Vivaldi Antenna Arrays Feed by Frequency-Independent Phase Shifter for High Directivity and Gain Used in Microwave Sensing and Communication Applications

Abstract

This paper describes a novel feed system for compact, wideband, high gain six-slot Vivaldi antenna arrays on a single substrate layer using a unique combination of power splitters based on binary T-junction power splitter topology, frequency-independent phase shifter, and a T-branch. The proposed antenna system consists of six Vivaldi antennas, three on the left, and three on the right arm. Each arm connects with T-junction power divider splitter topology, given that the right arm is linked through a frequency-independent phase shifter. Phase shifters ensure that the beam is symmetrical without splitting in a radiating plane so that highly directive radiation patterns occur. The optimal return losses (S-parameters) are well enriched by reforming Vivaldi's feeding arms and optimizing Vivaldi slots and feeds. A novel feature of our design is that the antenna exhibits the arrangements of a T-junction power splitter with an out-of-phase feeding mechanism in one of the arms, followed by a T-branching feeding to even arrays of proper Vivaldi antenna arrangement contributing high realized gain and front-to-back ratio up to 14.12 dBi and 23.23 dB respectively applicable for not only ultra-wideband (UWB) application, also for sensing and position detecting. The high directivity over the entire UWB frequency band in both higher and lower frequency ranges ensures that the antenna can be used in microwave through-wall imaging along with resolution imaging for ground penetration radar (GPR) applications. The fabricated antenna parameters are in close agreement with the simulated and measured results and are deployed for the detection of targets inside the voids of the concrete brick.

Keywords: Vivaldi antenna array; ground penetration radar; power dividers; ultra-wideband antenna.

Figure 1

Structure of antenna: (a) top view of the antenna presenting feed, substrate, and ground layer structure; (b) enlargement of the feeding top view section of an antenna from Figure 1a.

Figure 2

Proposed antenna with power divider: (a) power divider with E-field lines distribution at each segment 1, 2, 3, 4, 5 of a microstrip line; (b) top and bottom layer of the fabricated antenna.

Figure 2

Proposed antenna with power divider: (a) power divider with E-field lines distribution at each segment 1, 2, 3, 4, 5 of a microstrip line; (b) top and bottom layer of the fabricated antenna.

Figure 3

S-parameter with phase and magnitude of the power divider with phase-shifter at one of the arms: (a) output port return loss; (b) output port phase, and (c) magnitude.

Figure 4

Simulated and measured results of the antenna: (a) return loss; (b) realized gain.

Figure 5

Measured far-field radiation pattern at E-plane (a,c,e,g,i) and H-plane (b,d,f,h,j) at frequency 3, 4, 5.5, 7, 8.5 GHz, respectively.

Figure 5

Measured far-field radiation pattern at E-plane (a,c,e,g,i) and H-plane (b,d,f,h,j) at frequency 3, 4, 5.5, 7, 8.5 GHz, respectively.

Figure 5

Measured far-field radiation pattern at E-plane (a,c,e,g,i) and H-plane (b,d,f,h,j) at frequency 3, 4, 5.5, 7, 8.5 GHz, respectively.

Figure 6

Simulated electric field, gain, and radiation pattern of the antenna: (a) electric field distribution at 4.5 GHz; (b) simulated realized gain of six and eight Vivaldi antennas array; (c) simulated radiation pattern at 4.5 GHz without phase shifter.

Figure 6

Simulated electric field, gain, and radiation pattern of the antenna: (a) electric field distribution at 4.5 GHz; (b) simulated realized gain of six and eight Vivaldi antennas array; (c) simulated radiation pattern at 4.5 GHz without phase shifter.

Figure 7

The measured variation of beam components with frequency: (a) front-to-back ratio and beam width; (b) E-plane beam tilts.

Figure 8

Experimental measurement setup: (a) setup arrangement with antenna scanning the concrete beam with the target within; (b) proposed antenna with radar module support and concrete brick and; (c) UWB radar module.

Figure 9

The transmitted pulse shape and frequency spectrum of IR-UWB radar for PGSelect = 10; (a) transmitted signal in the time domain and; (b) transmitted signal pulse in the frequency domain.

Figure 10

The received pulse shape and correlated signals from IR-UWB radar for PGSelect = 10; (a) received raw signal strength and; (b) correlated signal pulse.

Figure 11

Scanned raw data from the radar module.

Figure 12

2-D cross-surface scanned image without the target.

Figure 13

2-D cross-surface scanned image with three targets.

Figure 14

2-D cross-surface scanned image with one target removed.