis, t was observed that there is a slight discrepancy between the antenna simulation and the actual application scenario. However, this error does not impact the antenna's performance on UAVs. The antenna demonstrates characteristics of broadband functionality, high gain, and low cross-polarization.

A polarization-reconfigurable metasurface wideband antenna with dual polarization and a low radar cross section (RCS) is presented. The antenna employs a diode positioned between two transmission lines to control the current direction and a resistor on a defected-ground branch to manage phase shifts, enabling seamless transitions between circular polarization and linear polarization. The elliptical metasurface design contributes to a reduced RCS. The design results are verified through measurement, showing an impedance bandwidth (IBW) of 49.1%, an axial ratio bandwidth (ARBW) of 23.2% for the diode is off, an IBW of 36.4% for the diode is on, the IBW of the connected resistor is 40.7%, and the peak gains for the three states are 6.4 dBi, 4.4 dBi, and 4.2 dBi, respectively. The metasurface achieves a low RCS bandwidth ranging from 2 GHz to 24 GHz, showing a 6 dBsm reduction in RCS from 4.9 GHz to 19.7 GHz, which corresponds to a 120.3% decrease compared to a perfect electric conductor (PEC) plate.

A low‐profile wideband circularly polarized (CP), single‐layer antenna with low radar cross section (RCS) reduction based on staggered elliptical metasurface using characteristic mode analysis (CMA) is presented. The staggered arrangement of the elliptical metasurface has a 90° relationship, ensuring the generation of circular polarization, and their modes of fusion can achieve RCS reduction by CMA. The defective ground shows that the difference in characteristic angle (CA) between the two pairs of modes is about 90°. The measured results show that the antenna has a 40.6% (5.5 GHz–8.3 GHz) impedance bandwidth (IBW), a 26.2% (6.3 GHz–8.2 GHz) 3‐dB axial ratio bandwidth (ARBW), and a peak gain of 5.1 dBic is achieved at 6.3 GHz, and with a large RCS reduces across the frequency range from 2.0 GHz to 22.0 GHz (166.7%). Monostatic RCS reduction of more than 5 dBsm is achieved within the frequency range from 4.6 GHz to 22.0 GHz (130.8%).

This paper presents a low-profile, single-layer, broadband, polarization-reconfigurable metasurface antenna with a low radar cross section (RCS). The design leverages characteristic mode analysis (CMA) applied to a staggered elliptical-shaped unit cell metasurface. The unique arrangement of the elliptical-shaped elements, oriented at 90 degrees, promotes mode fusion through CMA, effectively reducing RCS. Additionally, the analysis of a defective floor with branching reveals a critical characteristic angle (CA) of 90 degrees, essential for generating circular polarization (CP) waves. Experimental measurements indicate that the antenna prototype achieves a -10 dB impedance bandwidth (IBW) from 5.5 to 8.3 GHz (40.6%), a 3-dB axial ratio bandwidth (ARBW) from 6.3 to 8.2 GHz (26.2%) and a peak gain of 5.1 dBi at 6.3 GHz. By integrating resistors, the antenna supports switching between CP and linear polarization (LP), as well as across different frequency bands, resulting in three distinct operating states (with IBWs of 26.5%, 26.9%, and 26.9%, respectively). Additionally, the metasurface structure achieves a notable reduction in monostatic RCS across the frequency range from 2.0 to 22.0 GHz, resulting in a substantial 166.7% reduction and a 6 dBsm decrease in RCS within the IBW of 6.3 to 7.2 GHz. The exploded view of low-profile low-RCS wideband metasurface antenna with polarization reconfigurable.

A broadband and high gain polarization reconfigurable Fabry-Perot resonator antenna is presented. The antenna is principally made up of a microstrip source antenna, a single-layer 2x2 circular patch metasurface, a ground plane, a double-layer partially reflective surface (PRS), and four resistors. Characteristic Mode Analysis (CMA) reveals that the circular patch metasurface effectively excites circular polarization (CP) characteristics. The double-layer PRS exhibits a positive reflection phase gradient, transmitting the radiation of CP waves. Furthermore, additional CMA analysis shows that the inclusion of resistors modifies the direction of mutually orthogonal currents, thereby enabling the antennas polarization reconfiguration capabilities.

Three broadband non-uniform metamaterial mushroom antennas are designed with distinct mushroom configurations. The design trade-offs among the input impedance bandwidth, boresight gain, and the front-to-back ratio are considered with a genuine multi-objective Bayesian optimization method. The three non-uniform antennas attain a notable increase in impedance bandwidth with different degrees of trade-off in terms of the other two design targets when compared to the reference antenna with uniform mushroom configuration. All the four antennas are prototyped and measured, with strong alignment between simulation and measurement. The optimized designs can function in the n77 band of 5G New Radio.

