Chapter 3

The Square Monopole Antenna

Monopole antennas are used in communication systems at a wide range of

frequencies. Electrical properties of these antennas are dependent upon the

geometry of both the monopole element and the ground plane. The monopole

element is either electrically short with length much less than a quarter-wavelength

or near-resonant with length approximately a quarter-wavelength. This clement

can be thin with length-to-radius ratio much greater than 104 or thick with

length-to-radius ratio of 101 - 101 . In addition. the ground-plane dimensions

may vary from a fraction of a wavelength to many wavelengths [\Veilwr, 20O::~1.

Traditionally, a monopole geometry consists of a vertical cylindrical element at

the center of a perfectly conducting, infinitely thin. circular ground plane in free

space. Electrical characteristics of such antennas are primarily a function of

only three parameters: the element length, clement radius, and the ground-plane

radius, when each is normalized to the excitation wavelength. Radiation pattern

of such antpunas are uniform in the azimuthal direction.

U\VB monopole antennas fall in to volumetric and non- vol umetric categories

based on their structures. )JOll volumetric U\VB antennas are lllicrostrip pla­

nar structures evolved from the volumetric structares. ,vith different matching

techniques to improve the bandwidth ratio without loss of the radiation pattern

properties.

33

34 CHAPTER 3. THE SQUARE MONOPOLE ANTEN'IVA

3.1 Volumetric UWB Antennas

Volumetric U\VB antennas date from the days of spark gap systems. In 1898.

Oliver Lodge disclosed spherical dipoles, square plate dipoles, bi--conical dipoles

and bow -tie dipoles [Lodge, 1898] and int.roduced the concept of a monopole

antenna with earth as the ground. A renewed interest in the wide band antennas

led to the rediscovery of biconical and conical monopoles by Carter in 1939

[CarteL 1939aJ. Carter improved upon Lodge's original design by incorporating a

broadband transition between a feed line and radiating elements [Cartf'l', 1!)39bJ.

The complete analysis of these antenna.s can be found in [StutZllIHU, H.d.J.

Another remarkable invention is the classic "volcano smoke antenna developed

by Kraus in 1945, a deta.iled report of which can be found in [Lp\:, Palllsell,

2003]. This antenna topology offers exceptional bandwidth and azimuthal omni

directiollali ty.

Sleeve monopole configurations [StutZlllCill. luLJ excited using a coaxial

transmission line exhibit broad band radia.tion behavior. The sleeve exterior acts

as a radiating clement while its interior a.ct.s as the outer conductor of the feed

coaxial transmission line.

Stohr proposed t.he use of ellipsoidal monopoles and dipoles [Stohr, 1968J

which was re -discovered in [:.: ara~'all Prasad AgarwalL 199~]. This paper presents

t he extensive analysis carried out on square, rectangular and hexagonal disc

mOllopole antennas in addition to the elliptical design.

Square/ rect.angular monopole antennas are inherently bandwidth limited

and in order to improve the bandwidt.h, various techniques were proposed. In

[Lee E., 1999J. it was demonstrated t.hat. when a shorting pin is added to a planar

monopole antenna, an additional mode is excited belo,,, the fundamental mode.

By optimizing the dimensions 50% size reduction is obtained when compared to

an equivalent planar monopole without a shorting pin. In [Anoh P. V., 20(H].

two techniques are presented; offset feeding and the use of orthogonal square

monopoles on a. circular base to obtain wi(k band response and omnidirectional

radiation.

The use of beveling technique [AlllllH-lllll. 2001] and that of a shorting pin

[Anllll<lllll. 2003] can improve the overall impedance bandwidth of square monople

antennas. In [AntoIlillo-DClviu E.. 200:5J the use of double feeding and in [Kin-

3.1. VOLUAfETRIC U\VB ANTEi\lNAS 35

Lu \Vong. 200Sbj, 3 t.rident shaped feeding is proposed to improve the impedance

bandwidth of such antennas.

Effect of finite ground plane on the impedance band\vidth of planar monopole

antenna was studied in [Saou-\Ycll Su, 200-1]. Their study shows that the first

resonance is greatly affected by t.he ground plane and t hat there exists an optimal

diameter of the circular ground plane for achieving a maximum impedance

bandwidth. Large ground-plane effects on the radiation pattern and antenna

gain are also st.udied in this paper. especiall~' for t.he lmver frequencies in the

antennas impedance handwidth.

In [Kin-Lu Wong, 200,1b], a metal-plate monopole of inverted-L shape with

a ma.tching tuning portion is mounted at t.h(~ top edge of the supporting metal

frame to create an ant.enna with ultra wide bandwidth. Impedance bandwidth

of this antenna is from 1.89-10.14 GHz. A modified version of this antenna is

proposed in [Kin-Lu \Vong, 200-1aj. with bandwidth from 1.890·- 6.450 GHz t.o

integrate with laptops a.s it covers the U~ITS (1.920 - 2.170 GHz) and \VLAN

(5.150-5.350/ 5.725-5.875 GHz) bands.

To improve the impedance bandwidth. wide slots are embedded in the rectan­

gular monopole in [Valdera~ D., 2005]. The slots created additional I'e~onances

and the a.chieved bandwidth rat.io is 1 : 3.75.

In [Saou-'Ven Su, 2005a], a . U' shaped slot is incorporated to a square planar

antenna wit.h beveling to reali~e band Hotch to forbid interference with the IEEE

802.11a and HIPERLA~/2 systems. An annular slot inside the same monopole

effectively notched out the 5.15-5.35 and 5.15 5.825 GHz bands with a VS\VR

> 14 as demonst.rated in [.JinIlllling (lilt, 200G]. In [Kin-Lll \Yong, 200ficl] an arc

shaped slot is incorporated in to a circular disc monopolc autenna to achieve the

band notch. The length of the arc controls the frequency that is being not.ched.

