Array Antenna for MPAR ApplicationHadi Saeidi-Manesh , Student Member, IEEE, and Guifu Zhang, Senior Member, IEEE
Abstract— This paper presents a high-isolation, low cross-polarization dual-polarized patch antenna for multifunctionphased array radar applications. Its hybrid feed design hasbeen implemented, and the vertical and horizontal polarizationsare excited by a balanced-probe feed and a slot-coupled feed,respectively. Simulations and measurements have demonstratedan input isolation of 45 and 43 dB between the horizontaland vertical ports, respectively. For further improvement inthe cross-polarization level, the image feed method is alsoimplemented, and a 2 × 2-element array made up of designedelements with image configuration has been fabricated. Thesimulated and measured S-parameter and radiation patternsof the horizontal and vertical polarizations of the designed2 × 2-element array are presented and the measured cross-polarization level of less than −37 dB is achieved. To examine theperformance of the designed element in an array, a 3×3-elementarray of designed 2 × 2-element subarray is fabricated andtested. In the 6 × 6-element measurements, −35.4 and −36 dBcross-polarization levels for horizontal and vertical polarizationsare achieved, respectively. Also, using the measured embeddedelement patterns, the cross-polarization level lower than −36 dBfor scan angles up to 45° is achieved.
THERE are four radar networks in the United Statesthat consist of eight different radar systems. Each radar
system has its own designated specifications and serves itsown mission. Since these radar systems have overlaps incoverage, and data sharing between them is difficult, it is cost-effective and beneficial to integrate these missions into a singleradar system. The multifunction phased array radar (MPAR) isplanned to concurrently perform weather and air surveillanceby using a single PAR network [1], [2]. The national networkof WSR-88D Doppler radars has been updated from singularly
Manuscript received June 28, 2017; revised January 26, 2018; acceptedFebruary 25, 2018. Date of publication March 5, 2018; date of currentversion May 3, 2018. This work was supported by the NOAA underGrant NA16OAR4320115. (Corresponding author: Hadi Saeidi-Manesh.)
H. Saeidi-Manesh is with the School of Electrical and Computer Engineer-ing and Advanced Radar Research Center, University of Oklahoma, Norman,OK 73019 USA (e-mail: [email protected]).
G. Zhang is with the School of Meteorology, University of Oklahoma,Norman, OK 73019, USA, and also with the School of Electrical andComputer Engineering and Advanced Radar Research Center, University ofOklahoma, Norman, OK 73019 USA.
Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TAP.2018.2811780
polarized (i.e., linear horizontal) radar to dual-polarized radars(i.e., WSR-88DP) [3]. The dual-polarized radar system cansimultaneously transmit and receive horizontally and verticallypolarized waves, which can significantly improve weathermeasurements and characterization [4]. This dual-polarizationfunctionality provides more information about hydrometeors’size, shape, orientation, density, etc. [5]. However, havingaccurate polarimetric measurements requires a highly isolateddual-polarized antenna with low cross-polarization levels.
Any proposed radar for the multifunction applica-tion (MPAR) should operate according to the Manual ofRegulations and Procedures for Radio Frequency Management(47 Code of Federal Regulations Part 300) and FAA Order6050.19. MPAR is planned to operate from 2.7 to 2.9 GHzwhen replacing Airport Surveillance Radar and TerminalDoppler Weather Radar. The frequency band 2.7–2.9 GHz isallocated for aeronautical radio navigation [6].
The Planar Polarimetric Phased Array Radar (PPPAR) [7]and Cylindrical Polarimetric Phased Array Radar (CPPAR)[8], [9] are two possible configurations for MPAR. Significantefforts have been made to achieve a dual-polarized antennawith high isolation and low cross-polarization levels necessaryfor accurate weather measurements [10]. Toward this goal,various feeding techniques for a microstrip patch antennawere proposed, including an aperture coupled feed [11], [12],a combination of an aperture coupled feed and an L-shapedprobe feed, a capacitively coupled probe feed, and variousother probe feed methods [13].
