Impact of Using Resistive Elements for Wideband Isolation Improvement

Abstract

Abstract-Improving the isolation between antenna elements in compact arrays has been a major focus of recent research. In this paper, we present ideas to improve the wideband isolation between closely spaced antennas. We do this by connecting lumped lossy (resistive) elements between the antenna feeds. A simple analytical expression is provided to compute the impact of resistive elements on efficiency to analyse the power lost in the resistive element. Three configurations of decoupling circuits are designed and fabricated for two closely spaced monopoles operating at 2.4 GHz. The decoupling circuit contains transmission lines of different lengths at the antenna inputs such that the mutual admittance between the antenna elements is 1) resistive, 2) resistive and inductive, or 3) resistive and capacitive. Lumped elements are then connected between the transmission lines followed by matching circuit. The paper shows that with configurations 2) and 3) we can improve the wideband isolation compared to 1), as well as compared to using only lossless elements. The wideband isolation was improved by 17.6 dB across a 200 MHz band at 2.4 GHz, with a final isolation level of 20 dB over that band. Better than 30 dB isolation was achieved across a narrower band of 55 MHz. The proposed technique provides wideband isolation improvement for multiple-input multipleoutput (MIMO) as well as narrowband performance with large isolation suitable for in-band full-duplex (FDX) applications. The impact on efficiency is investigated to verify that the advantages from the improved wideband isolation outweighs the possible reduction in overall efficiency.

PCB-Based Design of a Beamsteerable Array With High-Gain Antennas and a Rotman Lens at 28 GHz

“…Passive decoupling networks that cancel the electromagnetic admittance between the antenna ports [23,29,32] and passive neutralization lines between antennas that create a cancelling signal path [22] have been used for isolation improvement between two antennas. However, their implementation complexity becomes increasingly prohibitive when more transmit and receive antennas are required.…”

“…Increasing the electromagnetic isolation between the transmitting and receiving antenna [19][20][21][22][23][24][25][26][27][28] 2. Adding cancellation circuits to cancel the self-interference in the analog stages of the transmitter and the receiver [23,[29][30][31][32] 3. Using digital cancellation algorithms in the digital baseband of the receiver [18,31,33] The research in this dissertation concentrates on decreasing the selfinterference in the antenna domain, i.e., increasing the electromagnetic isolation between the receiving and transmitting antennas.…”

Design of High-Isolation Wideband Dual-Polarized Compact MIMO Antennas With Multiobjective Optimization

“…After implementing the design flow for objectives defined in (8) is the wavelength at center frequency of the operation band. The optimized fragment-type isolation structure is shown in Fig.…”

“…Different structures have been applied to suppress mutual coupling between MIMO antennas. By using parasitic elements [5], neutralization lines [6], decoupling networks [7], coupled resonator decoupling networks [8], defected ground structures [9], and electromagnetic band-gap structures [10], surface current or surface waves were suppressed to lower mutual coupling. These designs achieved isolation around 20dB within a relative bandwidth of about 11% for MIMO antennas.…”

Characteristic Mode Theory of Wavetraps for Antenna Decoupling

“…It is shown that the required load can be made purely reactive by tuning the antenna elements. A typical method to describe the mutual coupling has been to derive a circuit model for the antenna system and then creating an additional path of coupling which neutralizes the original mutual admittance between the antennas [6], [7].…”