Compact Agile Antenna Concept Utilizing Reconfigurable Front End for Wireless Communications

Abstract

The conventional full-duplex radio communication systems require that the radio transmitter (Tx) is active at the same time as the radio receiver (Rx). The Tx and the Rx are using separate dedicated frequency bands and the Tx-Rx isolation is ensured by duplex filters. However, increasing number of frequency bands crave for multiband and multimode operation, which either require agile duplexers or a bank of narrow-band filters with a switch. While practical agile duplexers are not available, a bank of narrow-band filters with a switch is bulky and incurs switching loss. This paper proposes an approach that separates the Tx and Rx chain throughout the front end (FE). The complexity of the FE is reduced dramatically by replacing the duplex filters with tunable filters and closely integrating the tunable antennas in the FE, providing filtering which can be used to lower requirements for the tunable filters. For this purpose, very small narrow-band antennas are designed, which can cover 1710-2170 MHz by using tunable capacitors. Simulations and measurements of the antenna concept are carried out in the proposed FE architecture, serving as a proof of concept.Index Terms-Capacitive loaded antenna, highantenna, inductive loaded antenna, MEMS, radio frequency (RF) front-end (FE), Rx antenna, transmitter-receiver isolation, tunability, Tx antenna.

Multi-Band Compact Antenna for Smartphones Supporting LTE Carrier Aggregation

“…In an effort to further minimize the volume of the antenna and to keep the bandwidth in the low bands, the two resonators are inductively loaded using high Q air winded coils [18] thus achieving the best bandwidth potential [19], as illustrated in figure 2. The loading inductors are 22 nH respectively 27 nH for the resonator 1 respectively resonator 2.…”

A New Design Method for Frequency- Reconfigurable Antennas Using Multiple Tuning Components

“…This leaves electrical tuning methods as the most viable option for handset applications. This can be either switching (using MEMS switches [14], [15], [21], [23], [31], [32], p-i-n diodes [14], [15], [21], [23], [33]- [37], SOI/SOS [11], [20], j-pHEMT [20] or optical [14], [15], [21], [23]), using switches in banks with fixed components [38]- [40], or continuously tunable devices (semiconductor varactor diodes [15], [21], [23], [35], [39]- [43], BST tunable capacitors [11], [20], [44], [45] or MEMS [16], [18]). If it is desired to cover a large range of frequencies while maintaining a relatively small bandwidth, the continuously tunable devices are most desirable for handset applications.…”

“…This problem can be partly resolved by avoiding a high antenna Q while using high-Q components, e.g. RF-MEMS [16], [18], but these are relatively expensive. Therefore, for mobile applications it would be preferable to find a way in which e.g.…”

A Tunable RF Front-End With Narrowband Antennas for Mobile Devices

“…In [19]- [21], examples of a varactor, used for frequency reconfigurability, are shown where the relative high bias voltage levels and linearity are the main limitations. Recently RF microelectromechanical systems (MEMS) are getting more attention as they are approaching maturity and have started to be implemented in commercial mobile devices [9]. They are also used extensively in academia for creating reconfigurable circuits [22]- [24].…”

“…Afterwards, [8] suggested to provide isolation between the Tx and Rx antennas by having two Tx antennas, where the Tx antennas were properly weighted such that the near-field was zero forced in the direction of the Rx antenna. Later, in [9], [10], and [11], antenna concepts for the front-end with separate Tx and Rx chains were developed. These three papers also showed the entire front-end architecture on a fabricated PCB, similar to the one shown in this paper.…”