The frequency of analog signals as well as the data rate of digital signals are continuously increasing. For many high frequency applications like wireless telecoms, CATV, ATE, etc, relays are needed to switch these signals.
With the HF3 relay from Tyco Electronics AXICOM offers a low cost, high performance, high frequency relay capable of handling signals up to 3 GHz.
With excellent isolation, insertion loss and VSWR to high frequencies, this relay offers one of the smallest physical dimensions and has a surface-mount capability for cost effective assembly processes.
Standard telecom and signal relays cannot handle signals higher than 500 MHz as they do not have the required characteristics (insulation, impedance and insertion loss, etc). Broadband applications in emerging markets are using signals between the 1 and 3 GHz range. With electromechanical relays, there are a number of advantages over semiconductor switches. These are:
* Contacts do not cause any signal distortion, for example as amplitude distortion, phase distortion, cross modulation, or mutual modulation;
* Open contacts can be gas-insulated providing excellent high frequency insulation;
* Good metal contacts can suppress insertion loss;
* High frequency characteristics of electromechanical relays are not influenced by temperature.
However, the major disadvantages for electromechanical relays generally are the large dimensions, the high cost and the fact that SMD capability is not possible. As such, the target for Tyco's development of the HF3 relay was the combination of well-known high frequency performance advantages, with the surface-mount technology (SMT) and manufacturing technology of standard telecom relays. The result is a synthesis of a superior RF design technology, coupled with a well-proven highly efficient manufacturing technology, which allows for users to achieve competitive manufacturing costs.
Product description
The HF3 relay is a high frequency relay that can handle signals up to 3 GHz. With outside dimensions of 15 x 7,5 x 10 mm it is currently one of the smallest RF relay designs on the market that can be soldered with SMD processes. Two versions with different impedances (50 and 75 Ω) are available in order to serve both application fields - ATE and wireless communications that both require 50 Ω impedance, and CATV and satellite receivers that require a 75 Ω impedance.
Design and characteristics
For the internal design of RF relays, three design principles can be applied (see Figure 1). All methods use a signal layer, a ground layer and a dielectric layer, where the electric field is concentrated between signal and ground layer. Microstrip and coplanar designs are widely used for RF PCB designs, whereas a coaxial design is used for cables.
In order to realise a 50 Ω version as well as a 75 Ω version, the coplanar design principle offers better possibilities to achieve this in similar designs which can be manufactured on the same manufacturing line. The difference between the 50 Ω and the 75 Ω version is the width of the terminals and the dielectrics, which achieves a perfect match of the relay impedance to prevent any signal reflection.
The actuator used for the HF3 relay is a highly sensitive, polarised magnetic circuit that works with low power consumption and has non-latching as well as latching switching characteristics with one or two coils. The design is based on a modified standard telecom relay where high volume manufacturing methods can be used. This ensures low manufacturing cost and high quality manufacturing with low failure rate.
Typical applications for RF relays are: cable modems/cable TV; set-top boxes; measurement and test equipment; satellite/audio/video tuners; wireless base stations. Key specs for the HF3 relay are: coil voltage 3-24 V; sensitivity 100-200 mW; contact resistance <100 mΩ; and at 1 and 3 GHz respectively, isolation is -60 db and -45 dB, insertion loss is -0,3 dB and -0,3 dB, and VSWR is 1,3 and 1,3.
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