This paper gives a general idea about half impulse radiating antenna (HIRA). The antenna structure of HIRA has been modeled using CST-MW studio. This antenna is used in Ultra-Wideband (UWB) High Power applications. The operating range is from 100 MHz to 12 GHz.
This antenna has been designed to radiate High Power Electromagnetic pulse with minimum dispersion. This paper focuses on simulation results of different feeding arm angles. Simulations of different feeding angles are carried out to optimize proper angle for better bandwidth and gain.
We achieved a wide bandwidth of 12 GHz and a gain of 20.23dB for f/D ratio 0.34 with a diameter of half parabolic dish 50cm. The antenna has its applications in Electromagnetic Compatibility (EMC) testing, ground penetrating radar, mine detection etc. Keywords: Half Impulse Radiating Antenna, UWB, EMC, CST-MS Studio. I. Introduction Society for Applied Microwave Electronics Engineering and Research, EMI/ EMC division, IIT Powai, Mumbai.
High magnitude electromagnetic pulses were first observed after the lightning strike or nuclear explosion, but nowadays anyone can generate them with ease. This EMP wave can interfere with working electronic circuit or may even damage it. To avoid that we must have some international standard that electronic circuit must pass. To ensure electromagnetic susceptibility of the electronic circuit we must generate high power electromagnetic field. To generate such high field, we require special antenna called impulse radiating antenna (IRA). IRA was first introduced by C. Baum1.
II. Need of impulse radiating antennasTo generate a high power electromagnetic field, we require an antenna. The input or source to this antenna is a short pulse, so to radiate that antenna should be UWB. For UWB antennas few suitable candidates are available such as Log periodic, TEM Horn etc. But log periodic antennas have a drawback of being dispersive and in case of TEM Horn phase front at the end of the antenna is spherical2.
IRA uses parabolical reflector dish to convert spherical phase front to planner phase front. IRA has a property that fast-rising step-like input to the antenna gives impulse-like far-field response3, so the bandwidth is very high. Half impulse radiating antenna is modified version of IRA. III. Basic structure of hiraHIRA consist of half parabolic reflector dish, feed arms with matching terminating resistors mounted on the ground plane.
Figure 1. Half impulse radiating antenna The antenna consists of 50cm diameter half parabolic reflector dish of aluminium with the focus to diameter ratio of 0.34. The half parabola is mounted on aluminium ground plane of size 90×90×0.3cm. The HIRA have two feed arms at angles to the ground plane with a combined impedance of 100?, so each feed arm has 200? termination resistor near attachment point to reflector dish. Terminating resistors are supported with Teflon.
Terminating resistors reduces reflections. The feed arms are transmission lines from the feed point to the reflector. They are located at the focal point. For minimum power loss feed arm’s characteristics impedance should be matched. 50? to 100? impedance matching adapter is required at input side4. This whole structure is mounted on the table of height above ground approximately 1.7m. IV.
feed arm angles termination Y Figure 2. Feed arm angles The location of feed arms can be determined by calculating , , . For better improvement like effective gain, higher aperture efficiency, cross polarization rejection etc these angles are calculated by5, (1) (2) (3) (4)where, k=0.7513 & We can also change characteristics impedance of feed arms by changing angle with the vertical axis.d V. Simulation results for different feed arm angles Here we have simulated the structure of Half Impulse Radiating Antenna of diameter 50cm with different feed arm angles in CST-MW studio and compared them. We have carried out simulations for five different feed arm angles 60, 50, 45, 40, 30 at frequency 6 GHz. Simulation result for feed arm angle with respect to vertical axis Figure 3 (a).
S11 parameter for angle Figure 3 (b). Gain for angle The bandwidth obtained for feed arm angle is up to 7GHz below -9dB and gain 16.82dB. Simulation result for feed arm angle Figure 4 (a). S11 parameter for angle Figure 4 (b). Gain for angleThe bandwidth obtained for feed arm angle is up to 10 GHz below -9dB and gain 18.44dB.
Simulation result for feed arm angle Figure 5 (a). S11 parameter for angle Figure 5 (b) Gain for angle The bandwidth obtained for feed arm angle is up to 10.5GHz below -9dB and gain 19.06dB. Simulation result for feed arm angle Figure 6 (a).
S11 parameter for angle Figure 6 (b). Gain for angle The bandwidth obtained for feed arm angle is up to 8.5 GHz below -9dB and gain 20.59dB.Simulation result for feed arm angle Figure 7 (a). S11 parameter for angle Figure 7 (b). Gain for angle The bandwidth obtained for feed arm angle is up to 10.
5GHz below -9dB and gain 20.23dB. VI. Conclusion Here we have simulated Half Impulse Radiating Antenna for different feed arm angles with respect to the vertical axis. As noted above, as we decrease the feed arm angle with respect to vertical axis we get better bandwidth and gain. For the feed arm angle to the vertical axis, we got full bandwidth of 12GHz and 20.
23dB gain. AcknowledgementThe authors would like to thank Society for Applied Microwave Electronics Engineering & Research (SAMEER) EMI/EMC division, IIT Powai, Mumbai for their support and providing required resources for our work.