AbstractA low‐profile circularly polarised (CP) metasurface antenna is proposed, utilising characteristic mode analysis (CMA). The antenna design features a two‐layer laminated substrate, a 4×4 Butterfly‐shaped metasurface, a rectangular slot, an irregular transmission line, and a ground plane. The metasurface is analysed using mode significance (MS), characteristic angle (CA), and characteristic current to determine the resonance bandwidth and CA resonance points, which exhibit a near 90° difference. At the intersection of the two MS modes, their CAs differ by nearly 90°, and their far‐field radiation directions align, indicating the potential for achieving circular polarisation at the desired frequency. The integration of the metasurface with the slot antenna is simulated to validate the CMA findings. Additionally, the CP bandwidth is enhanced by modifying the transmission line branches. Measurement of the fabricated antenna reveals an impedance bandwidth (IBW) of 27.4%, a 3‐dB axial ratio bandwidth (ARBW) of 10.1%, and a peak gain of 6.9 dBic at 4.4 GHz. Compared to the design without branches, IBW and ARBW have increased by 10% and 7.3%, respectively.

A non-uniform metasurface circularly polarized patch antenna is designed using a genuine multi-objective Bayesian optimization (MOBO) method. Instead of aggregating the performance metrics into a single weighted sum, a genuine MOBO approach is adopted to explore the performance trade-offs, where three important antenna performance metrics, input impedance bandwidth, axial ratio (AR) bandwidth, and gain at boresight, are considered as the optimizing targets. Starting from a reference antenna with a uniform metasurface, the non-uniform metasurface antenna is designed by tuning ten physical design parameters automatically. The optimized antenna achieves an operating bandwidth of 25.6% (3.75 GHz–4.85 GHz) with |S11| < -10dB, axial ratio less than 3 dB, and a maximum realized gain of 7.15 dBic. Compared with the reference antenna, the optimized design realizes a 31% enhancement in operating bandwidth while keeping the identical size of 1.12λ 0 × 0.86λ 0 × 0.069λ 0 (λ 0 is the free space wavelength at center frequency of 4.3 GHz). Good agreement between measurement and simulation results validates the optimization methodology.

A metasurface based on unequal spacing between the rectangular-ring unit cells is used to propose a broadband, low profile, circularly polarized (CP) and linearly polarized (LP) antenna. This can be used for 5G New Radio and GNSS applications in navigation and telemetry on drone which uses remote sensing radar/lidar for survey mapping. The antenna structure comprises a stacked-metasurface based on unequal-spacing between the 7×7-unit cells, a radiating rectangular-patch, and a near diagonal line probe feed. A metasurface is considered using rectangular-ring 7×7-unit cells array with unequal-spacing’s in x- and y-directions and it is placed above a rectangular-radiator to realize a wide CP bandwidth for GNSS applications. The antenna example reaches a 3dB axial ratio of 25.3% (1.38 GHz – 1.78 GHz) with CP (3-dB axial ratio) bandwidth of 15.8% (1.51 GHz – 1.77 GHz) and gain of greater than 8.5 dBic.

Different types of microstrip antennas with non-uniform metasurfaces are designed and optimized using statistical methods with various formulations. The design objectives include impedance matching bandwidth, realized gain, and axial ratio bandwidth for linearly polarized antennas and circularly polarized antenna, respectively. The designed antennas are to operate in the sub-6 GHz frequency band of the 5G New Radio system.

A broadband non-periodic mushroom antenna is designed via Bayesian optimization. By tuning the length and width of the 16 patches of a 4 $\times\ 4$ meta mate rial mushroom structure, the non-periodic mushroom antenna achieves a 23.95% fractional bandwidth $(\vert \mathrm{S}_{11}\vert<\text{-}10\ \text{dB})$ , while keeping the gain variation small at boresight direction. Bayesian optimization is particularly suitable for design and optimization with a large number of design parameters, for example, 32 design parameters in this design, since the conventional exhaustive search becomes infeasible for such a large search space. The proposed antenna is prototyped and measured, with good agreement between the simulation and measurement achieved. The proposed antenna is able to operate in the widely deployed n78 band of 5G New Radio.

