What Is a High Frequency Relay?
A high frequency relay is one of the elements that switch high-frequency signals.
Since high frequency relays generally do not have connectors, they are used by soldering, and their high frequency characteristics are greatly affected by the substrate. When relays are used in high- frequency circuits, there are also issues of isolation (signal leakage between contacts (circuits) when the contacts are open) and insertion loss (signal loss when the contacts are closed).
Uses of High Frequency Relays
High frequency relays are used in devices that have a circuit called a high frequency circuit. In order to control high-frequency signals, a relay specialized for high frequency is needed, not an ordinary relay.
Examples include cell phone base stations, broadcasting equipment, measuring instruments, and radio equipment. Another application is wireless LAN and Bluetooth, which are widely used in homes. In both cases, the relay plays the role of smoothly switching signals inside various types of equipment.
Principle of High Frequency Relays
High frequency relays have the same structure as general relays.
1. Principle of Relay
In a relay, when a small amount of electricity flows through a coil wound around an iron core, an electromagnet draws the iron pieces together, causing them to contact each other and connect the circuit. When the electricity between the terminals is cut off, the magnetic field generated in the coil is dissipated and the electrical equipment stops operating.
When relays are used in high-frequency circuits, isolation and insertion loss become problems.
2. Isolation
Isolation corresponds to the resistance between output terminals when the relay is off. At high frequency relays, signal leakage occurs even when the relay is off. Isolation is a parameter that indicates the degree of this signal leakage.
The higher the frequency, the greater the leakage, and the smaller the value of isolation itself tends to be. This can cause interference between circuits.
3. Insertion Loss
Insertion loss, also called insertion loss, refers to the signal loss between contacts that occurs when the contacts are closed. The higher the frequency, the greater the signal loss between contacts (circuits), making it impossible to transmit signals accurately and causing heat to be generated.
In other words, it is important that there is little signal leakage between contacts when they are open and little signal loss when they are closed, even when the signal frequency increases.
4. Return Loss
When there is an impedance change in the middle of a signal path, a phenomenon called reflection occurs, in which part of the signal does not reach the receiving side but returns to the transmitting side.
The degree of signal reflection is called return loss, which is expressed as the ratio of input power to reflected power. Another indicator of the degree of reflection is VSWR (Voltage Standing Wave Ratio): the closer the VSWR value is to 1, the less reflection there is, meaning that it is a good characteristic.
Relays used in high-frequency circuits require high frequency characteristics in addition to general relay characteristics, so they must have high isolation and low insertion loss as described above. In addition, return loss, which indicates the degree of signal reflection, must be large, VSWR must be small, and characteristic impedance, which indicates the value of resistance, must be appropriate.
Other Information on High Frequency Relays
High-Frequency Circuits
High-frequency circuits refer to electronic circuits whose operation at high frequencies differs from that at low frequencies. Circuits that handle electronic signals with frequencies ranging up to several GHz, such as wireless LAN, are high-frequency circuits.
When electronic signals are at high frequencies, it is necessary to take into account that the current and voltage levels of the signals are different at different locations in the electronic circuit. Circuits that handle this behavior are called distributed constant circuits.