This paper presents a quadruple-band indoor base station antenna for 2G/3G/4G/5G mobile communications, which covers multiple frequency bands of 0.8-0.96 GHz, 1.7-2.7 GHz, 3.3-3.8 GHz and 4.8-5.8 GHz and has a compact size with its overall dimensions of 204 × 175 × 39 mm 3. The lower frequency bands over 0.8-0.96 GHz and 1.7-2.7 GHz are achieved through the combination of an asymmetrical dipole antenna and parasitic patches. A stepped-impedance feeding structure is used to improve the impedance matching of the dipole antenna over these two frequency bands. Meanwhile, the feeding structure also introduces an extra resonant frequency band of 3.3-3.8 GHz. By adding an additional small T-shaped patch, the higher resonant frequency band at 5 GHz is obtained. The parallel surrogate model-assisted hybrid differential evolution for antenna optimization (PSADEA) is employed to optimize the overall quadruple-band performance. We have fabricated and tested the final optimized antenna whose average gain is about 5.4 dBi at 0.8-0.96 GHz, 8.1 dBi at 1.7-2.7 GHz, 8.5 dBi at 3.3-3.8 GHz and 8.1 dBi at 4.8-5.0 GHz respectively. The proposed antenna has high efficiency and is of low cost and low profile, which makes it an excellent candidate for 2G/3G/4G/5G base station antenna systems. INDEX TERMS 2G/3G/4G/5G, base station antenna, compact antennas, optimization method, quadrupleband antennas.

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Microwave diplexers are often designed iteratively via manual channel-by-channel or resonator-by-resonator local optimization procedures due to high dimensionality in design variables and the complexity of structures. A one-off automated diplexer optimization method is yet to be developed. To achieve this, other than improved optimizers, an effective objective function is critical to allow optimizers to find desired designs. This paper realizes automated diplexer design by proposing key performance indicator (KPI)-based objectives. The KPIs are extracted from S-parameter responses. An all-resonator diplexer with 22 variables and a Tee-junction diplexer with 23 variables are designed using the proposed method via one-off optimization, showing 100% and 80% success rates, respectively.

Microwave filters are indispensable passive devices for modern wireless communication systems. Nowadays, electromagnetic (EM) simulation-based design process is a norm for filter designs. Many EM-based design methodologies for microwave filter design have emerged in recent years to achieve efficiency, automation, and customizability. The majority of EM-based design methods exploit low-cost models (i.e., surrogates) in various forms and artificial intelligence techniques assist the surrogate modeling and optimization processes. Focusing on surrogate assisted microwave filters designs, this paper firstly analyzes the characteristic of filter design based on different design objective functions. Then, the state-of-the-art filter design methodologies are reviewed, including surrogate modeling (machine learning) methods and advanced optimization algorithms. Three essential techniques in filter designs are included: 1) Smart data sampling techniques; 2) Advanced surrogate modeling techniques. 3) Advanced optimization methods and frameworks. To achieve success and stability, they have to be tailored or combined together to achieve the specific characteristics of the microwave filters. Finally, new emerging design applications and future trends in filter design are discussed.

A compact-size rectangular slot antenna required for ultra-wide band body centric applications is presented. The antenna design is based on etching a rectangular slot on a circular radiator. The antenna is optimized using a surrogate assistance differential evolution algorithm to produce the largest bandwidth in free space and close to the human body. Analysis of the proposed antenna was carried out and its performance assess in terms of bandwidth, gain, efficiency, and radiation pattern. Results investigated shows that the rectangular slot antenna maintains its bandwidth when placed in closed contact with the human body. The very close agreement between the simulated and measured results both in free space and on body indicates that the antenna is immune to variation in the human tissues and also robust to fabrication tolerances.

A metasurface-inspired low-profile circularly polarized (CP) slot array with a wide CP band and broadband low radar cross section (RCS) is proposed in this paper. The slot array consists of four element antennas, four grounded substrates, and a sequential-rotated feeding network. In terms of radiation performance, the array yields a wide CP band resulting from the CP element antenna and the sequential-rotated feeding network. The CP element antenna is achieved due to the polarization conversion property of the metasurface-based superstrate. The feeding network with multiple related design parameters is optimized by an AI-driven antenna design method to find the widest bandwidth. In terms of scattering performance, broadband RCS reduction is achieved by using a hybrid RCS reduction technique that combines two destructive interference principles. The |S11|<-10 dB bandwidth reaches 53.2%, the AR < 3 dB bandwidth reaches 50%, and the RCS reduction bandwidth reaches 147.8% for a low-profile structure with a relatively low number of metasurface unit cells. A prototype was fabricated and measured. The measured and simulated results are in good agreement. Index Terms-Metasurface (MS), circular polarization, radar cross section (RCS), antenna array, parallel surrogate model-assisted hybrid differential evolution for antenna optimization (PSADEA) I. INTRODUCTIONIn the last few decades, radar cross section (RCS) [1] associated with the stealth capability of a target has attracted a lot of interest. Antennas which are widely used in many devices to transmit and receive signals can also function as special scatters. Amongst them, the array antenna, which has a large aperture, makes a tremendous contribution to the overall RCS of a platform. Many methods such as structural shaping, and using radar absorbing material and frequency selective surfaces (FSS) have been studied to reduce the RCS of antennas [2][3][4][5][6]. These methods are mainly based on energy deflection or energy dissipation and their drawbacks include narrow bandwidth and deterioration of radiation performance.

In resonator-coupled bandpass filter 3D design, it is a routine that the filter optimization methods are guided/supervised by designers' experience to carry out an iterative design optimization process. To realize automated or unsupervised filter 3D design optimization, a new method, called hybrid surrogate model-assisted evolutionary algorithm for filter optimization (H-SMEAFO), is proposed. H-SMEAFO aims to automatically obtain a highly optimal filter 3D design without designers' interaction (i.e., unsupervised) and is also not restricted to certain kinds of filter structures. In H-SMEAFO, the key innovations include a hybrid response feature-based objective function and a hybrid surrogate model-assisted global optimization algorithm; both are designed bespoke for filter design landscape characteristics. The performance of H-SMEAFO is demonstrated by an 8th order dual-band waveguide filter with 4 transmission zeros and a 6th order waveguide filter with 2 transmission zeros, for which, unsupervised design optimization does not appear to be possible using existing methods. Numerical results show the effectiveness and advantages of H-SMEAFO.

This paper presents a new accurate and efficient design methodology for complex integrated lens antenna (ILA), to achieve wide-angle beam coverage with scan loss mitigation at the millimeter-wave (mmWave) spectrum. The proposed ILA comprises inhomogeneous curvatures with internal and external center off-sets, in which multiple parameters instigate high order and non-linear behaviors. A two-dimensional (2-D) ray-tracing model is used to estimate the refractions on the elliptically curved boundaries based on geometrical optics. This approach is integrated into the particle swarm optimization of the 2-D raytracing model to determine the near-optimum geometric configuration of the ILA. Denoted as Geometric Optics-based Multiple Scattering (GOMS), the computational memory usage is reduced by a factor of 10,000 using this approach. The devised ILA achieves a wide-angle beam coverage of 156 ° with a scan loss of 2.10 dB alongside a broad impedance bandwidth of 35.0 GHz to 42.0 GHz. The measurement results for the performance of the fabricated prototype of the ILA validate the wide-angle scanning with scan loss mitigation inferred from the simulation results. This confirms the effectiveness of this method for complex design challenges involving multi-variants and restricted computational resources.