To design a rectangular monopole antenna with improved bandwidth, a 'U'

shaped metal plate lllonopole in implement.ed in [Saou-\VPll Su, 200Gb].

In [XUClll Hili \Vu, 200fi] , t.he charact.eristics of four planar dipoles are studied.

Pulses radiated in different directions arc presented in this paper for bot h single­

band and multi-band schemes in U\VB applications.

In [CIWll. 2005] the design of broad band hi-arm rolled IIlollopole antenna.

constructed by wrapping a planar monopole is present.ed and its transfer response

have been analyzed.

36 CHAPTER 3. THE SQUARE JIONOPOLE ANTEI'n\lA

The coupled sectorial loop antenna in [1\ a.cler Bchdad, 2005] achieves ultra­

wide bandwidt.h t.hrough a magnetic coupling of two adjacent sectorial loops. The

antenna exhibits 8.5:1 frequency range with a VS\VR lower than 2.2. Dimension

of this antenna is smalk>r than 0.37 Ao at the lowest frequency of operation and

has consistent radiation pattern throughout the band.

The monopole in [Ka-Lcllug Lau, 2005] is formed by connecting four trape­

widal plates orthogonally. A circular patch which is short.ed to the circular

ground plane by four shorting wires is placed at the top of the Illonopole. The

antenna posses 10 dB bandwidth of 138 9C which is about 49 times that of the

corresponding monopole wire-patch antenna.

In [Vald(~rns D., 2006] a design process for improving the bandwidth of beveled

planar monopole antennas has been proposed by studying movements over the

Smit.h chart. The involved Illonopole variables WE're the height. the width. the

bevel angle of the lower edge. t.he feeding length, and the capacitance \vith the

ground plane. These parameters are conveniently combined t.o implement. a u\\rB

antenna with a frequency-independent bandwidth greater than 1 : 37 for VS\VR

< 2. The radiation patterns are nearly constant and omnidirectional at the

represent ativc frecllwncies.

The antenna optimization proposed in [I\ikoJay Tdzhell:-iky. 2006] makes use

of t.he genetic algorit.hm and is based on the time domain characteristics of the

antenna. Optimization procedure presented in t.his paper aims at finding an

antenna with low VS\VR a.nd low-dispersion to ensure high correlation bet'\veen

the time-domain transmitting antenna input signal and the receiving antenna

output signal. This procedure has been applied to a simplified version of the

volcano smoke antenna proposed by Kraus. and can be extended to any other

type of U\VB antenna.

In [Georg(' TholllCls K .. 2006J. the authors proposed a new ultra wide band,

sleeved transmission line-fed rectangular planar disc IIlonopole antenna with a

small ground plane. Objective of the authors was t.o design a. monopolE' antenna

with improved radiation performance than existing ones. The antenna offers an

ultra broadhand performance in the frequency band 0.5 9.0 GHz with a VS\VR

of less than 2.5 : 1.

Certain U\i\'B applications such as a win~less dongle require antennas ('on­

stricted in space and an ant.enna design suit able for such applications were

3.2. NON- VOLUMETRIC U\VB ANTE.NNAS 37

proposed in [Saou-\Veu Su, 2007]. This compact ant.enna comprises a L-shaped

rectangular monopole element and a matching section and is relatively easy t.o

fabricate. In [Jae\voong Shin. 2007] yet another design can be found suitable

for UWB dongle applications. In [Sa.oll- \Ven (St.ephell) Sl1. 2007] the antenna

is mounted at the top portion of the PCB and one end of the radiating arm is

short-circuited to the system ground plane. \Vith the proposed antenna st.ructure,

wide operating band,vidth of larger than 7.6 GHz is obtained that easily cover

the 3.1-10.6 GHz band.

In [In'IW Ang. 2007] design of a double layer. probe- proximity coupled. stacked

diamond-shaped microstrip patch antenna is proposed with ultra wide bandwidth.

The authors have shown that broad band characteristic can be achieved by exciting

all the higher order modes in the microstrip patch antenna simultaneously by

shorting the ringing tail through simple capacit.or coupling. The proposed antenna

has an impedance bandwidth of 101.8 % for VS\VR < 2.

A compact wide band folded-shorted antenna is presented in [Giuseppe Ruvio,

2007] that employs different impedance bandwidth enhancing techniques together

to cover the U\VB spectrum. The microstrip feed of the antenna is printed on FR4

and a folded t.hin metallic sheet is connected to the printed element and shorted

across the full length of the ground plane. This grounding significantly enhances

the impedance bandwidth and helps to mitigate the effect of the asymmet.ry due

to the offset feed arrangement

An omnidirectional mono pole antenna shaped by symnwtTically wrapping a

PEC sheet that. has two trapezoidal cut.s at the bottom corners is proposed in

[Xuan Hili \VIl. 200~1. It has an extremely wide impedance bandwidth of 132

% while keeping an omnidirectional and wide band radiation over the 3.1-10.6

GHz band. Finite ground plane of this antenna int.roduces ripples in the gain

versus frequency response which can be estimated by a simple expression with

the knowledge of ground plane size. Furthermore. the ripples can be removed by

resistively loading the edge of the ground plane.

3.2 Non-Volumetric UWB Antennas

As already mentioned, non-volumetric U\VI3 antennas are microstrip planar

structures evolved form the volumetric strnctures. In [Sdwntz H. G., 2001],

38 CHAPTER 3. THE SQUARE I\10NOPOLE A1'v'TENNA

the diamond and in [Lu G., 2003], the rounded diamond antennas have been

shown to have wide-band properties suitable for ultra wide band applications.

In [Gllofeng Lu, 2004]' theoretical analysis. simulation::; and experiments are

all conducted to further characterize these two antennas in terms of radiation

pattern. gain versus frequency and impedance properties.

