5. S.G. Weigand, H. Huff, K.H. Pan, and J.T. Bernhard, Analysis and design of broadband single layer rectangular U-slot microstrip patch antenna, IEEE Trans Antennas Propag 51 (2003), 457–468. 6. Y.X. Guo, K.M. Luk, and K.F. Lee, U-slot circular patch antennas with L-probe feeding, Electron Lett 35 (1999), 1694–1695. 7. A.A. Deshmukh, A.R. Jain, A.A. Joshi, T.A. Tirodkar, and K.P. Ray, Broadband proximity fed modified circular microstrip antenna, Proceedings of ICACC – 2013, 29–31 August 2013, Kochi, India. 8. A.A. Deshmukh and N.V. Phatak, Broadband sectoral microstrip antennas, IEEE Antennas Wireless Propag Lett 14 (2015), 727–730. 9. A.A. Deshmukh, A.R. Jain, and K.P. Ray, Broadband 2708 sectoral microstrip antenna, Microwave Opt Technol Lett 56 (2014), 1447– 1449. 10. IE3D 12.1, Zeland software, Freemont, USA, 2004. V C 2016 Wiley Periodicals, Inc. COMPACT DOUBLE-LAYER SUBSTRATE INTEGRATED WAVEGUIDE MAGIC TEE FOR X-BAND APPLICATIONS Giuseppe Venanzoni, 1 Davide Mencarelli, 2 Antonio Morini, 2 Marco Farina, 2 Onofrio Losito, 1 and Francesco Prudenzano 1 1 Dipartimento Di Ingegneria Elettrica E Dell’informazione, Politecnico Di Bari, Bari 70125, Italy; Corresponding author: g.venanzoni@univpm.it 2 Dipartimento Di Ingegneria Dell’informazione, Universit a Politecnica Delle Marche, Ancona 6013, Italy Received 4 August 2015 ABSTRACT: A substrate integrated waveguide Magic Tee with very compact size and operating over a wide band is proposed. The circuit is made of two stacked substrates connected by cutting a small aperture between them. This solution presents slightly higher complexity com- pared to a single substrate magic Tee but it avoids the radiation losses because the circuit is completely closed. A simple and effective proce- dure is used to design the circuit. A prototype is built and experimental results show a good agreement with simulations. V C 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:932–936, 2016; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.29707 Key words: substrate integrated waveguide; magic-Tee; directional coupler 1. INTRODUCTION Substrate integrated waveguide (SIW) is a relatively recent tech- nology which allows the realization of many waveguide compo- nents into a dielectric substrate [1]. The electromagnetic field inside the SIW is, practically, very similar to the one occurring inside a standard rectangular waveguide. This allows the use of the skills acquired for hollow waveguides. Therefore, simple equivalence between them is possible, for example by using for- mulas proposed in Refs. 2,3. The main goals of this technology are the possibility of easy integration of waveguide components into planar circuits, low cost, and fast prototyping. On the other hand, the main drawbacks are the higher losses due to the pres- ence of the dielectric and the lower power management due to the small height of waveguides. In the literature, there are many examples of waveguide devices redesigned in the SIW technol- ogy, such as couplers, antennas, filters, and many other [4–14]. One useful and largely employed microwave device which can be fabricated in SIW technology is the magic Tee. It is substan- tially a 3 dB directional coupler, where all ports are matched, thus having one of the output ports isolated. The scattering matrix of an ideal magic Tee is:  S5 1 ffiffi 2 p 0 1 1 0 1 0 0 1 1 0 0 21 0 1 21 0 2 6 6 6 6 6 4 3 7 7 7 7 7 5 (1) As it can be seen, if a signal is applied to port 1 or port 4 the power is equally divided into ports 2 and 3. On the other hand, if two signals are applied to ports 2 and 3, the signal on port 1 is the sum whereas the signal on port 4 is the difference of them. Applications of this circuit are several, such as in mea- surement set-up, antenna feeding, etc. A typical waveguide magic Tee is intrinsically 3D, in fact the difference port is usually orthogonal to all other ports [15], making the realization of this device not so easy by using planar technol- ogy. In the literature, there are some magic Tee implementations in SIW. Most of these solutions use mixed SIW/microstrip trans- mission lines in order to overcome the problem and make the device planar [16,17]. Waveguides and microstrips are connected together by using a slotline, which also enforce the isolation between the sum and difference ports, thanks to the field symme- try of its propagating mode. These circuits, however, suffer the radiation by the slot, that increases the losses. In this respect, a closed device allows better performance. Figure 1 Sketch of the designed magic Tee. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] Figure 2 Layer of the magic Tee implementing the sum part. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary. com] 932 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 58, No. 4, April 2016 DOI 10.1002/mop