Dual-polarized microstrip patch antennas with hybrid feeddesign can be implemented in applications which require lowcross-polarization and high isolation between horizontal andvertical polarizations. Compared to the dual-polarized differ-ential feed design, the hybrid feed design requires less spacefor feed lines, which results in a more compact design [14].Also, the hybrid feed design provides a more symmetricfeature which will improve the isolation between horizontaland vertical ports. In [15], a dual-polarized microstrip patchantenna is fed by two hybrid ports. These hybrid portsconsist of two in-phase aperture coupled feeds and two out-of-phase gap-coupled probe-feeds and the cross-polarizationlevel of −20 dB and input isolation of −40 dB were realized.In [16], a dual-polarized patch antenna is fed by an aperturecoupled feed and two capacitively coupled feeds of a 180°phase shift. In this design, the input isolation of −32 dBand cross-polarization level of −14.4 dB were reported.
SAEIDI-MANESH AND ZHANG: HYBRID FEED MICROSTRIP PATCH ARRAY ANTENNA 2327
Fig. 1. (a) Photograph of the fabricated single element. (b) 3-D view of thedesigned single element. (c) Side view of designed single element. (d) H-poland V-pol feed lines. (e) Geometry of H-pol slot.
Considering its low cross-polarization and high-input isolation,the hybrid feed design could be an ideal fit for MPAR applica-tions. This design is being introduced for MPAR applications,and its potential deserves to be explored.
In this design, a dual-polarized patch antenna is excitedby an aperture coupled feed and a differential probe feed.The measured input isolation of 43 dB is achieved. Forfurther improvement in the cross-polarization levels, the imagefeed method has been implemented, resulting in measuredcross-polarization levels as low as −37 dB.
This paper is organized as follows. Section II presents thesingle element design. In Section III, the 2×2-element designwith image configuration is described and measured radiationpattern of the designed subarray is presented. The radiationpattern of fabricated 6 × 6-element array is measured andpresented in Section IV. Also, the radiation pattern of thecenter 2 × 2-element subarrays of a 6 × 6-element array ismeasured and used to predict the radiation characteristics of20 × 20-element array and the results are presented. Finally,the conclusion is provided in Section V.
II. ANTENNA DESIGN
The geometry of the designed and fabricated single dual-polarized patch antenna is shown in Fig. 1. As shownin Fig. 1(b), the vertical polarization is excited by a differentialfeed method. The vertical polarization is excited by a pairof 180° out-of-phase currents to attain a low cross-polarizationlevel. In this design, the length of the transmission lines isadjusted to provide a 180° phase difference between twoprobes’ currents. Having a 180° phase difference will suppress
Fig. 2. Layer stack-up of designed single element.
TABLE I
DIMENSIONS OF THE DESIGNED SINGLE ELEMENT
the vertical polarization cross-polarization and increase theisolation between the horizontal and vertical polarizations.
The material used for this design is Rogers RT/duroid5880 with a dielectric constant of 2.2. As shown in Fig. 2,the feed lines are laid on the back side of the first substratewith the height of h1. The ground plane and slots are laidon the front side of the first substrate. The first radiatingpatch is etched on the front side of the second substrate witha thickness of h2. Since the microstrip patch antenna has alimited bandwidth, the stacked patch method is implementedand a parasitic square patch is placed on the front side ofthe third substrate with a height of h3. The key parametersin this design are attained by optimization performed in CSTMicrowave Studio and ANSYS HFSS. The dimensions of thedesigned single element are listed in Table I.
The �-shaped part of the feed line increases the dis-tance between the horizontal and vertical polarization feed
2328 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 5, MAY 2018
Fig. 3. Simulated and measured reflection coefficient and isolation ofhorizontal and vertical ports of a designed single element.
Fig. 4. Reflection coefficient magnitude versus scan angle in ϕ = 0° planefor horizontal and vertical polarizations.
Fig. 5. Reflection coefficient magnitude versus scan angle in ϕ = 90° planefor horizontal and vertical polarizations.
lines, which will increase the isolation between the twopolarizations. Also, since the 180° phase difference betweentwo excitation probes is realized by the length differenceof two arms of the vertical polarization transmission line,the �-shaped part of the feed line will increase the lengthof one arm, which will result in a more compact design.
The required length difference between the two arms of thevertical polarization transmission line is calculated analyticallyand then optimized in ANSYS HFSS. For a 1.7 mm widemicrostrip transmission line laid on a 1.574 mm thick Rogers
Fig. 7. Geometry of fabricated 2×2-element array of designed single elementwith image configuration. (a) Top view. (b) Bottom view.
