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					                           Performance Analysis
                  of Microstrip Ring Hybrid Power Divider
              1
               Surendra Kumar Sriwas, 1Kavita, 1D.C. Dhubkarya and 2Manoj Kr. Shukla
                                              & Communication Department, BIET, Jhansi
                                   1Electronics

                                                   Engineering Deptt., HBTI, Kanpur
                                         2Electronics

                              E-mail: surendrasriwas@gmail.com, manojkrshukla@rediffmail.com
         Abstract—Here a Microstrip Ring Hybrid Power Divider has been proposed. It provides substantially improved
    amplitude and phase characteristics over a broad frequency range compared to that of a conventional hybrid ring power divider.
    Simulation results are presented to confirm the performance.

INTRODUCTION
The microstrip ring hybrid is a four-port network with a 180° phase shift between the two output ports. A
power divider in the form of a hybrid ring that provides substantially improved amplitude and phase
characteristics over a broad frequency range compared to that of a conventional hybrid ring coupler.
The new design provides substantially improved coupling and phase characteristics over a very broad
frequency range; the usable bandwidth is limited primarily by the degradation in the other parameters
such as input VSWR and isolation between coupled ports. Bandwidth is approximately twice that of a
conventional hybrid ring power divider. A theoretical comparison of the performance characteristics of
the improved and the conventional design was accomplished using a IE3D program. Several important
characteristics that make it particularly appealing include: (1) the output arms are well isolated, a
characteristic that is essential to minimize mutual coupling effects, and (2) an in-phase relationship can
be obtained at the output ports, thereby eliminating the need for any phase-compensating element. The
configuration of a conventional hybrid ring coupler, as shown in fig.1, allows for an equal power split,
depending on the impedance chosen for the ring sections. Since the hybrid ring is a resonant type
structure, ideal performance is obtained only at the design frequency.
    In this we will discuss ring hybrid power divider only equal power division (3dB) and bandwidth
enhancement techniques. In addition, their characteristics such as coupling, directivity and isolation are
also described. Figure 1 shows the front view of ring hybrid.

DESIGN PROCEDURE
The 180° hybrid can be fabricated in several forms. The ring hybrid, or rate race is shown in figure 1, can
be easily constructed in planer ( microstrip or strip line) form, although waveguide versions are possible.




                           Fig. 1: A Ring Hybrid, or Rate Race, in Microstrip or Strip Line Form
                                                    Performance Analysis of Microstrip Ring Hybrid Power Divider   677


     The theoretical amplitude and phase of the output voltage at the two output ports of a conventional
equal-split hybrid ring coupler, when the input signal is fed into port 3 (sum mode), is shown in Fig.1. It
is observed that the amplitude and phase of the voltage at port 2, located on the opposite side of the
difference port, are much more frequency sensitive than at port 1, located on the same side as the
difference port. Alternatively, the difference port could be moved one half wavelengths clockwise from
its present location. A very important feature of identical amplitude and phase response at ports 1 and 2 is
that the difference in amplitude and phase between ports 1 and 2 is zero over all frequencies,
theoretically, over an infinite frequency range, although the coupling to ports 1 and 2 varies with
frequency.
     The operational bandwidth of this coupler is then limited by the other two parameters, namely, input
match at the ports and isolation between ports. An identical response at the output ports 1 and 2 makes
this coupler a perfect choice for applications where such a characteristic is required, e.g., beam-forming
networks for phased array antennas. It was found that compensating circuits are necessary at both the
difference port and the added port in order to achieve a proper match at the input and output ports and a
sufficient isolation between the output ports. The desired performance characteristics are dependent on
achieving the proper junction impedance with the ring impedance at both the difference port. The proper
junction impedances were optimized for output port VSWR and isolation with the aid of IE3D. A 100 Ω
impedance provided the optimum performance. A quarter-wave transformer can be used to achieve the
proper match at the difference port to a standard 50-52 termination. No further modifications are
necessary to achieve the broad-band performance.

