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10th Australian Symposium on Antennas, Sydney, Australia, 14-15 Feb. 2007

AN UWB PLANAR 180 HYBRID EXPLOITING PARALLEL STRIP-

MICROSTRIP AND MICROSTRIP-SLOT TRANSITIONSAmin M. Abbosh and Marek E. Bialkowski

School of Information Technology and Electrical Engineering,The University of Queensland, St Lucia, Queensland 4072, Australia

The 180 hybrid, also called magic-T, is a four-port network that offers out of phase (180 phaseshift) and in-phase (0 phase shift) signal/power division between its two output ports. The portenabling the out-of-phase signal division is called the E port while the one providing the in-phasesignal division is named the H port. The property of the ideal 180 hybrid is that all four ports areperfectly matched and the E and H ports, as well as the two output ports, are isolated. Theseproperties of the 180 hybrid make it very attractive for many applications, such as antenna feeds,amplifier combiners, balanced mixers and modulators. Most of these applications require the 180hybrid to be planar and compact in size for the easy integration with other microwave circuitry.There are many types of hybrids in the literature. Each category of them has its own merits and

drawbacks. The main shortcomings of the available hybrids are; most of them cannot cover the ultrawideband (UWB) (3.1-10.6GHz); others are large in size, or have non-planar structure [1-3].

In the present paper we propose a compact planar hybrid with UWB behaviour. The configurationof the proposed UWB hybrid is illustrated in Fig.1. The device uses two substrates supported by acommon ground plane and various parallel strip-microstrip and microstrip-slot transitions. Its Hport is formed by a slot-to-microstrip transition. In turn, the E port is created by a parallel strip totwo microstrip lines transition. The microstrip lines are connected to two elliptical conducting discs.The two discs are coupled by a slot, which is formed in the common ground plane. The use of thiscoupling structure serves the purpose of obtaining better quality return loss and isolation betweenthe two output ports. Note that in the parallel strip line region, the common ground plane isremoved. However, it exists in the two microstrip lines region.The software CST Microwave Studio is used to simulate the performance of the hybrid on a34.5cm substrate which is Rogers RO4003 with 3.38 dielectric constant and 0.508mm thickness.Results of the simulations are shown in Fig.2. Those results reveal that when E port is excited thepower is equally split between the two output ports with an insertion loss less than 0.5dB across theband 3.1 to more than 11GHz. Also the return loss for the E port is better than 15dB for the wholeband. The difference in phase between the two output ports (not plotted here) is 1800.25 overthe same band. Fig 2b shows the results when the H port is excited. In this case, the power isequally divided between the two output ports with an insertion loss less than 0.5dB across the band3.7-11GHz. The return loss of the H port is better than 12dB for the whole band. The difference inphase between the two output ports is 0.25 over the same band. When the two input ports (E andH) are excited at the same time, the isolation between them is better than 20dB over the whole band.REFERENCES[1] M. Park and B. Lee, Coupled-line 180 hybrid coupler,Microwave and optical technology letters, Vol.45, No.2,

pp.173-176,2005.[2] M. Ho, Wideband magic-T coupler using an asymmetric coplanar stripline or coplanar waveguide ring structure,

Microwave and optical technology letters, Vol.47, No.4, pp. 327-330, 2005.[3] C. Chi and C. Chang, A new class of wideband multisection 180 hybrid rings using vertically installed planar

couplers, IEEE Trans. Microwave Theory Tech., Vol.54, No.6, pp.2478-2486, 2006.

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(a) (b)Fig.1.Configuration of the proposed hybrid. Fig.2. Performance of the proposed hybrid. (a) E port is excited; (b) H port is excited.