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A printed, Linearly Tapered Slot Antenna for 11.0 GHz was theoretically
designed using the Stepped Approximation Method (SAM). The designed and calculated
values have been optimized for wide band performance using the Computer
Simulation Technology (CST) Microwave Studio. This microstrip antenna was fabricated
on polytetra fluoroethylene (PTFE) and finally tested for its RF wideband
performance. Various antenna parameters such as Voltage Standing Wave Ration (VSWR),
radiation pattern, energy loss and 1:2 VSWR bandwidth were measured and the same
recorded in the plots. The performance of this antenna system indicated its
multi-frequency operation as a wideband Traveling Wave Antenna in the end fire mode. Also,
the dielectric constant performance variation with frequency was tested in RF lab
to confirm the effectiveness of its wideband multi-frequency operation.
The planar end fire Tapered Slot Antenna (TSA) is a novel technique on which very
few theoretical studies have been done (Richard and Rainee, 1997). Hence, very
little information and analysis is available in refereed resource literature. These types of
radiating structures find wide applications (Schaubert et al., 1985) as a feed for reflector or
lens antennas, in radar, for imaging including phased array radars. The other
applications include: remote sensing, satellite communication and MMIC-based wireless
communication systems. Its accurate design, precise fabrication, impedance matching over a wide
range of frequencies (in case of multi-frequency wideband operations) and wide bandwidth
are quite time-consuming and laborious; and it demands high-end software to optimize
these kinds of structures. Experimental investigations have revealed that the electrical
and structural properties contribute to the overall performance of the radiating
structure. Various antenna parameters, such as the type of dielectric substrate, its
thickness, associated tangential loss, the permittivity variation with frequency and
temperature, significantly affect the overall performance of the planar
Linearly Tapered Slot Antenna (LTSA), especially under high frequency operations. The geometrical parameters
like size of the ground plane, slot dimensions, angle of taper, etc., are also to be considered
in analyzing the performance. Further, the LTSA is a slow surface wave structure
(Schaubert et al., 1985; and Richard and Rainee, 1997) with limitations like
non-resonant, and formation of standing waves that greatly reduce the RF bandwidth. TSA
structure offers significant distinguished advantages (Gupta and Garg, 1976; and Garg et al., 2000) over MSA, like uni-directional and bi-directional radiation fields, wide bandwidth,
low spurious radiation and cross polarization in the desired band.
Because of the complex mathematical limitations of the Transmission Line Method
(TLM), Moment Method (MOM) and Finite Difference Time Domain (FDTD), the LTSA
structure was analyzed using SAM (Gupta and Garg, 1976; Huang et al., 1995; Garg et al., 2000; and Stockbroeckx, 2000). As the impedance of printed LTSA depends on the
separation between the two surfaces that is a function of the linearly increasing width of the
slot opening, the tapered section is uniformly divided into a number of quarter
wavelength slots, i.e., subsections with progressively increasing width. Using this quarter
wavelength impedance matching method, the reflection coefficient associated with each of the
sub-sectioned step was calculated. The same was optimized in the simulation.
The assumption for the SAM analysis is that the lateral edges extend to infinity, while
the power conservation law validates at each step discontinuity; further, no reflection
or radiation occurs at the step junction, and hence a full wave analysis is not
necessary which creates a far field radiation pattern. Henceforth, in the light of the above
assumptions and approximations, total far field is determined by algebraically adding the
contribution from all different quarter wave sections. |
