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This paper will introduce the approaches for characteristics improvement of patch array antenna for electronic scanning radar application. The basic array antenna is designed on FR-4 substrate and we have used microstrip technique as feeding. This antenna is based on 4 patches operating at frequency 3GHz. This structure has two disadvantages; a low gain value caused by the lossy nature of substrate and a narrow bandwidth by dint of microstrip antenna limitations. Thus, the objective of this work is to improve the gain and the bandwidth of the basic structure. For this reason, two techniques will be presented and compared in this paper: Parasitic patches and multilayer techniques. The first one consists on adding a number of parasitic patches, two different ways of parasitic patches dispositions are proposed. The distance between driven and parasitic patches is evaluated. Regarding the second technique, a layer of FR-4 is added to the substrate distanced with air gap which thickness is 0.04. The design and the simulation will be performed using High Frequency structure simulator (HFSS) tool.
Electronic scanning is defined as a method of positioning an electromagnetic beam in space by electronic means with the antenna aperture remaining fixed in space and no mechanical mechanism involved in the scanning process. Admittedly, the mechanical mechanism has numerous disadvantages such as a complex high maintenance mechanical structure, slow orientation speed, high power requirements and large physical size. With electronic scanning radar, it is possible to obtain practically instantaneous slewing of an antenna beam to any position in a designated sector. Steerable antenna arrays are used in electronic scanning radar. In many applications, it is desirable to use phased array antennas, especially in aviation and spatial applications. In the late 1970s, microstrip antenna starts its journey and by the starting of 1980s, microstrip antennas were fully in operation for antenna design and modeling. For the last few decades microstrip antennas or printed antennas are extensively used for their inbuilt advantages like low profile, light weight, low cost and ease of fabrication. Microstrip antenna consists of a conducting or radiating patch on one side of the substrate and ground plane on the other side.. For its advantages, microstrip antenna type is chosen for our basic array antenna design. Despite their multiple advantages, microstrip antennas have limitations as narrow bandwidth and low gain. However, many of their limitations have been overcome by using different techniques. We can mention multilayer structures, broad folded flat dipoles, curved line and spiral antennas, impedance matched resonator antennas, resonator antennas with capacitive coupled parasitic patch element, log periodic structures, modified shaped patch antenna (H-shaped ).
- Steerable antenna arrays are used in electronic scanning radar
- Phased array antennas
- The mechanical mechanism has numerous disadvantages such as a complex high maintenance mechanical structure, slow orientation speed, high power requirements and large physical size.
- Not capable of working in mm wave applications.
- Less reception due to high return loss.
In this work, we have applied two techniques on the basic structure in order to improve its characteristics, the first one is about adding parasitic patches and the second one is related to the use of multi-layer. The parasitic patches are used widely in cellular applications, and going to be applied in our case for radar application. This operation is performed in order to make a comparison at the end between both techniques in terms of gain and impedance bandwidth. Next, second technique to improve array antenna characteristics which concerns the two layers substrate separated by air gap. In fact, the substrate thickness has a big role to improve the bandwidth while the surface waves are the cause of degradation of array antenna performance in particular. When a layer of air gap with dielectric constant equal to 1 is added, the surface waves are not excited easily because of the loss which is due to the decrease reflection. Moreover, a second layer of FR-4 which acts as a reflector is added to increase substrate thickness in order to get higher gain and also to redirect the propagation density from back lobe to main lobe.
- The proposed technique permits to obtain better value of bandwidth. In fact, by tuning air gap thickness, the resonant frequency of the microstrip structure is varied and the antenna bandwidth can be enhanced. In addition, better out-of-band rejection will be achieved in the proposed design.
- The multilayer technique gives a good gain value which equals to 16.6dB for air gap thickness of 4 mm separating two FR-4 layers. It has increased by 10.5 dB, besides the bandwidth has also raised by 278 MHz which gives us a value of 440MHz.
- It has good application value in modern wireless communication systems.
- Electronic scanning radar application
- ANSYS HFSS v14
In this paper, two major techniques for array antenna characteristics enhancement have been studied to see the impact on gain and bandwidth. First, the design and simulation results of the original 4×1 array antenna are presented. The structure, using FR-4 as substrate, is dedicated to electronic scanning radar application operating at 3GHz. Second, two techniques are applied consecutively to the basic array antenna; adding parasitic patches and using multilayer substrate. For the first technique, parasitic patches were added in parallel to the basic array and simulation results were investigated. Afterwards, the disposal of parasitic patches is modified to be arranged in tree structure in two branches. In both ways, the distance between radiating elements was varied to see the impact on gain. For the second technique, two layers of FR-4 separated by air gap are used as substrate. In this part, the thickness of air gap is evaluated in order to make a tradeoff between keeping the volume small and ensuring a good gain value.
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