220 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 Frequency-Selective Surface to Prevent Interference Between Radar and SATCOM Antennas Stefania Monni, Member, IEEE, Andrea Neto, Member, IEEE, Giampiero Gerini, Senior Member, IEEE, Frans Nennie, and Anton Tijhuis, Member, IEEE Abstract—Interference between neighboring antennas operating in nearby frequency ranges can lead to damage of the front-end electronics. This letter presents the design of a frequency-selective surface (FSS) aimed at preventing the saturation of the low noise amplifiers of a phased-array radar antenna due to the carrier of a satellite communication antenna located in its proximity. A fast design was possible thanks to the integral equation method for the derivation of multimode equivalent networks (IEMEN) and was then validated by reflection and transmission measurements of a hardware demonstrator. Index Terms—Antenna measurements, antenna phased arrays, frequency-selective surfaces (FSSs). I. INTRODUCTION T HE mast topside of modern military ships is a crowded en- vironment, hosting a large number of sensors and commu- nication systems. The proximity of antenna systems operating in nearby frequency bands can lead to performance degradation. In [1], the use of frequency-selective surfaces (FSSs) has been proposed to tackle this problem. In this letter, the electromagnetic interference between the phased-array antenna of an X-band multifunctional radar (MFR) and two satellite communication (SATCOM) antennas, also operating in X-band, mounted on the side of the mast of a military ship is considered. The carrier of the SATCOM antenna saturates the low noise amplifiers of the MFR array antenna. Three possible approaches can be identified to prevent this problem: physical separation of the MFR and the SATCOM antennas by means of absorbing walls (which would be against the trend toward integration in modern masts); active cancel- lation (difficult and expensive because of the large number of T/R modules involved); or passive cancellation through an FSS. The last solution is particularly appealing because it avoids a change in the antenna front-end, can offer weather protection, and reduces the vulnerability against splinter and blast if manufactured using strong artificial fiber materials [see Fig. 1(a)]. Manuscript received October 22, 2008; revised December 01, 2008. First pub- lished January 20, 2009; current version published April 29, 2009. This work was supported by TNO (Dutch Organization for Applied Scientific Research) and by NL Ministry of Defense in the frame of the research program Integrated Topside Design. S. Monni, A. Neto, G. Gerini, and F. Nennie are with TNO Defence, Security and Safety, 2597 AK The Hague, The Netherlands (e-mail: stefania.monni@tno. nl). A. Tijhuis is with the Faculty of Electrical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2009.2013166 Fig. 1. (a) Geometry of the waveguide phased-array antenna integrated with a multilayer dipole-based FSS. (b) Geometry of the FSS element. In this letter, the design of a multilayer FSS suitable to pre- vent this interference problem is described, and the results of the measurement of a hardware demonstrator manufactured on the basis of the design are reported. The frequency ranges indicated in the letter have been changed with respect to those corresponding to the original problem, which could not be disclosed for classification rea- sons. However, the FSS has been designed, manufactured, and measured at the frequencies indicated in the letter. II. DESIGN PROBLEM The MFR antenna transmits in X-band with a reflection loss of dB. The FSS should have a rejection band in the fre- quency range where the SATCOM carrier causes a saturation of the MFR low noise amplifier (10.8–11.4 GHz) and preserve the original antenna performance outside that range, for scan angles up to . The roll-off band should be limited to 0.5 GHz be- tween and dB. Since the transmission band is larger than the rejection band, a dipole-based FSS is a suitable configuration. In particular, we chose the folded dipole elements in Fig. 1(b) because this simple geometry allows meeting the requirements and is easy to manu- facture. The elements were arranged in a triangular lattice with the same periodicity as the array: mm, mm, and skew angle . We adopted a classical design procedure consisting first of a single-mode design, which is very fast since it exploits the slow dependence of the impedance on the frequency [2]. The FSS dipoles were characterized by a simple parallel load with respect to the transmission line equivalent to the main propa- gating Floquet mode. The actual value of as a function of the frequency was obtained with the integral equation method for the derivation of multimode equivalent networks (IEMEN) [3]. Then, thanks to the weak frequency dependence of this ad- mittance, it was approximated in the vicinity of the resonance 1536-1225/$25.00 © 2009 IEEE Authorized licensed use limited to: Technische Universiteit Delft. Downloaded on April 27,2010 at 13:46:18 UTC from IEEE Xplore. Restrictions apply.