Bandwidth Enhancement of L-Probe Proximity-Fed Annular Ring Microstrip Slot Antenna Abstract— A parametric study and simulation of wide-band orthogonally slit cut annular ring microstrip antenna (SC- ARMSA) fed by an L-shaped probe is investigated using Modal expansion cavity model and circuit theory concept. The radiating patch is located about 8mm (~0.1λ) above the ground plane. The broadband characteristic of antenna is achieved by employing a thick substrate (~0.1λ) of 1.07 relative permittivity (Rohacell Foam). The annular ring patch is cut ortogonally with slot of 1mm width. The E- and H-plane radiation pattern are presented and VSWR is compared with the simulated result. Good agreement is obtained between computed and simulated results. The effects of the geometric parameters of the L-strip like length of the horizontal portion of the strip are investigated. An impedance bandwidth of about 36.76% and 33.23% (VSWR < 2) at 13.5 mm and 15 mm length of horizontal L-probe respectively. Keywords- microstrip antenna; wide-band microstrip antenna; L- probe proximity fed microstrip antenna; wireless communication; I. INTRODUCTION With the definition and acceptance of the ultra wide-band (UWB) impulse radio technology in the USA [1]. Recently, the Federal Communication Commission (FCC)’s allocation of the frequency band 3.1–10.6 GHz for commercial use has sparked attention on UWB antenna technology in the industry and academia. Several antenna configurations have been studied for UWB applications [2–4]. The impedance bandwidth of a microstrip antenna depends primarily on both the thickness and the dielectric permittivity of the substrate. A thick substrate with a low dielectric permittivity can increase the bandwidth of the printed patch. Both these selections could be a solution of the problem of bandwidth enhancement[5]. Simultaneously these solution pose difficulties in integration of the antenna with other microwave circuits, and cause some other problems such as the surface wave propagation and the large inductive image part of the input impedance of the antenna, which makes its resonance unfeasible. Thus, a reasonable thickness should be considered in the selection of substrate and the bandwidth would be enhanced using additional techniques. The most common and effective of them are the loading of the surface of the printed element with slots of appropriate shape. The attractive features of annular ring microstrip antenna motivated the investigators [6-12]. The annular ring microstrip antenna is a popular antenna because of its small dimensions compared to other microstrip antennas resonant at the same frequency [13]. The L- probe proximity fed annular ring microstrip antenna is simple in structure and have been investigated [13-14] for various ultra wide-band system and other communication systems. In this paper, the L-probe proximity fed annular ring microstrip antenna with orthogonally loading of the surface of the printed element with slots is investigated using Modal expansion cavity model and circuit theory concept. Characteristics including VSWR, and radiation pattern are considered. II. THEORETICAL ANALYSIS Geometry of the L-probe proximity fed annular ring microstrip antenna with orthogonally slit loaded is shown in Fig. 1. The broadband performance of the proposed antenna is achieved by employing a thick substrate. In our design, a Rohacell foam layer (ε r = 1.07) of thickness 8 mm is used to support the radiating patch. Without L-probe, it is difficult to couple the energy from the microstrip line to the patch as the separation between them is too large. Therefore a step, which is designated as an L-probe. The horizontal part of the L-probe of y 0 incorporated with the patch provides a capacitance to suppress the inductance introduced by the vertical part of the L-probe. Fig. 1. Geometry of L-probe proximity-fed annular ring microstrip antenna with slit inserted. The vertical part of L-probe is equivalent to a series combination of resistance (R s ) and inductance (L s ). The resistance R s is because of finite conductivity of copper used. The expression for the resistance R s and inductance L s are given by [15] h 1 h2 H Z Y X Patch ground plane L-probe w s y0 b a side view top view A. K. Singh, (Research Scholar) Electronics Engineering, Indian School of Mines, Dhanbad, India. Email: anilei76@gmail.com. Ravi Kumar Gangwar Electronics Engineering, Indian School of Mines, Dhanbad, India. Email: ravi8331@gmail.com Binod K. Kanaujia Electronics and Commn. Engg., AIACTR, Gita Colony, Delhi, India Email: bkkanaujia@yahoo.co.in