Comparative study of defected ground structures harmonics rejection ability in a compact hybrid coupler

INTERNATIONAL JOURNAL OF ELECTRONICS AND
International Journal of Electronics and Communication Engineering & Technology
COMMUNICATION ENGINEERING 6472(Online) Volume 3, (IJECET)
(IJECET), ISSN 0976 – 6464(Print), ISSN 0976 –& TECHNOLOGYIssue 2, July-
September (2012), © IAEME

ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 3, Issue 2, July- September (2012), pp. 94-106
© IAEME: www.iaeme.com/ijecet.html
IJECET
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COMPARATIVE STUDY OF DEFECTED GROUND STRUCTURES
HARMONICS REJECTION ABILITY IN A COMPACT HYBRID
COUPLER
K. Annaram
Professor, Department of Electronics and Communication Engineering,
Kamaraj College of Engineering and Technology,
Virudhunagar, 626001, Tamilnadu, India
dr.k.annaram@gmail.com

ABSTRACT
In this paper defected ground structures (DGSs) featuring compact size and spurious free passband
in the context of 180° hybrid ring couplers are investigated. The design method for miniaturizing
the conventional 180° hybrid coupler is derived based on the fractal theory by replacing the
circumference of the hybrid ring coupler by Koch fractal curves. The advantage of this
miniaturization technique is no needs of any lumped elements, via hole or wire bond, but only
microstrip line. According to the fractal theory, almost the same frequency characteristics as those
of a conventional hybrid ring coupler are obtained. The experimental circuits were reduced to
32.85% in area with the good frequency characteristics. By etching various DGSs on the back-side
of compact hybrid coupler, the harmonics are rejected due to its slow-wave characteristics.
Furthermore, to demonstrate its practical viability, compact hybrid coupler with DGSs are designed,
simulated, fabricated and measured. This paper also compares the harmonic rejection ability of
various shapes of DGSs when these structures are etched in a compact hybrid coupler. Furthermore,
to show the improved harmonic rejection ability of the proposed hybrid couplers which are using
various shapes of DGSs are compared with the conventional hybrid ring coupler which one is not
having DGS by designing all the designs for the same design specifications. Finally the measured
and simulated results are compared for all the designs. The comparative study of these results
indicates that the harmonic rejection levels of the spurious resonance for the proposed couplers are
better than the conventional hybrid coupler at 3fo. It is also observed from the comparative study of
measured results the compact hybrid coupler with triangular DGS have better harmonic rejection
ability than other designs because it has minimum defected area than other DGSs. In addition, the
size of the RF-front-end becomes smaller by using the proposed couplers instead of using filters to
reject the unwanted harmonics. Hence this technique can be well suited to design any compact
microwave systems with low cost.
Keywords: Band-Gap Structure, Defected ground structure, Electromagnetic Interference, Fractals,
Frequency Selective Surfaces, Harmonic rejection, Hybrid coupler, Microstrip.

94

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME

1. INTRODUCTION
Recently, there has been increasing interest in the use of Monolithic microwave wave integrated
circuits (MMICs) in microwave and millimeter-wave communication systems. In these systems,
cost effectiveness, low power consumption, and mass productions are much desired. Microwave
mixer is one of the important component in the above systems, which includes radio frequency
(RF), intermediate frequency (IF) and local oscillator (LO) stages. It is mainly used for the base-
band signal up-conversion and down-conversion of the received signal. In up-converting
microwave and millimeter wave communication systems, the most important parameter is LO-to-
RF isolation. Since the LO frequency is too close to even overlapping the RF frequency, the
rejection of the LO signal by a low pass filter is difficult or sometimes even impossible. Similarly
in down-converting microwave and millimeter wave communication systems, the super heterodyne
receiver is one of the important component which includes RF, IF (base-band) and LO stages. It has
the advantages of good stability and sensitivity, high gain and low noise. But it has the
disadvantages of high power consumption, complex circuitry and image frequency problems. In
this receiver band-reject filters are mostly used to reject the unwanted image frequencies. In both
the up-down converting mixers the radiation of harmonics generated by the nonlinear circuit has
been identified as a major problem for microwave and millimeter wave communication systems.
These harmonics could radiate freely into the surrounding environment at significant power levels
to interfere with continuous or harm the immediate inhabitants. Thus high performance low-pass
and band-reject filters are necessary to reject the unwanted harmonics. Finally the size of the
microwave and millimeter wave communication systems front-end becomes complex and bigger.
Such demand has a significant impact on a number of design issues both at component and system
levels, namely size-reduction, broadband operation, low power consumption, low noise, and
interference problems.

