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.

No abstract

No abstract

Tunable antennas are very promising for future generations of mobile communications, where antennas are required to cover a wide range of operating bands. This reported work was aimed at characterising the loss mechanism of tunable antennas. Tunable antennas typically exhibit a high quality factor (Q), which can lead to thermal loss due to the conductivity of the metal. The investigation shows that copper loss is non-negligible for high-Q values. In the proposed design, the copper loss is 2 dB, for a Q of 260 at 700 MHz.Introduction: With the band proliferation that followed the standardisation of the fourth generation (4G) of mobile communications, active antennas have been investigated to enhance the operating bandwidth of mobile phone antennas while keeping a low profile. Active antennas can reconfigure their resonance frequency using microelectromechanical systems [1], pin diodes [2] or varactors [3]. These active components will add a varying reactance to the impedance of the antenna, thus modifying its resonance frequency. A recent overview of the tuning techniques is given in [4]. Independently of the tuning technique, when the antenna is forced into resonance at a lower frequency than its natural frequency, its bandwidth decreases and its quality factor, Q, increases inversely proportionally [5]. As the Q of the antenna increases, its efficiency decreases due to higher currents in the equivalent series resistance of the tuner. For high-Q values, the loss due to the tuner alone cannot explain the measured total loss [6]. In the work reported in this Letter, the authors investigated the existence of a thermal loss in high-Q antennas, due to the conductivity of copper. For this investigation, the authors have designed a large patch antenna, naturally resonating at 700 MHz, as it is the lowest frequency to reach with 4G nowadays [7]. Different widths of the patch result in different antenna Q, while maintaining the resonance frequency. The measured radiation efficiencies are compared to determine the influence of Q on the thermal loss of antennas.

This study presents reconfigurable antenna design for a front end (FE) that has separate transmit (Tx) and receive (Rx) path. In such an FE, the Tx and Rx antennas can be content with covering only the transmit and receive channels in a frequency band. Therefore they can be quite narrow-band. Narrow-band antennas can exhibit high losses, because of the relative high current density per area and limited tuning/matching component Q. To address this, a self-matched antenna design is introduced, having the tunable capacitor as the only physical component. The Tx and Rx narrow-band antennas are designed to cover the frequency range 1710-2170 MHz. Metrics as for example, impedance bandwidth and efficiency are obtained both in simulations and measurements.