microstrip monopulse feed for parabolic dish tracking antenna used in a radio theodolite system

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This article was downloaded by: [The University of Manchester Library] On: 12 November 2014, At: 04:04 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK IETE Technical Review Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/titr20 Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio Theodolite System Tapas K. Bhuiya a , Rajesh Harsh a & K. R. Tuckley a a Society for Applied Microwave Electronics Engineering and Research (SAMEER), R&D institute under Department of Information Technology(DIT), Ministry of Communication and Information Technology(MCIT), Govt. of India, IIT Campus, Powai, Mumbai, India Published online: 01 Sep 2014. To cite this article: Tapas K. Bhuiya, Rajesh Harsh & K. R. Tuckley (2010) Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio Theodolite System, IETE Technical Review, 27:2, 120-123 To link to this article: http://dx.doi.org/10.4103/0256-4602.60165 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

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Page 1: Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio Theodolite System

This article was downloaded by: [The University of Manchester Library]On: 12 November 2014, At: 04:04Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

IETE Technical ReviewPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/titr20

Microstrip Monopulse Feed for Parabolic Dish TrackingAntenna Used in a Radio Theodolite SystemTapas K. Bhuiyaa, Rajesh Harsha & K. R. Tuckleya

a Society for Applied Microwave Electronics Engineering and Research (SAMEER), R&Dinstitute under Department of Information Technology(DIT), Ministry of Communication andInformation Technology(MCIT), Govt. of India, IIT Campus, Powai, Mumbai, IndiaPublished online: 01 Sep 2014.

To cite this article: Tapas K. Bhuiya, Rajesh Harsh & K. R. Tuckley (2010) Microstrip Monopulse Feed for Parabolic DishTracking Antenna Used in a Radio Theodolite System, IETE Technical Review, 27:2, 120-123

To link to this article: http://dx.doi.org/10.4103/0256-4602.60165

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio Theodolite System

120 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010

Microstrip Monopulse Feed for Parabolic Dish Tracking Antenna Used in a Radio Theodolite System

Tapas K. Bhuiya, Rajesh Harsh, and K. R. TuckleySociety for Applied Microwave Electronics Engineering and Research (SAMEER), R&D institute under Department of Information

Technology(DIT), Ministry of Communication and Information Technology(MCIT), Govt. of India, IIT Campus, Powai, Mumbai. India

Abstract

This paper presents the design and development of a tracking antenna for the application of radiosonde tracking in a radio theodolite system. A parabolic dish reflector antenna with a microstrip monopulse feed has been developed and tested with the system. An array of 2 3 2 microstrip patch antenna has been pro-posed as a feed for the reflector dish. The monopulse tracking is executed by generating sum and difference patterns in both azimuth and the elevation plane. The tracking antenna has been characterized in the open space at the installation site. The sum and difference pattern of the individual feed system and the same with the reflector have been measured and presented. The pattern shows the different angle discrimination capabilities due to their different gain associated with the individual system.

KeywordsTracking antenna, Monopulse, Microstrip feed, Radio theodolite.

1. Introduction

Regular monitoring of the atmospheric conditions is an essential exercise for upper atmospheric studies. The information of the atmospheric parameter of the upper air over a long period contributes to a large extent in understanding the atmospheric phenomena and predicting the weather. The upper air observations are taken by radiosonde flights. For this purpose, a radiosonde transmitter along with atmospheric sensors is flown off with the help of a balloon. The radiosonde unit takes measurements of temperature, pressure, and humidity with the help of sensors and transmits the data to the ground station. Thus, the ground sta-tion gets the atmospheric parameter at the location of the balloon. A ground-based radio frequency (RF) system which receives the radiosonde data and tracks the radiosonde signal is called a radio theodolite (RT). Most of the conventional radio theodolites developed earlier offer manual mode tracking. It is carried out by an experienced operator with the help of visual signals available on the oscilloscope depending on the position of the beam. However, present theodolites perform an unattended tracking operation thus avoiding man-made mistakes.

The tracking of a radiosonde unit is performed by an amplitude comparison monopulse technique in real time. A monopulse, also known as simultaneous lobing, is one method of realizing a tracking mechanism. The monopulse uses a 2 3 2 array of microstrip elements [1] on a common reflector. The amplitude of the signals received by each element is continuously compared

in a comparator circuit [2] with those received in the other elements and difference signals are generated that indicates the relative position of the target with respect to the bore sight. Angle servo circuits receive these signals and correct the position of the antenna with an azimuth and elevation drive and direct it to keep the beam axis on target.

A radio theodolite tracking antenna has been designed and developed indigenously at SAMEER. Figure 1 shows the installed antenna at the site. It is a parabolic dish reflector with a monopulse feed. A 2 3 2 microstrip patch antenna is used as a feed for the dish. Since the microstrip antenna is small and lightweight, it reduces the complexity of the supporting structure and associ-ated circuits. The test has been carried out to obtain the sum and difference patterns of the feed system with and without a parabolic reflector. The measured patterns are presented and found very satisfactory.

