Thermal loss in high‐ Q antennas

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.

Use of ultra‐narrow band miniature antennas for internet‐of‐things applications

“…Moreover, it increases the antenna quality factor, thus adapting the antenna to the narrow bands needed by IoT systems and reducing the interference effects. However, the consequent decrease of the antenna efficiency must be carefully taken into account [6].…”

Thermal loss becomes an issue for narrow‐band tunable antennas in fourth generation handsets

“…Using narrow‐band and tunable antennas allows for designs exhibiting a very low profile. However, the dramatically increasing Q of narrow‐band antennas, as it is tuned, leads to thermal loss in the antenna structure itself [27]. The results presented in this paper show that the tuning loss is of two kinds: the loss owing to the ESR of the tuner and the loss owing to the metal conductivity.…”

“…If the tuner loss can be minimised with optimising its location and future manufacturing improvements, the loss owing to the metal conductivity is intrinsic to the antenna manufacturing. As the antenna is tuned towards lower frequencies, it becomes electrically smaller and higher Q , thus the conductive loss becomes significant [27]. This loss impacts directly the total efficiency of the system, therefore the feasibility of manufacturing such a design.…”

Miniaturized dual band consumer transceiver antenna for 5G‐enabled IoT‐based home applications

“…4 The interference effects are minimized due to the narrow bands needed for the IoT systems but care should be taken for the decrease in efficiency of the antenna because of miniaturization. 5 There are various steps for designing microstrip antennas of compact size having omni-directional radiation patterns. Chen et al 6 proposed square microstrip antenna (SMSA) with diagonally loaded slots for size reduction as well as achieving circular polarization while a modified patch was suggested by Yilmaz et al 7 for sub-GHz applications.…”

“…Compact antennas help in simple integration within IoT gadgets thus increasing the quality factor of the antenna which is inversely proportional to the bandwidth of the antenna 4 . The interference effects are minimized due to the narrow bands needed for the IoT systems but care should be taken for the decrease in efficiency of the antenna because of miniaturization 5 . There are various steps for designing microstrip antennas of compact size having omni‐directional radiation patterns.…”