Hybrid ring coupler is one of the fundamental component in both up-down converting mixers
which are mainly used to mix the RF/LO and IF signals. The most commonly used hybrid couplers
are branch-line (90°) and rat-race (180°) hybrid ring couplers. Among the above two a 180° rat-race
hybrid ring coupler has wider bandwidth and high isolation than the 90° branch-line coupler [1] -
[3].To reduce the size of the microwave and millimeter wave system front-end, the 180° hybrid ring
coupler is an ideal component. It consists of a ring that is 1.5λg in circumference at the center
frequency with four input/output ports. In order to achieve good port-to-port isolation, the 180°
hybrid couplers are widely used in balanced mixers which are mostly used in microwave and
millimeter wave systems. Also it can be used in balanced amplifiers, beam forming array antennas
and frequency multipliers, due to their simplicity, wide bandwidth in power dividing distribution,
and a high isolation between its two output ports. Numerous publications have addressed the topic
of how to reduce the size of the hybrid-ring coupler. Several design techniques have been proposed
to enhance the harmonic rejection ability and to reduce its size. In earlier days the hybrid ring
coupler is often implemented only by lumped capacitors and inductors. However, the appropriate
capacitor and inductor in the microwave frequency band are difficult to fabricate [4]. Hirota has
proposed a method for reducing the hybrid ring microstrip coupler length by adding lumped
elements for compensation. The advantage of this method is that the reduced size is arbitrary, but
the main limitation is that the capacitance or inductance which is calculated by this method is
usually not equal to the primary value available in the market. Moreover, the extra lumped elements
will increase the cost and complexity of manufacturing. The next category of the miniaturizing
technique is realized only by planar transmission lines such that the drawback of the method
described above can be avoided. Kim presented a strategy without any lumped elements, but the
total circumference is fixed at 1.25 λg or 7λg/6 and cannot be reduced further. Some approaches use
a phase-inverter structure to replace the half wavelength microstrip between ports 2 and 4, which is
the longest transmission line on a typical ring coupler [5] - [7]. Chang reduced the size of the rat-
race coupler by only using microstrip lines. It is achieved by connecting multiple open stubs on the
inside of the hybrid ring coupler. The main advantage of this method is that no lumped element or
extra transition circuit is needed. Thus, the minimum size is restricted. The meander line technique

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has been used for the coupled line structure size reduction. Moreover, due to technology limitations,
the size reduction is limited by coupling effects between long parallel sections. To reshape the
circular rat-race coupler the space filling curves are used to reduce the occupied surface area while
keeping the performance unchanged [8]-[11]. A new rectangular geometry for the conventional
hybrid ring coupler, based on computer aided design (CAD) tool is proposed. This geometry is not
only easy to automatize in a CAD tool, it gives a better concordance between best-match and best-
isolation frequencies than the standard design. Generally low pass filter is placed for harmonic
rejection in microwave front-end systems. Otherwise; the coupler suffers from the presence of
spurious pass-band at the harmonics of the operating frequency. But this solution increases the
complexity of the circuit, and the insertion loss [12] - [14]. It is very difficult to integrate the
conventional rat-race 180° hybrid ring coupler with other adjoining devices such as filters and
amplifiers; etc which has the perfectly matching geometry because of its multiple non-collinearly
aligned ports. Therefore it becomes necessary to use a vertically oriented feeding point. This
initiates the use of rectangular shape 180° hybrid ring coupler geometry which overcomes the
divergence problem caused by the circular or radial geometry in view of the port alignment even
though the size was not miniaturized [15].

