This article presents a low-cost, fan-shaped, tri-arm, circular microstrip antenna that is practically loaded with the three split-ring resonators (SRR) and also uses defected ground structure (DGS) to obtain ultra-wideband (UWB) performance. To compensate for the decreased value of gain because of the DGS structure, the antenna is further loaded parasitically with three split-ring resonators (SRR). The introduced metamaterial SRR triplet results in improved impedance matching and 7 dB improvement in reflection coefficient (S₁₁) at the designed frequency. This also leads to improvement in the gain of antenna and a gain of 7.16 dBi has been obtained. The paper reports 10 dB bandwidth from 1.81 GHz to 3.0 GHz which covers applications like Wi-MAX, Wi-Fi, GSM (1.9 GHz), public safety band, Bluetooth, ISM band (2.4–2.5 GHz), 3 G (2.1 GHz), 4 G LTE(2.1–2.5 GHz), WCDMA (1.9, 2.1 GHz) and other PCS applications. The measured values of S₁₁ is lower than −10 dB for the fractional bandwidth more than 48.98% and hence ultra-wideband performance has been achieved. The antenna is novel in the sense it contains three fractal rectangular arms in the basic circular patch. The addition of arms in patch increases the overall electrical length, which results in improvement in overall bandwidth.

An edge fed, dual band, quarter-wave transformer coupled, monopole, ultra-wideband (UWB), dodecagon-shaped miniaturized frequency reconfigurable antenna for ISM and wireless applications is designed, analysed and investigated. The impedance transformer is utilized in the structure for impedance matching and hence results in lower reflection coefficient values. The antenna uses defected ground structure (DGS) in the bottom and radiating patch that is practically loaded with three numbers of delta structures. The use of DGS reduces the value of gain and provides ultra-wideband bandwidth across the designed frequency. The addition of three delta structures in the patch improves the value of gain. Miniaturizing in the size of the antenna has been achieved by reducing the ground along the width that led to a total 30.41% size reduction in the fundamental circular patch antenna. The antenna exhibits two bands 1.82–3.61 GHz and 5.24–12.43 GHz thus antenna is suitable for ISM band, PCS, 5G, Wi-Fi/WiMAX/WLAN and other wireless applications. The fabricated antenna is frequency reconfigured by utilizing the switching property of four numbers of PIN diodes (BAP64-02V). Frequency reconfigurable antenna is used flexibly and versatile for various microwave applications based on the switching conditions (more than eight digital combination cases) of PIN diodes. The prototype measured results provide good agreements with the simulated reflection coefficients values in some mode of operations. Antenna radiating patch and ground is etched on FR-4 substrate of dimension 52 mm × 59 mm × 1.6 mm using printed circuit board technology.

This study introduces a novel antenna based on the binary operation of a modified circular patch in conjunction with the Koch fractal. The antenna is intended for applications in the sub-6 GHz band, partial C-band, and X-band. The low-cost antenna is fabricated on a 1.6-mm-thick FR-4 substrate. A frequency-selective surface (FSS) is used to overcome the decreased values of the gain and bandwidth due to the fractal operations. The introduced split ring resonator (SRR) and the antenna substrate dimension reduction reduce the bandwidth and antenna gain. The air gap between the FSS and the antenna not only enhances the antenna gain but also controls the frequency tuning at the design frequency. The antenna size is miniaturized to 36.67%. A monopole antenna ground loaded with an SRR results in improved closest tuning (3.44 GHz) near the design frequency. The antenna achieves a peak gain of 9.37 dBi in this band. The FSS-based antenna results in a 4.65 dBi improvement in the gain value with the FSS. The measured and simulated plots exhibit an excellent match with each other in all three frequency bands at 2.96–4.72 GHz. These bands cover Wi-MAX (3.5 GHz), sub-6 GHz n77 (3300–3800 MHz), n78 (3300–4200 MHz), and approximately n79 (4400–4990 MHz), in addition to C-band applications.

