Design and development of 2 kW, 3 dB tandem hybrid coupler for the frequency range of 155–225 MHz has been presented in this paper. The developed 3 dB coupler is to be used in a prototype of Ion Cyclotron Resonance Frequency (ICRF) system of Tokamak, which has been developed to test the resilience of ICRF network during continuously variable RF load excursions. The 3 dB coupler divides the RF power between two antennae of the prototype and protects the RF source by coupling of reflected power to the isolated port. The developed coupler shows excellent coupling flatness of −3 ± 0.3 dB over 38% of fractional bandwidth and also provides voltage standing wave ratio (VSWR) <1.3, isolation better than 32 dB and return loss better than 25 dB in full band. The presented work establishes a technique which can be useful for the development of high-power hybrid coupler in the range of high frequency (HF), very high frequency (VHF) and ultra high frequency (UHF).

A series of novel wideband filtering power dividers (WFPDs) with wide stopband rejection performances is proposed in this paper. The proposed WFPD structure consists of a parallel-coupled line, two transmission line (TL) sections, four loading terminations, and an isolation resistor. The coupled line is applied at the input port to provide wideband impedance transformation, while different types of loading terminations and TL sections are adopted to realize various out-of-band rejection performances. To verify the proposed concepts, three WFPDs operating at 3.0 GHz are designed and fabricated with 3 dB bandwidth of 79.7, 79.0, and 74.4%. In WFPD1, the measured out-of-band rejection of better than 13.4 dB extends to 2.57f0. Moreover, the measured out-of-band rejection of better than 17 dB extends to 2.47f0 (4.75f0) in WFPD2 (WFPD3), respectively. Good agreements between the simulated and measured results validate the presented ideas.

In through the wall imaging systems, wall parameters like its thickness and dielectric constant play an important role in the true and correct image formation of an object behind the wall made of various materials like brick cement, wood, plastic, etc. Incorrect estimation of these parameters leads to dislocation of the object and smearing or blurriness of the image too. A new autofocusing technique for a stepped frequency continuous wave -based radar at the frequency of 1–3 Ghz has been developed that corrects the wall's parameters like its thickness and dielectric constant and provides a better focused image of the target. For this purpose, a peak signal to noise ratio -based autofocusing technique has been developed by using curve fitting and the genetic algorithm. It is observed that the proposed technique has capability to focus the image up to good extent.

Electromagnetic wave of enemy radar propagated by troposcatter is a valuable candidate for beyond line-of-sight detection. There is no analytical study considering the operating range of passive troposcatter detection system. In this paper, we study the way to predict the operating range, which is dominated by propagation loss. The key propagation loss models including statistic model and real-time model are analyzed. During deducing the latter loss model, Hopfield model is introduced to precisely describe the tropospheric refractivity. Meanwhile, rain attenuation is also taken into consideration. Several examples demonstrate the feasibility of predicting operating range through the proposed method.

This paper presents a cavity-backed dual-slot antenna in 0.13-μm SiGe BiCMOS technology. The dual-slot structure is excited by a cross-shaped strip line and a cavity which is formed by the topmost metal layer connected to the bottom metal layer through vias in between. By adopting dual-slot and cross-shaped feed line, the bandwidth is significantly enhanced by 196% compared with the single-slot antenna with straight feed line. The reason for bandwidth enhancement has been analyzed. The proposed antenna shows a measured impedance bandwidth of 15.2 GHz from 248.2 to 263.4 GHz for |S11| < −10 dB. The simulated and measured peak gains of the cavity-backed dual-slot antenna are −1.3 and −2.1 dBi, respectively. The simulated radiation efficiency is 31.1%. The total size of the antenna is 0.46 mm × 0.48 mm.

A compact circularly polarized antenna with wide axial ratio bandwidth (ARBW) using quasi-self-complementary (QSC) structure is presented. A 3-dB ARBW is achieved by shortening the ground plane of the QSC structure. Furthermore, the wide ARBW is obtained by the introduction of a stepped stub in the extended ground plane of the QSC structure. The antenna is fabricated on a FR4 substrate with the overall dimensions of 25 mm × 22 mm × 0.8 mm. The proposed antenna has an impedance bandwidth of 5.9 GHz (2.4–8.3 GHz, 110%) and 3 dB ARBW of 1.6 GHz (2.4–4 GHz, 50%). A peak gain of 1–3 dBi is observed within the 3 dB ARBW.

The paper researches a kind of wideband dual-polarized Vivaldi antenna with improved balun feed which consists of slot line and two bent coplanar strip lines. The whole of antenna structure is composed of two orthogonal Vivaldi antenna elements, and the mode of feeding adopts electromagnetic coupling from micro-strip line to slot line. The improved balun can avoid the intersection of transmission lines, reduce the size, and simplify the assembly. The electromagnetic simulation and optimization design of proposed antenna are carried out by using electromagnetic simulation software, CST. Simulation results show that the isolation between two polarized ports is more than 15 dB within working frequency range of 2–3.5 GHz and VSWRs of two ports are lower than 2.5 at the range of 2–3.5 GHz. The designed antenna is fabricated and measured. The measured results indicate that the designed antenna achieves anticipated patterns and feasible design of the dual-polarized Vivaldi antenna. The dual-polarized Vivaldi antenna with improved balun feed is suitable for some application fields, such as passive electronic reconnaissance, passive radar, and wideband communication and detection.

