76-81 GHZ PLANAR ANTENNA DEVELOPMENT AND UTILIZATION FOR RADAR APPLICATIONS
4
Two examples of antennas on currently available automotive radar products are
presented below. Figure 1.5 shows the antenna used o radar sensor
ARS 300 [13]. It consists of four parts: a rotating drum with grooves, a dielectric waveguide,
a reflectarray, and a transreflector (not shown in the picture). The electromagnetic wave
propagates along the dielectric waveguide is periodically perturbed by closely placed grooves
of rotating drum so radiation occurs; the radiated beam is firstly reflected and then passes
through the top transreflector. Beam scanning is achieved by rotation of the drum and
auto-alignment could be performed by tilting the reflectarray. sensor
shown in Figure 1.6 is equipped with a number of microstrip patch antenna arrays [14]. Each
array is made up of several series-fed rectangular patch rows which are connected to a
corporate feed network, and amplitude taper is utilized to improve the sidelobe suppression.
Because the above-mentioned off-chip antennas are implemented separately from the
frontend chips, the transitions and connections in between will take up extra space and
increase total cost. Since early 2000s the solutions to further antenna integration has been
investigated, and new research topics such as antenna on chip (AoC) and antenna in package
(AiP) have received great attention in recent years. In 2010, researchers from Bosch reported
a 77 GHz radar transceiver chip with two integrated patch antennas separated by a distance of
[15]. The total chip size was 3.25×3.25 mm
2
and a parasitic resonator was placed above
each antenna to improve its performance. On the following year, A. Fischer et al. presented a
77 GHz folded dipole antenna in embedded wafer level ball grid array (eWLB) package [16].
The antenna was implemented on the redistribution layer and the whole package area was 6×6
mm
2
.
Despite their promising prospects, the on-chip antennas suffer from poor radiation
efficiency due to the low resistivity nature of silicon substrates, and the achievable gain of
AiP is limited since it is very difficult to increase the number of antenna elements within the
package size. Also, both AoC and AiP face EMI issues. To meet these challenges, more effort
will be put into future research.
The antenna group at Chalmers University of Technology has developed gap waveguide
[17]-[19] V-band, E-band and UWB antennas for future wireless communication and
automotive radar systems, e.g., slot array antennas [20], [21], horn array antenna [22] and
other different UWB antennas [23]-[27]. However, these antennas have not been
manufactured yet due to high costs.
1.3 Aim of the Thesis Project
The goal of this master thesis project is to build the receiving and transmitting antennas for
77 GHz automotive radar prototype. The antennas should be optimized at 76.5
GHz as well as providing adequate performance over the 76-81 GHz frequency range.
Microstrip technology is chosen for the implementation of antennas as it is an economical
solution from the commercial point of view. At millimeter-wave frequencies, the gain of a
single-element microstrip antenna is usually not high enough so various arrays are formed,
among which rectangular patch array and comb-line array are widely used for automotive
radar applications. Here the latter is selected for the sake of flexibility in polarization
orientation.