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0 EE 1996Electronics Letters Online No: 19961157G. Forma and J . M . Laheurte (Laboratoire d'Electronique, Antennes etTdlt'communications, Universitt' de Nice - Sophia Antipolis, CNRS, 250rue Albert Einstein, 06560 Valbonne, France)

1'9 July 1996

References1 GREISER,J.W : 'Coplanar stripline antenna', Microw. J., 1976, 19 ,2 LIU, Y . , CHA, K. , an d ITOH, T.: 'Non-leaky coplanar (NLC)waveguides with conductor backing', I E E E Trans., 1995, MTT-43,

( 5 ) , pp. 1067-1072GIAUFFRET, L , and LAHEURTE, J.M.: 'Theoretical and experimentalcharacterisation of CPW-fed microstrip antennas'. IE E Proc.M i c r ow . Antennas Propag., 1996, 143, (l), pp. 13-174 FORMA, G', and LAHEURTE, J M.: 'CPW-fed oscillating microstripantennas', Electron. Lett ., 1996,32 , (2), pp . 85-86

(lo), pp. 47-49

3

Microstr ip annular ring slot antenna!; formobi le applicationsJ.C. B a t c h e l o r and R.J. L a n g l e y

Indexing terms: Microstrip antennas, Antennas, Mobilecommunication systemsAn annular slot on triplate feed is discussed which is suitable foruse with vehicular mobile satellite systems. The slot is excited in ahigher order mode and circularly polarised to give a conicalradiation pattern. The slot can operate on a high dielectric baseand a superstrate improves the gain .

Introduction; One aim of recent work regarding m0bil.e comm uni-cations is to integrate an antenna with its associated R F circuitryinto an MMIC device on silicon or gallium arsenide. Work hasbeen done regarding the annular microstrip ring higher orderTM,, mode with a possible application for m obile satellite com-munications in non-equatorial countries, [11. The higher ordermicrostrip ring modes have a null in the direction normal to theplane of the patch and the TIM,, mode peaks at an elevation of55" from the az imuthal plane. There are however, some disadvan-tages with using microstrip radiating elements, namely surfacewaves giving rise to diffraction from substrate edges, poor radia-tion efficiencies on high dielectric materials and high crosspolarlevels for antennas fed electromagnetically through the substratewith a microstrip feed.To overcome the problems mentioned above an investigationinto narrow annular microstrip slot antennas (width

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superstrate due to diffraction from the alumina edges which wereunscreened in this measurement. The resonant frequency wasreduced to 6.1 G H z .The peak beam gain of the slot at ka =2 was measured to be-2.6dBi. This was increased to 4.6dBi by adding the superstrate.A good prediction of the composite dielectric constant,caused by introducing the superstrate is given by eqn. 1 [2]

where d an d h refer to substrate and superstrate heights, respec-tively. The slot radius IS then given by

where h, s the wavelength in free space.

Fig. 4 Circularly polarised far-f ield im mur eme nt

Circularly polarised slot antennas: To be of practical use; a mobileantenna used in conjunction with a satellite system would need tobe circularly polarised. Budgetary constraints in receiver manufac-ture require compon ents to be inexpensive and so a non-complexmethod for producing circular polarisation was sought. A simpleway to excite circularly polarised fields from annular slots operat-ing at the ku =1 mode h as been reported by [3]where notches areplaced 45" an d 225" from the feed point. Fig. 4 shows a far fieldmeasurement extrapolated from the near field of the ka = 2antenna, where four 2m m x 2mm notches were placed midwaybetween the E- and H-planes a t 22.5" and 112.5" from the feed. Itcan be seen that the radiation field was conical in all planes, thefield independence around the azimuthal plane making theantenna suitable for mobile applications. Peak beam axial ratiowas measured to be less than 3dB. Use of the notches removed thenecessity to provide orth ogon ally phased feedlines beneath the slotan d so reduced the component complexity significantly.Conclusion:A slot antenna operating at a higher order mode hasbeen proposed with a possible application for mobile systems asan alternative to microstrip antennas. The slot antenna has anadvantage over microstrip patches because of the screened feedwhich prevents spurious radiation. Higher order mode fields canbe excited that are both circularly polarised an d conical in shape.Gains of over 4dB were measured when an alumina superstratewas added. A strong advantage of this type of anten na is its lackof dependency on the dielectric substrate making it suitable forintegration with high E, semiconductor materials, a development ofconsiderable interest to recent mobile communication design.A ckn o w l ed g m en t : This work was supported by grants from theUK Engineering and Physical Science Research Council.0 EE 1996Electronics Lette rs Online No: 19961102J.C. Batchelor and R.J . Langley (University of Kent, Cunterbury, KentC T 2 7NT, United Kingdom)

28 June 1996

References1 BATCHELOR. J c , and LANGLEY, R.J.: 'Microstrip ring antennasoperating at higher order modes for mobile communications', ZEEProc. Microis. Antennas Propagat., 1995, 142, (2), pp. 151-1552 K A R M A K E R . N c., , and BHATTACHARYYA, A.: 'Electromagneticallycoupled patch antenna - theoretical and experimentalinLestizations'. .Micron.. & Opt. Technol. Left ., 1992, 5, (3), pp .115-1 18

H I R O S E . K.. and N A K A N O , H.: 'Dual-loop slot antenna with simplefeed'. Elect ion . Lef t . , 1989, 25, (18), pp. 1218-12193

Low offset, high voltage class AB bipolarvoltage-current converterG. Stochino

Indexing t e r m : Operational transconductance amplifiers, Linearintepiuted circuitsA new high voltage class AB bipolar voltage-current converter(VCCS), which features low offset voltage and is suitable formonolithic IC fabrication. is described. The architecture of theconverter is particularly suited for the implem entation of aprecision VCCS with wide input and output voltage range. SomeSPICE siinulations and experiiental results are also reported,w h c h demonstrate the effectiveness of the proposedconfiguration.

In t roduct ion: In a recent Letter [ I ] some circuit configurations forhigh speed class AB voltage controlled current sources ( V C C S ) ,%hich feature improved conversion accuracy, were proposed anddiscussed. However. the intrinsic input offset voltage and outputoffset current of these configurations are not better tha n their con-ventional counterpart. The aim of this Letter is to propose a newbipolar class AB VCCS architecture which, in addition to goodconversion accuracy, provides improved offset figures and is par-ticularly suitable for w ide inpuvout put voltage range implementa-tions."cc *-