RT/duroid 5880 with a dielectric constant of 2.2, the requiredlength difference for a 180° phase shift (L) can be approxi-mately calculated as follows [17]:
εreff = εr + 1
2+ εr − 1
2
[1 + 12
h
w
]−0.5
(1)
β = 2π
λ= 2π f
c
√εreff (2)
L = π
β= c
2 f√
εreff(3)
where εr , εreff, and h are the dielectric constant,effective dielectric constant, thickness of the substrate,c = 3 × 108 (m/s), and f = 2.8 GHz, respectively, and w isthe width of the transmission line. According to (1) and (3),the effective dielectric constant and required length difference
SAEIDI-MANESH AND ZHANG: HYBRID FEED MICROSTRIP PATCH ARRAY ANTENNA 2329
Fig. 8. Measured normalized radiation pattern of 2 × 2-element arrayof designed single element with image configuration. (a) H-Pol, ϕ = 0°.(b) H-Pol, ϕ = 90°. (c) V-Pol, ϕ = 0°. (d) V-Pol, ϕ = 90°.
at 2.8 GHz would be 1.77 and 40.2 mm, respectively, whichthe length difference has been optimized in the final design inANSYS HFSS and is reduced to 39.9 mm.
The horizontal polarization is excited through an H-shapedslot which is fed by a microstrip line laid below theground plane. The H-shaped slot is placed exactly in the mid-dle of the ground plane to increase the symmetry of radiation
Fig. 9. Geometry of fabricated 6×6-element array of designed single elementwith image configuration. (a) Back view. (b) Front view.
pattern. Although the spacing between vertical polarizationprobes and horizontal polarization feed line and slots is lessthan 1 mm, since the currents at the two probes are 180° out ofphase, they cancel each other’s coupling effect, which resultsin a high-input isolation.
The simulated and measured reflection coefficient and inputisolation between horizontal and vertical polarizations areshown in Fig. 3. As shown in Fig. 3, the simulated andmeasured Shh and Svv are below −10 dB from 2.7 to 2.9 GHz,and there is a satisfactory agreement simulated and measuredresults. The isolation between horizontal and vertical ports isbetter than 45 dB in simulation and around 43 dB in measure-ment, indicating a very good agreement between simulatedand measured results.
The simulated reflection coefficient of the proposed hybridfeed patch antenna at the scan angles in ϕ = 0° and ϕ = 90°planes are shown in Figs. 4 and 5, respectively. The mini-mum required reflection coefficient is taken to be −10 dBfor the intended scan volume. For a four-faced planar arrayantenna or a cylindrical array antenna which has a 90° activesector, the minimum required scanning angle is 45°. As shownin Figs. 4 and 5 in the ϕ = 0° and ϕ = 90° planes at the entirefrequency band, the reflection coefficients for horizontal andvertical ports remain under −10 dB across the scan angle from0° to 45°, except SV V at 2.8 GHz in ϕ = 90° plane whichapproaches −10 dB at 43° scan angle.
The copolarization and cross-polarization radiation patternof the horizontal and vertical polarizations at 2.7, 2.8, and2.9 GHz in ϕ = 0° and ϕ = 90° planes are shown in Fig. 6.In ϕ = 0° plane, the cross-polarization level above theground plane is better than −48 dB for horizontal polarizationand −39 dB for vertical polarization. In ϕ = 90° plane,the maximum cross-polarization level above the ground planeis −39 and −32 dB for horizontal polarization and verticalpolarization, respectively.
III. 2 × 2-ELEMENT ARRAY CONFIGURATION
For further improvement on the cross-polarization level,the image feed method is applied to the 2 × 2-elementarray of the designed single element [18], [19]. In thisconfiguration, the upper right and lower left elements in the2 × 2-element array are mirrored with respect to the vertical
2330 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 5, MAY 2018
plane. In this configuration, the phase of the copolarizationpattern of mirrored element will be 180° out of phase,compared to the original element. On the other hand, the phaseof cross-polarization pattern will not change by mirroring
Fig. 11. Simulated and measured gain of the designed single element andarray antenna.
the element. To compensate for the 180° phase shift in thecopolarization pattern, the mirrored elements are excited witha 180° phase shift. Consequently, the copolarization patternof two elements will be in phase and the cross-polarizationpatterns will be 180° out of phase, so the cross-polarizationpattern will be canceled, especially in the principal planes.
