An X-band substrate integrated waveguide (SIW) balun, based on a Y-type divider with enlarged bandwidth, is presented in this study. In most SIW Y-type dividers, the undesired TE₃₀ mode either leads to the deterioration of the in-band reflection or constrains the bandwidth by a transmission zero. The cause of the transmission zero is analysed and the modes coupling, rather than the step impedance matching, is utilised to reduce its impact. In the traditional Y-type divider, the frequency band is split by this transmission zero, while in the proposed wideband configuration, the co-existences of the TE₁₀ and TE₃₀ modes are employed to combine the two non-contiguous bands. A broadband balun is designed and fabricated, with the improved Y-type wideband divider serving for the power-dividing part. The dividing ports are connected to the reversely placed transitions, achieving inherent out-of-phase performance and good amplitude property. The measurement of the balun suggests a 43.94% bandwidth from 8.23 to 12.89 GHz, with 15 dB return loss. The measured amplitude and phase imbalance between two output ports are below 0.7 dB and ±3°, respectively. The performance of the fabricated balun is in agreement with the simulation, and it is promising for wideband applications.

A reconfigurable balanced bandpass filter with constant absolute bandwidth (ABW) and high common-mode (CM) suppression by using the interdigital coupling compensation circuit structure is presented here. The odd- and even-mode equivalent circuits of the presented balanced bandpass filter are presented and analysed. The differential mode and CM signals are misaligned by the half-wavelength resonators, which are coupled by interdigital coupling circuit to improve the coupling coefficient and decrease the circuit dimension. Changing the voltage of the four varactors, which are placed at two ends of the half-wavelength resonators with interdigital coupling circuits, can tune the coupling coefficient and resonant frequency at the same time. A tunable balanced bandpass filter with ABW is designed and realised. The measured results indicate that the differential-mode tuning centre frequency range extends from 0.97 to 1.72 GHz, the 3 dB ABW is 80 ± 5 MHz, and the CM suppression is >30 dB in the differential-mode operating passband. Experimental results are in good agreement with the theoretical and simulated ones.

Bow-tie antennas are widely used in practical ground-penetrating radars. In spite of simple structure and wideband characteristics, boresight gain of the antenna is small and the radiation pattern is omnidirectional. In this study, a cavity-backed bow-tie antenna with dielectric loading is presented. The bow-tie antenna is resistively loaded to reduce ringing effects. The resistively loaded antenna is placed within a rectangle cavity, which acts as a reflector, for unidirectional radiation and high gain. A dielectric is loaded on the antenna aperture to enlarge the operational bandwidth and stabilise the radiation patterns. Parameter studies of the dielectric substrate are performed to optimise the antenna performance. The final design is fabricated and measured. It has been shown that the antenna exhibits wide impedance bandwidth of 120% for . The boresight gain is more than 5 dBi. The radiation patterns are stable and unidirectional over the whole band, and the late-time ringing is small.

The capability of the capacitively loaded loop (CLL) metamaterial (MTM) superstrate to attenuate surface waves thereby reducing the back radiation of microstrip patch antennas is examined. To understand the surface wave suppression mechanism, theoretical approaches of a grounded dielectric slab waveguide is provided. Both theoretical and numerical analyses show that the proposed superstrate causes a drastic attenuation of surface wave propagation. To confirm the numerical simulations, the proposed antenna is fabricated and tested. The dimensions of the CLL-MTM covered patch antenna are 0.6λ × 0.8λ × 0.14λ. The radiated gain and efficiency are measured at 7.8 dB and 95%, respectively. Measurements show that the front-to-back ratio is enhanced by more than 12 dB. In comparison with the patch antenna without the CLL-MTM superstrate, the proposed antenna reduces the gain and efficiency by less than 0.1 dB and 2%, respectively.

Electromagnetic (EM) simulation tools are of primary importance in the design of contemporary antennas. The necessity of accurate performance evaluation of complex structures is a reason why the final tuning of antenna dimensions, aimed at improvement of electrical and field characteristics, needs to be based on EM analysis. Design automation is highly desirable and can be achieved by coupling EM solvers with numerical optimisation routines. Unfortunately, its computational overhead may be impractically high for conventional algorithms. This study proposes an efficient gradient search algorithm with numerical derivatives. The acceleration of the optimisation process is obtained by means of the two mechanisms developed to suppress some of finite-differentiation-based updates of the antenna response sensitivities that involve monitoring and quantifying the gradient changes as well as design relocation between the consecutive algorithm iterations. Both methods considerably reduce the need for finite differentiation, leading to significant computational savings. At the same time, excellent reliability and repeatability is maintained, which is demonstrated through statistics over multiple algorithm runs with random initial designs. The proposed approach is validated using a benchmark set of wideband antennas. The proposed algorithm is competitive to both the reference trust-region algorithm as well as its recently reported accelerated versions.

The parabolic equation (PE) method and finite-difference time-domain (FDTD) method are combined to predict long-range Loran-C additional secondary factors (ASFs) in situations with near-source complex topography. The non-uniform FDTD method is employed in the complex source region, while the PE method is used for propagation over smooth terrain to a long distance. By using the advantages of each algorithm, the hybrid FDTD–PE approach is capable of modelling the near-source topographic details, while saving much computational resources as compared to a full FDTD solution. Numerical results along several paths are used to validate the hybrid algorithm. Furthermore, the hybrid method is applied to analyse the effect of near-source topographic complexities, including non-flat land, land–sea transition, and island (cliff)–sea transition, on the navigational coverage for the planning of the Loran-C systems.

