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A Novel Differentially Fed Microstrip
Integrated-Antenna-Filter
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CHEN Xing, LI Bin
**
5
(School of Information and Electronics, Beijing Institute of Technology, Beijing 100081)
Foundations: Doctoral Program Foundation of Institutions of Higher Education of China (No. 20101101120017);
National Natural Science Foundation of China (No. 61001062)
Brief author introduction:CHEN Xing,Male, Master Candidate, Main research includes Antenna Integration and
Packaging
Correspondance author: LI Bin,Male,Associate Professor,Main research includes dielectric resonator antenna,
AIP,etc. E-mail: eelibin@bit.edu.cn
Abstract: A novel six-port differentially fed microstrip integrated-antenna-filter is proposed. The
fundamental TM01 mode of the H-shaped patch antenna is excited at 5GHz and the open-ring
resonator filter is excited at 1.3GHz. It is found that the differential mode response of the antenna and
filter are reasonable with good cross polarization and common mode suppression. In order to 10
miniaturize the circuit size of system-on-package devices and meet the demand of differential operation
in RFICs, the mutual coupling between the two components are investigated.
Key words: integrated antenna filter (IAF), differential, common-mode suppression, mutual coupling,
patch antenna
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0 Introduction
The colossal growth of the semiconductor industry has made on-chip antenna and filter designs
realizable. Many leading groups around the world have successfully obtained silicon-based
antennas and components for millimeter wave applications [1], etc. However, it is still a big
challenge to make them electronically small with desirable responses, especially for antennas. 20
Standalone packages are widely used for antenna and filter parts due to costs and efficiency.
Though it is bulkier than using silicon chip, the inherent advantages of low cost, small size, ease
manufacture and high performance have made microstrip antenna and filter desirable choice for
off-chip designs. The idea of integrated-antenna-filter (IAF) [2]-[3] is one of the effective ways for
compact system-on-package (SOP) design, as long as the mutual coupling between the antenna 25
and filter is low enough (<-20dB). In this paper, our design has made the mutual coupling even
lower (<-30dB), using a differentially fed antenna and filter.
An important advantage of differential operation over single-ended signaling is its higher
immunity to “environmental” noise. Along with that, direct differential design makes the circuit
uncomplicated by leaving out the balun module used to connect differential circuits and 30
single-ended antenna in the RF system, which will inevitably draw in extra losses (sometimes
even larger than 5dB) and circuit size. Recently, some differentially fed filters [4]-[5] and
microstrip antennas [6]-[8] have been studied in not only compact and broadband design, but also
methods for cross-polarization and common-mode suppression of antennas and filters,
respectively. The singly fed IAF was investigated in [2]-[3]. Nevertheless, no work has been done 35
on differentially fed integrated-antenna-filter.
In this paper, the differentially fed IAF is proposed the first time and the mutual coupling
between the antenna and filter is investigated. Two open ring resonators are the main part of the
bandpass filter, working at a frequency of 1.3GHz and a bandwidth of 100MHz. Common-mode
suppression of the microstrip circuit is under -30dB ranges from 0.5GHz to 3GHz by using 40
center-loaded resonators. The antenna is designed at 5GHz, which is a widely used frequency for
industrial, scientific, and medical (ISM) applications. The mutual coupling between the antenna