U\VB on-body propagation channel measurements \vere performed in [Alo­

mainy A., 2005J to study the deterministic channel characteristics. A printed

horn shaped self- complementary antenna and a planar inverted cone antenna

were investigated for their effects on the channel behavior. Results show that the

hybrid use of different types of UWB antennas can effectively improve channel

behavior in body-centric wireless networks.

In [Low Z. :\.,2005]. a monopole a.ntenna is proposed where the authors used

three techniques to realize compactness and wide bandwidth: dual slots on the

rectangular patch. a tapered connection between the rectangular patch and the

feed line and a partial ground plane flushed with feed line. This antenna shows

stable characteristics over the f'ntire U\VB frequency band.

The correspondence [Clwn Ying, 2005] presented a planar antenna in low­

temperature co- fired ceramic technology for a single -package solution of U\VB

radio. The antenna has an elliptical radiator fed through a microstrip line. The

radiator and the microstrip line share the same ground plane with the other U\VB

radio circuitry. The prototype antenna has achieved bandwidth of '" 110% from

3 10.6 GHz with broad patterns, and relatively constant group delay.

The printed circular disc monopole antenna fed by microstrip line is investi­

gated [.Tiallxill Liallg, 2005j. Impedance band width of this antenna is from 2.78

- 9.78 GHz and the first resonanc'c has becn well account.ed numerically. The

antenna has been cha.racterized in the frequency and time domains.

In [.Tocri It Vf'fhif'sL 200S], a new antenna topology is pn~sented bascd on

the' printed tapered monopole antenna.. A slot is added in the tapered radiating

clement. and in t he ground plane, t.o yield wide band b~~havior and good matching.

The matching performance and the pulse distortion of t.he antenna in th(~ presence

of human tissue are also studied.

In [Y1l-.Jill11 RPlI, 20()(j]. an annular ring is electromagneticall~' coupled to

nmlize U\VB. Ground plane of the microstrip line is removed beneath the annular

ring and the -10 dB impedance bandwidth of the antenna. is from 2.8 to 12.3

3.2. NON-VOLUMETRIC U\VB ANTENNAS 39

GHz. Radiation patterns are stable within the operating bandwidth with an

average antenna efficiency of 81 %.

In [Yildirilll. 200G], a. microstip fed, small, low profile, branched monopole

antenna is presented with ultra wide bandwidth. By adjusting the branch length

and/or adding another brauch, the design can be adapted for \VLAN, BIuetooth

and UWB applications. However, asymmetry in the geometry of the antenna has

affected the radiation pattern, which is slight.ly modified from omnidirectional.

A double-sided rounded bow-tie antenna with ultra wide bandwidth is propm;ed

in [Tu t ku Karacoi<lk, 2006]. The authors have shown that ant.ennas with rounded

patches provide wider bandwidth with higher co-polarization and lower cross­

polarizat.ion levels for the U\VB range compared t.o their fiat-end counterpart.s.

In [Shi-Wpi QIl. 200Gj an ultra wide band a monopole antenna wit.h rounded

corners is proposed. By introducing a coplanar waveguide resonant cell. the

proposed antenna could notch the \VLAX bands for a VS\VR > 10. This compact

antenna operates from 2.67 to over 12 GHz. and shows omnidirectional radiation

pattern.

The proposed antenna design in [Pe.Vl'ot-Solis ~1. A., 20()(j] uses the beveling

technique for both t.he radiator and the ground plane so as t.o provide necessary

feed gap betwE'en them to achieve widp impedance bandwidt h.

In [Young .lUll Cho, 2006]. a staircase shapE' is incorporated in the ll1onopole

element and t.he ground plane is redesigned to realize a U\VB antenna wit h a

compact configuration of 25x26 mm2. l\Ieasured bandwidt.h of the antenna is

from 2.9-14.5 GHz and a detailed chara.cterization in t.he frequency and time

domains have been presented.

In [),Iichit.Hka AUH'ya, 200G]. design of planar broadband antellnas consisting of

self-complementary radiating elements and a tapnred microstrip line is proposed.

Deta.iled FDTD analysis of thes(~ antennas are also prescnted in this paper.

In [Knr'<lllloto, 200(j]. design of a planar radiator that does not require a large

ground is presented. The design consists of large and small ellipt.i('al elcments in

parallel arrangemcnt. To reduce mutua.l coupling between t.hese elements and to

improve impedallcc bandwidth, an elliptica.l slot is designed in the large elliptical

element.

In [ShUIl-YlIll LiB. 200G], a pentagon ~haped monopole is proposed with ultra

wide bandwidth. By embedding a.n inverted V-shaped slot along the boundary of

40 CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

this antenna, controllable notch has been demonstrated.

Design of textile antennas for U\VB wireless body area network (\\lBAK)

applications is presented in [:"Ia.ciej Klcml1l, 2006]. The proposed coplanar

waveguide fed printed monopole and U\VB annular slot antennas offer direct

integration into clothing due to Cl very small thickness (0.5 mm) and flexibility.

The antennas cover the 3.1--10.6 band and the transfer functions are comparable

to the PCB reali2ation. The authors have successfully transmitted very short

pulses using textile antennas.

Design of the printed-circuit antenna in [Rambabu K., 200G] uses a stepped­

patch in combination with multiple resonating elements to realize a bandwidth

of more than 150%. The authors have performed a phase center analysis which

shows very small variations over the entire available bandwidth.

In [Sadlill Gnpta, 2006]. microstrip and CP\V bfh'"ied configurations of planar

invert.ed conical antennas are presented and compared for U\VB systems. Design

of these antellnas follo,vs a third order polynomial equation and hence can be

designed easily.

A variation of the defected microstrip structure technique is employed to

enlarge the baIHhvidth of a planar ultra wide-band monopole in [Pe~T()t-S()lis

t\l. A., 2007]. By introducing a defect in the mierostrip feed line, the lov·:er

bandwidth limit is lowered without affecting the antenna gain and radiation

pattern. The bevel technique in the ground plane near to the feeding point is used

to increase the highest bandwidth limit. The 50 x 50 mm2 planar oIIlnidirectional

antenna has a voltage standing wave ratio 2 from 2.1 to 12.3 GHz.

