Advances in Engineering Research (AER), volume 142
International Conference for Phoenixes on Emerging Current Trends in Engineering and Management (PECTEAM 2018)
Design Of Compact 180 Degree Hybrid Coupler
Using T-shape Structure.
B. Pavithra1, Dr.S.Maheswari2
1 2
PG Student , Professor , Department of Electronics and Communication Engineering
Panimalar Engineering College,Chennai, India
pavipavithra509@gmail.com,maheswarisp@yahoo.co.in
Abstract— The Hybrid couplers are the bidirectional couplers The efficient devices operating in high data rate and low
which can give equal power split and 180° phase shift between power signal are used in wireless Technology. The
the two output ports. At lower frequencies the size of the rat researchers working on development of RF technology to get
race coupler becomes larger. Hence, the size of hybrid coupler that result. In order to meet the circuit miniaturization in
should be reduced in order to agree with application wireless communication, it requires smaller device size.
requirements. Reduction of hybrid coupler size is achieved by Thus, size reduction becoming major design requirement for
𝝀
replacing each section using T-shape structures for different practical applications.
𝟒
characteristic impedance. The hybrid ring with T-shape
structure and conventional hybrid coupler is compared. By II. RAT-RACE HYBRID COUPLER
using T- shape structure 88% of size reduction has been The conventional rat-race coupler has four ports, each
achieved. 𝜆
placed length away from each other around one half of the
𝜆
Keywords— Hybrid coupler using T-shape structure; Hybrid ring. The another half of the ring is in length. The
Coupler;
characteristic impedance of ring should be √2 times the
characteristic impedance of the ports. If using port 2 as input
I. INTRODUCTION
ports, equal phase and amplitude signals emerge from port 1
The rat-race hybrid ring is an important structure in & port 3 and port 4 is isolated. If using port 1 as input port,
microwaves. It is a four port junction with 180 degree phase equal phase and amplitude signals emerge from port 2 & port
shift between two ports[1]. The mono-pulse comparator uses 4 and port 3 is isolated. When used as a power combiner,
four hybrid couplers and gathers angular position from one signals are fed to port 1 & port 3. Difference signals
pulse[2]. The port which providing the out-of phase division available at port 4 and sum signals are available at port 2. If
is called as ∆-port and the one providing is in phase signal input is fed on port 1 and output signals will split at ports 2
division called as ∑-port[3]. and 4 and port 3 will be isolated. The rat-race circuit is used
for combining two different signals or dividing the signals
into two signals. The port which providing the out-of phase
division is called as ∆-port and the one providing is in phase
signal division called as ∑-port. The scattering matrix for
conventional rat-race coupler is
Figure 1. 180 degree hybrid coupler Figure 2. Rat-Race Hybrid Coupler
A ring coupler consists of line of electrical length which The rat-race coupler is used in many microwave devices
contains standing waves, to which four arms are connected at such as power amplifiers, mixers, antenna systems,
interval [4]. The Rat- race coupler has two main bandwidth in power dividing distribution, and a high
disadvantages which is difficult to solve. isolation between the ports. Satellite communication, phased
Initially, the undesired interference occur when array radar antenna systems and radar are some applications
conventional rat- race coupler work at its odd harmonics [6]. where rat-race couplers are used widely.
The Microstrip hybrid coupler is designed by applying
the conventional hybrid coupler using T-shape structure. The
designed structure can achieve both reduction of size and
undesired interference.
Copyright © 2018, the Authors. Published by Atlantis Press. 248
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Advances in Engineering Research (AER), volume 142
III. HYBRID RING USING T-SHAPE STRUCTURE between stub lines in each branches the values of 𝜃 must not
The size of the hybrid coupler is reduced using T-shape exceed the value of 𝜃 .
𝜆 The impedance values 𝑍 and 𝑍 are calculated by
structure by considering the length transmission line to be
implemented using T- shape structure as shown. Hence, the 𝑍 = 𝑀𝑍
𝜆 𝑍
ABCD parameters of length transmission line and T- 𝑍 =
shape structure should be same. 𝐾
IV. COUPLER DESIGN AND ANALYSIS
In the given proposed model the dielectric material is
fr4(εr=4.4) and height is h=1.6mm for the operating
w
frequency=2.4GHz. The ratio is chosen as < 2.
ℎ
conventional Coupler dimension are calculated using the
following formulas
Figure 3.
𝜆
length transmission line and its equivalent T-shape structure
(i) The Width for input (Z = 50Ω) and width for
branches ( 𝑍 = 𝑍 = 70.7Ω) is calculated using the
The line (𝑍 , 𝜃 ) is represented as open circuited shunt formula
stub which is shown. By knowing the ( 𝑍 , 𝜃 ) line, the w 8 A w
= 2A − for <2
ABCD parameters of the T-shape structure can be found. ℎ
The shunt stub specified above is replaced by shunt
impedance 𝑍 ℎ , where, Z εr + εr − .
where, A= √ + . +
6 εr + εr
(ii) The effective dielectric constant εeff1(ZA= 50Ω)
and ε for Branches ( 𝑍 = 𝑍 = 70.7Ω) is calculated
using
εr + εr −
ε = +
h
Figure 4. T-shaped structure and shunt impedance is replaced instead of √ +
w
shunt stub.
