SIW Based Wideband Horn Antenna

In this paper, we have proposed CSRR (complementary split ring resonator) loaded Substrate Integrated Waveguide (SIW) horn antenna. The whole system is designed on a single substrate, having advantages of small size, low profile, and low cost, etc. The design process and simulation results of a CSRR-loaded SIW horn antenna at K-band and Ka-band are presented. The proposed antenna is an outstanding choice for K, Ka bands and even higher frequency synthesis. It has well-behaved gain and suitable reflection coefficient value less than 1.5 (-10dB S11 and VSWR<1.5). The simulated gain of antenna attains 7.48±1dB over majority of the bandwidth and with radiation efficiency of 85%. The simulation has been done using full-wave package, High Frequency Structure Simulator Software (HFSS) based on Finite element method (FEM).


INTRODUCTION
To facilitate enrich the demands of a wider bandwidth in support of exploding data transmission, the operating frequency of satellite and wireless communication systems have been increasing to the high range frequencies [1]. To migrate from low frequency bands to high frequency bands provide wider bandwidth and low atmospheric absorption. It also gives the capability of long range wireless data transmission for point to point communication. There are various applications, such as Imaging and communication satellites, uplink in the Ka band and downlink between Ku-band. All these type of applications require light weight, low cost, and high gain antennas, which constitute most critical parts of such systems.
Most suitable antennas for such kind of applications are from planar structure. However, this type of antennas like microstrip antennas suffers from serious losses particularly at bends and discontinuities by increasing frequency [2]. Although numerous planar antennas have been studied for Ka band communication and radar systems in which the increasing of frequency accompanied with the decreasing of radiation efficiency due to the inherent losses on the microstrip feeding network. Non-planar structure is the alternate for planar structure that provides low losses and high power handling capacity. However, it is difficult to configure the non-planar structure to planar active components. So, SIW was proposed to overcome the mentioned hurdles [3]. It enjoys not only the advantages of non-planar features, but also other benefits, namely, compact, low cost, light weight, easy to manufacture using PCB technique and other planar processing technologies, and also being easily connected to coplanar waveguide utilizing a wideband and uni-planar transition [4].
SIW structure consists of arrays of metallic posts created in a planar substrate. There various devices are designed and fabricated using these techniques. One of the vital application of this technique is horn antenna. It has numerous of applications because of its simplicity, wide bandwidth, and high gain. However, the dimension of the antenna becomes smaller with increased frequency (due to the shorter wavelength). It required a micromachining fabrication process [5].
SIW based horn antennas are less costly and can easily be interfaced with CPW or microstrip line [6][7][8]. However, its bandwidth is not wider and they radiates in parallel to the substrate that is not suitable for many practical applications [9]. So it is required to make a structure having wider bandwidth and better gain. Recently, it is found that the inclusion of SRR (Split Ring Resonator) and CSRR (Complementary Split Ring Resonator) not only improve the gain, it also increases the bandwidth of filters as well as antenna [10][11][12]. This type of structures is based on metamaterial concepts. In this paper, CSRRs structure is first cut from the ground plane in order to increase the bandwidth of a simple microstrip patch antenna. The sub-wavelength resonances can be chosen to realize an electrically small antenna. On the other hand, the higher modes of the CSRRs are selected to merge with the main resonance of the patch antenna. For this, the CSRRs rings are embedded to the boundary of the patch. On account of the wider bandwidth the right-handed resonance will yield to the design. Then, the CSRRs structure is modified with crossovers that are installed in the structure of a traditional MA. More details of the design principles of the proposed antennas are described and their simulation results are shown.

ANTENNA CONFIGURATION
As shown in fig. 1, it contains the basic horn antenna configured using planar technology (SIW technique). Integration of rectangular waveguide and horn antenna using SIW technology provide compact structure and ease of fabrication [13]. It shows that the horn antenna is created with the use of metallic vias (It connects top and bottom plane of the structure). Taper type of microstrip feed line is use for the microstrip to waveguide transition [13][14][15][16]. In this design, the dominant mode is TE10 and we have taken the center frequency 21.5GHz. For the propagation of fundamental mode, the width a and thickness b should be selected from, where is free space wavelength and is permittivity of dielectric medium.  This structure is simulated by using HFSS, it is full 3D EM solver based on FEM (finite element method). The Scattered parameter of this structure is shown in fig. 2. As shown in fig. 2, this structure is resonant at three different frequencies 21.28GHz (21.2 GHz to 21.82 GHz) , 24.2GHz (24.00 GHz to 24.30 GHz) and 26.4GHz (26.2 GHz to 27 GHz) respectively. It gives -10dB bandwidth is more than 250MHz. Fig. 3 show the gain plot of the antenna that contains more than 7dB gain. The radiation pattern in E-plane and H-plane is also shown in fig. 4. In this pattern, there is few side-lobes generated which is happened due to air gap between two posts of the SIW structure.  (1)If the equivalence capacitance of the CSRR is increased, the resonant frequency shifts towards the lower frequency. Fig. 6 shows the simulated scattering parameter of CSRR loaded SIW antenna. As shown in fig. 6, this proposed antenna resonates three different frequencies 21.7 GHz (K-band), 24.2 GHz (K-band) and 27.13 GHz (Ka-band) respectively. Inclusion of CSRR in ground plane is shifted the resonant frequency to the lower resonant frequency while it increased bandwidth around 600 MHz at first resonant frequency in K-band and 400MHz at 3rd resonant frequency in Ka-band. However, inclusion of CSRR in ground plane also reduces the radiation efficiency and return loss. Figure 6: S11 of Single CSRR-loaded SIW horn Antenna Figure 7: 3D plot Gain of CSRR-loaded SIW horn Antenna Finally, we have introduced another split ring into CSRR for improving response, the structure of 3 CSRR is shown in fig. 8a and its equivalent circuit is shown in fig. 8b. Fig. 9a, 9b and 9c shows the top, bottom and side view of the proposed antenna.    Gain in dB 7.07 6.7 6

CONCLUSION:
It is concluded from the proposed designs that inclusion of CSRR in SIW based horn antenna provides better gain, wider bandwidth (four times the without CSRR in SIW horn antenna) and multiple resonant frequencies. This type of structure is very compact and will be used in LEO to LEO satellite communication where more than one antenna is required for tracking to other satellite.