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oe (B), and 1600 oe (C). As Hin increases from A to B, main beamshifts toward �s = �40:1

� with an increasing sidelobe. As Hin in-creases further from B to C, the sidelobe at 30.5� (B) shifts toward�s = 9:1

� (C) and becomes a main beam.

IV. CONCLUSION

The beam-scanning capability of the ferrite-loaded groovy antennahas been demonstrated. Our proposed antenna structure is simple andeasy to implement as a beam-tunable leaky-wave antenna. The two-dimensional scattering theory proves to be useful for the analysis anddesign of the ferrite-loaded groovy antenna.

REFERENCES

[1] T. Itoh, “Application of gratings in a dielectric waveguide for leaky-waveantennas and band-reject filters,” IEEE Trans.Microw. Theory Tech., vol.25, no. 12, pp. 1134–1138, Dec. 1977.

[2] K. Uchida, “Numerical analysis of surface-wave scattering by finite pe-riodic notches in a ground plane,” IEEE Trans. Microw. Theory Tech.,vol. 35, no. 5, pp. 481–486, May 1987.

[3] K. Solbach, “Slots in dielectric image line as mode launchers and circuitelements,” IEEE Trans. Microw. Theory Tech., vol. 29, no. 1, pp. 10–16,Jan. 1981.

[4] J. W. Lee, H. J. Eom, K. H. Park, and W. J. Chun, “TM-wave radiationfrom grooves in a dielectric-covered ground plane,” IEEE Trans. An-tennas Propag., vol. 49, no. 1, pp. 104–105, Jan. 2001.

[5] A. Henderson, J. R. James, and A. Fray, “Magnetised microstrip antennawith pattern control,” Electron. Lett., vol. 24, no. 1, pp. 45–47, Jan. 1988.

[6] I. Y. Hsia and N. G. Alexopoulos, “Radiation characteristics of Hertziandipole antennas in a nonreciprocal superstrate-substrate structure,” IEEETrans. Antennas Propag., vol. 40, no. 7, pp. 782–790, Jul. 1992.

[7] H. How, T. M. Fang, D. X. Guan, and C. Vittoria, “Magnetic steerableferrite patch antenna array,” IEEE Trans. Magnet., vol. 30, no. 6, pp.4551–4553, Nov. 1994.

[8] H. Maheri, M. Tsutsumi, and N. Kumagai, “Experimental studies ofmagnetically scannable leaky-wave antennas having a corrugated fer-rite slab/dielectric layer structure,” IEEE Trans. Antennas Propag., vol.36, no. 7, pp. 911–917, Jul. 1988.

[9] K. C. Hwang and H. J. Eom, “Radiation from a ferrite-filled rectangularwaveguide with multiple slits,” IEEE Microw. Wireless Compon. Lett.,vol. 15, no. 5, pp. 345–347, May 2005.

[10] , “Radiation from a ferrite-loaded ground plane with multiplegrooves,” in Proc. Int. Symp. Microw. Opt. Tech. (ISMOT), Fukuoka,Japan, Aug. 2005, pp. 67–70.

Ka-Band Fresnel Lens Antenna Fed With an Active LinearMicrostrip Patch Array

Irfan Kadri, Aldo Petosa, and Langis Roy

Abstract—The design of a linear microstrip array and Fresnel lens com-bination as a potential candidate for Ka-band satellite communications ispresented. Medium-power amplifiers are distributed within the array toachieve a high EIRP required for satellite communications. This architec-ture may be used as an alternative to the conventional horn-fed reflectorantenna with a single high-power amplifier.

Index Terms—Active antennas, Fresnel lens, microstrip array, powercombining.