Therefore, attempts are continually being made to realize a rectangular shape 180° hybrid ring
coupler with vertically oriented feeding point with minimum in size, and rejection of odd
harmonics in microwave and millimeter-wave communication systems. Recently in order to
enhance the harmonic rejection ability split ring resonators (SRR), complementary split ring
resonators (CSRR), photonic band-gap (PBG), defected ground structure (DGS) techniques are
used in monolithic microwave integrated circuits (MMICs) which are mainly used in microwave
and millimeter wave communication systems [16].

Hence this paper experimentally compares the harmonic rejection ability of the various DGSs by
etching these structures in a compact 180° hybrid ring coupler. The design concept, compactness
and harmonic response of the proposed designs are illustrated in section 2 and 3. The compact 180°
hybrid ring coupler with harmonic rejection is then discussed and verified by measurement results
from a fabricated circuit in section 4 and 5. Finally the concluding remark is given in section 6.

2. MINIATURIZATION
Fractals: In recent years the beauty of fractals has attracted wide interest among mathematicians
and microwave researchers. A number of techniques for generating fractal shapes were developed
and used to produce miniaturized circuits. The most commonly used fractal shapes are Koch curve,
Sierpinski gasket, Cantor dirt and Hilbert curves. These fractal shapes are self similar in structure, a
portion of the fractal geometry always has the same shape as that of entire structure. The
microwave circuit size can be reduced by increasing the perimeter of the shape as the iteration
increases, while still being confined in the same area due its space filling property. By using these
properties the most commonly used techniques are construction and iteration function which are
popularized by Mandelbrot, for generating fractal shapes. This paper focused only Koch fractals
which are very useful for designing MMICs because these are simpler than other fractals because of
its structure.
According to Mandelbrot’s generalization, the Koch construction consists of recursively
replacing edges of an arbitrary polygon (called the initiator) by an open polygon (the generator),
reduced and displaced so as to have the same end points as those of the interval being replaced. For
example in figure.1, ao is length of the initiator and Ko is the generator transformation. The ad-hoc
iterative function system (IFS) algorithm is used to construct the Koch curves as follows:
a12
b= (1)
ao

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The initiator length ao corresponds to the λg/4 length. In order to construct the generator, n
arbitrary transformations Ko, K1, K2…..Kn are applied successfully as follows

K n+1 = ao ( K n ) = Ua p K ( n ) (2)

where p=1, 2, 3…..n;
K n+1 = an1 ( Kn ) U an 2 ( Kn ) .... U anp ( Kn ) (3)

After applying the above transformations the Koch curves generators physical parameters
should satisfy the equation a11 = a12 = a13 which are shown in Figure.1 because fractals are self
similar. In this paper, Koch fractal with iteration factor (b) 0.25 is chosen to design the proposed
miniaturized hybrid coupler. The geometrical properties of Koch fractals for various iterations are
shown in Figure.2 [17] [18].

Figure.1. Initiator and Generator

Figure.2 Koch fractal for various iterations

3. HARMONIC REJECTION

DGS: Many techniques were reported in order to suppress the unwanted harmonics such as PBG,
SRR, CSRR and DGSs in microwave and millimeter wave communication systems, which has
periodic array of defects. These periodic and non-periodic defects enhance the harmonic rejection
ability of a microwave and millimeter wave circuits. This harmonic rejection enhancement is vey
much needed in many microwave and millimeter wave circuits such as power amplifier, planar
antennas, power divider, hybrid couplers and filters. The research on PBG and EBG structures were
originally used for enhancing the harmonic rejection ability in the stop-band. However, these
structures are very difficult to model because of its too many design parameters also causes
radiation from the periodic defects in microwave and millimeter wave communication systems.
Hence DGSs have gained significant interest in microwave and millimeter wave circuits for
harmonic rejection.
Various shapes of DGSs are shown in Figure.3 which is very useful for designing proposed coupler.
The DGSs should be etched in the proposed compact hybrid coupler ground plane to reject the
harmonics. An etched defect in the ground plane disturbs the shield current distribution in the
ground plane. This disturbance can change the characteristics of a transmission line such as line
capacitance and inductance. It can be seen that employing the proposed DGSs increases the series
inductance to the microstrip line. This effective series inductance introduces the cut-off
characteristic at a certain frequency. In addition, the DGS has a self resonant frequency at the stop-
band. Due to this self resonant characteristic of the DGS section, the proposed coupler can provide