A compact dual-band ring-slots with grounded-via integrated square-patch antenna is planned for circular/linear waves radiations. Four small unequal circular-ring-slots with grounded-via are integrated at the square patch corners for circularly polarized (CP) waves to reduce size of the antenna. These ring-slots with grounded-via offer compact antenna with CP radiation at the L-band. The antenna operates at the global navigation satellite system (GNSS) L1-band of 1.6 GHz with CP w and 2.07 GHz with a LP for 5G New Radio (NR) applications. An integrated ring-slot with via acts as a composite right/left-handed structure, so that the four-ring-slots with via can miniaturize the antenna structure at 1.6 GHz. The confirmed outcomes of a prototype antenna with size of 0.32λ 0 ×0.32λ 0 ×0.0264λ 0 (λ 0 is the free-space wavelength at 1.6 GHz) are: the bandwidth of 5.6% (1.585 GHz - 1.675 GHz) at the L-band and 0.75% (2.04GHz-2.07GHz) at the S-band for 10-dB return loss; 2.5% (1.59GHz-1.63GHz) at the L-band for 3-dB axial ratio (AR); peak gain of 4.9 dBic at 1.62 GHz and 4.0 dBi at 2.07 GHz.

Wideband non-uniform mushroom antennas are designed via three different formulations of Bayesian optimization, including a single-objective method, a multi-objective approach by aggregating two objectives into a weighted sum, and a genuine multi-objective method. The main design target is set as enlarging the impedance bandwidth in the single-objective case. The two multi-objective approaches also include the realized gain as the design objective. A total of 36 design parameters are considered in all the three cases. It is found that the genuine multi-objective approach is able to obtain a mushroom antenna design that operates within the widely adopted n77 band of 5G with largest impedance bandwidth and smallest gain variation at boresight direction across the bandwidth with the least number of simulation runs.

A new 7-port structure for terahertz reflectometer is proposed and analyzed. Our structure for 7-port reflectometer can be designed and fabricated more easily at terahertz.. as compared with traditional 6 or 7 port reflectometers and achieved near-perfect phasor distribution. Our 300 GHz reflectometer was fabricated and validated with performances with VNA.

Increased commercial use of satellite terminals, broadband wireless communications and high-data link has created a strong demand for Ka-band high power amplifiers (HPAs) coupled with high power efficiency and good linearity performance. To meet the stringent linearity requirement without largely sacrificing output power and efficiency, linearization is the only solution. This paper demonstrates the effectiveness of digital predistortion (DPD) in linearization of Ka-band HPAs by presenting the experimental results from our memory polynomial predistorter based wideband DPD testbed. Tested on an in-house developed 15W Ka-band solid state power amplifier (SSPA), it is shown that with linearization 15-25 dB linearity improvement is achieved for 64-QAM and 8-tone signals. While meeting the required linearity, this will lead to an significant increase on the output power and efficiency, compared to the conventional back-off method.

There are challenges and opportunities in supporting the infrastructure for electric vehicle (EV) and smart grid in a dense urban city-state like Singapore. Automotive telematics which typically use cellular networks, can potentially be served by picocells of 5.9 GHz Dedicated Short Range Radio(DSRC) network for intelligent transport system(ITS), connected to our national fiber network (NG-NBN), which can provide up to 1 Gbps to every node (home, public lamp post, bus stop, etc). This integrated high speed network can potentially enhance the performance for EV ecosystem and users' experience. Our research, deployments and results in cyber security network, electric charging (wired and wireless) and telematics network for EV and smart grid will be presented.

An injection-controlled method for charge pumped phase-locked loop (CP-PLL) has been developed for beam scanning in a 76–77 GHz automotive radar. It exploits an additional and external current source with the CP-PLL to control the voltage controlled oscillator in a production-ready SiGe front-end transceiver to create phase shift. A new 76 to 77 GHz phased array system has been implemented using this technique. The results from measurements and computer simulations validate its performance.

In this paper, we propose a method for modeling the transient radiated and received pulses of ultra-wideband (UWB) planar aperture antennas. The proposed method is able to analytically model the angle-dependent pulse distortion of the antennas. The method relates the input pulse of an antenna to its transient radiated fields, and the incident transient fields to its output pulse. This method needs to estimate the antenna's aperture field distribution from time-domain antenna measurements. Using the proposed method, the received pulses from three different antennas-a ridged-horn, a dielectric loaded horn, and a Vivaldi antenna-are modeled and compared with the measured received pulses. A comparison of pulse shape, amplitude, and energy shows very good agreement. Different input pulses are also examined for the experimental evaluation of the proposed method. The method allows designers to analytically estimate the antenna effect on transmitted pulse enabling the inclusion of pulse distortion by the antenna into the ultra-wideband transceiver design.

This paper overviews the research and development (R&D) of microwave & millimeter-wave technology in public research institutions in Singapore. With increased investigation, Singapore government has supported several R&D programs related to microwave and millimeter-wave technology. The R&D activities of local universities and research institutions, in particular, from Agency of Science, Technology and Research (A*STAR) in these areas are briefed. Several R&D programs are introduced for information sharing and potential collaboration with overseas organizations.