DESIGN SPECIFICATION
The proposed geometry of the microstrip ring hybrid power divider is shown in figure 2 & 4.These
figures show the front view of the proposed geometry. The proposed design consist of a single layer of
thickness1.6mm and a ring hybrid power divider is deposited on it. Glassapoxi material is used as a
substrate. The dielectric constant of this substrate is 4.7. The Parameters of this power divider are shown
in given table.
Substrate Thickness                                                                 1.6mm
Dielectric Constant                                                                 4.7
Loss Tangent (tanδ)                                                                 0.001
Frequency                                                                           0.75GHz
Thickness of Metal                                                                   .002mm
Step Frequency                                                                      0.1 GHz




                                   Fig. 2: Ring Hybrid with Defined Ports No
678   International Conference on Recent Trends in Engineering, Technology & Management




                              Fig. 3: Variation of S-Parameters with Frequency for Fig. 2




                                      Fig. 4: Ring Hybrid with Defined Ports No.




                              Fig. 5: Variation of S-Parameters with Frequency for Fig. 4
                                                      Performance Analysis of Microstrip Ring Hybrid Power Divider   679




                                       Fig. 6: Phase Variation with frequency

RESULT AND DISCUSSION
The simulation of the proposed design has been carried out by using IE3D commercial software based
on the method of moment. The theoretical results show the proposed power divider can provide good RF
performances on return loss, amplitude balance and isolation. To confirm the performance of the broad-
band power divider design, an equal power divider and a 3 dB (between output ports) power divider were
designed. The design frequency for both couplers was 0.75 GHz and the circuits were etched on a 1.6
mm substrate with a relative dielectric constant of 4.7. The measured coupling, phase difference between
output ports, input VSWR, and output port isolation are plotted in Figs.3 and 5 for the equal and 3.0 dB
power dividers, respectively. The input VSWR is somewhat higher than expected and is due to the ring
impedances being different from the design values, caused by the manufacturing tolerances. Additional
iterations on the design would improve the match and improve the performance even further. The
coupler performance will be closer to theoretical results at the lower frequencies since the tolerance
errors in construction of these circuits are smaller at lower frequencies.

REFERENCES
[1] D.M. Pozer, “Microwave Engineering”, John Wiley & Sons, Singapore, 1998
[2] E.J. Wilkinson. An n-way hybrid power divider, IRE Trans Microwave Theory Tech MTT-8 (1960).
[3] M.D. Abouzahara and K.C. Gupta, Multipart power divider/combiner circuits using circular microstrip disk
    configurations, IEEE Trans Microwave Theory Tech MTT-35 (1987).
[4] G.L. Mathaei, L. Young and E.M.T. Hones, “Microwave filters, impedance matching networks and coupling
    structures” , Artech House, Dedham, Mass,1980.
[5] C. Y. Pon, “Hybrid ring directional couplers for arbitrary power division,” IEEE Trans. Microwave Theory Tech.,
    vol. MTT-9, pp. 529–535, NOV.1961
[6] H. Howe, Stripline Circuit Design Norwood, MA: Artech, 1974
[7] Y. Tarui, K. Nakahm, Y. Itoh, and M. Maisunaga, “A method for dividing ratio equalization of power
    dividedcombiner used in a power amplifier,” IEICE Trans. (GI), vol. J81-C-I, no.9, pp.553–558, Sept. 1998.
[8] K.C. Gupta and M.D. Abouzahra, “Analysis and design of four-port and five- port microstrip disc circuits,” IEEE
    Trans. Microwave Theory Tech., vol. MlT-33, n0.12,pp.1422–1427, Dec. 1985.
[9] K.C. Gupta and M.D. Abouzahra, “Planar circuit analysis,” Numerical Techniques For Microwave And MilZimeter-
    Wax Passive Circuit (Ed. by T. Itoh. ~hap.4)p~p. 214–333,John Wiley& Sons, 1989.
680   International Conference on Recent Trends in Engineering, Technology & Management


[10] M. J. D. Powell, “An efficient method for finding the minimum of a function of several variables without calculating
     derivatives,” Computer J., vo1.7, pp.155–162, July 1964.
[11] Hee-Ran Ahn, Ingo Wolff and Ik-So0 Chang, "Arbitrary termination impedances, arbitrary power division and
     small-sized ring hybrids," IEEE Trans. Microwave Theory Tech., vol. 45, pp. 2241–247, Dec., 1997.
[12] [Hee-Ran Ahn, Ik-So0 Chang and Sang Won Yun, "Miniaturized 3-dB ring hybrid terminated by arbitrary
     impedances," IEEE Trans. Microwave Theory Tech., vol. 42, pp. 22 16–222 1, Dec., 1994.
[13] E. J. Wilkinson, "An n-way hybrid power divider," IRE. Trans. Microwave Theory Tech., vol. MTT-13, pp.
     116–118, Jan. 1965.

				
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