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an attenuation pole in the upper stop-band. Due to this attenuation pole, the stop-band is wider than
that of conventional coupler. These attenuation poles can be explained by parallel capacitance with
the series inductance. This capacitance depends on the etched gap below the conductor line [19].
The physical parameter extraction method for various DGSs and its equivalent are described by LC
circuit as shown in Figure. 4.

a) Square-head DGS (b) Dumb-bell DGS

c) Arrow-head DGS (d) Fractal DGS
Figure 3. Schematic of DGSs

Figure.4. Equivalent Circuit of DGS

The capacitance Cp and inductance Lp are computed by

5 fc
Cp = F (4)
π  f o2 − f c2 
 

250
Lp = H (5)
C p (π f o2 )

where f c is the cut-off frequency of the band reject and f o is its pole frequency. At any frequency
f < f o , the parallel circuit behaves as an inductor and its value is

Lp
Leq = H (6)
  f 2 
1 −   
  fo  
 

It is observed that Leq is frequency dependent, which is inconvenient for the design of any
microwave circuits. However, variation in Leq is not very rapid for the frequency below fc. The
parameter extraction method is used to find the equivalent physical parameter of the DGSs. The

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shunt capacitance and series inductance will be implemented by employing the open stub and short
stub respectively. The length reduction of long DGS slot is achieved by creating the slot heads at
both ends DGSs. The following parameters are used to characterize the band-stop performance of
the DGSs

(1) Linear dimension of a slot
(2) Area/radius of a slot head
(3) Relative control of cut-off frequency fc and attenuation pole frequency fo by changing the
dimension of a slot
(4) Sharpness factor fc/fo

The slot-head area basically controls the inductance Lp whereas; the width (s) of connecting DGS
slot controls the capacitance. The separating distance (d) between the slot heads has influence on
both inductance and capacitance. Various dimensions involved in formation of various DGSs heads
have a different degree of control on fc and fo [20] - [22].
To design a circuit with any one of DGSs, the physical dimension of the DGS unit is obtained from
Lp and Cp values by full wave simulation and optimization is performed by using Agilent ADS. In
this paper, DGSs which are used for rejection of harmonics in a compact 180° hybrid coupler,
because

• The structures are simple to design and fabricate
• The stopband is very wider and deeper
The researchers have commented that for the equal area of slot head, any shape of slot can be
used. However, an equal area only ensures equal equivalent inductance and not the identical
response of the DGS circuit elements. The shape, size, and orientation of a slot can have an
influence on performance of the coupler and other neighboring circuits. In this paper, we
investigated the performance of a compact hybrid coupler by etching various shapes of DGSs on
the ground plane of a compact hybrid coupler.

4. DESIGN AND FABRICATION

By considering the above advantages of DGSs, these DGSs are used to construct a compact hybrid
coupler. In order to validate our idea, a rat-race hybrid coupler with various shapes of DGSs are
designed, fabricated and measured. The layout of the proposed hybrid coupler with DGSs which are
generated by using Agilent advanced design system software is illustrated in Figure.5. The center
frequency of the stopband (3fo) for the DGS is determined by the resonance frequency of each DGS
units. The proposed compact coupler with DGSs is designed at the operating frequency 2.44GHz
(fo) and the center frequency of stopband (3fo) at 7.32GHz. Both conventional and compact hybrid
couplers were designed and implemented on an inexpensive FR4 substrate (εr = 4.3, h = 1.6mm). A
prototype of a conventional and proposed hybrid couplers with DGSs were fabricated which are
shown in Figure.6. The optimized physical dimensions of the hybrid couplers and DGSs are
summarized in Table.1 and Table.2 to 5.

