A Numerical Procedure to Design a UWB Aperture-Coupled Microstrip Antenna Suitable for Space Applications  
[PERSON]  
Dipartiment of Industrial and Information Engineering and Economics, University of L'Aquila, 67100 L'Aquila, Italy  
Correspondence: [EMAIL_ADDRESS]; Tel.: +39-0862434412  
[PERSON]  
Dipartiment of Industrial and Information Engineering and Economics, University of L'Aquila, 67100 L'Aquila, Italy  
Correspondence: [EMAIL_ADDRESS]; Tel.: +39-0862434412  
[PERSON]  
Dipartimento  
Microstrip antennae, thanks to their particular features of compactness, low profile, light weight, and moderate cost, are widely used in wireless communication systems. Their structure is suitable for dual-polarized antennae as a single patch or organized in large arrays, such as antennae for satellite synthetic aperture radars, where each element is slot-fed by means of a multilayer beamforming network. A new generation of 3D T/R modules for space applications is being developed [25; 26; 27], which requires is increasingly performance-demanding in both electrical and mechanical terms for the radiating element. The well-known aperture-coupled microstrip antennae (ACMA) first proposed by [PERSON] [28] have been developed into a variety of dual-polarization slot-coupled patch antennae, as reported in [29; 30; 31; 32]. Much research has been made on dual-polarized antennae to achieve broad bandwidth, low back-radiation, low levels of cross-polarization, high efficiency, and high isolation [29; 30; 31; 32]. Their use in polarimetric radar requires high isolation and polarization purity; many design efforts have been devoted to this theme, and a review and a comparison of cross-coupling mechanisms has been shown in [33]. The cited works show specific models of dual polarized ACMA [29; 30; 31; 32; 33], but they do not explicitly report the procedure followed for the design. In general, they are unable to reach wide fractional bandwidths without considerably complicating the structure, as in the case of [32], where they use via holes. We present, instead, a multi-step procedure for designing a wide fractional bandwidth ACMA with good isolation levels using simple technology that minimizes costs for large-scale production.  
In this paper, we show a dual polarized high gain ACMA based on a stacked patch to be used in arrays for spaceborne applications. Since the envisaged CubeSat application has been conceived for an agile polarimetric radar at Ka-band that can arbitrarily change the working frequency and the bandwidth, we have constrained the design to match the antenna over the whole Ka-band. Therefore, we develop a specific design procedure that allows dual-polarization and ultra-wideband. It is distinguished from other design procedures by minimizing the complexity of construction, since it resorts to a simple multilayer structure without interlayer interconnections or inclusions. The developed architecture of ACMA permits minimization of the costs in large-scale production [34]. The design starts from assigned specifications in terms of fractional bandwidth constrained to be larger than 40%, return loss better than 10 dB, and polarization purity and polarization isolation better than 25 dB, using materials with adequate ohmic and dielectric losses. On the other hand, the design procedure is sufficiently general to allow simple frequency scaling so that after the design of ACMA at Ka band, which will require the use of specific technologies for realization (e.g., aerosol jet printing [35; 36] or similar micro-scale digital additive manufacturing), we can use the same procedure to replicate the design at lower frequencies (i.e., 2.8-4.8 GHz). That allows us to realize the designed antenna in our laboratory and to check the obtained simulated performance by comparison with measurements. Good agreement between simulations and measurements was obtained.