A CSRR Loaded Triple-Band Microstrip Patch Antenna with Suppressed Higher Order Modes for Sub-6 GHz Phased Array Application

In this paper, we design a CSRR loaded tripe band antenna with suppressed higher order modes. The CSRR loading is incorporated in a square microstrip antenna such that in addition to the triple band response at 3.52 GHz, 3.865 GHz, 4.39 GHz, antenna miniaturization is obtained yielding an overall footprint of $0.23\lambda_{0}\times 0.23\lambda_{0}$, where $\lambda_{0}$ is the free space wavelength at 3.52 GHz. Further, the higher order mode suppression is achieved using a plated through hole (PTH) placed close to the CSRR loading position. The proposed antenna achieves satisfactory impedance matching $\leq -15$ dB for all three operating frequencies. Further, the proposed antenna is arranged in $4\times 4$ configuration with an inter-element spacing of $0.25\lambda_{0}$ for phased array application. This $4\times 4$ array configuration enables beam steering up to $80^{0}$ without grating lobes, while maintaining lowest side lobe level $\geq 19\mathbf{dB}$ and satisfactory array gains of 12 dBi, 13 dBi, 14 dBi at 3.52 GHz, 3.865 GHz, and 4.39 GHz respectively are achieved. The proposed concept is experimentally validated by S-parameter and pattern measurements on fabricated prototype.

I. Introduction

Microstrip antennas are the most prominent candidate in the wireless industry due to their low cost, low profile, compact, lightweight, and ease of fabrication. However, it is suffered from the excitation of higher order modes (HOMs) due to its cavity-like structure [1]. There are various techniques available in open literature such as [4]–[7] to reduce HOMs. In [4], a simple inset-fed microstrip antenna is proposed with defected ground structure (DGS) and tuning stub to control the HOMs. In [5], another inset-fed microstrip antenna is proposed to suppress HOMs using coupled resonator and PTH. There are several other techniques also proposed for HOM suppression such as the use of shorting pin and slots [6], hairpin filter [7] etc. However, most of the studies on HOM reduction belong to isolated and single-band antennas.