In [;\ts(}lHjcrh C. A ZE'lllli , 2007], a compact crescent.-shape microstrip antenna

is proposed, evolved from the elliptical patch antenna by carving a circular hole

inside symmetrically. The circular aperture introduces an additional antenna

in-band resonance and provides wider bandwidth with more design flexibility.

Radiation properties of this antenna is similar to the full elliptical antenna, with

409(', reduction in area (GO(X of the ellipse area). The characteristic current modes

on the crescent antenna are identified and design equation are derived for the

lowest frequency of operation of this antenna_

In [Fram'is Jacoh K., 2007]. different branches arc top loaded on a planar strip

mOllopole and dimensions of the branches are optimized for U\VB performance.

The antenna shows 10 dB return loss from 3.1 - 9.6 G H~ and Illonopole- like

3.2. NON- VOLUl\,IETRIC Un'B A1\lTENT

NAS 41

radiation. The proposed antenna of dimension 65x35 'fnm2 can fit into the present

day mobile hand sets of typical dimension 100 x 45 mm2 .

The broadband mirrostrip-fed printed antenna proposed in [Eldek, 2007]

for phased antenna array systems consists of two parallel-modified dipoles of

different lengths. Tlw regular dipole shape is modified to a quasi-rhombus shape

by adding two triangular patches. A modified array configuration is proposed

to further enhance the antenna radiation characteristics and usable bandwidth.

The proposed antenna provides end fire radiation patterns ,vith high gain. high

front-to-back ratio, low cross-polarization level, wide beam width. and wide

scanning angles in a wide bandwidth of 103 %.

In [.Jin-Ping Zhang, 2007]. a microstrip fed semi-elliptical dipole antenna is

proposed and designed to cover the 3.1 10.6 GHz UvVB. Radiation patterns are

similar to those of a conventional dipole antenna with dimension only about one

third of the wavelength instead of half wavelength at the lower frequency. \Vith

simple and proper modification of the patches, a. frequency-notched antenna is

also designed.

In [Zhi King Chen, 2007]' a small printed antenna is described with n~duced

ground-plane effect. The radiator a.nd ground plane of the antenna arc etched

on a printed circuit board \""ith an overall size of 25 x 25 mm2 . A notch is cut

from the radiator and a strip is asymmetrically attached to the radiator. The

antenna achieves a broad operating bandwidth of 2.9-11.6 GHz for a lO-dB

return loss. Effect of the ground-plane on the impedance bandwidth is greatly

reduced by the notch in the radiator because the electric currents on the ground

plane are significantly suppressed at the lower edge operating frequencies. The

antenna features three-dimensional omni-directional radiation wit.h high radiation

efficiency of 79-95o/c across t.he U\VB band,vidth.

In [Yi-'\lin Lu, 2007]' ultra wide band antenna is designed using a double­

printed circular disc. Reasonable theoretical analysis of the antenna has been

carried out in this paper.

A simple design of a printed circul~tr monopole antenna with band-not.ch

characteristic is presented in [Chih- Yu Huaug. 2007]. Frequency notch in this

antenna is created by cntting a pie-shaped slot on the circular radiating patch.

A parametric study of t.he printed elliptical monopole antennas is presented in

[Anoh P. V .. 2001]. Based on this, design equations are derived for these antennas

42 CHAPTER 3. THE SQUARE MONOPOLE ANTE1VNA

which are validat(~d by measurements.

A planar shorted dipole antenna capable of generating a 9:1 bandwidth (820-

7340 :\JHz) is presented in [\Vei-Yu Li, 2007J. The radiating element consists

of two C- shaped radiating arms occupying a compact area of 0.30A x 0.47 A,

where A is the wavelength of the desired lower edge of the band of operation. In

addition to the use of C-shaped radiating arms, which reduces the total length

of the proposed antenna when compared to the case of using straight radiating

arms, the short circuiting of the two radiating arms further effectively decreases

t he lower frequency with a fixed antenna size.

In [Thyh-Ghu8.ng :\la, 2007], to achieve band-rejection at the \VLAN bands,

strips of t.he fork shaped monopole are folded back to result. in a pair of coupled

lines on the radiator. Based on the band-notched resonance, an equivalent

circuit model is proposed for the antenna and the calculated antenna input

admittance has been shown to agrees with the full-wave simulation dat.a. Using the

normalized antenna transfer function, the radiation characteristics are investigated

thoroughly. Th(~ transmission responses of a transceiving antenna system and

their corresponding transient analysis are also discussed in this paper.

The lov.·'cr edge curve of a monopolc antenna is a.n important parameter in

determining the impedance bandwidth. In [Chillg \\'('i Ling, 2007], a new edge

curve chara.cterized by the binomial function is proposed. The effect on the

impedance bandwidth with different order of the binomial function and the gap

between the antenna and ground plane has been investigated in this paper.

Impacts of the 3.1-10.6 GHz on-human-body UWB channel on the impulse

radio wireless body area network system has been studied in [Yu(=' Ping Zhang,

2007]. A performancf~ evaluation method is presented in this paper for the realistic

U\VB-\VBAN systems. which observes the waveform distort.ion along the signal

path. Measurement. and characterization of the 3.1-10.6 GHz on-human-body

U\VB channel are devised to generate the radiographs of path loss and delay

spread for the first time in this paper. The study shows that the human body

effect is more significant than environment effect when thf' propagation channel

contains no line-of-sight path. Various candidate pulse shapes and modulat.ion

schemes for U\VB \VBA:\ are studied and their performances \vith t he measured

vVBA:\ chamwl arc evaluated and compared.

