This letter presents a wideband/multi-band quad-antenna system for 4G/5G/GPS metal frame mobile phones. The quad-antenna system has two kinds of antenna elements and four antenna elements. The merit of the proposed antenna system is that a quad-antenna system is achieved under the condition of metal frame and without using any decoupling structure, the desired bands for 4G/5G/GPS are covered. A prototype was fabricated and measured. For the first kind of antenna elements (including two antenna elements), the bands of 698-960MHz, 1710-2690MHz and 3400-3600MHz are covered, the LTE700/GSM850/GSM900/GSM1800/GSM1900/LTE2300/LTE2500/3.5GHz bands all are covered. For the second kind of antenna elements (including two antenna elements), the bands of 1400-2690MHz, and 3400-3600MHz are covered, the GPS, GSM1800/GSM1900/LTE2300/LTE2500/3.5GHz bands are covered. The measured isolations are bigger than 10dB. The measured efficiencies are bigger than 40% at all the working bands. The measured envelope correlation coefficients are very suitable for MIMO communication systems.

This paper presents an eight-band antenna for full-screen metal frame LTE mobile phones with the size of 142mm×79mm×7.5mm. The proposed antenna mainly consists of two monopole branches, a match circuit and two ground branches. The two monopole branches and the match circuit are used to cover the lower band (698-960MHz) and part of the higher band (1710-2690MHz). One of the two ground branches is used to cover the other part of the higher band, and the other is mainly used to make the lower band matched. The merit of the proposed antenna is that eight bands can be realized under the conditions of an only 2mm ground clearance and a metal frame, it is very suitable for full-screen metal frame mobile phones. A prototype is manufactured and measured. The measured -6dB impedance bandwidths are 300MHz (665-965MHz) at the lower band and 1190MHz (1610-2800MHz) at the higher band. The LTE700, GSM850, GSM900, DCS, PCS, UMTS, LTE2300, and LTE2500 bands are covered. The measured efficiency is bigger than 42%, so it is practical for mobile phone applications.

This letter presents a compact eight-band monopole antenna whose size is 70mm×7mm×6mm for LTE metal frame mobile phones. The mainly radiating place of the proposed antenna is the metal frame, there are three gaps with the same size of 1mm in the frame. The gaps divide the antenna to two parts (branch1 and branch 2), besides, a match circuit are used to enlarge the bandwidth and make the lower band matched. The advantages of the proposed antenna are that eight bands can be covered with a metal frame under the condition of only 7mm ground clearance. To prove the correct of the antenna, a model is manufactured and tested. The measured impedance bandwidths under -6dB are 375MHz (0.675-1.05GHz), and 1.2GHz (1.6-2.8GHz), the bands of the LTE700, GSM850, GSM900, GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 are contained. The measured efficiencies are 52.7%-78.7% at the lower band and 45.6%-81% at the higher band. The measured gains are 0-2.1dBi at the lower band and 1.6-3.6dBi at the higher band.

An octa-band antenna for 5.7-in mobile phones with the size of 80 mm $\times6$ mm $\times5.8$ mm is proposed and studied. The proposed antenna is composed of a coupled line, a monopole branch, and a ground branch. By using the 0.25-, 0.5-, and 0.75-wavelength modes, the lower band (704–960 MHz) and the higher band (1710–2690 MHz) are covered. The working mechanism is analyzed based on the S-parameters and the surface current distributions. The attractive merits of the proposed antenna are that the nonground portion height is only 6 mm and any lumped element is not used. A prototype of the proposed antenna is fabricated and measured. The measured −6 dB impedance bandwidths are 350 MHz (0.67–1.02 GHz) and 1.27 GHz (1.65–2.92 GHz) at the lower and higher bands, respectively, which can cover the LTE700, GSM850, GSM900, GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 bands. The measured patterns, gains, and efficiencies are presented.

A low-profile microstrip antenna which has a broad impedance bandwidth by exciting three resonant modes is proposed. The proposed antenna mainly consists of a grid-slotted radiation patch, a metal ground, four vertical metal strips, and a vertical grounded balun feeding structure. The TM10, TM12, and antiphase TM22 modes are excited simultaneously. The vertical grounded balun feeding structure is used to avoid etching slot on the metal ground to get a high front-to-back ratio. The four vertical metal strips are introduced to enhance the impedance matching and reduce the sidelobe of the radiation pattern of the antiphase TM22 mode. With a profile of 0.07 $\lambda_0$ ( $\lambda_0$ is the center operating wavelength in the free space), the measured -15dB impedance operating band is 3.31-4.31 GHz and the relative bandwidth is 26.2%. The measured front-to-back ratio is larger than 16dB and the sidelobe level is lower than -10dB. The proposed antenna has a stable broadside radiation performance in the operating band.