2. ParabolicDishReflectorandtheFeed‑Supporting Structure

A parabolic dish reflector is a reflective device used to collect or transmit electromagnetic energy. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic dish is normally used to provide a high gain to the reflec-tor antenna. The electromagnetic waves arrive in parallel paths from a distance source and are reflected by the dish to a common point, called focal point. The parabolic dish concentrates the electromagnetic energy during recep-tion to a focal point where the feed is located. Similarly,

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121IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010

Bhuiya TK, et al.: Microstrip Monopulse Feed for Parabolic Dish Antenna

electromagnetic waves radiating from the feed to the dish can be transmitted outward in a beam that is paral-lel to the axis of the dish. The gain of the parabolic dish reflector antenna is given by

GA

dBi =

10

410 2log η

πλ

with reference to an isotropic radiator; h is the efficiency of the antenna, A is the aperture area, and λ is the operating wavelength.

The dish is mounted on a U-shape bracket which is fixed to the shaft of the elevation motor. The elevation assembly is mounted over an azimuth motor. The antenna is capable of rotating 0-3608 in azimuth and 25-908 in the elevation direction with a maximum slewing rate of 258/s. The antenna structure is devel-oped for the operation under all weather conditions and can sustain a survival wind speed of 140 km/h. The specifications of the developed dish antenna are tabulated in Table 1.

The feed and other associated circuits such as LNAs and the comparator circuit are mounted inside a cylindrical pipe at the focal distance of the dish. The pipe is fixed on the vertex of the paraboloid and acts as a support-ing structure for the feed assembly. It also protects the feed assembly from natural disasters. The material of the pipe is high-density polyethylene (HDFE) which

passes the RF signals. The length and the diameter of the cylinder are 25 cm and 90 cm, respectively. The sum and difference signals are carried from the feed assembly to the receiver encloser mounted just at the back of the dish by low-loss semiflex coaxial cables. The power supply and RF cables are routed along the length of the pipe.

3. Microstrip Monopulse Feed

In a parabolic reflector, the feed normally blocks the central region of the aperture and causes reduction in aperture efficiency and gain factors. A larger feed blocks a larger portion of the reflector’s central region and also requires heavier supporting structures. A microstrip feed is normally smaller and reduces the central block-age. Hence it reduces the complexity of the supporting structures and associated assembly due to its light weight and low-profile structure. The major drawbacks of the microstrip feed are the narrow bandwidth and the back radiation problem. The later occurs due to its finite ground plane discussed in [3]. The narrow band-width problem can be improved by applying any of the standard bandwidth enhancement techniques. The microstrip antenna finds application as a feed for the parabolic reflector described in [3-5]. Therefore, it can be used as a feed for the reflector antenna in high-gain applications.

We have developed an array of 2 3 2 rectangular microstrip patch antenna and proposed it as a feed for the parabolic reflector. An air gap has been introduced to enhance the bandwidth of the microstrip antenna. The elements are printed on a common substrate of dielectric constant 3.2 and thickness 3.18 mm. The dis-tance between the two elements in the 2 3 2 array is 0.5λ0. Figure 2 shows the photograph of the microstrip feed elements array. The impedance bandwidth for

Figure 1: Radio theodolite tracking antenna installed at the site.Figure 2: Photograph of the developed 2 3 2 microstrip array for the parabolic dish.

Table 1: Antenna specificationsAntenna type Parabolic dish reflectorFrequency 1680 MHzGain 30 dBiBeam width 60

Feed 2 3 2 rectangular microstrip antennaF/D 0.37Dish diameter (D) 2.1 mSurvival wind load 140 km/hMaterial Perforated 4-mm-thick MS sheet

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122 IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010

Bhuiya TK, et al.: Microstrip Monopulse Feed for Parabolic Dish Antenna

VSWR , 2:1 is 66 MHz [1] with an air gap of 2 mm which meets the requirement of the radio theodolite system as shown in Figure 3.

A single element is simulated in the Ansoft HFSS soft-ware and the simulated radiation pattern is presented in Figure 4. The half-power beam widths in the two principal planes are 808 and 788which lead to a typical element gain of 8 dBi. The feed assembly is placed on the focal point along with LNAs and the monopulse comparator photograph of the feed assembly is shown in Figure 5. The elements are symmetrically displaced from the focal points to get the four squinted beams in order to achieve tracking in azimuth and elevation direction. The displacement decides the beam deviation [6] from the bore sight axis.

4. Experimental Setup for Sum and DifferencePatternMeasurement

A deviation of the radiosonde transmitter from the bore sight produces error/difference signals which

are proportional to angular offset. This is studied by conducting two experiments as shown schematically in Figure 6. Setup (a) describes the experiment of measur-ing the sum and difference signals of the feed system alone whereas Setup (b) describes the same along with a reflector at the antenna site.