In [Ching-Hsing Lno, 2007], Cl dual band-notched CP\V fed monopole antenna

3.2. NON-VOLUMETRIC U\VB ANTENNAS 43

is proposed where a ring in the feeding structure is used to incn~ase the impedance

bandwidth. Two quarter-wavelength tuning stubs inserted into the feeding ring

and radiating ring: respectively, creates two band-notches at 5.15 and 5.75 GHz

across the U\VI3 from 2.6 - 12 GHz. The novel design is quiet compact and

suitable for creating U\VB antenna with dual narrO\v frequency notches.

In [Keyvan Bahadori, 2007], an elliptic-card ultra wide band planar antenna is

proposed. The design consists of an elliptic radiating element and a rectangular

ground plane. The feeding mechanism comprises of a microstrip line on the ot her

side of the substrate and connecting the line to the elliptic element by a via. The

structure of t h8 ant8Ima is miniaturized by optimizing its elliptic profile and the

required ground plane size is only 22x 40 m.m2. Housing effects on the antenna

performance arc also studied in this paper.

In [Vi Diug: 2007], a very compact elliptical monopole antenna with a size of

35x20 mm2 is designed with ultra wide bandwidth. \\ride impedance match is by

two matching slits at the lower section of the elliptical patch. In addition. using

a slot and embedded resonant cell, the authors have demonstrated band notch at

5.5 GHz.

The CP\V fed band-notched antenna proposed in [Sang-Ho Lee, :2007] uses

tilt steps of two different sizes for improving band width and two folded strip

lines for band notch.

The antenna proposed in [Chong Yu Hong: 2007] consists of Cl radiation patch

that has an arc-shaped edge and a part.ially modified ground plane. The ground

design comprises of two bevel slots on the upper edge and two semicircle slots at

the bottom edge of the gronnd plane to improve the input impedance bandwidth

and the high frequency radiation performance. By embedding a pair of T -shaped

stubs inside an elliptical slot ('ut in the radiation patch, a notch at 5.5 GHz is

obtained.

In [Reza Zaker. 2()()~]. a novel modified microstrip-fed ultra wide-band planar

monopole antenna with variable frequene:y band-notch characteristic is presented.

By inserting two slots in the ground plane on both sides of the microstrip feed

line, wide impedance bandwidth is produced. A modified H-shaped conductor­

backed plane with variable dimensions is uSt~d in order to generate the frequency

band-stop performance and control band-notch frequency and bandwidth. The

designed antenna has a small size of 22x22 rnm 2 and operates over the frequency

44 CHAPTER 3. THE SQUARE i\IO}'lOPOLE ANTENNA

band between 3.1 and 14 GHz for VS\VR < 2 while showing tlw band rejection

performance in the 5.1 to 5.9 GHz ff(~quency band.

The antenna design proposed in this chapter is a planar square monopole with

redesigned ground plane to opera.te in the ultra wide band. As already mentioned,

typical design practice to achieve U\VB with a square/ rectangular patch is by

beveling, parasitic strips or by employing multiple feeding, which may add t.o

the design complexity. The proposed design is novel by introducing Cllts in the

ground plane that. follow specific design guidelincs. From a parametric study,

design equations arc obtained to facilitate designing the antenna on laminates

of any permittivity. A band notch scheme is also proposed to limit. radiation

in the \VLA="J band. Studies conducted on the frequency domain radiation

characteristics of the prototype a.nt.enna is also present.ed in this chapter.

3.3 Antenna Geometry, Design and Optimization

3.3.1 Geometry

Geometry of the square monopole antenna is shown in Figure :L 1 and the ('orre­

sponding parameters in Table ;j.l. This antenna. shows a single resonance as in

Figure :~.2 in accordance with a quarter wave variation in h. Figure 3.2(a) shO\vs

the effect of the ground plane in this resonance and Figure 3.2(b) that of the gap

between the ground plane and the square patch. It. is clear that these parameters

affect only the matching of the antenna.

To design this antenna for ultra wide bandwidth, the design procedure outlined

in Figure 3.:3 is followed. As shown in Figure 3.:3(a), the ground plane \vith length

1 is divided in to 9 equal sections having ·width wand few sections in the ground

plane arc removed. This antenna can be designed with a microstrip feed either

as in Figure :3.3(b) or Figure :3.3(c). The return loss plots of these antennas are

shown in Figure 3.,) and the resonances are indicated in Table 3.l. Antenllas-b.(',J

with modified ground plane have wide impedance bandwidth and among them,

Ant.-b exhibits a superior performance in terms of the overall bandwidth. It has

been seen, hov-.'ewr, that hy adjusting l, d and w. impedance bml(hvidths of

Antenna-c and d call be improvecl. A variation study performed \vith 'W is shown

in Figure 3.4. As w is increased, the second and third resonances merge and

improve the -lOdB bandwidth. Since the resonances shift to the Imver side of the

3.3. ANTENNA GEOMETRY, DESIGN AND OPTIMIZATION

• .,.

~ ·10

" • .,. ... .,.

2 •

-.-, , , , , , \ B , , , , _...,.:t---, \' , \b\ , , , , , ,

I _ _ J.-... ----

, -------~ ,,_----------L

Figure 3.1: The square monopole ant.enna (Ant.-a) .

• .,. ----.,.

-1- Uull! - d " O.lS Iml

- / - 14 11111 .,. - d - O.50nm / - 161ml si - O.7Snm

- 1- 18 1m1 ... - J - I 001Tl1l - / - 2Qtml -d-UOrrm

.5O

• 8 ,. 12 .. 16 " 2. 2 • • • 10 12 " Frequency, GHz Frequency, GHz

(.) (b)

45

16 " ,.

Figure 3.2: Effect of (a) ground plane on the resonance, d ~ 0.5 (b) gap between

tbe ground plane and the square patch, I ~ 16 (c) Effect of the variation of w on

the return loss (in mm)

spectrum with increase in UJ, it should be fixed at an optimum value that give

maximum bandwidth.

For the work presented ill t his thesis, Antenna-b is select.ed.

