Fault detection of antenna arrays using infrared thermography Khalid Muzaffar ⇑ , Lalat Indu Giri, Krishnendu Chatterjee, Suneet Tuli, Shiban Koul Centre for Applied Research in Electronics, Indian Institute of Technology Delhi, New Delhi 110016, India highlights  A fast method for fault detection of antenna arrays using lock-in thermography is proposed.  Temperature distribution on a thin microwave absorption screen helps in finding the faulty elements.  Amplitude images are used for detecting the faulty elements. article info Article history: Received 3 January 2015 Available online 21 June 2015 Keywords: Infrared thermography IR Camera Electric field Absorption screen Faulty elements abstract A fast and easy method for fault detection in antenna arrays using infrared thermography is presented. A thin, minimally perturbing, microwave absorption screen made of carbon loaded polymer is kept close in front of the faulty array. Electromagnetic waves falling on the screen increase its temperature. This tem- perature profile on the screen is identical to electric field intensity profile at the screen location. There is no temperature rise observed on the screen corresponding to non-radiating (faulty) elements and hence can be easily detected by IR thermography. The array input power is modulated at a low frequency which permits thermography to detect even weak fields. It also improves the resolution of thermal images. The power fed to the array is only 30 dBm. In order to show the utility of this technique, an example of 14 GHz 4  4 patch antenna array is given. The simulations are carried in CST Microwave Studio 2013. A good agreement between simulation and experimental results is observed. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Infrared thermography has been used for the visualization of electric fields [1–14]. This technique uses a thin absorption screen of carbon loaded polymer. Such screens are commercially avail- able. The electromagnetic waves impinging on this absorption screen are partially absorbed by the screen. The power absorbed by the screen is given by P abs ¼ 1 2 E 2 Z s ð1Þ where E is electric field strength, Z s is the surface impedance of the absorption screen. The absorbed radiations increase the tempera- ture of the screen by joule heating. This temperature rise is moni- tored by an IR Camera. The temperature rise (DT) at each pixel location is related to modulus of electric field strength E by Eq. (2) as reported in [10] E ¼ k ffiffiffiffiffiffi DT p ð2Þ where k is a constant. Therefore the temperature rise at each pixel location on the screen is proportional to square of electric filed strength. Infrared thermography has been used earlier for array diagnos- tics [11]. Our technique differs from the earlier approach as we are modulating the array input. The advantages of our approach are as: 1. Modulation eliminates the convection effects of heat on the screen and helps even in the detection of weak electromagnetic fields [12]. 2. The lateral diffusion of heat on the screen is inversely propor- tional to square root of modulation frequency of the electro- magnetic wave source [12]. Therefore modulation improves the resolution of the thermal images. 3. For quantification of electromagnetic field values on thin screens using Lock-in thermography we need only amplitude images of the temperature distribution on the screen, the phase images are of no significance for such an application [12]. Further for antenna arrays radiating at higher frequencies the individual elements are closely spaced and the dimensions of the array elements are also small. In absence of modulation, the lateral http://dx.doi.org/10.1016/j.infrared.2015.06.010 1350-4495/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: Khalidmuzaffar123@yahoo.co.in (K. Muzaffar). Infrared Physics & Technology 71 (2015) 464–468 Contents lists available at ScienceDirect Infrared Physics & Technology journal homepage: www.elsevier.com/locate/infrared