A metal‐rimmed multiple‐input multiple‐output (MIMO) antenna design operating below the 1 GHz frequency band is proposed that offers a wide bandwidth, high isolation, low correlation, and compact size. The proposed technique is based on metal‐rimmed mobile phones with four gaps, and the overall design occupies a small size in the ground plane. Orthogonal ground mode resonances are controlled to be equal to the operating frequencies, providing high antenna performance and good diversity performance. The proposed main antenna is achieved by utilizing the upper‐side rim to tune the ground mode resonance along the length of the ground plane to be equal to the operating frequency; moreover, a coupling slot couples strongly with the ground mode resonance to achieve a ‐6 dB bandwidth from 0.695 to 1 GHz (305 MHz). The orthogonal ground mode along the width of the ground plane is used for diversity antenna design. Similarly, the ground mode resonance is made equal to the operating frequency by controlling the left‐side metal rim such that a simulated ‐6 dB bandwidth from 0.850 to 0.920 GHz (70 MHz) is achieved. The simulated isolation is more than 11.5 dB in the operating band, and the measured envelope correlation coefficients is below 0.1.

A new feed structure with a loop-type radiator is proposed for achieving a wide bandwidth characteristic. The method for achieving a wide impedance bandwidth characteristic is to control the input impedance of the feed structure using a parallel capacitor and inductor. The size of the ground plane is 50 3 20 mm 2 , which is usually used as the ground for USB dongle applications. The size of the rectangular ground clearance for the loop-type antenna is 8 3 4 mm 2 . The proposed antenna was designed and measured using HFSS and a 3D CTIA OTA chamber. The center frequency is 2.45 GHz and the impedance bandwidth under VSWR 5 2:1 is 550 MHz (2.18-2.73 GHz), which is adequate for long term evolution bands (7, 30, 40) and Wi-Fi applications.

In this study, optimum locations for a loop-type ground radiation antenna are evaluated for C-shaped ground planes of two different sizes. To achieve good radiation performance, the antenna needs to be located such that it couples with the dominant current mode of the ground plane. Antenna locations are proposed using the characteristic mode analysis of the ground planes. The measured bandwidths of the antennas at the proposed locations have more than twice the bandwidths of the cases in which the antennas are coupled with nondominant modes. The operating frequency of the antennas is 2.45 GHz.

In this article, an antenna design using an audio wire is proposed for a compact Bluetooth ear set. The length of the audio wire is less than a quarter of a wavelength in Bluetooth ear sets. Therefore, an appropriate feed structure needs to be designed to utilize the wire as an antenna. The antenna has been tuned using an inductor and impedance matching is accomplished by a loop‐type feeding structure with lumped capacitors. The feeding structure can be used to tune various lengths of the antenna. Full wave simulations are conducted to observe the effectiveness of the proposed technique. The measured and simulated bandwidths of the antenna are in good agreement. The measured bandwidth and average efficiency of the antenna were 116 MHz and 54.74%, whereas the average total isotropic sensitivity was 80.12 dBm that comply with the desired criteria for operation of the Bluetooth ear set.