The feed assembly containing the feed elements, LNAs, and the comparator circuit is mounted on a rotating wooden stand of a height 2 m. On the other side, the same type of element is used for 1680 MHz signal transmission. The transmitting antenna is mounted on a similar wooden stand at a distance 12 ft from the feed assembly. The signals received by four feed elements are amplified at the separate LNAs and then applied to a monopulse comparator to generate sum and dif-ference signals. The pattern of the sum and difference signals has been measured by rotating the feed assembly with respect to the transmitting antenna. The obtained pattern is shown in Figure 7a. Thus, a 2 3 2 array of microstrip elements having an individual gain of 8 dBi provides a total gain of 14 dBi which agrees with the pattern obtained in Figure 7a. The same experiment has been carried out when the feed assembly is fitted on the parabolic reflector and the transmitting antenna is kept at the terrace of a four-storied building at a distance 60 m

Figure 4: Simulated radiation pattern of an element in the array.

Figure 5: Photograph of the feed assembly.

Figure 3: Measured input impedance of an element in the array.

(a) (b)

Figure 6: Sum and difference pattern measurement setup: (a) Feed illumination pattern; (b) Reflected pattern.

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123IETE TECHNICAL REVIEW | VOL 27 | ISSUE 2 | MAR-APR 2010

Bhuiya TK, et al.: Microstrip Monopulse Feed for Parabolic Dish Antenna

AUTHORSTapas K. Bhuiya received his B. Tech. degree in Radio Physics & Electronics from Calcutta University in 1996 and M. Tech. degree in Communication Engineering from IIT Bombay in 2003. He joined SAMEER in 1997 as a scientist. He has been working on different kind of radar system. He has worked on low power microwave sub-system such as receiver, antenna, modulator,

simulator etc. His fields of interest include radar system, receiver, low power RF/microwave sub-systems/circuits, microstrip antennas and EBG antennas. E-mail: [email protected]

Rajesh Harsh received his M. Sc. degree in Applied Physics from Madhav Institute of Technology and Science, Gwalior. He Joined SAMEER in 1986 and has contributed in the development of RF systems for different projects of SAMEER. Currently he is handling various projects like development of Radio Theodolite system, High power radio frequency

heating systems etc.

E-mail: [email protected]

DOI: 10.4103/0256-4602.60165; Paper No TR 169_ 09; Copyright © 2009 by the IETE

from the antenna site. The measured reflected pattern is shown in Figure 7b. The reflected pattern is very narrow due to the high-gain reflector. A 68 beam width in the sum pattern ensures the tracking antenna gain of 30 dBi.

5. Conclusion

A 2 3 2 microstrip patch antenna array has been proposed as a monopulse feed for a parabolic dish reflector antenna. The sum and difference patterns have been measured for the both feed and reflector systems and presented in this paper. The pattern shows a beam width of 68 which agrees with the 30 dBi gain of the

antenna system. The antenna is tested and operated for tracking the radiosonde signals.

Acknowledgment

Authors would like to acknowledge the supports from all the team members involved in the Radio Theodolite project.

References

1. T.K. Bhuiya, and K.R. Tuckley. “Design and development of the feed for parabolic reflector tracking antenna deployed in radio theodolite,” Proc. National Symposium on Antennas and Propagation (APSYM-2006), Cochin University of Science and Technology, Kochi, India, pp. 245, Dec. 14-6, 2006.

2. T.K. Bhuiya, R. Harsh, and K.R. Tuckley. “Design and Development of Mono-Pulse Comparator for Balloon Tracking in Radio Theodolite System,” Proc. Int. Sympo. Microwaves (ISM-08), pp.156-9, Dec. 03-06, 2008.

3. A.A. Kishk, and L. Shafai. ”Optimization of Microstrip Feed Geometry for Prime Focus Reflector Antennas,” IEEE Trans. Antenna Propagat., vol. 37, no. 4, pp. 445-51, Apr. 1989.

4. P.S. Hall, and C.J. Prior. “Microstrip feeds for prime focus fed reflector antennas,” Proc. Inst. Elec. Eng., pt. H, vol. 134, no. 2, pp. 185-93, 1987.

5. P.S. Hall, and C.J. Prior. “wide bandwidth microstrip reflector feed elements,” 15th European microwave conference, Paris, pp. 1029-44, 1985.

6. Y.T. Lo. “On the Beam Deviation Factor of a Parabolic Reflector,” IEEE Trans. Antenna Propagat., vol. 8, no. 3, pp. 347-9, May. 1960.

Figure 7: Sum and difference patterns: (a) Feed system; (b) Reflector system.

Kushal R. Tuckley received his B. Tech., M. Tech. and Ph.D. degree in Electrical Engineering department from IIT Bombay. He Joined SAMEER in 1985 and has contributed in the development of RF and microwave systems. Currently he is heading the Signal Processing and Navigational Electronics Division in SAMEER.

E-mail: [email protected]

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