2326 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 5, MAY 2018 High-Isolation, Low Cross-Polarization, Dual- Polarization, Hybrid Feed Microstrip Patch Array Antenna for MPAR Application Hadi 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 multifunction phased array radar applications. Its hybrid feed design has been implemented, and the vertical and horizontal polarizations are excited by a balanced-probe feed and a slot-coupled feed, respectively. Simulations and measurements have demonstrated an input isolation of 45 and 43 dB between the horizontal and vertical ports, respectively. For further improvement in the cross-polarization level, the image feed method is also implemented, and a 2 × 2-element array made up of designed elements with image configuration has been fabricated. The simulated and measured S-parameter and radiation patterns of the horizontal and vertical polarizations of the designed 2 × 2-element array are presented and the measured cross- polarization level of less than -37 dB is achieved. To examine the performance of the designed element in an array, a 3 × 3-element array of designed 2 × 2-element subarray is fabricated and tested. In the 6 × 6-element measurements, -35.4 and -36 dB cross-polarization levels for horizontal and vertical polarizations are achieved, respectively. Also, using the measured embedded element patterns, the cross-polarization level lower than -36 dB for scan angles up to 45° is achieved. Index Terms— Array antenna, cross-polarization suppression, differential feed, dual-polarized, image arrangement, phased array radar (PAR). I. I NTRODUCTION T HERE are four radar networks in the United States that consist of eight different radar systems. Each radar system has its own designated specifications and serves its own mission. Since these radar systems have overlaps in coverage, and data sharing between them is difficult, it is cost- effective and beneficial to integrate these missions into a single radar system. The multifunction phased array radar (MPAR) is planned to concurrently perform weather and air surveillance by using a single PAR network [1], [2]. The national network of WSR-88D Doppler radars has been updated from singularly Manuscript received June 28, 2017; revised January 26, 2018; accepted February 25, 2018. Date of publication March 5, 2018; date of current version May 3, 2018. This work was supported by the NOAA under Grant 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: hadi.saeidimanesh@ou.edu). G. Zhang is with the School of Meteorology, University of Oklahoma, Norman, OK 73019, USA, and also with the School of Electrical and Computer Engineering and Advanced Radar Research Center, University of Oklahoma, Norman, OK 73019 USA. Color versions of one or more of the figures in this paper are available online 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 can simultaneously transmit and receive horizontally and vertically polarized waves, which can significantly improve weather measurements and characterization [4]. This dual-polarization functionality provides more information about hydrometeors’ size, shape, orientation, density, etc. [5]. However, having accurate polarimetric measurements requires a highly isolated dual-polarized antenna with low cross-polarization levels. Any proposed radar for the multifunction applica- tion (MPAR) should operate according to the Manual of Regulations and Procedures for Radio Frequency Management (47 Code of Federal Regulations Part 300) and FAA Order 6050.19. MPAR is planned to operate from 2.7 to 2.9 GHz when replacing Airport Surveillance Radar and Terminal Doppler Weather Radar. The frequency band 2.7–2.9 GHz is allocated 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. Significant efforts have been made to achieve a dual-polarized antenna with high isolation and low cross-polarization levels necessary for accurate weather measurements [10]. Toward this goal, various feeding techniques for a microstrip patch antenna were proposed, including an aperture coupled feed [11], [12], a combination of an aperture coupled feed and an L-shaped probe feed, a capacitively coupled probe feed, and various other probe feed methods [13]. Dual-polarized microstrip patch antennas with hybrid feed design can be implemented in applications which require low cross-polarization and high isolation between horizontal and vertical polarizations. Compared to the dual-polarized differ- ential feed design, the hybrid feed design requires less space for feed lines, which results in a more compact design [14]. Also, the hybrid feed design provides a more symmetric feature which will improve the isolation between horizontal and vertical ports. In [15], a dual-polarized microstrip patch antenna is fed by two hybrid ports. These hybrid ports consist of two in-phase aperture coupled feeds and two out- of-phase gap-coupled probe-feeds and the cross-polarization level of -20 dB and input isolation of -40 dB were realized. In [16], a dual-polarized patch antenna is fed by an aperture coupled feed and two capacitively coupled feeds of a 180° phase shift. In this design, the input isolation of -32 dB and cross-polarization level of -14.4 dB were reported. 0018-926X © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.