Shahrokh Jam

Bio: Shahrokh Jam is an academic researcher from Shiraz University of Technology. The author has contributed to research in topics: Wideband & Antenna (radio). The author has an hindex of 12, co-authored 42 publications receiving 485 citations. Previous affiliations of Shahrokh Jam include Shiraz University.

Improved Radiation Performance of Low Profile Printed Slot Antenna Using Wideband Planar AMC Surface

Abstract: In this paper, a novel design of low profile printed slot antenna using wideband artificial magnetic conductor (AMC) is presented with improved radiation performance. For this purpose, the radiating slots with three unequal arms fed by coplanar waveguide are employed for broadening the impedance bandwidth with three resonances. It achieves a wide impedance bandwidth in the measured frequency range of 7.96–12.56 GHz ( $S_{11}\leq -10$ dB) for X-band applications. By loading a novel wideband planar AMC surface as the antenna ground plane, the radiation properties of this printed slot antenna are enhanced. This design includes the measured −10 dB impedance bandwidth from 5.75 to 14.51 GHz (86.48%). The proposed wideband planar AMC design operates at the frequency of 10.15 GHz with ±90° reflection phase bandwidth of 8–12.38 GHz (43.15%). The AMC surface is designed with the $5\times 8$ array of periodic patches which are developed underneath the broadband printed slot antenna. In comparison with the proposed design without AMC, the printed slot antenna loaded with AMC introduces 62.82% size reduction, a bandwidth enhancement of 41.65%, and better impedance matching. It also contributes considerable features like a low profile antenna with unidirectional radiation patterns and an increased gain of more than 10.6 dBi.

Optimum design of tapered slot antenna profile

Abstract: The optimum design of the tapered slot antenna (TSA) profile and geometry is achieved through its modeling by a stepline terminated in free space intrinsic impedance. The impedance matching of the TSA input impedance (obtained by the transmission matrix properties) to the generator impedance is achieved by minimizing an error criterion constructed as the magnitude squared of the difference between the generator and input impedances over the desired bandwidth. The attenuation constant of the stepline is computed by the broadside radiation of TSA (which is an endfire antenna) and the longitudinal power flow. The spectral domain immitance approach is used to compute the broadside radiation, by first determining the electric field components in the slot by the Galerkin's method and then obtaining the equivalent magnetic surface current densities. The power flow in the endfire direction of TSA may be computed by the Poynting's vector in the substrate. The attenuation constant is calculated for various values of slot width. Finally, the minimization procedure gives the slotline widths and lengths.

Enhanced Bandwidth of Shorted Patch Antennas Using Folded-Patch Techniques

Abstract: This letter introduces novel designs of miniaturized wideband microstrip patch antennas for ultrawideband (UWB) applications. The antennas are achieved by using folded-patch feed's techniques and shorting pins to provide the impedance bandwidths $({\rm VSWR} \leq 2)$ of 94.17% (4.13–11.48 GHz) and 98.22% (3.57–10.46 GHz), respectively. By introducing a folded ramp-shaped feed, the impedance bandwidths of the proposed antennas are considerably enhanced. Shorting pins are utilized to miniaturize the size of the patches. In the first design, unequal arms fed by a folded ramp-shaped patch produce three resonances to broaden the impedance bandwidth. Also at the second design, by adding one pin in the center of the shorted patch with a folded ramp-shaped feed, a broadband antenna is obtained. In addition, the wideband mechanism of the proposed antennas is described and discussed by investigating the effects of some key parameters.

Miniaturised asymmetric E-shaped microstrip patch antenna with folded-patch feed

Abstract: A design of probe-fed compact wideband microstrip patch antenna which is configured of an asymmetric E-shaped patch, a folded-patch feed and shorting pins, is presented in this study. In this design, unequal resonance arms fed by a folded patch produce three resonances to broaden the impedance bandwidth. Shorting pins are applied to miniaturise the size of the patch. The performance of broadening the impedance bandwidth is explored by investigating the behaviour of the surface currents on the patch. The antenna presents resonance tuning ability within the impedance bandwidth by varying the length of unequal arms. The measured -10 dB impedance bandwidth of the fabricated antenna is 76.18% from 3.34 to 7.45 GHz for ultra-wideband applications. The size of this antenna is 0.379 λ L × 0.145 λ L × 0.078 λ L , where λ L is wavelength at the lower frequency of the measured operating bandwidth in the free space. Fabrication of this antenna is less complex than similar wideband antennas with folded-patch feed. In addition, parametric studies are performed by investigating the effects of different key parameters on obtaining an optimal design of the proposed antenna design.

A compact triple-band dual-element MIMO antenna with high port-to-port isolation for wireless applications

Abstract: In this literature, a compact planar triple-band multiple input multiple output (MIMO) antenna with two monopole elements is presented. Each element includes a defective complementary open-loop resonator (COLR), two slots on both sides of the feedline, two stepped stubs and a monopole ground plane. This structure operates in the frequency bands of 2.22–2.54 GHz, 3.14–3.9 GHz and 5.3–5.7 GHz for WiFi, WiMAX and WLAN applications, respectively. The antenna is not based on a common ground plane, so antenna is low cost and compact. High measured isolation is achieved which is better than 34 dB in all operating bands without using additional decoupling structure. An equivalent circuit model is proposed to investigate the behaviour of the antenna. The envelope correlation coefficient of antenna is less than 0.001 and diversity gain is about 10. The proposed MIMO antenna is fabricated and there is a good agreement between the experimental measurements with the simulation results.