I. INTRODUCTION

Extremely high frequency (EHF) communication systems are cur-rently being used in various military satellite communication appli-cations and more recently are beginning to make an appearance incommercial applications. The advantages of using the EHF band in-clude increased frequency spectrum for high-data rate applications, andmore compact, lighter-weight antennas and transceivers for improveddeployability of portable systems. One of the major challenges withEHF designs is achieving the high transmit power required to satisfythe link margin for satellite communications. The traditional approachuses a single high-power amplifier and a high-gain reflector antennato achieve required effective isotropic radiated power (EIRP). Thesesingle high-power amplifiers are costly and if they were to fail the linkwould be lost. Thermal management of these amplifiers is also a chal-lenge. An alternative approach is to use a number of smaller amplifiersand combine their output powers. One efficient way is through spatialpower combining [1]–[3]. In thismethod, each amplifier is connected toan antenna element, and the output powers are combined in free space.This approachminimizes losses in conventional microstrip power com-bining networks, which become less efficient at the EHF band. How-ever, it may not be practically or physically possible to integrate oneamplifier for each antenna element, and even if it were, the complexityof the biasing network and the increased costs may not warrant the in-crease in efficiency. In this paper, a hybrid technique is adopted, whereamplifiers are distributed within the feed network of the array, whereeach amplifier feeds a sub-array, the outputs of which are then spatiallypower combined. There is thus a tradeoff between cost and complexityversus efficiency. A prototype antenna is designed and tested to studythe performance and assess the potential of the proposed configuration.

II. ANTENNA ARCHITECTURE

A sketch of the antenna is shown in Fig. 1. The conventional para-bolic dish, fed by a single horn and high-power amplifier is replacedby a one-dimensional Fresnel lens fed by a linear array with a set ofdistributed amplifiers integrated in the feed network. The Fresnel lensis used to focus the fan-shaped beam of the linear array into a pencilbeam and also eliminates the degradation due to feed blockage whichis an issue for centre-fed parabolic reflectors. Although the Fresnel lens

Manuscript received April 26, 2005; revised August 15, 2005.I. Kadri and L. Roy are with the Department of Electronics Engineering,

Carleton University, Ottawa, ON K1S-5B6, Canada (e-mail: ikadri@doe.car-leton.ca; lroy@doe.carleton.ca).

A. Petosa is with the Advanced Antennas and Propagation Group,Communications Research Center, Ottawa, ON 77005, Canada (e-mail:aldo.petosa@crc.ca).

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4176 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 12, DECEMBER 2005

Fig. 1. Schematic of active antenna.

is not as efficient as a lens with a hyperbolic cross-section, it is easierto manufacture and is thinner [4].

As a proof of concept, a prototype antenna was designed for oper-ation at 30 GHz, consisting of a 16-element linear array of microstrippatches and a 15 cm � 15 cm dielectric Fresnel lens designed with afocal length-to-diameter ratio (F=D) of 0.5 and with 90� phase cor-rection [4]. The lens was fabricated out of Plexiglas (with a dielectricconstant of "r = 2:6) and the dimensions are shown in Fig. 2.

A photograph of the passive 16-element linear array of microstrippatches is shown in Fig. 3. The patches, spaced 5 mm apart, are fedthrough an aperture in the ground plane with the power distributionnetwork located beneath the ground plane to isolate the feed from theradiating aperture. The measured pattern at 30 GHz of the passive arraywithout the lens is shown in Fig. 4, along with the theoretical patterns ofan ideal lossless array. The absolute gain of the array was obtained bycomparing it to a calibrated standard gain horn and was measured to be16.3 dBi. By integrating the ideal 3D pattern, the directivity of the arraywas estimated to be 18.5 dBi, resulting in a radiation efficiency of 60%,where the losses are attributed to the power distribution network. Usinga commercial full-wave analysis software tool to model the entire array(feed network and patch elements), the simulated gain was estimatedto be 17.3 dBi, which underestimates the measured losses by 1 dB.

Four 1 watt, 22 dB nominal gain MMIC amplifiers (TriquintTGA4509-EPU) were selected to be integrated into the power distri-bution network, as shown in Fig. 5. Once the amplifiers were mountedonto the carrier substrate and bonded to the RF lines, their gain wasmeasured to be 20 dB at 30 GHz. The number of amplifiers chosenwas a tradeoff between achievable EIRP, complexity, and physicalsize constraints. Instead of integrating amplifiers for every radiatingelement, the amplifiers are distributed one each per four radiating ele-ments. This is thus a partial-spatial power combining structure wherethe overall output power of the array is combined in free space butwhere the intermediate combining between elements of the sub-arrayis carried out by the microstrip feed network.

III. ACTIVE PROTOTYPE MEASUREMENTS

In order to remove the excess heat generated by the amplifiers (whichconsume a total of 10.9 W of DC power), a heat sink was required toprovide passive cooling, as shown in Fig. 6. The heat sink was initiallylocated in the same plane as the radiating elements, which caused un-wanted scattering. The microstrip array substrate was therefore bent by90� so that the radiating aperture is now orthogonal to the heat sink, sig-nificantly reducing the scattering. A photograph of the entire antenna

Fig. 2. One-dimensional Fresnel lens.