3.3.2 Design

To study t.he radiation mechanism of this ant.enna, the surface current distribut.ion

is analyzeci at the three resonances; 3.8 GHz, 7.9 GHz and 13.4 GHz. Inspecting

46 CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

Table 3. 1: Geometric parameters of the antennas (in mm) in Figure 3.1 and

Figure 3.3 on substrate with er = 4.4 , tan,(6) = 0.02 , h, ub = 1.6 mm

, 9

Antenna-a 2.3 0.48

Antenna-b 2.3 0.48

Antenna-c 3

Ant.enna-d 3

, .... .. .. -1' ... .. ..

. ,

I b d h w

14.57 13 0.5 16 -14.57 13 0.5 16 1.4

16 13 0.5 16 1.4

16 13 0.5 16 1.4

I ll' I~. I i I Tt' I j,'4 : : f ..... ·.,--....• ..

~ ~ ~. ~ flr.d .. ~ , . 1·1

\. \\ , \ , ' .~

(b)

LxB h , h." (GHz)

32x29.6 3.8

32><29.6 3.77, 7.94 , 13.4

32x29.6 3.65, 6.78, 10.17

32><29.6 3.60, 7.36, 9.8

I ~. 1 1 . .. _- ----- - - ----- - ---- ------- - ..

11 .. 1 1

1<1

\., \ \ 8 \ '. b\ '1.

Antmna-e I Antenna-d

Figure 3.3: Design of UWB square monopole antennas (8) Antenna-b (b) Antenna­

e (c) Antenna-d.

Fig. 3.6(a) , the first resonance can be accounted. as,

I ....... "\g.1 ,--4

(3.1 )

3.3. ANTENNA GEOMETRY, DESIGN AND OPTIMIZATION 47

as.

0

.\0

'" ·20 "" . - - .. ,· 0111111

'" ·30 - w - O.5 1lU1l w- Imm

-40 - w - I. S nun - ... - 2I11nl

.50 .l-~~-2~~_..!::::;===~ 2 4 6 8 10 12 14 16 18 20

Frequency, GHz

Figure 3.4: Effect of the variation of 1lJ on the retmn loss

'" "" ..:

'"

Or-----------,

·10 HIt-·~

·20

·30

-40

·50 2 4 6

-- AlllcrUla- a -- Antenna- b

ATlIenn3· c -- Amenn.1- d

8 \0 12 14 16 18 20

Frequency, GHz

Figure 3.5: Ret.urn loss of the antennas in Table 3.l

Similarly, from Fig. 3.6(b) and Fig. 3.6(e), the second and third resonanees

and

1 Ag.2 2'" - 4

A,3 13 '" _._. 4

(3.2)

(3 .3)

Here, Ag,i is the wavelength in the dielectric which is computed from the free

18 CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

• • ..• ",t ...

I.'" I.'" ".1, ..... -,,0' . ., .. ' n .' ..

Z

(a) (b) (c)

Figure 3.6: Surface current distrihution on the antenna at (a) 3 . ~ GHz (b) 7.9

CHz (c) 13.4 CHz

spaC'e wavelength >'0" as ,

, '\0.. . 2 3 "g,i = r;:-,l = 1, ,

vEre (3.4 )

where Ere is the effective permittivity of the subst.rate which is computed from.

'f-ere. = v c.,. . cair (3.5)

3.3.3 Optimization

Based 011 the observations aforementioned, a de;ign procedure for the U\~lB

square monopole antenua is framed as below. The three resonances are fixed at

3.8, 7.9 and 13.4 GHz.

1. Design a 50 n CP\V I ~li<:rostri)J line on a substrate with permittivity er

and thickness h sub'

JJ .~HE!'i!'iA GEOMETRY. DESIGN AND OPTIMIZATION 49

Table 3.2: Antenna descript ion

Antcnna- l Alltenna~2 Antenna-3 Antennll·4 Antenna-S

Laminate Rogers Taconic FR4 Epoxy Rogers Rogers

5880 RP·30 R03006 6010LM

h, .. " 1.57 1.52 1.6 1.28 0.635

:,. 2.2 3 4.4 6.15 10.2

tU7I (6) 0.001 0.0013 0.02 0.001 0.001

,~ (mm) 2.3 2.3 2.3 2.3 2.3

9 (mm) 0.12 0.18 0.28 0.34 0.6

• 0

.\0 ·10

= ·20 -20 ~

~

~ .)0 -,-, .3<) -~-, --, - ............ ~ M-' M_'

"" -M~ -4, -M~ _M_' -M_' .,. .,. , 4 • • 10 12 14 16 " 20 , 4 • , 10 " " I. " 20

Fn:qucncy, GHz FrcqUCllcy, GHz

(.) (b)

Figure 3.7: Return los. ... of the ant.ennas (a) with comput.ed geometric parameters

(b) wit.h opt imized geomet.ric parameters

2. Design the square pat(:h to haw the first resonance at. 3.8 GHz using £qn.

3.1. The length of the ground plane is

I ~ )..9,1/4, for Antenna-b and c and

I::::: >.g.I/4 + s + g, for Antenna-d.

3. Incorporate the pockets in the ground plane by following the guideline in

Fig. 3.3. Adjust w to merge the second and third resonanees.

4. Perform minor adjustments in l, d and w for the three resonances to be at

3.8. 7.9 and 13.4 GHz.

This design guideline is OOE'! of the many approaches that. can bE'! tried t.o

design this ant.enna. Using the parameters so computed, the antenna was studied

Tab

le 3

.3:

Co

mp

nte

d a

nd

opt

imiz

('d

geom

et.r

ic p

aram

eter

s fo

r th

e sq

uare

mon

opol

p an

ten

na

Par

amet

er

Au

t.en

na-

l Allt~lll1a-

2 A

nt.c

llua

<1

Ant

.enn

a-4

(mm

) C

Oll

lPut

ed

Op

tim

izeu

C

om

pu

ted

O

pti

miz

ed

Co

mp

ute

d

Opt

illl

izf'

d C

om

pu

ted

O

pti

miz

ed

I IG

.4:2

16

.'12

IG.H

l 16

.17

l:t8

14

.01

12.7

11

.01

b 15

1

;,

1:1

1 :1

1:3

1:1

B

13

d O

.:!

