Compact Reconfigurable Band Notched UWB Cylindrical Dielectric Resonator Antenna Using Single Varactor Diode

This p aper p resents compact UWB c ylindrical d ielectric resonator antenna with reconfigurable band notch capability using single varactor diode. Theoretical results are achieved for th e d esign with the range o f f requencies 4-10.6 GHz. Using single varactor diode, different notch frequencies can be obtained using different capacitance values. The effect of changing t he varactor position is al so ex amined. A Wide range of notch frequencies can be achieved using this simple configuration, which covers most of coexisted narrow band systems. The notch frequency can be lower by increasing the capacitance value. Finite Element Method (FEM) and Finite Integration T echnique ( FIT) a re hired t o s imulate t he proposed a ntenna s tructure using H FSS and C ST M WS respectively. The n otch f requency co vers t he W LAN b and when C =0.9 pF a nd c overs t he W iMAX b and when t he capacitance i s ch anged t o 0 .8 pF f or t he s ame an tenna configuration and varactor position. The antenna with DRA has a d irective r adiation p attern i n E -plane a nd omnidirectional p attern in H -plane. A lso, the ga in i s suppressed i n t he no tched f requency. The gr oup d elay i s nearly stable in the UWB frequency range, except at the notch frequencies


Introduction
Due to Federal Communications Commission (FCC) defined UWB between 3.1 - 10.6 GHz with a band width of 7.5GHz [1].Hence, researchers have attracted for ultra-wide band r adio t echnology d ue t o i ts a dvantages s uch a s highspeed data r ate, l ow co st, s mall s ize, an d more secure [2].Planner monopole antenna is characterized by low cost, ease of f abrication, lo w p rofile, wide b andwidth, a nd h igh radiation e fficiency so th at it is o ne o f th e most c ommon UWB an tennas [3].A narrow band system as W LAN, WiMAX, a nd X -band are co existed i n t he same U WB frequency band.Recently a lot of UWB monopole antennas with single o r multiple no tch frequencies t o a void t his interference h ave been i ntroduced.The ba nd n otch characteristics ca n b e ach ieved t hrough; various s lots i n radiating p atch [4][5][6][7], s lots i n f eed lin e [8][9][10], s lots in the ground plane [11][12][13], and parasitic patches [14].The wide range and UWB features achieved by the dielectric resonator antennas ( DRAs) make t hem potential c andidates for U WB systems [ 15]. S everal U WB D RAs with a b and-stop performance have be en pr oposed.Dielectric r esonator antennas ( DRAs) ha ve s everal f eatures, i ncluding l ow dissipation loss, high radiation efficiency, various excitation mechanisms, different DR shapes, nearly constant gain, and compact a ntenna s ize [ 16].It has more s hapes s uch as cylindrical [ 17], r ectangular [18], hemispherical [ 19], a nd cylindrical r ing [ 20].H owever, t hese a ntennas ha ve f ixed band n otch c haracteristics a nd i n cas es where t here i s no interference, t hey ar e u nable t o utilize the al l o ver U WB frequency r ange.H ence, u sing r econfigurable b and no tch structure can improve the performance of the UWB system.In r econfigurable band no tch UWB a ntennas, c hanging the notch frequency is achieved by using lumped elements such as PIN diodes or varactor diodes [21][22].
Our goal i n t hi s paper , t o achi ev e a simple reconfigurable b and no tch U WB a ntenna using cylindrical DRA.A slot is made o n feed lin e to be l oaded by single varactor d iode.A w ide r ange o f f requency band-notches, which cover almost all the narrow band coexistence systems, can be obtained simply by changing the capacitance value and position.A variable capacitor or a v aractor diode instead of using single capacitor element can do reconfiguration.Finite element method (FEM) in the frequency domain and finite integration technique ( FIT) i n the time domain are us ed t o simulate the proposed structures using Ansys HFSS [23] and CST MWS [24], respectively.The proposed antenna with a directive r adiation p attern i n E -plane a nd o mnidirectional pattern in H-plane.Also, the gain is suppressed in the notched frequencies.The group delay i s the almost flat response is noticed over the operating bandwidth, which i ndicated very little distortion sharply in the notch frequency.These results ADVANCED ELECTROMAGNETICS, VOL. 7, NO. 3, AUGUST 2018 suggest t hat t he p roposed a ntenna will b e us eful widely in UWB applications.