Fig. 3. Passive 30 GHz linear microstrip array.

assembly is shown in Fig. 6. Tests done showed that bending the sub-strate had negligible effects on the RF performance of the feed network[5].The gain of the active linear array was measured to be 35.1 dBi,

which is 1.2 dB less than ideal value of 36.3 dB, obtained by addingthe antenna gain to the amplifier gain. This additional loss is attributedto bond wires and discontinuities between RF transmission lines re-quired for amplifier integration within the feed network. The efficiencyof the active array (not including the Fresnel lens) was then estimatedby subtracting the ideal directivity of the active array (38.5 dBi) from

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 12, DECEMBER 2005 4177

Fig. 4. Measured patterns of the passive array at 30 GHz.

Fig. 5. Array feed network with integrated amplifiers.

Fig. 6. Fully-assembled active antenna prototype.

the measured gain (35.1 dBi), resulting in a value of 46%. This valueshould be close to the power combining efficiency of the antenna.

The pattern at 29.6 GHz of the entire antenna prototype is shown inFig. 7. The lens focuses the fan-shaped beam into a pencil beam, with ameasured peak gain of 42.3 dBi. The high sidelobes in the H-plane aredue to the feed pattern spillover. Since the prototype was intended as aproof of concept, the F=D was not optimized for the microstrip patchelement pattern. By redesigning the lens, the spillover energy could bereduced and a higher efficiency achieved.

Fig. 7. Measured patterns of the active antenna prototype at 29.6 GHz.

Fig. 8. Estimated EIRP of the prototype antenna.

The EIRP curve of the prototype antenna was estimated by mul-tiplying the measured antenna gain with the measured output power(Pout) versus input power (Pin) performance. Fig. 8 shows the Pout

versus Pin curve of a single amplifier and the corresponding EIRP ofthe total array. The EIRP curve was estimated by summing the outputpowers of the four individual amplifiers and multiplying by the ac-tive antenna gain. For the bias condition of Vds = 6:5 V and Ids =420mA, each amplifier achieved an output power at 30GHz of approx-imately 29.5 dBm for an input power of 10 dBm. The correspondingEIRP of the antenna (which combines all four amplifiers) was thus cal-culated to be 59.3 dBm.

IV. SUMMARY

A Ka-Band prototype antenna consisting of a Fresnel lens and lineararray of microstrip patches with distributed amplifiers was designed,fabricated and tested. Using four 1 watt amplifiers and a lens apertureof 225 cm2, an active gain of 42.3 dBi was achieved with an estimatedEIRP of 59.3 dBm. Typical EIRP values for Ka-band Satcom applica-tions are on the order of 75 dBm. It should be relatively easy to attainthis value by increasing the lens aperture dimensions and replacing the1 watt amplifiers with higher powers (2 and 4 watt amplifiers are com-mercially available). Reported spatial power combining efficiencies for

4178 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 12, DECEMBER 2005

various Ka-band configurations range from between about 45% to 75%[6]–[8]. Since the proposed configuration is a hybrid approach, it isexpected to have poorer power combining efficiency than a true spa-tial power combining array (with one amplifier per radiating element);however the advantage of this approach is the reduced number of am-plifiers, which decreases cost, complexity and dc power consumption.

This is the first demonstration of a hybrid Fresnel lens andmicrostrippatch array, Ka-band transmitter. It has the potential for significant costreduction, by substituting traditional reflector and high power ampli-fiers with more economical distributed, medium-power amplifiers andsimple patch arrays.

ACKNOWLEDGMENT

The authors wish to thank John Bradley and Soulideth Thirakouneof the Communications Research Centre for their help in assemblingand testing the prototypes.

REFERENCES

[1] M. P. DeLisio and R. A. York, “Quasioptical and spatial power com-bining,” IEEE Trans. Microw. Theory Tech., vol. 50, no. 3, pp. 929–936,Mar. 2002.

[2] B. Deckman, D. S. Deakin Jr., E. Sovero, and D. Rutledge, “A 5-Watt37-GHzmonolithic grid amplifier ,” inProc. IEEE Int. Microwave Symp.MTT-S, vol. 3, May 2001, pp. 1843–1845.