The geometry of the fabricated 2×2-element array antennais shown in Fig. 7. The fabricated array antenna is testedin the far-field anechoic chamber of the Advanced RadarResearch Center (ARRC) and the measured results at 2.7, 2.8,and 2.9 GHz are presented in Fig. 8. Also, not shown here,the simulated cross-polarization level of the 2 × 2-elementarray with image configuration is below −80 dB for horizontalpolarization and below −56 dB for vertical polarization.As shown in Fig. 8 the maximum measured cross-polarizationlevel in the whole bandwidth is below −40 dB above theground plane (θ = −90° to θ = 90°) for both polarizations inthe ϕ = 0° plane. In the ϕ = 90° plane the cross-polarizationlevel is below −37 dB.
Although there is a gap between the maximum mea-sured and simulated cross-polarization levels, it should benoted that the difference between −56 and −40 dB is lessthan 10−4. Therefore, small backscattering from the cable andpedestal could increase the cross polarization to −40 dB. Also,the cross-polarization level of the standard transmitter antennain the test will increase the measured cross-polarization level.
IV. 6×6-ELEMENT ARRAY
A 6×6-element array of proposed dual-polarized hybridfeed patch antenna has been designed and fabricated to validatethe radiation characteristics of the 2 × 2-element subarray,especially its low cross-polarization level. As shown in Fig. 9,the fabricated 6×6-element array is made of nine 2×2-elementsubarrays, mounted on a fixture made of polycarbonate andacrylic.
The radiation pattern of the fabricated 6×6-element array ismeasured in the far-field anechoic chamber of ARRC. Fig. 10shows the array antenna horizontal and vertical polarizations’radiation patterns at 2.7, 2.8, and 2.9 GHz. In the ϕ = 0° plane,the cross-polarization level is below −35.4 and −36.1 dB forhorizontal and vertical polarization, respectively. As shownin Fig. 10, in ϕ = 90° plane, the cross-polarization level for
SAEIDI-MANESH AND ZHANG: HYBRID FEED MICROSTRIP PATCH ARRAY ANTENNA 2331
Fig. 12. Calculated radiation pattern of 10 × 10-element array of designed2 × 2-element subarray based on measured embedded element patterns at2.8 GHz. (a) H-Pol, ϕ = 0°. (b) H-Pol, ϕ = 90°. (c) V-Pol, ϕ = 0°.(d) V-Pol, ϕ = 90°.
horizontal polarization is below −35.5 dB and for the verticalpolarization it is below −36 dB.
The simulated gain of the designed single element and6 × 6-element array and the measured gain of the fabricated
6×6-element array are shown in Fig. 11. As shown in Fig. 11,the difference between the simulated and measured gain of the6 × 6-element array does not exceed 1.23 dB.
The 6×6-element array is used to predict the copolariza-tion and cross-polarization level of large arrays by using itsmeasured embedded element pattern. Since the elements inthe center 2 × 2-element subarray are not identical, eachelement in the center 2 × 2-element subarray is separatelyexcited while all other elements are terminated. Accordingly,the four measured embedded element patterns are used tocharacterize a large array radiation pattern. The measuredembedded element patterns have been used to calculate theradiation pattern of a 20×20-element array. The horizontal andvertical polarizations radiation patterns of the 20×20-elementarray in ϕ = 0° and ϕ = 90° planes at 0°, 15°, 30°, and 45°scan angles are shown in Fig. 12. For horizontal polarization inϕ = 0° and ϕ = 90° planes, the maximum cross-polarizationlevel at broadside is below −38.55 dB and cross-polarizationlevel remains under −36 dB across the scanning to 45°. For thevertical polarization in ϕ = 0° and ϕ = 90° planes, the cross-polarization level at broadside is below −38 dB and it remainsbelow −36 dB while the main beam direction is steered to 45°.
V. CONCLUSION
The design, simulation, and measurement results of a2 × 2-element array of low cross-polarization, high-isolationhybrid feed dual-polarized microstrip patch antenna are pre-sented. An input isolation of better than 45 and 43 dB isachieved in simulation and measurement, respectively. The ele-ments in 2 × 2-element array are arranged in image configura-tion and −56 dB maximum cross-polarization level is achievedin simulations. The radiation pattern of the 2 × 2-elementarray was measured in the ARRC far-field anechoic chamberand showed a −37 dB maximum cross-polarization level.Also, the cross-polarization level of less than −40 dB at thelocation of the copolarization peak is achieved which showsthat the proposed element could be an ideal choice for theweather and MPAR applications.
