Analysis of slot-based radiators using TCM and its application in MIMO antennas

Abstract

In this article, with the help of the theory of characteristic modes (TCM), it is found that the introduction of circular slots in a chassis modifies the chassis modes. Based on the location of the slot, different chassis modes will be affected. For a fixed location, the slot to chassis size ratio plays an important role in its effect on the radiating bandwidth (BW). For a small size ratio, a modified chassis mode will be created without affecting the radiating BW. The current concentration across the slot depends on the shape of the slot (circular, rectangular, triangular, or square) and its location on the chassis. Moreover, the effect of multiple circular slots on the chassis modes is investigated. For slots introduced in a symmetrical fashion, that is, four elements, the modes are not affected and are similar to the original chassis ones. We also investigate the principle behind frequency reconfigurability using TCM analysis. The varactors used for frequency reconfigurability do not alter the radiating BW (Modal Significance plots) but only help in the input impedance matching at different frequency bands of the same mode. If a mode is excited purely using a proper feeding arrangement, the same frequency reconfigurable antenna will behave as a wide band one. Based on the detailed analysis presented in this work, a compact multiple‐input‐multiple‐output annular slot frequency reconfigurable antenna operating between 1.8 and 2.45 GHz is presented. Frequency tuning is achieved using varactor diodes.

Characteristic Mode Analysis of Wideband Microstrip Antenna

“…The impact of changes in the parameters, such as the length of the ground G L and slot width of the ground g on S 11 , is illustrated as follows. When a single parameter is varied, remaining parameters are maintained at constant.…”

“…The TCM is based on the method of moment formulation of electric field integral equation and is found to be useful in proving various antenna parameters in the literature. In recent years, different types of antennas well designed by using characteristic mode theory (CMT) for different applications are Slot antennas [7][8][9][10], MIMO antennas [11][12][13][14], UWB antennas [15][16][17], Platform antennas [18][19][20][21], Metasurface antennas [22][23][24][25][26], and Wideband antennas [27][28][29][30][31][32][33][34].…”

Review of isolation enhancement with the help of theory of characteristic modes

“…TCM is widely used for the analysis of various different types of antennas such as wire antennas [7], handset antennas [8], small antennas [9], dielectric antennas [10], printed MIMO antennas [11][12][13][14][15][16] and slot antennas [17][18][19] Multiple-input-multiple-output (MIMO) antennas are widely used for the enhancement of antenna capacity and this technology is used for 4G and 5G communications [20,21]. The performance of such antennas can be degraded, if the antennas are not properly isolated [21,22].…”

New antenna mode generation based on theory of characteristic modes

“…In many existing works, , a mobile terminal chassis was considered as the main radiating element for frequencies greater than 1 GHz when the chassis modes were excited. Remember that all these antennas have different applications such as MIMO, pattern reconfigurability, and wide‐band but the common thing is that all of them rely on the chassis as the main radiator.…”