Performance Analysis of Slotted Monopole Antenna with Pin Diodes for Wireless Applications

This paper deals with Performance Analysis of slotted monopole antenna with pin diodes for wireless applications. The antenna is designed on a 1.6 mm thick FR4 substrate with the dielectric constant (εr ) of 4.4. Antenna is electrically reconfigured incorporating pin diodes as switching elements to tune desired frequency and to achieve frequency reconfigurability. The antenna parameters like return loss, bandwidth, radiation pattern, directivity and gain are simulated and characterized in this paper. The proposed antenna covers resonating frequencies ranging from the 3.7-13.4GHz. The proposed microstrip monopole frequency reconfigurable antenna can be considered as electrically small, low weight, low profile. The design and analysis of the proposed antenna is accomplished through HFSS EM simulator.


Introduction
Modern wireless system structures usually have more than one standard in order that they require modern-day antenna structures with multiple skills and capabilities without enlarging occupied volume. The reconfigurable antenna becomes a popular answer as it presents variety in antenna performance to fulfill various communication necessities and reduce the interference [1]. Single antenna can be used for multipurpose application by way of changing their parameter which includes frequency, pattern or polarization [2]. With multiband capability, reconfigurable antennas can make use of extra efficaciously radio frequency spectrum, facilitating a better get right of entry to wireless services in modern radio transceivers [3]. Responding to the ever-increasing antenna bandwidth needs, significant effort is currently under way to improve multiband antennas. For all of these applications, frequency reconfigurable multiband antennas are attractive where it is advantageous to have a single antenna which can be dynamically reconfigured to transmit and/or receive on multiple frequency bands.For these structures, mainly planar designs are chosen because of their added benefit of small scale, low cost of manufacture and conformability. PIN diode design and manufacturing technology for RF circuits has had a substantial positive effect on the frequency reconfigurable antennas [1]. For an antenna reconfigurable for frequency [2],the challenging task is to connect the radiating elements together, such that the resulting module will have desired operating frequency bands, or in other words to determine which switches to turn ON / OFF, so that a specific set of elements will be active to make the structure operating at desired frequency bands.In this paper , an attempt was made to integrate the technique of electrical reconfigurability to decide the RF switches to be made ON / OFF to make the antenna resonate at specified frequencies. The formulations produced are measured and are observed with satisfactory results.

Problem formulation
A performance analysis of slotted monopole antenna with pin diodes for wireless applications is designed on a substrate of FR4 dielectric material with thickness of 1.6mm and dielectric constant ( ) of 4.4 [4]. The size of the substrate is 40X47mm. The radiating element constitutes two monopole arms associated with two radiating patches. The design on the bottom side having partial ground plane with 40X10mm with two inverted F shaped slots. The radiating elements which are fed with a 50Ωmicrostrip feed line with the length of 12.5 mm and width of 3.3 mm below the microstrip feed line [6]. Two pin diodes have been deployed between the two arms and the associated radiating patches to attain the frequency reconfiguration on biasing them to ON/OFF. The proposed antenna operates at a frequency range 3.7-13.4GHz providing multiband operations.
The proposed antenna is designed and simulated in HFSS EM simulator and observed with acceptable parameters to accomplish frequency reconfigurability with multiband operations. The rest of the research work is organised in the following section. In section 3, the designed antenna geometry specification, in the section 4, the simulation and results, in section 5, the paper is concluded.  Table 1 gives dimensions of the proposed. The antenna consists of radiating patches incorporated with PIN diodes o the top plane, partial and truncated ground plane on bottom, The patch is designed on a 1.6mm thick FR4 substrate (with dielectric constant =4.4 and loss tangent =0.019). In order to obtain the monopole characteristics and better gain the ground as been truncated with two inverted F shaped slots [6].

. Proposed antenna design (a)Front view (b)Rear view A. Formulation
To design the conventional patch antenna following formulae were used:  To find the width of the patch, The proposed antenna is fed with Microstrip feed line with a line impedance (Z 0 ) of 50Ω. Equation (6) and (7) and 0r 377 B 2Z p e   To design the Length ( ) and width ( ) of ground plane: The length and width of a substrate is equal to that of the ground plane. The length of a ground plane ( ) and the width of a ground plane ( ) are calculated using the following equations. 6 Lg h L  (9) 6 Wg h W  (10)

B. Design of PIN diode
The pin diode was modelled using lumped element s in HFSS. The corresponding circuit was shown i n Fig.2 for both ON state (Forward bias) and OFF state (Reverse bias).

Simulation and results
The proposed antenna for performance analysis of slotted monopole antenna with pin diodes for wireless applications [9] is designed and analyzed using the Finite Element Method ( FEM) used in HFSS to solve the equations of electromagnetic waves in time and frequency domains.To solve the EM wave or Maxwell equation in the time and frequency domain, the proposed compact dualarm reconfigurable microstrip planar monopole with truncated ground plane for c, x and ku band applications is constructed and simulated using the EM simulator which is HFSS v 15.0. Lumped port is assigned to the microstrip line for excitation of the antenna. Return loss, gain, radiation pattern and current distribution were analysed in this design. For perfect impedance matching, the reactance should be negligible and impedance should be 50 Ω.The simulation is done with respect to four switch states .state A, state B, state C and state D. State A considered to be the condition when both pin diodes in OFF condition, state B represents pin diode 1(the left side of from top view of Fig (1) is OFF and pin diode 2 is ON, state C represents pin diode 1 is ON and pin diode 2 is OFF and State D represents both pin diodes are in ON condition.   The 3 D view of a gain total in all the directions is shown in Fig .6. The observed 3-D radiation patterns for all the 4 views were plotted. The pattern of radiation is the relative distribution of the radiated power in function of direction. In thefarfield area, the pattern of radiation is usually determined.

Conclusion
In this paper, performance analysis of slotted monopole antenna with pin diodes for wireless applications is designed and optimized in HFSS. The proposed antenna exhibited characteristics of frequency reconfigurability to operate in multifrequency and multiband by changing the state of RF PIN diodes. The proposed antenna is simple to design and fabricate and exploits two PIN diodes for switching in to different bands. The proposed antenna covers a wide 3.7-13.4GHz frequency range. The antenna is showing the omnidirectional radiation pattern with monopole character, better impedance matching and satisfactory gain is achieved with tunable frequencies for various wireless applications.