To examine the copolarization and cross-polarization radia-tion pattern characteristics of the designed 2 × 2-element sub-array at the scan angles, a 3×3-element array of 2×2-elementsubarray is fabricated and tested. The radiation pattern of the6 × 6-element array is measured and the cross-polarizationlevels of −35.4 dB for horizontal polarization and −36 dB forvertical polarization are achieved. Also, the radiation pattern ofeach element in the center 2×2-element subarray is measuredand the measured embedded element patterns are used forcalculating the radiation pattern of 20 × 20-element array atfour scan angles from θ = 0° to θ = 45° in ϕ = 0° andϕ = 90° planes and the cross-polarization level of lowerthan −36 dB is achieved.
[2] M. Mirmozafari, G. Zhang, S. Saeedi, and R. J. Doviak, “A duallinear polarization highly isolated crossed dipole antenna forMPAR application,” IEEE Antennas Wireless Propag. Lett., vol. 16,pp. 1879–1882, 2017.
2332 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 5, MAY 2018
[3] M.-H. Golbon-Haghighi, G. Zhang, Y. Li, and R. J. Doviak, “Detectionof ground clutter from weather radar using a dual-polarization and dual-scan method,” Atmosphere, vol. 7, no. 6, p. 83, 2016.
[4] H. Saeidi-Manesh and G. Zhang, “Characterization and optimizationof cylindrical polarimetric array antenna patterns for multi-missionapplications,” Prog. Electromagn. Res., vol. 158, pp. 49–61, 2017.
[5] L. Lei, G. Zhang, and R. J. Doviak, “Bias correction for polarimetricphased-array radar with idealized aperture and patch antenna elements,”IEEE Trans. Geosci. Remote Sens., vol. 51, no. 1, pp. 473–486,Jan. 2011.
[6] H. Saeidi-Manesh, S. Karimkashi, G. Zhang, and R. J. Doviak, “High-isolation low cross-polarization phased-array antenna for MPAR appli-cation,” Radio Sci., vol. 52, no. 12, pp. 1544–1557, 2017. [Online].Available: http://dx.doi.org/10.1002/2017RS006304
[7] R. J. Doviak, V. Bringi, A. Ryzhkov, A. Zahrai, and D. Zrnic, “Con-siderations for polarimetric upgrades to operational WSR-88D radars,”J. Atmosp. Ocean. Technol., vol. 17, no. 3, pp. 257–278, 2000.
[8] G. Zhang, R. J. Doviak, D. S. Zrnic, R. Palmer, L. Lei, and Y. Al-Rashid,“Polarimetric phased-array radar for weather measurement: A planar orcylindrical configuration?” J. Atmosp. Ocean. Technol., vol. 28, no. 1,pp. 63–73, 2011.
[9] H. Saeidi-Manesh, M. Mirmozafari, and G. Zhang, “Low cross-polarisation high-isolation frequency scanning aperture coupledmicrostrip patch antenna array with matched dual-polarisation radiationpatterns,” Electron. Lett., vol. 53, no. 14, pp. 901–902, 2017.
[10] H. Saeidi-Manesh and G. Zhang, “Cross-polarisation suppression incylindrical array antenna,” Electron. Lett., vol. 53, no. 9, pp. 577–578,2017.
[11] R. Caso, A. Serra, A. Buffi, M. Rodriguez-Pino, P. Nepa, and G. Manara,“Dual-polarised slot-coupled patch antenna excited by a square ringslot,” IET Microw., Antennas Propag., vol. 5, no. 5, pp. 605–610, 2011.
[12] M. Kaboli, S. A. Mirtaheri, and M. S. Abrishamian, “High-isolationX-polar antenna,” IEEE Antennas Wireless Propag. Lett., vol. 9,pp. 401–404, 2010.
[13] P. K. Mishra, D. R. Jahagirdar, and G. Kumar, “A review of broadbanddual linearly polarized microstrip antenna designs with high isolation[education column],” IEEE Antennas Propag. Mag., vol. 56, no. 6,pp. 238–251, Dec. 2014.