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a) With square-head DGSs (b) With dumb-bell DGS

(c) With arrow-head DGSs (b) With fractal DGSs

Figure .5. Layout of the compact hybrid couplers with DGSs

Table 1. Dimensions of the hybrid couplers

Width (mm) Length (mm) Area mm2
Type of coupler
Feed Ring Feed Ring

Conventional hybrid coupler 2.909 1.497 16.899 17.417 68.35×59.19

Proposed hybrid couplers 2.909 1.497 7.5 9.826 30 ×44.293

Table 2. Dimensions of square-head DGSs

Parameter Dimensions of DGS (mm)

Area of the square-head DGS (a) a = 1.5
Spacing length between square-head (d) d = 4.3
Spacing width between square-head (s) s = 0.5

Table 3. Dimensions of dumb-bell DGS


Radius of dumb-bell DGS (r) r = 1.5
Spacing length between dumb-bell heads (d) d = 4.3
Spacing width between dumb-bell heads (s) s = 0.5

Table 4. Dimensions of an arrow-head DGS

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0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July September (2012), © IAEME
July-September


Area of an arrow-head DGS (b) b=3

Spacing length between an arrow
arrow-heads (d) d = 4.3

Spacing width between an arrow-
-heads (s) s = 0.5

Table 5. Dimensions of fractal DGSs

Area of the fractal DGS (a) a = 3.1
Spacing length between fractal (
(d) d = 4.3
Spacing width between fractal edges (a3) a3 = 0.5

(a) Front-side view

b) Back-side view with (c) Back-side view with
square- head DGSs dumb
umb-bell DGSs

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d) Back-side view with (c) Back-side view with
arrow- head DGSs fractal DGSs

Figure 6. Fabricated prototypes of compact hybrid couplers with DGSs

5. RESULTS AND DISCUSSION

To compare the harmonic rejection ability of the DGSs, compact hybrid coupler with DGSs and the
conventional hybrid ring coupler were designed and fabricated which one is not having DGSs with
the same design specifications. Finally the measured and simulated results are compared for both
the structures. Before the prototypes fabrication, full wave EM simulation results have been
obtained with the aid of Agilent advanced design system software. The S-parameter measurements
were performed by using Agilent N5230 PNA series vector network analyzer.

Figure 7 presents the measured and simulated S11 parameters for a compact hybrid coupler with, as
well as without DGSs. A passband seen in the operating resonance frequency 2.44GHz and
stopband is centred around 7.32GHz. It is observed that the harmonic rejection in the stopband
extends up to 10GHz for the proposed couplers with DGSs over the conventional 180° hybrid ring
coupler. Also it can be clearly seen in Figure.7, the S11 happens to be much better for arrow-head
DGSs. For fo and 3fo, all the designs return loss is below -20dB and above -1.5dB respectively. It
can be noticed that the optimal harmonic rejection happens to be much better than which one is not
having DGSs. It is observed that the compact hybrid coupler with triangular DGS has slightly better
harmonic rejection ability than other designs. The experimental S13 comparison response is shown
in Figure.8. It was found to be isolation is better than -18dB for the whole band for all the designs
which are having DGS.

Figure 7. Return loss (S11)

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Figure 8. Isolation loss (S13)

Figure 9. Coupling loss (S12)

Figure 10. Coupling loss (S14)

Figure 9 and 10 shows the coupling responses of S12 and S14 respectively. It is clearly observed that,
the proposed couplers have the coupling ratio of -3.91dB at 2.44GHz and below -10 dB up to
10GHz for all the designs except conventional coupler. It is clear from the results that the third
harmonics of the proposed coupler were perfectly suppressed. Therefore the harmonic rejection
ability of the proposed coupler have improved lot and better than the conventional hybrid coupler,
while maintaining 3dB power dividing performance. Figure 11 and 12 shows the simulated and
measured phase differences between its output ports of the compact hybrid couplers with DGSs and
conventional hybrid coupler. It is worth noting that the good out-of-phase (180º ± 6º) characteristics
between the output ports are obtained at the desired frequency 2.44GHz (in the passband), while
rejecting harmonic elements effectively only for the designs which are having DGSs. Finally it is
observed that the proposed compact hybrid coupler with triangular DGS has better harmonic
rejection ability compared to other designs because it has only minimum defected area.