(iii) The Wavelength is calculated with the known C
8
The ABCD matrix for the above given shunt impedance = 3X m⁄s (velocity of light ) and with given
is given as: operating frequency f= 2.4 GHz
𝑐
λ =
𝑓
λ
Similarly, the ABCD matrix calculated for the T-shape λ =
structure is expressed as √ε
(iv) The outer and inner radius of the Rat-Race
The values of 𝜃 and 𝜃 and total electrical length 𝜃𝑇 is coupler is calculated using
calculated using λ
R=
π
The total electrical length value depend only on M. From w
Inner radius of the ring ( r ) = r −
the above statement it states that the total electrical length
decreases as M increases but for certain K there is a limit of
choosing the value M. in order to avoid the overlapping
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Advances in Engineering Research (AER), volume 142
w
Outer radius of the ring ( r1)= r +
Hence the calculated parameters to design hybrid coupler
at frequency 2.4GHz like width for input, width for branches,
radius of the ring, inner radius, outer radius, and wavelength
is listed in the table given below.
TABLE I. PARAMETERS FOR CONVENTIONAL HYBRID COUPLER
S.no Parameters Values
1. Frequency 2.4GHZ
2. Width for input 3.0608mm
3. Width for branches 1.6227mm
4. Radius 16.749mm
5. Inner radius 15.937mm
6. Outer radius 17.560mm
The conventional hybrid coupler is designed and
simulated using the above values and shown in Figure 5. Figure 7. Simulated results for conventional hybrid coupler
( 𝑆 , 𝑆 , 𝑆 )
The figure 6 & 7 shows the return loss parameters, Isolation
and coupling coeffecients of the conventional rat-race
coupler.
Hybrid coupler using T-Shape structure is designed and
simulated using the formula given in section III and it is
shown in Figure 8.
Figure 5. Conventional hybrid coupler
Figure 8. Reduced size hybrid coupler using T-shape structure
Figure 6. Simulated results for conventional hybrid coupler
( 𝑆 , 𝑆 , 𝑆 , 𝑆 )
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Advances in Engineering Research (AER), volume 142
TABLE III. COMPARISON TABLE OF CONVENTIONAL HYBRID COUPLER
AND CONVENTIONAL HYBRID COUPLER USING T-SHAPE STRUCTURE OF
ISOLATION(S41) AND COUPLING
COEFFICIENT(S31, S21)
S.No Types of rat- Freq S41 S31 S21
race (GHZ) (dB) (dB) (dB)
Conventional
1. Hybrid 2.87 -32.17 -2.93 -3.23
coupler
Conventional
hybrid
2. coupler using 2.9 -16.01 -3.02 -3.70
T-shape
structure
Figure 9. Simulated results for hybrid coupler using T-shape structure From table 3 and table 4 it is observed that the operating
( 𝑆 , 𝑆 , 𝑆 , 𝑆 ) frequency 2.4GHz is shifted to 2.9GHz and the size of
hybrid coupler is reduced by using T-shape structure.
V. CONCLUSSION
In this paper, the conventional rat race hybrid coupler
using T-shape is presented. The spurious harmonic
suppression and reduction of size at desired frequency can be
achieved in the rat-race hybrid coupler. Using T-shape
structure in hybrid coupler reduces large amount of size than
conventional rat-race hybrid coupler. The conventional
hybrid coupler is 44.68mm * 50mm. by using T-shape in
hybrid coupler the size is reduced to 15.3mm * 17.456mm.
By using T- shape structure 88% of size reduction has been
achieved.
REFERENCES
Figure 10. Simulated results for hybrid coupler using T-shape structure
( 𝑆 , 𝑆 , 𝑆 ) [1] Kai-Xu Wang, Xiu Yin Zhang,Shao Yong Zheng,, and
Quan Xue”Compact Filtering Rat RaceHybrid With
Figure 9 & 10 shows the return loss parameters, Isolation Wide Stopband” ,Vol. 63,No.8,August 2015.
and coupling coefficient of the conventional rat-race coupler [2] Y. J. Sung , C. S. Ahn, and Y.-S. Kim , “Size Reduction
using T-shape structure. and Harmonic Suppression of Rat-Race Hybrid Coupler
Using Defected Ground Structure” IEEE microwave
and wireless components letters Vol.14,No.1,January
The size of conventional hybrid coupler is 44.68mm * 2004,p.7-9.
50mm. By using T-shape in hybrid coupler the size is [3] “Advanced Microstrip Trainer Kit User’s Manual,”The
reduced to 15.3mm * 17.456mm. Thus, by using T- shape Scientific Instruments Co. ltd., IIT Delhi.
structure 88% of size reduction has been achieved which is [4] Sanjay Bhilegaonkar, Ashwinikumar Dhande , “Monopulse
shown in Figure 8. Comparator Network System with Hybrid Rings”,
The 19th Asia Pacific conference on Communication
TABLE II. COMPARISON TABLE OF CONVENTIONAL HYBRID COUPLER APCC2013,Bali-Indonisia,August 2013,p.562-563.
AND CONVENTIONAL HYBRID COUPLER USING T-SHAPE STRUCTURE OF [5] Samuel Y. Liao,Microwave Devices and Circuits,3rd
RETURN LOSS PARAMETERS edition,New Jersey:Prentice Hall,p.147-148.
S.No Types of Freq S11 S22 S33 S44 [6] Qing He, Yinghong Wen, Song Chen, and Kai Wang”A
rat-race (GHZ) (dB) (dB) (dB) (dB) Compact Uniplanar Rat-Race Coupler with Arbitrary
Power Division Ratio and Harmonics Suppression” ,Vol. 52,
Conventional p.71,March 2015.
- -
1. Hybrid 2.87 -38.12 -24.35
24.36 38.09
coupler
Conventional
hybrid
coupler - - - -
2. 2.9
using T- 12.73 17.126 13.133 16.74
shape
structure
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