0.3

0.5

0.

;;

0.5

n.;'

(J.G

O

.G

h ](

i.·1~

16.1

2 15

.19

16.4

1:

1.8

IG

12.7

1,

1.4

In

1.3

1.3

1:1

13

1.4

1.1

1.5

I.!)

L:r

W

:!5.G

x :

HX

2

3H x

32.

1 33

.2,1

x 2

8(;

9

:15

x 2!

l.H

26 x

27.

3 29

.5 x

32

:26.

3 x

:2I'U

H

31 x

2!l

.5

ft·J

zJl

:1.:

2,7.

;;,1

:3.;

1 3.

2, 7

.5,

B.3

,I

, 9,

Hi

3.6.

8.8

. 15

.4

4, H

.67,

H.7

:1

.7;'

;.8

,13

.4

4. K

65

, 14

.7

,3.7

9, 8

, 13

.5

(GH

z)

I A

nte

nll

a-5

Comput.~d

Opt

.ill

lize

d

11.1

9 11

12

12

0.75

0.

75

11.1

9 14

I.G

1.6

2,1.

8 x

2:1.

94

:10.

4 x

26

.7"

4.4H

, 8.

9, 1

!i.7

3.

HS,

7.H

9,

13

c., ....

o 9 ~ 'V

~ ~ ~ ~ (f}

.0

c::: ~

~

t:r1

:;;-. ....... o :? ~ ,-.. '-'

t-<

t:r1 ~

?' ~ > ~ ~

3.4. BAND NOTCH DESIGN 51

on substrates \vith different permittivit.y, described in Table 3.2. Figure 3.7(a)

shows t.he return losses of the antennas \\'it.h the computed geometric parameters

given in Table :3.3. Resonances of these antennas show slight deviation from the

designed values but the bandwidth is almost similar for all the antennas except

for AntEmna-5. Due to the shift in the resonance towards the higher side. the

lower edge of the band has also been shift.ed and hence the designs needed to

be optimized to cover the 3.1- 10.6 U\VB. The optirnized design parameters are

tabulat.ed in Table J.J and the return loss is shmvn in Fig. 3.7(b). The slight

disparit.y in the computed and optimized design parameters can be attributed to

the ambiguity in the exact. val11e of Ere.

3.4 Band Notch Design

In the proposed antenna. to avoid int.erference with electronic systems operating

in the IEEE802.11a and HIPERLA~/2 ba.nds, a band reject mechanism is

incorporated by symmetrically cutting t.v.m narrmv slot resonators perpendicular

the lower edge of the square patch (Fig. :3.8). The slut parameters can control

the centre frequency. width of the rejection band as \vell as the peak VSWR of

the rejection band. The centre frequency of t he band to be rejected is determined

by length '.~ as shown in Fig. 4.5(3). \Vhi1e designing the resonator. 18 is fixed

first. Then, the width of the rejection band a.nd its VS\\TR is tuned by ds and ts.

Fig. 4.5(b) and (c) show the effect of these parameters on the rejected bcUlCl.

Simulation studies on subst.ratcs wit.h different permittivity have shown that

for a. given notch frequency, length of the slit is giwm by

(3.6)

where Ag.5.5 = A/..;s;; and Ere = (c~ + 1)/2

Referring to Fig. 3.8(b), a.t 5.5 GHz. current is concentrated around the slits

and opposit.ely directed on either sides of the slot. The slots fundion as shorted

transmission lines having an elect.rical length of approximately Ag /4 at 5.5 GHz.

giving a high input impedance [V"iSSCL 2()()5: Pozar. 1~)!)8l. The eST simulated

value of this impedance is 22+j160 O.

The optimized design parameters for getting ultra wide band performance

with Cl rejection ba.nd centered at. 5.5 GHz is: Is, d.~. t.~ = 7.8 mm. 6.8 mm, 0.15

52

l' : I, ,

Jv .-..-

CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

,

d. 1< ---~

(.)

w. , ... '.tl •• &

;:~ ~ ~ un }: :r' . '-_::{ 'If 'C._ .J. , , r . , 1.....__ ••

(b)

Figure 3.8: UWB Square monopole antenna with slot resonator for band notch

(a) design parameters (b) current distribution along the periphery of the slot at

5.5 GHz

•

2

o ,

". , " , ~ ~ ,

0 2 •

•

-1, - 1-

-1,---1,-'­-t-·-

• " Frequency, GH:t ,.,

_'. G"'_ _,._II.U_

'. 'U_ - ', gp-_',_lUJ_

• • " Frequency, Gttz

,<,

"

"

o

"

JO

" " ~

~ " ~

" • 0

"

_01,'11_

_,I, 31_ ~._H_

_.1, ' 6.1 _

_ 01,_11_

\ ) ~ , , • • " "

Frequency, GHz

(b,

-_"' 11.001 -_"-GoJ -. •• I

/'~ • • , •

Frequency, GHz

(d,

Figure 3.9: VSWR vs. Frequency of the band notch UWB antenna for different

(a) slot lengths while t. = O.15mm and d. = 6.8mm (b) slot position while

t, = O.15mm and I. = 7.8mm (c) slot width while I. = 7.8mm and d. = 6.8mm.

; 3.5. EXPERIMENT RESULTS 53

mm. Simulation studies have also shown that sharp notch edges and high VSWR

(> 15) can be obtained if low loss substrates are used.

3.5 Experiment Results

Measured return loss of the U\VB square IIlonopole antenna shown in Fig. 3.1 O( a).

