Novel Low Profile Rectangular Microstrip Patch Antenna for L-Band Applications Using High Permittivity Substrate

A novel low-profile and miniaturized patch antenna on a substrate material of high dielectric constant has been designed, fabricated and tested in an indigenous laboratory. It is highly important to reduce the size of patch antenna as it limits the reduction of the sizes of the devices using this antenna. A number of techniques have been given for the size reduction of patch such as DGS (Defected Ground Structure), use of fractals and the use of metamaterials but in this paper the technique of high permittivity substrate has been implemented. The substrate as well as this conventional antenna has been prepared locally in Pakistan.A ceramic material of chemical composition {(Sr 0.5 Pb 0.25 Ca 0.25 )-Tio 3 -3Bi 2 O 3 .TiO 2 } having a high dielectric constant has been used in the substrate of the antenna. The fabricated prototype was investigated experimentally for important parameters using Vector Network analyzer. The total measure of the antenna is 20.5x26.5x1.5 mm. The antenna presented a large bandwidth of 186 MHz (1070-1256 MHz) in L-Band with a Return Loss of 21.10 dB at resonance. The VSWR (Voltage Standing Wave Ratio) remained under the standard value of 2 in the whole operating range. The proposed antenna may be employed in GPS (Global Positioning System) devices, Amateur Radio, Terrestrial Mobile Communication, Aeronautical and Maritime Mobile and other Military and Low Earth Orbit Satellite Communications.


INTRODUCTION
A ntenna is a vital part of radio frequency transmitter or receiver. Antenna, commonly a mechanical structure is used to transmit or receive radio waves [1]. Microstrip Patch Antenna due to its inherent attractive properties has drawn the attention of antenna researchers and designers for past many years. Present day's smart wireless communication equipment has made it essential that antenna to be integrated in such devices should be of low profile [2]. Microstrip antennas are planar structures having three layers, central substrate layer and metallic radiating patch on its one side and a large metal ground on its other side [3] as displayed in Fig. 1 [4]. The patch and ground are conducting materials like copper, silver or gold while the substrate is a dielectric insulator. The radiations from the patch antenna are due to fringing fields from the edges of the Patch as depicted in Fig. 2 [5].
The patch may be printed on the substrate using printed circuit board technology. The patch pattern may be of any shape, however some common shapes are as shown in Fig. 3 [7]. Numerous feeding techniques are available to couple EM energy to the patch antenna; among them are contacting and non-contacting methods [8]. Many models have been suggested to analyze patch antenna in which transmission line model is the most common model [9]. The main distinguished features of patch antennas are small size, low weight, conformability to different shapes and curvatures, easy fabrication and easy integration with printed electronic circuits [10].
However, patch antennas inherently suffer from small bandwidth low gain and comparatively large size at low frequencies [11]. Extensive research in past years has been dedicated to overcome these shortcomings. Many useful techniques have been proposed to enhance bandwidth [12] and increase gain [13]. In today's scenario of smart devices era size reduction of the patch antenna is becoming a hot issue. The antenna size is proportional to the wavelength of designed frequency.
Hence the size reduction at lower frequency is more critical. In past, a lot of work has been done for achieving miniaturization of patch antenna. Different techniques have been suggested like implementing defected ground structure [14], implementing slots in patch [15], use of shorting pins [16], use of high permittivity substrates [17] and introduction of parasitic patches [18]. Use of dielectric with high constant is very fruitful mechanism for achieving size reduction [19]. The same concept has been worked on in this paper. A ceramic material whose chemical composition is mentioned in the abstract has been implemented in this design. Firstly, all constituents were mixed proportionally to their weight. The powder format material was then mixed for many hours in a ball mill machine. Pellets were prepared shaped in a dye of required format using a high-pressure press machine.
The pellets were sintered in high temperature furnace giving a stay at 1300C for 3 hours. The sintered items were then cleaned and polished to final shape using grinding machine. The material has very high dielectric constant and it has drastically reduced the antenna size at the desired frequency.
It has been described in [20] that the structure and dimensions of the antenna changes the output  [7] performance. In addition, the permittivity of the substrate material plays a crucial role in antenna's characteristics.
The So some researchers are of the opinion that these materials are costly and as this material has been prepared locally so it is cost effective. Secondly the material that has been used in this design has a reasonable bandwidth.
A miniaturized significant gain triple band patch antenna of antenna size (31.25x37.05x0.762mm) has been demonstrated in [22] and it has larger size than the proposed antenna in this paper.
Ali et. al. [23] has mentioned a microstrip patch antenna which has a size of 65x56mm and its center frequency is 960MHz. Its return loss at the center frequency is 12.3dB while the return loss of the proposed antenna is 21dB. So the size as well as the return loss of the proposed patch antenna in this paper are far better than [31].

DESIGN AND FABRICATION OF THE PROPOSED ANTENNA
The three selections to be made before designing of a The optimal parameters are listed in Table 1 (1)

RESULTS AND ANALYSIS
Important performance characteristics of the fabricated antenna were experimentally investigated using Vector Network Analyzer. Bandwidth, VSWR, Return Loss and Input Impedance were measured and are briefed given in Table 2.

Resonance Frequency, Bandwidth and Return Loss
The as well is 1256MHz.

Voltage Standing Wave Ratio
The VSWR graph is shown in Fig. 6

Smith Chart and Antenna Impedance
The

CONCLUSION
Experimental investigation of a novel compact rectangular patch antenna loaded with a locally synthesized high permittivity ceramic was carried out.
The miniature antenna may be used for the desired resonant frequency resonated in L-band. The size of the antenna has been drastically reduced for such a low frequency due to loading of novel material. High permittivity materials are not available; however, these may be synthesized by preparing different composition of ceramic materials. The concept was introduced that small sized patch antennas may be realized using these ceramics. This antenna is a better candidate for low earth orbit satellites, GPS and other aeronautical and maritime wireless communications.