omni directional cylindrical patch antenna

International Journal of Latest Research in Science and Technology Volume 4, Issue 4: Page No.78-83, July-August 2015 http://www.mnkjournals.com/ijlrst.htm

ISSN (Online):2278-5299

OMNI DIRECTIONAL CYLINDRICAL PATCH ANTENNA Sukhdas Ahirwar, Takeshore Khumanthem, Chandana Sairam, Sheilu Singh Defence Electronics Research Laboratory Chandrayangutta Lines, Hyderabad-500005, India Fax No. 91-040-24440525 Abstract- In this paper, design and development of an omni directional patch antenna is presented. A planar patch antenna is transformed into cylindrical shape like the shape of wire antennas. This shape being symmetrical in horizontal plane provides omni directional radiation patterns in azimuth plane. Planar patch antenna is conformed into semi-cylindrical and finally in cylindrical shape. Impedance and radiation characteristics are compared for these conformal antennas with conventional planar patch antenna. Simulated and measured results are presented. Key words- Antenna, Cylindrical patch, Conformal, Omni directional

I. INTRODUCTION Omni directional antennas are the antennas which provide uniform radiation patterns in a plane and directional patterns in orthogonal plane. Such types of antennas are preferred antennas in broadcast and different types of communication systems. In these systems, there is no directional restriction on the coverage of the antenna. Wire antennas such as dipole, monopole and their variants are the conventional omni directional antennas [1-10]. Patch antennas are conventionally directional antennas. Different types of modified patch antennas for achieving more bandwidth and beamwidth can be found in literature [11, 12]. Conformal antennas are gaining more attention now days to reduce their projection on platform, concealing the antenna within the platform to make it as integral part of the platform and to improve the aesthetic of the system. Such types of conformal antennas and antenna arrays are also reported [13-16]. In this paper, the planar antenna is conformed to semi cylindrical and finally in cylindrical shape to get omni directional radiation patterns. The effect of this conformity on electrical behaviour is also studied in the frequency range of 0.849GHz- 0.864GHz. II. ANTENNA DESIGN AND REALIZATION A planar patch antenna is modeled in MoM based EM Simulation software. Patch dimensions for planar patch antenna are taken as L=110mm and W=152mm on a grounded RT- Duroid (år = 2.2) substrate of dimensions 160mm X 200mm and thickness 1.6mm. These dimensions in terms of wave length (ë) are 0.47ë x 0.64ë at centre frequency 0.857GHz where ë is wave length in dielectric. Similarly, ground plane dimensions are 0.68ëx 0.85ë. This planar antenna is conformed into semi cylindrical form taking ground plane width (200mm) as semi circumference of cylinder and 63.7mm as radius. Similarly this structure is transformed into cylindrical form by taking ground plane width (200mm) as circumference of cylinder and radius of 31.8mm. In this configuration, both the sides of ground plane are joined together electrically and it takes the shape of ISSN:2278-5299

cylinder. Similarly patch is transformed into cylinder with a gap of 48mm between its non- radiating edges. The antenna was realized on double sided printed laminate (RT- Duroid, 5880, ht.=1.6mm, år = 2.2). The same antenna hardware is used for other two antenna configurations. For this, the antenna is bent into semi cylindrical and cylindrical shapes. Simulation models and corresponding photographs for these three antenna configurations are shown in Fig. 1(a-c) and Fig. 2(a-c) respectively.

Fig. 1(a) Planar

Fig. 1(b) Semi cylindrical

Fig. 1(c) Cylindrical Fig. 1(a-c): Simulation models of three antenna configurations

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International Journal of Latest Research in Science and Technology.

Planar Semi cylindrical Cylindrical

Fig. 2(a): Planar Fig. 2(b): Semi cylindrical

Fig.4: Measured impedance plots of Planar, Semi cylindrical and cylindrical patch Antennas

Fig. 2(c): Cylindrical Fig. 2(a-c): Photographs of three antenna configurations III. RESULTS AND DISCUSSIONS All the three antenna configurations were evaluated for their impedance characteristics. VSWR of these antennas were measured using M/s Agilent Vector Network Analyzer E5071C. Comparison of simulated and measured VSWR plots for all three antenna configurations are shown in Fig.3. Measured impedance plots comparison is shown in Fig.4.for planar, semi cylindrical and cylindrical patch antennas.