This study presents the realisation of reactive impedance surface (RIS) in an implantable environment to design a compact wideband antenna for biotelemetry communication. The antenna is designed to operate at 2.45 GHz industrial, scientific and medical (ISM) band using a one-layer skin model. The proposed mushroom-based circular RIS successively improves the impedance matching, gain, and bandwidth of the antenna. The improvement in −10 dB impedance bandwidth and gain is observed by 270 MHz and 7 dB, respectively. The overall volume of the antenna is compact and measured only 99.69 mm³. The peak specific absorption rate value of the loaded antenna is noted at 595 W/kg for input power of 1 W, while the radiation efficiency of the antenna is noted by 7.5% at the resonance. The fabricated prototype is inserted into the minced pork and dipped into a skin mimicking gel for the measurement purpose. Furthermore, the link margin has been analysed, which predicts a possible transmission range up to 40 m for a signal bit rate ≤5 Mbps. The impact of associated circuit components on the antenna performance has also been investigated.

In this study, a rhombus-shaped patch antenna is proposed using metamaterial transmission line. The motivation of this work is to overcome the problem of low gain while designing miniaturised antennas. The proposed design is based on coplanar waveguide feeding technique. A rhombus-shaped patch is chosen in this structure in which striplines are provided to connect the ground planes and to obtain the shunt inductance. Asymmetric meandered line inductors are integrated with the striplines for miniaturising the electrical size of the antenna. Further to improve the gain of the antenna in the lower bands, asymmetric ground plane and complementary closed ring resonator have been employed in the proposed structure. The electrical size of the proposed antenna is 0.168λ ₀ × 0.151λ ₀ corresponding to the physical size of 25 mm × 22.5 mm, where λ ₀ = free space wavelength at 2.02 GHz. Considering below −10 dB input reflection coefficient, this antenna operates in three bands covering 1.96–2.07, 4.06–4.72, and 6.43–7.79 GHz. In addition, the proposed antenna exhibits gain of 1.49, 2.68, 2.19, and 4.31 dB at 2.02, 4.48, 6.72, and 7.43 GHz, respectively, in the maximum direction of radiation.

A new set of symplectic operators for the symplectic multi-resolution time-domain (S-MRTD) method is obtained by using the time reversible constraint and the growth factor. Then, the perfectly matched layer absorbing boundary condition based on splitting field technique is introduced into the S-MRTD method and its iterative formula is derived. The stability and numerical dispersion of S-MRTD method with optimised symplectic operators are discussed in detail. Finally, the optimal S-MRTD method is applied to the calculation of electromagnetic radiation and scattering. Numerical calculation and simulation results show that the S-MRTD is more accurate and efficient than the traditional FDTD method.

A novel differentially fed fractal antenna coated with a layer of a dielectric film and operating at two bands of Medical Implant Communication Services 402–405 MHz and Industrial, Scientific, and Medical 2.4–2.48 GHz, is investigated to enable sufficient data transmission rates, while featuring a ‘mode-control’ signal to prolong the battery life. The symmetrical fractal technology of Hilbert curve is employed to miniaturise the dimension. To facilitate interfacing with peripheral integrated circuits, differentially feeding is adopted. To demonstrate how common-mode noises are suppressed, for the first time, a detailed analysis about the noise suppression of the differential configuration with two feedings is presented. A layer of thin film is coated around the proposed antenna to isolate the effect of human tissues and alleviate the electromagnetic coupling with human body. Moreover, to draw a design methodological guideline, the key geometrical parameters are analysed numerically and theoretically. Health safety considerations, radiation performance, and link budgets are also discussed to validate the proposed antenna's applicability in biomedical telemetry.

Original work on direction of arrival (DOA) estimation relied on uniform linear arrays (ULAs) of antennas. Most of the work focused on improving the algorithms and the configuration of the antenna array and overlooked the effects of practical antennas on the algorithm performance. Very limited work studied DOA estimation within the physical limitations of handheld devices. In this work, we introduce three nonuniform linear coprime arrays based on patch and monopole antenna elements operating in 2.1 and 5.8 GHz bands and assess their behaviour in DOA estimation. The complex radiation patterns of the arrays were incorporated in the DOA estimation algorithm using compressed sensing (CS). Estimation accuracy is quantified by the root mean square error (RMSE) and the results are compared with those obtained by using isotropic antennas, showing that physical antennas can introduce up to 8° of error. Simulations were also carried out using the multiple signal classification (MUSIC) algorithm to demonstrate the advantage of CS in coprime arrays. The MUSIC algorithm failed to detect all sources even at maximum SNR. The impact of reducing the fundamental inter-element spacing in coprime arrays below to achieve smaller array sizes is investigated as well.

A multiple-input–multiple-output (MIMO) microstrip patch antenna array of four elements is proposed to cover the 5.8 GHz WLAN band. The characteristic mode analysis is carried out to design a defected ground structure that improves the MIMO performance without impacting negatively the radiation characteristics of the four-element array. Simulations and measurements demonstrate that the implemented prototype reaches a maximum mutual coupling of −32 dB and a gain-per-element of 5.3 dB with good MIMO attributes, surpassing many other proposals in the antenna literature: maximum envelope correlation coefficient of 0.0001, diversity gain very close to 10 dB, capacity loss near to 0.0023 bps/Hz at the resonant frequency, multiplexing efficiency of 0.935, and a total active reflection coefficient weakly dependent on the excitation phases. The presented design is proposed for operation on the IEEE 802.11a/n standard.