[3] J. Harvey, E. R. Brown, D. B. Rutledge, and R. A. York, “Spatial powercombining for high power transmitters,” IEEEMicrow. Mag., pp. 48–58,Dec. 2000.

[4] H. D. Hristov, Fresnel Zones in Wireless Links, Zone Plate Lenses andAntennas. Norwood, MA: Artech House, 2000.

[5] I. Kadri, A. Petosa, and L. Roy, “Folding high frequency substrate forinterference mitigation in active antennas,” in Proc. Int. Symp. AntennaTechnology and Applied Electromagnetics, ANTEM/URSI, Ottawa, ON,Canada, Jan. 2004, pp. 105–108.

[6] J. T. Deslisle, M. A. Gouker, and S. M. Duffy, “45-GHz MMIC powercombining using a circuit-fed, spatially combined array,” IEEE Microw,Guided Wave Lett,, vol. 7, no. 1, pp. 15–17, Jan. 1997.

[7] S. Ortiz, A. Al-Zayed, and A. Mortazawi, “A Ka-band perpendic-ularly-fed patch array for spatial power combining,” in Proc. IEEEMTT-S Dig., 2002, pp. 1519–1522.

[8] X. Jiang, L. Liu, and S. C. Ortiz, “A Ka-band power amplifier based on alow-profile slotted-waveguide power-combining/dividing circuit,” IEEETrans. Microw. Theory Tech., vol. 51, no. 1, pp. 144–147, Jan. 2003.

Design of Tapped-Delay Line Antenna Array Using VectorSpace Projections

Junjie Gu, Henry Stark, and Yongyi Yang

Abstract—We design a tapped-delay line (TDL) structured wide-bandsmart antenna array using vector-space projection (VSP) method. Thestructure consists of a one-dimensional antenna array with a TDL at-tached to each antenna. By controlling the weight coefficients at the TDLtaps using VSP method, we achieve beamforming the array over widefrequency bands. Constraints and associated projections are furnishedto meet the design specifications. We demonstrate the capability of VSPmethod adapted to solve this array design task.

Index Terms—Broad-band operation, smart antenna arrays, tapped-delay line (TDL), vector space projections (VSP).

I. INTRODUCTION

So-called smart antenna arrays are of interest in wireless commu-nications because of their potential in overcoming multipath fadingand increasing the system capacity for information throughput. Awide-band beamformer combines spatial and temporal filtering toachieve these desirable properties. Wide-band beamformers, usingvariable weight coefficients, can generate multiple beams in differentdirections thus providing spatial diversity. In recent research, bothplanar [1]–[3] and one-dimensional (1-D) tapped-delay line (TDL)antenna structures such as finite impulse response (FIR) filters, infiniteimpulse response (IIR) fan filters [4]–[6] have been proposed to designwide-band adaptive arrays [7]–[10].Recently, we used the method of vector space projections (VSP)

[11]–[15] to design two-dimensional (2-D) wide-band antenna arraysand compared our results with existing methods [9]. In this paper, weshow that 1-D wide-band arrays using TDL processing and subject tooperational constraints can also be easily designed using VSP.The 2-D design case we considered in our earlier work [9] is a fun-

damentally different problem from the 1-D case with TDL processingconsidered in this work. This is reflected in the literature where thetwo problems were studied separately by Ghavami [7], [8] and others.In this work we recognize that the TDL processing lends itself to aVSP solution, which superficially appears similar to that of our 2-Dwork. However, examination of the technical details involved in thetwo methods shows significant differences. For example, the mappingfrom the frequency azimuth-phase to the normalized 2-D auxiliary “fre-quencies” is different in the two cases; the 1-D case actually has a morecomplex mapping. Consequently, the constraint sets are defined differ-ently in this work. To our knowledge, the VSP method has never beenapplied to the 1-D TDL design problem.The organization of this paper is as follows. In Section II we review,

for the reader’s benefit, the operation of TDL structured beamformersand their broad-band characteristics. In Section III, we formulate VSPfor designing the broad-band TDL arrays. Simulations and a compar-ison with another method are furnished in Section IV and a Conclusionis furnished in Section V.

Manuscript received December 15, 2004; revised July 21, 2005.The authors are with the Department of Electrical and Computer Engi-

neering, Illinois Institute of Technology, Chicago, IL 60616 USA (e-mail:gujunji@iit.edu).

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