Modified Compact Antipodal Vivaldi Antenna for 4–50-GHz UWB Application

Abstract: A novel way capable of improving low-frequency performance of Vivaldi antennas is presented in this paper. Traditional Vivaldi antennas are modified via introducing the loading structure, i.e., circular-shape-load or slot-load, to match the termination. This modified antenna has been demonstrated to have the impedance bandwidth of over 25:1. It also exhibits symmetric radiation patterns in both the E- and H-plane in addition to the gain varying from 3 to 12 dBi in the measurement bandwidth of 4-50 GHz.

Improved Radiation Performance of Low Profile Printed Slot Antenna Using Wideband Planar AMC Surface

Abstract: In this paper, a novel design of low profile printed slot antenna using wideband artificial magnetic conductor (AMC) is presented with improved radiation performance. For this purpose, the radiating slots with three unequal arms fed by coplanar waveguide are employed for broadening the impedance bandwidth with three resonances. It achieves a wide impedance bandwidth in the measured frequency range of 7.96–12.56 GHz ( $S_{11}\leq -10$ dB) for X-band applications. By loading a novel wideband planar AMC surface as the antenna ground plane, the radiation properties of this printed slot antenna are enhanced. This design includes the measured −10 dB impedance bandwidth from 5.75 to 14.51 GHz (86.48%). The proposed wideband planar AMC design operates at the frequency of 10.15 GHz with ±90° reflection phase bandwidth of 8–12.38 GHz (43.15%). The AMC surface is designed with the $5\times 8$ array of periodic patches which are developed underneath the broadband printed slot antenna. In comparison with the proposed design without AMC, the printed slot antenna loaded with AMC introduces 62.82% size reduction, a bandwidth enhancement of 41.65%, and better impedance matching. It also contributes considerable features like a low profile antenna with unidirectional radiation patterns and an increased gain of more than 10.6 dBi.

Self-Folding Origami Microstrip Antennas

Abstract: This communication presents antennas that incorporate self-folding polymer substrates that transform planar, two-dimensional structures into three-dimensional antennas when exposed to a light source. Pre-strained polystyrene sheets supporting a patterned copper foil form the light-activated structures. Black ink that is inkjet printed on the polymer substrate selectively absorbs light and controls the shape of the transformation. This approach represents a simple method to reconfigure the shape of an antenna and a hands-free method to assemble 3D antennas from many of the conventional methods that are used to pattern 2D metal foils. We demonstrate and characterize two embodiments that highlight this concept: a monopole antenna that transforms from a conventional microstrip transmission line and a microstrip patch antenna that converts within seconds into a monopole antenna.

A Survey and Study of Planar Antennas for Pico-Satellites

Abstract: Works on pico-satellites have gained momentum recently, especially those that consider pico-satellites as part of a much larger constellation or swarm. This feature allows pico-satellites to provide high temporal resolution of observational data and redundancy. In particular, it reduces the need for satellite-to-ground communications and, hence, helps save energy and allows the execution of distributed processing algorithms on the satellites themselves. Consequently, satellite-to-satellite or cross-link communication is critical. To realize these advantages, the cross-link antenna employed on pico-satellites must meet many criteria, namely, small size, lightweight, low-power consumption, high gain, wide bandwidth, circular polarization, and beam steerability. To date, no works have examined the suitability of existing planar antenna designs for the use on pico-satellites. To this end, this paper contributes to the literature by focusing on microstrip patch and slot antennas that have the ability to achieve high gain, beam steering, and wide bandwidth. This paper reviews 66 planar antenna designs, which includes 38-patch and 28-slot antennas. In addition, we provide an extensive qualitative comparison of these antennas in terms of their mass, size, gain, beam steerability, type of polarization, operating frequency band, and return loss. In addition, we have evaluated three antenna designs that best address the pico-satellite challenges on a common platform. We find that the asymmetric E-shaped patch antenna design is the most suitable for the use on 2U CubeSats. This is because of its small size ( $34\times 13$ mm $^{2})$ and high gain (7.3 dB). In addition, the E-shaped patch antenna yields a wide −10-dB bandwidth of 2300 MHz and a small return loss of −15.2 dB.

A Meta-Surface Antenna Array Decoupling (MAAD) Method for Mutual Coupling Reduction in a MIMO Antenna System

Abstract: In this paper, a method to reduce the inevitable mutual coupling between antennas in an extremely closely spaced two-element MIMO antenna array is proposed. A suspended meta-surface composed periodic square split ring resonators (SRRs) is placed above the antenna array for decoupling. The meta-surface is equivalent to a negative permeability medium, along which wave propagation is rejected. By properly designing the rejection frequency band of the SRR unit, the mutual coupling between the antenna elements in the MIMO antenna system can be significantly reduced. Two prototypes of microstrip antenna arrays at 5.8 GHz band with and without the metasurface have been fabricated and measured. The matching bandwidths of antennas with reflection coefficient smaller than −15 dB for the arrays without and with the metasurface are 360 MHz and 900 MHz respectively. Using the meta-surface, the isolation between elements is increased from around 8 dB to more than 27 dB within the band of interest. Meanwhile, the total efficiency and peak gain of each element, the envelope correlation coefficient (ECC) between the two elements are also improved by considerable amounts. All the results demonstrate that the proposed method is very efficient for enhancing the performance of MIMO antenna arrays.