This paper presents a low-loss, high-transmission, broadside-coupled, transverse, reciprocal, two-port, and nature-inspired Ka-band transition design to move the electromagnetic energy of a rectangular waveguide (RWG) to the microstrip (MS) line. The proposed transition is simple in structure, with an excellent insertion loss, S₁₂/S₂₁, (IL) near −0.40 dB and return loss, S₁₁/S₂₂, of <−21 dB, while the VSWR value is very close to one. Thus, this transition is an outstanding candidate for MIC/MMIC-based millimeter wave, military, and RADAR applications, as well as in wireless and satellite communications as a compatible connector. This transition also provides a bandwidth of 21.50 GHz (23.52–45.0 GHz) for the abovementioned microwave applications, at a <−10 dB return loss (RL). The proposed transition model also exhibits a −15 dB absolute bandwidth of 27.06–23.44 GHz, with an insertion loss < −0.60 dB. Due to a return loss of <−15 dB over an ultra-wide bandwidth, the proposed transition is not only a good candidate for full Ka-band (26–40 GHz) applications but also covers applications for K-band from 23.74 GHz to 26.0 GHz, Q-band applications from 33.0 to 45.0 GHz, and U-band applications from 40.0 GHz to 45 GHz, with approximately 97% power transmission between the transmission lines and only 3% power reflections. The impedance matching at the designed frequency between the RWG and MS line is achieved by flaring one end of the MS line inside the RWG in a fishtail shape, without the need for a quarter-wave/tapered/exponential/Binomial, or multi-section Chebyshev transformer. The main goal of this research was to design a multi-section impedance-transformer-free, simple, and easy-to-fabricate MS line, to share electromagnetic (EM) energy between an MS line and RWG in 30 GHz satellite applications and 30 GHz high-frequency applications, for interconnects screen printed on an organic substrate for flexible, wearable, textile conformal antennas. This work also presents an exact RLC electrical equivalence model of the MS line (fishtail) to RWG transition at 30 GHz. The novelty of this work is that the proposed transition can be used for four microwave bands of electromagnetic energy transmission, with extremely low reflection, and with a compact, simple-design MS line, and simple RWG.

This article demonstrates the design and development of WR-15 transition using an antipodal microstrip dipole antenna at a frequency of 60 GHz for space applications. An inline microstrip line to rectangular waveguide (MS-to-RWG) transition is proposed for the V-band (50–75 GHz) functioning. The RF energy is coupled and launched through an antipodal dipole microstrip antenna. Impedance matching and mode matching between the MS line and dipole are achieved by a quarter wave impedance transformer. This results in the better performance of transitions in terms of insertion loss (IL > −0.50 dB) and return loss (RL < −10 dB) for a 40.76% relative bandwidth from 55.57 GHz to 65.76 GHz. The lowest values of IL and RL at 60 GHz are −0.09 dB and −32.05 dB, respectively. A 50 μm thick double-sided etched InP substrate material is used for microstrip antipodal dipole antenna design. A back-to-back designed transition has IL > −0.70 dB and RL < −10 dB from 54.29 GHz to 64.07 GHz. The inline transition design is simple in structure, easy to fabricate, robust, compact, and economic; occupies less space because the transition size is exactly equal to the WR-15 length; and is prepared using an InP substrate with high permittivity of 12.4 and thickness of 50 μm. Thus, the devices have the lowest insertion loss value and lowest return loss (RL) value, of <−31 dB, as compared to earlier designs in the literature. Therefore, the proposed design has the lowest radiation loss (because of thickness) and highest transmission (about 97% power). Easy impedance matching using only a single-step quarter-wave transformer between the antipodal dipole antenna and 50 Ω microstrip line (avoiding the multi-sections’ demand and microstrip line’s tedious complexity) is needed. Since, when the InP dielectric substrate is inserted in WR-15, the waveguide becomes a dielectric-filled waveguide (DFWG), and its characteristics impedance reduces to 143 Ω from 505 Ω at an operating frequency of 60 GHz. In the proposed transition, no ridge waveguide or waveguide back-short is utilized in WR-15. The microstrip line did not contain any via, fence, window, screw, galvanic structure, post, etc. Hence, the transition is suitable for high-data-rate 5G communications, satellite remote sensing, missile navigation, MIC/MMIC circuits’ characterization, and mm-wave applications. The electrical equivalent model of the proposed design has been generated and validated using an RF circuit simulator and was found to have excellent matching.