Band Gap Based Power Dividers in Parallel Plate Waveguide Technology

In this paper is described a novel and low-cost method for the realization of electromagnetic band gap (EBG) based power dividers in Parallel Plate Waveguide Technology (PPW). The proposed configuration can be employed as a basic element of the highly efficient Continuous Stub (CTS) array antenna feeding network. The resulting band-gap feeding network overcomes the problem of good electrical contact between the metallic layers thanks to the use of printed mushroom-type EBG embedded inside the PPW. The EBG is designed to provide a forbidden band that covers the operating frequency range of the waveguide, in this manner electromagnetic leakage from the air gap between layers is avoided simplifying the mechanical assembly of the antenna with a significant reduction of manufacturing costs and complexity. The metallic units of the CTS antenna can be easily fixed by screws, and no additional welding assembly is required. A design example operating in the 27.5-31 GHz band (Tx Satcom band) is presented and compared with a classical configuration. The proposed solution provides a good matching on the whole bandwidth, while the insertion loss remains unchanged.

I. Introduction

Continuous Transverse Stub (CTS) planar arrays have attracted considerable attention since their invention in the early 1990s [1]. This type of antenna provides advantages in terms of compact size, low loss, low cross-polarization and high efficiency. CTS arrays are usually composed of an arrangement of parallel-plate waveguide apertures radiating in free space, providing wideband and wide-scanning properties. Parallel Plate Waveguide (PPW) based corporate feeding networks are usually employed to feed these arrays [2]–[5] to guarantee high gain and power handling capability (figure 1). These type of array naturally radiate in linear polarization while circular polarization can be achieved by using polarizers [6]. One of the main disadvantages of CTSs is the complex manufacturing procedure that requires costly bonding or brazing processes. Layers of corrugations and adhesive are often needed to guarantee good electric contact between the metallic components of the array. Air-gaps between the assembled metallic layers need to be accurately avoided to guarantee good antenna performance. In this work is described a novel and low-cost method for the realization of electromagnetic band gap (EBG) based power dividers in Parallel Plate Waveguide Technology (PPW). The EBG is designed to provide a forbidden band that covers the operating frequency range of the waveguide, in this manner electromagnetic leakage from the air gap between layers is avoided. The units of the CTS array can be simply fixed by screws, and no additional welding assembly is required. A design example operating in the 27.5-31 GHz band (Tx Satcom band) [7] is presented in this work and compared with a classical configuration. The new configuration provides a good matching in the whole bandwidth, while the insertion loss remains largely unchanged. Figure 1.

CTS array antenna with parallel plate waveguide (ppw) based corporate feeding network

Figure 2.

(A) parallel plate waveguide t-junction (classical configuration), wu1=1.03mm, step1=0.445mm, hs1=0.962mm, h1=0.962mm,wd1=2mm. wu2=1.03mm, step2=0.445mm, h2=0.962mm,wd2=2mm, h3=2mm. (c)mushroom ebg elementary cell, p=. 8mm, hsub=0.762mm,h2=0.962mm,w=1.7mm, r=0.3mm.