[14] H. Saeidi-Manesh and G. Zhang, “Hybrid-fed microstrip patch antennafor MPAR application,” in Proc. IEEE Int. Symp. Antennas Propag.USNC/URSI Nat. Radio Sci. Meeting, Jul. 2017, pp. 1895–1896.
[15] T.-W. Chiou and K.-L. Wong, “Broad-band dual-polarized singlemicrostrip patch antenna with high isolation and low cross polarization,”IEEE Trans. Antennas Propag., vol. 50, no. 3, pp. 399–401, Mar. 2002.
[16] K.-L. Wong and T.-W. Chiou, “Broadband dual-polarized patch antennasfed by capacitively coupled feed and slot-coupled feed,” IEEE Trans.Antennas Propag., vol. 50, no. 3, pp. 346–351, Mar. 2002.
[17] C. A. Balanis, Antenna Theory: Analysis and Design. Hoboken, NJ,USA: Wiley, 2016.
[18] K. Woelder and J. Granholm, “Cross-polarization and sidelobe suppres-sion in dual linear polarization antenna arrays,” IEEE Trans. AntennasPropag., vol. 45, no. 12, pp. 1727–1740, Dec. 1997.
[19] Y. Rahmat-Samii et al., “A novel lightweight dual-frequency dual-polarized sixteen-element stacked patch microstrip array antenna forsoil-moisture and sea-surface-salinity missions,” IEEE Antennas Propag.Mag., vol. 48, no. 6, pp. 33–46, Dec. 2006.
Hadi Saeidi-Manesh (S’16) received the B.S. andM.S. degrees in electrical engineering (Electromag-netics) from the K. N. Toosi University of Technol-ogy, Tehran, Iran, in 2010 and 2012, respectively.He is currently pursuing the Ph.D. degree in elec-trical and computer engineering (Electromagnetics)with the University of Oklahoma, Norman, OK,USA.
He is a member of the Advanced RadarResearch Center, University of Oklahoma. His cur-rent research interests include the area of antenna
arrays, polarimetric phased array radars, and reflector antennas.Mr. Saeidi-Manesh is a member of the IEEE Antenna and Propagation
Society.
Guifu Zhang (S’97–M’98–SM’02) received theB.S. degree in physics from Anhui University, Hefei,China, in 1982, the M.S. degree in radio physicsfrom Wuhan University, Wuhan, China, in 1985,and the Ph.D. degree in electrical engineering fromthe University of Washington, Seattle, WA, USA,in 1998. His dissertation work was focused on themodeling and calculation of wave scattering fromtargets buried under rough surfaces and he exploredthe detection of targets in the presence of clutterusing angular correlation functions. He also studied
wave scattering from fractal trees.From 1985 to 1993, he was an Assistant Professor and an Associate Profes-
sor with the Space Physics Department, Wuhan University. In 1989, he was aVisiting Scholar with the Communication Research Laboratory, Tokyo, Japan.From 1993 to 1998, he was with the Department of Electrical Engineering,University of Washington, where he was a Visiting Scientist. From 1998 to2005, he was a Scientist with the National Center for Atmospheric Research(NCAR), Boulder, CO, USA. In 2005, he joined the School of Meteorology,University of Oklahoma, Norman, OK, USA, where he is currently a Pro-fessor. At NCAR and the University of Oklahoma, he developed algorithmsfor retrieving raindrop size distributions and cross-beam wind measurements.He led the development of the spectrum-time estimation and processingalgorithm to improve weather radar data quality and of the polarimetric radardata simulators that link weather physics state variables to radar variables.He formulated theories of weather radar interferometry and phased arrayradar polarimetry. He has authored over 10 intellectual property disclosuresand published over 100 journal publications for his research work. He holdsthree U.S. patents. His current research interests include the optimal use ofpolarimetric radar data in quantitative precipitation estimation and quantitativeprecipitation forecast, the research and development of polarimetric phasedarray radars for weather measurements and multimission capability, wavepropagation and scattering in random and complex media, remote sensingtheory and technology for geophysical applications, algorithms for retrievingphysical states and processes, cloud and precipitation microphysics and modelparameterization, target detection and classification, clutter identification andfiltering, radar signal processing, and optimal estimation.
