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`Petitioner Samsung - SAM1015
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`combining a number of feed networks into a single
`antenna system, an antenna with multiple independently
`steerable beams is achieved.
`
`TRAVELLING WAVE MICROSTRIP
`PATCH RADIATORS
`
`The radiating elements chosen for the antenna array were
`rectangular microstrip patches [2]. Patches are desirable
`dueto theirlow costand their extremely low profile. They
`are inexpensive to manufacture and due to the use of
`printed circuit techniques in their production, the design
`is highly repeatable. Since they are low profile, they also
`can be sha
`conformally to cylindrical surfaces. They
`are ideal e emcnts to use in cylindrical arrays since they
`have low back radiation.
`There are some problems with patch antennas which
`make their use somewhat less attractive. Powerefficiency
`of a patch antenna is usually quite low since the radiation
`resistance is typically on the order of a few hundred ohms.
`Since a patch antenna behaves much like a cavity reso-
`nator. it has a narrow VSWR-bandwidth, typically in the
`order of 2%. Wider VSWR-bandwidths, in the order of
`7%, can be obtained using travelling wave antennas.
`One of the difficulties in making patch antenna arrays
`cost and power efficient is in coming up with suitable feed
`networks for the array. Corporate feeds are both lossy,
`space consuming and complex for shaped patterns. For
`this reason the travelling wave antenna is ideally suited
`for microstrip patch arrays. This type of antenna achieves
`the desired current distribution by varying the width and
`spacing of patches spaced along a microstrip fecdline. It
`has been shown in [4] that the desired shaped antenna
`pattern can be obtained using a travelling wave patch array
`while at the same time maintaining good antenna power
`efficiency.
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`H-PLANE PATTERNS
`
`The cylindrical shape of this antenna increases the diffi-
`culty in analyzing the far field radiation pattern arialyti-
`cally. To compensate for this difficulty, a program was
`written which plots the radiation pattern of a cylindrical
`array of patches with arbitrary element excitation.
`Selection of appropriate array parameters can be
`accomplished by relating the theory used for periodic
`linear arrays to the cylindrical array. The main parameters
`to vary are the array radius. the number of elements, and
`the magnitude and phase of the power radiated by the
`elements.
`The geometry used to analyze a circular array [3] is
`shown in Figure 7. Assuming far-field conditions and
`linear polarization the radiation pattern from the array can
`be expressed by the following summation [3].
`
`E9(9, tb) = }’:‘.lI_SF’_(8,¢t—¢_)e
`
`,1: uinem-to - 0.)
`
`(1)
`
`The term SF,_(e, o — ¢,_) takes into account the magnitude
`variations of each patch as a function of angle. The term
`I, is a complex number representing the square-root-
`magnitude and phase, C , of the power to each patch. The
`propagation constant is represented as It.
`The phase of the current distribution is chosen to
`compensate for the curvature of the cylinder. Figure 8
`shows the geometries involved in calculating the phase
`distribution. Using simple geometry.
`
`c=a-acos¢_
`
`(2)
`
`Any phase shift which is constant to all elements can be
`deleted with no change to the pattern. Therefore, the phase
`distribution should be
`
`C=-ka 0°5¢..
`
`(3)
`
`A cosine amplitude distribution along the array surface
`was chosen in order to achieve a good tradeoff between
`beamwidth and sidelobe level. The chosen current
`distribution was found to give quite reasonable antenna
`patterns. This current distribution can however, be varied
`to cater to other pattern shapes. By altering the phase
`distribution, wider pattern beamwidths can be obtained
`This characteristic can be used to add another dimension
`of flexibility to the antenna in terms of variable sector
`size. Figure 9 shows different patterns obtained by
`varying the phase distribution.
`The number of elements needed for the array is mainly
`determined by the desired beamwidth and the scanning
`step size. The number of elements may also be adjusted
`to allow for switching matrix optimization. Since the
`radiators used do not produce much radiation past 90
`degrees it is not useful to excite elements that are more
`than 90 degrees from boresight. Otherwise, back lobes
`may increase considerably which will
`interfere with
`adjacentcells. It was found that a 32 element cylindrical
`array in which 8 elements are excited at a time will achieve
`a 12degree scanning step size anda20 degreebeamwidth.
`Calculations show that a narrower beam can be obtained
`by increasing the number of elements which are excited
`in the array (Figure 10).
`In linear arrays. the optimum spacing for maximum
`directivity and no grating lobes is N). [3]. Fora cylindrical
`array a similar analogy can be made. If the problem is
`looked at geometrically, a circular-sector array in which
`the sector angle is small can be approximated as a linear
`array. 50 if the elements are spaced a distance of N2 then
`the cylinder radius, a, must be chosen so that
`
`7»
`Zita
`7'2
`
`(4)
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`2
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`Calculations show that this radius is indeed close to the
`optimum value. Figure 11 shows the antenna pattern for
`circular arrays with varying values of radius. For an 800
`MHz antemta. (5) gives a radius value of 0.95m. The
`ligurealso shows thatby making theradius slightly larger,
`the beamwidth becomes narrower at the cost of higher
`side lobes. Making the radius smaller reduces side lobe
`levels at the cost of a wider beamwidth.
`
`CONCLUSIONS
`
`The use of cylindrical array scanning antennas in the
`mobile communication field looks quite promising. The
`antennacanbeusedtorealizeadvantagessuchasreduced
`portable transmit power, reduced co-channel interfer-
`ence. hardware savings, low manufacturing costs, low
`installation costs, and increased system capacity. Work is
`proceeding on the fabrication of a subset of the system.
`
`REFERENCES
`
`[1]
`
`J.E. Boyns et-al, "Step-Scanned Circular-/Array
`Antenna," IEEE Trans. Antennas and Propagat,
`Vol. AP-18, No. 5. pp. 590-596, Sept. 1970.
`
`[2] A.G. Demeryd, "Linearly Polarized Microstrip
`Antennas," IEEE Trans. Antennas and Prapagat,
`Vol. AP-24, No. 6, pp. 846-851, Nov. 1976.
`
`[3] C.A.Balanis,Antenna Theory, New Yorkzl-larper &
`Row, 1982
`
`C. Alakija, A Power Efiicient Pattern Synthesis
`Algorithm for Travelling Wave Microstrip Patch
`Antenna Arrays: Application to Mobile Base Sration
`.?3ée1nnl2.l‘, Masters Thesis. Simon FraserUniversity,
`
`Uni-d|r9c1|ona£ oovarage area
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`\\l
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`Colllslon ls blodteflIII
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`III/
`"— Antenna owmfie
`’zI
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`-—”
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`Figure 3: Cylindrical array of travelling wave patch
`antennas.
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`Bum Forming Food
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`I -Mobile User
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`Figure 1: Digital communication system with scan-
`ning beam.
`
`Figure 5: Scanning array system diagram.
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`Figure 9: Simulated cylindrical array patterns
`with different phase distributions.
`
`,,,.
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`Figure 10: Patterns of a 32 clement array with
`varying number of excited elements.
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`Figure 8: Geometry for calculating phase distribution.
`
`Figure 11: Antenna pauems versus array radius.
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