Proceedings of 2011 International Microwave Symposium, Baltimore, MD, June 2011. IEEE Copyright © Integrated Antenna/Electro-Optic Modulator for RF Photonic Front-Ends Rodney B. Waterhouse and Dalma Novak Pharad, LLC, Glen Burnie, MD, 21061, USA Abstract — We present an efficient, integrated antenna/electro-optic modulator assembly for RF photonic front- ends in phased array applications. The integrated radiator/photonic device incorporates a non-contact fed stacked patch antenna that has been designed to radiate efficiently between 9 – 11 GHz and is easily coupled to the Lithium Niobate Mach-Zehnder modulator, requiring minimal modification to the electrode structure of this photonic device. We discuss the design procedure for the integrated assembly, the predicted characteristics of the antenna in this environment and test a proof-of-concept version of the module. Finally we verify the performance of the module through a link demonstration. Index Terms — Microwave photonics, integrated antennas, optical modulators, phased arrays, printed antennas. I. INTRODUCTION The application of RF photonic links for fiber remoting of phased array antennas and wireless communication systems continues to evolve with recent developments in RF photonic device technologies, transmission techniques and receiver architectures [1]. A fundamental aspect of the implementation of next generation high performance communication systems is the creation of efficient wideband transducers from free- space RF to the guided optical domain and vice-versa. It is imperative that the insertion loss of these interfaces is kept to a minimum, as this will directly impact the dynamic range of the system and therefore the overall capacity. Figure 1 illustrates the general architecture of a fiber remoted phased array antenna that incorporates a photonic- based RF front-end. Here the radar waveform to be transmitted by each individual element in the antenna array is generated remotely from the antenna and the full RF signal is encoded onto an optical source (E/O conversion) for transport over fiber to the remote antenna. The optical signal is then detected at each antenna array element by a photodetector (PD) to regenerate the encoded transmit waveform. As depicted in Figure 1, in a fiber remoted phased array system the detected transmit waveform is amplified in a high power amplifier (HPA), for example, which then directly drives the antenna element. For the receiver portion of the phased array radar RF front-end, the return signal is captured by a receive antenna element (which may be the same as the transmit antenna), amplified in a low noise amplifier (LNA), and then encoded onto the amplitude or phase of an optical carrier using an electro-optic modulator (EOM) for transport over fiber back to a central location where appropriate electronics digitize and process the signal. Fig. 1. Schematic showing the architecture of a fiber remoted radar system and electro-optic RF front-end. The generic radar architecture shown in Figure 1 includes amplifiers between the photonic components and the antenna elements, however increasing the overall efficiency of the RF photonic link may remove the need for any electronic amplification at the Transmit (TX) and (Receive) RX antenna. This could be achieved through devices that improve the E/O (electrical to optical) and O/E (optical to electrical) conversion processes, as well as techniques to increase the power transferred between the antenna and the photodetector or electro-optic modulator. A significant challenge in increasing RF photonic link efficiency is how to increase the transfer of power between the RF and optical domains over a wide operating bandwidth. In this paper, we present the design and experimental verification of a novel, efficient integrated antenna/modulator assembly. The integrated module was designed for efficient operation over the frequency range of 9 – 11 GHz. The assembly utilizes a proximity coupled stacked patch antenna that is placed over the Lithium Niobate (LiNbO 3 ) wafer of the EOM and requires minimal modification to the electrodes of the wafer itself. We utilized a full-wave electromagnetic simulation tool (CST™) to accurately model the performance of the antenna when coupled to the LiNbO 3 wafer and located in the modified housing for the electro-optic modulator. We then made modifications to the antenna to ensure it would operate efficiently in this environment. We created a proof- of-concept version of the antenna to verify its electromagnetic (EM) performance and then developed the integrated antenna/EOM module. We undertook an experimental link investigation of the proposed integrated antenna/EOM assembly and demonstrated its efficient operation over 9 – 11 GHz. Remote Waveform Generation and Return Processing Fiber Remoting of Transmit waveform TX (O/E) PD HPA EOM LNA RX (E/O) Antenna Elements Fiber Return of Echo Signals Digitization and Processing O/E TX Waveform Synthesis E/O Photonic RF Front-End