5 4 1

2

3

VSWR

6

7

Planar (Simulated) Planar (Measured) Semi cylindrical (Simulated) Semi cylindrical (Measured) Cylindrical (Simulated) Cylindrical (Measured)

As evident from Fig.3 and Fig.4, the impedance of planar patch antenna is more reactive with lesser resistive part. VSWR for this configuration is 2:1. In semi cylindrical patch antenna, reactive part of the antenna impedance decreased and improvement in the VSWR is observed. Finally in cylindrical patch antenna still better VSWR is achieved due to reduction in reactive part and improvement in resistive part of antenna impedance. At centre frequency (0.857GHz), the impedances were 42.7+j31.7Ω, 47.5+j11.7Ω and 52.9-j5Ω respectively for planar, semi cylindrical and cylindrical patch antennas. All the three antenna configurations were simulated and evaluated for their radiation characteristics. Elevation and azimuth plane radiation patterns were measured in anechoic chamber. These radiation patterns are overlaid for comparison at four different frequencies. Simulated and measured E-plane radiation patterns are shown in Fig. 5(a-d) and Fig.6 (a-d) respectively.

Start 830 MHz

Stop 880 MHz

Fig.3: VSWR comparison of three antenna configurations Fig. 5(a): E-Plane: Freq.0.849GHz ISSN:2278-5299

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Fig. 6(a): E-Plane: Freq.0.849GHz Fig. 5(b): E-Plane: Freq.0.855GHz


Fig. 6(b): E-Plane: Freq.0.855GHz Fig. 5(c): E-Plane: Freq.0.860GHz


Fig. 6(c): E-Plane: Freq.0.860GHz Fig. 5(d): E-Plane: Freq.0.865GHz Fig.5 (a-d): Simulated E-plane radiation patterns of Planar, Semi cylindrical and cylindrical patch Antennas ISSN:2278-5299

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Fig. 6(d): E-Plane: Freq.0.865GHz

Fig. 7(b): H-Plane: Freq.0.855GHz

Fig. 6(a-d): Measured E-plane radiation patterns of Planar, Semi cylindrical and cylindrical patch Antennas As can be seen from Fig.5 and Fig.6 there is good agreement between simulated and measured elevation plane radiation patterns. The beam width for all three antenna configurations is of the similar order. Gain variation in these antenna configurations is within ±0.5dB. Although a larger back lobe is observed for cylindrical patch antenna due to its omni directional behaviour but it shows better gain compared to other two antenna configurations because of better impedance match. Measured gain of the antenna varies from 4dBi to 5dBi. Simulated and measured H-plane radiation patterns are shown in Fig. 7(a-d) and Fig. 8 (a-d) respectively. As evident from these plots, simulated and measured radiation patterns are in good agreement. Planar patch antenna has directional Hplane radiation patterns as it is expected. For semi cylindrical patch antenna, the H-plane radiation patterns are approximately omni directional as omni deviation is more. In cylindrical patch antenna, the H-plane radiation patterns are omni directional. Hence in this case, radiation properties of the antenna are similar to conventional omni directional antennas.

Fig. 7(c): H-Plane: Freq.0.860GHz

Fig. 7(d): H-Plane: Freq.0.865GHz Fig. 7(a): H-Plane: Freq.0.849GHz ISSN:2278-5299

Fig.7 (a-d): Simulated H-plane radiation patterns of Planar, Semi cylindrical and cylindrical patch Antennas 81




Fig. 8(a): H-Plane: Freq.0.849GHz

Fig. 8(d): H-Plane: Freq.0.865GHz Fig.8 (a-d): Measured H-plane radiation patterns of Planar, Semi cylindrical and cylindrical patch Antennas


Fig. 8(b): H-Plane: Freq.0.855GHz

IV. CONCLUSIONS A patch antenna is designed, realized and it is conformed to semi cylindrical and cylindrical shapes. Simulated and measured results of conventional planar patch antenna are compared with semi cylindrical and cylindrical patch antennas. It is found that there is improvement in impedance matching for these conformed geometries of patch antenna. The H-plane beam width of patch antenna increases with increase in curvature of bending of the antenna. For fully cylindrical shape of patch antenna (sides of ground plane adjacent to non radiating edges of patch antenna are joined together electrically), H-plane radiation patterns are omni directional similar to other conventional omni directional antennas. This type of antennas can be preferred antennas structures for vehicular and body borne communication systems where omni directional coverage can be achieved with minimum risk of RF exposure. As RF exposure to human body can be limited by the ground plane of the antenna. REFERENCES


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Fig. 8(c): H-Plane: Freq.0.860GHz 6.

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