The document discusses the design and development of a phased array antenna intended for FMCW radar, addressing its application in snow avalanche detection. It outlines the antenna's features, including a unique overlapping subarraying technique to improve performance while minimizing unwanted grating lobes. Additionally, the document highlights testing results indicating the antenna's effectiveness in producing high-resolution images of snow avalanches.

2. Introduction ~
 Snow avalanche - A significant threat to human life and infrastructure.
 Based on analysis of area, risk zones calculated.
 FMCW radar- An remote sensing tool that can be used to characterize the
snow avalanche by transmitting chirp towards the target continuously.
 Radar requires an antenna with steering capabilities.
 This seminar presents the design and development of an Advanced Phased
Array Antenna for an FMCW radar.

3. PHASED ARRAY ANTENNA ~
 Gain or Radiation pattern requirements- single element antennas are
unable to fulfil.
 An antenna array - Set of N individual separated antennas which is common
for the receiving arrays.
 Improves the reception and transmission patterns of antennas used in (WCS)
 Enabled - electronically steered – to receive or transmitte info from a
particular direction without mechanically moving the structure.
 The signals from the individual
antennas are combined in order to
achieve improved performance over
that of a single antenna.

5.  In designing the antenna the unwanted grating lobes are the function of
phased array inter-element spacing.
 Several techniques can be utilized to avoid grating lobes. One approach is
to utilize,
 Overlapped Subarrays based on Butler matrix.
 Amplitude tapering technique .
 Developing a phased array antenna
 Modeling of an array of radiating elements .
 Power distribution network to each array element.
 The microstrip patch antenna is a good coz
 Its low-profile and simple structure.
 The microstrip antenna suffers from narrow bandwidth.
 Sol’n- Techniques using parasitic elements and slot techniques.

6.  Power distribution feed network design play a impt role in assigning the
required amount of power to each phased array element.
 Types of phased array feed network-
 Optical space feed. (reflection loss and low level of flexibility)
 Series feed . (α Path Length α Frequency α Bandwidth)
 Parallel feed.
 The parallel feed is independent on the path lengths and it has a simple
structure .
 Wilkinson power divider is been widely used for radar applications.
 Therefore, Diamond Two-in Two-out splitter is proposed which assigns the
required amount of power to the overlapping elements.
Fig. Diamond Two-in Two-out splitter layout

7.  Parameters in designing a phased array antenna-
 Number of elements -16
 Inter-element spacing
 Beamwidth.
 Config. of Phased Array Antenna ~
 200 MHz bandwidth at 5.3 GHz centre frequency Fig. Sub-arraying technique
 ±14º beamwidth in azimuth and ±22.5º fixed elevation angle.
 14.4 dBi gain and -20.3 dB sidelobe level.
 16-element fully populated phased array.
 Subarraying: Utilized by combining elements in the inter-element
spacing to act as a given array element.
 Advantages - Aperture size is increased
 Higher gain and Narrower beamwidth.

8.  Overlapped Subarray: The overlapping technique thus increases the
distance between the grating lobes ie. narrows down the phased array
beamwidth.
Fig. Overlapping subarray with two shared
elements.
Fig. Overlapping subarray with one shared
element.

9.  Elevation angle: Antenna requirement- fixed ±22.5◦ elevation angle.
Achieved by adding a second row of elements.
 Phased array antenna modelling-
 Step 1- Model a radiating element to get the reqd antenna config.
 Step 2- Design phased array feed network based on the weightings.
 Step 3- Design a bandpass microstrip filter to reject the unwanted band
of frequencies.

10.  Developed in the University College London (UCL) workshop.
 Fabricated by TrackWise manufacturer.
 Avalanche test site at Alps, Switzerland
 Radiating element design - The microstrip antennas also have several
drawbacks.
 Narrow bandwidth.
 Spurious feed radiation .
 Fabrication tolerances.
 A multilayer phased array structure was proposed to compensate for the
drawbacks.
 The array radiating elements are mounted on thicker substrate to
increase the antenna bandwidth.
 Feed network design - Is used to deliver the required power to the
phased array elements.

11.  A feed network is flexible and easier to develop for the cases where 2 D
array orientation is required.
 Required to achieve 3 db power difference between the phased array
non-overlapping elements and overlapping elements.
 The half of the power at the centre of each sub-array should go towards the
non-overlapping elements while a quarter of the power should go towards
the overlapping elements.
 To achieve 3 db power difference -Diamond two-in two-out power splitter
was proposed.
Fig. Three element
phased array
antenna

12.  16-ELEMENT PHASED ARRAY BEAM STEERING –
 It was optimized and designed based on results achieved for a single
element prototype.
 The steering capability of the antenna was tested by applying phase shift
to the 16-element antenna elements.
 Antenna was nominally steered to 0◦,10◦ and 14◦.
 Fig. 16-element phased 10◦ 14◦
array pointing to 0◦

13.  Full-scale avalanche antenna –
 To show the functionality of the antenna to produce high resolution image
of the snow avalanche, the initial results from the large avalanche which was
artificially triggered.

14.  The signature of moving helicopter is captured by the developed phased
array system which proves that the antenna can be used for high resolution
imaging.
 In Fig the phased array radar system captures the full avalanche, which
is a complex, distributed target.

15. Disadvantages of the Antenna –
 The unwanted grating lobes.
 Narrow bandwidth.
 Fabrication tolerances.
 Coverage limited to 80 degree sector(approx).

16.  Others Applications……………
 Weather research usage

17.  Avionics usage –

18.  Military usage-

19.  Conclusion -
 In this paper a phased array antenna for an FMCW radar is
presented.
 This system has the potential to produce high resolution images in
two dimensions.
 The proposed phased array antenna for the FMCW radar is a 16-
element fully populated uniformly spaced antenna with a unique
structure to achieve the required antenna beamwidth while
suppressing unwanted grating lobes, utilizing an overlapping
subarraying technique.

20. REFERENCES
Antenna theory , Constantine A. Balanis, Wiley, 1997
Phased array antenna handbook, Robert J. Mailloux, Artech
House, 1994
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
http://www.radartutorial.eu/06.antennas/an16.en.html