103


Figure 11. Phase response (S12)

Figure 12. Phase response (S14)

6. CONCLUSION
It can be concluded that a proposed couplers can be implemented in a few mm2 area without
any lumped element and will be easy to integrate with other devices. Usually low pass filter and
band reject filters were used in the microwave and millimeter wave front-end to reject the unwanted
harmonics. However, this approach increases the overall RF-front-end size and insertion loss. To
overcome the above limitations the proposed coupler can be used because it has the ability to mix
the RF and LO signal as well as rejects the unwanted harmonics. Hence there will be no need of
separate filters for harmonic rejection. Thus the size of the microwave and millimeter wave-front-
end size becomes smaller by using the proposed couplers. So it is well suited for designing any
compact and low cost MMICs circuits which can be used in microwave communication systems. It
is also observed that variation in the measured performance is mainly due to imprecise fabrication,
simulation mesh density and also by the junction discontinuities. It is believed that better quality
(harmonic rejection) results can be obtained by optimizing the DGS section and by using other
fractal curves. This task is left for further investigations, which can be used for further size
reduction and harmonic rejection.

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ACKNOWLEDGEMENT
The author wish to acknowledge the fabrication and testing support of the TIFAC-CORE in
Wireless Technologies, Thiagarajar Advanced Research Center, RF Systems Lab, Thiagarajar
College of Engineering, Madurai, Tamilnadu, India.

REFERENCES

[1] T.Wang, and Ke Wu, “Size-reduction and band-broadening design technique of
uniplanar hybrid ring coupler using phase inverter for M(H)MIC’s,” IEEE Trans.
Microwave Theory Techniques, vol.47, no.2, pp. 198-206, February 1999.
[2] Y.J.Sung, C.S.Ahn, and Y.S.Kim, “Size reduction and harmonic suppression of rat-race
hybrid coupler using defected ground Structure,” IEEE Microwave Wireless
Components letters, vol.14, no.1, pp. 7-9, January 2004.
[3] S. Dwari, and S.Sanyal, “Size reduction and harmonic suppression of microstrip
branch-line coupler using defected ground structure,” Microwave and optical letters,
vol. 48, no.10, pp. 1966-1969, October 2006.
[4] M.L. Chuang, “Size reduced ring coupler using multiple open stubs with restricted
minimum line width,” Microwave and optical letters, vol.48, no.1, pp. 172-174, January
2006.
[5] T.Hirota, A.Minakawa, and M.Muraguchi, “Reduced-size branch-line rat-race hybrids
for uniplanar MMICs,” IEEE Trans. Microwave Theory Techniques, vol.38, no.3, pp.
270-275, March1990.
[6] D.I.Kim, and G.S.Yang, “Design of new hybrid-ring directional coupler using λ/6 or
λ/8 section,” IEEE Trans. Microwave Theory Techniques, vol.39, no.10, pp. 1779-1784,
October 1991.
[7] T.Wang, and K.Wu, “Size reduction and band-broadening design technique of
uniplanar hybrid ring coupler using phase-inverter for M (H) MICs,” IEEE Trans.
Microwave Theory Techniques, vol.47, no.2, pp. 198-206, February 1999.
[8] M.L.Chuang, “Miniaturized ring coupler of arbitrary reduced size,” IEEE Microwave
Wireless Components letters, vol.15, no.1, pp. 16-18, January 2005.
[9] H.Tanaka, N.Banba, S.Ari, and T.Nishikawa, “2GHz one octave-band 90º hybrid
coupler using meander line optimized by 3D FEM” in IEEE Microwave Theory
Techniques Symp. Digest, pp. 903-906, 1994.
[10] S.M.Wang, C.H.Chen, and C.Y.Chang, “A study of meander microstrip coupler with
high directivity” IEEE Microwave Theory Techniques Symp. Digest, pp. 63-66, 2003.
[11] K. W. Eccleston, and Sebastian H.M. Ong, “Miniaturized planar microstrip line
branch-line and rat-race coupler,” IEEE Trans. Microwave Theory Techniques, vol.51,
no.10, pp. 2119-2125, October 2003.
[12] Joanna Qiszewska, S.Vaccaro, J.F. Zurcher, and A.K. Skrivervik, “A new hybrid ring
geometry well suited for CAD implementation,” Microwave optical technology letters,
vol.40, no.4, pp.285-287, April 2004.
[13] K.M.Shum, Q.Xue, and C.H.Chan, “A novel microstrip ring hybrid incorporating a
PBG cell,” IEEE Microwave Wireless Component letters, vol.11, no .6, pp. 258-260,
June 2001.
[14] Y.J.Sung, C.S.Ahn, and Y.S.Kim, “Size reduction and Harmonic suppression of Rat-
Race Hybrid Coupler using Defected Ground Structure,” IEEE Microwave and
Wireless Components Letters, vol.14, no.1, pp. 7-9, January 2004.