The plots are in agreement at the lower frequencies alld t.he slight variation at the

higher side could be due to the S~IA connector. which, has not been accounted

in the simulation. As shown in Fig. 3.1O(b), measured and simulated VSWR

plots of the band notched UV/B antenna also has good agreement and is high (>

3) in the 5.2 - 6 GHz sub band.

Radiation patterns of the antenna at diff(~rent. frequencies are shO\vn in Fig.

3.11 for co and cross polarizations. Each pattern is normalized with respect to

the peak value of the corresponding plane. It is found t.hat. the patterns are

omnidirectional in the H-plane (x-y plane). Across the 3.1-10.6 GHz U\VB, t.he

patterns are stable and at higher frequencies, they are slightly distorted.

Radiation pattern of the ant.enna at the notched frequency is shown in Fig. 3.12.

Pattern at 5.5 GHz has been normalized W.r.t that. at 3.75 GHz for comparison.

Measured gain and radiation dfici('ncy of the square mono pole antenna without

the band notch resonator and with band notch resonat.or is shown in Figure

3.l3( a) and (b) respectively. Antenna polarization is found t.o be along the z

direction. l\Ieasured gain remains const.ant t.hroughout the band and the average

value is found to be 3.75 dBi in t.lw 3.1-10.6 GHz band as shown in Figure :3.13(a).

As shown in Figure :U 3(b), there is large decrease in gain when there is a band

rejection mechanism as low as -9dB compared to the rest of the band. l\Ieasured

radiation efficiencies are also reasonably good and is in agrement with simulation.

54

'" '" 0 -'"

'" ~ '"

0

- 10

-20

-30

-40

CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

I

19.6GHz

Experiment Simulation

(a)

-so l-_~ ____ -'=-=====i

10

8

6

4 3

2

0

2 4 6 8 \0 12 14 16 18 20

Frequency. GHz

, -- Expcrin'K:nt Simulation

52 Gllz 6 Gllz

.Ji~J_G.!:'~ 7GHz

-/----------""" -

2 4 6 8 10 12

Frequency, GHz

(b)

Figure 3.10: Measured and simulated (a) SII of the UWB square monopole

ant-enna (b) VSWR of the band notch antenna

3.5. EXPERIMENT RESULTS 55

..... e ~9IP • ... ..... , , , , " ." " • ." -, .. ~ '/"' 1 "" .. ~ '00 00 ...

.,., .. r .. • .. I !70 ... " . no ·lO • • .,.

'" '" " ,~ ,,. ,~ ,,. -'--.. '" '" 210 ,~ '" '" , .. ,. ,.

to) ..... ..... • ..' • ... , • • • " '" • • •• • ~- • • • • .. --" Q "(- ~

-, ... . ' • .,. , •• m .. .. • m

" • , ,. ,,. , '" , -----' ,. • !IO ,M • '" ,. • ,.

'" ,. ,. ,.

(bI .... •• 00 • " ....

• • • • • • ~ • • ••

D • ·w- " t·1O "I ... .. ~

, , .,. • \ '''t, I • j l:'t ,. l'll) • r '" .,. I:' . :..

. , \_ 'I ,. ~

,,. \ " 1- ,. '" '" -" '''' ,. -, JIG ,. • ,. ,. • '" •• '" ,. •• , . ,.

t" Co. N .. ElJIl -------<o . .. oL~ e. 1'01 .• Ex", (',"-' .. s,""' .....

Figure 3.11: Radiation patterns of the U\VB square monopoie in the (a) x-y

plane: 3.75. 8, 13 CHz, 17 CHz (b) y-z plane: 3.75, 8, 13 CHz. 17 CHz (c) x-z

plane: 3.75, 8. 13. 17 CHz

56 CHAPTER 3. THE SQUARE MONOPOLE ANTENNA

e. !100 •• ,.p • • 0' • • • ~ ,~ ~ .- ,~ ~ ,- ,~ .. ,.,

/","lIl' -....:

~ ". ~ no 90 m

• ,~ l~ ' ,~ ,~

,~ '" ,~ • ~lO ,~ • '" , .. ,0> ,. t.) ~) ,,,

-Co P<JI . E>.pl --_-Co. PoLSimubboa C. Po! . Eopl. Cr. PoI .. S"" .. lalian - 3 75 mu, Co. Pal

Figure 3. 12: Radiation patterns of the band notch antenna at 5.5 GHz (a) x-y

plane (b) y-z plane (c) x-z plane

6 tOO

/ 95 '" 4 - ~ ~

co 90 ~.

~ 2 0

" " .~ SS en ('l 0 0 , '" ~

, o. ~ 80 a 0 " "- -2

" 75 ~ -4

70 , 4 6 8 !O !2

Frequency, GHz

6 100 -4

co 2

" 0 0 .~ -2 0 ~ -4 .. 0

"- -6

·8

; ; .-

~ I -7

'I I _- __ 0;>-II V

II I I '-II I I

I ~I id 11"", : F..:lpmmcnl I I Broken line , Simut.lic>n

90 '" • 80

e, ~ 7. 0· " (b)

60 en

'" 50 o. 0

" 40

" 30 ~

-10 20 2 4 6 8 10 !2

Frequency, GHz

Figure 3.13: Measured and simulated p~..ak gains and radiat ion efficiency of the

square monopoie antenna (a) without slot resonator (b) v..ith slot resonator

3.6. CONeL USION 57

3.6 Conclusion

A Square l\Ionopole Antenna ,,,,it h ultra wide band'width is designed and character­

ized in this chapter. U\VB is achieved by a novel ground modification technique.

which minimize pernicious reflections 'within the antenna structure. This antenna

can be designed on any commercially ava.ilable microwave la.minate since universal

design guidelines are available. Impedance bandwidth of the antenna is from

3.1-19.6 GHz with stable radiation pat.terns and gain in the 3.1-10.6 operationa.l

band. A band notch technique is also proposed to limit interference with \VLAN

systems, which is tunable.

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