The problem of positioning of antennas on large platforms such as aircraft or body of a vehicle involves design steps which require careful electromagnetic analysis of antenna in both standalone implementation as well as its fine tuning in the overall design. Capabilities of the Wave3D suite allow to perform such design with ease and rigour.
Below we outline the steps of Wave3D suite for design of a roof-mounted GPS antenna for 1.525GHz operation on board of Dodge Charger automobile (Fig. 1):
- Step 1: Coarse level parametrized electromagnetic modeling of standalone antenna for identification of appropriate geometrical parameters;
- Step 2: Fine tuning of the standalone antenna model to satisfy the design specifications;
- Step 3: Coarse level analysis of antenna in the presence of car body platform;
- Step 4: Parametrized electromagnetic modelling of the entire large model for final tuning of the overall design.
Fig. 1: Dodge Charger model (left) and roof-mounted microstrip GPS antenna (right) designed for operation at 1.525GHz.
Step 1: Coarse level parametrized sizing of antenna
As we intend to obtain low-gain omni-directional radiation characteristics we select pin-fed microstrip antenna design shown in Fig. 1 (left). We start off by creating initial design of the antenna in GMSH to parametrized over the width of the radiating element a and height of antenna b shown in Fig. 2 below.
Fig. 2: Designs of pin-fed microstrip antenna parametrized over width of patch a and antenna height b at the extreme corners of the design space (left and right) as well as at the optimal design parameters a=3.8 [cm], b=2.6625 [cm] (center).
Choosing the antenna substrate permittivity of 4.0 and considering approximately 1.5GHz targeted frequency of operation we initially perform electromagnetic analysis of the antenna over broad range of design parameters a and b. In Fig. 3 below the real and imaginary parts of the antenna input admittance Y11 are depicted for 56 competing designs parametrized over antenna width a and height b.
Fig. 3: Real and imaginary parts of the antenna input admittance Y11 for 56 different competing parameters of antenna width a and height b.
The line of intersection of the input admittance imaginary part ImY11 line with the zero level identifies the resonant design parameters a and b at which the return loss of the antenna can be made minimal as shown below in Fig. 4
Step 2: Fine tuning of the antenna parameters to satisfy design specifications
From the coarse level parametric sweep over design space we note that while antenna input impedance is sharply dependent on the antenna heigh b and is only weakly dependent over width a of the radiating element. Thus, to fine tune the design we fix the width a at 3.8 cm and conduct the fine step sweep over antenna heights a from 2.6 cm to 2.6675 cm and frequency range from 1.5 GHz to 1.525 GHz as shown in Fig. 5 below:
Fig. 5: Imaginary part of input admittance ImY11 (left), real part of input admittance ReY11 (center), and corresponding return loss magnitude |S11| (right) over the frequency range from 1.5 GHz to 1.55 GHz parametrized over antenna height b.
The fine sweep over height b reveals its optimal value b=2.6625 cm under the objective of minimizing the antenna return loss.
Step 3: Electromagnetic analysis of the overall system
Once standalone antenna design has been finalized we mount the antenna on the roof top of the car body and perform a large scale simulation of the overall system design. The analysis reveals intricate details of the antenna performance and changes in its parameters due to the presence of the car body. Visualization of the currents and near field for the overall system are depicted in Fig. 5 and Fig. 6 below
Fig. 5 Near field and current magnitude on the surface of the Dodge Charger vehicle produced by the designed pin-fed microstrip antenna.
Fig. 6 Vector current and E-field in the dielectric of the antenna in the overall model of the pin-fed microstrip antenna mounted on the roof of Dodge Charger vehicle.