Antenna design
The pr oposed c ylindrical D RA monopole a ntenna structure i s s hown i n F ig. 1 .The a ntenna i s p rinted on a n RO3003 dielectric substrate having a thickness of 0.75 mm with a relative permittivity of 3.Where the total size of the antenna is Wa, La.The ground plane which is on the back side with Wa, L width a nd length respectively.Cylindrical DRA with radius R and height h.Rectangular slot with length S is made i n t he micro s trip line t o f it a varactor d iode.A n SMV2019-040LF varactor from 0.

Results and discussion
In the beginning, the cylindrical DRA shape is optimized to ach ieve UWB characteristic the r eflection c oefficient i s examined.Figure 2 shows the reflection coefficient S11 with different Er.As Er decreases, the antenna has wide band width and a n ull i s f ound between 4 and 9 GHz.At E r = 13 t he antenna s et t he U WB ch aracteristics a nd h as a c ontinuous bandwidth between 4 a nd 10.6 GHz. Figure 3 demonstrates the effect of dielectric length on the reflection coefficient.As shown in fig3.decreasing the dielectric length, increasing the antenna ba nd width be yond 1 1GHz.Figure 4 ill ustrates t he effect of dielectric radius on reflection coefficient.It is clear that when R = 3.6mm t his a chieving U WB c haracteristic.Figure5 demonstrates t he e ffect o f gr ound l ength o n t he reflection co efficient.I t i s cl ear t hat when L= 9 .5mmthis achieving U WB ch aracteristic.A s ingle varactor d iode i s loaded in the slot.The varactor position is changed two times as s hown in F ig. 5 In each p osition, t he cap acitance is changed an d t he co rresponding r eflection co efficient i s stored.Figures 6-7 show the return loss versus frequency for the different capacitance values and position.In each position increasing t he cap acitance v alue, d ecreasing t he notch frequency.A wide range of notch frequencies can be obtained using t his simple c onfiguration, w hich covers m ost of t he narrow band coexistence systems.For example, as shown in Figure 5  Figure8: The simulated S11 of the proposed antenna with c=1pf using CST and HFSS

THE RADIATIONS PATTERNS, GAIN, and GROUP DELAY
In this section, the radiation pattern gains, and group delay for the Previously stated cases will be achieved.

Conclusion
In t his paper, ul tra-wide band a ntenna w ith s ingle ba nd notched characteristics has been proposed and analyzed.The UWB antenna is examined on substrate RO3003 with relative permittivity of 3 and has cylindrical D RA r adiation patch.D ifferent n otch f requencies can be obtained through make a rectangular slot on micro strip and loaded by varactor to achieve tunable notch frequencies.A wide range of notch frequencies c an be o btained using t his s imple c onfiguration, w hich covers most of the narrow band coexistence systems.The effect of the capacitance v alue o f t he v aractor d iode o n t he n otch f requency i s investigated.FEM is used to simulate the proposed antenna structure using A NSYS H FSS. T he not ch f requency c overs t he W LAN ba nd when C= (0.8-1) pf.The proposed antenna yields a directive radiation pattern in the E-plane omnidirectional t he pattern in H-plane.Also, the gain is suppressed in the notch frequency 3 pF to 1.4 pF depending on t he ap plied r everse D C voltage.The v aractor has two different p ositions a s s hown in F ig. 1 .All t his parameter shows in table1.

Figure 1 :
Figure 1: cylindrical DRA shaped UWB planar monopole antenna loaded by a single varactor diode.Table 1: The design parameters of the proposed antenna

Figure3:Figure4:
Figure2: Simulated S11 characteristics of the proposed UWB cylindrical DRA monopole antenna without slots for different E

Figure 9
shows the different radiation pattern at different frequencies 4,6,10 GHz for the proposed antenna with capacitors elements.From figure, it's clear the pattern is directive in the E-plane and omnidirectional in H-plane.The gain is shown in fig.10.AS shown in figure, the gain is suppressed in the notched frequencies at5.2GHz for given capacitor value.The group delay is shown in Figure 11.The group delay has very little variations across the operating band within a range of 1 ns, but at the notch frequency, the group delay has very sharp changes.

Figure 6 :Figure 7 :
Figure 6: S11 characteristics of the proposed antenna for different capacitance values in position one

Table 1 :
The design parameters of the proposed antenna