Users within mobile networks require ever increasing data rates. However, the frequency spectrum, reserved for mobile networks, is highly saturated. The millimeter wave spectrum, by contrast is relatively under utilised. Nonetheless, this area of the spectrum suffers from higher propagation losses, necessitating the use of highly directional antennas. To support mobility these antennas require beam steering capabilities. For several applications wide beam scanning capability is required. A valuable approach for increasing the beam scanning range is to use element factor plus array factor control . Although several authors have presented designs based on this approach the lobe performance of those antennas is generally quite poor. In this paper we seek to address that issue.
This paper presents two different designs for frequency reconfigurable antennas capable of continuous tuning. The radiator, for both antenna designs, is a microstrip patch, formed from liquid metal, contained within a microfluidic channel structure. Both patch designs are aperture fed. The microfluidic channel structures are made from polydimethylsiloxane (PDMS). The microfluidic channel structure for the first design has a meander layout and incorporates rows of posts. The simulated antenna provides a frequency tuning range of approximately 118% (i.e. 4.36 GHz) over the frequency range from 1.51 GHz to 5.87 GHz. An experimental result for the fully filled case shows a resonance at 1.49 GHz (1.3% error compared with the simulation). Experienced rheological behavior of the liquid metal necessitates microfluidic channel modifications. For that reason, we modified the channel structure used to realise the radiating patch for the second design. Straight channels are implemented in the second microfluidic device. According to simulation the design yields a frequency tuning range of about 77% (i.e. 3.28 GHz) from 2.62 GHz to 5.90 GHz.
This paper presents a continuously tunable microstrip patch antenna formed from liquid metal (eutectic gallium indium). The concept and design of the antenna have been validated through computer simulation. The antenna is capable of reconfiguring its operating frequency in a continuous manner. The proposed design consists of a microstrip patch which is excited via aperture coupling. The EGaIn liquid metal is contained within a microfluidic channel which is formed within a polydimethylsiloxane (PDMS) substrate. Frequency tuning is achieved by altering the amount of fluid within the channel to vary the electrical length of the antenna. The simulated antenna provides a frequency tuning range of approximately 104% and a total usable spectrum (S11 <; -10 dB) of 105%. The antenna can be tuned from 3.21 GHz to 10.12 GHz. The maximum realized gain is 6.9 dBi and the total efficiency is 82%.
Alqurashi Khaled, Kelly James R., Wang Zhengpeng, Crean Carol, Mittra Raj, Khalily Mohsen, Gao Yue (2020) Liquid Metal Bandwidth-Reconfigurable Antenna,IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS19(1)pp. 218-222
Institute of Electrical and Electronics Engineers
This letter shows how slugs of liquid metal can be used to connect/disconnect large areas of metalization and achieve a radiation performance not possible by using conventional switches. The proposed antenna can switch its operating bandwidth between ultrawideband and narrowband by connecting/disconnecting the ground plane for the feedline from that of the radiator. This could be achieved by using conventional semiconductor switches. However, such switches provide point-like contacts. Consequently, there are gaps in electrical contact between the switches. Surface currents, flowing around these gaps, lead to significant back radiation. In this letter, the slugs of a liquid metal are used to completely fill the gaps. This significantly reduces the back radiation, increases the bore-sight gain, and produces a pattern identical to that of a conventional microstrip patch antenna. Specifically, the realized gain and total efficiency are increased by 2 dBi and 24%, respectively. The antenna has potential applications in wireless systems employing cognitive radio (CR) and spectrum aggregation.