105


[15] Su-Yeol Lee, Y.Chung, T.Itoh, and Dal Ahn, “Design of 90º hybrid coupler with
harmonic rejection characteristics,” in IEEE Microwave Theory Techniques Symp.
Digest, pp. 335-338, 2004.
[16] J. D. Beana, J. Bonache, F.Martin, R. M. Sillero, “Equivalent circuit models for split
ring resonators, and complementary split Ring Resonators coupled to planar
transmission lines,” IEEE Trans. Microwave Theory Techniques, vol.53, no.4, pp.1451-
1461, April 2005.
[17] H. Ghali, T. A.Moselhy, “Miniaturized fractal rat-race, branch-line and coupled-line
hybrids,” IEEE Trans. Microwave Theory Techniques, vol.52, no.11, pp. 2513-2519,
November 2004.
[18] H. Ghali, T.A.Moselhy, “Design of fractal rat-race coupler” in IEEE Microwave Theory
Techniques Symp. Digest, pp. 323-326, 2004.
[19] K.Kim, N.Kingsley, M.A.Morton, S. Pinel, J.Papaolymeru, Manos M.Tentzeris, J.
Laskar, and J.G. Yook, “Koch fractal shape Microstrip band pass filters on high
resistivity silicon for the suppression of the 2nd harmonic,” Journal of the Korea
Electromagnetic Engineering Society, vol .6, no.4, pp. 1-6, April 2006.
[20] Ze-Hai Wu, “Characteristic Investigation of Koch Island Fractal patch”, IEEE APMC
2005 proceedings.
[21] J.L.Park, C.S.Kim, J.S.Park, Y.Qian, D.Ahn, and T.Itoh, “Modeling of a photonic band
gap and its application for the low-pass filter design,” IEEE Proceedings of APMC’99,
pp.331-334, 1999.
[22] Adel B. Abdel-Rahman, A.K.Verma, A. Boutejdar, and A.S.Omar, “Control of band
stop response of Hi-Lo microstrip low pass filter using slot in ground plane,” IEEE
Trans. Microwave Theory Techniques, vol.52, no.3, pp. 1008-1013,March 2004.

K. Annaram was born in India in the year 1977. She completed B.E and
M.E degree in Electronics and communication engineering and
Communication systems from Thiagarajar College of Engineering, Madurai
Kamaraj University, India in 1999 and 2001 respectively. She received her
Ph.D degree from Anna University Chennai in 2010. She is now working as
a Professor in Kamaraj College of Engineering and Technology, Department
of electronics and communication engineering. She is a life member in ISTE, ATMS and
IEICE. Prior to coming to Kamaraj College of Engineering and Technology, she was a
research associate for the Thiagarajar advanced research center, Madurai and RF design
engineer for Quasar Innovations limited, Bangalore. Her research interest includes Meta
materials, defected ground structures and miniaturized RF and microwave circuits and
systems.

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