In this paper, a novel low-profile planar monopole internal antenna for GSM/DCS/PCS/ IMT/UMTS/WLAN/ISM/LTE operation in the mobile phones is designed and developed. The proposed antenna is composed of multi-branches, F-shaped slots in the system ground plane and tapered feeding line which can improve the impedance matching at the feeding point. The antenna occupying a small area of 18.5 × 46 mm2 is placed on the top no-ground portion of the system circuit board, which makes it suitable for practical mobile applications. A prototype of the proposed antenna is fabricated and tested. In addition, the planar monopole antenna can provide two wide lower and upper bands to respectively cover the frequency range of 848–1152 MHz, and 1736–3000 MHz, for the GSM850/GSM900/DCS1800/PCS1900/IMT2000/UMTS2100/WLAN2400/ISM2450/LTE2300/LTE2500 operation in the mobile phone. Good radiation patterns and antenna peak gain for frequencies over the operating bands have been observed. The antenna is simulated and designed by using Ansoft HFSS and CST Microwave Studio. Details of the antenna design, results on the reflection coefficient, radiation characteristics, directivity, antenna gain, realized gain, and efficiency of the antenna are given and discussed. Finally, the specific absorption rate (SAR) of the proposed antenna placed at the bottom of the mobile phone is also investigated. The obtained SAR values meet the limit of 1.6 W/kg for the 1 g head tissue and 2.0 W/kg for the 10 g head tissue.

A simple design for triple-band circularly polarized (CP) wide slot antennas is proposed and experimentally investigated. The proposed antenna having a microstrip-fed rectangular patch with T-shaped notch for triple-band operation and a modified wide square slot on ground plane for CP operation. The measured 10 dB reflection bandwidths are 1.24% (≈340 MHz from 2.56 to 2.9 GHz), 9.63% (≈430 MHz from 4.25 to 4.68 GHz), and 5.34% (≈490 MHz from 8.93 to 9.42 GHz). The generated 3 dB axial ratio bandwidths of the proposed antenna are 7.54, 8.98, and 1.65% at operating frequencies around 2.65, 4.45, and 9.09 GHz, respectively. The measured peak gains within the 3 dB axial ratio bands are 3.03, 3.5, and 5.64 dBi. The simulated and measured results for the return loss, axial ratio, and antenna gain show a good agreement, which validate the antenna design.

A planar inverted F-Antenna with the dual band-dual polarization property is presented for medical body area networks applications. The designed antenna covers the 2.45 GHz industrial, scientific and medical, 4 G long term evolution (2.5–2.69 GHz) bands for ON body communication and Wi-Fi and WLAN (3.5–3.6 GHz) bands for OFF body communication. At the lower band, an equivalent offset fed magnetic microstrip type dipole has been utilized that generate field parallel to the surface of the body for supporting ON body communication. The broadside radiation pattern has been realized using the slotted patch counterpart for supporting OFF body communication. This technique has resulted in a design of dual band dual mode property using a single radiator. The footprint of the antenna is only 0.35λg × 0.17λg × 0.08λg. Owing to its compactness, lightweight, and easy mountable property (due to foam substrate), the proposed antenna is found to be robust for MBAN applications. The maximum permissible transmitted power for the 1st band is 25.78 and 20.3 dBm for the 2nd one to maintain standard specific absorption rate limitations of 1.6 W/Kg. Experimental investigations over human body showed minimal deviations from the free space conditions which makes it a potential candidate for body-centric communications.

A novel low profile dual band patch antenna is presented. It consists of a composite right/left-handed transmission line (CRLH TL) unit cell gap coupled with the radiating edge of a rectangular patch antenna. The dual band behavior is achieved by coupling the zeroth order resonance mode of CRLH TL and TM10 mode of the patch antenna. It is shown that frequency ratio can be changed by varying the gap between the patch and CRLH TL unit cell. The proposed configuration enables frequency reconfigurability by changing the CRLH TL unit cell using a switch. A prototype of the antenna having frequency ratio f2/f1 = 1.08 is designed and fabricated. The proposed antenna shows measured S11 ≤ −10 dB bandwidth of 100 and 50 MHz at resonance frequencies of f1 = 4.84 and f2 = 5.22 GHz, respectively. A 2 × 2 dual band CRLH TL coupled patch array is also presented, showing more than 12.7 dBi gain at both resonance frequencies.

In this study, the implicit Crank–Nicolson finite-difference time-domain (CN-FDTD) method is applied to discretize the governing telegrapher's equations of a composite right-/left-handed (CRLH) coupled-line coupler. The unconditionally stable CN-FDTD is compared with the conventional leap-frog (LF) FDTD method. The results obtained from the CN-FDTD scheme show up to 10 times increase in the temporal step size, reflecting in a dramatic decrease in processing time; in addition to having a good agreement with the LF method and the measurements.